The latest on protein and amino acids in ruminant nutrition

Written by ADSA Graduate Student Division member  Alexis Weston of  Virginia Tech .

Based on the oral presentations in Ruminant Nutrition 2: Protein and Amino Acids at the 2023 ADSA Annual Meeting, there is no shortage of interesting research being done in the field of protein and amino acids. Researchers from all over the world—from the University of Guelph, the University of Wisconsin, Virginia Tech, Wageningen University & Research, the University of Florida, and Cornell University—are working on a wide range of such research. Their work ranges from investigating the most minute detail of the effects of amino acid deficiency on transcription factors in mammary epithelial cells to the management applications of feeding rumen-protected amino acids every other day, rather than daily. 

It seems that this year, in vivo researchers are focused on the effects of rumen-protected methionine, lysine, histidine, and arginine. It appears that rumen-protected methionine, lysine, and histidine have shown fairly consistent results in increasing milk production and milk protein production in dairy cows; however, this work is at the stage of identifying the most optimum feeding practices. In fact, Kelly Nichols, PhD, of Wageningen University & Research discovered that the arterial concentrations of methionine, lysine, and arginine were the same when supplemented, regardless of how often they were supplemented (every other day or daily), indicating possible nitrogen recycling. These findings could lead to different management-practice options that could give farmers more “bang for their buck” when feeding expensive rumen-protected amino acids. 

Arginine is new on the scene in the world of rumen-protected amino acids. Researchers at the University of Florida demonstrated that rumen-protected arginine increased energy-corrected milk without affecting dry matter intake when supplemented in the first three weeks postpartum, which persisted following the end of the treatment. 

It is also interesting that nonessential amino acids are no longer ignored when it comes to their potential effects on milk-protein production. Researchers at Cornell investigated the effects of supplemented essential amino acids and nonessential amino acids on milk production and energy signals. Interestingly, no significant production responses were seen with any treatment, which was attributed to the research farm switching from conventional to brown midrib corn silage. 

In addition to rumen-protected amino acids, researchers are also investigating ties to amino acids and milk fat. We often only associate amino acids with milk protein; however, amino acids such as isoleucine, leucine, and methionine have been identified as signalers in the mammalian target of rapamycin signaling pathway, which has downstream effects on milk fat synthesis. Researchers at the University of Wisconsin observed an increase in milk fat production with methionine and leucine supplementation; one of their objectives was to counter milk fat depression caused by dietary fat sources, but the amino acids were unable to combat these effects. 

On the in vitro side, researchers are delving deep into discovering the explanations behind some of the effects we see in vivo related to amino acids. For example, Boning Li, from the University of Guelph, discovered that individual deficiencies of lysine, methionine, and histidine affected the expression of transcription factors. Further, the transcription factors affected indicated two major pathways in which protein synthesis was affected: through protein synthesis capacity per cell and secretory cell number. In addition, in vitro work at Virginia Tech has identified a multitude of amino acid interactions affecting the uptake of other amino acids in mammary epithelial cells, signifying another level of complication to amino acid balancing in amino acid models. These results were attributed to the possible downregulation of certain amino acid transporters, which act like doors for amino acids in and out of the mammary glands. 

Overall, research in the field of amino acids and protein has made great strides in the last year, and I look forward to seeing how nutrition models will change in future years. I anticipate that more research on lesser-studied amino acids will allow for better fits of those amino acids already incorporated into NASEM 2021 and create enough data to incorporate other amino acids (and perhaps nonessential amino acids). Future models may be able to integrate the complicated signaling that occurs intracellularly and amino acid–amino acid and amino acid–transporter interactions to even further increase model precision.

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