Breed and environmental effects on components of ewe productivity in terms of multiple births, artificial rearing and 8-month breeding cycles

The productivity of three synthetic breeds (Canadian, Outaouais and Rideau Arcotts) and two breeds established in North America (Suffolk and Finnsheep), housed indoors year-round in a controlled environment were studied using 12 661 ewe records collected over 8 years. Their lambs were raised from birth to weaning at 21 days of age on milk replacer diets. Ewes were divided into two flocks and mated to lamb alternately at 4-month intervals in February, June and October at the end of a period of short days using artificial lighting regimens and exogenous hormones to synchronize estrus. Significant influences of year, litter size, breed, age of ewe and lambing season on reproduction, growth performance and lamb mortality were observed. Total lamb weight per ewe lambing increased 2 kg at birth, 4 kg at 21 days and 15 kg at 91 days of age, for each unit increase in litter size from single to quintuplet or more. Concurrently, lamb mortality also increased by 6.6% to 21 days and 6.9% to 91 days of age. Ewes of the Outaouais, Rideau and Finnsheep breeds were more fecund and prolific with a greater proportion of multiple births (triplets or more) than ewes of the Canadian and Suffolk breeds. At breeding, Suffolk ewes were heavier than Canadian ewes, the Outaouais and Rideau ewes were intermediate while Finnsheep ewes were lighter. At each lambing, Outaouais and Rideau ewes produced more total lamb weight than Finnsheep ewes. Correspondingly, Canadian and Suffolk ewes produced lower lamb weight. The proportion of multiple births in 12-month-old ewes was 12% compared with 34% in 20-month-old ewes and 45% or more in older ewes. Total lamb weight per ewe lambing in ewes 18-months and older was greater than in 12-month-old ewes. Ewes lambing in June had significantly larger litters, greater lamb mortality and lower total lamb weight at 91 days than those lambing in February or October. These results demonstrate the important influences of multiple births, breed, age of ewe and lambing season on productivity under conditions of an 8-month breeding cycle, when lambs are fed milk replacer diets and raised artificially in a controlled environment. © 1995