Timing of growth hormone injections and reproduction in gilts

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Sixty-eight Yorkshire × Landrace gilts were selected at 85 kg body weight (BW) and exposed to a mature boar for 20 min d−1 to detect puberty. At the onset of puberty, gilts were allocated to receive daily intramuscular injections of porcine growth hormone (pGH, 90 μg kg−1 BW) from either 14 to 17 d (GH17, n = 22) or from 14 to 22 d (GH22 n = 22) after puberty, inclusively. A third group of gilts served as controls (n = 24) and received vehicle buffer. A single blood sample was obtained from each gilt on days 14, 17 and 20. Also, four gilts from each pGH treatment and eight control gilts were sampled at 15-min intervals for 8 h on day 16. Gilts were slaughtered 30 d after puberty at which time their ovaries were recovered for the determination of ovulation rate. Injection of pGH resulted in elevated serum concentrations of triiodothyronine, insulin and glucose (P < 0.01). There was no significant (P > 0.1) treatment effect on mean serum concentrations of LH or FSH. However, pGH treatment tended (P = 0.1) to increase LH pulse frequency and to decrease (P = 0.01) LH pulse amplitude. The incidence of a second estrus was reduced (P < 0.01) in GH22 compared to control gilts, with GH17 being intermediate (72.7 vs. 90.9 vs. 100% for GH22, GH17 and control gilts, respectively). Ovulation rate was not affected by pGH treatment (15.1 vs. 14.3 vs 14 0 for GH22, GH17 and control gilts, respectively). The present data confirm an adverse effect of pGH on ovarian function and suggest that an altered LH pulsatility may be involved. Key words: Gilts, growth hormone, estrus, endocrinology