Abstract:
BODYWEIGHT CRITERIA AND POST SHEARING DEATHS K. J. HUTCHINSON* Summary Substantial mortality (24%) of sheep occurred over a 14-day period immediately after shearing. The peak of mortality occurred on the seventh day and was related to wind exposure and rainfall. The sheep comprised 14 experimental groups in a stocking rate/fodder conservation experiment in which the treatments gave a wide range of values for two bodyweight criteria. A strong association was found between data for mortality and relative rate of bodyweight loss (k) prior to shearing. The inclusion of bodyweight at shearing (w) was not significant. It appears that values for k may reflect with greater sensitivity than w the degree of nutritional difficulty faced by newly shorn sheep at pasture. Alternatively, k may better represent some physiological condition. I. INTRODUCTION There appears to be no published evidence of an association between postshearing deaths in sheep and either bodyweight or body condition. Geytenbeek ( 1963) in a survey of losses during adverse weather reported that 'owners generally believed that ` ' sheep generally succumbed before sheep in ` fat store' or ` forward store ' condition'. However, the data failed to prove this. In a more recent survey of losses covering a representative sample of properties in the higher rainfall and sheep wheat belts of Australia (Hutchinson, J. C. D., personal communication), some evidence was obtained that sheep in 'poor ' condition were more liable to die than those in 'store' or 'fat' condition. II. EXPERIMENTA L The observations arose from a fodder conservation experiment at Armidale, based on 14 groups of fine woolled Merino wethers aged from two to three years and grazed at stocking rates of 4-16 sheep per acre. The units, each of 1 The region was acre, were contiguous and of equal shape and exposure. declared drought stricken in March 1965 and it was decided to shear early in April to ensure the recovery of wool production records. For shearing (April 4, 1965 to April 6, 1965) the groups were handled as a single flock which was grazed for short intervals around the shed and put under cover at night. The sheep were regrouped and returned to their units and to their pre-shearing nutritional regimes on April 7, 1965. Supplemented groups were being fed thrice weekly and this schedule was undisturbed by the shearing operation. Hessian shelters (L shaped) were erected in the south eastern corners of each plot on April 7, 1965. They were changed to the south western corners on April 12, 1965, the day following a reversal in wind direction. The responses in wool, bodyweight and survival to the experimental treatments will be reported elsewhere. These have a common origin in the varying *C.S.I.R.O. Pastoral Research Laboratory, Armidale, N.S.W. 229 nutritional levels achieved. In this paper the bodyweight data for the period immediately prior to shearing was examined for association with post-shearing deaths in order to determine an appropriate basis for prediction. A wide range of values of group means was available for both bodyweight at shearing (w) and relative rate of bodyweight change during the month prior to shearing (k). Values for k were calculated as :[log, w2 - log, WJ k . 1O-3 = t2 - h the time interval for t being in days and the observations for w in kilograms. Bodyweights were adjusted for the amounts of fleece carried. All the deaths occurred (3 l/128) in those 11 groups with negative values for k, i.e., the sheep were losing weight prior to shearing. For these, mortality percentage data were transformed angularly and the values (m) were weighted according to the number of sheep per group following the procedure described by Fisher and Yates (1963). Multiple regression analysis was employed to determine associations between mortality (m) and the two criteria for bodyweight, k and w. There were no deaths in the remaining 3 groups which had high values for bodyweight (46 - 54 kg) and a range of positive values for k (+0.09 + 1.79). III. RE' SULTS AND DISCUSSION The course of mortalities and the accompanying weather data are set out in Figure 1. The greatest number of deaths was recorded on the seventh day and this appears to have been related to a sharp change in weather (Figure 1) together with a delay of 24 hours in changing the position of the shelters. Thus the mortality peak coincided with increased wind exposure and rain. There was no association between trends in screen temperature and the course of losses. The losses surveyed by Geytenbeek ( 1963) also occurred during high wind and heavy rainfall. Data for mortality and the two expressions for bodyweight are shown in Figure 2. The analysis of variance (Table 1) shows that the multiple relationship accounts for 82.4% of the variation in mortality (R = 0.908**). Th e full relationship is represented bym = 27.4 - 8.37 k - 0.617 w Analysis of variance fov the multiple regression of mortality (m) on pre-shearing relative rate of bodyweight loss (k) and pre-shearing bodyweight (w) TABLE 1 * ** Significant at P<O.OOl 230 Fig. 1.` Weather coliditions for the 14 day post-shearing period and the course of deaths. 231 Fig. 2.-Relationship between transformed mortality percentage (m) and relative rate of bodyweight loss (k) prior to shearing. Values for bodyweight at shearing (w) in kilograms have been included below the respective points. In apportioning the variation in m due to the two bodyweight criteria, the importance of k is outstanding (P<O.OOl ). In these data the contribution of bodyweight variation by itself failed to reach significance. The findings recorded were derived from data which, although few in number, were unusual in their range. They support the view that heavier post-shearing losses are likely when sheep are in poor rather than good body condition, but they emphasise that the rate at which bodyweight is being lost is an important qualification. It appears that values for k may reflect with greater sensitivity than w the degree of current nutritional difficulty faced by sheep at pasture or may better represent some important physiological condition. IV. ACKNOWLEDGMENT Thanks are due to Mr. P. F. May, C.S.I.R.O. Division of Mathematical Statistics, for consultation on statistical matters. 232 V. REFERENCES F ISHER , R. A., and Y ATES , F. ( 1963). 'Statistical Tables for Biological, Agricultural and G EYTENBEEK Medical Research'. Sixth Edition. (Oliver and Boyd: London). , P. E. (1963). A survey of post shearing losses due to adverse weather condiItions. Experimental Record, Department of Agriculture, South Australia, No. 1, p. 21. 233