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Dairy cows fed a low-energy diet around dry-off show signs of hunger

30 September 2021

Aarhus University

Researchers from Aarhus University have studied to which extent the feed energy density affects dairy cows’ feeding motivation during dry-off.

A motivational test showed that using low energy diets to dry-off high-yielding dairy cows results in hunger despite ad libitum access.

Cows are milked two to three times daily. However, approximately two months before expected calving, the milking is ceased, and the cow is “dry” until the beginning of the next lactation after birth of the calf. The purpose of the dry-period is to facilitate productivity and promote health in the next lactation. Before the last milking, some farmers seek to reduce the cow’s milk production gradually, typically by milking her fewer times during the days prior to the last milking and/or by reducing the feed energy density.

Nowadays, cows often yield more than 25 kg/day of milk at the time of dry-off, and their energy demand corresponds to this high yield. Consequently, dry-off may be a welfare challenge due to accumulation of milk in the udder when reducing the number of milkings and due to hunger when the cow is fed a low-energy diet. In this study, we investigated the effect of a low-energy diet on indicators of hunger during dry-off.

Assessment of the cows’ motivation to eat

In order to quantify the cows’ feeding motivation, we used a special feed trough with a “weighted gate”. The gate could be made gradually heavier by adding 10-kg counterweights so that the cows had to push increasingly more weight to receive a reward, consisting of 0.8 kg of concentrate. The harder the cows were willing to push, the higher their feeding motivation (the hungrier they were).

In total, thirty-two Holstein cows were included in our study. Prior to start-up, all cows were trained to eat from the feed trough and to push the gate open. During the seven-day test period – the last seven days before the last milking – half of the cows were fed the normal lactation diet while the other half were fed a low-energy diet in which the lactation diet was diluted by approximately 30% chopped barley straw. The cows’ feeding motivation was tested twice during this week: five and two days prior to the last milking, respectively.

Low-energy feed shows clear signs of hunger

During both tests, the cows fed the low-energy diet pushed more than five times the weight that the normal fed cows did to earn a feed reward. Furthermore, these cows were almost ten times as fast eating the first reward than the cows fed the normal lactation diet. The results show that the cows are hungry during dry-off if fed a low-energy diet despite ad libitum access. This underlines the importance of including animal welfare when considering choice of dry-off management. The study also illustrates a method for quantifying cattle’s feeding motivation, which can be used to assess how different types of feeding management affect the animals’ hunger and thus welfare.

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