|Chase, Chadwick - Chad|
|Hammond, Andrew - Andy|
Submitted to: Journal of Reproduction and Fertility
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/1999
Publication Date: N/A
Interpretive Summary: Differences in reproductive characteristics between Angus (temperate Bos taurus) and Brahman (tropical Bos indicus) cattle include longer gestation length and shorter and less intense oestrus in Brahman vs Angus females. In addition, puberty occurs at an older age and twinning rate is much lower in Bos indicus cattle. Disparities in several reproductive parameters including blood metabolites, secretion of metabolic and reproductive hormones, and growth and development of ovarian follicles and the corpus luteum may account for these differences in reproductive performance. Furthermore, reproductive characteristics of Senepol, a tropical Bos taurus breed, have not been well characterized. We conducted a study to determine breed differences in endocrine (hormone), ovarian follicular activity and luteal development using daily rectal ultrasonography and blood sampling conducted on Angus, Brahman and Senepol cows during an oestrous cycle in summer. Results indicated that Brahman cows as well as Senepol cows had a greater number of follicles in all size categories and greater diameter of the corpus luteum than Angus cows. These ovarian differences may be due to changes in the pattern of secretion of follicle stimulating hormone, insulin, insulin-like growth factor (IGF)-I and growth hormone but not luteinizing hormone, IGF-II or IGF binding protein-2 or -3.
Technical Abstract: To determine breed differences in endocrine, ovarian follicular activity and luteal development, daily rectal ultrasonography and blood sampling was conducted on multiparous lactating Angus (temperate Bos taurus), Brahman (tropical Bos indicus) and Senepol (tropical Bos taurus) cows during an oestrous cycle in summer. Numbers of small, medium and large follicles were greater in Brahman than in Angus and(or) Senepol cows. Length of the oestrous cycle was longer in Senepol than in Angus or Brahman cows which was associated with a delayed regression of the corpus luteum (CL). The secondary surge of FSH (between days 1 and 2; day 0 = oestrus) was greater in Angus than Brahman or Senepol cows. Between days 2 and 14 of the oestrous cycle, concentrations of progesterone, LH, insulin-like growth factor (IGF)-II, and binding activities of IGF binding protein (IGFBP)-3, IGFBP-2, and the 27-29 kDa IGFBP in plasma did not differ among genotypes. Concentrations of growth hormone (GH), IGF-I, insulin, and plasma urea nitrogen (PUN) were greater and binding activities of the 22 kDa and 20 kDa IGFBPs tended to be greater in plasma of Brahman than in Angus or Senepol cows. In conclusion, Brahman cows as well as Senepol cows had greater number of follicles in all size categories and greater diameter of CL than Angus cows. These ovarian differences may be due to changes in the pattern of secretion of FSH, insulin, IGF-I and GH but not LH, IGF-II or IGFBP-2 or -3.