Submitted to: Domestic Animal Endocrinology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/6/1998
Publication Date: N/A
Citation: Interpretive Summary: Sickness and death continue to be significant problems in baby pigs. Environmental temperature is considered to be an important factor in maintaining the health and performance of neonatal pigs. Additionally, it is known that growth hormone (GH) treatment increases growth rate, feed efficiency and leanness, as well as increases metabolism in livestock. Therefore, we evaluated the growth, as well as the hormones responsible fo growth, in neonatal pigs exposed to cool or warm temperature with and without supplemental GH being provided. We have found that supplemental GH does not enhance growth in the baby pig, but it does alter the secretion and production of hormones associated with growth. Additionally, we found that a somewhat cool ambient temperature results in enhanced growth and significant changes in growth related hormone production. This information will be useful to individuals in academia, government, and industry who have an interest in the effects of environmental temperature on neonatal biology.
Technical Abstract: Age-dependent interactions between environmental temperature (ET) and pGH treatment on the function of the somatotrophic axis were evaluated in neonatal pigs. At 3 d of age, 40 crossbred piglets received recombinant pGH (0.5 mg/day; n=20) or vehicle (Control; n=20) by intraperitoneal implants. Piglets were housed at either a low (21 deg C; n=20) or high (32 2deg C; n=20) ET with 50% relative humidity. At 4 wk and 6 wk of age, 1/2 of the piglets from each group were sacrificed for tissue collection. Blood samples were analyzed for serum GH, IGF-1, and IGF-2. Liver RNA was analyzed for GH receptor, IGF-1, IGF-2, and IGF binding protein 3 (IGFBP-3) mRNAs. There was no effect of pGH treatment on ADG; but, there was an effect (P<0.003) of age and ET on ADG such that those animals maintained at a low ET and those sacrificed at 6 wk had greater ADGs. Serum GH was elevated by pGH treatment and declined with age (P<0.009). Serum IGF-1 was selevated by pGH treatment and increased with age (P<0.02). Serum IGF-2 tended (P=0.06) to be elevated by pGH treatment. GH receptor mRNA was unaffected by pGH treatment, but was greater in the 6-wk age group and in piglets maintained at the high ET (P<0.05). IGF-1 mRNA was enhanced by pGH treatment and by exposure to the high ET (P<0.05), but did not differ between age groups. IGF-2 mRNA was greater (P<0.008) in the 4-wk age group and in piglets maintained at the high ET, but was unaffected by pGH treatment. IGFBP-3 mRNA increased with age and was stimulated by pGH treatment in the 6-wk age group (P<0.04). The relatively lower level of GH receptor and IGF mRNAs, coupled with greater growth in the cold ET suggests that somatotrophic gene expression in the liver is not rate-limiting for growth in the neonatal pig.