Abstract
Simple SummaryRumen fermentation, the level of hormones and major metabolites in the blood, and tissue heat production, as well as milk composition, were studied in high-producing cows with different milk fat content. It was found that low milk fat is associated with neither a lack of acetate formation in the rumen, nor a change in the hormonal profile. The result is an increase in the availability of cows for metabolizable energy, the likelihood of ketosis, and the extension of their productive use.In order to clarify the mechanism of the depression of milk fat formation and preserve the health of animals, the aim of the research was to study the characteristics of rumen digestion, energy metabolism, and milk composition in high-producing dairy cows with high and low levels of milk fat that are fed the same diet. Two groups of cows with normal milk fat content (3.94 ± 0.12; n = 10) and low milk fat content (2.95 ± 0.14, n = 10) contained in the same diet were identified. Gas exchange (O2 uptake and CO2 output) was studied in cows and blood samples, rumen contents (pH, NH3-N), and VFA and milk (fat, protein, and fatty acid composition) were collected and analyzed. It was determined that cows with low fat milk are more efficient at using the metabolized energy of their diets due to the tendency to have a decrease in the proportion of heat production (by 6.2 MJ; p = 0.055) and an earlier start of a positive energy balance. At the same time, the fat content in milk did not depend on the level of hormones in the blood or on the formation of acetate in the rumen. An analysis of the duration of the productive use of cows on this farm (n = 650) showed that the number of lactations was inversely correlated with the level of fat in milk (r = −0.68; p < 0.05, n = 1300). These results indicate the advantages of cows that can reduce the fat content of their milk in the first months of lactation.
Highlights
Maintaining the normal physiological state of animals is the key to their long-term productive use and the guarantee of obtaining high-quality milk
The main negative aspect when feeding high-concentration diets is a decrease in rumen pH, which causes a change in rumen metabolism accompanied by the acidification of the contents of the rumen, a violation of microbial activity, a decrease in acetate formation, a drop in milk fat, and a number of other negative consequences associated with subacute rumen acidosis, or SARA
In order to clarify the mechanism of the depression of milk fat formation and preserve the health of animals, the aim of the research was to study the characteristics of rumen digestion, energy metabolism, and milk composition in high-productivity cows with high and low levels of milk fat that are fed the same diet
Summary
Maintaining the normal physiological state of animals is the key to their long-term productive use and the guarantee of obtaining high-quality milk. The main breakdown occurs in the first months of lactation, when the feed consumption potential lags behind the growth rate of milk production [1]. There is an increased mobilization of fat depots to reduce the negative energy balance in the body of cows. The main negative aspect when feeding high-concentration diets is a decrease in rumen pH, which causes a change in rumen metabolism accompanied by the acidification of the contents of the rumen, a violation of microbial activity, a decrease in acetate formation, a drop in milk fat, and a number of other negative consequences associated with subacute rumen acidosis, or SARA (acidosis, laminitis, and infertility). A diet in which the rumen has a pH of medium to lower than 6.0 can cause the depression of fat formation, and the addition of buffers to correct milk fat depression is an effective means to increase pH and milk fat in such situations [2]
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