Antimicrobial stewardship and managing ruminal acidosis

By Kristen Davis, GippsDairy and Dr. Steph Bullen, Dairy Australia

Provision of adequate levels of energy and protein in cows’ diets is critical for optimising milk production as well as maintaining body condition, maximising reproductive performance and preventing animal health conditions such as lameness.

However, high energy diets, such as those high in grain/concentrates and even very high-quality pasture, as well as transitioning dry cows onto the milking ration, increase the risk of ruminal acidosis. If changes in diet are made too quickly, or the diet contains inadequate levels of fibre, volatile fatty acids (VFAs) accumulate in the rumen and result in a decline in rumen pH. This disrupts digestion of feed and results in reduced milk production, production of milk fat and loose manure. In severe cases, cows may become sick and die.

There are several ways to manage ruminal acidosis. These include:

• Implementing a sound transition feeding program for the three weeks before and after calving.
• Avoiding sudden changes in diet and making any changes over at least three weeks.
• Provision of adequate levels of effective fibre (at least 10% of the diet; at least 32% NDF) as close as possible to the time of grain feeding.
• Managing and monitoring your pasture allocation to graze at the optimal leaf stage, maintain proper grazing residuals and ensure the whole herd has equal access (e.g., heifers and cows milked last).

Often additional dietary control measures are required. These may include buffers (e.g., bicarb), neutralising agents (e.g., magnesium oxide) and rumen modifiers, including both antibiotic and non-antibiotic rumen modifiers.

Antibiotic rumen modifiers include virginiamycin (Eskalin®), tylosin, monensin (e.g. Rumensin®) and lasalocid (e.g. Bovatec®). The dairy industry (Australian Dairy Industry Council, made up of Australian Dairy Farmers and Australian Dairy Products Federation) has committed to using antibiotics responsibly, as little as possible as much as necessary.

In addition, under Australia’s antimicrobial importance rating system, virginiamycin is classified as an antibiotic of high importance to human antimicrobial resistance. Antibiotics in this class should only be used in exceptional circumstances and when no other alternative is available.

Therefore, if you have antibiotic rumen modifiers routinely included in your feed it’s recommended that you check in with your vet and ruminant nutritionist to determine if they’re still necessary or if there’re modifications to your ration, transition feeding program or other nonantibiotic additives that may be suitable for your farm. This becomes critical if you are feeding Eskalin®, and it’s recommended you review your Eskalin®-containing ration with both your vet and nutrition advisor, together, on a monthly basis.

More information on ruminal acidosis can be found on the Ruminal Acidosis page on the Dairy Australia website.