Pre-natal losses in sheep in western Victoria.

Abstract

PRE-NATAL LOSSES IN SHEEP IN WESTERN VICTORIA P. D. MULLANEY* In observations on 10,000 sheep aged 2-3 years or 4-9 in the Western District of Victoria, 0-12% of ewes failed 9-30% returns to service at intervals greater than 13 days, that mated failed to lamb. At least 15-44% of potentially not represented by a birth at full term. years in eight to mate, there and 3-30% of fertilisable ova flocks were ewes were I. INTRODUCTION Whilst some information sheep in Australia (Watson Watson 1955; Alexander and natal reproductive wastage in is available on the level of post-natal wastage in 1957; Moule 1954; Alexander, McCance an d Peterson 1961)) there is little on the level of presheep. Results are presented in this paper of observations on incidence of failure to mate, returns to service, failure to lamb after having mated, and wastage of potentially fertilisable ova in eight flocks in Western Victoria. II. MATERIAL AND METHODS The type and strain of sheep and the location of the individual flocks have been described by Mullaney and Hyland ( 1966). The flocks were joined for mating in November-December of each year, except Cl which was joined in February. Vasectomised rams ( 1% ) were run with the ewes for lo-14 days, before they were joined with entire rams (2% ) for eight weeks. The rams were fitted with Sire-Sine harnesses and crayons (Radford, Watson and Wood 1960) and the colour of the crayons was changed every 14 days. The ewes were yarded and examined every 7 days for crayon marks. Ewes were classified as having returned to service if they were marked at intervals greater than 13 days. During lambing the ewes on all properties were inspected at least once daily and the mothers of all lambs were identified. III. RESULTS The results are set out in Tables 1 and 2. Of the ewes aged four to nine years, almost all in each flock mated. Almost all maiden ewes also mated, but generally the proportion was slightly lower than that among the older ewes. There were 9-30% returns to service. Of the ewes that mated, 3-16% failed to lamb except in one flock of 13 year old Polwarth ewes in which the percentage was 33. *Department of Agriculture, Melbourne, Victoria. 56 TABLE 1 Incidence of failure to mate, returns to service, failure to lamb and wastage potentially fertilisable ova in ewes 4-9 years old of * Percentages calculated relative to number of ewes joined in each flock. ? Percentages calculated relative to number of ewes that mated in each flock. 100 (R + L) $ Percentages minimum wastage of ova calculated as It represents the (100 + R) ' percentage of oestrus periods accompanied by copulation which did not result in a birth at full term. The minimum wastage of ova was calculated assuming a minimum ovulation rate of 1.0. As reflected in both returns to service and failure to lamb, the minimum wastage of ova varied from 1544% of all ova shed. In-so-far as the ovulation rate was constant throughout the mating period, this also represents the proportion of ova that did not appear as viable lambs since the same ovulation rate would apply to both the numeration and denomination of the ratio. There were no constant trends of any of these features between maiden ewes and aged ewes or between breeds. 57 TABLE 2 Incidence of failure to mate, returns to service, failure to lamb and wastage of potentially fertilisable ova in maiden ewes 2-3 years old *, t, and &-See corresponding footnotes Table 1. _-Ewes mated as maidens at 2% years. II-Ewes mated as maidens at 11% years. IV. DISCUSSION A high incidence of mating was also observed by Watson (1953, 1957) in similar flocks under similar conditions. The incidence of returns to service was somewhat lower than that recorded by Watson (1957), but in some of the flocks the proportion of ewes that failed to lamb after mating, 3.3-33.3%, was substantially higher than that observed by Watson, 5-10%. The wastage of ova, at least 12-44%, covers the range of results o f other workers. The data of Watson (1953) indicate ova wastage of 22-43% in similar sheep under similar conditions. In examination of ovaries and uteri of slaughtered ewes, Hammond ( 1921), Clark ( 1934)) Henning ( 1939), Brambell ( 1948)) El Sheikh et al. ( 1955), and Bellows et al. ( 1963) found at varying stages of pregnancy that 8-40% of corpora lutea were not represented by foetuses. Including both returns to service and corpora lutea not represented by viable foetuses. Watson and Radford (personal communication) observed wastage in one flock of ewes with some rams as low at 13 % of all ova shed and as high as 33% with other rams. A variety of factors no doubt contributes to wastage of this nature. The present observations merely define the magnitude of the wastage. They do not provide any evidence as to the factors that contribute to it. 58 V. ACKNOWLEDGMENTS The co-operation of the owners and staff of each of the eight properties is gratefully acknowledged. Thanks are also due to members of the Sheep and Wool Branch of the Victorian Department of Agriculture who recorded the mating data and supervised the lambings. Grateful acknowledgment is made of Dr. R. H. Watson for his help and advice in preparation of the manuscript. This work joined part of a project carried out with the financial assistance of the Wool Research Trust Fund. VI. REFE' RENCES , G., MCCANCE, I., and W ATSON , R. H. (1955). Some observations on losses among Merino lambs. A ustralian Veterinary Journal 31: 85. A LEXANDER , G., and P ETERSON , J. E. (1961). Neo-natal mortality in lambs. Australiun A LEXANDER Veterinary Journal 37: 371. , R. 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