Endocrine control of pig growth.

The title I was given for this contribution implies that a definitive statement can be made about the hormonal control of the growth of pigs. Any such expectation must be dismissed at the outset for there is enough debate about how pigs grow to prevent it, let alone how the neuroendocrine system controls it. Nevertheless, if we are to establish food requirements, solve the problems of assessing energetic efficiencies or predict and manipulate carcase and meat quality we must define the precise nature of the fundamental physiological mechanisms which bring about major differences in the performance of animals. Moreover, since we probably know as much about these topics in relation to pigs as we do for men or beasts generally a perspective, at least, is possible. The fist obstacle to our understanding of the endocrinology of growth is that the measurable changes in the size and form of animals represent the net consequences of the anabolic and catabolic aspects of metabolism. Fat and protein accretion are easy to assess in the body but the endocrinologically-induced differences in the balance between lipogenesis and lipolysis or protein synthesis and proteolysis, are not. Similarly, for a full understanding, we ought to consider the physiological basis of variations in the flow of blood to tissue due to environmental effects or feeding, for all contribute to these net effects. I t is extraordinarily difficult for the mathematical modellers to illustrate the interplay between the calculated energetics of biochemical transformations and experimental results, but it is well-nigh impossible for the physiologist to define the nature of all the control mechanisms which operate simultaneously in vivo. Thus, we must resort to the examination of the very simplest of models in the search for clues.