Submitted to: Domestic Animal Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2000
Publication Date: N/A
Interpretive Summary: Neonatal growth is a cornerstone of efficient swine production. Previous research has examined the effects of altered levels of growth-stimulating hormones in the young pig. In this related study, we focused on the transition from the prenatal to postnatal environment (i.e., birth) which is a fragile time in the life of many animals. In swine, cortisol, a stress related hormone, begins to rise during the last 2 weeks of pregnanc with a final peak occurring just prior to or during labor. This elevation in fetal cortisol is thought to trigger adjustments necessary for optimal growth and performance in the outside world. Thus, our objective was to determine whether elimination of the birth process would alter the normal growth axis of the neonatal pig. In the present study, we found that elimination of the natural birth process, via caesarian birth, alters the production of growth-stimulating hormones, as well as growth itself, in the eyoung pig. This study provides unique information regarding the effect of early neonatal events that will be useful to other scientists working in the area of neonatal growth and development. Additionally, this information could prove beneficial to swine producers who maintain pathogen-free herds by introducing new stock via caesarian births.
Technical Abstract: This study was designed to determine what effects the birth process would have on development of the somatotrophic axis in neonatal pigs. Eight crossbred sows were selected (n = 4 natural birth and n = 4 Caesarian-section) for the present study. Blood and tissue samples from 38 pigs were collected at birth. Twenty pigs were maintained with natural birth sows until sacrificed for blood and tissue collection at 2 wk of age Gestational age at birth did not differ (P>0.16) between natural birth and C-section pigs. Average daily gain (ADG) from birth until 2 wk of age was reduced (P<0.0001) by 39.3% in the C-section pigs as compared to the natural birth pigs. Serum growth hormone (GH) did not differ (P>0.86) at birth, but was greater (P<0.024) at 2 wk in C-section pigs. Serum insulin-like growth factor 1 (IGF-1) was greater at birth (P<0.0025) and at 2 wk of age (P<0.035) in the natural birth pigs. Serum concentration of IGF-2 did not differ at birth (P>0.8) but was greater (P<0.043) in natural birth pigs at 2 wk of age. Pituitary content of GH mRNA and GH-releasing hormone receptor mRNA did not differ (P>0.90) between groups regardless of age; however, expression of both mRNAs declined (P<0.0003) from birth until 2 wk of age. There tended to be a birth type X age interaction (P<0.082) for liver IGF-1 mRNA such that C-section pigs had a greater expression at 2 wk of age. Liver IGF-1 mRNA expression increased (P <0.0001) in both groups from birth to 2 wk of age. Liver expression of GH receptor mRNA was greater in C-section pigs at birth (P<0.04) and 2 wk of age (P<0.03). These data provide evidence that the natural birth process affects postnatal development and/or function of the somatotrophic axis in the neonatal pig.