ABSTRACT Feed intake is the cornerstone of animal productivity. The consequences of inadequate intake include inhibited growth, delayed puberty, infertility, reduced milk production, and lowered resistance to parasites and disease. Factors that influence intake include age, metabolic demand (gestation, lactation, and level of physical activity), thermal environment, photoperiod, disease, and psychosocial stress. Under some conditions intake is adequate for health and well-being but is limiting for optimum performance and productivity. The role of the central nervous system, particularly the hypothalamus, has long been recognized in the control of appetite. A variety of hormones and neurotransmitters are involved in the modulation of neural pathways that stimulate or suppress appetite. Complementary DNA sequences and clones for these regulatory factors in livestock are rapidly being generated, providing new tools for physiological studies and the production of recombinant/synthetic hormones and analogs. An understanding of the interactions between environmental factors and the mechanisms of appetite control is fundamental to the development of practical approaches to optimize feed intake, which will usher in a new era of research in redefining the limits of productivity. An important component of this future research will be to ensure that enhanced intake is used efficiently for the production of high-quality food products.
Implications
The importance of feed intake in livestock is unquestioned. However, studies of appetite control in domestic species are relatively few compared with those in laboratory rodents. Worldwide interest in feed intake regulation, coupled with the advent of new research technologies and approaches, has prompted new appetite-related research in a growing number of domestic animal laboratories. New physiological data will establish model conditions that will reliably provide high contrasts between animals in the expression of appetite regulators. Transcript profiling studies, using cDNA from such animals, have been initiated. These studies offer an exciting potential for new advances in our understanding of feed intake control. New roles for known genes may be identified, as well as the detection of as yet unknown gene products. The analysis of reading frames of novel gene sequences may well reveal additional neurohormones and new central targets for appetite regulation.
Key Words: Appetite, Feed Intake, Livestock
© 2001, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2001. 79:E148-E158
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