Written by John Swire
Mid-season grass growth and summer temperatures may require fat supplementation for milk quality recovery
Dairy farmers on milk quality contracts need to pay close attention to grass growth and heat stress conditions to mitigate mid and late grazing season butterfat depression, advises Wesley Habershon, grazing consultant and nutritionist for The Farm Consultancy Group.
“A combination of weather-influenced grazing conditions and an increase in grass growth towards the end of June has resulted in milk butterfat taking as much as a 10 percent dip recently in many herds throughout the UK,” explains Mr Habershon. “As we get into the warmer months, feeding strategies for high temperatures also need to be taken into consideration.”
While a surge in grass growth results in reduced fibre content of grass, weather leading up to it can decrease dry matter intake due to damp grazing conditions.
According to Dr Richard Kirkland, Global technical manager for Volac Wilmar Feed Ingredients, young grass also has a high sugar content, making it rapidly fermentable in the rumen. This combined with the lower fibre levels can compromise rumen pH. Low-fibre pasture can pass through the digestive system much more quickly.
“Acetate and butyrate from digestion of fibre in the rumen are the building blocks of milk fat. Without sufficient fibre, rumen pH will drop and can lead to milk fat depression,” explains Dr Kirkland.
While high fibre ingredients such as straw are an effective buffer to slow down flow of feed through the digestive system, they also fill the rumen with low feed quality bulk that can compromise energy intake and milk protein. Digestible energy sources such as sugar beet pulp and soya hulls can be good choices in this situation.
“High starch energy supplements like cereals will lead to accumulation of acid in the rumen during fermentation, further compromising rumen pH and putting the animal at risk of acidosis, although caustic or other alkali treatment will help,” says Mr Habershon. “Instead, choose a rumen-protected fat supplement that will improve rumen conditions while providing a dense energy source. If unprotected, fatty acids will physically coat fibre and reduce fibre digestion. The dense energy provided by fat supplements also make them ideal during periods of hot weather to protect rumen function as forage dry matter consumption declines.”
It is now known that rumen-protected fat supplements with high levels of C16:0 fatty acids induce insulin resistance to increase partitioning of nutrients to milk. In return, milk and milk fat production will improve. When balanced with a source of rumen-protected C18:1 fatty acids, as with the calcium salt-type fat supplements, energy will also be directed to body condition while also helping improve egg and embryo development.
“An optimum balance of C16:0 and C18:1 fatty acids will not only help lift butterfat content and yield, but it will also support reproductive function to help get cows back into calf,” adds Dr Kirkland.
Preparing for late season grass changes
As the grazing season progresses, dairy producers also need to be prepared for the impact a change in grass quality can have on butterfat percentages.
“Throughout the end of July and into mid-August, the oil concentration in grass will begin to increase as it comes out of the reproductive (flowering) phase. The result will be a leafier, high oil grass that can trigger a similar rumen response as early-season grass,” concludes Dr Kirkland. “However, being prepared for this ahead of time by implementing an appropriate feeding strategy will help minimise any impact it has on milk quality.”
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