Lactation response to soybean meal and rumen-protected methionine supplementation of corn silage-based diets

INTRODUCTION:

Soybean meal is one of the important protein sources in dairy cattle nutrition. This protein source is rich in the amino acid lysine but deficient in methionine. Sometimes, to improve nitrogen efficiency, it is necessary to feed protein supplements to increase milk composition and production. Nitrogen fed to dairy cows that is not utilized in milk ends up being excreted in feces and urine. Besides the loss of dietary nitrogen, nitrogen excretion causes groundwater pollution. Therefore, this issue reduces the environmental sustainability of livestock farming.

The best approach to increase nitrogen efficiency in dairy cows, without compromising production, is to reduce the crude protein in the diet while increasing the metabolizable amino acids in the ration. Studies have shown that crude protein levels between 16.7% and 17.1% in dairy cow diets are sufficient for maximizing production.

Methionine is one of the essential amino acids. It is limiting in diets based on legumes and corn silage. Supplying methionine in the nutrition of dairy cows appears to improve both milk production and milk protein content.

MATERIALS AND METHODS:

In the study by Nursoy and colleagues, aiming to supplement methionine in corn silage-based diets with soybean meal as the protein source, the quantitative and qualitative milk production performance of dairy cows was investigated. For this purpose, 36 multiparous cows with an average weight of 623 kg and a milk production of 48 liters per day were tested in a 4 × 4 Latin square design for 4 weeks. These animals were assigned to four treatments with crude protein levels of 11%, 13%, 15%, and 17%, along with a methionine source. Typically, the ratio of methionine to lysine ranges between 3.5 and 4.0. In this study, by adjusting the concentration of methionine and lysine as a percentage of metabolizable protein to 6.8% and 2.2% respectively, the amino acid ratio was reduced to 3.1.

RESULTS AND DISCUSSION:

It has been reported that the typical conversion rate of dietary nitrogen to milk nitrogen ranges between 23% and 34%. In this study, nitrogen efficiency was reported to be the same in cows fed with 15% and 17% crude protein diets supplemented with methionine. Interestingly, the apparent nitrogen efficiency in cows fed 15% crude protein was 3 percentage points higher than in cows fed with higher crude protein levels.
 

The use of methionine supplementation in dairy cow diets led to increased milk production, total protein concentration, true protein, and casein content in the milk. Although lower protein levels in dairy cow diets improve nitrogen efficiency, they are usually associated with reduced production performance. To compare animal performance, diets with 15% and 17% crude protein supplemented with methionine were evaluated in terms of ECM (energy-corrected milk), milk yield, milk protein, and other parameters. According to the results of this study, using methionine supplementation in diets containing 15% crude protein not only resulted in production outcomes similar to those achieved with 17% crude protein diets but also demonstrated better nitrogen efficiency compared to the 17% protein diet.

CONCLUSIONS:

It appears that feeding solely soybean meal as the protein source in corn silage-based diets leads to insufficient amino acid supply and reduced nitrogen efficiency. Therefore, using methionine supplementation improves the quality of amino acids received by the animal, which enhances the performance of the protein source used. This not only improves the nitrogen efficiency of the diet but also makes the ration more economically feasible. Additionally, reducing the use of protein sources can help decrease competition between livestock and humans for these resources.

REFERENCES:

https://doi.org/۱۰.۳۱۶۸/jds.۲۰۱۷-۱۳۲۲۷

Nursoy, H., et al., Lactation response to soybean meal and rumen-protected methionine supplementation of corn silage-based diets. Journal of dairy science, ۲۰۱۸. ۱۰۱(۳): p. ۲۰۸۴-۲۰۹۵.