Energy expenditure is lower in efficient compared to inefficient lactating dairy cattle

Abstract Text:

Measuring the energy expenditure (EE) of an animal, particularly while it is at pasture exhibiting natural behaviours, is of particular importance to improve management, breeding and feeding practices. Recently, the estimation of EE based on heart rate (HR) has been explored. In cattle, this relationship appears to be more stable than in other non-domestic animals, likely due to the acclimation and low fear response of domestic, particularly dairy, cattle. Sixteen lactating, primiparous Holstein-Friesian cows previously classed as efficient (n=8) or inefficient (n=8) based on residual feed intake (RFI) were housed in open circuit respiration chambers for a period of 48 hours. Animals were fed lucerne hay cubes ad libitum and recieved 6 kg DM crushed wheat grain (and minerals) at milking  (total diet CP 18% and ME 10.5 MJ/kg DM). Real time measurements of methane, CO₂ and O₂ flux were obtained in the chamber and real time HR measurements obtained using a Polar Equine HR monitor fitted to the cows for the duration of the chamber measurement period. Production measures (intake, MY and milk content etc.), heart rates and O₂ consumption were not different between the efficiency groups. Oxygen consumption per heart beat (HB), defined as O₂ pulse, was calculated for the first 24 hours of the study. The O₂/HB over the entire 24 hours there was a significant effect of efficiency group such that efficient cows consumed less (0.01029 g min^-1 per HB, P<.05) O₂ per heartbeat than inefficient cows. The finding of a relationship between efficiency and O₂ pulse being present in lactating dairy cattle is novel. Taken together, the lower pulse O₂ in efficient animals without a variance in intake or production indicates that there are fundamental differences in maintenance energy consumption between inefficient and efficient groups. This finding supports the idea that a more efficient animal will deliver less O₂ per HB whilst maintaining a level of health and production similar to that of an inefficient animal.

Keywords: Energy expenditure, efficiency, residual feed intake