Negative energy balance during early lactation is a demanding physiological state for the cow at the best of times and can be made worse through the feeding of butyric silage. The cow’s liver requires optimal condition as the demand for glucose increases from 1kg/d in late gestation to 2.5kg/d 3 weeks post-calving. A successful transition determines the success of the subsequent lactation, with energy levels crucial to immune function during the transition period. The feeding of butyric silage, however, can increase the risk of ketosis in cows at all stages of lactation. This is often referred to as type III ketosis, which is the focus of this article.
Butyric silage is a consequence of several factors: wet late-season grass, low sugars and high nitrate content. A combination of these encourages the growth of clostridium bacteria that ferment carbohydrate to butyric acid, instead of lactic acid. Soil contamination can provide an additional risk factor. Once affected, the silage is predisposed to higher fermentation losses, further reducing the quality of the forage through increased ADF levels. The concentration of butyric acid found in silage is dependent on its association with lactic acid - ideally, this ratio should be greater than 3:1 (lactic acid: butyric), as lower ratios suggest a failure to ferment satisfactorily.
How does the high butyric acid induce ketosis?
Whilst the cow’s liver metabolises the majority of propionic and Acetate, butyric acid is converted to β-hydroxybutyrate by the epithelium of the rumen wall. This mechanism ensures that the liver is focused on the production of glucose and maintaining plasma glucose concentration. β-hydroxybutyrate or ketones derived from normal rumen fermentation are used as energy source for muscle tissue, adipose tissue deposition and the formation of milk fat. This equates to around 750g/day. Excess butyric acid from feeding butyric silages results in higher levels of plasma Ketones.
Figure 1 shows the fate of Butyrate and ketones during carbohydrate fermentation, digestion and metabolism. The effect of elevated blood ketones on performance and whether it causes ketosis is dependent on the stage of lactation and other factors. For example, feeding butyric silage to transition cows can add to their already elevated blood ketones derived from the metabolism of NEFA’s, or in later lactation if energy intake if below requirements due to poor quality forage. Ketosis reduces both DMI and milk yield, resulting in increased rates of metabolic diseases and poor fertility.
My advice with regard to butyric silages is to either dilute, divert or destroy. Apart from dumping the forage the other two options will still influence productivity, resulting in reduced dry matter intake in the stock being fed. Daily doses of over 50 - 100g of butyric acid can cause ketosis, with doses above 200g able to induce severe ketosis, and 450 - 950g guaranteed to induce severe ketosis in a fresh cow. The general rule of thumb is therefore to feed no more than 50g per head per day of butyric acid. (Oetzel, 2007).
Feeding butyric silage has long term negative effects on production, fertility and health, thus impacting the bottom line of the farm business. Prevention is always better than cure, so consideration should be made to prevent the production of silages high in butyric acid. It is therefore key to learn from previous mistakes and change the practices causing them to reduce the risk of repeat in the future.
References
Oetzel, G.R., 2007, September. Herd-level ketosis–diagnosis and risk factors. In Proceedings of the 40th annual conference of bovine practitioners, Vancouver, Canada.
Ospina, P.A., Nydam, D.V., Stokol, T. and Overton, T.R., 2010. Evaluation of nonesterified fatty acids and β-hydroxybutyrate in transition dairy cattle in the northeastern United States: Critical thresholds for prediction of clinical diseases. Journal of Dairy Science, 93(2), pp.546-554.
