High energy levels in fats make them useful for boosting energy intakes of cows, to increase production, improve fertility or condition at key times during the year. Unsaturated fats can be toxic to rumen microbes at high concentrations, so may adversely affect fibre degradation. Therefore, supplementary fats must be “protected” from rumen activity if they are to increase energy intakes.
There are four major types of “protected” fat products on the market, of different compositions and nutrient value, so it is important to understand the differences when deciding which product to use.
One option is to raise the melting point through hydrogenation, i.e. turning an unsaturated fat into a saturated fat, often referred to as a “hardened” fat. These fats consist primarily of three long chain fatty acids attached to glycerol, hence the term triglycerides.
Rumen microbes break the link between the fatty acids and glycerol, and use the glycerol as an energy source. The free fatty acids are then hydrogenated by the bacteria to pass through to the small intestine where they are absorbed. Ruminants absorb fats as free fatty acids not triglycerides. The digestibility of hardened triglycerides has been reported to be about two thirds or less that of free fatty acids, so their net energy levels are only about 65% that of those based on free fatty acids products.
Consequently, free fatty acids have been used in all the other types of protected fat products. One type popular in Europe (liquid milk market), contains high levels of palmitic acid which contains 16 carbon atoms (High C16). Although, it is highly digestible, it promotes milk fat in preference to body fat, making it less useful, when targeting improved body condition to improve fertility rates.
Another approach is to produce “calcium soaps” by reacting palm fatty acid distillate (PFAD) with calcium hydroxide. These products have lower fat (84%) and energy levels, as they about 12% ash, mainly as calcium. They start to dissociate below a pH of about 6, so may not be fully protected from rumen activity, particularly when grazing lush spring pasture. Calcium soaps are less palatable and have reduced feed intakes in many trials.
Hardened PFAD products contain roughly equal proportions of palmitic (C16) and stearic (C18) acids, which promote milk production and body condition. Hardened free fatty acid products are highly digestible, thus deliver the highest net energy levels without adversely affecting intakes.
As featured in NZ Dairy Farmer