Prof Mulligan stressed that milk revenue is still the single most important factor that influences dairy producer profitability. Dairy farmers are now paid for milk using the A + B - C system. With this payment system, milk protein and fat production are more important than milk volume for milk revenue. Whilst a lot of research projects and extension programmes have concentrated on the more valuable milk protein component, not as much attention has focused on the still valuable milk fat component. Importantly milk fat percentage has huge potential to be suboptimal during the period of peak milk production from April through to June.
Dr Morgan Sheehy said that a recently published peer-reviewed paper by UCD and Devenish showed that 10% of herds had milk fat depression (bulk tank for milk fat below 3.3%, with a normal milk protein percentage). However, it was found that close to 40% of herds had a bulk tank fat percentage of less than 3.6% (with a normal protein content). Dr Morgan Sheehy stressed that "There is a significant cost associated with low milk fat percentage. If milk fat percentage fell from 4.2% to 3.6% in a herd milking 28 litres/day for a two month period it would cost the farmer up to €80 per cow. Many believe that low milk fat percentage is normal for grazing cows at certain times of the year. However, data from the high output grazing herd in UCD (a research project that Devenish have also supported) indicates an average milk fat percentage of 4.09 for the period from 60 to 120 days in milk, which is the risk period for low milk fat percentage."
In many cases, the problem of low milk fat percentage can be avoided/minimised. In the long-term, it may be possible to greatly reduce this problem by correct breeding decisions. It is also possible to make gains by using appropriate nutrition. The main causes of milk fat depression are the ingestion of high quantities of polyunsaturated fatty acids in a scenario where rumen pH is low. In the months of May and June, the lipid content of grass is often recorded up to 6%. Normally in the rumen of the dairy cow fatty acids are biohydrogenated. However, when rumen pH is low a significant amount of these fatty acids are only partially biohydrogenated in the rumen. This change in fatty acid metabolism results in the production of powerful milk fat depressing intermediates, most notably trans 10 cis 12 conjugated linoleic acid. The impact of pasture lipid content on milk fat depression has been demonstrated by Professor Adam Lock, Michigan State University using data on perennial ryegrass from Tasmania. Low rumen pH which contributes to this problem is very common in grazing cows. Research from UCD has shown that approximately 50% of cows have a rumen pH of 5.8 or less with is low enough to cause milk fat depression.
Dr Morgan Sheehy continued to outline that farmers and nutritionists should be mindful in a grazing scenario to limit the effect of diet in depressing milk fat percentage and rumen pH.
Considerations include:
Devenish Nutrition offer a rumen buffer called Mag12. It supplies 12g of soluble magnesium per 100g. The product has been trialled in SRUC and has significantly increased butterfat %, butterfat yield, milk protein % and milk protein yield. The product is widely used at farm level and farmers are delighted with the benefits and in particular its financial return to the farmer. Dr Morgan stressed that Mag12 is a key ingredient that minimises the incidence of low butterfat’s and is part of the armoury used to maximise milk price at farm level.
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