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DEAR SIR: In the Irish Farmers Journal (20 April 2019), you published an article in the livestock section relating to feed supplements and milk fat depression. It is good to see this area being highlighted in your paper. However, there are a number of clarifications that should be made in order to give the reader a more complete picture.
From reading the article, one could easily take the view that following a specific research experiment at UCD Lyons with cows at grass fed a specific yeast supplement that no results were reported. This is not correct, there were in fact three peer-reviewed scientific papers published from this work.
In the article, it was stated that there were no significant differences between the treatments in this research. This is true for milk fat yield. However, there were other significant treatment effects. For example, the specific yeast supplement in question significantly reduced time at low rumen pH and significantly reduced body fat mobilisation in early lactation. The cows in this study were either grazing from the day of calving for the first 10 weeks, or fed TMR for the first three weeks and then grazing for the remainder of the 10 weeks.
The report stated that feeding acid buffers caused a slight increase in milk fat. The outcome of this research, which was conducted at UCD Lyons, was that feeding a specific mineral buffer supplement resulted in a statistically significant increase in milk yield and solids output. Milk solids output was higher by 90g per day, most of which was milk fat. The cows in this study were fed 8kg of concentrate at grass and the diet could be considered a risk for acidosis. The reader should be made aware that the ingestion of polyunsaturated fatty acids from grass is a major contributor to this issue. Leading international experts also believe that low rumen pH and rumen environment are important.
In my opinion, the specific milk fat depression that we see in Ireland in April, May and June is not driven solely by stage of lactation, as UCD research shows that autumn-calving cows also have the highest occurrence of milk fat depression at this time.
Finally, the holistic approach to dealing with milk fat depression that was published in your management notes recently, which considered the concentrate make up, grazing management and animal breeding, is what should be considered for the problem in my opinion.
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