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University of Wisconsin, Madison
Abstract
Breed of sire differences among crossbred lambs at birth were determined from a two-year study. The lambs were first-crosses resulting from mating Suffolk, Hampshire, and Shropshire rams to Western ewes. The characters studied on the lambs at birth were weight, head width, head length and circumference at chine and shoulder points. The characters studied on the dams at parturition were width at hips, width at pins and parturition difficulty which was believed to be due to shape, size or position of the fetus.
Breed of sire differences among crossbred and straightbred lambs at 120 days of age were determined from a two-year collection of data from Wisconsin farms. The crossbred lambs were first-crosses from Western ewes bred to Suffolk, Hampshire, Oxford and Shropshire rams. The 120-day characters studied were live weight, staple length and live grade. The straightbred lambs (purebreds and high grades) were of Suffolk, Hampshire and Shropshire breeds. Four crossbred lambs, two females and two wethers, from the progeny of each sire were used for carcass studies. The carcass characters studied included carcass weight, cross-sectional length and area of the longissimus dorsi, height of the spinous process of the vertebra, circumference of both thighs and U.S. carcass grade.
Shropshire sired crossbred lambs were significantly less in birth weight and in the sizes of various body parts than Hampshire and Suffolk sired lambs. The last two did not differ significantly from each other in any of the birth characters. These differences gave no evidence of being associated with dystocia.
Fitting constants to the data gave 120-day weights for the Suffolk, Hampshire, Oxford and Shropshire sired crossbred lambs of 70.8, 67.9, 65.4 and 63.1 lb., respectively. Suffolk and Hampshire crosses weighed significantly more than Shropshire crosses and Suffolks than Oxfords in each year. The other breed differences in 120-day weight were consistent in direction over both years but not significant in both years. Wethers and singles weighed significantly more than females and twins by 2.8 and 9.6 lb., respectively.
The weights of straightbred Down breed lambs (Suffolk, Hampshire and Shropshire) were found to rank in the same order as the crossbreds by the same breed of sire. There was a high degree of consistency from group to group in favor of the straightbreds for Suffolks and Hampshires and in favor of the crossbreds for the Shropshires when compared within sex, type of birth and year groups. Three independent additive estimates of the 120-day weights of the Westerns based on the comparison of the Suffolk, Hampshire and Shropshire straightbreds with their Western crossbreds were highly consistent. This implies that the combinability of Westerns with the Down breeds for 120-day weights is genetically simply additive or reflects a constant heterotic effect.
For live grade, there were no breed differences which were consistently significant from one year to the next. Singles graded a significant 0.5 of a grade higher than twins. Carcass characters were analyzed on the basis of carcasses unadjusted as well as adjusted for weight. Regardless of the adjustment, there was little evidence of breed differences for any1 of the carcass characters.
1 Paper from the Department of Genetics No. 684 and the Department of Animal Husbandry, University of Wisconsin, published with the approval of the Director of the Agricultural Experiment Station.
2 Present address: Georgia Experiment Station, Experiment, Georgia.
3 Credit is given to Dr. Newton Morton, Genetics Department, University of Wisconsin, for suggesting the method of statistical analysis which was used in this study. Also gratefully acknowledged is the cooperation and help of the staff of Oscar Mayer and Company in making the carcass phase of this study possible.
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