Abstract
Recombinant bovine somatotropins (rbST) have been synthesized and manufactured using recombinant DNA (rDNA) techniques. The rbST has increased milk production in dairy animals, including cow, sheep and goats. There are management factors including dosage of rbST, injection interval, genetic potential and environmental conditions which affect the magnitude of the animal-response to rbST. For dairy cows, the optimal dose of rbST treatment is between 25 and 50 mg/day. Daily injection of rbST may produce better response, but sustained-release formulations of rbST are more practical. The magnitude of milk production response to rbST range from 10 to 35% in dairy cows. The rbST has no or little effects on the milk composition, processing properties and taste. The rbST did not affect digestion of feeds or the efficiency of utilizing absorbed nutrients for milk synthesis, and it has no or little effect on rumen fermentation, flow of nutrients to the small intestine and total tract digestibility, but it improves the feed efficiency in dairy cows. The rbST induced significant increase in serum bST. It has a galactopoietic effect, since it increase the metabolic activity of mammary cells or slow their involution, thereby allowing more secretory cells to persist over time and contribute to increasing milk synthesis and yield. It has a great impact on mammary gland development and subsequently milk-producing capacity in dairy heifers. The rbST increase the hypothyroid status of lactating cows and maintain euthyroid condition in the mammry gland, thus enhancing its metabloic priority. The rbST did not adversely affect reproduction, and the observed decreases in reproductive performance in rbST-treated cows may be attributed more to the increases in milk yield than to direct effect of rbST. The increased production responses to rbST in heat-stressed dairy cows is less than that under more moderate conditions. The incidence of mastitis in rbST-treated cows is due more to increased milk yield than to any direct effects of rbST. The rbST was efficacious in increasing milk yields in sheep and goats without adverse effects. Key words: Recombinant bovine somatotropin, dairy animals, physiological responses. 
Highlights
Journal of Cell and Animal BiologyPhysiological responses of dairy animals to recombinant bovine somatotropin: A review
Bovine somatotropin is naturally-occuring protein produced by the pituitary gland in all cattle
As Recombinant bovine somatotropins (rbST) increased, the weight gain of cows decreased, the main effect of rbST decreased body fat reflecting the partitioning of calories by rbST to milk at the expense of fat deposition (Chalupa et al, 1996)
Summary
Physiological responses of dairy animals to recombinant bovine somatotropin: A review. The rbST has increased milk production in dairy animals, including cow, sheep and goats. The rbST induced significant increase in serum bST It has a galactopoietic effect, since it increase the metabolic activity of mammary cells or slow their involution, thereby allowing more secretory cells to persist over time and contribute to increasing milk synthesis and yield. It has a great impact on mammary gland development and subsequently milk-producing capacity in dairy heifers. The increased production responses to rbST in heat-stressed dairy cows is less than that under more moderate conditions.
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