The diet of high producing crossbred cows is usually deficient in energy during transition period (3 weeks before and after parturition) and early lactation. The animals are not able to eat more during advanced stage of pregnancy; therefore we need to increase the energy density of their ration with minimal changes in dietary forage to concentrate ratio and fibre intake. It improves the energy balance that leads to an improvement in reproductive 
efficiency and the metabolic health of the cow. If the cows require additional energy, then the supplementation of fats may be useful provided dry matter intake is not compromised. Fat supplementation has little effects on rumen fermentation, as indicated by the acetate to propionate ratio but the fat from different sources had variable effects. Unsaturated fatty acids, especially in the non-esterified form, are toxic to rumen microbes and may decrease fibre degradation in the rumen. If the energy dense ration is not offered to the animals then they may lose more body weight after parturition due to negative energy balance (NEBAL). Such animals are very weak and come into heat with great difficulty. They are also prone to several metabolic disorders like fatty liver, ketosis, displaced abomasum etc. The delayed conception in such cases leads to longer inter-calving periods in cows.
These animals produce less milk after parturition which leads to great economic losses to the dairy farmers. There is a practice of offering raw vegetable oils to cows by our farmers which is not reasonable. Just 2% vegetable oil in the diet can dramatically reduce rumen fiber digestion. Unprotected fats cause physical and chemical changes in the microbial fermentation of the feed and depress rumen cellulolytic microbial activity. The supplementation of the raw vegetable oils is detrimental for the health of cows after a certain limit as it affects the digestion of fibres adversely in the rumen. Therefore, we need to supplement fats in such a way that it doesn’t interfere with its digestion in the rumen. Rumen bypass or “protected” fats are in fact, the dry fats which are processed to be easily handled and mixed into all animal feeds. Dry fats are mostly insoluble at rumen body temperature due to the high melting points. Just to summarize, dry fats are not as much “protected” as completely insoluble in the rumen but they have little impact on rumen fermentation. Bypass fat is generally used to increase the energy density in the ration of cows. Bypass fat gets digested later in the abomasum or true stomach of ruminants as it is not affected by the rumen microbes. Thus bypass fats are very useful in improving not only the body condition score of the weaker animals but also increase the productivity of milk. Bypass fats are made up of fatty acids linked to calcium ions instead of glycerol backbone. By virtue of this association bypass fat becomes inert to the rumen microbes and escapes fermentation. It has low solubility and less susceptible to bio-hydrogenation by microbes. The bypass fat has 4-5% moisture and 7-9% calcium while the remaining part is protected fat. Calcium salts of fatty acid are produced by the double decomposition and fusion methods. The calcium soaps are insoluble in rumen pH of 6.2-6.8 but these are soluble in the abomasum where the pH stays between 2 and 3. In double decomposition method, fat source is heated in a metal container followed by addition of aqueous sodium hydroxide solution with constant stirring until the fatty acids are dissolved. Thereafter, the calcium chloride solution is added slowly with constant stirring, while the contents are still warm. It leads to the precipitation of calcium soaps. The calcium soap is dried at low temperature and grounded before mixing into the ration. Different varieties of bypass fats may differ slightly in their palatability. Calcium salts of palm oil have pungent odour and slightly bitter taste. Animals that have not any previous exposure to these fats may require an adaptation period. In addition to this, a care should be taken to ensure the mixing of products thoroughly into the ration, so that the feed intake is not affected. Most classes of bypass fats are handled and mixed into dairy feeds with relative ease.
The crossbred cows may be offered prilled fat (a bypass fat) @100g/d while the buffaloes may be offered @150g/day during postpartum periods. It can be safely fed to the growing calves also. The bypass fat may be added as 1.5-2.0% of the feed intake. This is sufficient to increase the energy density that meets all the requirements of the body. The bypass fat has many advantages to the animals such as-
1. It increases the amount of energy in the feed so that the animals seldom come under negative energy balance especially during the period of transition and early lactation.
2. It meets the energy requirements of the high producing animals without any problem.
3. It not only increases the milk production but also improves the persistency of lactation.
4. Animals in positive energy balance have better reproduction ability through early heat symptoms and better conception rate.
5. It increases the overall productive life of animals.
6. It helps to control many metabolic disorders like ketosis and milk fever in the high producing animals.
7. It can positively affect the efficiency of dairy cows through a combination of caloric and non-caloric effects
Now-a-days prilled fat is used as a bypass fat which is a non-hydrogenated vegetable oil and consists of more than 85% palmitic acid with high melting point. Saturated fats like animal fats, palm oil have a higher melting point between 50-60°C in contrast to the temperature of 38-39°C in the rumen that is why prilled fat is not affected by the ruminal temperature and pH. It rather bypasses rumen degradation and is digested in small intestine by the enzyme called lipase. Prilled fat is prepared by liquefying mixture of fatty acids by spraying it under pressure into the cooled atmosphere. Prilled fat remains inert in the rumen and resist hydrolysis and association with the bacterial cells within the feed particles. Thus total supplemented energy in diet of a lactating animal is available for the productive processes. The prilled fat is economical to buy and highly palatable to animals. The supplementation of prilled fat can be used to augment lactation performance without affecting milk composition, plasma metabolites and hormonal levels in dairy cows. The experiments conducted under field conditions have demonstrated an increase of 10-15% milk in crossbred cows with the supplementation of prilled fat which translates into a profit of Rs 80-120/- per day per animal for the dairy farmer.
by Ashwani Kumar Roy, Mahendra Singh and Meeti Punetha
National Dairy Research Institute, Karnal (Haryana)
