The use of blood metabolites in the determination of energy status in beef cows

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Abstract
The objective of the studies reported was to examine the potential usefulness of measurements of concentrations of plasma glucose, 3-hydroxybutyrate and non-esterified fatty acids as means of assessing in quantitative terms the adequacy of energy intake of beef cattle.Relationships between the concentrations of these metabolites and of either energy intake or energy status were examined in three experiments conducted respectively on 56 housed, mature, non-pregnant, non-lactating cows, on 115 housed, mature, pregnant cows, and on groups of 10 to 12 mature, non-pregnant, non-lactating cows grazing five plant communities.The results indicated that under the conditions pertaining in these studies plasma glucose concentration was not likely to constitute a useful index of energy status in housed or grazing animals.Plasma 3-hydroxybutyrate concentration was closely related to estimates of energy status in the pregnant cows and was considered to be potentially valuable as an index of energy status in animals in which there is a relatively high glucose demand.Plasma non-esterified fatty acids concentration was closely related to and a potentially useful index of either energy intake or energy status in all cases, but postulated effects of diurnal variations in circulating concentrations make it imperative that relationships used for predictive purposes are derived under the conditions in which they are to be applied.