Effects of bovine somatotropin and ruminally undegraded protein on feed intake, live weight gain, and mohair production by yearling Angora wethers
J. J. Davis, T. Sahlu, R. Puchala, M. J. Herselman, S. P. Hart, E. N. Escobar, S. W. Coleman, J. P. McCann, and A. L. GoetschJournal of Animal Science 77:1029-1036. 1999.
Effects of growth hormone on wool growth are variable. Exogenous ovine growth hormone generally depresses wool growth during the period of administration, although bovine somatotropin (bST) has increased wool growth by sheep during and after treatment. A biphasic response in wool growth to bST treatment has been reported, with a decrease during treatment but an increase thereafter; the decrease during treatment was largely a result of reduced fiber diameter. Effects of bST on mohair production by Angora goats have not been extensively studied. Source of dietary protein can impact magnitudes of response in animal performance to bST. For example, bST effects on average daily gain, feed efficiency, and hind limb muscle mass were greater for diets formulated with fish meal, to elevate ruminally undegraded protein, compared with diets containing soybean meal. Comparable interactions in milk production by lactating dairy cows have been observed as well. Interactions in fiber growth by Angora goats may differ from those for lactating dairy cows or growing sheep or cattle. Effects of growth hormone on nutrient partitioning are not skin- or fiber-specific; nutrient requirements for fiber growth differ from those for milk synthesis and accretion of peripheral muscle; and body composition, which impacts potential nutrient partitioning properties of bST, varies among animal types. Therefore, the objectives of this study were to investigate effects and interactions of bST treatment and dietary level of ruminally undegraded protein on feed intake, average daily gain, and mohair production by yearling Angora wethers. Based on results of this experiment, dietary addition of ruminally undegraded protein can increase mohair production by yearling Angora goats with and without somatotropin treatment. Treatment with somatotropin does not appear promising as a means to increase mohair production by yearling Angora goats regardless of dietary concentration of ruminally undegraded protein. However, somatotropin can influence change in feed intake by Angora goats elicited by dietary inclusion of ruminally undegraded protein, thereby impacting the ratio of fleece production to feed intake.
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