A note on reproductive performance and plasma progesterone level during early pregnancy of Scottish Blackface and Cheviot ewes in relation to body condition and level of nutrition prior to mating

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Abstract
Seventy-nine Scottish Blackface and 79 North × South Country Cheviot ewes were fed to increase their mean condition score by 0·5 over periods of either 4 (M/H group) or 8 (I group) weeks prior to mating. Thereafter, they were fed a live-weight maintenance ration until they were slaughtered at 50 to 65 days after mating. Reproductive tracts were recovered, corpora lutea counted and embryos counted and examined. Plasma progesterone levels were monitored at selected times after mating. The proportion of ewes in each treatment group that were pregnant at the time of slaughter was similar (0·75 to 0·83) but there was evidence of differences in the pattern of reproductive failure with treatment. The proportion of non-pregnant ewes which had apparently been pregnant initially was 0·55 in the M/H group compared with only 0·27 in the I group. Circulating progesterone levels were not affected by premating nutritional treatments but differed with breed.