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Milk Composition & Synthesis
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Milk Synthesis

Carbohydrate Metabolism

In nonruminants, glucose is absorbed through the intestine and is the major source of metabolic energy and short carbon chains.
In ruminants, fermentation of dietary carbohydrate in the rumen results in formation of volatile fatty acids (VFA's): Especially, acetate, propionate, and butyrate.

Regardless of the source or origin of glucose -

***Glucose is absolutely essential to the mammary gland for milk synthesis.***

***It can not be replaced with any other sugar.***

Leaving out acetate or amino acids as substrates in a perfused mammary gland primarily decreases milk fat and protein output, but does not alter milk yield by the gland very much. This suggests that secretion of lactose, fat and protein are somewhat independent of each other.

Glucose can be a limiting factor to maximum milk secretion under normal management. For example, in high yielding goats, intravenous infusion of acetate has no effect on milk secretion. However, infusion of glucose increases yield by 62%, increases milk lactose yield by 87%, but results in no change in milk fat. The lactating mammary gland of a high yielding goat uses 60-85% of the total body glucose. The correlation between milk yield and mammary uptake of glucose is about 0.93.

Low producing cows do not utilize as high a percentage of body glucose as high producers. Infusion of glucose into the dairy cow can increase milk yield. However, this may be partially offset by decreased endogenous glucose availability.

Milk Composition & Synthesis