Reproductive performance of commercial sheep flocks in South Island districts

Abstract

In 1975-1978 predominantly 4-tooth ewes from 64 flocks on 21 commercial sheep farms in four South Island districts were studied to identify various sources of reproductive wastage between joining and tailing.Average flock size was 426 ewes (range 100-742),of the Romney. Coopworth,Perendale,Borderdale,Drysdale, Half-bred,and first cross (e.g ., Coopworth × Romney) breeds.Flock live weights during the prejoining-joining period ranged from 42.8 to 72.7 kg. with mean values for all flocks between times of weighing ranging from 55.1 to 56.5 kg. 86. 1% of ewes were marked in the first period of joining. Rates of return to service were low. with a mean of 11.8% of marked ewes returning at least once. Ovulation rates. recorded on an average of 93 (50-168) ewes in each flock. varied from 1.12 to 2.31 corpora lutea per ewe (mean 1.6\). Lambs born per ewe lambing also varied considerably (100.&-192.7%). witha mean of 141.2%. Barrenness levels ranged from 1.0 to 14.4% with a mean value of 4.0%. Lamb deaths averaged 9.7% oflambs born. In 44 flocks it was estimated that 8.7% of single-born and 10.6% of twin-born lambs died between birth and tailing. Percentage of lambs tailed per ewe present at joining ranged from 8 1.8% to 163.0%. with a mean of 120.4%. From a potential of 161 lambs per 100 ewes in 57 of the flocks. determined by ovulation rates. various sources of reproductive wastage calculated as eggs or lambs lost per 100 ewes were: ewes falling to mate. 0.6; ewes mated-failed to lamb. 5.5; ewe deaths mating-tailing. 1.7; partial failure of multiple ovulation. 18.8; and lambs dying birtlHailing.13.1.Partial failure of multiple ovulation. predominantly ewes having two corpora lutea but giving birth to one lamb. was responsible for a major proportion of the wastage recorded.Of ewes with two corpora lutea 29.6% (range 10.5-56.3%) gave birth to one lamb.