Lamb losses in south Western Australia.

Abstract

LAMB LOSSES IN SOUTH-WESTERN AUSTRALIA H. LLOYD DAVIES* I. INTRODUCTION The observations of lamb losses reported in this paper were made in an experiment designed to study the effects of stocking rate and lambing time on growth and reproduction in grazing Merinos (Davies 1962). There is little information on the effect of stocking rate and lambing time upon peri-natal mortality, or on losses among lambs in south-western Australia. II. MATERIALS AND METHODS (a) Outline of experiment Medium woolled Merino ewes of Peppin origin grazed over a four year period on an annual type pasture (mainly Bromus spp., Hordeum spp., Cryptostemma calendula and Erodium botrys) at Kojonup. Mean rainfall was 22 in. (560 mm) with most of the rain occurring from April to October. Three stocking rates (15, 3 00 and 5-O ewes per acre) and three lambing times (autumn, winter and spring) were examined. Details of the environment, mating systems and supplementary feeding were given by Davies (1962). (b) Observations The plots and ewes grazing thereon (14 ewes per plot) were examined twice daily during the peak of lambing and at least once daily at other times. Lambs were weighed daily between 9 a.m. and 11 a.m. during the lambing period. Lambs were classified as stillborn if the lungs were unexpanded. Birthcoats were classified according to Schinckel (1955) into fine, intermediate and hairy. The secretion in the udder of each ewe which had lambed was classified when the birthweight of her offspring was taken. Thus, there could be differences of up to 24 hours between parturition and the observation. The five classifications are as shown in Figure 1. Death of lambs which were eartagged at birth and then vanished without trace were classified as due to predation. Lambs which were found dead and had eyes, anus or umbilicus picked out showed signs of severe attack by crows, eagles, dogs or foxes were classified as predator losses; these predators were known to be active in the district. III. RESULTS (a) Mortality and lambing time For single lambs, the loss during winter lambing was 41% higher (P<O*Ol) than during lambing in the autumn and 55% higher than during lambing in the spring (Table 1). This seasonal difference was especially evident at the high and T.S.I.R.O., Division of Plant Industry, W.A. Regional Laboratory, Nedlands, W.A. 107 intermediate stocking rates (Table 2) and may be There were no significant seasonal differences in the 47%, winter 38% and spring 50%). The deaths associated with predation occurred and were not necessarily due to predator attack (see associated with predation. losses among twins (autumn during the neo-natal period below). -- lA.-The relation of lamb birthweight to mortality (1 lb = 0.45 kg). rrg. Fig. lB.-The relation between nature of secretion in the udder and incidence of lamb losses ( 1960, 1961 and 1962) 0 - No secretion. A - Yellow waxy material of very high viscosity. B - Yellow secretion of moderate viscosity. C - Creamy-yellow secretion of low viscosity (colostrum) . D - Opaque, white non-viscous fluid (normal milk). In Figs. 1A and lB, the numbers at the foot of the columns represent respectively, the total number of lambs in each birth weight class and the number of ewes with each class of secretion. 108 TABLE 1 EfjFect of lambing time on losses among single lambs (b) Mortality and stocking rate Losses amongst single lambs increased with increasing stocking rate 3). There were no obvious trends in the losses amongst twins. In spite losses being more severe at the higher stocking rate, the number of lambs per acre was higher at the higher stocking rate. The incidence of twinning was too low to draw any conclusion about ment effects. (c) Birthweight and litter size Mortality and birthweight were inversely related (Figure 1A). weights of lambs born in winter and spring were similar (Table 4) significantly higher (P<O.Ol) than those of lambs born in the autumn. Losses were higher (P<O.OOl) among twins (76 out of 195, i.e. amongst singles (195 out of 940, i.e. 21% ) (Chi2 = 29.5, d.f. = 1). birthweight of twins was 7.2 lb (3.3 kg) and of singles 8.8 lb (4.0 kg). The birthbut were 39%) than The mean (Table of the reared treat- (d) Mortality and birthcort type Losses among lambs classed as fine, medium and hairy were 16.2% (87 out of 499), 18.9% (58 out of 306) and 17.6% (51 out of 290) respectively; there were no obvious trends. TABLE 2 109 Effect of TABLE 3 stocking rate on total lamb losses de) Mortality and the nature of the secretion in the udder The absence of any secretion in the udder (Class 0) and the presence of a very highly viscous-waxy material (Class A) were both associated with heav y lamb losses (Figure lb). Often lambs born to ewes with either secretion or 'A' had low birthweights. The mean birthweights of lambs born to ewes recorded as 0, A, B, C and D were 6.58, 659, 8.54, 8.67 and 8.74 lb respectively (2.99, 2.99, 3.87, 3.93 and 3.96 kg). There was a loss of 25% of the lambs when 'thick colostrum' was present, and 18 -7% when there was a colostrum of low viscosity but only 11~4% when normal milk was present. There were no striking differences in the nature of the udder secretion as a result of either stocking rate or lambing time. (f) Class of death The incidence of stillbirths was apparently independent of lambing time (Table l), stocking rate (Table 3) or of the year of the experiment. Predator activity was highest in winter (P<O.O5) (Table 1) and possibly at the higher stocking rates (Table 3), but it was impossible to determine how many of the deaths associated with predator activity were due primarily to the predator. 110 IV. DISCUSSION These data indicate that lamb losses may well be a serious problem in Merino flocks in the agricultural regions of south-western Australia. There have been reports from the West Australian Department of Agriculture (Nairn, personal communication) that lamb losses are higher during a spring lambing on clover dominant pasture in the Esperance region than during an autumn lambing. The older pastures where this work was done were not dominated by subterranean clover, which is consistent with the small difference in lamb losses during autumn and spring. Lamb losses during mid-June to July lambing were always high in spite of better pasture conditions than in autumn. The higher losses in winter are probably due to a combination of wet and windy weather and predator activity. Increased stocking rate led to an increase in numbers of lambs reared per acre (Davies 1962). With each increase in stocking rate, there was a reduction in the percentage of the mated ewes that reared a lamb. This reduction cannot simply we ascribed to difference in the level of nutrition at mating time, because the groups at the low and intermediate stocking rates were comparable in bodyweight during mating (Davies 1962). The results on lamb losses in relation to birthcoat do not provide support for the suggestion of Alexander (1962), based on physiological studies, that hairy lambs would have a survival advantage. He showed that wet lambs with a coarse birthcoat had a physiological advantage in reducing heat loss from evaporation over wet lambs with a fine birthcoat. However, a practical advantage would not be expected unless many of the deaths were due to cold. The results on losses in relation to udder secretion are causal relationship need not necessarily be inferred. Some of ewes with secretions of Classes 0 and A may also have been may not have reached the udder. No estimates of quantity estimates may have explained some of the differences in lamb with secretions of types C and D (Figure 1B). of interest, but a the lambs born to of poor vigour and were made. Such loss between ewes Lamb losses were higher among twins than singles and also among the lighter of the single lambs in agreement with the findings of workers, Moule (1954), Alexander, McCance and Watson (1955), Alexander, Peterson and Watson (1959), Watson and Elder (1961). More critical data are required on the causes of the high peri-natal losses among twin lambs, since an increase in twinning rate is likely to be of importance in increasing sheep production in south-western Australia. V. ACKNOWLEDGMENTS The author is indebted to Mr. I. N. Southey for technical assistance and to Mr. G. W. Anderson, Farm Manager, 'Glen Lossie' Research Station, Kojonup, for facilities and assistance. VI. REFERENCES A LEXANDER G., MCCANCE, I., and W ATSON , R. H. (1955). Some observations on losses among Merino lambs. The Australian Veterinary Journal 31: 85. , 111 A A , G., P ETERSON , J. E., and W ATSON , R. H. (1959). Neo-natal mortality in lambs: Intensive observations during lambing in a Corriedale flock with a history of high lamb mortality. The Australian Veterinary Journal 35: 43. LEXANDER , G. (1962). Temperature regulation in the new-born lamb. IV. The effect of wind and evaporation of water from the coat on metabolic rate and body temperature. AusLEXANDER tralian Journal D AVIES of Agricultural Research 13: 82. H. LLOYD (1962). Studies on time western Australia. Proceedings of the M OULE , G. R. ( 1954). Observations tralian Veterinary Journal 30: 153. S CHINCKEL , P . G. ( 1955) . 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