Long-term administration of recombinant bovine somatotropin (rbST) significantly increased milk and 3.5% fat-corrected milk production without altering milk composition. These effects occurred regardless of breed, parity or drug delivery system (daily or sustained-release) utilized. Somatotropin did not affect apparent digestibility of rations, dry matter intake, crude protein intake, energy intake or energy balance. Body energy reserves, measured as body condition scores, decreased during rbST treatment resulting, together with the increase in milk yield, in an improvement of the efficiency of conversion of feed to milk for cows treated with rbST. Body condition was completely regained during the dry period. No effects of rbST on mastitis or metabolic diseases were observed. During lactation, injection of rbST produced elevated circulating concentrations of non-esterified fatty acids, glucose, insulin, bST and IGF-I but lipid composition of liver and ketogenic functions were not altered. These lipolytic and diabetogenic activities might contribute to the galactopoietic response elicited by rbST. Somatotropin did not modify the nutritional status of cows during pregnancy or the nutritional status and growth rate of their calves from birth to weaning. / With regard to reproduction, somatotropin augmented ovarian progesterone production during the first two estrous cycles post-injection and during gestation. These effects may have been mediated through increased ovarian IGF-I synthesis. Somatotropin enhanced the GnRH-induced LH response at 14 d postpartum. In spite of these positive observations, somatotropin treatment tended to produce longer calving to conception intervals. Nevertheless, the higher persistency of milk production by cows treated with rbST may compensate for this difference economically.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74303 |
| Date | January 1989 |
| Creators | Gallo, Guillermo Federico |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001069725, proquestno: AAINN63556, Theses scanned by UMI/ProQuest. |
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