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Dietary fat – the importance of taking the right pathway

10 April 2017

Nutrition plays an important role in manipulating milk fat and, with turnout approaching, producers should review diets to avoid drops. Trident Feeds investigates the potential negative effect of turnout on milk composition and steps farmers can take to mitigate its impact.

“Grass is a huge feed resource for dairy farmers, and has the potential to greatly improve profitability over the grazing period. However, this is only possible if grazing is managed proactively to ensure effective utilisation of high quality pasture. The effects of grazing on milk fat can be significant and therefore it’s important to have a strategy in place to maintain milk production, body condition and milk fat over the summer,” says Will Tulley of Evidence Based Veterinary Consultancy.

“The main issues with grazed grass are that it’s high in polyunsaturated fatty acids and rapidly fermentable carbohydrates, and it’s low in structural fibre. These factors can all have a significant impact on rumen function, which can alter the process by which the rumen metabolises dietary fats,” adds Will.

He explains how traditionally, milk fat depression (MFD) was associated with a lack of effective fibre which was reported to reduce the precursors of butterfat synthesis, mainly acetic acid. However, this has been disputed by research as the sole explanation, because although acetic levels can drop, it’s been proven there are still sufficient volatile fatty acids (VFA) for milk fat production. 

Therefore, while not a limiting factor, the role of fibre in diets has been correlated with milk fat percentage, as it maintains positive rumen conditions, especially the balance of the appropriate micro-organisms to produce milk fat precursors.

“Fat appears in the milk through two routes. Approximately half is absorbed from the intestine as fat from dietary components, or part of the rumen microbes as they’re digested, with a small additional contribution from the breakdown of the animals’ fat reserves. These travel via the circulation to the mammary gland, where they’re used to produce milk fat. The balance of the milk fat is synthesised in the mammary gland by utilising volatile fatty acids that are produced in the rumen, primarily acetic acid, from the blood,” he says.  

However, Will explains the significance of rumen conditions in determining milk fat levels. “The rumen microbes will always use hydrogen to turn unsaturated fats into saturated fats, via intermediary fat compounds, as unsaturated fats are toxic to many of rumen microbes.

“There are two routes which this process can take and ultimately they both produce the same product, a largely saturated fat, which can be used for milk fat. The problem is that the intermediary compounds produced in the rumen ‘detox’ pathway, can inhibit subsequent milk fat production in the udder, so steps should be taken to minimise this route.

“For instance, if you lower rumen pH by feeding a low fibre, highly fermentable sugar carbohydrate, and polyunsaturated fat diet, which are typical characteristics of grazed grass, you will push rumen fat metabolism down this less desirable pathway. This will result in the production of intermediary compounds, e.g. trans 10, and the main culprit, cis 12 conjugated linoleic acid (CLA).

“If this compound passes out of the rumen and into the circulation it has a very direct and profound negative effect on butterfat synthesis, because it alters gene expression within the udder, which is where approximately half of milk butterfat is produced.

“Therefore, to reduce the effects of turnout on milk butterfat levels, diets should be formulated to minimise changes to the rumen environment, to avoid the production of the detrimental intermediary compounds,” explains Will.  

He adds that at turnout, farmers must ensure that they feed a high proportion of forage with a sufficient digestible and structural fibre fraction; moderate amounts of supplementary feeds such as confectionary and biscuit meal which are high in free unsaturated oil, which can affect the rumen environment, in favour of non-forage fibre sources, e.g. sugar beet feed and soya hulls; increase particle size of blends and straights; and feed a rumen buffer. However, producers can additionally consider using a rumen-protected fat product to increase butterfat production.

“A C16 saturated fat by-passes the ‘detox’ process in the rumen, and more moves directly to the udder as a preformed carbon 16 fatty acid, which can instantly increase milk butterfat levels,” says Will.

He adds that when planning ration changes to maximise milk solids production, it’s also important to consider the overall likely impact on yield and the associated feed costs.

Bethany May, ruminant nutritionist at Trident Feeds, supports Will’s comments, and explains how a palatable C16:0 rich protected fat can immediately improve milk butterfat levels with only positive impacts on milk yield.

“There has to be financial gain if you’re investing in C16:0 products, as they may at first appear a costly way of maintaining milk butterfat levels. However, we’ve seen cases where there’s opportunity to lift butterfat percentage, drive yield and increase net profit by up to 22p/cow/day*.”

This is because a C16:0 rich product, like Butterfat Extra, will increase the amount of free fatty acids available directly to the mammary gland without the need for energy expensive body fat depletion and subsequent repletion.

“A good production response to Butterfat Extra can increase butterfat percentage by around 0.4% and lift milk yield by up to one extra litre,” adds Bethany.   

“In terms of return on investment, feeding 400g of Butterfat Extra to a 30-litre cow could increase net profit by up to 22p/cow/day. Based on a 200-cow herd, this would mean an extra profit of £6,600, for the first 150 days of lactation*.”

Will supports Bethany’s view, but reiterates that the use of any specific products to maximise production should be carefully costed, to ensure that there will be a financial benefit.

“Producers should pay close attention to rumen health prior to turnout and put steps in place to prevent any negative effects on milk composition, and where there is opportunity the value of milk should be maximised to hit premiums.”

* Prices of fat are correct only at time of publication and are subject to change

Will Tulley, Dairy Vet and Head of Farm Consultancy at Evidence Based Veterinary Consultancy

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