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Discipline: supplementation; Key words: amino acids, milk protein, meta-analysis, immune-metabolism, methionine, transition period.
Research results have shown that several amino acids may be in short supply in diets of high-producing dairy cows, even when well-formulated. Noteworthy is methionine, which has subsequently been accepted as the first limiting amino acid. Others such as lysine, histidine and triptophane have also on occasion been implicated as limiting. However, most studies targeted methionine and a number of commercial products to protect methionine from degradation in the rumen came on the market and were used in experiments to study the response of methionine supplementation on milk yield and composition. Not all results were conclusive and therefore Dr J. Lean and colleagues decided to use the powerful statistical analysis tool of meta-analysis to study the relationship between milk yield and composition, and methionine and other amino acids implicated in the metabolizable protein system of the widely recognized Cornell Net Carbohydrate and Protein System (CNCPS). Their results were published in the Journal of Dairy Science, Volume 101 of 2018, pages 340 to 364. The title of the paper is: Meta-analysis to predict the effects of metabolizable amino acids on dairy cattle performance.
The function of methionine and other essential amino acids are not limited to promoting milk yield and composition. Circumstantial evidence appears to indicate that it could be associated with immune function, especially in the vulnerable peri-parturient phase of the productive cycle of the cow. This was the topic of the study of Dr Batistel and colleagues which was also published in the Journal of Dairy Science, Volume 101 of 2018, pages 480 to 490. The title of their paper is: Ethyl-cellulose rumen-protected methionine alleviates inflammation and oxidative stress and improves neutrophil function during the periparturient period and early lactation in Holstein dairy cows.
In the meta-analysis study of Dr Lean and associates a total of 63 publications were incorporated to determine the statistical relationships between metabolizable amino acid supplies and milk yield, milk protein percentage and milk protein yield. CNCPS version 6.5 was used to determine dietary nutrient parameters, including metabolizable amino acids.
The results showed that the CNCPS-predicted metabolizable methionine (g per day) was associated with milk protein percentage and yield, whereas milk yield was positively associated with the CNCPS-predicted metabolizable histidine, leucine, triptophane, threonine and the non-essential amino acids (g per day). Milk true protein yield was also associated with CNCPS-predicted metabolizable leucine (g per day). Predicted metabolizable lysine (g per day) did not increase responses in production outcomes. However, the mean metabolizable lysine supply was less than typically recommended which could have been the reason for the lack in response. In general, the meta-analysis study supports other research indicating a positive effect of methionine and histidine as co-limiting amino acids in dairy cows and suggests that leucine, triptophane and threonine should be given more emphasis in future research.
The peri-parturient period is often characterized by impairment of the immune system. Therefore, the objective of the Batistel et al study was to evaluate the effect of feeding ethylcellulose rumen-protected methionine (ECRPM) on liver and leukocyte function during this period and beyond. Sixty multi-parous Holstein cows were used in a block design and assigned to either a control or the control plus ECRPM (fed as Mepron). Mepron was supplied from day 28 before calving to day 60 in milk at a concentration of 0.09% and 0.10% of the feed dry matter during the pre- and postpartum period. That concentration ensured the ratio of lysine to methionine in the metabolizable protein was close to the recommended 2.8:1. Blood samples from 15 clinically healthy cows per treatment were collected at days 30 and 14 pre-partum and at days 1, 7, 21, 30, and 60 postpartum, and analyzed for biomarkers of liver function, inflammation and oxidative stress. Neutrophil and monocyte function in whole blood was also studied in vitro.
Compared with control, ECRPM increased plasma cholesterol and paraoxonase after calving. Among the inflammation biomarkers measured, ECRPM led to greater albumin (negative acute-phase protein) and lower haptoglobin than control cows. Cows supplemented with ECRPM also had greater plasma concentration of ferric-reducing antioxidantpower, β-carotene, tocopherol and total and reduced glutathione, whereas reactive oxygen metabolites were lower compared with control cows. Furthermore, ECRPM enhanced neutrophil phagocytosis and oxidative burst. Overall, the results indicate that ethylcellulose rumen-protected methionine (ECRPM), supplied to obtain a lysine-to-methionine ratio of 2.8:1 in the metabolizable protein during the peri-parturient period and early lactation, is an effective approach to help mitigate oxidative stress and inflammation as well as enhance liver and neutrophil function in dairy cows. It, therefore, does have a significant positive effect on the immune system.