Two clinical studies were conducted to evaluate the effects of recombinant bovine somatotropin in daily, weekly or bi-weekly injected preparations on milk yield, feed efficiency and reproduction. In the first study, a linear dose-response effect of recombinant bST on milk yield with doses of up to 150 mg · 7d-1 was observed. Feed intake was not affected and feed efficiency was increased by bST during lactation. Body condition at the end of lactation was lower in cows supplemented with bST. Feed intake during the dry period following bST supplementation was not affected by bST given during lactation. When differences in body condition were taken into account, efficiency of conversion of dietary energy to milk energy was not affected by bST supplementation. In another study of bST supplementation during lactation, a daily dose of 10.3 mg · d-1 and a sustained release formulation of 350 mg · 14d-1 did not increase milk production or feed efficiency. In the absence of a milk production response, reproductive performance was not affected by bST supplementation. Progesterone production in the second oestrous cycle post partum was higher in cows receiving bST but oestrous activity was not affected. Body condition at calving did not affect milk production, response to rbST or reproductive performance. Cows calving with a body condition less than 3.25 consumed more feed per unit of body weight and resumed ovarian cyclic activity later than cows calving with a body condition greater or equal to 3.25. An epinephrine challenge during the dry period was performed to evaluate whether the effects of bST supplementation during lactation on adipose tissue metabolism persisted during the dry period. Lipid mobilisation by cows having received bST during lactation, as described by the release of non-esterified fatty acids following the epinephrine challenge, did not differ from control cows. Two studies designed to evaluate the effect of bST on oestradiol-induce
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34995 |
| Date | January 1998 |
| Creators | Lefebvre, Daniel Maurice. |
| Contributors | Block, Elliot (advisor) |
| 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: 001609868, proquestno: NQ44488, Theses scanned by UMI/ProQuest. |
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