title: The effect of a depot injection of recombinant bovine somatotropin on follicular development and embryo yield in superovulated Holstein heifers.
abstract: Superovulated Holstein heifers (n = 32) were given a depot injection of 500 mg recombinant bovine somatotropin (rBST) or vehicle at Day 4 of the estrous cycle (7 days before the first FSH injection); at Day 11, coincidentally with the first FSH injection; or at Day 15, the time of artificial insemination. Embryos were collected nonsurgically, and the number of corpora lutea was counted by ultrasonography at Day 7 after insemination. Blood samples were taken every second day, from Day 2 of the superovulatory cycle until the day of embryo collection, and were analyzed for progesterone, somatotropin and insulin-like growth factor-1 (IGF-1). Somatotropin-treated heifers at Day 11 had a significantly higher mean number of corpora lutea than the controls (18.1 vs 13.4; P </= 0.05). Day 4 treatment tended to increase the mean number of corpora lutea (15.4; P <- 0.10), and significantly increased the overall percentage of transferable embryos (74.6 vs 58.6%; P </= 0.01). In the control animals, plasma IGF-1 was uncorrelated to somatotropin (P > 0.63), but it was negatively correlated with progesterone (P </= 0.01), suggesting that IGF-1 production in the superovulated heifer may be related to ovarian development.
authors.affiliation: Department of Biomedical Sciences, University of Guelph Guelph, Ontario, Canada, N1G 2W1.
authors.forename: L F
authors.initials: LF
authors.lastname: Kuehner
authors.forename: D
authors.initials: D
authors.lastname: Rieger
authors.forename: J S
authors.initials: JS
authors.lastname: Walton
authors.forename: X
authors.initials: X
authors.lastname: Zhao
authors.forename: W H
authors.initials: WH
authors.lastname: Johnson