Effect of Nutrition on Milk Components

Nutrients and milk composition

Nutrition has an impact on milk composition. Cows ferment the complete ration in the forestomach with the help of billons of microbes. The different fermentation products from those microbes determine the composition of the milk, including milk protein, milk lactose and milk fat (Figure 1).

Milk Fat

The milk fat content is determined by the acetic and butyric acid production from rumen fermentation, constituting 50% to 60% and 12% to 18% respectively of the total VFAs. Diet and status of the methanogenic population in the rumen greatly influence the proportion of VFAs. Diets with a high starch content reduce the absolute and relative concentrations of the milk fat. From this point of view, a balanced ration is needed to ensure cows produce as much milk fat as possible while also securing a healthy rumen. Rumen acidosis must be avoided. Besides the absolute milk fat content, the composition of the fatty acids inside the milk fat are of interest and can play a role in the interpretation of the health status of a cow. Only 40% of milk fatty acids are produced directly out of carbohydrate degradation in the rumen. The remaining 60% of the milk fat are produced over metabolomics synthase from VFA’s of the digestive tract and free non-esterified fatty acids from body fat degradation. Both milk fat content and composition are therefore influenced by the feedstuffs (fiber, carbohydrates, fats). In addition, the milk fat composition is affected by a variety of complex factors, including the metabolic health of cows. An excess of long-chain fatty acids (resulting from fodder fat and body fat degradation) in the blood limits or prevents de novo synthesis of short- to medium-chain fatty acids. Milk fat content can thus be influenced by multiply factors.

Milk Protein

Several factors influence milk protein production in dairy cows. These factors consist largely of the genetic potential of the cows, how the cows are managed, and the diet. Of all the dietary nutrients that impact milk protein synthesis, energy, as well as the optimal supply of usable crude protein, are by far the most important. Increasing the energy intake of a dairy cow increases both the yield and concentration of milk protein. Understanding how each of the diet components influences milk protein synthesis is critical to maximize efficiency and production. The type of energy supplied in the ration has a significant effect on lactation performance. Carbohydrates represent the bulk of the energy components in the ration and are present on a scale from non-degradable, i.e. passing through the gastrointestinal tract unaltered, to slowly and rapidly fermentable, which are broken down by rumen microbes. Ruminal carbohydrate fermentation generates propionate, acetate, butyrate and lactate VFAs. Changes in the forage to concentrate ratio in the diet have been shown to influence milk protein yield in dairy cattle. When fed either a high-forage or high-concentrate diet, milk protein yields tend to be depressed, while a forage to concentrate ratio closer to the median elicits a greater milk protein yield. Rations that are higher in more rumen-fermentable carbohydrates can lead to an improved milk protein content without any increase in dietary protein. This is partially through an increase in microbial protein outflow from the rumen, but is also due to an improved energy status, which has been shown to stimulate milk protein synthesis.

In a trial conducted in Austria,  44 dairy cows (Simmental) with similar milk yield, including ten heifers, received a standard ration (grass silage, corn silage, ground corn, protein concentrate and wheat flour).

The 44 cows were separated into two treatment groups. One group received 20g/cow/day of yeast additive Levabon® Rumen (trial group) with the concentrate.

The other 22 cows were the control group and received the standard diet without the additive. The energy corrected milk (ECM) increased after the start of the trial and reached on average one kg more compared to the control group over the total trial period (Figure 2). The tested additive increased milk yield, as well as led to improved milk fat and milk protein. This result shows that the use of autolyzed yeast can increase the digestibility of the ration and therefore improve feed intake. The result is a better milk yield with consistent milk constituents.