Garrett R. Oetzel, DVM, MS — School of Veterinary Medicine, UW-Madison

Introduction

Ruminal acidosis is the consequence of feeding high grain diets to ruminant animals, which are adapted to digest and metabolize predominantly forage diets. Feeding diets that are progressively higher in grain tends to increase milk production, even in diets containing up to 75% concentrates. However, short-term gains in milk production are often substantially or completely negated by long-term compromises in cow health when high grain diets are fed.

Compromises in dairy cow health due to ruminal acidosis are a concern not only for economic reasons, but also for animal welfare reasons. Lameness is probably most important animal welfare issue today in dairy herds, and a good portion of the lameness observed in dairy cows may be attributed to laminitis secondary to high grain feeding. Public perception of dairy production is becoming increasingly important, and lame cows do not portray a good image of our industry. Lameness (along with secondary reproductive failure and low milk production) is commonly the most important cause of premature, involuntary culling and unexplained cow deaths in a dairy herd.

Ruminal acidosis can be a direct human health concern as well. Low ruminal and intestinal pH due to high grain feeding increases the risk for shedding enterohemorrhagic E. coli such as 0157:H7 (Russell and Rychlik, 2001). Switching cattle to a high forage diet just prior to slaughter decreases this shedding.

Dairy production in areas with relatively inexpensive grains and with no limit to the amount of milk they can market (e.g., the US) are likely to experience the most ruminal acidosis. The economics of dairy production under these circumstances favor heavier grain feeding. However, producers and veterinarians may be ignorant of the health costs of ruminal acidosis and therefore may be reluctant to decrease grain feeding.

Areas of the world with relatively more expensive grains and/or milk production quotas probably experience less ruminal acidosis than the US. However, bouts of ruminal acidosis are always possible whenever grains or very high quality forage are consumed by dairy cows.