Energy and protein as nutritional drivers of lactation and calf growth of farmed red deer

Livestock Science 140 (2011) 8–16

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Energy and protein as nutritional drivers of lactation and calf growth of farmed red deer G.W. Asher a,⁎, D.R. Stevens a, J.A. Archer a, G.K. Barrell b, I.C. Scott a, J.F. Ward a, R.P. Littlejohn a a b

AgResearch, Invermay Agricultural Centre, Private Bag 50034, Mosgiel, New Zealand Lincoln University, Faculty of Agriculture and Life Sciences, P.O. Box 84, Canterbury 8150, New Zealand

a r t i c l e

i n f o

Article history: Received 21 October 2010 Received in revised form 3 February 2011 Accepted 3 February 2011 Keywords: Red deer Cervus elaphus Lactation Nutrition Energy Protein

a b s t r a c t Red deer calf growth rates from birth to 12 weeks of age seldom exceed 450 g/day on the best quality ryegrass/white clover pastures offered to lactating hinds over summer. However, the genetic potential for calf growth exceeds that observed on most farms. The metabolisable energy (ME) content of feed is traditionally used as the measure of feed quality for lactating hinds. The present study investigated the possibility that protein, rather than energy, content of forage may be a more important determinant of hind lactation performance and calf growth for red deer. A total of 16 mature red deer hinds pregnant to a red deer stag were calved indoors in individual pens. For the duration of their 12-week lactation they were each given daily ad libitum offers of pellet ration (+5% by weight of lucerne hay) that contained either low energy/low protein (LE/LP), low energy/ high protein (LE/HP), high energy/low protein (HE/LP) or high energy/high protein (HE/HP) (i.e. n = 4 per treatment). Calves and hinds were weighed weekly during the study. The mean dry matter intake of hinds was significantly higher (by about 35–40%) for hinds receiving low energy rations (i.e. LE/LP and LE/HP groups) irrespective of protein content. This resulted in all treatment groups exhibiting the same average energy intake, providing strong evidence for ‘energy balancing’ of feed intake (i.e. intake compensates for energy content of feed). As a consequence of “energy balancing” there was substantial between-treatment group variance in mean protein intake (400– 1200 g crude protein/hind/day). However, there was no relationship between protein intake and calf growth performance. In contrast, regression analysis of individual hind variation in energy intake and calf growth revealed that energy intake during lactation was a major determinant of calf growth performance. Overall, calf growth during the 10–12 weeks of lactation was lower than expected within the indoor system, and probably reflects a low intake of pellets by the calves themselves. The results of the study support the concepts of energy maximisation and do not support the central hypothesis of potential protein deficiency. Data from this experiment suggest that 400 g/day crude protein intake is adequate for lactation in red deer hinds. © 2011 Elsevier B.V. All rights reserved.

1. Introduction The efficiency of venison production is, in no small part, governed by the growth performance of young deer within the first 3–4 months of life, when they are dependent on their dam for the majority of their nutrition (Beatson et al., 2000). Calf growth rates and weights during this period are largely ⁎ Corresponding author. Tel.: + 64 3 4899048; fax: + 64 3 4899035. E-mail address: [email protected] (G.W. Asher). 1871-1413/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2011.02.002

driven by nutrition and the lactation outputs of the hind. However, very little is known about the effects of variable maternal nutrition on the quality of lactation in red deer hinds. Summer lactation often coincides with deteriorating pasture quality in the New Zealand pastoral environment (Asher et al., 1996; Nicol et al., 2000). In line with nutritional practises for traditional ruminant domesticants (sheep and cattle), farmers strive to provide pastures and supplementary feeds of high energetic value (i.e. N 10 MJME/kg DM) in sufficient quantities to promote optimum lactation yields of

G.W. Asher et al. / Livestock Science 140 (2011) 8–16

hinds. This is indirectly measured by calf growth rates up to weaning (recognising that there is also a contribution of direct pasture intake by the calf from about 6 weeks of age). The metabolisable energy (ME) content of feed for grazing ruminants has long been viewed as the primary measure of feed quality (ARC, 1980; NRC, 1985; AAC, 1990). For lactating red deer hinds, feed quality recommendations indicate a desirable ME content of about 10–11 MJME/kg DM to enable high lactation outputs (Beatson et al., 2000). For traditional perennial ryegrass/white clover pastures in New Zealand, the ability to provide feed of such quality can be difficult over summer months due to drought conditions in many regions and the natural process of seasonal pasture senescence due to reproductive partitioning of growth of grasses (Waghorn and Barry, 1987; Asher et al., 1996; Nicol et al., 2000; Litherland et al., 2002). Prevention of the reproductive state of ryegrass through judicious utilisation of leaf prior to seed head formation can lead to forage of 10–11 MJME/kg DM over summer lactation if other factors are not limiting (e.g. water availability and high temperatures). However, even under such conditions of quality pasture supply most farmers experience red deer calf growth rate caps of ~ 450 g/day between birth and weaning 3 months later (Beatson et al., 2000). The demonstration that the genetic potential for growth of young red deer exceeds this cap (Beatson et al., 2000) raises questions about factors limiting expression of growth potential. In this study we questioned the assumption that energy intake is the major determinant of lactation performance of red deer, as measured by calf growth. In both sheep and cattle, crude protein (CP) concentrations in the diet of 14 to 18% are required to maximise lactation (ARC, 1980). Similarly, in red deer the estimate is 15% (NRC, 2007). Often summer pastures in New Zealand fall below this level (Litherland et al., 2002) and so we test the hypothesis that during lactation, protein availability may be limiting to red deer performance. This hypothesis is based partly on research that suggests that red deer milk may have a slightly higher protein density (7.1%–8.1%) than is the case for sheep and cattle (Arman et al., 1974; Krzywinski et al., 1980; Loudon and Kay, 1984; Csapo et al., 1987; Landete-Castillejos et al., 2000). Furthermore, the importance of protein for optimising calf growth is supported by the studies of Landete-Castillejos et al. (2001, 2003, 2005) with the demonstration that milk protein concentrations of red deer hinds were positively correlated with calf growth. Calf milk intake and calf growth rates from this study have been published previously by Scott et al. (2008). The current paper includes the influence of feed quality on nutrient intake of hinds and the subsequent influence of hind feed intake on calf growth. 2. Materials and methods 2.1. Experimental design and composition of feed rations The experiment was a two by two factorial design with four replicates. The factors were energy and protein. Diet energy densities were approximately 10.3 and 12.4 MJME/kg DM for low and high energy diets respectively. Diet protein densities were approximately 120 and 230 g CP/kg DM for low

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and high protein diets respectively. Pelletised rations were formulated to contain known but differing ratios of energy to protein content. This was achieved by altering the ratios of several primary ingredients, principally grass seed fibre, barley/wheat, molasses and soybean meal (Table 1). Four experimental rations were formulated; (1) low energy/low protein (LE/LP), (2) low energy/high protein (LE/HP), (3) high energy/low protein (HE/LP) and (4) high energy/high protein (HE/HP). The ‘standard’ pellet ration was a commercially available mix formulated for red deer but containing similar principal ingredients.

2.2. Animals and management A pool of 24 mature (5–7 years old), pregnant red deer hinds (Cervus elaphus scoticus), with known conception dates, was selected in June 2005 (around Days 70–90 of pregnancy). They were maintained as a single group at pasture on the Invermay Agricultural Centre, Mosgiel, NZ (45o 51′S, 170o 23′ E) from early July 2005. Based on assessment of temperament, 18 of these hinds were selected in September 2005 to calve indoors within individual pens. It was anticipated that 16 of these hinds, based on successful calving, would enter the trial near their parturition date. The 18 hinds were pre-conditioned to ‘standard’ pellet rations at pasture from 3 November to pen entry on 14 November. During pre-conditioning, the hinds within this group were offered amounts of the standard supplementary pellet rations increasing from 200 g/head/day to 1 kg/hind/day 10 days later. Hinds were individually housed in their pens from 14 November on total ad libitum concentrate rations based on ‘standard pellets’ and of lucerne chaff at 5% by weight of the total feed offered for roughage. Pens had a minimum area of 10 m2, had natural lighting and ad libitum water. The flooring was a deep (10 cm) layer of untreated Pinus radiata sawdust over timber or concrete. One corner of each pen contained a calf refuge area of ~ 0.5 m2 that could not be accessed by the hind.

Table 1 Energy/protein concentrations, dry matter content and ingredients of pelleted rations used in the study, classified by treatment group. LE/ LP = low energy, low protein; LE/HP = low energy, high protein; HE/ LP = high energy, low protein; HE/HP = high energy, high protein. Group

Standard

Ration Dry matter (%) Energy (MJME/kg DM) Protein (g/kg DM) Ingredients (g/kg as fed) Grass seed fibre Barley Wheat Molasses Soy bean meal Oaten chaff Mineral mix a

87.7 10.5 140

1

2

3

4

LE/LP

LE/HP

HE/LP

HE/HP

89.3 10.3 121

89.3 10.3 241

88.8 12.5 120

88.8 12.3 212

654 145 – 40 – 60 101

509 – – 40 290 60 101

– 380 500 40 20 – 60

– – 670 40 230 – 60

a Mineral mix included bentonite, limestone, dicalcium phosphate, sodium chloride, calcined magnesite and a trace element mix, in the ratio 50:30:10:7:3:1 for low energy diets and 10:20:10:7:3:1 for high energy diets.

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Feed to hinds was placed in wooden feed bins approximately 1.0–1.2 m above floor level. Calf refuges also contained a small feed bin accessible by calves only. Hinds had visual contact with other hinds via netting or slatted wood partitions. Feed was offered daily while hinds were released into large outside pens for exercise. Residuals from the previous day's allocation were weighed before providing the current offer. If no residuals were present the offer was increased by approximately 10% from the previous day until at least 10% of the offered feed was refused. Intake was calculated as the difference between offer and residual within each 24-hour period, corrected for dry matter. As hinds calved, they were individually randomly allocated to treatment group, approximately balanced for birth date and calf sex. Calves were tagged and weighed within 24 h of birth, but never within the first 4 h. Once hinds had calved, the treatment ration was introduced over 10 days by replacing the ‘standard’ pellet at a rate of 10% per day. Thereafter, the hind remained on the allocated treatment ration (1, 2, 3 or 4) until calf weaning at 12 weeks of age. Calves received a ration offer of Ration 4 (HE/HP) plus chaff weighed and replaced on a weekly basis or as necessary. Hinds were weighed weekly from 3 November until calf weaning. Calves were weighed at birth, 2 weeks later and thereafter weekly until 10 weeks of age (weight data for weeks 11 and 12 were collected but lost through an electronic storage error). For daily feeding, hinds were separated from their calves for 30–60 min. Calves remained within the pen until approximately 6 weeks of age, at which point they were also placed in outside pens with other calves during feed offer replacements. Calves were weaned off their dams at each calf's 12-week anniversary. Animals were all returned to pasture at completion of the trial. 2.3. Estimation of calf milk water intakes When calves were approximately 3, 7 and 10 weeks of age, their milk water intakes (MWI) were estimated by the double isotope dilution method as a proxy for milk intake. Each measurement involved yarding the animals on Day 0 to commence milk intake measurement, and Day 5 to complete milk intake measurement. MWI measurements were conducted using the double isotope dilution technique of Dove (1988). On Day 0 the hinds and calves were yarded at approximately 0830 h and hinds were separated from calves, with both refused access to food and water. Following separation the hinds were weighed and individually restrained in a pneumatic crush and a blood sample collected by jugular venepuncture for determination of residual isotope levels. Sixteen megabecquerel of tritiated water (H32O) was then administered intramuscularly to hinds at 10 MBq/ml. Two hours after separation, the calves were weighed and manually restrained while a blood sample was collected by jugular venepuncture for determination of residual isotope levels. The calves were then administered a dose of 0.1 mg/kg live-weight deuterium oxide (H22O 99.2%) by intramuscular injection. At a minimum of 2 h after administering deuterium a blood sample was collected from the calves for determination of deuterium oxide levels following equilibration in the body water pool. At approximately 5 h after dosing with tritiated water, a further blood sample was collected from hinds for determination of

tritiated water concentration after equilibration in the hind's body water pool. Following this, samples of milk were collected from hinds about 2 min after intravenous injection of 10 i.u. (1 ml) oxytocin (Ethical Agents Ltd, Auckland, NZ).They were milked from all four quarters using a non-pulsating pump and single cup. Duplicate milk samples (50 ml) were frozen for later dry-matter assessment. Finally, all hinds and calves were reunited at the same time and returned to their pens around 1630 h, with time of re-uniting being recorded. On Day 5 the animals were yarded again and calves and hinds separated around 8.30 am and refused access to food and water. The hinds and calves were weighed. Two hours after separation a blood sample was collected from all animals for determination of isotope levels. Following this, samples of milk were collected from hinds for determination of tritium isotope to ensure that the isotope concentration in milk was equivalent to the isotope concentration in blood. Calves and hinds were then reunited and returned to their pens. Following all blood sampling serum was drawn off and stored at −20 °C for later isotopic analysis. Concentrations of tritium and deuterium isotopes were analysed in serum of hinds and calves. Tritium analysis was conducted by liquid scintillation counting using the protocol of Dove and Freer (1979). Deuterium analysis was performed by Isotope Ratio Mass Spectrometry (Iso-trace New Zealand Ltd). Body water pools were calculated from the difference in isotope concentrations between the initial and equilibrated samples on Day 0, so that residual concentrations of isotopes remaining from previous milk intake measurements did not influence the outcome. Growth of the body water pool of the calf over the measurement period was accounted for following Dove and Freer (1979) by adjusting for any increase in body weight observed over this period. Calculation of water turnover of the hinds and calves, and milk intake of calves followed the principles outlined in equations presented by Dove (1988), but allowance was made for the concentration of deuterium in water entering the body water pool of calves from the outside environment (i.e. through ingestion of milk or water). This was necessary due to the lower dose rates for deuterium given to the calves, which meant that the background intake of the isotope was non-trivial relative to the dosed concentrations. The calculation of water turnover for calves was calculated by iteration. Initial conditions for deuterium concentration were set and growth in the body water pool was assumed. The water turnover was then adjusted iteratively until the predicted concentration at the final measurement matched the observed concentration. A convergence criterion of ± 0.00004 atom percent enrichment deuterium–hydrogen (APE D/H) for deuterium concentration and a time-step of 0.001 day (86.4 s) were used in the iterations. The background concentration of deuterium was assumed to be 0.0155 APE D/H, based on isotopic analysis of environmental samples from the region in which the animals were located (Isotrace Ltd, Dunedin, New Zealand), and on concentrations observed in serum from animals prior to any dosing with deuterium. Dry matter assessments of milk samples were performed by freeze-dry lyophilisation. Duplicate 30 ml samples were accurately weighed, lyophilised for 48 h and then re-weighed. The dry:wet weight ratio was used to calculate the DMI of calves from MWI data for each sampling time.

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2.4. Ethical considerations Hinds considered temperamentally unsuited to indoor housing were excluded from the study prior to feed conditioning. Assessment was based on general yarding temperament towards handlers and reaction to humans within the field. A contingency was established to remove any hind/calf unit from the indoor trial if weekly weighing of calves indicated failure of a calf to achieve a minimum of 200 g/day growth rate during the preceding week. These studies were undertaken with the approval of the AgResearch Invermay Animal Ethics Committee, as required in New Zealand under the Animal Welfare Act 1999. 2.5. Statistical analysis Daily intake, energy and protein data, and weekly calf and hind live weights and growth rates at each time, as well as appropriate summary statistics for these variables over time, were analysed by analysis of variance, with the treatment structure given by the factorial interaction of dietary energy and protein treatments. In addition, calf growth rates for each sampling interval were analysed by least squares, fitting the factorial interaction of energy and protein treatments plus calf sex. Individual calf and hind live-weight changes from 2 to 10 weeks were analysed by linear regression against both total energy intake and total protein intake, also fitting calf sex and its interaction with the respective explanatory variables. MWI data were analysed using restricted maximum likelihood (REML), with calf as the random effect and the factorial interaction of energy and protein treatments, hind liveweight, calf sex and sample day as the fixed effects. The dependence of calf growth rate on MWI and DMI was analysed using REML, with calf as the random effect and MWI/DMI, sample day and their interaction, plus sex, as fixed effects. A principal component analysis was conducted on total energy and protein intake, mean and change in hind live-weight, and change in calf live-weight. Statistical significance was assessed at the 5% level unless otherwise indicated. 3. Results 3.1. General Of the 18 hinds that calved indoors, 16 produced viable singleton calves that survived to weaning at 12 weeks of age (Table 2). Two of the hinds presented stillborn calves, including a set of twins. One hind/calf unit in Group 1 (LE/LP) was removed from the study due to failure of the calf to attain the threshold growth rate of 200 g/day between weeks 7 and 8 from birth. The hind exhibited an unusually low voluntary intake (~1–1.5 kg DM/ day) of Ration 1 (LE/LP). The pair was placed on a ‘rescue’ ration (Ration 4, HE/HP) until calf weaning at 12 weeks of age; and the data for this pair were excluded from the analysis. 3.2. Hind feed intake While attempts were made to prevent calves accessing feed offered to their dams, casual observation indicated that

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Table 2 Summary statistics for hind and calf parameters, including group composition and mean pre-calving live-weights and post-calving growth rate for hinds and calves, as well as mean hind and calf daily dry matter intake (DMI) and calf daily milk water intake (MWI), with standard errors of difference (SED) and significance (sig) levels (ns indicates P N 0.05; * is P b 0.05; *** is P b 0.001). LE/LP = low energy, low protein; LE/HP = low energy, high protein; HE/ LP = high energy, low protein; HE/HP = high energy, high protein. Group

1

Ration

LE/LP LE/HP HE/LP HE/HP

2

3

4

SED

Sig

Number of hind: calf units Calf sex ratio (M:F) Hind live-weight (kg) b Calf birth weight (kg) Calf weaning weight (kg) c Calf growth rate (g/day) d Hind growth rate (g/day) e Hind daily DMI (g/kg LW) e Calf MWI (L/day) f Calf DMI (g/day) f Calf growth rate (g/day) e

3a

4

4

4

2:1 105 9.6 37.4 386 149 47.2

3:1 117 9.8 38.5 404 163 40.5

2:2 118 9.8 37.5 394 174 31.8

2:2 112 9.7 38.5 403 221 33.1

8.4 0.68 2.7 36.6 82 2.53

ns ns ns ns ns ***

2.57 530 384

2.18 455 392

2.07 449 405

2.52 525 414

0.24 * 45.4 * 28.2 ns

a

n = 3 in group 1 following ‘rescue’ of one hind: calf unit. Pre-calving live-weight of hind. Live-weight at 10 weeks of age. d Birth to weaning. e Days 10 to 84 from calving/birth (period representing differential feeding regimen). f Mean for observations at 3, 7 and 10 weeks of age. These data do not include any potential contribution of pellet diet obtained by some calves from their dam's feed box. b c

some calves were able to reach the feed boxes and ingest some of the dam's feed offer from about 6–8 weeks of age. Few calves ingested pellets offered to them within their refuge areas. Therefore, the ‘dam’ feed intake data are deemed to represent combined intakes of the dam/calf unit, with the calf contribution to feed disappearance occurring in the latter half of the study period. Daily DMI (Table 2) varied enormously between individuals and days, ranging from b 1.0 kg to N 7.0 kg DM/day. Mean intakes for treatment groups (Fig. 1a) generally increased from around 0.07 to 0.10 kg DM/kg0.75/day around calving to a plateau of 0.12 to 0.15 kg DM/kg0.75/day 20–40 days later. Overall mean intake was significantly higher (by about 35–40%) for hinds receiving low energy rations than those receiving high energy rations, irrespective of crude protein level (Pb 0.05). Average energy intake (0.8 to 1.5 MJ/kg0.75/day) was similar across all treatment groups (PN 0.1: Fig. 1b). Consequently, average protein intake (Fig. 1c) varied enormously across treatment groups (Pb 0.001), with a range at mid-late lactation of b 10 to N 30 g/kg0.75/day from Group 3 (HE/LP) and Group 2 (LE/HP), respectively. 3.3. Calf MWI, DMI and growth rate The dry matter content of individual milk samples ranged from 17.2% to 23.0% with a mean of 20.8%. There was no significant effect of calf age (3, 7 or 10 weeks) on calf intake (PN 0.05; Table 2). However, MWI and DMI of the calves showed a significant energy/protein interaction (Pb 0.05) such that calves whose dams were on LE/LP and HE/HP rations had a higher mean MWI and DMI averaged over the three samples, than those whose dams were on LE/HP and HE/LP (Table 2). Average growth

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G.W. Asher et al. / Livestock Science 140 (2011) 8–16

Fig. 1. Mean (with SED) daily (a) dry matter (DM) intake, (b) metabolisable energy (ME) intake and (c) total protein intake for hinds in each treatment group relative to calving date, expressed as a function of metabolic live-weight (kg 0.75): LE/LP = low energy, low protein; LE/HP = low energy, high protein; HE/LP = high energy/low protein; HE/HP = high energy, high protein.

rate of the calves declined as they got older (525±21.5, 362± 12.5, 344±13.3 g/day from birth to 3 weeks, 3 to 7 weeks and 7 to 10 weeks of age, respectively) and there was no significant difference (PN 0.05) between treatments in mean calf growth rate over the 12-week study period (Fig. 2a). However, male calves grew faster on average (Pb 0.01) than female calves (429 vs. 356 g/day) despite having ingested similar quantities of milk (PN 0.05). From birth to 3 weeks of age mean calf growth rate was significantly greater for HE (570 g/day) than for LE (473 g/ day; Pb 0.005), but there were no other effects of treatment on calf growth rate. There was a highly significant positive

relationship (Pb 0.001) of calf MWI or DMI on calf growth rate from birth to 3 weeks, with an increase of 1 L/day in MWI or ~ 200 g/day in DMI corresponding to an increase of 113 (SED=30; Pb 0.001) g/day in calf growth rate. This relationship was not significant (P N 0.05) for later samplings. Fig. 3 shows the relationship of calf live-weight change on total hind energy (3a) and protein (3b) intake. An increase of 100 MJ in hind energy intake corresponded at 10 weeks of age to an increase in calf weight of 2.5 kg (SED = 0.66 kg; p b 0.001) for both males and females, with males growing on average 3.1 kg (SED = 0.63 kg; P b 0.01) more than females at any given

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Fig. 2. Mean (with SED) profiles for (a) calf and (b) hind live-weights and growth rates by treatment group: LE/LP = low energy, low protein; LE/HP = low energy, high protein; HE/LP = high energy/low protein; HE/HP = high energy, high protein.

level of hind energy intake. However, the regression of hind protein intake on calf growth rate was not significant (P N 0.05). 3.4. Hind live-weight changes Mean live-weights of hinds generally increased by approximately 10 kg during the 10-week period immediately post calving. While there was a 10 kg difference in mean pre-partum and post-partum weights of hinds across groups (an artefact of treatment allocation based on birth date and calf sex), there were no significant treatment group differences in mean live-weight change over the next 10 weeks of lactation (Fig. 2b). However, as with calf growth, there was wide within-treatment group variation between individuals. Fig. 3 shows the relationship of hind live-weight change on total energy (3c) and protein (3d) intake. An increase of 100 MJ in hind energy intake corresponded to an increase in hind live-weight of 0.67 kg (SED=2.9 kg; Pb 0.05), with no evidence of difference with calf gender (PN 0.05). However, there was no effect of protein intake on live-weight change (PN 0.05). 3.5. Principal component analysis The first two principal components from the analysis of total energy and protein intake, mean and change in hind live-weight, and change in calf live-weight, are shown in

Fig. 4. The first axis may be described as the ‘hind axis’ and explains 56% of the variation; it shows a clear association between hind live-weight, energy intake and calf growth rate, and is dominated by 3 large hinds (live-weight N 120 kg) which are fairly central on the second axis. The second axis may be described as the ‘calf axis’ and explains 17% of the variation; it expresses a gradient among the remaining hinds, from those with relatively lower protein intake, greater hind growth and lower calf growth rates associated with female calves, to those with high protein intake, no hind growth but higher calf growth, associated with male calves. 4. Discussion Perhaps the most striking feature of these data is the clear demonstration that energy content of feed drove voluntary feed intake under circumstances (pellet ration) in which rumen fill and passage rate were not limiting. Lactating red deer hinds appeared to compensate for low energy content in feed by increasing their voluntary intake in an attempt to meet their energy requirement. Thus, while hinds on low energy rations (10 MJME/kg DM) exhibited higher voluntary intakes than those on high energy rations (12.5 MJME/kg DM), irrespective of protein levels, the overall mean energy intakes of all groups were the same at equivalent stages of the lactation cycle (e.g. 1.2–1.4 MJME/kg0.75/day N 20 days from birth). Previous research has shown that ruminants are able

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Fig. 3. Regression plots of change in calf growth rate between 2 and 10 weeks of age on (a) metabolisable energy (ME) intake, and (b) protein intake of individual hinds (n = 15); and regression plots of hind growth rate between 2 and 10 weeks from parturition on (c) ME intake, and (d) protein intake of individual hinds (n = 15). The plots differentiate calf sex for individual points (○ = female; ● = male) and modelled regression lines (dashed = female; solid = male).

to adjust voluntary feed intake to meet energy demands when given pellet diets of varying energy density (Dinius and Baumgardt, 1970; Webster et al., 2000) or preferentially select high energy forages within a free-range environment (van Wieren, 1996; Berteaux et al., 1998; Forbes, 2007). Pellet diets have a small particle size and therefore give the animal the opportunity to attain their metabolic requirements for energy and protein without the bulk limitations associated with variations in energy density in forages such as pasture. Therefore, this research has given us the ideal regimen to investigate the true role of protein in determining lactation output from hinds without the limitations to intake that may be exerted in pasture diets. However, it should be noted that foraging behaviour of wild red deer has also been associated with discrimination of selected diets favouring plants higher in energy than protein (van Wieren, 1996; Verheyden-Tixier et al., 2008). In essence, the results of the present study strongly support the concepts of ‘energy balancing’ but provide little support for

the central hypothesis of potential protein deficiency. Data from this experiment suggest that an individual hind intake of as little as 400 g/day of protein had no discernable impacts on calf growth or body weight of hinds over the period of this study. The principal component analysis does suggest that smaller hinds rearing faster-growing male calves within the study may have adjusted their protein intake to accommodate the higher demand. However, for hinds of larger body mass and smaller hinds rearing female calves, there was no indication that availability of protein restricted either hind or calf growth. These results are supported by studies on caribou and reindeer (Rangifer tarandus) which have demonstrated that energy intake of hinds was the only nutritional variable influencing body mass and lactational performance in this species (ChanMcLeod et al., 1994). However, studies on Iberian and Scottish red deer by Landete-Castillejos et al. (2001, 2003, 2005) showed significant associations between protein density of hind milk and calf growth rate, but no such associations between energy density of hind milk and calf growth. While this appears to

G.W. Asher et al. / Livestock Science 140 (2011) 8–16

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Fig. 4. The first two components from the principal component analysis of total energy and protein intake, mean and change in hind live-weight, and change in calf live-weight. The plots differentiate calf sex (○ = female; ● = male), and indicates the relative contributions of the observed variables.

contrast with current findings, it is important to differentiate between effects of dietary nutrients available to lactating hinds in the present study and milk constituent density variables monitored in earlier studies. Clearly, neither study has related individual hind nutrient intake with milk composition, and other variables such as hind age, body size and body condition prior to calving may influence lactational outputs and calf growth performance independent of available nutrition during lactation (Landete-Castillejos et al., 2001, 2005; Carrion et al., 2008). Variables related to pre-lactation fat and protein reserves of the hinds were not factored into the present study, but may have important implications for the dietary energy and protein requirements of individual hinds. The observed effect of male calves on protein intake of the smaller hinds, detected by principle components analysis, indicates that this may be the case. The general overall lack of interaction between protein and energy suggests that if 5 kg DM/day was eaten then the protein concentration could be as low as 8% with no detrimental impact on lactation output. However, in normal pasture situations forage with 8% crude protein will also have a very low energy density and a high bulk limitation to intake. This would then limit intake to below 5 kg DM, and so increase protein requirements. Therefore, extrapolating protein requirements beyond pellet diets would be unwise. The demonstration that between-hind variation in overall energy intake (despite similar group mean intakes) was positively correlated with calf growth rate and change in hand liveweight supports the notion that feed energy value is a major determinant of lactation performance of red deer hinds. This indicates the potential for increased calf growth rates by feeding high energy forages over lactation. However, recent studies suggest that calf demand for milk is a more important

determinant of milk yield than feed quality per se (J.A. Archer, unpublished data). The calf growth rates measured in this study were below the 450 g/day exhibited in many pasture situations. This suggests that the calves were gaining most of their nutrition from the hind, with little intake of the pellet diet. Of interest is the relationship between calf and hind live-weight gain and hind energy intake. The overall gain of the hind/calf unit was 3.17 kg/100 MJME. This then translates into an energy requirement for gain of 31.5 MJME/kg. This is similar to previous estimates of live-weight gain for young weaner stags (Fennessy et al., 1981) and lower than others (Webster et al., 2000) and indicates that the breeding hind/calf pair converts energy intake to live-weight gain very efficiently. While the results of the present study clearly indicate that energy, rather protein, may be the major determinant of lactation performance/calf growth in red deer, there were some issues encountered with the methodological model used. Indeed, the use of indoor housing of individual hinds during parturition and lactation is a radical departure from more conservative methodologies of outdoor group feeding used in the past. It did, however, provide a precise feeding model that generated detailed information on individual variation in feed, energy and protein intake over lactation that would not be possible in a group or field situation. Calves habituated well to handlers during daily hind/calf separation. Few incidents of panic occurred and most calves actually became very tame. However, the growth rate of the calves was lower than expected given the type of nutrition available to them and their dams. While it is likely that most calves relied entirely on their dam's milk for nutrition throughout the trial, a few calves were observed to ingest pellets from their dam's trough even though it was elevated N 1.0 m off

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the floor. Despite this observation, it is believed that overall pellet intake by calves was low, and may have limited their growth potential during the course of the study. Future studies of this nature may need to seek means of attracting calves to ingest feed other than their dam's milk. 5. Conclusions The study has demonstrated that the energy density of feed appears to be a more important determinant of growth of lactating hinds and their calves than protein density. Furthermore, hinds appear capable of ‘energy balancing’, whereby they adjust total feed intake volumes to ensure an adequate total energy intake. Total daily protein intakes as low as 400 g/day do not appear to be limiting to animal performance, with the possible exception of smaller hinds rearing fast-growing male offspring. Acknowledgements This project was jointly funded by DEEResearch Ltd and the Foundation of Research, Science and Technology (FRST contract C10X0709). References AAC, 1990. Feeding Standards for Australian Livestock: Ruminants. CSIRO, East Melbourne, Australia. ARC, 1980. The Nutrient Requirements of Ruminant Livestock. Agricultural Research Council, Farnham Royal, UK. Arman, P., Kay, R.N.B., Goodall, E.D., Sharman, G.A.M., 1974. The composition and yield of milk from captive red deer (Cervus elaphus l.). Journal of reproduction and Fertility 37, 67–84. Asher, G.W., Fisher, M.W., Fennessy, P.F., 1996. Environmental constraints on reproductive performance of farmed deer. Animal Reproduction Science 42, 35–44. Beatson, N.S., Campbell, A.G., Judson, H.G., 2000. Deer Industry Manual New Zealand. Herald Print Ltd, Timaru, New Zealand. 134 pp. Berteaux, D., Crete, M., Huot, J., Maltais, J., Ouellet, J.-P., 1998. Food choice by white-tailed deer in relation to protein and energy content of the diet: a field experiment. Oecologia 115, 84–92. Carrion, D., Garcia, A.J., Gaspar-Lopez, E., Landete-Castillejos, T., Gallego, L., 2008. Development of body condition in hinds of Iberian red deer during gestation and its effects on calf birth weight and milk production. Journal of Experimental Zoology 309A, 1–10. Chan-McLeod, A.C.A., White, R.G., Holleman, D.F., 1994. Effects of protein and energy intake, body condition, and season on nutrient partitioning and milk production in caribou and reindeer. Canadian Journal of Zoology 72, 938–947. Csapo, J., Sugar, L., Horn, A., Csapo-Kiss, Z., 1987. Chemical composition of milk from red deer, roe and fallow deer kept in captivity. Acta Agronomica Hungary 36, 359–372. Dinius, D.A., Baumgardt, B.R., 1970. Regulation of food intake in ruminants. 6. Influence of caloric density of pelleted rations. Journal of Dairy Science 53, 311–316.

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