INFLUENCE OF DAILY INJECTIONS OF PORCINE SOMATOTROPIN ON GROWTH, PUBERTY, AND REPRODUCTION IN GILTS

To determine whether recombinant porcine somatotropin (rpST) alters reproduction, 40 crossbred gilts weighing 59.1 +/- .5 kg at 125 +/- 1 d of age were assigned randomly to an experiment arranged as a 2 x 2 factorial. Eight gilts were given daily injections of diluent until they reached 104 kg BW (DW), and eight received diluent injections until puberty (DP). Twelve gilts were given rpST (4 mg/d) until 104 kg BW (PW) and 12 were given rpST injections until puberty (PP). All gilts were individually fed on an ad libitum basis an 18% CP corn-soybean meal diet (1.2% lysine and 3.1 Mcal/kg of ME). Beginning at 5 mo of age, gilts were exposed 20 min daily to mature boars. Serum concentrations of progesterone were measured weekly from 5 to 8 mo of age to verify age of puberty. Gilts observed in pubertal estrus were mated to two different boars 10 h apart. At 47 +/- 1 d of gestation, gilts were slaughtered to assess fetal development. After 60 d of treatment, serum LH and FSH profiles were determined in blood samples drawn at 20-min intervals for 4 h from eight diluent- and eight rpST-treated gilts fitted with indwelling jugular catheters. By 28 d, feed intake, feed/gain, and blood urea nitrogen were decreased (P < .005) by rpST. Treatments did not affect (P < .05) the proportion of gilts attaining first ovulation (DW = 6/6; DP = 10/10; PW = 7/9; PP = 14/14) or conception rate (DW = 5/6; DP = 7/10; PW = 4/6; PP = 11/12). Proportion of ovulatory gilts exhibiting estrus (DW = 6/6; DP = 10/10; PW = 6/7; PP = 12/14) and age at puberty (DW = 185; DP = 197; PW = 196; PP = 203; SEM = 6 d) were unaffected (P > .05) by treatments. Weight and number of corpora lutea, litter size, and fetal survival were unaffected (P > .05) by rpST. Fetal length and weight were reduced (P < .05) in PP gilts compared with DP gilts. Mean serum concentrations of LH, FSH, and the number of LH secretory peaks were similar (P > .05) between gilts that received diluent and rpST. These data indicate that daily injections of rpST (4 mg/d) to prepubertal gilts improved feed efficiency 15% while reducing feed intake 19% without altering the onset of puberty and reproductive performance.