Abstract:
SOME PHYSIOLOGICAL AND BEHAVIOURAL CONSEQUENCES OF SHEARING M. E. D. WEBSTER* and J. J. LYNCH Summary The voluntary food intake and thermo-regulatory responses of sixteen Merino wethers have been studied before and after shearing. The sheep were in shaded single pens, sheltered from wind and rain but otherwise exposed to climatic variations of temperature and humidity. Average daily food intake increased after shearing in eleven of the sixteen animals. Grazing times of sheep at pasture appeared to decrease for a period after shearing and grazing patterns seemed to be disturbed. Changes in daily food intake were not related to ambient temperatures except , that intakes were depressed during the coldest weather. I. INTR0DUCTIQN I Wodzicka-Tomaszewska ( 1963 ) has demonstrated an increased voluntary food intake in sheep after shearing. Blaxter ( 1964) has referred to these increases as adjustments to cold conditions but considers them to be of small magnitude * in sheep. Similarly, Balch ( 1962), in his review of the regulation of voluntary. food intake in ruminants, thought that changes in heat production might be implicated, but concluded that food intake is unlikely to be regulated by an y single mechanism. The aim of this study was to investigate the relation between voluntary intake after shearing and daily variation in climatic environment. II. EXPERIM*ENTAL Eighty-six 6-tooth Merino wethers were used. Seventy of these were left at pasture and sixteen were placed in individual pens. Twelve of the paddock sheep carried grazing clocks and six of them were left unshorn throughout the experiment. The group of sixteen sheep, selected for similar body weight (23.5-26.5 kg) and conformation, were placed in sheltered, shaded pens one month before shearing. Except for these restrictions, they were exposed to climatic variations in their environment. They` were given free access to a pelleted ration containing 15 % crude protein, made from finely ground materials including 30% lucerne meal. The animals were weighed at the beginning of the experiment, immediately after shearing and again 23 days later. *Department of Physiology, University of New` England, Armidale, N.S.W. 'fDivision of Animal Physiology, C.S.I.R.O. Pastoral Research Laboratory, Armidale, . N.S.W. 234 . Fig. 1.-Mean 'day'dnd 'over-night' intakes in relation to daily thermal conditions after shearing. 235 A fresh ration was placed before the animals at 9.00 a.m. each day, and routine re-weighing at 4.30 p.m. the same day, and 8.30 a.m. the next day, established the amount eaten. Rectal temperature and skin temperature at three sites on each sheep (mid-side, ear and lower hind leg) were recorded by means of thermo-couples connected to two recording potentiometers. This system permitted continuous recording from 24 temperature sensors at any one time. III. RESULTS Figure 1 illustrates the pattern of daily food consumption, 'day' and 'night ' consumptions, and 'day' and 'night' thermal conditions. Over-night food intake was depressed during the three days following shearing and during nights on which there were frosts. Otherwise, there was no DAYS AFTER SHEARING Fig. 12.-Change in mean heart rate in relation to daily mean temperatures after shearing. Open circles: 'weight gain' group; filled circles: 'weight loss' group. 236 apparent relation between feed intake and immediate thermal environment in either the sheep that gained weight after shearing ('weight gain' group) or the 'weight loss' groups. Intake tended to be lower in animals that were shivering. The relative change in mean daily heart rates is illustrated in Figure 2. Mean heart rates increased by 5-10 beats per minute on the day of shearing and continued to increase slowly for eight days. Although heart rates did not change markedly with the low temperature of the third day there was a sharp increase in heart rate coinciding with the onset of cold weather on the ninth day after shearing. The 'weight loss ' group showed the greater increase in heart rate during this period. Heart rates subsequently decreased in both groups as environmental temperatures increased. Sheep were ranked according to their cumulative respiratory frequencies during each of the seven days prior to shearing. Although individual rankings changed from day to day, the members of the group that gained weight after shearing had the greatest respiratory frequency totals on five of the seven days. Sheep that lost weight before shearing had the lowest totals on all seven days. Respiratory frequencies fell in all sheep from tachypnoeic to eupnoeic levels within seven hours of shearing and continued to fall, reaching their lowest values for the entire experimental period on the second day. Thermal tachypnoeic responses re-appeared in sheep of the 'weight gain' group on the eighteenth day after shearing. Skin temperatures at all three measurement sites fell after shearing but there was no change in rectal temperature. There was no immediate association between changes in surface temperature distribution and rectal temperature, ambient conditions, daily food consumption, or tendency to gain or lose weight. The progress of acclimatisation was indicated by the conditions associated with elevated ear temperatures. At 2.30 p.m. on the eighth day after shearing, the temperatures of both ears in ten of the sheep were close to air temperature (20.3'C) while TABLE 1 another two sheep had one ear temperature close to air temperature. On the sixteenth day, all sheep had high ear temperatures with respect to air at 9.30 a.m. and 20.8'C. Air movement was slight on both days. Observations on the sheep at pasture showed a depression of grazing time for a period after shearing. The pattern of grazing was also disturbed, sheep eating only in short bursts of ten to twenty minutes. On the third day the animals began to move and graze freely. The effect of shearing on grazing time is shown in Table 1. The daily movement pattern of the sheep was unaltered by shearing, except for a variation associated with a storm on the 9th day. During this storm, dry bulb temperature fell by 1 l�C, 70 points of rain were recorded and wind speed was estimated at Force 8 according to the Beaufort scale. The sheep moved before the wind and remained, shivering in one corner of the paddock until the wind dropped. They then resumed their grazing while light rain was still falling. During the next day-the coldest of the whole period-the sheep remained close to shelter and reduced their grazing time. IV. DISCUSSION The results reported above confirm the suggestion by Wheeler, Reardon and Lambourne ( 1963) and the report by Wodzicka-Tomaszewska ( 1963) that there is a delay in the increase in voluntary food intake of wethers after shearing. However, although climatic conditions were similar, there were some differences between the results reported above and those of Wodzicka-Tomaszewska ( 1963). In this experiment, 11 sheep gained weight during the three weeks following shearing. Heart rate changes were also markedly different from those reported by Wodzicka-Tomaszewska. There were no substantial increase immediately after shearing, nor a return to control values when intakes began to increase. In the present case, the greatest increase in heart rates occurred nine days after shearing in association with a cold spell and after the feed intake of one group had increased. There were differences in the rations used by Wodzicka-Tomaszewska and in the present case. Wodzicka-Tomaszewska fed a mixture of hay and nuts offered ad libitum. In the work reported here, only pelleted feed was offered, but of a higher digestibility coefficient (76% ) than Wodzicka-Tomaszewska 's sheep nuts (67% ) . There was no evidence that the pelleted ration caused digestive upsets in the Merinos. The Merinos seemed to differ from the Romneys in the character and magnitude of their response to shearing. Although Merinos might be expected to show a greater response to cold than Romneys, it is interesting to note that the Merinos did not exhibit a marked increase in heart rate during the week after shearing. The Merino heart rates increased relatively gradually during this period but then, unlike the Romney response, they remained at high levels for the next three weeks. The average intake of Wodzicka-Tomaszewska's sheep doubled and remained high, while the intakes of the Merino 'weight gain' group increased by less than 50% . 238 The increase in voluntary intake after shearing has been explained as a simple and direct compensatory adjustment to cold (Blaxter 1964). However, the food consumption of the 'weight loss' group was reduced on the coldest days and the grazing time of the sheep at pasture was also reduced during cold weather. The gradually increasing intake of the 'weight gain' group was not accelerated by a period of cold weather, while the group that seemed to be most affected by cold did not increase their intake. These responses do not accord well with a direct thermoregulatory relation between food consumption and the cold. V. ACKNOWLEDGMENTS The authors wish to thank Mr. W. M. Willoughby, Ofhcer-in-Charge, Pastoral Research Laboratory, Armidale, and Professor J. V. Evans for their interest and co-operation. We are also indebted to the Australian Wool Research Committee, The ` Rural Credits Trust Fund and the University of New England for their financial support. VI. REFERENCES , C. C. ( 1962). Regulations of voluntary food intake in ruminants. Nutrition Abstructs and Reviews 32: 669. B LAXTER , K. L. ( 1964). The effect of outdoor climate in Scotland on sheep and cattle. The Veterinary Record 16: 1445. B ALCH W HEELER , J. L., REARDON, T. F., and L AMBOURNE , L. J. (1963). The effect of pasture availability and shearing stress on herbage intake of grazing sheep. Australian Jo' urnal of W ODZICKA Agricultural Research 14: 364. -TO MASZEWSKA, M. (1963). The effect of shearing on the appetite of sheep. New Zealand Journal of Agricultural Research 6: 440. 239