Dr Asim Faraz and Dr Abdul Waheed
Department of Livestock and Poultry Production, FVS, BZU Multan
Corresponding Author’s Email: drasimfaraz@gmail.com
As health concerns continue to emerge, the nutritional image of bovine milk fat, especially of buffalo milk, has suffered a lot because of the association of saturated fatty acids with coronary heart diseases. Forages, despite containing a relatively low level of lipids, are the cheapest and major source of beneficial unsaturated fatty acids in ruminant diets. As a major consumer of milk higher in fat content, we should have knowledge about the butter fat contents of milk and how it is affected by forage feeding. Forage is a type of animal feed, in which any agriculture foodstuff is used to feed domesticated livestock such as cattle, buffalo, sheep, goat, camel and equines. Common forages grown in Pakistan are lucerne, burseem, oats, maize, barley, wheat, sorghum, millet etc.
After the fermentation of forages in the fore gut (mainly rumen & reticulum) the end product formed is VFA’s which are absorbed by the rumen & reticulum wall especially via villi. These VFA’s (mainly acetic, propionic and butyric acids) contribute the milk fat synthesis. The fatty acids in milk occur almost entirely as triglycerides not from phospholipids in plasma. Milk fat mostly arose from short chain fatty acids derived from triglycerides in plasma. Triglycerides are the precursor of milk fat. Mammary glands can take palmitic and stearic acids from the blood plasma and also lauric, myristic and oleic acid if they are present. The fatty acids in milk are synthesized from acetic acid (from butyric to palmitic acid). Some of lower ones can be synthesized from beta hydroxybutyrate. It has been established that the amount and kind of fatty acids in the diet and thus in the blood plasma have a larger influence on the amounts and proportions of specific ones in milk fat.
Normal fat concentration ranges from 5.5-7.5%. Fibrous diet produces more relative concentration of lower VFAs which contribute to the milk fat. Low intake of roughages has a marked affect in lowering of milk fat. Milk fat precursors are acetic acid, triglycerides and beta hydroxybutyrate. A decrease in acetic acid lessens the short chain fatty acids synthesis. While a decrease in triglycerides lowers the production of C 16 and higher acids. Since propionic acid has an anti ketogenic action, its increase in concentration in blood decrease the beta hydroxybutyrate concentration which is also precursor of lower fatty acids.
Milk from animals fed/grazed on fresh forage, especially from species rich or legumes has a considerably higher ratio of unsaturated fatty acids to saturated fatty acids and higher contents of nutritionally beneficial trans-fatty acids (e.g. CLA, vaccenic acid) than milk from animals fed silage or hay. Grass and legumes silage seem to affect the fatty acid profile more propitiously than maize silage.
