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HETEROSIS AND GENETIC PARAMETERS FOR REPRODUCTION IN SHEEP
Abstract
Lamb production, including the components of fertility, litter size, survival and lamb growth, of first cross, and F(,1), F(,2) and F(,3) generation ewes of two maternal composite lines, as well as the parental purebreeds, was investigated to determine levels of heterosis and seasonal effects. The lines were 1/2 Finnsheep 1/4 Rambouillet 1/4 Dorset, joined in an 8-monthly lambing system, and 1/2 Finnsheep 1/4 Suffolk 1/4 Targhee joined in an annual lambing system. Heritability, repeatability and phenotypic and genetic correlations for the various measures of reproduction and lamb production and their components were estimated. Age at puberty and pubertal ovulation rate also were investigated as indirect selection criteria. The data comprised 4219 ewes, which represented 412 known sires, with a total of 10959 joining records. Reproductive performance varied greatly between seasons. Fertility (ewes lambing per ewe joined) over all breed types was .57, .72 and .27, and litter size 1.9, 1.8 and 1.6 for January, May and September lambings for 1976 to 1979 inclusive. April lambings, which only occurred in 1978 and 1979, had higher fertility and litter size than the other three seasons. Consequently ewe reproduction traits were standardised across seasons and years, and adjusted to a three-year-old ewe basis for calculation of heterosis effects and genetic parameters. Retained heterosis was about 40 percent for weight of lamb weaned per ewe joined, 20 percent for fertility, 15 to 20 percent for survival, but near zero for litter size and mean lamb weaning weight. Paternal half-sib heritability estimates of composite and component production traits were low and ranged from .02 to .11. Estimates for the mean of repeated ewe records were higher and ranged from .10 to.16. Daughter-dam regression estimates were similar.
Subject Area
Livestock
Recommended Citation
FOGARTY, NEAL MICHAEL, "HETEROSIS AND GENETIC PARAMETERS FOR REPRODUCTION IN SHEEP" (1981). ETD collection for University of Nebraska-Lincoln. AAI8203214.
https://digitalcommons.unl.edu/dissertations/AAI8203214