With the latest maize silage analyses showing average starch levels around 5% higher than in 2005, dairy producers are being advised to pay close attention to ration formulations this winter. Where maize silage is a high proportion of the forage fed, the resulting high starch level in the overall diet can create a very real risk of sub-acute ruminal acidosis.
The risk is greatest where high starch concentrates, such as cereals, are also fed as part of the ration, and KW Alternative Feeds nutritionist Dave Collett is urging all milk producers to be vigilant for signs of low rumen pH.
"Lost milk output is one of the first indicators of acidosis, and at sub-acute levels there may not be any other significant symptoms," he explains. "But if cows aren't producing as well as they should, and you're feeding a high-starch ration with a large proportion of maize silage, this year there's an increased likelihood that acidosis is the culprit."
The general trend towards higher levels of starch in this year's maize silage is yet another effect of the extreme summer weather. Many maize crops were slightly stunted but with large cobs, creating a much higher cob:plant ratio than normal, with cobs often maturing ahead of the rest of the plant.
And with no quota restrictions on output again this year, some producers are feeding higher levels of concentrate than normal in order to push yields. But as Mr Collett is quick to point out, the importance of keeping a cow healthy, in terms of life-time performance as well as current output, cannot be over-emphasised.
"It shows just how important it is to get silages properly analysed, and this year we've seen individual samples containing more than 35% starch. On many units, the cows will be getting a lot of the starch they need from the maize silage, so any starchy concentrates are likely to tip the balance towards acidosis and should be replaced by fibre-based energy feeds like soya hulls and sugar beet feed.
"There's also good evidence to support the routine use of rumen buffers and yeasts in these high-risk situations to help maintain optimum rumen pH. Products such as Biosaf and BioBuf are much more effective than traditional sodium bicarbonate, and go a long way towards optimising the rumen environment when feeding high-starch rations."
BioBuf is a product containing both the yeast Biosaf and the buffer Acid Buf. Acid Buf has been shown to reduce the amount of time the rumen remains below pH5.5 in cows fed acidotic diets by up to 75% compared to no buffer, and by nearly 55% compared to traditional sodium bicarbonate buffers (Stollenbosch University, South Africa). This was accompanied by an increase in milk output of 2.7 litres/cow/day compared to cows fed sodium bicarbonate and 4.2 litres/cow/day compared to cows fed no buffer.
