Effect of Prepartum Bovine Somatotropin in Primigravid Ewes on Mammogenesis, Milk Production, and Hormone Concentrations

• Published in: Journal of dairy science 1993-04, Vol.76 (4), p.992-1001
• Main Authors: Stelwagen, K., Grieve, D.G., Walton, J.S., Ball, J.L., Mcbride, B.W.
• Format: Article
• Language: English
• Subjects: adn; Animals; Biological and medical sciences; blood plasma; brebis; Cattle; Cell Count; Cell Division; cells; cellule; celulas; disorders; dna; DNA - biosynthesis; ewes; Female; Food industries; Fundamental and applied biological sciences. Psychology; gestacion; gestation; gestation period; glande mammaire; glandulas mamarias; Growth Hormone - pharmacology; insulin; Insulin-Like Growth Factor I - metabolism; insulina; insuline; lactacion; lactation; Lactation - drug effects; Magnetic Resonance Spectroscopy; mammary glands; Mammary Glands, Animal - cytology; Mammary Glands, Animal - drug effects; Mammary Glands, Animal - physiology; mammogenesis; Milk and cheese industries. Ice creams; milk production; milk yield; oveja; ovine; periode de gestation; periodo de gestacion; plasma sanguin; plasma sanguineo; Pregnancy; rendement laitier; rendimiento lechero; Sheep - physiology; somatotropin; somatotropina; somatotropine; trastornos; trouble
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(93)77427-5

Twenty-five primigravid ewes were used to investigate the effect of bST, between 97 and 124 d of gestation, on mammogenesis and subsequent milk production. Five ewes (reference group) were slaughtered at 96 d of gestation, and the remaining ewes were injected daily with saline (control group: n = 10) or .1 mg/kg of BW of bST (bST group: n = 10). Following bST treatment, 5 control and 5 bST group ewes were slaughtered (slaughter group). The remaining ewes were slaughtered after lambing and being milked for 8 wk (production group). Weekly blood samples were obtained from both slaughter and production group ewes. Slaughter group ewes were also subjected to 8-h serial blood sampling at 98 d (period 1) and 123 d (period 2) of gestation. Milk production was 42% higher in ewes treated prepartum with bST than in those treated with saline. Results suggest that the increase in milk was due to an increase in mammary parenchymal cell number rather than to an increase in cellular activity. The high rate of [3H]thymidine incorporation into parenchymal tissue in reference group ewes suggests that the increase in parenchyma during the second trimester of gestation is due to cellular hyperplasia but that cellular hypertrophy may be more important during the last trimester. Plasma IGF-I concentrations were significantly higher during bST treatment and remained elevated between daily injections; the increase was greatest in period 2.