Heritability and repeatability were estimated for ewe productivity of three synthetic sheep breeds (Canadian, Outaouais and Rideau Arcotts) using 11 106 ewe records from 3528 ewes and their 814 sires collected over 8 years (1983-1990) and 24 lambings. Two flocks of ewes were housed indoors year-round in a controlled environment. Ewes were mated to lamb in February, June and October at the end of a period of short days, using artificial lighting regimens and exogenous hormones to synchronize estrus to lamb alternately at Lt-month intervals in an 8 month breeding cycle. All lambs were raised on milk replacer diets from birth to weaning at 21 days of age. Traits examined included fertility, prolificacy, multiple birth, fecundity, ewe weight at breeding, lamb mortality at 21 and 91 days of age, and total lamb weight per ewe lambing (and per 100 kg ewe weight) at birth, 21 and 91 days. Paternal half-sib estimates of heritability based on least squares mixed model methodology ranged from -0.04 to 0.20 for the reproductive traits, 0.05 to 0.17 for lamb mortality, 0.03 to 0.21 for ewe weight at breeding and 0.01 to 0.22 for total lamb weight. Corresponding values for repeatability estimates ranged from 0.05 to 0.21, 0.21 to 0.28, 0.06 to 0.13 and 0.03 to 0.19, respectively. The heritability and repeatability estimates did not vary among breeds(P > 0.05) and were significantly different from zero for all traits except multiple birth. There was a tendency for estimates based on restricted maximum likelihood and maximum likelihood procedures to be lower than those based on the least squares procedure for fertility, multiple birth and lamb mortality (P > 0.05). The study demonstrates that there is significant potential to genetically increase reproductive rate and lamb weight and for reducing lamb mortality in Canadian, Outaouais and Rideau sheep under conditions of an 8 month breeding cycle when lambs are fed a milk replacer diet and raised artificially in a controlled environment. (C) 1997 Elsevier Science B.V.
