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United States Department of Agriculture

Agricultural Research Service

Title: Effects of Weaning and Piglet Size on Neuroendocrine Regulators of Feed Intake

Authors
item Kojima, Cheryl - UNIVERSITY OF TENNESSEE
item Carroll, Jeffery
item Matteri, Robert
item Touchette, Kevin - CARGILL, INC., MINNEAPOLI
item Allee, Gary - UNIVERSITY OF MISSOURI

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 9, 2007
Publication Date: May 19, 2007
Citation: Kojima, C., Carroll, J.A., Matteri, R.L., Touchette, K., Allee, G. 2007. Effects of weaning and piglet size on neuroendocrine regulators of feed intake. Journal of Animal Science. 85:2133-2139.

Interpretive Summary: The inhibition of piglet growth rate caused by weaning is well recognized and clearly associated with reduced feed intake. The biological mechanisms underlying the postweaning growth lag are poorly understood. Suppressed intake may result from stressors encountered at weaning, such as maternal separation, relocation to new housing, introduction into new social groups, and changing to a dry diet. There is a paucity of studies that have evaluated metabolic and endocrine responses of the pig during weaning.Typical of the endocrine profile seen during inadequate feed intake, weaning the piglet increases concentrations of growth hormone (GH) and decreases serum concentrations of insulin-like growth factors 1 and 2 (IGF-1 and IGF-2). Importantly, while weaning clearly decreases feed intake, associated changes in the expression of appetite-controlling genes remain to be determined. An inadequate understanding of the effects of weaning on these gene products limits our capability to develop targeted strategies for maintaining early postweaning performance. The objective of the present study was to evaluate the expression of appetite-regulating genes in response to weaning. Two-week-old barrows were cross-fostered to a sow (SOW, n=8) or weaned and fed a nursery diet containing either 0 or 7% spray-dried plasma (NP, n=8, and SDP, n=8; respectively). Piglets were allocated such that two size groups existed within each experimental group (small, 3.5-4.3 kg and large, 4.6-5.7 kg). Animals were sacrificed 4 d after weaning for tissue collection. There was a weaning group by size interactive effect on hypothalamic neuropeptide Y mRNA expression such that expression was least in the small SDP pigs. No size or weaning group effects were seen on adipose leptin, hypothalamic leptin receptor, or hypothalamic proopiomelanocortin gene expression. An effect of size was seen on hypothalamic neuropeptide Y (NPY), agouti-related protein, orexin and type 2 orexin receptor gene expression such that large pigs expressed greater amounts of these transcripts. Strong positive correlations in gene expression were found among all of these genes whose products are known to stimulate appetite. Partial correlation controlling for initial body weight revealed that pre-weaning size explained most, if not all, of these associations. This is the first known study of the effects of weaning on measures of appetite control in any species. The positive relationships observed between preweaning body weight and post-weaning hypothalamic agouti-related protein, orexin, type 2 orexin receptor, and NPY gene expression may reflect physiological roles of these factors in the regulation of growth in the young pig. We have determined that levels of specific mRNAs encoding proteins which regulate appetite do not differ between nursed and dry-fed pigs 4 d after weaning. These data raise important questions relating to the temporal relationships between postweaning changes in gene expression and function. Continued studies of the effects of weaning on the pig's physiology will provide a better understanding of the regulation of appetite, growth, and adaptation to stressors encountered within the production environment.

Technical Abstract: A depression in feed intake and growth often occurs in the weaned pig. Spray-dried plasma is often added to nursery diets in an attempt to stimulate feed intake during this lag. The present study evaluated gene expression of appetite regulators in hypothalamus and adipose tissue 4 d after weaning. Two-week-old barrows were cross-fostered to a sow (SOW, n=8) or weaned and fed a nursery diet containing either 0 or 7% spray-dried plasma (NP, n=8, and SDP, n=8; respectively). Piglets were allocated such that two size groups existed within each experimental group (small, 3.5-4.3 kg, and large, 4.6-5.7 kg). Animals were sacrificed 4 d after weaning for tissue collection. There was a weaning group by size interactive effect (P < .05) on hypothalamic neuropeptide Y mRNA expression such that expression was least in the small SDP pigs. No size or weaning group effects were seen on adipose leptin, hypothalamic leptin receptor, or hypothalamic proopiomelanocortin gene expression. An effect of size was seen on hypothalamic neuropeptide Y, agouti-related protein, orexin and type 2 orexin receptor gene expression such that large pigs expressed greater amounts of these transcripts (P < .002). Strong positive correlations in gene expression were found among all of these genes whose products are known to stimulate appetite. Partial correlation controlling for initial body weight revealed that pre-weaning size explained most, if not all, of these associations. These data suggest that the postweaning expression of appetite-regulating genes is more dependent on preweaning conditions than on weaning strategy.

Last Modified: 7/25/2014
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