We are the UK leaders in ruminant nutrition and we have  forged links with experts and leading research institutions around the world.

In this edition of our Knowledge Network we return to speak to Professor of Animal Science at the University of Illinois in the USA, Jim Drackley. He is a global expert on calf nutrition and has been involved in the recent review of our specialist dry calf feeds. 

This month he takes a look at some of the latest research on reducing the risk of ruminal acidosis in calves.

Don't let acidosis rob your calves

James K. Drackley, Professor of Animal Sciences at the University of Illinois

You’ve likely seen it - lethargic weaned calves with rough hair coats and runny diarrhoea. 

The culprit is usually ruminal acidosis, a pH of the rumen of less than 5.6 causing subacute acidosis or 5.2 causing acute acidosis. 

The immature rumen of the young calf can’t absorb enough of the acids and the saliva buffering system is underdeveloped, resulting in the low pH.

Rumen pH in young calves is normal soon after birth, averaging around 6.0. As the calf begins to consume more starter, rumen pH begins to decrease (see Figure 1) and often reaches levels that should signal acidosis. 

However, many calves do not show signs of acidosis, despite the very low rumen pH, and the reasons aren’t clear. The pH decreases sharply after a meal and in calves fed once daily, slug-feeding may contribute to acidosis. 

A research study attempted to produce rumen acidosis in calves to help understand its causes and effects (Gelsinger et al., 2020). The researchers created acidosis by feeding a starter containing 43% starch and 15% NDF, compared with control calves fed a starter containing 35% starch and 25% NDF. 

No forage was fed to either group and the calves were housed on rubber mats to prevent them from eating bedding. Rumen pH for  the calves fed the control starter fell from 5.8 to 5.5 at 12 hours  after feeding. 

But, in the calves fed the high-starch starter, pH decreased to 5.4 two hours after feeding and continued to fall to about 4.9 at 12 hours after feeding. 

Starter intake was less for the acidotic group and those calves ate more slowly. The body weights of the acidotic calves fell behind the weights of the control calves (see Figure 2).

Another study, Porter et al. (2007) recorded a rumen pH of 4.95 for calves fed a high starch starter compared with a pH of 5.50 in calves fed a higher fiber starter. No forage was fed.

From available research, we know the risk factors for acidosis are higher starch and lower NDF contents in starter, small feed particle size, ground vs. unground starter ingredients, lack of forage feeding, no straw bedding and higher starter intakes. 

Usually signs of acidosis are not observed in calves before weaning but may become apparent shortly after weaning as intake of starter increases rapidly.

The situation is often difficult to correct. Feed a high-quality starter that is moderate in starch (23-28%) and NDF (18-25%), and offer limited amounts of forage such as straw, grass hay,  
or oat hay. 

To avoid slug-feeding, offer the starter free choice, or provide it in two meals daily. By addressing the risk factors, you should be able to avoid the acidosis thief that steals your calf performance.

For more information contact the Feed Team on 01566 780261 or email feeds@molevalleyfarmers.com

_{References:
Gelsinger, S. L., W. K. Coblentz, G. I. Zanton, R. K. Ogden, and M. S. Akins. 2020. Physiological effects of starter-induced ruminal acidosis in calves before, during, and after weaning. Journal of Dairy Science 103:2762-2772.
Porter, J. C., R. G. Warner, and A. F. Kertz. 2007. Effect of fiber level and physical form of starter on growth and development of dairy calves fed no forage. Professional Animal Scientist 23:395–400.
Suarez-Mena, F. X., A. J. Heinrichs, C. M. Jones, T. M. Hill, and J. D. Quigley. 2016. Straw particle size in calf starters: Effects on digestive system development and rumen fermentation. Journal of Dairy Science 99:341-353.}