Maintenance

The underestimated component of energy efficiency in grazing dairy cows?: Doctoral thesis abstract

Abstract

Grazing dairy cows have a higher maintenance energy cost than indoor-fed cows, as a result of increased physical activity related to walking and harvesting their own feed. However, according to the current literature, there is no quantification of these components in dairy cows. The main objective of this thesis was to quantify the energy cost of grazing and walking in dairy cows. To this end, the oxygen pulse-heart rate (O2P-HR) technique was validated in respiration chambers for use in measuring the heat production (HP) of dairy cows under real production conditions. Then, using HP measurements obtained with the O2P-HR technique, synchronized with activity records of the cows, the energy cost of grazing and walking was estimated. The results of this study show that the energy cost of grazing in dairy cows is 7.24 kJ/kg0.75 per hour, and that, per unit of time, it is not different from the energy cost of eating a total mixed ration at a feed bunk. Therefore, the lower intake rate of grazing animals and the longer time they spend eating are the factors that increase the daily energy cost of eating or the energy cost per unit of feed consumed. On the other hand, cows required 1.5 kJ/kg per km walked to travel from the pasture to the milking parlor and back. These results indicate that, in an average dairy production system in our country, feeding cows under a grazing system would result in a cost equivalent to 2 to 3 liters of milk per cow per day when compared to confinement feeding. This indicates that the lower milk production and feed conversion efficiency observed in grazing dairy systems, compared to indoor-fed systems, are mainly due to a lower feed intake rather than the increased maintenance energy costs associated with grazing and walking.