Rumen acid production from dairy feeds. 2. Effects of diets based on corn silage on feed intake and milk yield

A new approach to evaluating feeds has been developed based on in vitro estimates of rumen acid load (acidogenicity value). The present work was conducted to establish effects of rumen acid load on dry matter intake and milk production of early-lactation dairy cows fed corn silage-based diets. The effects of diet acidogenicity were investigated independently of ingredient composition using a series of isoenergetic and isonitrogenous concentrates that used different raw materials to achieve the same acidogenicity value. Six concentrates were formulated to be fed at 7 kg/d, and two at 10 kg/d. Continuous culture equipment, which had been modified to control and record infusions of acid and alkali to maintain pH in the range 6.2 to 6.3, confirmed the ranking of concentrates based on the in vitro technique. The concentrates were offered to dairy cows in early lactation with corn silage available ad libitum. Forage intake declined with increasing concentrate acidogenicity, particularly at the higher level of concentrate feeding. However, concentrate acidogenicity had a significant negative effect on dry matter intake even at 7 kg/d. Feed intakes were similar for concentrates that were formulated to be isoacidogenic, but using different raw materials. There were only small and inconsistent effects of concentrate acidogenicity value on milk yield and milk fat percentage, while milk protein percentage was higher with the high AV concentrates. Effects on milk composition likely reflect differences in nutrient supply and there was no evidence for effects of rumen acid load per se on milk composition.