Fat level in Milk and Profitability

The Fat and Solid-not -fat (SNF ) contents in cow milk are the two important constituents . The price of milk and consumer’s interest varies with milk components especially fat and solid -not- fat which may directly affect the farm income . The above factors not only fetches more profit but also indicates the Health and Nutrition of cows.

The Fat and SNF usually form the basis of payment to milk producers in India. Further , the composition of milk particularly the Fat has greater importance for dairy industry and the composition of raw milk determines the nutritive value and technological properties of milk and milk products. Knowing the composition of milk also helps to assess the adulteration and quality of milk for consumers and milk processing industries.

The Fat content in Holsein Freisian, Jersey and their crosses range from 3.4 to 4.5 %. While the milk of Holsein Freisian has 3.4 % fat, milk of indigenous cows of India like Red Sindhi, Shahiwal, Tharparker, Gir respectively contains 4.90 , 4.55 , 4.55 and 4.73 percent. The milk of Buffaloes in India contains as high as 7-8 percent fat.

The Fat level in milk is the main parameters that vary greatly both by Nutritional and many Non-nutritional reasons. Digestion of fibre in the rumen by microbes produces the volatile fatty acids (VFA) acetate and butyrate. Butyrate is converted to beta-hydroxybutyrate in the rumen wall tissue and provides energy for milk fat synthesis . About half of the fat in milk is synthesized in the udder from acetate and beta-hydroxybutyrate. The other half of milk fat is transported from the pool of fatty acids circulating in the blood. These can originate from body fat mobilization, absorption of fat from the diet, or from fats metabolized in the liver. Feeding cows with high energy and low fibre diets will reduce milk fat level.

Milk fat differs from other sources of animal fat in that it contains significant amount of short chain fatty acids and relatively lower concentrations of long chain fatty acids. About 50% of the fatty acids present in milk are derived directly from dietary long-chain fatty acids, adipose tissue and microbial synthesis of fatty acids. The second half of milk fatty acids is derived from de novo synthesis of short chain fatty acids, the precursor of which are acetate and butyrate. Therefore, milk fat composition is influenced by both end products of ruminal fermentation as well as the supply of dietary long chain fatty acids to the mammary gland.

Depression in Milk Fat content:

Milk fat depression is indicated by a decrease in milk fat by 0.2% percentage units or more . It is one of the very frequently encountered problems among milk producers in India .This problem fetches very low price for the milk .

I) Non-nutritional Factors

a) Stage of Lactation of cows:

Stage of lactation affects milk fat percentage. The fat level will be very low when the cow is at it’s peak production after calving and at third quarter of lactation b) Age of Cows:

The milk fat content will decrease with advance in age of cows. Milk fat falls about 0.2% each year from the first to fifth lactation c) Udder infection like Mastitis: Mastitis infected udder secretes milk with low fat. The Somatic Cell Count ( SCC ) in such milk will also be high. d) Sickness: Milk fat content is reduced in sick cows . Cows with ketosis an Sub Acute Ruminal Acidosis etc., will have low milk fat

II) Nutritional Factors affecting Milk Fat content

Milk fat can be changed by 0.1 to 1.0 percentage points by nutritional changes. Normal fat level in milk can be achieved by way of Nutritional management by feeding a balanced ration that meets the nutritional requirement of the cow

a) Forage level in Ration:

Rations for lactating cows on dry matter should contain at least 40 to 45% of forage. Low forage intake can cause a major reduction in the fat content of milk due to low fibre levels. The total forage fed to the cows should be at the rate of 0.9 % of body weight of the cow. In other words a correct Forage : concentrate ratio should be maintained

b) Level of Feeding:

Any condition that reduce feed intake will in turn reduce the fibre intake Vis-a- vis fat level in milk. Providing freshly harvested fodder, offering the ration in increased frequency, providing very comfortable environment to the cows will increase the feed intake and Vis-s vis milk fat in milk. If any change in the feed is to be done, it should be done gradually to facilitate the rumen micro organisms to get adopted. Weight loss in early lactation increase milk fat content for a short period of time. Milk in late lactation will have low milk fat.

c) Non-fibre Carbohydrates:

When the ration provided for the cow contains high grain ,highly digestible Non-fibre Carbohydrate ( NFC ) with and low fibre component, the milk fat will be reduced. Excessive amounts of NFC will depress fibre digestibility, which will result in reduced production of acetate(Short chain Fatty Acid) in the rumen of cow. This reduction in Acetate leads to low milk fat (1% or more reduction).

d) Fat level and the Fatty Acid composition in the Ration:

The ration should have 5- 6 % fat. The Milk fat level is reduced at higher level of dietary fat, especially with polyunsaturated oils. At high level of fat or oil the rumen microbes will be affected and fibre digestibility and Vis-à-vis milk fat level is reduced. If fat or oil is rancid, milk fat content will further decrease even at low levels of consumption.

The extent to which dietary fat alters the fatty acid composition of milk fat is influenced by:

Fatty acid composition of dietary fat 2)The extent of hydrolysis and biohydrogenation of unsaturated fatty acids by ruminal microbes 3) Effect of dietary fatty acids on de novo synthesis of short chain fatty acids by the mammary gland 4) The extent of conversion of saturated fatty acids to mono-unsaturated fatty acids (mainly C18:0 to C18:1) as a result of intestinal and mammary gland desaturase activity.

Feeding oil seeds such as sunflower has been found to reduce the concentrations of short (C4-C10) and medium chain (C16:0) fatty acids and increase the concentrations of C18:0 and C18:1 fatty acids. The inclusion rate of oils seeds in dairy rations is limited by the negative impact of polyunsaturated fatty acids on ruminal fibre digestion. In general, the maximum inclusion level oilseeds should result in 3-4% added dietary fat. At a higher inclusion of fat or if a greater change in the concentration of unsaturated fatty acids in milk is desired, some form of protection (e.g. heat treatment) should be applied to avoid negative effects on fibre digestion in the rumen.

To prevent depression in milk fat

a) By-pass Fat:

Maintain 5-6 percent of fat in the ration. To further increase the energy level the diet fat may be added to the diet only up to 7% in the total ration . For this fat and oil can be added not in their original form, but as calcium salts of fatty acids, ( By-pass Fat ).These bypass fats bypass microbial digestion process in the rumen and undergoes enzymatic digestion at intestine .This technology not only avoids adverse effect of oil on fibre digestion but also provide the fatty acids in their original form. It is well established that feeding of bypass fat to early lactating cows not only increase the milk fat content but also helps in early conception after calving. The Bypass fat products should contain 4-5 % moisture,80-85% fat ,7-9% Calcium and provide 80% protection to the fat from microbial degradation in the rumen.

For crossbred cows the Bypass fat should be added at the rate of 100 -150 grams and for Buffaloes at the rate of 150-200 grams per day.

b) Bypass starch:

Rapid fermentation of starches in the rumen of cows causes a drop in ruminal pH and lower milk fat percentage because synthesis of milk fat in the mammary gland is disrupted. Cows will choose to eat the starch portion before the fibrous portion of their feed. Hence the forage allowance be fed to cows first followed by Concentrate allowance.

c) Feed enough fibre:

Rations for lactating cows on dry matter should contain at least 40 to 45% of forage or 0.9% of body weight. The NDF in total ration should be about 35% of the ration.

d) Restrict the grain or soluble carbohydrate component at less than 1% of the body weight.

e)?Forage concentrate:

A ration with ideal Roughage to Concentrate ratio (60 : 40) of proportion of the concentrate in the ration maintains milk fat . Feeding high Concentrate feed reduces milk fat . This is mainly because of the lower ruminal production of acetate and butyrate (precursors of milk fatty acid synthesis in the mammary gland) associated with feeding high concentrate diets.

f) The extent of milk fat depression is influenced by other feeding practices such as frequency of feeding and feeding system. Feeding cows less frequently especially if the concentrates are fed separately from the forage results in a reduced ruminal acetate: propionate ratio which in turn can result in reduced milk fat %. In general, the impact of feeding high levels of concentrates on milk fat % will be less where total mix rations are fed and / or if feed is offered three or more times daily.

g) It is better to feed the high yielding cows in 8-10 meals and medium yielders in 4-5 meals. Feeding cows in increased frequency daily will prevent milk fat depression, but will not recover cows that are already experiencing milk fat depression

h) Supplement the cows with Sodium bi carbonate (NaHCO3) buffers to cows fed with high grain or low roughage ration. The NaHCO3 is generally recognized as an efficient buffer because of its high acid-consuming capacity in the rumen, and its mode of action is well documented . The buffers prevent decline of milk fat.

i) If any change in the feed is to be done it should be very gradual giving enough time for the rumen microbes for adoption. Usually the Milk Fat Depression occurs within 7-10 days following a dietary change and 10-14 days is expected to recover milk fat to normal levels

j) Milk Fat depression on account of High grain ration is induced by 3-5 d, and recovery achieved at 15-19 d.

k) During the recovery period offer a diet with increasing NDF and decreasing Poly Unsaturated Fatty Acids . These measures will modify diet fermentability.

l) The ruminal fungi and ciliate protozoa population decrease by more than 90% during the milk fat depression phase and increase during the recovery phase. The Protozoa play a major role in altering the rumen environment by engulfing large amounts of fermentable starch

m) Supplementing ionophores like Monensin not only increase milk yield but also reduces prevent acidosis ( Acidosis predisposes fall in milk fat level )

n) Forage particle size (forage processing): Feeding finely chopped forages has a negative impact on milk fat % and may cause milk fat depression syndrome (drop of milk fat % below 3%). Cows fed finely chopped forages spend less time chewing and therefore will produce less saliva. Ruminal pH will drop as less saliva is produced to buffer the acid production in the rumen. As the ruminal pH drops below 6, the activity of the cellulolytic bacteria is reduced and so is the production of acetic and butyric acids (precursors of short chain fatty acid synthesis in the mammary gland.

o) Only 80% of the fodder should be fed in chaffed form and the rest 20% fed as un chaffed

p) Do not feed gruels and very finely ground carbohydrate sources

About the Author

Prof Dr M Murugan- Consultant, Animal Nutrition,?Animeta AgriTech YourFarm. Former Dean, Tamil Nadu Veterinary and Animal Sciences University, Chennai. Animal Nutrition Specialist with 35+ years of experience in the field of Teaching, Research and Technology transfer to farming communities. His field of Research is Fodder production with special emphasis to Agroforestry systems and the class of livestock is small ruminant. Dr. M.Murugan has published 43 Research papers in both National and International Journals. He has also published 45 Popular articles ,authored 5 books and 2 manuals. His research articles are cited in several text books. He is the member of several Professional bodies like Indian Poultry Science Association Dairy Technology Society of India , Animal Nutrition Society of India and Tamil Nadu Veterinary Council.