The cost of ketosis are associated with a lower milk yield and an increased risk of a wide range of diseases. The direct costs include the veterinarian’s and the herdsman time, drugs, discarded milk, reduced yield and other costs. The indirect costs include increased risk of other diseases, extended calving intervals, higher culling rates, extra services per conception and the increased risk of fatality.
For each affected cow the total costs of subclinical ketosis have been calculated to be $955 (€735). On a farm with a prevalence of subclinical ketosis between 20-30% this represents a cost between $190-286 per average cow in the herd. For a farm with 100 dairy cows the total costs can add up to $29,000 per year.
Choline is considered a non-essential nutrient for ruminants, meaning that the dairy cow can produce it by herself. However there are indications that the quantity is limited and consequently adding extra choline to the ration is a good strategy to optimise health.
Supplemented choline needs to be available on an intestinal level. Unprotected choline will be broken down in the rumen and will lose its effects. To overcome degradation in the rumen, several rumen protected products are available.
Rumen protection or rumen bypass means that the choline is covered by a protective layer. This is mostly a layer of a fatty acid matrix, which restrain the rumen microbes from utilising the choline. The protective layer must be broken down later on in the digestive tract at the site of the small intestine. Here, the digestive enzymes break down the fatty layer and the choline is free for absorption.
Rumen bypass as such does not necessarily mean the product is effective. Some products are over protected. The protection can be so strong that the choline is not released in the intestine at all. Other products are under protected, which means that the protection layer is not able to provide sufficient rumen survival. This leads to the choline being partially or even completely degraded in the rumen before it even reaches the intestine.
Combined in vitro/in vivo trial work demonstrates this ‘overprotection’ and ‘under protection’ of some products. In this test the rumen protection is measured with a so called ‘In Sacco method’ and a Daisy incubator. Samples of the product are introduced into the incubator and after 12 hours how much choline remains is measured (means rumen stable).
Next the products are entered into the small intestine of a duodenum-cannulated dairy cow and collected in the faeces. This so called ‘mobile nylon bag method’ is a well accepted method to determine the intestinal digestibility of products. The amount of choline that is eventually available for the animal is the result of the rumen stability times the intestinal digestibility. The results for rumen stability as well as for the intestinal available choline are shown in Fig. 2.