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Effects of sward height and concentrate supplementation on the ingestive behaviour of spring-calving dairy cows grazing grass-clover swards
APPLIED ANIMAL BEHAVIOUR SCIENCE
E LS EV I ER
Applied Animal Behaviour Science 40 ( 1994 ) 101-112
Effects of sward height and concentrate supplementation on the ingestive behaviour of spring-calving dairy cows grazing grass-clover swards A.J. Rook*, C.A. Huckle, P.D. Penning AFRC Institute of Grassland and Environmental Research, North Wyke, Okehampton EX20 2SB, UK
(Accepted 1 March 1994)
Abstract
Forty-eight, lactating, spring-calving, multiparous, Holstein-Friesian cows, continuously stocked on mixed grass-clover swards, were blocked by calving date, parity and milk yields in week 2 of lactation and randomly allocated to six treatments: 0 (U) or 4 (S) kg concentrate supplementation at sward heights of 40, 60 or 80 mm as measured by a rising plate meter. Jaw movements were recorded automatically for 24 h for a different cow on each treatment on each of 6 days during two periods (15-25 June (P1) and 25 July-6 August (P2)). Swards of 40 mm height were not used in P2. Total time grazing, ruminating or idling, and the number and duration of bouts of these activities, biting rate while grazing and chewing rate, number of boluses and chews per bolus while ruminating were recorded. Data were smoothed to give a minimum bout duration of 5 min. Herbage intakes were estimated using n-alkanes. Grazing time was greater at 40 mm than at 60 or 80 mm when unsupplemented but less when supplemented. Proportionately 0.88 of grazing time and 0.67 of ruminating time by dairy cows occurred during daylight with a large evening meal particularly evident. On the 40 mm sward unsupplemented animals grazed for longer with a higher biting rate but lower bite mass and less mastication and rumination. When supplement was offered at the 40 mm sward height animals appeared to 'give up' harvesting the sward more readily. Durations of ruminating and idling bouts were similar across all treatments with low variability. Keywords: Dairy cows; Grazing; Ingestive behaviour
*Corresponding author. 0168-1591/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10168-1591 (94)00488-Z
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A.J, Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
I. Introduction The effects of supplementation on the performance of lactating cattle at pasture have been reviewed by Mayne (1992). He reported that substitution rate can be accurately predicted at different herbage allowances but that insufficient information is available to allow similar prediction as a function of sward surface height for continuously stocked cattle. Rook et al. (1994) reported the effect of maintaining sward heights of 40, 60 or 80 m m as measured by a rising plate meter (Holmes, 1974) and of supplementation with 4 kg of concentrate on milk production and intake by dairy cows continuously stocked on a perennial ryegrass (Lolium perenne L. ) - white clover (Trifolium repens L. ) sward. Milk yields, milk component yields, live weight and herbage intakes were all significantly (P<0.05) lower at the 40 mm sward height. Supplementation significantly ( P < 0.05 ) increased milk and component yields at all sward heights. Mean herbage intakes were consistently lower at all sward heights but this effect was not significant. This concurrent study using the same animals was designed to investigate the behavioural mechanisms underlying any observed intake effects.
2. Animals, materials and methods Forty-eight multiparous, Holstein-Friesian cows, calving between 1 March and 11 April were continuously stocked on mixed perennial ryegrass-white clover swards from 6 May. All cows had ad-libitum access to feed blocks consisting of molasses impregnated with 50 mg kg- ~poloxalene as an anti-bloat prophylactic. The cows were blocked by calving date, parity and milk yield in week 2 of lactation and randomly allocated within blocks to one of six treatments, 0 (U) or 4 (S) kg concentrates with swards maintained at a sward height of 40, 60 or 80 mm, as measured by a rising plate meter (30.4 cm × 30.4 cm ) beneath which the sward is compressed before measurement. Stocking rates were adjusted by varying the grazed areas using moveable electrified fences. Spare animals were used to maintain the areas behind these fences as close as possible to the target heights. Cows were milked twice daily at approximately 06:00 and 15:00 h British Summer Time (BST). Equal amounts of concentrates were offered at each milking. Cows consumed all concentrate offered. The proportional composition of the concentrate was 0.225 maize gluten, 0.225 sugar beet pulp, 0.14 cotton seed 0.125 wheat, 0.075 extracted rapeseed, 0.075 molasses, 0.052 extracted sunflower, 0.025 extracted soya, 0.018 fat prills and 0.04 mineral mix. Chemical composition of concentrates and herbage is shown in Table 1. To avoid social facilitation between supplemented and unsupplemented animals, the two groups at each sward height grazed separate paddocks, although complete visual isolation was not achieved. As this could have led to unwanted differences in the swards being grazed by the two groups at each sward height, animals were swapped between paddocks on a daily basis. Owing to drought there was severe loss of body-weight
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
103
Table 1 Mean composition of herbage and concentrates (g kg - ~DM ) %C
DOMD
N
ADF
WSC
768 566 771 595 770 588
45.0 22.9 48.8 25.5 46.1 22. l
173 314 160 289 157 294
53 107 50 114 59 140
769 652 760 637
45.7 33.4 43.3 30.1
188 248 191 258
51 100 51 123
656
32.8
155
Herbage 15-18 June
40 m m 60mm 80 m m
25 July-2 August
60ram 80 m m
Concentrate
Clover Grass Clover Grass Clover Grass Clover Grass Clover Grass
7 13 8 12 12
%C, percentage of clover in sward; DOMD, digestible organic matter in the dry matter; N, nitrogen; ADF, acid detergent fibre; WSC, water soluble carbohydrates.
by the animals grazing the 40 m m swards and it became impossible to sustain these treatments after 27 June. Behavioural measurements were made between 15 and 25 June (P1) and between 25 July and 4 August (P2). Photoperiod, defined as 0.5 h prior to sunrise to 0.5 h after sunset, was approximately 17 h in P1 and 16 h in P2. On each of 6 days during these periods, the ingestive behaviour of a different animal from each treatment was recorded using the methods of Penning et al. (1984), as modified for cattle by Huckle et al. ( 1989 ). Briefly, gnathometers were used to record analogue electrical signals of the jaw movements on miniature tape recorders carded on the cows. The equipment was fitted during morning milking and remained on the animals for a recording period of approximately 24 h. Animals had been acclimatised to the equipment previously. The recordings were subsequently replayed and the waveforms analyzed by computer to give the time spent grazing, ruminating or idling and to count the jaw movements associated with these activities. The data were summarised on a minute by minute basis and an animal was deemed to be either grazing, ruminating or idling if it spent at least 30 s in any 1 min performing one of these activities. The activities occurred in discrete bouts and for the purpose of analysis the data were smoothed such that the minimum bout duration for any activity was 5 rain. This was achieved by examining a window of 9 min and assigning to the mid-point minute in the window the predominant activity, on a minute by minute basis, within the window. A minimum bout duration of 5 rain was chosen on the basis of data from previous experiments (A.J. Rook and C.A. Huckle, unpublished, 1991 ) in which the method of Forbes et al. ( 1986 ) was used to distinguish inter- and intra-meal intervals. Metz ( 1975 ) also reported a minimum inter-meal
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A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994.) 101-112
interval for cows of 4 min in indoor feeding trials. All results presented are for smoothed data. The algorithms used to analyze the gnathometer output could not distinguish between prehension and mastication bites while grazing (Penning and Hooper, 1985 ) or identify the use of the tongue in grazing. Therefore, while automatic recording was taking place, each animal was also observed visually and the number of prehension bites, mastications and tongue extensions were recorded separately during two 3-min periods for each activity, one after each milking. Herbage intakes were estimated using a modification of the n-alkane technique of Mayes et al. (1986). Cows were dosed with hard gelatin capsules containing C2s and C32 alkanes (500 mg per capsule) twice daily at milking over a period of 6 days. Grab samples of faeces were collected on the 3 subsequent days at the same time as dosing. Intake was thus estimated for a period corresponding to the day on which the animals jaw movements were recorded. Pluck samples of grass and clover, intended to be representative of the grazed horizon and samples of faeces and concentrate were analyzed for C28 to C33 alkanes using the Soxhlet extraction method of Mayes et al. (1986). Herbage intakes (I) (kg (dry matter (DM)) day-1 ) were calculated using the equation
I-
f31 - - ( D 3 2 + $32Is) -$31 Is f~2
H~
F~I -F3 H32
where H31, $3~, and F31 are the concentrations (mg kg -1 ) of C3~ alkane in herbage, concentrate and faeces, respectively,//32, $32, D32 and F32 are the concentrations of C32 alkane in herbage, concentrate dose and faeces, respectively, and I~ is the intake of concentrate supplement (kg (DM) day-i). Data were analyzed as a 2 × 3 factorial in randomised blocks using the analysis of variance facilities ofGENSTAT (Lawes Agricultural Trust, 1987). Patterns of activity within the observation periods were compared between treatments using the X2 test for homogeneity of two way contingency tables.
3. Results and discussion
Proportionately 0.88 of grazing time occurred during the 17 h of daylight in P 1 (Fig. 1 ) and 0.88 in the 16 h of daylight in P2 (Fig. 2) with peaks of grazing activity in mid morning and late evening. These values were significantly greater than the expected values of 0.71 and 0.67 if the total grazing time had been uniformly distributed over a 24 h day. In both periods approximately 0.56 of the available daylight was spent grazing. There were no significant treatment effects on the distribution in either period. Differences in total grazing time between treatments, discussed below, were thus achieved by altering the proportion of the night spent grazing. These results are in line with those of Penning et al. ( 1991 a)
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112 40
mm
105
award
milking
milking
+ llllJlllil ill o
60
-~
mm
sward
+++° 1i,illlil t111 8e
O
80
mm
sward
o 7.00
12.00
1 e.00 Time (BST)
0.00
15.00
Fig. 1. Mean time grazing in each hour of day for P1. [] 0 kg concentrates (U); • 4 kg concentrates (S); shaded area, scotophase.
who found that 90% of grazing by sheep occurred in dayJight in July, and Tayler (1953) who reported that 93% of grazing by bullocks occurred during daylight between April and July. Phillips and Leaver (1986) also found that grazing by dairy cows was concentrated in the daylight hours in early season. It seems that dairy cows were unwilling to graze during the substantial periods of darkness, despite their daylight grazing time being restricted by removal from the pasture for between 30 and 60 min at each milking. This may be an anti-predatory adaptation. Phillips and Denne ( 1988 ) found that coefficients of variation in grazing time both between cows and between days were much higher at night. This sug-
106
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112 60
mm
sward milking
Irlllklng 80-
°ii0
ll /m ill 80
38-
"¢~
24 12-
mm
sward
0 7'.00
12.00
1 B.00 Time (BST)
0.00
15.00
Fig. 2. Meantime grazingin each hour of day for P2. [] 0 kg concentrates (U); • 4 kg concentrates (S); shadedarea, scotophase. gests that cows may be able to adjust their night grazing time more easily than their day grazing time. The occurrence of greater grazing activity in the morning and afternoon could be a short term fasting effect following milking. Penning et al. ( 1991 a) suggested that the large evening meal they observed for sheep may have been an optimal foraging response to a build up of readily digestible products of photosynthesis in plant leaves at this time. A similar mechanism might explain the evening meal seen here. However, it should be noted that large evening meals have been observed in species whose food does not show such diurnal variation and other mechanisms may therefore be operating. Phillips and Leaver ( 1986 ) found that as daylight hours decreased grazing time before morning milking decreased and was compensated by a midnight meal. However, the evening meal was present throughout. Phillips and Denne ( 1988 ) found that the between cow and between day coefficients of variation for grazing time were particularly low during the evening meal, again indicating its possible importance in an optimal foraging strategy. In P1, 0.67 of rumination time occurred during daylight and 0.38 in P2 (expected value from uniform distribution 0.71 ), representing 0.20 and 0.14 of daylight, respectively. Even when total rumination time was reduced in treatment
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112
107
40U a similar proportion (0.62) still occurred during the day. The substantial proportion of the day spent ruminating may indicate a need to ruminate during the day in order to aid passage from the rumen and hence facilitate further intake. It is also possible that daytime idling is obligatory in order to avoid fatigue. Mean daily grazing times on the 60 and 80 mm swards in P1 (Table 2) were 10.93 and 10.38 h, but on the 40 mm sward this rose to 12.75 h when animals were unsupplemented and fell to 9.2 h when supplemented. In P2 (Table 3 ) the mean daily grazing times were 11.19 h on the 60 mm sward and 9.5 h on the 80 mm sward. Phillips and Leaver ( 1986 ) found that dairy cows spent 6-9 h d a y - t grazing at this time of the year on a sward of 80-90 mm sward surface height as measured with a sward stick (Bircham, 1981 ), which may be taken as approximately equivalent to a 60 mm rising plate height. They suggested that this represents a maximum grazing time for dairy cows in general. The present results do not agree with this contention. Ruminating and idling bout durations were both remarkably similar across treatments with small variability compared with that for meal duration. The physiological processes of ruminating may, therefore, require it to continue for periods of approximately 30 min at any one time. There were no significant differences in boluses per ruminating minute ( P > 0.05 ). However, chewing rate per bolus was significantly higher on 80S than on 80U in P 1 (Table 2 ) and for 80 vs 60 mm in P2 (Table 3 ). Particle size of digesta in the rumen is primarily reduced by rumination (Poppi et al., 1981 ). Thus, if longer material was ingested by cows on the 80 mm treatment this would have required more chewing to reduce particle size. Total jaw movement rate while grazing for automatically recorded data, which consists of both prehension bites and mastications, was greater than the sum of these two components recorded visually. Penning and Hooper ( 1985 ) also found that visual recording gave a lower rate than automatic recording. There are a number of possible reasons for this. The gnathometers sometimes produce signals with low signal to noise ratio. These signals may be misinterpreted and thus overestimate the true rate. Conversely, it is sometimes difficult to observe all jaw movements when recording visually which may lead to underestimation of the true rate. The visual recordings were made for only two 3-min periods on each cow in the 2 h following each milking and may thus be less representative. In addition, mastication rate and tongue movements were not recorded simultaneously with prehension bites and this could also give rise to errors. Mastication rate was similar across all treatments, except 40U, where it was reduced with a concomitant increase in prehension biting (Table 2). The standard error was also small. Penning and Hooper ( 1985 ) remarked on the similarity in mastication rates of cattle across a range of different sward heights which accounted for about 10% of the total jaw movements in their data compared with 17% in the present data except 40U at 8%. Chacon et al. ( 1976 ) found that nonlactating Jersey cows had 6-11% of head-down jaw movements accounted for by mastication and a further number of head-up mastications equivalent to 20% of the total head-down jaw movements, i.e. 21-25% of total jaw movements were
Herbage intake (kg (DM) day -~ ) Total grazing time (min day- ~) Total ruminating time (min day- ~) Total idling time (min day- ~) No. grazing meals per day No. ruminating bouts per day No. idling bouts per day Mean grazing meal duration (min) Mean ruminating bout duration (min) Mean idling bout duration (min) Total jaw movements (grazing) (per min) (automatic recording) Prehension biting rate (per min) ( visual recording) Mastication rate (grazing) (per min) ( visual recording) Tongue extensions (per min) (visual recording) Chewing rate (ruminating) (per min) Boluses/ruminating min Chews/bolus Intake rate while grazing (g m i n - ~) Intake per prehension bite (g)
Table 2 Intake and ingestive behaviour in P 1
12.2 553 368 505 8.4 13.1 17.8 80 28 28 79.1 44.8 15.3 42.0 53.3 1.08 54.4 22.6 0.51
62.3 5.6 58.7 50.9 0.79 66.2 17.8 0.28
40S
13.9 765 250 422 9.5 8.4 13.8 87 32 31 78.4
40U
Treatment
62.4 0.77 68.5 24.3 0.52
42.9
13.8
46.7
15.3 651 342 443 6.8 10.6 10.7 103 31 42 73.7
60U
56.1 0.73 76.3 21.1 0.33
57.3
8.7
60.7
13.8 660 379 374 9.2 12.1 14.7 75 32 27 77.2
60S
44.3 0.77 49.2 26.2 0.54
51.3
11.2
52.7
16.8 639 311 492 10.0 12.0 14.0 63 27 36 76.7
80U
65.2 0.75 106.0 28.0 0.58
50.1
10.8
51.7
16.5 606 382 425 7.7 12.9 15.3 81 30 28 88.5
80S
22.49 0.51 45.42 5.12 0.17
10.38
3.35
8.50
3.22 136.3 124.5 120.5 3.16 4.36 3.23 29.2 10.1 9.39 24.5
1.s.d.
0.637 0.755 0.520 0.003 0.026
0.985
0.758
0.865
0.019 0.677 0.459 0.339 0.612 0.526 0.033 0.256 0.737 0.337 0.692
height
0.371 0.216 0.175 0.417 0.509
0.688
0.129
0.477
0.223 0.049 0.042 0.599 0.705 0.061 0.003 0.488 0.931 0.004 0.436
concentration
F-test probability
0.212 0.295 0.096 0.091 0.006
0.001
<0.001
<0.001
0.728 0.061 0.631 0.127 0.097 0.390 0.386 0.102 0.548 0.227 0.784
interaction
~"
'~
-~
~.
5
"~ ~.
-..
¢%
oo
Herbage intake (kg (DM) day -~ ) Total grazing time (min day- l ) Total ruminating time (min day-~ ) Total idling time (min day- ~) No. grazing meals per day No. ruminating bouts per day No. idling bouts per day Mean grazing meal duration (min) Mean ruminating bout duration (min) Mean idling bout duration (min) Total jaw movements (grazing) (per min) (automatic recording) Prehension biting rate (per min) ( visual recording) Mastication rate (grazing) (per min) ( visual recording) Tongue extensions (per min) (visual recording) Chewing rate (ruminating) (per min) Boluses/ruminating (min) Chews/bolus Intake rate while grazing (g min-~ ) Intake per prehension bite (g)
Table 3 Intake and ingestive behaviour in P2
59.1
52.7
56.8 53.9 0.88 59.8 20.0 0.34
49.6 61.0 0.93 72.8 20.1 0.39
8.94
13.5 672 339 425 11.8 10.8 15.7 59 38 28 72.2
13.5 671 328 444 9.0 9.8 13.7 80 35 33 81.9
11.44
60S
60U
Treatment
70.7 0.76 116.0 24.8 0.38
59.5
9.63
64.8
14.1 537 368 501 10.1 14.0 18.1 60 27 27 85.5
80U
66.9 0.68 101.3 22.5 0.48
47.1
11.16
49.9
13.9 603 373 453 10.2 14.5 17.0 64 25 26 94.3
80S
0.389 0.576 0.464 0.591 0.694
0.981 0.089 0.113 0.039 O.llO 0.281
11.92 18.85 0.34 56.48 6.24 0.17
0.508
0.882
4.08
0.721
0.262
0.699
11.09
0.935 0.457 0.809 0.357 0.139 0.583 0.724 0.305 0.909 0.327 0.957
concentration
0.710 0.036 0.276 0.242 0.787 0.015 0.035 0.342 0.092 0.175 0.118
height
F-test probability
4.09 133.2 99.6 106.6 2.87 4.24 3.71 24.9 17.2 8.4 23.59
1.s.d.
0.792 0.901 0.965 0.602 0.204
0.026
0.153
0.012
0.921 0.471 0.923 0.687 0.171 0.873 0.217 0.142 0.715 0.409 0.249
interaction e~
110
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112
mastications. Visual observations suggested that the mastications recorded here were essentially mouth clearing operations at the end of each sub-meal taken as an animal moved to a new grazing station, with its head up. Penning et al. ( 199 lb) have shown that, in sheep, prehension biting and mastication are mutually exclusive and are traded off within a constant, physiologically limited, total number of jaw movements. A similar effect can be seen here which is at odds with the suggestion of Newman et al. ( 1993 ) that prehension and mastication are not mutually exclusive in cattle. Penning et al. ( 199 lb ) suggested that the lower biting rate of sheep grazing tall swards was due to greater bite mass with the animals needing more mastication time. In the present study, cows on 40U had a lower mean bite size than those on other treatments, in line with this hypothesis (Table 2 ). The harvesting cost per unit of food was thus high for these animals because they not only ate for longer but took more bites per unit time for a smaller intake per unit time. On 40U animals were forced to bite fast in order to compensate for the low bite mass but on 40S they grazed less intensely and for less time owing to the difficulty of grazing the short sward. This suggests that there was some total energy intake threshold below which the behaviour of the animals changed. Ruminating time on 40U was low compared with other treatments (Table 2 ). However, idling time was similar, suggesting that the increased grazing time on this treatment occurred at the expense of ruminating time rather than idling time. Rumination may have decreased because there was no time available for any more. Alternatively, less rumination may have been required to handle the smaller bites taken on this treatment and, hence, more time was available for grazing. Demment and Greenwood (1988) have argued that animals become less selective as bite rate increases and thus have a lower quality diet which requires more rumination. They also suggest that reduced mastication leads to a need for more rumination to achieve an equivalent amount of particle breakdown. Neither appears to be the case here and it would seem that the small bite strategy is being used to produce small particles directly without the need for as much subsequent handling or rumination. The model of Demment and Greenwood (1988) also predicts an increase in bite mass at low forage density, contrary to the results seen here. They also suggest that rumination will increase at low forage density but this is based on the assumption that selectivity will decline and hence cell wall content of ingesta will increase. The animals in this trial may have had little opportunity to select and were thus unable to compensate in this way. Demment and Greenwood ( 1988 ) suggested that there is less mastication at low sward densities. Animals can thus increase intake rate and achieve a higher lumen fill and hence a better digestible energy yield from the available food. This lower mastication rate was seen in the present experiment. The lower ruminating time on 40U was achieved by decreasing the number rather than the duration of ruminating bouts (Table 2). Both the mean number and mean duration of grazing meals were toward the higher end of the range on 40U but individual animals appeared to adopt different meal size strategies to achieve the higher grazing times on this treatment. Demment and Greenwood
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
111
(1988) suggested that small meals and short ruminating periods with a rapid alternation between the two would lead to higher average rumen fill and hence longer retention times so increasing digestible energy obtained per unit time. However, they pointed out that large ruminants generally graze for relatively long periods as seen here. Tongue extension rate was similar to prehension biting rate. It is thus likely that cows extend their tongue on every prehension bite. However, the degree of extension was less on short swards.
Acknowledgements We thank M.E. Williams, J. Rish and C. Raine for skilled technical assistance and J. White and S. Hammond for care of the animals. This study forms part of a commission from the Ministry of Agriculture, Fisheries and Food.
References Bircham, J.S., 1981. Herbage growth and utilisation under continuous stocking management. Ph.D. Thesis, University of Edinburgh. Chacon, E., Stobbs, T.H. and Sandland, R.L., 1976. Estimation of herbage consumption by grazing cattle using measurements of eating behaviour. J. Br. Grassl. Soc., 3 l: 81-87. Demment, M. and Greenwood, G.B., 1988. Forage ingestion: effects of sward characteristics and body size. J. Anim. Sci., 66: 2380-2392. Forbes, J.M., Jackson, D.A., Johnson, C.L., Stockill, P. and Hoyle, B.S., 1986. A method for the automatic monitoring of food intake and feeding behaviour of individual cattle kept in a group. Res. Dev. Agric., 3: 175-180. Holmes, C.W., 1974. The Massey Grassmeter. Dairy Farm. Annu,, pp. 26-30. Huckle, C.A., Clements, A.J. and Penning, P.D., 1989. A technique to record eating and ruminating behaviour in dairy cows. In: C.J.C. Phillips (Editor), New Techniques in Cattle Production. Butterworths, London, pp. 236-237. Lawes Agricultural Trust, 1987. Genstat 5 Reference Manual, Oxford University Press, Oxford. Mayes, R.W., Lamb, C.S. and Colgrove, P.M., 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agric. Sci., 107:16 l-170. Mayne, C.S., 1992. Effect of supplementation on the performance of both growing and lactating cattle at pasture. Br. Grassl. Soc. Occas. Symp., 25: 55-71. Metz, J.H., 1975. Time patterns of feeding and rumination in domestic cattle. Meded Landbouwhogesch. Wageningen, 75: 12. Newman, J.A., Parsons, A.J. and Penning, P.D., 1994. A note on the behavioural strategies used by grazing animals to alter their intake rates. Grass Forage Sci. (in press). Penning, P.D. and Hooper, G.E., 1985. Measurement ofbehaviour in grazing cattle. Annual Report Grassland Research Institute, Hurley 1984-85. Penning, P.D., Steel, G.L. and Johnson, R.H., 1984. Further development and use of an automatic recording system in sheep grazing studies. Grass Forage Sci., 39:345-351. Penning, P.D., Rook, A.J. and Orr, R.J., 1991a. Patterns of ingestive behaviour of sheep continuously stocked on monocultures of ryegrass or white clover. Appl. Anita. Behav. Sci., 31: 237-250. Penning, P.D., Parsons, A.J., Orr, R.J. and Treacher, T.T., 1991b. Intake and behaviour response by sheep to changes in sward characteristics under continuous grazing. Grass Forage Sci., 46:15-28.
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Phillips, C.J.C. and Denne, S.K.P.J., 1988. Variation in the grazing behaviour of dairy cows measured by a vibracorder and bite count monitor. Appl. Anim. Behav. Sci., 21" 329-335. Phillips, C.J.C. and Leaver, J.D., 1986. Seasonal and diurnal variation in the grazing behaviour of dairy cows. Grazing, Br. Grassl. Soc. Occas. Symp., 19: 98-104. Poppi, D. P., Minson, D. J. and Ternouth, J. H., 198 I. Studies of cattle and sheep eating leaf and stem fractions of grasses. III. The retention time in the rumen of large feed particles. Aust. J. Agric. Res., 32:123 Rook, A. J., Huckle, C. A. and Wiikins, R. J., 1994. The effects of sward height and concentrate supplementation on the performance of spring calving dairy cows grazing perennial ryegrass-white clover swards. Anim. Prod., 58: 167-172. Tayler, J. C., 1953. The grazing behaviour of bullocks under two methods of management. Br. J. Anita. Behav., l: 72-77.
E LS EV I ER
Applied Animal Behaviour Science 40 ( 1994 ) 101-112
Effects of sward height and concentrate supplementation on the ingestive behaviour of spring-calving dairy cows grazing grass-clover swards A.J. Rook*, C.A. Huckle, P.D. Penning AFRC Institute of Grassland and Environmental Research, North Wyke, Okehampton EX20 2SB, UK
(Accepted 1 March 1994)
Abstract
Forty-eight, lactating, spring-calving, multiparous, Holstein-Friesian cows, continuously stocked on mixed grass-clover swards, were blocked by calving date, parity and milk yields in week 2 of lactation and randomly allocated to six treatments: 0 (U) or 4 (S) kg concentrate supplementation at sward heights of 40, 60 or 80 mm as measured by a rising plate meter. Jaw movements were recorded automatically for 24 h for a different cow on each treatment on each of 6 days during two periods (15-25 June (P1) and 25 July-6 August (P2)). Swards of 40 mm height were not used in P2. Total time grazing, ruminating or idling, and the number and duration of bouts of these activities, biting rate while grazing and chewing rate, number of boluses and chews per bolus while ruminating were recorded. Data were smoothed to give a minimum bout duration of 5 min. Herbage intakes were estimated using n-alkanes. Grazing time was greater at 40 mm than at 60 or 80 mm when unsupplemented but less when supplemented. Proportionately 0.88 of grazing time and 0.67 of ruminating time by dairy cows occurred during daylight with a large evening meal particularly evident. On the 40 mm sward unsupplemented animals grazed for longer with a higher biting rate but lower bite mass and less mastication and rumination. When supplement was offered at the 40 mm sward height animals appeared to 'give up' harvesting the sward more readily. Durations of ruminating and idling bouts were similar across all treatments with low variability. Keywords: Dairy cows; Grazing; Ingestive behaviour
*Corresponding author. 0168-1591/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSD10168-1591 (94)00488-Z
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A.J, Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
I. Introduction The effects of supplementation on the performance of lactating cattle at pasture have been reviewed by Mayne (1992). He reported that substitution rate can be accurately predicted at different herbage allowances but that insufficient information is available to allow similar prediction as a function of sward surface height for continuously stocked cattle. Rook et al. (1994) reported the effect of maintaining sward heights of 40, 60 or 80 m m as measured by a rising plate meter (Holmes, 1974) and of supplementation with 4 kg of concentrate on milk production and intake by dairy cows continuously stocked on a perennial ryegrass (Lolium perenne L. ) - white clover (Trifolium repens L. ) sward. Milk yields, milk component yields, live weight and herbage intakes were all significantly (P<0.05) lower at the 40 mm sward height. Supplementation significantly ( P < 0.05 ) increased milk and component yields at all sward heights. Mean herbage intakes were consistently lower at all sward heights but this effect was not significant. This concurrent study using the same animals was designed to investigate the behavioural mechanisms underlying any observed intake effects.
2. Animals, materials and methods Forty-eight multiparous, Holstein-Friesian cows, calving between 1 March and 11 April were continuously stocked on mixed perennial ryegrass-white clover swards from 6 May. All cows had ad-libitum access to feed blocks consisting of molasses impregnated with 50 mg kg- ~poloxalene as an anti-bloat prophylactic. The cows were blocked by calving date, parity and milk yield in week 2 of lactation and randomly allocated within blocks to one of six treatments, 0 (U) or 4 (S) kg concentrates with swards maintained at a sward height of 40, 60 or 80 mm, as measured by a rising plate meter (30.4 cm × 30.4 cm ) beneath which the sward is compressed before measurement. Stocking rates were adjusted by varying the grazed areas using moveable electrified fences. Spare animals were used to maintain the areas behind these fences as close as possible to the target heights. Cows were milked twice daily at approximately 06:00 and 15:00 h British Summer Time (BST). Equal amounts of concentrates were offered at each milking. Cows consumed all concentrate offered. The proportional composition of the concentrate was 0.225 maize gluten, 0.225 sugar beet pulp, 0.14 cotton seed 0.125 wheat, 0.075 extracted rapeseed, 0.075 molasses, 0.052 extracted sunflower, 0.025 extracted soya, 0.018 fat prills and 0.04 mineral mix. Chemical composition of concentrates and herbage is shown in Table 1. To avoid social facilitation between supplemented and unsupplemented animals, the two groups at each sward height grazed separate paddocks, although complete visual isolation was not achieved. As this could have led to unwanted differences in the swards being grazed by the two groups at each sward height, animals were swapped between paddocks on a daily basis. Owing to drought there was severe loss of body-weight
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
103
Table 1 Mean composition of herbage and concentrates (g kg - ~DM ) %C
DOMD
N
ADF
WSC
768 566 771 595 770 588
45.0 22.9 48.8 25.5 46.1 22. l
173 314 160 289 157 294
53 107 50 114 59 140
769 652 760 637
45.7 33.4 43.3 30.1
188 248 191 258
51 100 51 123
656
32.8
155
Herbage 15-18 June
40 m m 60mm 80 m m
25 July-2 August
60ram 80 m m
Concentrate
Clover Grass Clover Grass Clover Grass Clover Grass Clover Grass
7 13 8 12 12
%C, percentage of clover in sward; DOMD, digestible organic matter in the dry matter; N, nitrogen; ADF, acid detergent fibre; WSC, water soluble carbohydrates.
by the animals grazing the 40 m m swards and it became impossible to sustain these treatments after 27 June. Behavioural measurements were made between 15 and 25 June (P1) and between 25 July and 4 August (P2). Photoperiod, defined as 0.5 h prior to sunrise to 0.5 h after sunset, was approximately 17 h in P1 and 16 h in P2. On each of 6 days during these periods, the ingestive behaviour of a different animal from each treatment was recorded using the methods of Penning et al. (1984), as modified for cattle by Huckle et al. ( 1989 ). Briefly, gnathometers were used to record analogue electrical signals of the jaw movements on miniature tape recorders carded on the cows. The equipment was fitted during morning milking and remained on the animals for a recording period of approximately 24 h. Animals had been acclimatised to the equipment previously. The recordings were subsequently replayed and the waveforms analyzed by computer to give the time spent grazing, ruminating or idling and to count the jaw movements associated with these activities. The data were summarised on a minute by minute basis and an animal was deemed to be either grazing, ruminating or idling if it spent at least 30 s in any 1 min performing one of these activities. The activities occurred in discrete bouts and for the purpose of analysis the data were smoothed such that the minimum bout duration for any activity was 5 rain. This was achieved by examining a window of 9 min and assigning to the mid-point minute in the window the predominant activity, on a minute by minute basis, within the window. A minimum bout duration of 5 rain was chosen on the basis of data from previous experiments (A.J. Rook and C.A. Huckle, unpublished, 1991 ) in which the method of Forbes et al. ( 1986 ) was used to distinguish inter- and intra-meal intervals. Metz ( 1975 ) also reported a minimum inter-meal
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A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994.) 101-112
interval for cows of 4 min in indoor feeding trials. All results presented are for smoothed data. The algorithms used to analyze the gnathometer output could not distinguish between prehension and mastication bites while grazing (Penning and Hooper, 1985 ) or identify the use of the tongue in grazing. Therefore, while automatic recording was taking place, each animal was also observed visually and the number of prehension bites, mastications and tongue extensions were recorded separately during two 3-min periods for each activity, one after each milking. Herbage intakes were estimated using a modification of the n-alkane technique of Mayes et al. (1986). Cows were dosed with hard gelatin capsules containing C2s and C32 alkanes (500 mg per capsule) twice daily at milking over a period of 6 days. Grab samples of faeces were collected on the 3 subsequent days at the same time as dosing. Intake was thus estimated for a period corresponding to the day on which the animals jaw movements were recorded. Pluck samples of grass and clover, intended to be representative of the grazed horizon and samples of faeces and concentrate were analyzed for C28 to C33 alkanes using the Soxhlet extraction method of Mayes et al. (1986). Herbage intakes (I) (kg (dry matter (DM)) day-1 ) were calculated using the equation
I-
f31 - - ( D 3 2 + $32Is) -$31 Is f~2
H~
F~I -F3 H32
where H31, $3~, and F31 are the concentrations (mg kg -1 ) of C3~ alkane in herbage, concentrate and faeces, respectively,//32, $32, D32 and F32 are the concentrations of C32 alkane in herbage, concentrate dose and faeces, respectively, and I~ is the intake of concentrate supplement (kg (DM) day-i). Data were analyzed as a 2 × 3 factorial in randomised blocks using the analysis of variance facilities ofGENSTAT (Lawes Agricultural Trust, 1987). Patterns of activity within the observation periods were compared between treatments using the X2 test for homogeneity of two way contingency tables.
3. Results and discussion
Proportionately 0.88 of grazing time occurred during the 17 h of daylight in P 1 (Fig. 1 ) and 0.88 in the 16 h of daylight in P2 (Fig. 2) with peaks of grazing activity in mid morning and late evening. These values were significantly greater than the expected values of 0.71 and 0.67 if the total grazing time had been uniformly distributed over a 24 h day. In both periods approximately 0.56 of the available daylight was spent grazing. There were no significant treatment effects on the distribution in either period. Differences in total grazing time between treatments, discussed below, were thus achieved by altering the proportion of the night spent grazing. These results are in line with those of Penning et al. ( 1991 a)
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112 40
mm
105
award
milking
milking
+ llllJlllil ill o
60
-~
mm
sward
+++° 1i,illlil t111 8e
O
80
mm
sward
o 7.00
12.00
1 e.00 Time (BST)
0.00
15.00
Fig. 1. Mean time grazing in each hour of day for P1. [] 0 kg concentrates (U); • 4 kg concentrates (S); shaded area, scotophase.
who found that 90% of grazing by sheep occurred in dayJight in July, and Tayler (1953) who reported that 93% of grazing by bullocks occurred during daylight between April and July. Phillips and Leaver (1986) also found that grazing by dairy cows was concentrated in the daylight hours in early season. It seems that dairy cows were unwilling to graze during the substantial periods of darkness, despite their daylight grazing time being restricted by removal from the pasture for between 30 and 60 min at each milking. This may be an anti-predatory adaptation. Phillips and Denne ( 1988 ) found that coefficients of variation in grazing time both between cows and between days were much higher at night. This sug-
106
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112 60
mm
sward milking
Irlllklng 80-
°ii0
ll /m ill 80
38-
"¢~
24 12-
mm
sward
0 7'.00
12.00
1 B.00 Time (BST)
0.00
15.00
Fig. 2. Meantime grazingin each hour of day for P2. [] 0 kg concentrates (U); • 4 kg concentrates (S); shadedarea, scotophase. gests that cows may be able to adjust their night grazing time more easily than their day grazing time. The occurrence of greater grazing activity in the morning and afternoon could be a short term fasting effect following milking. Penning et al. ( 1991 a) suggested that the large evening meal they observed for sheep may have been an optimal foraging response to a build up of readily digestible products of photosynthesis in plant leaves at this time. A similar mechanism might explain the evening meal seen here. However, it should be noted that large evening meals have been observed in species whose food does not show such diurnal variation and other mechanisms may therefore be operating. Phillips and Leaver ( 1986 ) found that as daylight hours decreased grazing time before morning milking decreased and was compensated by a midnight meal. However, the evening meal was present throughout. Phillips and Denne ( 1988 ) found that the between cow and between day coefficients of variation for grazing time were particularly low during the evening meal, again indicating its possible importance in an optimal foraging strategy. In P1, 0.67 of rumination time occurred during daylight and 0.38 in P2 (expected value from uniform distribution 0.71 ), representing 0.20 and 0.14 of daylight, respectively. Even when total rumination time was reduced in treatment
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112
107
40U a similar proportion (0.62) still occurred during the day. The substantial proportion of the day spent ruminating may indicate a need to ruminate during the day in order to aid passage from the rumen and hence facilitate further intake. It is also possible that daytime idling is obligatory in order to avoid fatigue. Mean daily grazing times on the 60 and 80 mm swards in P1 (Table 2) were 10.93 and 10.38 h, but on the 40 mm sward this rose to 12.75 h when animals were unsupplemented and fell to 9.2 h when supplemented. In P2 (Table 3 ) the mean daily grazing times were 11.19 h on the 60 mm sward and 9.5 h on the 80 mm sward. Phillips and Leaver ( 1986 ) found that dairy cows spent 6-9 h d a y - t grazing at this time of the year on a sward of 80-90 mm sward surface height as measured with a sward stick (Bircham, 1981 ), which may be taken as approximately equivalent to a 60 mm rising plate height. They suggested that this represents a maximum grazing time for dairy cows in general. The present results do not agree with this contention. Ruminating and idling bout durations were both remarkably similar across treatments with small variability compared with that for meal duration. The physiological processes of ruminating may, therefore, require it to continue for periods of approximately 30 min at any one time. There were no significant differences in boluses per ruminating minute ( P > 0.05 ). However, chewing rate per bolus was significantly higher on 80S than on 80U in P 1 (Table 2 ) and for 80 vs 60 mm in P2 (Table 3 ). Particle size of digesta in the rumen is primarily reduced by rumination (Poppi et al., 1981 ). Thus, if longer material was ingested by cows on the 80 mm treatment this would have required more chewing to reduce particle size. Total jaw movement rate while grazing for automatically recorded data, which consists of both prehension bites and mastications, was greater than the sum of these two components recorded visually. Penning and Hooper ( 1985 ) also found that visual recording gave a lower rate than automatic recording. There are a number of possible reasons for this. The gnathometers sometimes produce signals with low signal to noise ratio. These signals may be misinterpreted and thus overestimate the true rate. Conversely, it is sometimes difficult to observe all jaw movements when recording visually which may lead to underestimation of the true rate. The visual recordings were made for only two 3-min periods on each cow in the 2 h following each milking and may thus be less representative. In addition, mastication rate and tongue movements were not recorded simultaneously with prehension bites and this could also give rise to errors. Mastication rate was similar across all treatments, except 40U, where it was reduced with a concomitant increase in prehension biting (Table 2). The standard error was also small. Penning and Hooper ( 1985 ) remarked on the similarity in mastication rates of cattle across a range of different sward heights which accounted for about 10% of the total jaw movements in their data compared with 17% in the present data except 40U at 8%. Chacon et al. ( 1976 ) found that nonlactating Jersey cows had 6-11% of head-down jaw movements accounted for by mastication and a further number of head-up mastications equivalent to 20% of the total head-down jaw movements, i.e. 21-25% of total jaw movements were
Herbage intake (kg (DM) day -~ ) Total grazing time (min day- ~) Total ruminating time (min day- ~) Total idling time (min day- ~) No. grazing meals per day No. ruminating bouts per day No. idling bouts per day Mean grazing meal duration (min) Mean ruminating bout duration (min) Mean idling bout duration (min) Total jaw movements (grazing) (per min) (automatic recording) Prehension biting rate (per min) ( visual recording) Mastication rate (grazing) (per min) ( visual recording) Tongue extensions (per min) (visual recording) Chewing rate (ruminating) (per min) Boluses/ruminating min Chews/bolus Intake rate while grazing (g m i n - ~) Intake per prehension bite (g)
Table 2 Intake and ingestive behaviour in P 1
12.2 553 368 505 8.4 13.1 17.8 80 28 28 79.1 44.8 15.3 42.0 53.3 1.08 54.4 22.6 0.51
62.3 5.6 58.7 50.9 0.79 66.2 17.8 0.28
40S
13.9 765 250 422 9.5 8.4 13.8 87 32 31 78.4
40U
Treatment
62.4 0.77 68.5 24.3 0.52
42.9
13.8
46.7
15.3 651 342 443 6.8 10.6 10.7 103 31 42 73.7
60U
56.1 0.73 76.3 21.1 0.33
57.3
8.7
60.7
13.8 660 379 374 9.2 12.1 14.7 75 32 27 77.2
60S
44.3 0.77 49.2 26.2 0.54
51.3
11.2
52.7
16.8 639 311 492 10.0 12.0 14.0 63 27 36 76.7
80U
65.2 0.75 106.0 28.0 0.58
50.1
10.8
51.7
16.5 606 382 425 7.7 12.9 15.3 81 30 28 88.5
80S
22.49 0.51 45.42 5.12 0.17
10.38
3.35
8.50
3.22 136.3 124.5 120.5 3.16 4.36 3.23 29.2 10.1 9.39 24.5
1.s.d.
0.637 0.755 0.520 0.003 0.026
0.985
0.758
0.865
0.019 0.677 0.459 0.339 0.612 0.526 0.033 0.256 0.737 0.337 0.692
height
0.371 0.216 0.175 0.417 0.509
0.688
0.129
0.477
0.223 0.049 0.042 0.599 0.705 0.061 0.003 0.488 0.931 0.004 0.436
concentration
F-test probability
0.212 0.295 0.096 0.091 0.006
0.001
<0.001
<0.001
0.728 0.061 0.631 0.127 0.097 0.390 0.386 0.102 0.548 0.227 0.784
interaction
~"
'~
-~
~.
5
"~ ~.
-..
¢%
oo
Herbage intake (kg (DM) day -~ ) Total grazing time (min day- l ) Total ruminating time (min day-~ ) Total idling time (min day- ~) No. grazing meals per day No. ruminating bouts per day No. idling bouts per day Mean grazing meal duration (min) Mean ruminating bout duration (min) Mean idling bout duration (min) Total jaw movements (grazing) (per min) (automatic recording) Prehension biting rate (per min) ( visual recording) Mastication rate (grazing) (per min) ( visual recording) Tongue extensions (per min) (visual recording) Chewing rate (ruminating) (per min) Boluses/ruminating (min) Chews/bolus Intake rate while grazing (g min-~ ) Intake per prehension bite (g)
Table 3 Intake and ingestive behaviour in P2
59.1
52.7
56.8 53.9 0.88 59.8 20.0 0.34
49.6 61.0 0.93 72.8 20.1 0.39
8.94
13.5 672 339 425 11.8 10.8 15.7 59 38 28 72.2
13.5 671 328 444 9.0 9.8 13.7 80 35 33 81.9
11.44
60S
60U
Treatment
70.7 0.76 116.0 24.8 0.38
59.5
9.63
64.8
14.1 537 368 501 10.1 14.0 18.1 60 27 27 85.5
80U
66.9 0.68 101.3 22.5 0.48
47.1
11.16
49.9
13.9 603 373 453 10.2 14.5 17.0 64 25 26 94.3
80S
0.389 0.576 0.464 0.591 0.694
0.981 0.089 0.113 0.039 O.llO 0.281
11.92 18.85 0.34 56.48 6.24 0.17
0.508
0.882
4.08
0.721
0.262
0.699
11.09
0.935 0.457 0.809 0.357 0.139 0.583 0.724 0.305 0.909 0.327 0.957
concentration
0.710 0.036 0.276 0.242 0.787 0.015 0.035 0.342 0.092 0.175 0.118
height
F-test probability
4.09 133.2 99.6 106.6 2.87 4.24 3.71 24.9 17.2 8.4 23.59
1.s.d.
0.792 0.901 0.965 0.602 0.204
0.026
0.153
0.012
0.921 0.471 0.923 0.687 0.171 0.873 0.217 0.142 0.715 0.409 0.249
interaction e~
110
A.J. Rook et aL / Applied Animal Behaviour Science 40 (1994) 101-112
mastications. Visual observations suggested that the mastications recorded here were essentially mouth clearing operations at the end of each sub-meal taken as an animal moved to a new grazing station, with its head up. Penning et al. ( 199 lb) have shown that, in sheep, prehension biting and mastication are mutually exclusive and are traded off within a constant, physiologically limited, total number of jaw movements. A similar effect can be seen here which is at odds with the suggestion of Newman et al. ( 1993 ) that prehension and mastication are not mutually exclusive in cattle. Penning et al. ( 199 lb ) suggested that the lower biting rate of sheep grazing tall swards was due to greater bite mass with the animals needing more mastication time. In the present study, cows on 40U had a lower mean bite size than those on other treatments, in line with this hypothesis (Table 2 ). The harvesting cost per unit of food was thus high for these animals because they not only ate for longer but took more bites per unit time for a smaller intake per unit time. On 40U animals were forced to bite fast in order to compensate for the low bite mass but on 40S they grazed less intensely and for less time owing to the difficulty of grazing the short sward. This suggests that there was some total energy intake threshold below which the behaviour of the animals changed. Ruminating time on 40U was low compared with other treatments (Table 2 ). However, idling time was similar, suggesting that the increased grazing time on this treatment occurred at the expense of ruminating time rather than idling time. Rumination may have decreased because there was no time available for any more. Alternatively, less rumination may have been required to handle the smaller bites taken on this treatment and, hence, more time was available for grazing. Demment and Greenwood (1988) have argued that animals become less selective as bite rate increases and thus have a lower quality diet which requires more rumination. They also suggest that reduced mastication leads to a need for more rumination to achieve an equivalent amount of particle breakdown. Neither appears to be the case here and it would seem that the small bite strategy is being used to produce small particles directly without the need for as much subsequent handling or rumination. The model of Demment and Greenwood (1988) also predicts an increase in bite mass at low forage density, contrary to the results seen here. They also suggest that rumination will increase at low forage density but this is based on the assumption that selectivity will decline and hence cell wall content of ingesta will increase. The animals in this trial may have had little opportunity to select and were thus unable to compensate in this way. Demment and Greenwood ( 1988 ) suggested that there is less mastication at low sward densities. Animals can thus increase intake rate and achieve a higher lumen fill and hence a better digestible energy yield from the available food. This lower mastication rate was seen in the present experiment. The lower ruminating time on 40U was achieved by decreasing the number rather than the duration of ruminating bouts (Table 2). Both the mean number and mean duration of grazing meals were toward the higher end of the range on 40U but individual animals appeared to adopt different meal size strategies to achieve the higher grazing times on this treatment. Demment and Greenwood
A.J. Rook et al. / Applied Animal Behaviour Science 40 (1994) 101-112
111
(1988) suggested that small meals and short ruminating periods with a rapid alternation between the two would lead to higher average rumen fill and hence longer retention times so increasing digestible energy obtained per unit time. However, they pointed out that large ruminants generally graze for relatively long periods as seen here. Tongue extension rate was similar to prehension biting rate. It is thus likely that cows extend their tongue on every prehension bite. However, the degree of extension was less on short swards.
Acknowledgements We thank M.E. Williams, J. Rish and C. Raine for skilled technical assistance and J. White and S. Hammond for care of the animals. This study forms part of a commission from the Ministry of Agriculture, Fisheries and Food.
References Bircham, J.S., 1981. Herbage growth and utilisation under continuous stocking management. Ph.D. Thesis, University of Edinburgh. Chacon, E., Stobbs, T.H. and Sandland, R.L., 1976. Estimation of herbage consumption by grazing cattle using measurements of eating behaviour. J. Br. Grassl. Soc., 3 l: 81-87. Demment, M. and Greenwood, G.B., 1988. Forage ingestion: effects of sward characteristics and body size. J. Anim. Sci., 66: 2380-2392. Forbes, J.M., Jackson, D.A., Johnson, C.L., Stockill, P. and Hoyle, B.S., 1986. A method for the automatic monitoring of food intake and feeding behaviour of individual cattle kept in a group. Res. Dev. Agric., 3: 175-180. Holmes, C.W., 1974. The Massey Grassmeter. Dairy Farm. Annu,, pp. 26-30. Huckle, C.A., Clements, A.J. and Penning, P.D., 1989. A technique to record eating and ruminating behaviour in dairy cows. In: C.J.C. Phillips (Editor), New Techniques in Cattle Production. Butterworths, London, pp. 236-237. Lawes Agricultural Trust, 1987. Genstat 5 Reference Manual, Oxford University Press, Oxford. Mayes, R.W., Lamb, C.S. and Colgrove, P.M., 1986. The use of dosed and herbage n-alkanes as markers for the determination of herbage intake. J. Agric. Sci., 107:16 l-170. Mayne, C.S., 1992. Effect of supplementation on the performance of both growing and lactating cattle at pasture. Br. Grassl. Soc. Occas. Symp., 25: 55-71. Metz, J.H., 1975. Time patterns of feeding and rumination in domestic cattle. Meded Landbouwhogesch. Wageningen, 75: 12. Newman, J.A., Parsons, A.J. and Penning, P.D., 1994. A note on the behavioural strategies used by grazing animals to alter their intake rates. Grass Forage Sci. (in press). Penning, P.D. and Hooper, G.E., 1985. Measurement ofbehaviour in grazing cattle. Annual Report Grassland Research Institute, Hurley 1984-85. Penning, P.D., Steel, G.L. and Johnson, R.H., 1984. Further development and use of an automatic recording system in sheep grazing studies. Grass Forage Sci., 39:345-351. Penning, P.D., Rook, A.J. and Orr, R.J., 1991a. Patterns of ingestive behaviour of sheep continuously stocked on monocultures of ryegrass or white clover. Appl. Anita. Behav. Sci., 31: 237-250. Penning, P.D., Parsons, A.J., Orr, R.J. and Treacher, T.T., 1991b. Intake and behaviour response by sheep to changes in sward characteristics under continuous grazing. Grass Forage Sci., 46:15-28.
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Phillips, C.J.C. and Denne, S.K.P.J., 1988. Variation in the grazing behaviour of dairy cows measured by a vibracorder and bite count monitor. Appl. Anim. Behav. Sci., 21" 329-335. Phillips, C.J.C. and Leaver, J.D., 1986. Seasonal and diurnal variation in the grazing behaviour of dairy cows. Grazing, Br. Grassl. Soc. Occas. Symp., 19: 98-104. Poppi, D. P., Minson, D. J. and Ternouth, J. H., 198 I. Studies of cattle and sheep eating leaf and stem fractions of grasses. III. The retention time in the rumen of large feed particles. Aust. J. Agric. Res., 32:123 Rook, A. J., Huckle, C. A. and Wiikins, R. J., 1994. The effects of sward height and concentrate supplementation on the performance of spring calving dairy cows grazing perennial ryegrass-white clover swards. Anim. Prod., 58: 167-172. Tayler, J. C., 1953. The grazing behaviour of bullocks under two methods of management. Br. J. Anita. Behav., l: 72-77.