Effects of active immunization against somatostatin (SRIF) and/or injections of growth hormone-releasing factor (GRF) during gestation on hormonal and metabolic profiles in sows

Abstract

The hormonal responses of gestating sows to immunization against somatostatin conjugated to bovine serum albumin (SRIF-IMM) and/or injections of growth hormone-releasing factor (GRF) were studied with thirty-eight second parity sows. Immunization against bovine serum albumin (BSA-IMM) was used as control. First immunizations were done on day 30 and boosters were given on days 44, 58, 72, 86 and 100 of gestation. Injections of GRF (9 mg of GRF (1–29)NH 2 per injection) or saline were given at 0800, 1400 and 2000 hr daily from day 90 of gestation until parturition. Mean body weights of sows at 85 and 110 d of gestation were 196.3 and 210.5 kg, respectively (SE = 0.8). Jugular blood samples were collected from 0740 hr to 1100 hr at 20 min intervals on days 90, 101 and 112 of gestation. On day 112, additional samples were collected from 1340 hr to 1700 hr and from 2140 hr to 2300 hr. At 112 d of gestation, antibody titers against SRIF (% binding, 1:150 dilution) were higher (P<0.01) for SRIF-IMM (13.5%) vs BSA-IMM (0.95%) sows. There was no effect of SRIF-IMM nor was there a GRF by SRIF-IMM interaction on any variable measured (P>0.05). Injections of GRF increased (P<0.01) the area under the curve (AUC) for growth hormone (GH; 305 vs 1623 ng/min/ml). The increase was greater as days of injection increased (P<0.05). Administration of GRF did not affect prolactin (Prl) AUC (P>0.05). There was no effect of time of injection on GH or Prl AUC (P>0.05). There was no effect of treatments on free fatty acids (FFA), glucose or insulin (P>0.05) but insulin-like growth factor I (IGF-I) concentrations increased in GRF-treated sows (P<0.01; 66 vs 101 ng/ml). Concentrations of FFA and IGF-I increased (P<0.01) as gestation advanced. Treatment with GRF increased weight gain of sows during late lactation (P<0.01). In conclusion, GH AUC was increased by GRF injections but not by SRIF-IMM in gestating sows. Concentrations of FFA, glucose and insulin were not altered by either treatment, but those of IGF-I were increased by GRF.