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Avoid too much fat for early-lactation cows

In the last year, there has been a few supply-management incentives for dairy producers to increase milk and milk fat yield in their milk cows. Because nutrients such as energy largely drive dairy performance, many people are increasing dietary energy density by adding different types of edible fats to early lactation diets. Despite being a successful way to meet incentive days/cover-offs; dairy producers should be aware of the dire consequences of feeding too much fat to dairy cows, while insuring that maximum feeding limits are always followed.

Adding safe amounts of edible fat to total mixed rations (TMRs) of early-lactation cows has been common advice given by dairy nutritionists and veterinarians for years. It is effective in eliciting positive milk and milk fat persistency and often slows down rapid weight loss in dairy cattle during the first 100 days of milk production.

That’s because dietary fats contain more than 2-1/4 times the calories of those found in carbohydrates (barley or corn starch). Common fat sources include oilseeds such as full fat soybeans and whole sunflower seeds (20 to 40 per cent fat) and 100 per cent fat sources, namely pork tallow and canola oil. A third group of dietary fats are commercial manufactured “bypass” fats.

The overall rule for adding these fat supplements to an early-lactation dairy ration is take in account all the natural sources of fat already present and add in these latter fats; making sure not to exceed five to six per cent total fat of the entire dairy diet. One can follow this rule by breaking the dairy diet down into three sections:

  • 50 lbs. of forages mixed with defatted proteins (soybean or canola meal) and grains contains three per cent natural fat — 1.5 lb.
  • Supplement vegetable oil or tallow (100 per cent) — 0.75 lb.
  • Supplement inert rumen-protected fat (99 per cent) — 0.75 lb.

Total = 3.0 lb. or 6.0 per cent total fat

The chemical structures of unadulterated fats found in forages, grains, and pork tallow and canola oil are very similar. Long chains of fatty acids are linked to a triglyceride molecule or exist as free fatty acid chains. The fatty acid chains are of two types, either saturated or unsaturated.

Saturated fatty acids are “saturated” with hydrogen atoms, while unsaturated chains have one or two hydrogen atom pairs missing. Saturated fatty acid chains pass through the cow’s rumen largely untouched, and are digested in the lower gut. Pork tallow contains about 50 per cent saturated and 50 per cent unsaturated fatty acids while canola oil is almost completely made up of unsaturated fatty acids.

There is a limit

Generally unsaturated fatty acids such as found in canola oil are relatively toxic to rumen microbes, particularly forage-fibre digesting species, but that doesn’t mean that canola oil and other unsaturated vegetable oils should not be fed to dairy cows. Fortunately, most rumen microbes have the ability to detoxify and reduce the toxic effects of unsaturated fats through a process known as “bio-hydrogenation” (re: hydrogen is added to the unsaturated fats and turns them into rumen-protected saturated fats). However, excessive amounts of unsaturated fats and oil added to a dairy diet (re: over one pound or 450 g/head/d) often overwhelm this process and as a result interfere with rumen fermentation.

To compliment added saturated and unsaturated from natural feedstuffs in early lactation diets, commercial “rumen bypass” fats are designed to be chemically inert in the rumen, to be digested and absorbed as energy source in the cow’s lower gut. One group of bypass fats achieves protection by locking the fatty acids chains to a calcium molecule to form a ruminal insoluble calcium salt. This bond is broken during digestion in the small intestine. Another group of bypass fats hydrolyzes normally unsaturated fatty acids (such as palm oils) into rumen inert saturated fatty acids.

Regardless, the kind of fat supplement finally chosen and added to the dairy diet, it is important to avoid overfeeding fat in one capacity or another to lactation dairy cows. It is also important that these dairy diets still be balanced with available carbohydrates such as sugar, starch and effective forage fibre (20 to 22 per cent eNDF) in the diet as well as protein, minerals and vitamins in order to support health and normal activities of the resident microbes in the rumen.

Problems to avoid

Here are problems that might be experienced when feeding excessive fat to lactating cows:

  • Inconsistent and/or low dry matter intake — Some research indicates overfeeding fat to dairy cows may quickly satisfy their natural appetite for feed (much like us eating a greasy hamburger and fries). Some speculation may also involve reduction in the rate of feed digestion and passage (bypass fats) in the lower gut. Other explanations might involve digestive upsets in the rumen (unsaturated fat toxicity).
  • Milk fat depression (MFD) — As mentioned, unsaturated fats are toxic to many fibre-digesting rumen bacteria; cause reduction in acetate/butyrate production that contributes to milk fat production. It is also believed too much tallow or vegetable oil can coat forage fibre particles in the rumen and allow incomplete fermentation. On a different note: University of Illinois demonstrated that two to four per cent tallow caused acidotic conditions in the rumen of dairy cows fed corn silage and MFD, but both conditions were alleviated when corn silage was replaced with an alfalfa-based diet.
  • vHigh milk urea nitrogen (MUN) — It is conceivable that supplying too much bypass fat to the lower gut, while literarily starving the rumen microbes of available starch energy could cause incomplete protein digestion and large amounts of urea to be released in the rumen. High MUN levels are linked to lower conception rates in dairy cattle.

Such quantifiable adversity might not occur if dairy diets are well balanced with just the right amount of fats coming from different edible sources. Adding any fats should also complement the rest of the dairy diet, particularly for early lactation cows, which helps them get a good start with milk and milk fat production. Such success should contribute to the profitability of the dairy barn.

About the author


Peter Vitti is an independent livestock nutritionist and consultant based in Winnipeg. To reach him call 204-254-7497 or by email at [email protected]



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