The Influence of Body Weight on the Efficiency of Dairy Cows
Questions about the efficiency of dairy cows are a consequence of the increasing pressure on milk prices. Efficiency is defined as the relationship between energy output (milk energy) and energy input (feed energy). For methodological reasons, it is often only the energy output (milk) which is assessed, ignoring the energy input (feed energy). As a result, research into the efficiency of dairy cows has so far shown uneven results. The aim of this study was to calculate efficiency by measuring the effective daily energy intake and energy expenditure in milk, and to investigate whether the body weight of cows had an influence on their efficiency. Efficiency was defined as: efficiency = (milk energy (MJ)/net energy intake (MJ NEL)
Data were collected from the Holstein Frisian and Brown Swiss dairy cows at the research centre of the Swiss Federal Institute of Technology (Zurich). Throughout lactation and the subsequent dry period, the cows were weighed daily. The quantity of milk produced was recorded twice daily and the milk ingredients measured monthly. Feed samples of all ration components were taken every month and analysed. Using scales installed under each feed trough, the feed intake of individual cows was measured continuously during the whole lactation. In this way, the daily energy intake and the daily energy output in milk could be quantified. Data from 450 lactations of 158 cows were collected. After eliminating incomplete datasets, 105 lactations of 65 cows (40 Holstein Frisian and 25 Brown Swiss cows) were submitted to statistical analysis.
The results show that the body weight of cows with two or more lactations positively correlated with both daily feed intake (p=0.018) and milk yield (p=0.022). This means that an additional 100 kg body weight required 2.0 kg DM/day more feed intake and yielded 630 kg more milk per lactation. However, there was no significant correlation between body weight and efficiency (p=0.39), not even after dividing the samples by breed and lactation numbers. In this sample, heavy cows were equally efficient as light cows, compensating for their increased maintenance requirement by higher feed intake and higher milk yield. The differences in efficiency between individual cows must therefore be explained by other factors.
Keywords: Dairy cow efficiency