Analysis Method of Energy Revenue and Expenditure in Grazing Holstein Heifers Using Estimated Heat Production

Abstract

It is known that heart rate (HR) which is used to estimate heat production(HP), is a useful way of assessing the approximate HP of grazing heifers. The purpose of this paper was to examine the method of analyzing energy revenue and expenditure from metabolic energy intake (MEI), heat production, and net energy for gain (NEg). MEI was calculated as the sum of forage intake estimated by the cutting method and intake mass of formula food. HP was calculated from a regression equation for HP on HR determined from housed experiment using tread mill. NEg was calculated from daily gain (DG) by the NRC equation. DG was calculated from the mean body weight of four heifers before and after grazing. We examined energy revenue and expenditure to determine whether MEI=HP+NEg is realized or not. The percentages of HP+NEg to MEI in four grazing experiments were 95.2, 101.8, 98.9, and 111.8%. Except for one negative value DG, the sum of HP and NEg in three grazing experiments agreed well with MEI, making it possible to analyze the energy revenue and expenditure of grazing heifers. However, without DG value, it was difficult to calculate NEg and a difference between MEI and HP+NEg was not small. It is necessary that MEI is stable for analyses of energy revenue and expenditure, because NEg is mean value for a few weeks. It is also necessary that the range of HR in equation HP on HR covers up the range of HR in grazing heifer.