268. Experimentally induced hypoglycemia: a model to examine the effects of lactation on reproductive function in dairy cows?
S. Meier A , P. J. S. Gore A , C. M. E. Barnett B , R. T. Cursons B , D. E. Phillips A , K. A. Watkins A and G. A. Verkerk AA Dexcel Limited, Hamilton, New Zealand
B Biological Sciences, Univerisity of Waikato, Hamitlon, New Zealand
Reproduction, Fertility and Development 17(9) 110-110 https://doi.org/10.1071/SRB05Abs268
Submitted: 26 July 2005 Accepted: 26 July 2005 Published: 5 September 2005
Abstract
The metabolic changes subsequent to lactogenesis have been associated with poor reproduction in high-producing dairy cows.1,2 Periods of hypoglycaemia reflect severe energy deficit and are associated with changes in plasma levels of growth hormone (GH), insulin-like growth hormone-I (IGF-I) and insulin-like growth hormone-II (IGF-II). Somatotropic activity has been shown to influence reproductive functions.3–5
This study evaluated the effects of experimentally induced hypoglycaemia in seven non-lactating cows, over a 7-day period. Phloridizin treatment (8 g/d) resulted in urinary glucose loss (control: 3.5 ± 1.0 g/d and phloridizin: 468 ± 46 g/d) and decline in plasma glucose (control: 60.6 ± 0.6 mg/dL and phloridizin: 71.8 ± 0.4 mg/dL; P < 0.001). Treatment increased plasma beta hydroxybutyrate (BOH), non-esterified fatty acids (NEFA) and IGF-I concentrations (P < 0.001). Plasma insulin and GH concentrations did not differ. During treatment, expression of mRNA for total growth hormone receptor (GHR(tot); P = 0.012) and GHR(1A) (P < 0.001) in liver tissue declined. Luteal and follicle diameters in ovaries recovered after treatment did not differ. Expressions of mRNA for IGF-I (P = 0.052) and interleukin-1β (IL-1β) in corpus luteum and for 3β-hydroxysteroid dehydroxyenase (3β-HSD) within dominant follicles were significantly elevated, while mRNA for GHR(tot), cytochrome P450 cholesterol side chain cleavage enzyme (P450-SCC), and steroidogenic acute regulatory protein (StAR) tended to increase (P < 0.1) with treatment.
The treatment resulted in changes similar to those of nutritional stress or the initiation of lactogenesis. Phloridizin-induced hypoglycaemia may be a model to investigate mechanisms linking glucose metabolism, and the somatotropic axis to reproductive function. The advantages of such a model, is that it allows for strict control of the level of hypoglycaemia. The use of non-lactating cows also removes the feedback mechanisms that modulate mammary gland requirements, and therefore will minimize the between cow variance when using lactating cows.
This work was completed with the help from Dexcel Farms and the Dairy Cattle Fertility team. This study was funded by the New Zealand Foundation for Research, Science and Technology (DRCX 0202).
(1) Roberts et al. (1997) Journal of Animal Science 75, 1909–1917.
(2) Thatcher et al. (1996) Reproduction, Fertility and Development 8, 203–217.
(3) Royal et al. (2000) Animal Science 70, 487–501.
(4) Butler (2000) Animal Reproduction Science 60, 449–457.
(5) Lucy (2000) Journal of Dairy Science 84, 1635–1647.
