Graduate Thesis Or Dissertation
 

Some genetic and environmental factors affecting weaning weights of lambs

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  • Eight purebred rams (four Suffolk and four Panama) previously selected as high and low on the basis of post-weaning performance feed test of 84 days were used each of three years. Each of the rams was mated to approximately 25 grade Panama ewes each year. One ram and 25 ewes representing the high and low performance of each of the breeds were kept continuously in drylot while the other comparable group was grazed on pasture during the summer and fed in drylot during the winter. Thus, a total of four groups were in drylot, the drylot groups, and four groups were on pasture, the pasture groups. The data on birth and weaning weights of the lambs, the fleece weights and body weights of the ewes were analyzed by the method of least squares. There was evidence for heterosis because the Suffolk-sired lambs exceeded the Panama-sired lambs by 0.9 pound at birth and 7.8 pounds at weaning. The lambs sired by the rams having a high post-weaning rate of gain were no larger at weaning than those sired by rams having a low rate of gain. Post-weaning rate of gain does not reflect itself in pre-weaning gains which might indicate that gains in the two periods are not controlled by the same genes. The drylot ewes produced lambs that weighed more at birth and at weaning than the pasture ewes, produced fleeces equal to the pasture ewes, and had heavier body weights than the pasture ewes. There were significant yearly variations in body weights of the ewes and weaning weights of the lambs. Also, the age of the ewe affected her body weight, fleece weight, and the birth weight and weaning weight of the lambs. Fleece weights corresponded closely with body weight because two-year-old ewes and those seven years old or over were lower in body weight and fleece weight than mature ewes in the peak of production. Weaning weights of lambs were highest for three- and four-year-old ewes, intermediate for ewes five years of age or older and lowest for two-year-old ewes. Single lambs were heavier at birth and at weaning than each member of a set of twin lambs. Male lambs exceeded females in birth weight, and wether lambs exceeded ewe lambs in weaning weight. Ewes nursing twin lambs were lower in body weight than those nursing singles, and those raising single lambs were lower in body weight than non-nursing ewes.
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