Energy, the single largest nutrient requirement of most lactating dairy cows, is often in short supply for several weeks after cows calve. In this state of “negative energy balance,” high milk-producing dairy cows cannot consume enough forage and grains to make up the deficit, and breakdown their own body reserves to cover the energy shortfall.
Such a heavy reliance upon mobilizing body fat often leads to long-term and sometimes deadly metabolic disorders such as ketosis and fatty liver syndrome. Furthermore, the longer the energy deficit lasts, the more health problems occur and unstable early-lactating cows take longer to get back into a satisfactory dietary position. At this point, dairy producers cannot simply increase the amount of grain fed, because excessive grain feeding threatens sensitive rumen health and usually depresses economically important milk fat levels. Instead, one practical and safe option is to increase the dietary energy density of diets by mixing a good source of edible fats into the ration.
After these edible fats (and oils) are inadvertently consumed by the dairy cows on the milkline, it is digested and absorbed as a high-energy source in their small intestine with little actual digestion by the rumen bugs. Most dairy research demonstrates a positive effect upon milk production, milk persistency and a general reduction in body condition scores of dairy cattle often during the first 100 days of lactation, when diets are effectively balanced with supplemental energy from a variety of fat sources.
Common fat supplements available to high-producing dairy cows include oilseeds such as full-fat soybeans and whole sunflower seeds (20-40 per cent fat) as well as 100 per cent animal fat sources, namely pork tallow and canola oil. A third group of dietary fats for dairy cows are commercially made and are called “bypass” fats. Most dietary fat and fat-enriched feedstuffs typically supply more than 2 times the caloric intake of feedstuffs found in carbohydrates (barley or corn starch) when given comparable amounts to feed milking dairy cows.
The overall rule for adding fat supplements to an early lactation ration is take in to account all existing natural fat sources and add in these latter fats; making sure not to exceed five to six per cent total fat of the entire ration.
One can follow this rule by breaking the dairy diet down into 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 = three pounds or six per cent total fat
Not only is it important not to exceed the total amount of fat, but be careful not to feed too much of one type of fat supplement. Most supplemental fats (see above example) are often long chains of fatty acids linked to a triglyceride molecule. These fatty acid chains are either 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 by rumen bacteria and are digested in the lower digestive tract. In contrast, unsaturated fats interact and are relatively toxic to rumen microbes, particularly those forage fibre-digesting bacteria.
Fortunately, most rumen microbes can detoxify and reduce the toxic effects of unsaturated fats through a process known as “biohydrogenation” (re: hydrogen is added to the unsaturated fats and turns them into saturated fats). However, large amounts of unsaturated fats and oil added to a diet can overwhelm this process and as a result interfere with rumen fermentation. One consequence of feeding too much unsaturated fats to early-lactating dairy cows is significant milk fat depression. Therefore, when feeding ingredients of high natural unsaturated fat content, such as distillers’ grains (10 per cent fat), full fat soybeans (20 per cent) or sunflower seeds (20-40 per cent); many people often limit the amount of unsaturated vegetable oil as illustrated in the above sample diet.
Many dairy producers have avoided such unsaturated fat perils by either limit-feeding it or forgoing altogether. Some people have also turned to special commercial bypass fats that are designed with three specific feeding features: (1) a highly concentrated energy source (2) chemically inert in the rumen and (3) easily digested and absorbed in the lower gut. Consequently, manufacturers of bypass fats do this by offering a wide range of inert fat products, which include hydrogenated saturated tallows, prilled free fatty acids or encapsulated or ruminal protected unsaturated fats. Another group of commercial bypass fats achieves rumen protection by locking similar fatty acids chains to a calcium molecule to form “calcium soap.”
Regardless of the kind of fat supplement used, it is still important to follow all rules necessary to provide a well-balanced diet. Of particular importance is meeting all necessary fiber requirements for dairy cows, which maintains a 20-22 per cent effective fibre level (eNDF) and an acid detergent fibre (ADF) level of 19-20 per cent in the diet to assure good rumen fermentation function and to counteract any adverse effects of feeding unsaturated fats. Some nutritionists go one step farther and add more bypass protein to the diet, so slightly higher protein requirements caused by the addition of bypass fats are met.
Such attention to the nutritional details of an early lactation diet for dairy cows, almost guarantees their milking success while they are going through one of the most difficult nutritional periods of their lactation cycle. They might be saddled with “negative energy balance,” but the proper addition of high energy fats to their post-calving diets tends to lead them toward significantly better energy intakes, producing better performance and ultimately more profitability.
PeterVittiisanindependentlivestock nutritionistandconsultantbasedinWinnipeg. Toreachhimcall204-254-7497orbyemailat [email protected]