Abstract
The objective of this study was to determine if alterations in dietary intake of heifers can influence IGF-I concentrations in plasma and(or) follicular fluid (FFL), size of follicles, and steroid concentrations in FFL (as an indicator of steroidogenic capacity). Cyclic heifers [n=23; mean ± SE body weight (BW) = 373 ± 7 kg were individually fed for 10 weeks either: a) 1.8% of BW in dry matter (DM) per d (GAIN; n=7), b) 1.1% of BW in DM per d (MAINT; n=8) or c) 0.7% of BW in DM per d (LOSE; n=8). After 10 wk of treatment, heifers were ovariectomized 36–40 hr after the second injection of prostaglandin F2α analog (2 injections 11 d apart), and plasma and ovaries were collected. Heifers weighed 444 ± 13, 387 ± 8 and 349 ± 9 kg in the GAIN, MAINT and LOSE groups, respectively, at time of ovariectomy. Mean diameter of follicles ≥ 10 mm was greater (P<.05) for GAIN (15.6 mm) than for MAINT (11.0 mm) or LOSE (12.5 mm) heifers. Numbers of follicles and concentrations of IGF-I in plasma and FFL did not differ (P>.20) between LOSE, MAINT and GAIN heifers. Progesterone concentrations were greater (P<.05) in small and medium follicles of GAIN than MAINT or LOSE heifers, but were unaffected by diet in large follicles. Estradiol concentrations in FFL in small, medium and large follicles were unaffected (P>.20) by dietary treatment. However, estradiol concentrations in estrogen-active follicles were two-fold greater (P<.05) in GAIN heifers than either MAINT or LOSE heifers. In conclusion, IGF-I, of ovarian and(or) systemic origin, was unlikely the primary mediator of dietary alterations in ovarian follicular function of heifers in the present study.
Published Version
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