Factors Affecting the Composition of Milk

The main constituents of milk are fat, protein, lactose and ash. The proportion of these constituents varies with type of milk. This variation in composition of milk is due to several factors such as species, breed, stage of lactation, feeding, etc. Cow,buffalo, goat and sheep milk are often consumed and have been studied in detail.

Some of the factors which affect the composition of milk are:

1. Species: The milk from various species of manmals have different composition(Table). This variation in milk composition is due to species effect.

Difference in milk composition due to species

2. Breed: Like species composition of milk is also determined by breed. Exotic as well as indigenous breeds differ somewhat in their composition. Within the different breeds fat is the major constituent, which is affected most. This variation in fat content in different breeds is evident from the data in Table.Generally milk containing a higher percentage of fat is also rich in solids not fat as vice versa Tables

Variation in the composition of milk of exotic breeds

Variations in composition of milk amongst
Indian breed of cows

3. Individuality of Animal: Under identical condition of management and feeding,within the same breeds, individual variations in the composition of milk always exist. These may affect milk components like fat or protein, which may be high or low. These variations have been attributed to the individuality of the animal.

4. Milking Intervals: Milking intervals also affect the composition and yield of milk. As a rule longer the milking interval lower is the fat content, which is compensated with a higher milk yield. However, variation in the fat content of both the individual and herd milk between the morning and evening bulk milk samples occur (Table).

Variation in fat content of milk due to the
time of milking (fat percent)

5. Milking Efficiency: Milking efficiency is a very important factor to obtain high milk yield and fat. As the udder is emptied during milking fat also increases.No appreciable differences other than in milk fat have been found between fore milk and strippings. The fore-drawn milk contain about 1 to 2 percent fat and as the milking progresses the fat content increases upto 6 percent or more in strippings. However, there seems to be a general relationship between fat percentage and solids-not-fat. The first portion is poorest in fat but richest in solids-not –fat but later portion is poorest in S.N.F. and vice versa (Table).

Variation is composition of different portions of milking

6. Stage of Lactation: The composition of milk varies with lactation. The first secretion after parturition, namely the colostrum is totally different from milk in its composition and general properties (Table ). Colostrum is very thick in nature with a high viscosity. It has a high concentration of immunoglobulin,lactoferrin, chloride and low lactose content. Its fat content may be higher or lower than that of milk. Colostrum from different cows and buffaloes varies much more in composition than does milk. With successive milking, the composition rapidly approaches that of milk, and the variability decreases.

The transition from colostrum to a composition within the range of variation of normal milk is complete in about 4 days, the protein content being slowest to complete the transition. The yield of milk increases to a maximum in early lactation and than falls to normal. When yield of milk increases, fat and solids-not-fat decreases and vice versa. This decrease is between 0.2 to 0.4 percent. The only change in lactose percentage attributable to stage of lactation is a slight decrease towards the end.

Because of low lactose concentration the osmotic pressure also remain low and in order to rectify the low osmotic pressure, the concentration of chlorides, sodium and soluble non-protein nitrogenous compounds, which restores the osmotic pressure to its normal level increases. Due to an increase in calcium towards the end of lactation it is a common experience that a salty taste may be detected in the milk of cows in advanced lactation. Calcium decreases to a minimum concentration and then increases, whereas total phosphorus remains constant throughout.

7. Feeds and Nutritional Level: Excessive feeding of fooder and concentrate is known to slightly increase solids-not-fat content in milk. Excessive protein in the feed does affect the protein content but may increase non-protein nitrogen content and sometimes fat. On feeding on pastures solids-not-fat content increases. The lactose content is not changed.

Rations low in roughages lower the fat content by 0.5% with no change in milk yield. Additional feeding with palm oil, butterfat, lard and coconut oil increases the fat percentage while cod liver oil lowers the same. Food fats modify the composition of milk fats to a limited extent. Feeding of minerals such as calcium and phosphorus does improve their level in milk.

8. Season: Seasonal variations are directly related to temperature, humidity, sunshine and drought. In summer months drop in milk yield occur with slight decrease in fat content. However, vitamin D content increases due to exposure to sunlight.During rainy season when green fodders are available in plenty carotene and riboflavin level increases. During the period of drought the solids-not-fat content decreases while there is no change in fat percentage. Fat content is highest in May and minimum in November while S.N.F is highest in October and lowest in July and September.

9. Disease: Disease adversely affect the composition. During infection of the udder with mastitis or foot and mouth disease there is lowering of lactose and casein. There is an increase in chloride content, increase in soluble nitrogen and reduction in natural acidity. There is also an increase in ash content.

10. Age of the Animal: With the advancement of age there is a slight decrease in fat content. An irregular decline in S.N.F also occurs. Within S.N.F, lactose and casein are the main components, which are affected. Maximum milk yield in milk occur from fifth to the ninth month of lactation. Age factor is highly effective with advancement of lactation.

11. Hormones: Injections of hormones such as prolactin and oestrogen is known to have a favourable role in enhancing milk production, fat and solids-not-fat content. However, excessive dose has a negative effect with depression of milk. These hormones enhance the metabolic activity of the body but excessive dose have a deleterious effect.

12. Heat or Oestrum: During the heat period the yield of milk and fat is slightly affected. This is due to the excitability and nervousness of the animal due to heat or hormonal secretion. Variations in fat occur due to the holding up of the milk by the animal.

13. Gestation: During the gestation period especially towards the end of lactation changes in milk composition occures. These variations are reflected in solids- not-fat content, which is increased. The composition is affected from fourth month onward.