Although it has been demonstrated in the rat that the local ovarian IGF-l concentration is elevated after growth hormone administration in vivo , the influence of growth hormone treatment and elevated serum IGF-I concentrations on ovulation rate has not been determined.Therefore, an experiment was undertaken to test the hypothesis that exogenous growth hormone would increase the ovulation rate in post-pubertal gilts.MATERIALS AND METHODS Thirty-two prepubertal gilts tYorkshire x Landrace) were selected at 78.0 + 1.5 kg body weightand 138.0 + 3.5 dofage, andtransported from the finishing to the breeding barn on a daily basis. The gilts were exposed to a mature boar for 30 min d I and observed for signs of estrus.Fourteen days after the onset of puberty the gilts were assigned to one of two treatment groups involving the daily injection (i.m.) of either porcine growth hormone (1.0 mg ml--r of 1.7 IU mg -' pGH in carbonate-buffered saline, pH 9.4, administered at 9O p.g kg-' bodyweight; GH, n :20) or vehicle buffer (CT, n = l2). The growth hormone dose employed was similar to that considered to give an optimal improvement in growth rate (Etherton et al. 1987) and which, from a pilot study conducted in our laboratory, also resulted in a marked increase in serum IGF-I concentrations (Kirkwood, unpublished data

30-32 d after the first observed estrus at which time their ovaries were recovered for the determination of ovulation rates. All controi gilts and all but one GH17 gilt exhibited normal estrous cycles. However, of the 21 gilts assigned to GHl4, only 9 (43%)had normal estrous cycles (P<0.001). In gilts exhibiting a second estrus, there was no effect of pGH treatment on the duration of the estrous cycle (20.4, 20.9 and 20.5 d) or on ovulation rate (14.6,13.9 and 13.5) for GHl4, GH17 and controls, respectively.

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