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Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in Horses
Journal Pre-proof Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in Horses Tara E. Campbell, Hunter Doughty, Patricia A. Harris, Melody A. de Laat, Martin N. Sillence PII:
S0737-0806(19)30618-5
DOI:
https://doi.org/10.1016/j.jevs.2019.102869
Reference:
YJEVS 102869
To appear in:
Journal of Equine Veterinary Science
Received Date: 25 February 2019 Revised Date:
4 November 2019
Accepted Date: 16 November 2019
Please cite this article as: Campbell TE, Doughty H, Harris PA, de Laat MA, Sillence MN, Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in Horses, Journal of Equine Veterinary Science (2019), doi: https://doi.org/10.1016/j.jevs.2019.102869. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier Inc. All rights reserved.
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Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in
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Horses
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Tara E. Campbella, Hunter Doughtya, Patricia A. Harrisb, Melody A. de Laatc, Martin N.
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Sillencec, *
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a
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NSW, Australia
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b
School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga 2650,
Equine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds,
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Leicestershire LE14 4RT, United Kingdom
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c
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Brisbane, Queensland 4001, Australia
Earth, Environmental and Biological Sciences, Queensland University of Technology,
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Animal care and welfare/ethical statement: All experimental protocols were approved by the
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Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035,
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05/048, 05/067).
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Conflict of interest statement: PA Harris is an employee of the WALTHAM Centre for Pet
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Nutrition who funded this project. PA Harris had a role in the study design, interpretation of
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the data and in the decision to submit the article for publication.
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*Corresponding author at: Martin N. Sillence, Earth, Environmental and Biological Sciences
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School, Science and Engineering Faculty, Queensland University of Technology,
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2 George Street, GPO Box 2434,Brisbane, Qld 4001, Australia.
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E-mail address: [email protected] (M.N. Sillence).
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Abstract
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The rapid intake of high-cereal, low-roughage meals may cause gastrointestinal and
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behavioural disorders. We investigated some of the factors that can affect the rate of intake
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(ROI) in four separate studies. Study 1 investigated the effect of chaff length and addition
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rate on the ROI of oats. The ROI decreased as more chaff was added to the diet, attaining
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significance (P < .05, n = 6) at levels above 15% addition and reaching a plateau at ~50%.
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This was independent of stalk length (1.4 cm vs 4.1 cm). Study 2 showed that meal size
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(varying from 0.5 to 4 g/kg BW) did not affect the ROI for a cereal-based meal, nor was ROI
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altered by the addition of 10% molasses (n = 6). Study 3 demonstrated that ROI changed
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markedly over the course of a meal, commencing at an average rate of 74 g/min for the first
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5 min and decreasing to 15.8 g/min after 30 min (n = 6). Study 4 examined the effects of
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breed, BW, exercise and gender in 71 horses. In Clydesdales, BW affected ROI (P < .05), and
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Clydesdales had a faster ROI than Thoroughbreds of similar BW (81.8 ± 6.8 versus 66.0 ±
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3.35 g/min; P < .05). Exercise level, age and gender did not impact ROI significantly. The
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results highlight the effectiveness of feeding chaff to slow ROI and demonstrate the need for
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a standardised protocol if ROI is to be compared between different studies.
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Keywords: equine; starch; roughage; nutrition; concentrates
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2
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1. Introduction As a foraging species, horses have evolved to eat small amounts of fibre-based feeds
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virtually continuously, grazing for up to 70% of each 24 h period [1,2]. Selective grazing
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ensures a well-balanced herbivorous diet that promotes optimal digestion by the
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gastrointestinal tract (GIT) [2,3]. Although some modern forages can exceed nutritional
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requirements for horses in light work, when energy demands are high, it is common to either
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supplement or replace the free-ranging, predominantly forage-based diet with high-energy
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rations, fed at infrequent intervals to horses confined to small paddocks or stables. This
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practice typically employs cereal grain or cereal-based feeds that contain energy in a
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concentrated form [4,5].
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Unfortunately, such cereal-based diets can predispose horses to metabolic,
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gastrointestinal and behavioural problems, such as obesity, gastric ulceration, colic and
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stereotypies [6-10]. In general, cereal-based rations require less chewing effort than long
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fibre, resulting in less saliva production, and an increased risk of lateral hook development on
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the dental arcade. They are also ingested more quickly (higher rate of intake: ROI) than meals
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based on long fibre such as hay. When large meals of either pellets or cereal grains are fed
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infrequently, a transient state of hypovolaemia occurs as a result of upper gastrointestinal
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secretions. The loss in plasma volume that occurs in ponies within 1 h of feeding has been
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shown to be 15% on average, and up to 24% in quick or greedy feeders [11].
65 66
For a horse ration to be safe, there is an upper limit to how much starch it should
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contain and a lower limit to its roughage content [7,12]. Excessive dietary starch can
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predispose a horse to insulin resistance (IR) and hyperinsulinaemic laminitis, as well as
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increasing the risk of gastrointestinal ulcers [9,13,14]. Furthermore, an elevated ROI may
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lead to insufficient insalivation and mastication of the food, choke, and an alteration in the
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rate of passage (ROP) of digesta through the GIT [15]. It is the decreased pre-caecal digestion
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which may lead to acidosis, colic and alimentary-associated laminitis [14,16].
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Therefore, controlling the ROI of cereal-based feeds is highly desirable. In addition to
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diet composition, many other factors may affect the ROI of a meal in horses, including grain
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processing methods, roughage particle size, frequency and size of meals, palatability,
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moisture content, exercise level, sex, age, bodyweight, breed and occlusal surface
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area/dentition [18]. Previous studies have examined some of these factors with variable
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results [18-22]. However, most literature agrees that the inclusion of chopped roughage
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(chaff) to a cereal-based meal is an important factor in decreasing ROI. This was reflected in
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a survey of Australian racehorse trainers, which found that more than 95% of trainers added
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chaff to cereal diets to decrease ROI [23].
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Studies on the effect of the physical form of chopped roughage added to equine diets
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are conflicting, and this topic requires further investigation [22,24,25]. Of particular interest
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is the observation that longer stalk-length (~4 cm) chaff is typically fed in Europe than in
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Australia (~2 cm). Historically, the feeding of very short chaff in Germany was viewed as a
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serious risk factor for impaction, and roughage with a longer stalk-length has been associated
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with decreased ROI [24].
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Initially, the sole aim of this study was to examine the effect of roughage inclusion on
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the ROI of a cereal-based meal, with respect to addition rate and stalk length. However, when
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comparing our results with earlier reports [26,27] it was clear that we were working from a
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different baseline i.e. the ROI for cereal alone observed in our study was much lower than
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that reported in those earlier studies. Therefore, we pursued the additional aim of identifying
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the factors that can affect ROI other than the meal composition, and of developing a
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standardised methodology that would control for these factors. The study was expanded to
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test the hypotheses that ROI is also dependent on meal size, palatability, observation period,
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exercise, age, gender, breed and bodyweight. Our ultimate aim was to better understand the
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variables that affect ROI, in order to inform safer feeding practices, facilitate future studies
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and promote consistent methodologies.
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2. Materials and methods Four studies were performed and all experimental protocols were approved by the
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Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035,
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05/048, 05/067).
107 108 109
2.1 Animals The characteristics of the animals used in studies one to three are presented in Table
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1. The horses were all geldings, drawn from a group of twelve horses belonging to the Equine
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Centre at Charles Sturt University, Wagga Wagga NSW. The horses had been housed in
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stables or yards for several weeks prior to the studies, and were all accustomed to being fed
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oats from time to time.
114 115
All the horses were examined by a veterinarian and treated by an equine dental
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technician to ensure good general and oral health prior to the studies. They were also treated
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with an anthelmintic drench (200 µg/kg BW; MecWorma, Farnam, Phoenix AZ) at least 8
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days before any feeding observations were made. The horses were stabled individually (4 m x
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4 m) on 30 cm deep sawdust bedding at Charles Sturt University Equine Centre. In the first
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three studies all horses were exercised for 1 h/day every day, at a continuous walk on a
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mechanical horse walker (Irongate, Netley SA, Australia).
122 123
In Study four, a population survey of 71 horses of mixed sex and breed (Table 3)
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from the Riverina district of NSW, was conducted to examine factors affecting the ROI of a
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standardised meal of 1 kg oats. Informed consent for the survey was provided by all owners
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at an initial visit undertaken to assess the horses and facilities. To avoid neophobic behaviour,
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horses were only enrolled in the survey if they had received oats previously. Observations
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were performed during a subsequent visit. The horses were weighed using a calibrated
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portable scale suitable for use in horses (Ezy-weigh, Darwin NT, Australia), and owners were
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asked to complete a questionnaire to provide information about the breed, gender, age,
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exercise intensity, current diet, history of feed-related digestive disorders and any stereotypic
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behaviours of their horse.
133 134
2.2 Study Design
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The design of each study is described in Table 1.
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2.2.1 Study One
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Study one aimed to determine the relationship between the addition rate of chaff to a
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cereal-based feed and the ROI of that feed; and to measure any difference in ROI between the
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addition of short (1.43 ± 0.09 cm) chaff and longer (4.09 ± 0.14 cm) chaff cut from the same
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batch of straw. The horses were acclimatised to a daily feeding routine: cereal-based meals
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were fed at 0900 hours and 1400 hours; hay plus a vitamin and mineral supplement (50
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g/day; Hoss-Amin-R, Troy Laboratories, Glendenning NSW, Australia) were fed at 1700
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hours.
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6
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The cereal-based meal contained whole, unprocessed oats obtained from a single
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batch. During the acclimatisation/adaptation period, the quantity of oats fed was increased
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incrementally from 0.5 g/kg BW to 3 g/kg BW (as fed) per meal over six days. Once this
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level of oats was reached, this was maintained for a further 2 days to bring the adaptation
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period to a total of 8 days. During this phase, the cereal-based meals included an equal
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quantity of short and long wheaten chaff fed at 1.8 g/kg BW (as fed). Although oats and chaff
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are sometimes wetted to reduce the risk of choke, in the present study they were fed dry, in
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line with the prevailing practice at this equine centre. Not wetting the feed also eliminated a
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potential source of variation.
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The 1700 hours meal consisted entirely of ryegrass clover hay given at a level that
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provided the balance of each individual’s maintenance digestible energy (DE) requirements,
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as calculated using published estimates of DE and DM for the relevant feedstuffs [28]. The
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ryegrass clover hay also provided a minimum forage intake of approximately 1% BW/day.
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The feed was presented in feed troughs fabricated from inverted car tyres, measuring
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approximately 66 cm in diameter and 22 cm in height. Water intake was unrestricted, with
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tap water supplied in large buckets.
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During the 22 day experimental phase, 11 different diets were fed in random order.
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Each treatment was repeated four times for each horse as two meals per day for two
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consecutive days. The cereal-based meals consisted of oats (3 g/kg BW, as fed), with either
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short chaff (1.43 ± 0.09 cm) or longer chaff (4.09 ± 0.14 cm) at addition rates of 0, 7.5, 15,
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30, 50 or 60 % by mass (i.e. the 50% diet contained 3g/kg BW oats plus 1.5 g/kg BW chaff,
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as fed). The chaff was cut by a local supplier according to specifications and the average
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chaff length was verified by using a rule to measure the length of 100 individual pieces of
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chaff chosen at random from batches of both short and long chaff.
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To enable the collection of spillages and feed refusals, the horses were fed in an
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adjoining stable with a bare concrete floor. To reduce anxiety, feeders were secured at the
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mid-point of a wall that was not common to another horse, although all horses were visible to
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each other. To limit disturbances during feeding, observations were made in a central
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observation room via remote TV monitors connected to video cameras (VideoHi8 Handycam,
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Sony Australia, North Sydney NSW, Australia) with wide angle lenses, mounted on the
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stable rafters. Horses were monitored repeatedly to determine if they were feeding or not.
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Observations were made every 5 min for the first 30 min, then every 2 min until the meal was
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consumed, or they refrained from eating, or were recorded as not moving for longer than 2
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consecutive min. Any feed refusals were collected and weighed at the end of the total
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observation period. To determine the ROI (g/min), the weight of feed eaten was divided by
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the time taken to consume the meal
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2.2.2 Study Two
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Because the results of Study one showed a lower ROI overall than that seen in
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previously published work, we examined several factors that might have contributed to this.
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Specifically, in Study two we used a different group of horses and examined the effect of
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meal size and palatability on ROI. The horses were acclimatised to the daily feeding routine
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for a total of 10 days (oats at 1000 hours and hay at 0600 hours, 1200 hours and 1700 hours).
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The amount of oats fed was increased incrementally over the first 8 days from 0.5 g/kg BW
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up to 4 g/kg BW (as fed), and once this level of oats was reached it was maintained for a
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further 2 days. Lucerne hay was fed in equally divided portions to provide the balance of
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individual DE requirements for maintenance (as estimated from published values [28]) and/or
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at least 1% BW/day forage intake as fed. Water intake and vitamin and mineral
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supplementation were provided as for Study one.
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During the next 14 days, seven different rations were fed twice to each horse in a
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random order: oats at 0.5, 1, 2, 3 or 4 g/kg BW as fed; oats at 4g/kg BW as fed plus 10%
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molasses; or no oats, but lucerne hay (~2 kg/horse as fed) at a mass equivalent to 4g/kg BW
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oats. To maintain a consistent diet, all horses received a total of 4 g/kg BW (as fed) of oats
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daily, with the balance fed at 1700 hours with their hay meal.
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2.2.3 Study Three Study three examined another factor with a potential impact on the observed ROI,
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which was the change in ROI over the 30 min duration of a meal. The feeding regimen was
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the same as that described in Study two. A standard meal of oats (2 kg) was fed, with uneaten
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feed removed and weighed, at one of five different time-points following meal
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commencement (5, 10, 15, 20 and 30 min). Each observational period (time-point) was
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replicated twice for each horse over two consecutive days. The five observational periods
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were applied to the horses in a random order. The entire study lasted 10 days and comprised
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30 observations.
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Apart from the procedures listed above, the same feeding conditions and procedures,
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including remote monitoring by video camera, were applied as described in Study one.
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Horses were fasted between 0800 hours and the 1000 hours meal (i.e. any long fibre was
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removed from the stall – as well as any uneaten oats). The horses were monitored every
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minute of the observation period. To ensure a consistent daily intake of oats and prevent
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artificial increases in ROI related to anxiety about feed removal, the uneaten portions of feed
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were returned to each horse once weighed.
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2.2.4 Study Four Having developed a standard 10 min protocol to measure ROI, in Study four we
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applied this to protocol to a larger group of horses to determine the size and possible sources
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of variability within a population. In Study four, each horse was fasted for 1 h prior to a
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cereal meal of 1 kg of oats (as fed) being offered at their usual cereal meal time. All horses
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had free access to water. The horses were monitored continuously for 10 min following
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commencement of eating. After 10 min any remaining feed was removed and weighed and
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ROI was calculated for each horse.
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2.3 Statistical Analysis As the data were distributed normally (Shapiro-Wilk test), parametric tests were used
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for their analysis. Due to the complexity of the experimental design, a step-wise approach
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was taken. For the measurements that were replicated on each animal, paired Student’s t-tests
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were used to compare the ROI between morning and afternoon meals, and meals fed on
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consecutive days. As no significant differences were found, these data were pooled and a
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mean value was generated for each horse on each diet.
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In Study one, the effects of chaff length and the five chaff addition rates were
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analysed as a factorial design by ANOVA, with effects sought for addition rate, chaff length,
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and any rate x length interaction. Polynomial regression was used to model the relationship
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between ROI and chaff addition rate; linear, quadratic and cubic models were fitted to the
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data and compared using contrasts. Finally, to identify the level at which chaff addition
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altered the ROI significantly, each addition rate was compared to a control diet containing no
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chaff, using Dunnett’s test.
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A similar approach was taken to analyse the data from studies two and three, which
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examined meal size and pattern of intake. After determining that there was no difference
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between replicates the mean observations for each horse were compared using ANOVA for
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repeated measures. For Study two the repeated variable was the quantity of oats given (the
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diets containing oats plus molasses, or lucerne hay only, were analysed separately by
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comparing them to each other, and to the oats-only diet, using Student’s paired t-test); for
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Study 3 the repeated variable was time. Linear regression was used to describe the
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relationship between the pattern of intake and ROI (Study three).
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In Study four, the effects of breed, BW, age, gender and exercise on ROI were sought
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initially by one-way ANOVA, followed by stepwise regression. Significant effects were
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found for breed and BW, but these variables were confounded. Thus, the ANOVA was
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repeated to explore breed effect in a subgroup of the population with a similar bodyweight.
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Post-hoc analyses were performed with Tukey’s test. To further explore the effect of BW
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without the confounding breed factor, linear regression of BW versus ROI was performed
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within each breed as well as within the entire population. All parametric tests incorporated a
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confirmatory test for normality of the data distribution and homogeneity of the variances. The
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data were analysed with SAS software and significance was accepted at P < .05. Results are
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expressed as mean ± se.
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3. Results
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3.1 Study 1
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The ROI for the same cereal meal did not differ between morning and afternoon
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meals, nor on consecutive days. Cereal ROI was markedly faster than the ROI for a similar
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quantity of hay (Fig. 1), but decreased as chaff addition increased (P < .05; Fig. 1). The
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relation between ROI and the rate of chaff addition was broadly linear (r2 = 0.67, P < 0.001;
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ROI = 47.5 – (0.29 + chaff addition %), up to addition rates of 50%, but ROI did not decrease
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further when 60% chaff was added. When compared to an oats-only control meal, the
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addition of 15% chaff or more was required before the decrease in ROI reached statistical
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significance. There was neither a significant effect of chaff length on ROI, nor any interaction
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between chaff length and addition rate (Fig. 1).
278 279 280
3.2 Study 2 The ROI for a cereal meal was independent of meal size (39.8 ± 3.26 g/min for ~ 250
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g oats vs. 39.1 ± 3.42 g/min for ~ 2 kg oats) and did not change significantly following the
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addition of 10% molasses (43.6 ± 5.36 g/min; P = .27), although with or without molasses,
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the oats were consumed faster than 2 kg of lucerne hay (23.9 ± 3.65 g/min; P < .01).
284 285 286
3.3 Study 3 The ROI showed marked variability between horses for the first 5 min of feeding, but
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the variability was lower and was reasonably constant thereafter (Table 2). However, the
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average ROI was not constant over the 30 min period, but decreased steadily over the course
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of a meal.
290 291
A plot of cumulative intake is shown in Fig. 2. The average ROI declined over the
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observation period, from 73.7 g/min at 5 min, to 47.8 g/min after 30 min (Table 3, P < .05).
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However, when calculated for each time-point after adjusting for the average amount eaten
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by that horse in the previous 5 min period, the actual ROI was found to decrease more
295
sharply, following a linear pattern (P = 0.05) as represented by the equation: ROI at time t =
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77.9 – (2.07t). Thus, the actual ROI would have been approximately 77.9 g/min at time 0,
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decreasing at a rate of 2.07 g/min, to reach only 15.8 g/min after 30 min.
298 299
This marked change in ROI over time highlighted the need to adopt a standardised
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measurement time to enable comparisons of ROI from different studies. Based on the actual
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ROI and on degree of variability seen at each time point, 10 min was selected as the preferred
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standard measurement time for use in Study four.
303 304 305
3.4 Study 4 No effect of exercise, age or gender on ROI was found (Table 3). There was a
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significant effect of BW (P < .05) and breed (P < .05) on the ROI, but there was no BW x
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breed interaction. Clydesdales (CY) had a faster ROI than both TB and SB (P < .05; Table 3).
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Between breed subpopulations of a similar BW, a breed difference was observed between the
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CY and TB groups (P < .05; Table 4). Overall, BW had a positive linear relationship (r2 =
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0.56; P < .05) to ROI (Fig. 3) and this effect was also seen within the CY breed, but not with
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the TB or SB breeds which fell into a narrower weight range.
312 313
4. Discussion
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The ROI of a cereal-based meal was seen to be considerably faster than a roughage-
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only meal of the same mass, and this finding is in agreement with prior studies [24,25].
316
Furthermore, the addition of chaff to a cereal meal slowed ROI incrementally up to an
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addition rate of about 50%, with a minimum of 15% roughage required to decrease ROI
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significantly. These findings are consistent with our previous observations that the addition of
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6% chaff to a cereal mix did not alter ROI significantly, whereas an apparent decrease in ROI
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(when measured as volume, but not mass) was seen when 36% chaff was added to either oats
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or a sweet feed mix [28]. They are also comparable to a report by Ellis et al. [27] who
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showed that including chaff at a rate of 30% or more can lead to longer and slower eating
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periods, with a concomitant increase in chewing. Overall, this information should assist
324
horse owners and trainers to optimise roughage addition rates in order to control the ROI of
325
cereal-based diets.
326 327
The present findings were applicable irrespective of meal time, as ROI did not vary
328
between meals in this controlled study. However, under natural housing conditions ROI may
329
well alter between meals if the meals are unevenly spaced, or if cereal meals are preceded by
330
a large hay meal, for example. Similarly, more vigorous exercise would likely influence ROI
331
at a given mealtime.
332 333
The fact that the longer stalk-length chaff did not decrease ROI when compared to
334
shorter chaff may have been affected by the relatively small difference in stalk-length (~2.7
335
cm). The lengths selected (<2 cm vs. 4 cm) were representative of the average difference
336
between Australian and European chaff. Un-cut hay has been associated with a slower ROI
337
compared with cut hay, and it is possible that feeding chaff with a longer stalk-length (> 4
338
cm) may decrease ROI [24]. Further studies to investigate this theory are needed. A possible
339
confounding factor in the current study was the fact that the longer chaff was ground,
340
whereas the short chaff was chopped. Grinding would have affected the width, thickness,
341
density and weight of the longer chaff, and these factors may work together with length to
342
alter masticatory requirements, thereby affecting our ability to detect a change in ROI.
343
However, no significant differences were found in ROI between short and long chaff in a
14
344
previous study where both chaffs were chopped [27], or in a study comparing long-stemmed
345
and cut haylage [22]. This suggests that factors other than stalk-length, such as feeding a
346
heterogeneous diet, are more important in influencing ROI [24].
347 348
At about 40 g/min, the ROI of a cereal meal in the current study was considerably
349
slower than that of up to 129 g/min reported in a similar study where a 2 kg meal of oats,
350
maize and soybean meal was fed to horses undergoing light exercise [26]. Other studies
351
conducted in Europe have also reported relatively fast ROI [27]. This difference may be
352
related to the fact that the horses in the current study were only acclimatised to the stabled
353
environment for 8 to 10 days, whereas horses in other studies might have been permanently
354
stabled, impacting on their behaviour. Different ROI might also be related to differences in
355
exercise intensity between different studies. Although the survey component of the current
356
study found that exercise did not appear to affect ROI, the difference in exercise regimes in
357
the surveyed horses was large. Furthermore, the survey data were limited by being
358
qualitative, nominal and subjective. Controlled experiments using quantitative parameters
359
and a standardised exercise test are recommended to further explore the effect of exercise on
360
ROI, particularly in light of the potential impact of long-term stabling on ROI.
361 362
Molasses is sometimes added to feed to improve palatability, but in the present study
363
10% molasses did not increase the ROI of oats significantly. This suggests that the oats were
364
already palatable, and that palatability was not a major factor in accounting for the relatively
365
slow ROI observed, as discussed above. The addition of molasses would have also increased
366
the moisture content of the meal slightly - a factor which has been shown to increase ROI in
367
both sheep and cattle [30,31]. Therefore, either moisture content was not an important factor
368
in the present study, or the molasses had only a small effect on this variable and higher
15
369
moisture levels are needed before this becomes significant. Further studies would be
370
necessary to investigate this.
371 372
There appears to be little data on the impact of meal size on ROI in horses. One study
373
did show a higher ROI when smaller vs larger quantities of a pelleted mixed-feed were
374
offered, provided the pellets were small (5 mm diameter), with less of an effect seen when the
375
pellets were larger in size [32]. Other studies on voluntary feeding in humans and production
376
animals have shown that food consumption is affected by satiety, ambient temperature and
377
body condition [33]. Meal size did not affect ROI in the current study where these factors
378
were kept constant. This finding suggests that the provision of smaller, more frequent meals
379
in an attempt to emulate foraging behaviour is unlikely to affect ROI. Horses may self-
380
regulate their intake irrespective of meal size, and investigation of this theory is
381
recommended.
382 383
One of the most significant factors affecting ROI was the duration of the meal or
384
observation period. For a cereal-based meal, the ROI was found to be fastest at the start of a
385
meal and this may be related to hunger, behavioural effects, or insalivation of the food. The
386
initial 15 min period may represent a danger zone for the development of digestive problems
387
and could be targeted by owners and trainers. Strategies to decrease ROI during this period
388
could include feeding long stemmed roughage prior to a cereal meal to reduce hunger levels
389
and place roughage in the GIT of the horse [34]. Secondly, horses could be separated during
390
feeding to reduce the effect of competition and/or hierarchy on ROI. The ROI during the
391
initial 5 min period of cereal meal consumption was highly variable and this was largely due
392
to behavioural effects (pacing, head tossing) during this time. This needs to be taken into
393
account when attempting to measure ROI during this initial feeding period. A time-point of
16
394
10 min post-commencement of the meal was found to be the most stable time for measuring
395
ROI, and this finding could guide future studies on ROI.
396 397
The finding that larger horses eat more quickly than smaller horses concurs with
398
previous studies and is likely to be related to occlusal surface area and chewing rate [35,36].
399
The larger head of the CY when compared to smaller breeds (e.g. TB) is likely to enable
400
larger amounts of feed to be consumed with each mouthful and account for this disparity. The
401
effect of breed may also depend on the type of meal, as it has been reported in a comparison
402
of ponies and warmblood horses, that breed differences were seen using a fibre-rich pelleted
403
mixed feed, but not with a muesli or crushed grain feed [25].
404 405
It appears that bodyweight also has an impact on ROI, with the failure to detect BW
406
differences within the TB and SB groups likely to be related to the narrow bodyweight range
407
found in these groups. This finding may be important for the dietary management of obese
408
horses that are predisposed to IR, where careful control of nutrition is paramount to reducing
409
bodyweight and preventing laminitis. The current results also suggest that both breed and BW
410
should be controlled for in future ROI studies. Comparison between horses and ponies ROI
411
was not made in this study but justifies further investigation given that ponies may have the
412
capacity for a higher daily dry matter intake than horses reflecting either longer time spent
413
ingesting feed or a higher ROI.
414 415
Although gender did not impact on the ROI of a cereal meal in the current study,
416
further in-depth studies on the effect of gender on ROI are required. Nutritional requirements
417
between geldings and breeding stallions or dry and lactating mares vary, and an investigation
418
of the effect this may have on ROI is warranted. Surprisingly, age also does not appear to
17
419
impact on ROI. Younger horses could be expected to have higher energy requirements,
420
superior dentition and a more competitive nature, but this does not appear to increase ROI
421
when compared to sexually mature and older horses. Fortunately, considering that age and
422
gender are among the more difficult factors for horse owners to control, the findings of the
423
current study suggest that they appear to have little impact of the ROI of cereal meals.
424 425
5. Conclusions
426
The results of the current study support the hypotheses that roughage is consumed
427
more slowly than cereal-based feed and that the addition of chopped roughage to a cereal
428
meal decreases the ROI of that meal, with addition rates of 15% to 50% roughage shown to
429
be effective. These data can be used by horse owners and trainers to control the ROI of
430
cereals, thereby decreasing the ROP of ingesta, leading to improved GIT health and
431
potentially, behaviour. Current data suggest that chaff with stalk-lengths between 2 cm and 4
432
cm will be equally effective at reducing the ROI when added to cereal-based meals, however
433
further study is required to investigate the impact of longer stalk-lengths (> 4cm) on ROI.
434
Meal size, palatability, age and gender do not appear to affect ROI and this finding allows
435
owners to focus on managing other factors, such as BW. Strategies to reduce ROI of cereal
436
meals have been suggested and these may be of particular benefit in the initial 15 min period
437
of eating when the ROI is highest.
438 439
Acknowledgements
440
This study was funded by The Waltham Centre for Pet Nutrition and Charles Sturt
441
University. Both sponsors were involved in the experimental design and interpretation of the
442
results.
443
18
444 445
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446
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hindgut starch fermentation and acidosis in the Australian racing Thoroughbred. Aust Vet J
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[24] Brokner C, Norgaard P, Hansen HH. Effect of feed type and essential oil product on
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equine chewing activity. J Anim Phys Anim Nutr 2008; 92: 621-630.
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patterns of sport ponies and warmblood horses following iso-energetic intake of pelleted
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fibre-rich mixed feed, muesli feed and semicrushed oat grains. J Anim Physiol Anim Nutr
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[26] Gallagher JR, Hintz F. Rate of feed intake and horse health. Proc Aust Soc Anim Prod
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[27] Ellis AD, Thomas S, Arkell K, Harris P. Adding chopped straw to concentrate feed: The
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effect of inclusion rate and particle length on intake behaviour of horses. Pferdeheilkunde
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[28] NRC. Nutrient requirements of horses. Washington DC: National Academy Press; 1989. 21
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[29] Harris PA, Sillence M, Inglis R, Siever-Kelly C, Friend M, Munn K, Davidson H. Effect
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of short (<2cm) lucerne chaff addition on the intake rate and glycaemic response of a sweet
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feed. Pferdeheilkunde 2005; 21: 88-89.
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[30] Gibb MJ, Huckle CA, Nuthall R. Effect of time of day on grazing behaviour by lactating
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dairy cows. Grass and Forage Sci 1998; 53: 41-46.
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[31] Kenney PA, Black JL, Colebrook WF. Factors affecting diet selection by sheep: dry
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matter content and particle length of forage. Aust J Agric Res 1984; 35: 831-838.
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[32] Bochnia M, Goetz F, Wensch-Dorendorf M, Kölln M., Zeyner A. Chewing patterns in
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horses during the intake of variable quantities of two pelleted compound feeds differing in
527
their physical characteristics only. Res Vet Sci 2019; 125: 189-194.
528
[33] Gaughan JB, Mader TL, Holt SM. Cooling and feeding strategies to reduce heat load of
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grain-fed beef cattle in intensive housing. Livestock Sci 2008; 113: 226-233.
530
[34] Vervuert I, Voigt K, Hollands T, Cuddeford D, Coenen M. The effect of mixing and
531
changing the order of feeding oats and chopped alfalfa to horses on: glycaemic and
532
insulinaemic responses, and breath hydrogen and methane production. J Anim Physiol Anim
533
Nutr 2009; 93: 631-638.
534
[35] Fleurance G, Fritz H, Duncan P, Gordon IJ, Edouard N, Vial C. Instantaneous intake rate
535
in horses of different body sizes: Influence of sward biomass and fibrousness. App Anim
536
Behav Sci 2009; 117: 84-92.
537
[36] Stover KK, Williams SH. Intraspecific scaling of chewing cycle duration in three species
538
of domestic ungulates. J Exp Biol 2011; 214: 104-112.
539 540 541 542
22
543
Figure captions
544
Fig. 1. The effect of adding wheaten chaff at various addition rates and with long (4.1 cm, ●)
545
or short (1.4 cm, ○) stalk-length, on the mean (± se) rate of intake of oats (3 g/kg BW) in
546
horses (n = 6). The horizontal line represents the average rate of intake for a 2 kg meal of
547
hay.
548 549
Fig. 2. Mean (± se) cumulative feed intake over 30 min in six Thoroughbred horses presented
550
with a 2 kg meal of oats.
551 552
Fig. 3. The rate of cereal intake measured over a 10 min period in Clydesdale (○, n = 28),
553
Thoroughbred (●, n = 34) and Standardbred (∆, n = 9) horses, presented with a 1 kg meal of
554
oats. The straight line represents a first order regression fitted to the data.
23
555 556
Table 1 Subjects and experimental design for three studies to examine factors that influence the rate of intake of a cereal-based meal. Study 1
Study 2
Study 3
Study 4
6 geldings
6 geldings
6 geldings
36 geldings, 35 mares
Breeds
5 Thoroughbreds 1 Standardbred
6 Thoroughbreds
6 Thoroughbreds
34 Thoroughbreds 28 Clydesdales 9 Standardbreds
Mean BW (± se), kg
479 ± 5.33
489 ± 27.4
489 ± 27.4
603 ± 22
Mean age (± se), years
7 ± 0.93
7.8 ± 1.6
7.8 ± 1.6
See Table 2
Balanced 2 x 6 factorial1
Randomized factorial2
Repeated measures3.
Multivariable population study
Dependent variable
Rate of intake
Rate of intake
Rate of intake
Rate of intake
Fixed effects
Chaff length (x 2) Addition rate (x 5) Feeding time Replicate number
Dietary component ( x 3) Level of component (x 6)
Time allowed to feed
Random effects
Horse
Replicate number Horse
Replicate number Horse
Horses Sex
Experiment Design
557 558 559
1
Age, breed, gender, exercise level
Order of presentation of each diet (treatment combination) assigned at random; each diet replicated four times over two consecutive days and the replicate observations were pooled.
560 561 562 563
2
Three dietary components; one component fed at five levels; seven treatments in total. Order of treatments for each subject assigned at random; each treatment replicated twice over two consecutive days; 3 Each observation was replicated twice over two consecutive days and the replicates were pooled. Time was used as the repeated factor in the analysis.
2
564
Table 2
565
Mean (± se) rate of intake (ROI) of a 2 kg meal of oats measured in six geldings at five time
566
intervals after feeding, showing a significant reduction in ROI over time (P < 0.05). Time after feeding, min ROI, g/min
567 568
5
10
15
20
30
73.7 ± 13.4
66.2 ± 7.5
63.8 ± 6.3
57.7 ± 8.7
48.0 ± 5.7
569
Table 3
570
Mean (± se) rate of intake (ROI) of a 1 kg meal of oats in Clydesdale, Thoroughbred and
571
Standardbred horses surveyed in the Riverina district of NSW, Australia
572 Item
ROI (g/min)
n
P-value
All horses
78.9 ± 2.85
71
-
Clydesdale
99.3 ± 3.35a
28
< 0.05
Thoroughbred
66.8 ± 2.94b
34
Standardbred
60.9 ± 6.07b
9
Yes
74.7 ± 4.24
27
No
81.4 ± 3.77
44
1–2
74.8 ± 4.27
21
3–8
77.9 ± 4.82
28
9+
83.9 ± 5.54
22
Female
80.7 ± 4.21
35
Male
77.1 ± 3.88
36
Breed
Exercise 0.25
Age (years) 0.45
Gender
573 574
ab
0.53
Means with different superscripts differ (P < .05, Tukey’s test)
2
575 576
Table 4
577
The effect of breed on rate of intake (mean ± se) in a subpopulation of heavy and light horses
578
matched for bodyweight (mean (range)).
579 Breed
Body weight
Rate of intake
n
(kg)
(g/min)
Clydesdale
533 (452-639)
81.8 ± 6.80
8
Thoroughbred
542 (442-640)
66.0 ± 3.35
24
Thoroughbred
433 (410-480)
71.0 ± 2.40
14
Standardbred
451 (403-476)
61.9 ± 6.10
9
Effect of breed (P-value)
Heavier .03
Lighter
3
.08
Declaration of interest statement Professor Pat Harris is an employee of The WALTHAM Centre for Per Nutrition who funded this study. Prof Harris had a role in the study design, interpretation of the data, revising the manuscript and the decision to submit the article for publication.
All experimental protocols were approved by the Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035, 05/048, 05/067).
S0737-0806(19)30618-5
DOI:
https://doi.org/10.1016/j.jevs.2019.102869
Reference:
YJEVS 102869
To appear in:
Journal of Equine Veterinary Science
Received Date: 25 February 2019 Revised Date:
4 November 2019
Accepted Date: 16 November 2019
Please cite this article as: Campbell TE, Doughty H, Harris PA, de Laat MA, Sillence MN, Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in Horses, Journal of Equine Veterinary Science (2019), doi: https://doi.org/10.1016/j.jevs.2019.102869. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier Inc. All rights reserved.
1
Factors Affecting the Rate and Measurement of Feed Intake for a Cereal-Based Meal in
2
Horses
3 4
Tara E. Campbella, Hunter Doughtya, Patricia A. Harrisb, Melody A. de Laatc, Martin N.
5
Sillencec, *
6 7
a
8
NSW, Australia
9
b
School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga 2650,
Equine Studies Group, WALTHAM Centre for Pet Nutrition, Waltham-on-the-Wolds,
10
Leicestershire LE14 4RT, United Kingdom
11
c
12
Brisbane, Queensland 4001, Australia
Earth, Environmental and Biological Sciences, Queensland University of Technology,
13 14
Animal care and welfare/ethical statement: All experimental protocols were approved by the
15
Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035,
16
05/048, 05/067).
17
Conflict of interest statement: PA Harris is an employee of the WALTHAM Centre for Pet
18
Nutrition who funded this project. PA Harris had a role in the study design, interpretation of
19
the data and in the decision to submit the article for publication.
20
*Corresponding author at: Martin N. Sillence, Earth, Environmental and Biological Sciences
21
School, Science and Engineering Faculty, Queensland University of Technology,
22
2 George Street, GPO Box 2434,Brisbane, Qld 4001, Australia.
23
E-mail address: [email protected] (M.N. Sillence).
24 25
26
Abstract
27
The rapid intake of high-cereal, low-roughage meals may cause gastrointestinal and
28
behavioural disorders. We investigated some of the factors that can affect the rate of intake
29
(ROI) in four separate studies. Study 1 investigated the effect of chaff length and addition
30
rate on the ROI of oats. The ROI decreased as more chaff was added to the diet, attaining
31
significance (P < .05, n = 6) at levels above 15% addition and reaching a plateau at ~50%.
32
This was independent of stalk length (1.4 cm vs 4.1 cm). Study 2 showed that meal size
33
(varying from 0.5 to 4 g/kg BW) did not affect the ROI for a cereal-based meal, nor was ROI
34
altered by the addition of 10% molasses (n = 6). Study 3 demonstrated that ROI changed
35
markedly over the course of a meal, commencing at an average rate of 74 g/min for the first
36
5 min and decreasing to 15.8 g/min after 30 min (n = 6). Study 4 examined the effects of
37
breed, BW, exercise and gender in 71 horses. In Clydesdales, BW affected ROI (P < .05), and
38
Clydesdales had a faster ROI than Thoroughbreds of similar BW (81.8 ± 6.8 versus 66.0 ±
39
3.35 g/min; P < .05). Exercise level, age and gender did not impact ROI significantly. The
40
results highlight the effectiveness of feeding chaff to slow ROI and demonstrate the need for
41
a standardised protocol if ROI is to be compared between different studies.
42 43
Keywords: equine; starch; roughage; nutrition; concentrates
44
2
45 46
1. Introduction As a foraging species, horses have evolved to eat small amounts of fibre-based feeds
47
virtually continuously, grazing for up to 70% of each 24 h period [1,2]. Selective grazing
48
ensures a well-balanced herbivorous diet that promotes optimal digestion by the
49
gastrointestinal tract (GIT) [2,3]. Although some modern forages can exceed nutritional
50
requirements for horses in light work, when energy demands are high, it is common to either
51
supplement or replace the free-ranging, predominantly forage-based diet with high-energy
52
rations, fed at infrequent intervals to horses confined to small paddocks or stables. This
53
practice typically employs cereal grain or cereal-based feeds that contain energy in a
54
concentrated form [4,5].
55 56
Unfortunately, such cereal-based diets can predispose horses to metabolic,
57
gastrointestinal and behavioural problems, such as obesity, gastric ulceration, colic and
58
stereotypies [6-10]. In general, cereal-based rations require less chewing effort than long
59
fibre, resulting in less saliva production, and an increased risk of lateral hook development on
60
the dental arcade. They are also ingested more quickly (higher rate of intake: ROI) than meals
61
based on long fibre such as hay. When large meals of either pellets or cereal grains are fed
62
infrequently, a transient state of hypovolaemia occurs as a result of upper gastrointestinal
63
secretions. The loss in plasma volume that occurs in ponies within 1 h of feeding has been
64
shown to be 15% on average, and up to 24% in quick or greedy feeders [11].
65 66
For a horse ration to be safe, there is an upper limit to how much starch it should
67
contain and a lower limit to its roughage content [7,12]. Excessive dietary starch can
68
predispose a horse to insulin resistance (IR) and hyperinsulinaemic laminitis, as well as
69
increasing the risk of gastrointestinal ulcers [9,13,14]. Furthermore, an elevated ROI may
3
70
lead to insufficient insalivation and mastication of the food, choke, and an alteration in the
71
rate of passage (ROP) of digesta through the GIT [15]. It is the decreased pre-caecal digestion
72
which may lead to acidosis, colic and alimentary-associated laminitis [14,16].
73 74
Therefore, controlling the ROI of cereal-based feeds is highly desirable. In addition to
75
diet composition, many other factors may affect the ROI of a meal in horses, including grain
76
processing methods, roughage particle size, frequency and size of meals, palatability,
77
moisture content, exercise level, sex, age, bodyweight, breed and occlusal surface
78
area/dentition [18]. Previous studies have examined some of these factors with variable
79
results [18-22]. However, most literature agrees that the inclusion of chopped roughage
80
(chaff) to a cereal-based meal is an important factor in decreasing ROI. This was reflected in
81
a survey of Australian racehorse trainers, which found that more than 95% of trainers added
82
chaff to cereal diets to decrease ROI [23].
83 84
Studies on the effect of the physical form of chopped roughage added to equine diets
85
are conflicting, and this topic requires further investigation [22,24,25]. Of particular interest
86
is the observation that longer stalk-length (~4 cm) chaff is typically fed in Europe than in
87
Australia (~2 cm). Historically, the feeding of very short chaff in Germany was viewed as a
88
serious risk factor for impaction, and roughage with a longer stalk-length has been associated
89
with decreased ROI [24].
90 91
Initially, the sole aim of this study was to examine the effect of roughage inclusion on
92
the ROI of a cereal-based meal, with respect to addition rate and stalk length. However, when
93
comparing our results with earlier reports [26,27] it was clear that we were working from a
94
different baseline i.e. the ROI for cereal alone observed in our study was much lower than
4
95
that reported in those earlier studies. Therefore, we pursued the additional aim of identifying
96
the factors that can affect ROI other than the meal composition, and of developing a
97
standardised methodology that would control for these factors. The study was expanded to
98
test the hypotheses that ROI is also dependent on meal size, palatability, observation period,
99
exercise, age, gender, breed and bodyweight. Our ultimate aim was to better understand the
100
variables that affect ROI, in order to inform safer feeding practices, facilitate future studies
101
and promote consistent methodologies.
102 103 104
2. Materials and methods Four studies were performed and all experimental protocols were approved by the
105
Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035,
106
05/048, 05/067).
107 108 109
2.1 Animals The characteristics of the animals used in studies one to three are presented in Table
110
1. The horses were all geldings, drawn from a group of twelve horses belonging to the Equine
111
Centre at Charles Sturt University, Wagga Wagga NSW. The horses had been housed in
112
stables or yards for several weeks prior to the studies, and were all accustomed to being fed
113
oats from time to time.
114 115
All the horses were examined by a veterinarian and treated by an equine dental
116
technician to ensure good general and oral health prior to the studies. They were also treated
117
with an anthelmintic drench (200 µg/kg BW; MecWorma, Farnam, Phoenix AZ) at least 8
118
days before any feeding observations were made. The horses were stabled individually (4 m x
119
4 m) on 30 cm deep sawdust bedding at Charles Sturt University Equine Centre. In the first
5
120
three studies all horses were exercised for 1 h/day every day, at a continuous walk on a
121
mechanical horse walker (Irongate, Netley SA, Australia).
122 123
In Study four, a population survey of 71 horses of mixed sex and breed (Table 3)
124
from the Riverina district of NSW, was conducted to examine factors affecting the ROI of a
125
standardised meal of 1 kg oats. Informed consent for the survey was provided by all owners
126
at an initial visit undertaken to assess the horses and facilities. To avoid neophobic behaviour,
127
horses were only enrolled in the survey if they had received oats previously. Observations
128
were performed during a subsequent visit. The horses were weighed using a calibrated
129
portable scale suitable for use in horses (Ezy-weigh, Darwin NT, Australia), and owners were
130
asked to complete a questionnaire to provide information about the breed, gender, age,
131
exercise intensity, current diet, history of feed-related digestive disorders and any stereotypic
132
behaviours of their horse.
133 134
2.2 Study Design
135
The design of each study is described in Table 1.
136
2.2.1 Study One
137
Study one aimed to determine the relationship between the addition rate of chaff to a
138
cereal-based feed and the ROI of that feed; and to measure any difference in ROI between the
139
addition of short (1.43 ± 0.09 cm) chaff and longer (4.09 ± 0.14 cm) chaff cut from the same
140
batch of straw. The horses were acclimatised to a daily feeding routine: cereal-based meals
141
were fed at 0900 hours and 1400 hours; hay plus a vitamin and mineral supplement (50
142
g/day; Hoss-Amin-R, Troy Laboratories, Glendenning NSW, Australia) were fed at 1700
143
hours.
144
6
145
The cereal-based meal contained whole, unprocessed oats obtained from a single
146
batch. During the acclimatisation/adaptation period, the quantity of oats fed was increased
147
incrementally from 0.5 g/kg BW to 3 g/kg BW (as fed) per meal over six days. Once this
148
level of oats was reached, this was maintained for a further 2 days to bring the adaptation
149
period to a total of 8 days. During this phase, the cereal-based meals included an equal
150
quantity of short and long wheaten chaff fed at 1.8 g/kg BW (as fed). Although oats and chaff
151
are sometimes wetted to reduce the risk of choke, in the present study they were fed dry, in
152
line with the prevailing practice at this equine centre. Not wetting the feed also eliminated a
153
potential source of variation.
154 155
The 1700 hours meal consisted entirely of ryegrass clover hay given at a level that
156
provided the balance of each individual’s maintenance digestible energy (DE) requirements,
157
as calculated using published estimates of DE and DM for the relevant feedstuffs [28]. The
158
ryegrass clover hay also provided a minimum forage intake of approximately 1% BW/day.
159
The feed was presented in feed troughs fabricated from inverted car tyres, measuring
160
approximately 66 cm in diameter and 22 cm in height. Water intake was unrestricted, with
161
tap water supplied in large buckets.
162 163
During the 22 day experimental phase, 11 different diets were fed in random order.
164
Each treatment was repeated four times for each horse as two meals per day for two
165
consecutive days. The cereal-based meals consisted of oats (3 g/kg BW, as fed), with either
166
short chaff (1.43 ± 0.09 cm) or longer chaff (4.09 ± 0.14 cm) at addition rates of 0, 7.5, 15,
167
30, 50 or 60 % by mass (i.e. the 50% diet contained 3g/kg BW oats plus 1.5 g/kg BW chaff,
168
as fed). The chaff was cut by a local supplier according to specifications and the average
7
169
chaff length was verified by using a rule to measure the length of 100 individual pieces of
170
chaff chosen at random from batches of both short and long chaff.
171 172
To enable the collection of spillages and feed refusals, the horses were fed in an
173
adjoining stable with a bare concrete floor. To reduce anxiety, feeders were secured at the
174
mid-point of a wall that was not common to another horse, although all horses were visible to
175
each other. To limit disturbances during feeding, observations were made in a central
176
observation room via remote TV monitors connected to video cameras (VideoHi8 Handycam,
177
Sony Australia, North Sydney NSW, Australia) with wide angle lenses, mounted on the
178
stable rafters. Horses were monitored repeatedly to determine if they were feeding or not.
179
Observations were made every 5 min for the first 30 min, then every 2 min until the meal was
180
consumed, or they refrained from eating, or were recorded as not moving for longer than 2
181
consecutive min. Any feed refusals were collected and weighed at the end of the total
182
observation period. To determine the ROI (g/min), the weight of feed eaten was divided by
183
the time taken to consume the meal
184 185
2.2.2 Study Two
186
Because the results of Study one showed a lower ROI overall than that seen in
187
previously published work, we examined several factors that might have contributed to this.
188
Specifically, in Study two we used a different group of horses and examined the effect of
189
meal size and palatability on ROI. The horses were acclimatised to the daily feeding routine
190
for a total of 10 days (oats at 1000 hours and hay at 0600 hours, 1200 hours and 1700 hours).
191
The amount of oats fed was increased incrementally over the first 8 days from 0.5 g/kg BW
192
up to 4 g/kg BW (as fed), and once this level of oats was reached it was maintained for a
193
further 2 days. Lucerne hay was fed in equally divided portions to provide the balance of
8
194
individual DE requirements for maintenance (as estimated from published values [28]) and/or
195
at least 1% BW/day forage intake as fed. Water intake and vitamin and mineral
196
supplementation were provided as for Study one.
197 198
During the next 14 days, seven different rations were fed twice to each horse in a
199
random order: oats at 0.5, 1, 2, 3 or 4 g/kg BW as fed; oats at 4g/kg BW as fed plus 10%
200
molasses; or no oats, but lucerne hay (~2 kg/horse as fed) at a mass equivalent to 4g/kg BW
201
oats. To maintain a consistent diet, all horses received a total of 4 g/kg BW (as fed) of oats
202
daily, with the balance fed at 1700 hours with their hay meal.
203 204 205
2.2.3 Study Three Study three examined another factor with a potential impact on the observed ROI,
206
which was the change in ROI over the 30 min duration of a meal. The feeding regimen was
207
the same as that described in Study two. A standard meal of oats (2 kg) was fed, with uneaten
208
feed removed and weighed, at one of five different time-points following meal
209
commencement (5, 10, 15, 20 and 30 min). Each observational period (time-point) was
210
replicated twice for each horse over two consecutive days. The five observational periods
211
were applied to the horses in a random order. The entire study lasted 10 days and comprised
212
30 observations.
213 214
Apart from the procedures listed above, the same feeding conditions and procedures,
215
including remote monitoring by video camera, were applied as described in Study one.
216
Horses were fasted between 0800 hours and the 1000 hours meal (i.e. any long fibre was
217
removed from the stall – as well as any uneaten oats). The horses were monitored every
218
minute of the observation period. To ensure a consistent daily intake of oats and prevent
9
219
artificial increases in ROI related to anxiety about feed removal, the uneaten portions of feed
220
were returned to each horse once weighed.
221 222 223
2.2.4 Study Four Having developed a standard 10 min protocol to measure ROI, in Study four we
224
applied this to protocol to a larger group of horses to determine the size and possible sources
225
of variability within a population. In Study four, each horse was fasted for 1 h prior to a
226
cereal meal of 1 kg of oats (as fed) being offered at their usual cereal meal time. All horses
227
had free access to water. The horses were monitored continuously for 10 min following
228
commencement of eating. After 10 min any remaining feed was removed and weighed and
229
ROI was calculated for each horse.
230 231 232
2.3 Statistical Analysis As the data were distributed normally (Shapiro-Wilk test), parametric tests were used
233
for their analysis. Due to the complexity of the experimental design, a step-wise approach
234
was taken. For the measurements that were replicated on each animal, paired Student’s t-tests
235
were used to compare the ROI between morning and afternoon meals, and meals fed on
236
consecutive days. As no significant differences were found, these data were pooled and a
237
mean value was generated for each horse on each diet.
238 239
In Study one, the effects of chaff length and the five chaff addition rates were
240
analysed as a factorial design by ANOVA, with effects sought for addition rate, chaff length,
241
and any rate x length interaction. Polynomial regression was used to model the relationship
242
between ROI and chaff addition rate; linear, quadratic and cubic models were fitted to the
243
data and compared using contrasts. Finally, to identify the level at which chaff addition
10
244
altered the ROI significantly, each addition rate was compared to a control diet containing no
245
chaff, using Dunnett’s test.
246 247
A similar approach was taken to analyse the data from studies two and three, which
248
examined meal size and pattern of intake. After determining that there was no difference
249
between replicates the mean observations for each horse were compared using ANOVA for
250
repeated measures. For Study two the repeated variable was the quantity of oats given (the
251
diets containing oats plus molasses, or lucerne hay only, were analysed separately by
252
comparing them to each other, and to the oats-only diet, using Student’s paired t-test); for
253
Study 3 the repeated variable was time. Linear regression was used to describe the
254
relationship between the pattern of intake and ROI (Study three).
255 256
In Study four, the effects of breed, BW, age, gender and exercise on ROI were sought
257
initially by one-way ANOVA, followed by stepwise regression. Significant effects were
258
found for breed and BW, but these variables were confounded. Thus, the ANOVA was
259
repeated to explore breed effect in a subgroup of the population with a similar bodyweight.
260
Post-hoc analyses were performed with Tukey’s test. To further explore the effect of BW
261
without the confounding breed factor, linear regression of BW versus ROI was performed
262
within each breed as well as within the entire population. All parametric tests incorporated a
263
confirmatory test for normality of the data distribution and homogeneity of the variances. The
264
data were analysed with SAS software and significance was accepted at P < .05. Results are
265
expressed as mean ± se.
266 267
3. Results
268
3.1 Study 1
11
269
The ROI for the same cereal meal did not differ between morning and afternoon
270
meals, nor on consecutive days. Cereal ROI was markedly faster than the ROI for a similar
271
quantity of hay (Fig. 1), but decreased as chaff addition increased (P < .05; Fig. 1). The
272
relation between ROI and the rate of chaff addition was broadly linear (r2 = 0.67, P < 0.001;
273
ROI = 47.5 – (0.29 + chaff addition %), up to addition rates of 50%, but ROI did not decrease
274
further when 60% chaff was added. When compared to an oats-only control meal, the
275
addition of 15% chaff or more was required before the decrease in ROI reached statistical
276
significance. There was neither a significant effect of chaff length on ROI, nor any interaction
277
between chaff length and addition rate (Fig. 1).
278 279 280
3.2 Study 2 The ROI for a cereal meal was independent of meal size (39.8 ± 3.26 g/min for ~ 250
281
g oats vs. 39.1 ± 3.42 g/min for ~ 2 kg oats) and did not change significantly following the
282
addition of 10% molasses (43.6 ± 5.36 g/min; P = .27), although with or without molasses,
283
the oats were consumed faster than 2 kg of lucerne hay (23.9 ± 3.65 g/min; P < .01).
284 285 286
3.3 Study 3 The ROI showed marked variability between horses for the first 5 min of feeding, but
287
the variability was lower and was reasonably constant thereafter (Table 2). However, the
288
average ROI was not constant over the 30 min period, but decreased steadily over the course
289
of a meal.
290 291
A plot of cumulative intake is shown in Fig. 2. The average ROI declined over the
292
observation period, from 73.7 g/min at 5 min, to 47.8 g/min after 30 min (Table 3, P < .05).
293
However, when calculated for each time-point after adjusting for the average amount eaten
12
294
by that horse in the previous 5 min period, the actual ROI was found to decrease more
295
sharply, following a linear pattern (P = 0.05) as represented by the equation: ROI at time t =
296
77.9 – (2.07t). Thus, the actual ROI would have been approximately 77.9 g/min at time 0,
297
decreasing at a rate of 2.07 g/min, to reach only 15.8 g/min after 30 min.
298 299
This marked change in ROI over time highlighted the need to adopt a standardised
300
measurement time to enable comparisons of ROI from different studies. Based on the actual
301
ROI and on degree of variability seen at each time point, 10 min was selected as the preferred
302
standard measurement time for use in Study four.
303 304 305
3.4 Study 4 No effect of exercise, age or gender on ROI was found (Table 3). There was a
306
significant effect of BW (P < .05) and breed (P < .05) on the ROI, but there was no BW x
307
breed interaction. Clydesdales (CY) had a faster ROI than both TB and SB (P < .05; Table 3).
308
Between breed subpopulations of a similar BW, a breed difference was observed between the
309
CY and TB groups (P < .05; Table 4). Overall, BW had a positive linear relationship (r2 =
310
0.56; P < .05) to ROI (Fig. 3) and this effect was also seen within the CY breed, but not with
311
the TB or SB breeds which fell into a narrower weight range.
312 313
4. Discussion
314
The ROI of a cereal-based meal was seen to be considerably faster than a roughage-
315
only meal of the same mass, and this finding is in agreement with prior studies [24,25].
316
Furthermore, the addition of chaff to a cereal meal slowed ROI incrementally up to an
317
addition rate of about 50%, with a minimum of 15% roughage required to decrease ROI
318
significantly. These findings are consistent with our previous observations that the addition of
13
319
6% chaff to a cereal mix did not alter ROI significantly, whereas an apparent decrease in ROI
320
(when measured as volume, but not mass) was seen when 36% chaff was added to either oats
321
or a sweet feed mix [28]. They are also comparable to a report by Ellis et al. [27] who
322
showed that including chaff at a rate of 30% or more can lead to longer and slower eating
323
periods, with a concomitant increase in chewing. Overall, this information should assist
324
horse owners and trainers to optimise roughage addition rates in order to control the ROI of
325
cereal-based diets.
326 327
The present findings were applicable irrespective of meal time, as ROI did not vary
328
between meals in this controlled study. However, under natural housing conditions ROI may
329
well alter between meals if the meals are unevenly spaced, or if cereal meals are preceded by
330
a large hay meal, for example. Similarly, more vigorous exercise would likely influence ROI
331
at a given mealtime.
332 333
The fact that the longer stalk-length chaff did not decrease ROI when compared to
334
shorter chaff may have been affected by the relatively small difference in stalk-length (~2.7
335
cm). The lengths selected (<2 cm vs. 4 cm) were representative of the average difference
336
between Australian and European chaff. Un-cut hay has been associated with a slower ROI
337
compared with cut hay, and it is possible that feeding chaff with a longer stalk-length (> 4
338
cm) may decrease ROI [24]. Further studies to investigate this theory are needed. A possible
339
confounding factor in the current study was the fact that the longer chaff was ground,
340
whereas the short chaff was chopped. Grinding would have affected the width, thickness,
341
density and weight of the longer chaff, and these factors may work together with length to
342
alter masticatory requirements, thereby affecting our ability to detect a change in ROI.
343
However, no significant differences were found in ROI between short and long chaff in a
14
344
previous study where both chaffs were chopped [27], or in a study comparing long-stemmed
345
and cut haylage [22]. This suggests that factors other than stalk-length, such as feeding a
346
heterogeneous diet, are more important in influencing ROI [24].
347 348
At about 40 g/min, the ROI of a cereal meal in the current study was considerably
349
slower than that of up to 129 g/min reported in a similar study where a 2 kg meal of oats,
350
maize and soybean meal was fed to horses undergoing light exercise [26]. Other studies
351
conducted in Europe have also reported relatively fast ROI [27]. This difference may be
352
related to the fact that the horses in the current study were only acclimatised to the stabled
353
environment for 8 to 10 days, whereas horses in other studies might have been permanently
354
stabled, impacting on their behaviour. Different ROI might also be related to differences in
355
exercise intensity between different studies. Although the survey component of the current
356
study found that exercise did not appear to affect ROI, the difference in exercise regimes in
357
the surveyed horses was large. Furthermore, the survey data were limited by being
358
qualitative, nominal and subjective. Controlled experiments using quantitative parameters
359
and a standardised exercise test are recommended to further explore the effect of exercise on
360
ROI, particularly in light of the potential impact of long-term stabling on ROI.
361 362
Molasses is sometimes added to feed to improve palatability, but in the present study
363
10% molasses did not increase the ROI of oats significantly. This suggests that the oats were
364
already palatable, and that palatability was not a major factor in accounting for the relatively
365
slow ROI observed, as discussed above. The addition of molasses would have also increased
366
the moisture content of the meal slightly - a factor which has been shown to increase ROI in
367
both sheep and cattle [30,31]. Therefore, either moisture content was not an important factor
368
in the present study, or the molasses had only a small effect on this variable and higher
15
369
moisture levels are needed before this becomes significant. Further studies would be
370
necessary to investigate this.
371 372
There appears to be little data on the impact of meal size on ROI in horses. One study
373
did show a higher ROI when smaller vs larger quantities of a pelleted mixed-feed were
374
offered, provided the pellets were small (5 mm diameter), with less of an effect seen when the
375
pellets were larger in size [32]. Other studies on voluntary feeding in humans and production
376
animals have shown that food consumption is affected by satiety, ambient temperature and
377
body condition [33]. Meal size did not affect ROI in the current study where these factors
378
were kept constant. This finding suggests that the provision of smaller, more frequent meals
379
in an attempt to emulate foraging behaviour is unlikely to affect ROI. Horses may self-
380
regulate their intake irrespective of meal size, and investigation of this theory is
381
recommended.
382 383
One of the most significant factors affecting ROI was the duration of the meal or
384
observation period. For a cereal-based meal, the ROI was found to be fastest at the start of a
385
meal and this may be related to hunger, behavioural effects, or insalivation of the food. The
386
initial 15 min period may represent a danger zone for the development of digestive problems
387
and could be targeted by owners and trainers. Strategies to decrease ROI during this period
388
could include feeding long stemmed roughage prior to a cereal meal to reduce hunger levels
389
and place roughage in the GIT of the horse [34]. Secondly, horses could be separated during
390
feeding to reduce the effect of competition and/or hierarchy on ROI. The ROI during the
391
initial 5 min period of cereal meal consumption was highly variable and this was largely due
392
to behavioural effects (pacing, head tossing) during this time. This needs to be taken into
393
account when attempting to measure ROI during this initial feeding period. A time-point of
16
394
10 min post-commencement of the meal was found to be the most stable time for measuring
395
ROI, and this finding could guide future studies on ROI.
396 397
The finding that larger horses eat more quickly than smaller horses concurs with
398
previous studies and is likely to be related to occlusal surface area and chewing rate [35,36].
399
The larger head of the CY when compared to smaller breeds (e.g. TB) is likely to enable
400
larger amounts of feed to be consumed with each mouthful and account for this disparity. The
401
effect of breed may also depend on the type of meal, as it has been reported in a comparison
402
of ponies and warmblood horses, that breed differences were seen using a fibre-rich pelleted
403
mixed feed, but not with a muesli or crushed grain feed [25].
404 405
It appears that bodyweight also has an impact on ROI, with the failure to detect BW
406
differences within the TB and SB groups likely to be related to the narrow bodyweight range
407
found in these groups. This finding may be important for the dietary management of obese
408
horses that are predisposed to IR, where careful control of nutrition is paramount to reducing
409
bodyweight and preventing laminitis. The current results also suggest that both breed and BW
410
should be controlled for in future ROI studies. Comparison between horses and ponies ROI
411
was not made in this study but justifies further investigation given that ponies may have the
412
capacity for a higher daily dry matter intake than horses reflecting either longer time spent
413
ingesting feed or a higher ROI.
414 415
Although gender did not impact on the ROI of a cereal meal in the current study,
416
further in-depth studies on the effect of gender on ROI are required. Nutritional requirements
417
between geldings and breeding stallions or dry and lactating mares vary, and an investigation
418
of the effect this may have on ROI is warranted. Surprisingly, age also does not appear to
17
419
impact on ROI. Younger horses could be expected to have higher energy requirements,
420
superior dentition and a more competitive nature, but this does not appear to increase ROI
421
when compared to sexually mature and older horses. Fortunately, considering that age and
422
gender are among the more difficult factors for horse owners to control, the findings of the
423
current study suggest that they appear to have little impact of the ROI of cereal meals.
424 425
5. Conclusions
426
The results of the current study support the hypotheses that roughage is consumed
427
more slowly than cereal-based feed and that the addition of chopped roughage to a cereal
428
meal decreases the ROI of that meal, with addition rates of 15% to 50% roughage shown to
429
be effective. These data can be used by horse owners and trainers to control the ROI of
430
cereals, thereby decreasing the ROP of ingesta, leading to improved GIT health and
431
potentially, behaviour. Current data suggest that chaff with stalk-lengths between 2 cm and 4
432
cm will be equally effective at reducing the ROI when added to cereal-based meals, however
433
further study is required to investigate the impact of longer stalk-lengths (> 4cm) on ROI.
434
Meal size, palatability, age and gender do not appear to affect ROI and this finding allows
435
owners to focus on managing other factors, such as BW. Strategies to reduce ROI of cereal
436
meals have been suggested and these may be of particular benefit in the initial 15 min period
437
of eating when the ROI is highest.
438 439
Acknowledgements
440
This study was funded by The Waltham Centre for Pet Nutrition and Charles Sturt
441
University. Both sponsors were involved in the experimental design and interpretation of the
442
results.
443
18
444 445
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of short (<2cm) lucerne chaff addition on the intake rate and glycaemic response of a sweet
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feed. Pferdeheilkunde 2005; 21: 88-89.
521
[30] Gibb MJ, Huckle CA, Nuthall R. Effect of time of day on grazing behaviour by lactating
522
dairy cows. Grass and Forage Sci 1998; 53: 41-46.
523
[31] Kenney PA, Black JL, Colebrook WF. Factors affecting diet selection by sheep: dry
524
matter content and particle length of forage. Aust J Agric Res 1984; 35: 831-838.
525
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526
horses during the intake of variable quantities of two pelleted compound feeds differing in
527
their physical characteristics only. Res Vet Sci 2019; 125: 189-194.
528
[33] Gaughan JB, Mader TL, Holt SM. Cooling and feeding strategies to reduce heat load of
529
grain-fed beef cattle in intensive housing. Livestock Sci 2008; 113: 226-233.
530
[34] Vervuert I, Voigt K, Hollands T, Cuddeford D, Coenen M. The effect of mixing and
531
changing the order of feeding oats and chopped alfalfa to horses on: glycaemic and
532
insulinaemic responses, and breath hydrogen and methane production. J Anim Physiol Anim
533
Nutr 2009; 93: 631-638.
534
[35] Fleurance G, Fritz H, Duncan P, Gordon IJ, Edouard N, Vial C. Instantaneous intake rate
535
in horses of different body sizes: Influence of sward biomass and fibrousness. App Anim
536
Behav Sci 2009; 117: 84-92.
537
[36] Stover KK, Williams SH. Intraspecific scaling of chewing cycle duration in three species
538
of domestic ungulates. J Exp Biol 2011; 214: 104-112.
539 540 541 542
22
543
Figure captions
544
Fig. 1. The effect of adding wheaten chaff at various addition rates and with long (4.1 cm, ●)
545
or short (1.4 cm, ○) stalk-length, on the mean (± se) rate of intake of oats (3 g/kg BW) in
546
horses (n = 6). The horizontal line represents the average rate of intake for a 2 kg meal of
547
hay.
548 549
Fig. 2. Mean (± se) cumulative feed intake over 30 min in six Thoroughbred horses presented
550
with a 2 kg meal of oats.
551 552
Fig. 3. The rate of cereal intake measured over a 10 min period in Clydesdale (○, n = 28),
553
Thoroughbred (●, n = 34) and Standardbred (∆, n = 9) horses, presented with a 1 kg meal of
554
oats. The straight line represents a first order regression fitted to the data.
23
555 556
Table 1 Subjects and experimental design for three studies to examine factors that influence the rate of intake of a cereal-based meal. Study 1
Study 2
Study 3
Study 4
6 geldings
6 geldings
6 geldings
36 geldings, 35 mares
Breeds
5 Thoroughbreds 1 Standardbred
6 Thoroughbreds
6 Thoroughbreds
34 Thoroughbreds 28 Clydesdales 9 Standardbreds
Mean BW (± se), kg
479 ± 5.33
489 ± 27.4
489 ± 27.4
603 ± 22
Mean age (± se), years
7 ± 0.93
7.8 ± 1.6
7.8 ± 1.6
See Table 2
Balanced 2 x 6 factorial1
Randomized factorial2
Repeated measures3.
Multivariable population study
Dependent variable
Rate of intake
Rate of intake
Rate of intake
Rate of intake
Fixed effects
Chaff length (x 2) Addition rate (x 5) Feeding time Replicate number
Dietary component ( x 3) Level of component (x 6)
Time allowed to feed
Random effects
Horse
Replicate number Horse
Replicate number Horse
Horses Sex
Experiment Design
557 558 559
1
Age, breed, gender, exercise level
Order of presentation of each diet (treatment combination) assigned at random; each diet replicated four times over two consecutive days and the replicate observations were pooled.
560 561 562 563
2
Three dietary components; one component fed at five levels; seven treatments in total. Order of treatments for each subject assigned at random; each treatment replicated twice over two consecutive days; 3 Each observation was replicated twice over two consecutive days and the replicates were pooled. Time was used as the repeated factor in the analysis.
2
564
Table 2
565
Mean (± se) rate of intake (ROI) of a 2 kg meal of oats measured in six geldings at five time
566
intervals after feeding, showing a significant reduction in ROI over time (P < 0.05). Time after feeding, min ROI, g/min
567 568
5
10
15
20
30
73.7 ± 13.4
66.2 ± 7.5
63.8 ± 6.3
57.7 ± 8.7
48.0 ± 5.7
569
Table 3
570
Mean (± se) rate of intake (ROI) of a 1 kg meal of oats in Clydesdale, Thoroughbred and
571
Standardbred horses surveyed in the Riverina district of NSW, Australia
572 Item
ROI (g/min)
n
P-value
All horses
78.9 ± 2.85
71
-
Clydesdale
99.3 ± 3.35a
28
< 0.05
Thoroughbred
66.8 ± 2.94b
34
Standardbred
60.9 ± 6.07b
9
Yes
74.7 ± 4.24
27
No
81.4 ± 3.77
44
1–2
74.8 ± 4.27
21
3–8
77.9 ± 4.82
28
9+
83.9 ± 5.54
22
Female
80.7 ± 4.21
35
Male
77.1 ± 3.88
36
Breed
Exercise 0.25
Age (years) 0.45
Gender
573 574
ab
0.53
Means with different superscripts differ (P < .05, Tukey’s test)
2
575 576
Table 4
577
The effect of breed on rate of intake (mean ± se) in a subpopulation of heavy and light horses
578
matched for bodyweight (mean (range)).
579 Breed
Body weight
Rate of intake
n
(kg)
(g/min)
Clydesdale
533 (452-639)
81.8 ± 6.80
8
Thoroughbred
542 (442-640)
66.0 ± 3.35
24
Thoroughbred
433 (410-480)
71.0 ± 2.40
14
Standardbred
451 (403-476)
61.9 ± 6.10
9
Effect of breed (P-value)
Heavier .03
Lighter
3
.08
Declaration of interest statement Professor Pat Harris is an employee of The WALTHAM Centre for Per Nutrition who funded this study. Prof Harris had a role in the study design, interpretation of the data, revising the manuscript and the decision to submit the article for publication.
All experimental protocols were approved by the Animal Care and Ethics Committee of Charles Sturt University (approval numbers: 05/035, 05/048, 05/067).