ANN 121: Applied Animal Nutrition-I (2+1)

NUTRIENTS REQUIREMENT FOR THE LACTATING COW

• The nutrient requirement of the dairy cow for milk production depends upon the amount of milk being produced and upon its composition.

Milk Yield

• The yield of the cow is decided primarily by the breed of the cow. Older cows tend to have higher yields than younger animals but the main short-term factor affecting milk yield is the stage of lactation.
• Yield generally increases from parturition to about 35 days post partum and then falls regularly at the rate of about 2.5 percent per week to the end of lactation.
• Peak yield may be calculated as 1.1 times the yield recorded two weeks post partum. eg,a cow yielding 23 kg at this time could be expected to have a peak yield of 25 kg.

Energy requirement for lactation

• The energy standards for milk production is derived factorially. This involves an estimate of the gross energy value (EV_l) of the milk, which may be used along with the yield to estimate the net energy requirement for milk production.

  

Energy requirements

• Energy requirements for milk production are based on the composition of the milk and milk yield and the efficiency of conversion of dietary energy into milk energy. Generally, the energy requirement increases with fat content of milk.

Lactation energy requirements

• The NE required for lactation (NEL) is defined as the energy contained in the milk produced. The NEL concentration in milk is equivalent to the sum of the heats of combustion of individual milk components (fat, protein, and lactose). The reported heats of combustion of milk fat, protein, and lactose are 9.29, 5.71 and 3.95Mcal/kg, respectively.
• Milk lactose content is the least variable milk component and is essentially a constant 4.85 percent of milk and varies only slightly with breed and milk protein concentration
• Usually animals produce milk with varying fat (percentage) content and the number of liters of milk produced by dairy cattle may also vary from 2-20 liters or more per day. So the milk yields are adjusted to a 4% fat equivalent in case of cattle or 6 % in case of buffaloes to compare them on an equal-energy basis.
• Gaines Formula for 4% fat corrected milk (FCM) kg = (0.4 + 0.15F) X M Where F = Fat % in the milk produced by the animal M = Quantity of milk produced/day

Protein requirement

• Milk secretion represents a direct loss of protein to the animal body which needs to be replaced. Estimates of the efficiency of utilization of digestible protein for milk production vary from 60 to 70%;
• In the ruminants, dietary protein performs two functions :
• It must satisfy the nitrogen demands of the rumen microorganisms.
• It must supply the absorbable true protein required to satisfy the demand for amino acid nitrogen at tissue level.

Metabolisable protein requirement

• The metabolisable protein requirement may be defined as the quantity of truly absorbable true protein required to satisfy the demand for amino acids nitrogen at tissue level.