THE EFFECTS OF MAJOR DIETARY CHANGES ON MILK PRODUCTION AND RUMEN HEALTH IN DAIRY COWS – June 2018
First 100 Days
The impact on dairy cow production during the transition between pasture and forage supplements in systems in Ireland and temperate Australia

By Dr Martin Auldist

UPDATE: Dr Vicky Russo successfully completed her PhD in 2019 – The impact on dairy cow production during the transition between pasture and forage supplements in systems in Ireland and temperate Australia

With winter upon us, experiments at Ellinbank have mostly stopped until spring when we will again have enough pasture – and cows – to work with. In this so-called “downtime” researchers are busy collating data, getting samples analysed and, importantly, writing up the results from previous experiments.

One person who is especially busy is Agriculture Victoria Research Scientist Victoria Russo, who is in the final throes of writing up her PhD and the scientific papers associated with it. Victoria has spent the last three years investigating the effects of major dietary changes on milk production and rumen health in dairy cows, and the ways in which any negative effects might be mitigated.

“When pasture becomes scarce, farmers often need to move their cows quite quickly on to a high concentrate diet, then when pasture becomes available again the reverse occurs’” says Victoria. “Farmers report that during these changes, milk yield often declines, at least until the cows adapt to their new diet.”

During the course of her PhD studies, Victoria conducted a series of experiments, one at the Teagasc research farm in Moorepark, Ireland, and the rest at the Agriculture Victoria Research farm at Ellinbank. What she found, overall, was that the effect of dietary changes on milk production and ruminal pH was highly dependent on the accompanying forage being fed.

Photo: Dr Vicky Russo at Ellinbank Research Farm

In an experiment in which cows initially being fed a 100% lucerne hay diet had 8 kg DM of wheat grain introduced into their diet either rapidly or slowly and in small or large increments, the adaptation strategy made no difference to either milk production or the pH in the rumen. In other words, none of the strategies compromised rumen function, despite the high amount of grain fed.

“It didn’t matter how quickly we introduced the grain, the pH in the rumen showed the same patterns and dropped to the same level after feeding the grain” says Victoria. “We had a rumen bolus in each cow that measured ruminal pH every few seconds or so, so we were able to monitor the rumen pH very intensively.

“We put this result down to the buffering capacity of the lucerne. We guessed that it was creating a rumen environment that was able to withstand changes in pH”, says Victoria. “It was our first evidence that the type of forage used might be an important factor in mitigating adverse effects of rapid changes in diet.”

In further experiments, Victoria showed that hay was much better than fresh forage at maintaining milk production and pH in the rumen during a grain challenge. Similarly, there were differences between types of hay.

“When we fed lucerne hay during a grain challenge, we found that cows were able to take on board more energy on shorter period of time – and therefore produced more milk – than when pasture hay was fed,” says Victoria.

“Overall these results show that if we have the right accompanying forage, we could potentially be more aggressive with the way we introduce grain during a diet change, and there are production benefits to this.”