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Characterization of Ram and Ewe Breeds. I. Reproductive Traits^1,2,

Louisiana State University, Baton Rouge 70803

Abstract

A 3-year crossbreeding study was conducted to evaluate the reproductive performance of several breeds and breed crosses in a fall lambing scheme and to ascertain the potential value of crossbred rams for improved reproduction. Rambouillet, Suffolk and Suffolk x Rambouillet rams were bred to Native (an indigenous strain from Western Louisiana noted for its fertility and hardiness), Hampshire x Native, Rambouillet x Native and Suffolk x Native ewes. Estrus was induced in ewes by a hormone treatment and the results obtained can only be applied to such a breeding management scheme. Differences among dam breeds were observed for percent ewes lambing, percent lambs weaned per ewe exposed and per ewe lambing and gestation length. Total reproductive efficiency (percent lambs weaned per ewe exposed) favored straightbred Native ewes over the three crossbred groups. Rambouillet x Native ewes were the most fertile but ranked last in prolificacy. Hampshire x Native and Suffolk x Native ewes were prolific but their low fertility greatly reduced the percent lamb crop weaned per ewe exposed. Mortality of lambs from Hampshire x Native ewes was also extremely high. Based on the poor reproductive performance of the Hampshire x Native ewes in this study, it appears that Hampshire sheep are not adapted to a fall lambing program in the Gulf Coast region. Rambouillet breeding, whether from the sire or dam, resulted in increased gestation lengths and reduced prolificacy. Breed-of-sire and sire within breed differences were unimportant for all traits except the nested sire effect on gestation length. Crossbred rams demonstrated a consistent but nonsignificant advantage over the purebred rams in measures of fertility and prolificacy. The paternal heterosis estimates for percent lambs weaned per ewe exposed were 10.4%, 5.3% and 8.6%, respectively.

¹ Published with the approval of the Director of the Louisiana Agricultural Experiment Station.

² The authors acknowledge the assistance of Dr. J. W. Turner in the planning stages of the study.

³ Department of Animal Science.

⁴ Department of Experimental Statistics.