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

Cows are milked two to three times daily. However, approximately two months before the expected calving, milking is ceased, and the cow is “dry” until the beginning of the next lactation after the 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, Aarhus said.

Modern cows often yield more than 25 kg per 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 the 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, the researchers said.

In this study, Aarhus doctoral student Guilherme Amorim Franchi and senior scientist Margit Bak Jensen investigated the effect of a low-energy diet on indicators of hunger during dry-off.

In order to quantify the cows’ feeding motivation, the researchers used a special feed trough with a “weighted gate,” which 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, Aarhus explained. The harder the cows were willing to push, the higher their feeding motivation (the hungrier they were).

In total, 32 Holstein cows were included in the study. Prior to startup, all cows were trained to eat from the feed trough and to push open the gate. 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 with approximately 30% chopped barley straw. The cows’ feeding motivation was tested twice during this week: five days and two days prior to the last milking.

During both tests, the researchers said to earn a feed reward, the cows fed the low-energy diet pushed more than five times the weight that the normal-fed cows did. Furthermore, cows fed the low-energy diet were almost 10 times as fast at eating the first reward than the cows fed the normal lactation diet.

The results show that cows are hungry during dry-off if fed a low-energy diet despite ad libitum access, Aarhus said. 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, the university said.

The study was published in Scientific Reports.