Milk fever in dairy cattle is a well-known disease that primarily occurs in older cows in connection with calving. The disease is characterized when the cow is cold, rolling and possibly paralyzed.
The disease is often combined with lower milk yields, and the cows have an increased risk of developing mastitis, metritis and ketosis — diseases that all significantly influence the animals’ welfare and the farm economy.
The occurrence of milk fever at organic farms may be higher than at the conventional farms, according to researchers at Aarhus University in Denmark. Previous studies have even found considerable differences in the occurrence of milk fever at the herd level within a group of organic farms, but without being able to explain why.
A new study from Aarhus found that the farmers assess the problem in very different ways and that the occurrence of milk fever is very dependent on access to summer pasture.
The study also found that many organic farmers are critical of legislation in Denmark that prevents them from treating milk fever with calcium directly into the cow’s vein, and organic farmers are working with different strategies when it comes to prevention, Aarhus said.
In this study, 56 organic farmers with herds of more than 100 cows were interviewed over the phone about their understanding of milk fever, their practical procedures regarding prevention and how they deal with milk fever. The answers were analyzed and compared to data from herds in the Danish Cattle Database.
Of the 56 farmers, 38 said they did not think that they had a problem with milk fever. One farmer explained that even though a veterinarian thought there was a problem, she chose to accept that milk fever was inevitable, especially in old (fourth lactation or older) and slightly fat cows. Others accepted the problem but also tried to reduce it to, for instance, a condition that happens only periodically, according to Aarhus. Furthermore, the problem was related to certain seasons, to the cows' age and to human handling.
Twenty-six farmers answered that they found milk fever to be a very problematic condition because of secondary complications, such as retained placenta, mastitis, ketosis, reduced yield and displaced abomasum.
Twenty-five farmers said they had a hard time understanding why they were not allowed to treat the cows with calcium in the blood, as the rules of the organic regulations state, the university said. Several pointed to the fact that, while they do understand that only vets are allowed to treat with antibiotics, they do not understand why the vet must also administer the calcium.
Several of the farmers added that the method they are allowed to use -- giving the cow the calcium orally -- is a method they do not find scientifically good enough, because organic calcium products that are considered to have a sufficient effect do not exist.
Regarding a question about preventing milk fever via feeding, almost all farmers focused primarily on good feeding of dry cows -- for instance, by using a separate dry-cow blend and dry-cow minerals, Aarhus said. Their method of choice for drying off varied a lot, with some using an abrupt withdrawal (the cow is fed straw and water for a period to stop milk production) while others supplied their cows with hay, silage, wrap or a dry-cow blend.
The farmers also differed on how they feed dry cows during summer and winter. For instance, the feeding was almost the same during winter and summer for some, while others said they supplement the grass with dry-cow minerals and allocate feed according to needs, Aarhus noted.
Comparing to milk fever data
All interviewed farmers gave the researchers their permission to collect the farm’s data for 2016 from the cattle database on registered calving, and all occurrences of milk fever were listed. The number of percentages of milk fever in cows of third parity or more in 2016 in the 56 herds varied from 0% to 14.9%.
The 10 herds with the fewest registered occurrences were those where owners mentioned good dry-cow feeding as the most important preventing initiative, whereas the group with the most registered occurrences of milk fever to a higher degree mentioned minerals and calcium products as means of prevention, Aarhus said.
In the group with the fewest occurrences of milk fever, seven out of 10 producers fed their dry cows in the same way when grazing during summer and winter. In the group with the most occurrences of milk fever, only two out of 10 producers supplied another feed besides the grazing.
So far, the Aarhus researchers concluded that correct summer feeding of dry cows is very essential in preventing milk fever. Previous studies have shown that grazing cows are at higher risk of developing milk fever, and this study confirms this statement. This study also shows that there is a difference in the occurrence of milk fever at summer feeding (primarily grass) compared to cows fed almost the same way all year-round.
On the other hand, this study could not confirm anything about the significance of the different types of winter feeding. This may be because the farmers have different descriptions of how dry-cow feeding is allocated. The next phase of this study will go more in depth into this matter.