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Ruminant Nutrition and Forage Utilization
Asian-Australasian Journal of Animal Sciences 2000;13(8): 1121-1126.
https://doi.org/10.5713/ajas.2000.1121    Published online August 1, 2000.
Daily Profiles of Blood Insulin, Insulin-Like Growth Factor-I, Thyroxine and Triiodothyronine in Ewes Under Three Levels of Feed Intake
R. M. Caldeira, M. I. Vasques, A. Vaz Portugal
Abstract
Daily variation in the serum concentrations of insulin and insulin-like growth factor-I and in the plasma concentrations of thyroxine and triiodothyronine were evaluated in ewes fed 30%, 100% and 200% of theoretical maintenance energy requirements. The single daily meal has had significant effects (p<0.05) on almost all profiles. In general, serum or plasma hormone concentrations have increased after the meal, in particular at the two higher levels of energy intake. In the group submitted to the lowest level of energy intake, the consequences of the meal on circulating levels were almost imperceptible. The effects of feeding levels on serum or plasma concentrations have widely varied among hormones, not showing any objective pattern or relationship. Because these variations may affect the interpretation of these blood indicators, knowledge of daily profiles and of the effect of feed level must be considered. In order to maximize the diagnostic value of those indicators, the most suitable times for blood collection seem to be 16 h after the meal and (or) just before the meal. The collection 16 h after the meal apparently allows the characterization of a relatively steady metabolic state, intermediate between the close effects of food intake and the final phase of the intensification of body reserves mobilization. The collection just before the meal will give a good indication of the level of activity of those mobilization mechanisms.
Keywords: Blood; Insulin; Insulin-Like Growth Factor-I; Thyroxine; Triiodothyronine; Sheep
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