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

Abstract

The objective of this experiment was to investigate the effect of cow body condition score on fasting heat production. Twelve nonpregnant, nonlactating Holstein-Friesian cows were selected from within the dairy herd at the Agricultural Research Institute of Northern Ireland. Six of these animals (group A) had condition scores ≥4.5, and the remainder (group B) had condition scores <2. All cows were offered dried grass pellets at estimated maintenance energy level (0.58 MJ of metabolizable energy/kg0.75) for a minimum of 21 d. The diet also supplied 2.5 times the metabolizable protein requirement for maintenance. Following this, each cow underwent a 5-d fast in open circuit respiration calorimeters during which fasting 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 condition scores were achieved, dried grass pellets were again offered at maintenance for a minimum of 21 d, and fasting heat production was measured. It was observed that fasting heat production (MJ/kg0.75) was significantly higher for cows with low body condition (<2; ultrasonic fat depth ≤2.9 mm) compared with cows displaying high body condition (≥4.5; ultrasonic fat depth ≥ 8.2 mm). A linear relationship between condition score and fasting heat production (MJ/kg0.75) was defined by regression analysis as; FHP (MJ/kg0.75) = 0.501(SE 0.0121) - 0.030CS (SE 0.0035).