Milk components are the main source of revenue on dairy farms and vary with milk volume and fat and protein content.
Effect of nutrient supply on milkfat production
It is generally accepted that both milk yield and milk composition are affected by energy and protein supply.
However, from a study, researchers demonstrated that "fat content" was the only measured response not affected by dietary treatments.
Meaning, neither changes in energy or protein supply nor the associated changes in milk production affected milkfat content.
Fat yield on the other hand, increased with both energy and protein supply as a function of milk yield.
These results support the concept that as long as rumen function is not impaired, the cows will express their potential for milkfat content.
Milkfat content decreased by trans fatty acids absorbed from the rumen
From many years of studies, it is shown that milkfat depression is mainly due to production of specific "trans" fatty acids in the rumen due to microbial biohydrogenation of polyunsaturated fatty acids (PUFA).
There are 3 ways in which the amounts of trans fatty acids produced in the rumen, and risk of milkfat depression can be affected:
1) Alter the amount of C18 PUFA entering the rumen:
Milkfat depression is associated with feeding higher levels of unsaturated fats, found in oils and oilseeds.
Feeds such as alfalfa and grass or corn grain can also be substantial sources of PUFAs due to their fatty acid composition and level of inclusion in the diet.
2) Alter bio-hydrogenation pathways:
Milkfat depression has been associated with high-starch feeding, low rumen pH and the feeding of monensin.
3) Alter rates of biohydrogenation:
It is possible that diet induced changes in microbial population and rumen environment could also change the relative rates of biohydrogenation within different pathways.
Studies have also shown that increasing level of mono-unsaturated fat in the diet also increased trans fatty acid production.
Primary risk factors affecting milkfat content can be summarise as follows: feeding excessive amounts of non-rumen protected unsaturated fat, providing rations that lower rumen pH and feeding monensin, either individually or in combination.
Here are some ways to optimise milkfat production:
Limit unprotected fat sources. Limit the combined total of all unprotected sources of unsaturated fats including oils, oil seeds and byproducts such as distillers grains. Use rumen protected sources for supplementation.
Limit starch. Limit starch levels according to both the type of grain fed and its degree of processing to reduce rate of fermentation and ruminal acid load.
Provide sufficient NDF from forage. Formulate a minimum of 21% NDF from forage sources to maintain optimal rumen function and rumination.
Prevent ration sorting. Ensure that majority of forage particles are sufficiently processed.
Feed and push up feed more often. Feeding at least twice a day and pushing up feed regularly decreases the effectiveness of sorting behavior.
Use bi-carb and yeast. Studies have shown that bi-carb and yeast can enhance rumen function and support milkfat content, limiting the extent of drops in rumen pH following the feeding.
Pay extra attention when using monensin. Monensin has been shown to increase feed efficiency but it may also reduce milkfat content when fed at higher levels and in diets that increase rumen acid load.