Relationships between serum IGF-I concentrations and piglet development or neonatal viability following porcine somatotropin (pST) and insulin administration to gestating gilts.
This study was designed to evaluate the effects of exogenous treatment with pST, insulin and their combination on periparturient serum IGF-I levels, prenatal piglet development and viability. Pregnant Yorkshire gilts were injected daily with either 5 ml of saline (C), n = 23; 5 mg pST (P), n = 23; 0.50 IU/kg of insulin (I), n = 23; or pST plus insulin at the above dosage, according to 2 x 2 factorial design from Day 30 to 70 of gestation. All gilts were sacrificed on Day 113 of gestation. Peripartum IGF-I serum levels were determined by RIA following a 36 h incubation in 0.2 M gly-gly HCL. Recovery of human rIGF-I standard was > 95%, while the intra-assay CV was 5.74%. Measures of piglet viability were compared using Randall's adaptation of Apgar score for human neonates. Piglet weight and crown-to-rump length were determined prior to dissection. Treatments (P, I and P + I) elicited highly significant increases in maternal serum IGF-I concentrations (321.9, 337.0, 375.0 vs 247.6 ng/ml; P = 0.0001) on Day 113 of gestation. Nonsignificant differences were detected in piglet serum IGF-I (94.8, 102.6, 110.2 vs 92.2 ng/ml; P = 0.06). These results revealed no relationship between piglet weight and maternal (r = 0.03) or piglet serum IGF-I levels (r = 0.08). Only a weak association between gilt and piglet serum IGF-I concentrations (r = 0.26) was detected. Injections with pST and or insulin did not influence piglet viability scores (P = 0.74). Viability scores were highly correlated with piglet weight (r = 0.66), crown -rump length (r = 0.70), but not with IGF-I concentrations in gilt (r = 0.09) and piglet serum (r = 0.16). Body weights, crown -rump length and visceral organ weights of piglets did not differ between control and hormone -treated gilts (P >/= 0.05). These results indicate 1) that there was no direct treatment effects on in utero piglet development or neonatal viability; 2) that IGF-I production in gilt and piglet compartment is independent, suggesting fetal endocrine autonomy regarding IGF-I production; and 3) that the usual low IGF-I concentrations in mid-late gestation in swine could be replenished by maternal pST and or insulin therapy.
Okere
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C
Department of Animal and Poultry Science University of Guelph, Guelph, Ontario N1G 2W1 Canada.
Hacker
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RR
Werchola
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G