The influence of body condition on the fasting energy metabolism of nonpregnant, nonlactating dairy cows

The objective of this experiment was to investigate the effect of cow body condition score on fasting heat production. Twelve nonpregnant, nonlactatin g Holstein-Friesian cows were selected from within the dairy herd at the Ag ricultural Research Institute of Northern Ireland. Six of these animals (gr oup A) had condition scores greater than or equal to 4.5, and the remainder (group B) had condition scores <2. All cows were offered dried grass pelle ts at estimated maintenance energy level (0.58 MJ of metabolizable energy/k g(0.75)) for a minimum of 21 d. The diet also supplied 2.5 times the metabo lizable protein requirement for maintenance. Following this, each cow under went a 5-d fast in open circuit respiration calorimeters during which fasti ng heat production (FHP) was measured. On completion of measurement, group A was fed to reduce condition score (CS) below 2, while group B was fed to raise each individual condition score above 4.5. When the appropriate condi tion scores were achieved, dried grass pellets were again offered at mainte nance for a minimum of 21 d, and fasting heat production was measured. It w as observed that fasting heat production (MJ/kg(0.75)) was significantly hi gher for cows with low body condition (<2; ultrasonic fat depth less than o r equal to 2.9 mm) compared with cows displaying high body condition (great er than or equal to 4.5; ultrasonic fat depth greater than or equal to 8.2 mm). A linear relationship between condition score and fasting heat product ion (MJ/kg0.75) was defined by regression analysis as;