Applied Animal Behaviour Science, 21 (1988) 329-335 329 Elsevier Science Publishers B.V., AmsterdAm - - Printed in The Netherlands

Variation in the Grazing Behaviour of Dairy Cows Measured by a Vibrarecorder and Bite Count Monitor

C.J.C. PHILLIPS and S.K.P.J. DENNE

School of Agricultural and Forest Sciences, University College of North Wales, Bangor, Gwynedd, LL57 2UW (Gt. Britain)

(Accepted for publication 16 August 1988)

ABSTRACT

Phillips, C.J.C. and Denne, S.K.P.J., 1988. Variation in the grazing behaviour of dairy cows mea- sured by a Vibrarecorder and bite count monitor. Appl. Anim. Behav. Sci., 21: 329-335.

Ten Friesian dairy cows were fitted on the neck with a Walker pedometer to evaluate the pe- dometer as a low-cost means of recording grazing bite number, and a Vibrarecorder for comparison and to evaluate the between-cow and between-day coefficients of variation (CV) of grazing bouts, in order to evolve an optimum recording strategy. The total number of daily bouts averaged 5.01 with a mean duration of 1.85 h, giving a total grazing time of 9.27 h per cow per day. The grazing time recorded by the Vibrarecorders was generally linearly related to total daily bites recorded by the pedometers, although in some cases a quadratic function was significant which was assumed to arise from variation in the biting rate at high grazing times. The between-cow CV of daily grazing time was greater than the between-day CV, but at certain times of the day, particularly at night, the between-day CV was very high. More variation occurred in grazing bout duration than bout number and the variation in total bite number tended to be greater than grazing time.

INTRODUCTION

Prog re s s in the field of graz ing b e h a v i o u r r e sea rch has been h a m p e r e d by the high cost o f r ecord ing da ta , w i th o b s e r v a t i o n - b a s e d s tudies be ing labor ious a n d t i m e consuming , a n d a u t o m a t i c record ing devices be ing cos t ly a n d fre- quen t ly c u m b e r s o m e . A l though in o b s e r v a t i o n s tudies fair ly large n u m b e r s of a n i m a l s a t one t i m e can be r eco rded (up to 40 ca t t l e ) , t he p r o p o r t i o n of t i m e t h a t is s a m p l e d is i nva r i ab ly low. T h e h igh cost of a u t o m a t i c record ing devices usua l ly m e a n s t h a t a smal l n u m b e r of devices have to be used on a s amp le popu la t ion , bu t a g rea te r p r o p o r t i o n of the t i m e can be s a m p l e d wi th l i t t le ex t r a cost. T h e accu racy of t he two m e t h o d s depends on the r e l a t ionsh ip b e t w e e n the b e t w e e n - c o w a n d b e t w e e n - d a y v a r i a t i o n in graz ing behav iour . T h e use of

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the pedometer, either mechanical or electronic, has become popular for meas- uring human and cattle walking activities (Schofield and Phillips, 1987), and when attached to the neck of a grazing animal could provide a method of au- tomatically recording total daily bites that is sufficiently low cost to be used on a large number of animals. This study reports the results of an investigation into the relationship between Kienzle Vibrarecorders used to record grazing time and pedometers used to record daily bite numbers, and examines the be- tween-day and between-cow variation in grazing behaviour.

MATERIALS AND METHODS

Ten British Friesian dairy cows were each fitted with a Kienzle Vibrarecor- der (Kienzle Apparate GmBH Villingen, Schwarzwald, F.R.G. ) (Stobbs, 1970) attached to the neck to record grazing time, and a Walker pedometer (Silva (U.K.) Ltd., Feltham, Gt. Britain) also attached to the neck, so that the pen- dulum functioned with the vertical movement of the head associated with graz- ing activity and recorded the number of grazing bites. Both devices were attached to the neck by securing them in the correct plane to a plastic head collar (Dalton, U.K., Ltd). Initial tests of the pedometer in this position as- certained that it did not function during walking activity. Pedometers were set to record 50 000 bites per revolution of the dial and were read at least four times daily in the field, with the values added to give the total daily bites. They were calibrated by hand shaking for ~ 100 000 movements. Five pedometers and five Vibrarecorders were then placed in pairs on the cows over a 4-week period, giving at least 7 days' data for each cow and records for at least three cows for each pair of recording devices. Cows were continuously grazed during this period on a predominantly perennial ryegrass (Loliumperenne) sward at a mean herbage height of 6-7 cm, and were only removed for milking for 1 h at 07.00 and 16.00 h. Mean day length was from 05.30 to 20.30 h.

Measurements of the number and length of grazing bouts were taken from the Vibrarecorder charts for each of the three major periods of the cow's day: the Day Period between morning and afternoon milkings; the Evening Period from afternoon milking to 23.00 h; the Night Period from 23.00 h to morning milking. Visual assessment of the Vibrarecorder charts from these periods es- tablished that there was no overlap of grazing activity between these periods. A grazing bout was defined as a period of continuous grazing activity separated from the preceding and subsequent periods of grazing activity by at least 15 min non-grazing.

Statistical analysis

Stepwise regression analysis between the grazing time recorded by Vibra- recorders and the total daily number of bites recorded by pedometers was per- formed using the statistical package Minitab (1985). The linear and quadratic

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coefficients of grazing time were used as the independent variables and were included in the predictive equations when P < 0.05. The choice of a quadratic model was made from studying the daily distribution of grazing times. A small number of recordings of daily grazing times < 5 h were obtained on the day that the recording devices were attached, which were included in the data sets.

Analysis of variance of the number and duration of grazing bouts and their respective between-day coefficients of variation (CV) was also completed us- ing the Minitab package.

RESULTS

Vibrarecorder and pedometer comparison

Some difficulty was experienced in ascertaining the exact level of calibration for each pedometer, so the comparison of Vibrarecorder and pedometer read-

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TABLE 1

Predictive equations for the five data sets of grazing t ime x (h per day ) recorded by Vibrarecorder and total bite number y (bites per day) recorded by pedometer

Data set Equation r 2 Significance SE of predicted mean value (x=6)

1 y=4420x 0.963 *** 1774 2 y=7460x 0.889 *** 6247 3 y = 321x 2 0.913 *** 2001 4 y=6780x-370x 2 0.930 *** 1973 5 y=6790x 0.896 *** 4376

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Fig. 2. The relationship between grazing t ime and total bite number for the entire data set.

ings is presented for each pair of devices. The relationships between the graz- ing times recorded by each Vibrarecorder and the total bite number, recorded by the corresponding pedometer, are shown in Fig. 1. The predictive equations derived by stepwise regression for the five data sets are given in Table 1. For three data sets (1, 2 and 5), grazing time was positively correlated with bite number in direct proportion, although the quadratic term was almost signifi- cant in the first data set. For Set 3, bite number was positively correlated with grazing time 2, and for Set 4, bite number was positively correlated with grazing time and negatively correlated with grazing time 2. Taking the data sets as a whole (Fig. 2 ), bite number was positively correlated with grazing time, with a tendency to be positively correlated ( P > 0.05) with grazing time<

Grazing bout analysis

The total number of daily bouts averaged 5.01 with a mean duration of 1.85 h, giving a total grazing time of 9.27 h per cow per day (52% of the Day Period,

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TABLE 2

Mean grazing bout number and duration, and the between-day coefficients of variation (CV) for bout number and duration

Period SED Significance

Day Evening Night

Bout number (no. per day) 2.41 a 1.645 0.96 ¢ 0.117 ***

Bout duration (h per bout) 1.83 b 2.65 a 0.52 ¢ 0.175 ***

CV bout number (%) 195 33 b 73" 7.4 *** CV bout duration (%) 23 ¢ 45 b 77 ~ 5.8 ***

Within each row, means with different superscripts are significantly different (P < 0.05). ***P < 0.001.

TABLE3

Between-cow coefficients of variation (CV) for grazing bout number, bout duration and grazing time

Coefficients of variation (%)

Day Evening Night 24 hours

Bout number 14.9 28.5 38.0 21.7

Bout duration 33.9 20.1 47.5 24.0

Grazing time 29.7 17.6 46.5 24.0

54% of the Evening Period and 11% of the Night Period). The number of grazing bouts and the durat ion of each bout was least during the Night Period (Table 2). During the Day Period, there was a large number of short bouts compared with the Evening Period which had a smaller number of longer bouts. The between-day CV of both bout number and bout durat ion was greatest for the Night Period, and the CV of the evening bout number and durat ion was greater than tha t for the Day Period. Bout durat ion tended to have higher CV values than bout number, The mean between-day CV for total daily grazing t ime recorded by the Vibrarecorders and bite number recorded by the pedom- eters was 15.1 and 27.2% (SED 5.93), respectively. This difference was not quite significant at the 5% level.

The between-cow CV of bout number and durat ion for the Night, Day and Evening Periods are shown in Table 3. The between-cow CV in bout number

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and duration was greatest during the Night Period, with the Day Period tend- ing to show high variation in bout duration variation, but low bout number variation. By contrast, the Evening Period tended to show a greater variation in bout number than bout duration, indicating a tendency for more individual behaviour by the cows during this period. The between-cow CV for total graz- ing time (as a proportion of total time ) was highest for the Night Period and was higher in the Day than the Evening Period.

DISCUSSION

The use of the pedometer to record total daily bites of the dairy cow appears to offer an inexpensive and reliable method, providing the calibration is known before fitting to the cow, and will be particularly useful where it is desirable to measure the activity of a large number of animals over a prolonged period of time. Unlike the Vibrarecorder, the pedometer does not give the periodicity of grazing, only the total activity between recordings. It records the total number of bites taken, unlike the Vibrarecorder which records grazing time and may, therefore, be a better indicator of grazing intensity. The difficulty experienced in calibrating the Walker pedometer used in this study could explain the high values for bite number by pedometer Number 2.

The results indicate that although grazing time is positively related to the number of bites taken, this relationship is not always linear, i.e., biting rate is not always constant. In two of the data sets, 1 and 3, there was a tendency for biting rates to be increased at high grazing times, but in the fourth data set biting rate was reduced at high grazing time. This suggests that some cows will increase grazing time and reduce biting rate in response to a temporary feed shortage, whereas others will increase grazing time and biting rate. Conceiva- bly, the effect on biting rate at high grazing times may depend on the time of day of the additional grazing. Recent research (Hecheimi, 1987) has shown that the biting rate of set-stocked cows increases over the period of daylight grazing, but is low at night. This study shows that night grazing, and to a lesser extent evening grazing, have the highest between-day variability and are there- fore most likely to be affected when grazing time varies. When night grazing is increased, daily biting rate will be reduced, but when evening grazing is in- creased daily biting rate will be increased. An alternative explanation is that between-cow variation exists in the behavioural response to feed shortages, which could also explain some of the variation in behavioural response to feed shortage that has been recorded so far.

Both between-day and between-cow variation analysis showed that the bout duration is more variable than the bout number, with the exception of be- tween-cow variation for the Evening Period, caused by some cows having one and some two grazing bouts. This is to be expected because of the gregarious nature of cattle grazing and the allelomimetic forces controlling the grazing

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activity appear to be strongest at the start of the day's grazing activity and weaken in the evening. The high between-cow CV of bout number in the even- ing may be due to the varied requirement for lying behaviour which has accu- mulated during the day and assumes a higher priority during deprivation than feeding (Metz and Wierenga, 1984).

The between-cow CV measured in this study was higher than the CVs re- corded by Jamieson (1975) of 5-7% for grazing time and 6-12% for total daily bites. The CV for ingestive behaviour variables will be mainly determined by the uniformity of the animal population with regard to feed intake require- ments, so some differences between populations are to be expected. This study is, however, in agreement with Jamieson (1975) and Phillips (1983) that the between-cow CV for total daily bites is higher than that for grazing time.

This study shows that the between-day CV for grazing time (15%) is less than the between-cow CV (24%), indicating that it is preferable to monitor a large number of cows for a short time period than vice versa. At certain times of the day, however (e.g., at night) the between-day CV is much higher than the between-cow CV so it is important to conduct ingestive behaviour studies in multiples of 24 h.

REFERENCES

Hecheimi, K., 1987. The effect of grass height and silage supplementation on the ingestive behav- iour of dairy cows. M.Sc. Thesis, Faculty of Science, University College of North Wales, Bangor.

Jamieson, W.S., 1975. Studies on the herbage intake and grazing behaviour of cattle and sheep. Ph.D. Thesis, Faculty of Agriculture and Food, University of Reading.

Metz, J.H.M. and Wierenga, H.K., 1984. Spatial requirements and lying behaviour of cows in loose housing systems. In: J. Unshelm, G. van Puttem and K. Zeeb (Editors), Proceedings of the International Congress on Applied Animal Ethology in Farm Animals, Kiel, pp. 179-183.

Minitab, 1985. State College, Pennsylvania, U.S.A. Phillips, C.J.C., 1983. Conserved forage as a buffer feed for dairy cows. Ph.D. Thesis, Faculty of

Science, University of Glasgow. Schofield, S.A. and Phillips, C.J.C., 1987. The use of pedometers to detect oestrus in dairy cows.

Anita. Prod., 44:460 (Abstract). Stobbs, T.H., 1970. Automatic measurement of grazing time by dairy cows on tropical grass and

legume pastures. Trop. Grassl., 4: 237-244.