Dairy farmers are being encouraged to gradually transition cows to grazed grass at turnout to avoid a drop in milk yields and compromised rumen health.

Mark McFarland, feed additive product manager at Lallemand Animal Nutrition, says the challenge posed by turnout on a cow’s digestive system cannot be underestimated.

“When you change what goes into the cow’s rumen, you change the microbial environment in there and it can take as much as six weeks for the rumen and its microbiota to adapt to the new diet,” he explained.

“Using dry matter (DM) to quantify this, cows on a total mixed ration (TMR) are receiving a diet of 40-50% DM through the winter; however when you turn them out to grass their diet is suddenly changing to something much wetter, with spring grass likely to contain no more than 20% DM.”

He said spring grass is also higher in rapidly fermentable sugars and crude protein than a TMR diet, which combined with the difference in DM can result in a higher risk of acidosis, a drop in milk yields, loose cows, and body condition loss.

“With milk prices relatively good, producers should be really motivated to try to reduce these challenges and maximise productivity at grass, because the extra litres are worth so much more now,” added Mr McFarland.

He recommended a gradual introduction to grazing, by slowly building up the number of hours that the cows are out grazing each day, alongside feeding a forage-based buffer ration indoors to support the rumen through the change.

“Within the buffer ration, essentially you want to provide structural fibre – because that’s what’s lacking in the grass – to help stimulate rumination and maintain a more stable rumen pH,” explained Mr McFarland.

He said the introduction of a rumen-specific live yeast, such as Saccharomyces cerevisiae CNCM I-1077, ahead of and during the grazing season will also help cows cope better with the transition to grazed grass.

“The live yeast helps cows to manage dietary changes at turnout from the inside out, by helping raise and stabilise rumen pH and by supporting the fibre digesting microbiota,” explained Mr McFarland.

The benefits of feeding the yeast to cows during grazing were demonstrated in an on-farm trial in Southern Ireland where an estimated 90% of dairy herds are grazed.

“The farm previously had problems with loose cows; however manure consistency was greatly improved with the addition of the yeast, alongside a 0.5 litre a day increase in milk production,” said Mr McFarland.

The cows supplemented with the live yeast also showed improved milk quality parameters with average protein and butterfat levels of 3.43% and 4.14% respectively, compared to 3.39% protein and 3.97% butterfat for those cows not receiving yeast in their diet.

“By taking steps to manage rumen function at turnout, you can help ensure cows stays in good body condition and consequently have a greater chance of getting back in calf,” added Mr McFarland.

“All the while, you will keep producing milk from one of the cheapest feed sources available.”