Date of Award

8-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

Cheryl J. Kojima

Committee Members

Arnold M. Saxton, Brynn H. Voy

Abstract

The synthetic met-enkephalin syndyphalin-33 (SD-33) increases feed intak in sheep and recently-weaned pigs. An experiment focused on changes in hypothalamic levels of mRNA transcripts from the following genes: μ-opioid receptor (MOR), neuropeptide Y (NPY), orexin (hypocretin; HCRT), melanocortin 4 receptor (MC4R), and agouti-related protein (AGRP). There was no effect of treatment on BW or FI at any point in the study. There is a strong positive correlation (p <0.001) between MOR and MC4 that remains regardless of treatment or time. Weaning resulted in a numerical increase in hypothalamic MOR mRNA expression. There was a treatment effect of MOR expression levels 4 days postweaning. Hypothalamic NPY expression was unchanged through time or treatment. In VEH pigs, weaning resulted in increased hypothalamic expression of the HCRT gene at d 1 and d 7 postweaning (P(time) < 0.01). In SD pigs, an increase in HCRTexpression (relative to d 0) was observed at d 4 postweaning. Expression of HCRT did not significantly differ between treatment groups at d 1 and d 4, but HCRT expression was greater in VEH pigs than in SD pigs at d 7 (P(time x treatment) < 0.05). Expression of hypothalamic MC4R did not change through time, but a trend (P(treatment) = 0.07) was observed such that expression was less in SD pigs than in VEH pigs on d 1 and d 4 postweaning, possibly due to a numerical increase in expression in VEH pigs on d 1 relative to d 0. Expression of AGRP was decreased 1 d postweaning in VEH pigs but not in SD pigs,. On d 4, levels of AGRP expression were lower in SD pigs than in VEH pigs, and lower than d 0 levels as well. On d7, AGRP expression was less in VEH pigs than in SD pigs (P(time x treatment) < 0.01). Syndyphalin-33 has the potential to alleviate the negative effects of stress during weaning, and has the potential to increase feed intake through the melanocortinergic pathway. Further investigation is needed to more fully elucidate the complex mechanisms by which syndyphalin-33 may act to abrogate the post-weaning growth lag in pigs.

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