Genetic and phenotypic relationships between gestation length, litter size and litter birth weight in Yankasa sheep

Abstract

The genetic and phenotypic relationships between gestation length, litter size and litter birth weight in Yankasa sheep were investigated using records of 834 lambings collected over an 8 year period (1983–1990). Litter size, year of birth and litter birth weight had significant influences on gestation length, while the effects of parity, season of birth and sex of lamb were not significant ( P>0.05). Single lambs had a gestation length longer by 1 day than twin lambs (151.9 vs. 150.9 days). The relationship between litter birth weight and gestation length was curvilinear with partial regression coefficients of 0.67 and −0.24 for the linear and quadratic components respectively. Mean gestation length for the breed was 151.4 days. Heritability estimates by paternal half-sib analyses, taking gestation as a trait of the foetus, were 0.20, 0.11 and 0.05 for gestation length, litter size and litter birth weight, respectively. Genetic and phenotypic correlations between gestation length and litter size, gestation length and litter birth weight, and litter size and litter birth weight were −0.29 and −0.15, 0.93 and −0.04, and 0.25 and 0.74 respectively. The negative genetic correlation between gestation length and litter size is an indication that selection for large litter size would be accompanied by a reduction in gestation length.