Date of Award:

1983

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Advisor/Chair:

Lyle G. McNeal

Abstract

Growth data were collected on 1848 Targhee and Targhee crossbred lambs from the Utah Agricultural Experiment Station flock at Cedar City for 1981 and 1982. The study objectives were to establish growth curves for seven lamb genotypes and examine within genotype growth differences among four grazing treatments (sheep alone, sheep and cattle mixed, both continuous and rotation).

Body weights were measured at birth, and at mean ages of 56, 120, and 154 (weaning) days of age. Linear, quadratic, and cubic regressions of weight on age were used to establish growth curves. Among genotype comparisons of entire growth curves were impossible as non-linear components were significant. (p<.05). Thus, weights per weigh period and average daily gain between weigh periods were examined to determine differences. Rearing type, birth type, genotype, and pasture treatment were 50.9%, 22.7%, 12.4%, and 6.1%, respectively, of the total variance accounted for by the effects on weaning weights examined.

Overall growth patterns were the same for all genotypes with the most rapid gains occurring between 56 and 120 days of age (combined mean .66 pounds). Suffolk-sired lambs from Suffolk-Targhee and Targhee-Finn-Targhee ewes were faster gaining (p<.05) than straight-bred Targhee lambs as well as those from Suffolk sires bred to finn-Targhee, Targhee-Suffokl-Targhee ewes.

The second most rapid gains (combined mean .56 pounds) occurred between birth and 56 days. All crossbred lambs had higher average daily gains than Targhee lambs (p%lt;.05). The slowest rate of gain (mean .16 pounds) occurred int he 34 days prior to weaning.

Not all differences in body weight among pastures can be attributed to grazing treatments as three genotypes exhibited a significant (p<.05) effect of pasture assignment on weight prior to treatment implementation. Despite initial weight imbalances, genotypes responded similarly to pasture treatments. Sheep rotation pastures had the lightest (p<.05) lambs for most genotypes exhibiting differences in grazing treatments at 120 days and in all genotypes at weaning. The fastest gains and heaviest lambs were in mixed species pastures. In sheep alone pastures, lamb performance was better in continuously grazed pastures than in the rotation pastures.

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