Although apparent, the positive correlation between ruminal pH and milk fat concentrations, are not strong (r2=0.39; Allen, 2007). There are other factors, such as body fat mobilization and the quantity and type of fat in the diet that can influence milk fat percent and yield.
As a result, a low milk fat percentage should not be considered as definite sign of ruminal acidosis. In addition, cows affected with SARA do not always show low milk fat concentration.
The optimum NFC concentration for dairy cow diets is not well defined in the latest Nutrient Requirements of Dairy Cattle (NRC. 2001). The concentration range suggested varies between 36 and 44% on a dry basis. Total NFC includes starch, sugars, soluble fiber, and organic acids. Because of NFC differences in degradation rate and chemical composition, different NFC sources have a different potential to reduce ruminal pH.
Sugars and starch can ferment to lactic acid, which has greater effect in decreasing ruminal pH than acetic, propionic, or butyric acids. To prevent rumen acidosis, it is critical to control the amounts and types of NFC in the diet. Although, the starch content recommended in dairy cow diets is between 24 and 26% (Staples, 2007).
The starch concentration should be reduced when feedstuffs that are rich in digestible fiber, such as gluten feed, distillers grains, and/or soy hulls are included. The concentration of starch and sugars should not exceed 35% of the diet dry matter in order to maintain adequate ruminal pH. There should also be a minimum of 22% of physically effective NDF in the diet to stimulate adequate rumination and cud chewing.
The best way to achieve these concentrations of effective fiber is by maximizing forage quality. However, one must exercise caution with such substitutions and rebalance the diet and/or verify there is enough effective fiber. Substituting equal amounts of 150 RFV hay with a different hay of 200+ RFV in a borderline “hot ration”, can shift the balance and result in SARA in a herd with a previously adequately balanced ration.
Using forages of high energy concentrations allow for an increase in their inclusion rate in the diet. Once the forage: concentrate ratio is increased the risk of acidosis is reduced. To ensure the amount of fiber supplied by the diet is sufficient to maintain adequate rumen health, it is important to routinely monitor animals and diets. Below are some parameters to monitor in a herd or group of animals: