Amino acids and the regulation of oxidative stress and immune function in dairy cattle

Dairy cattle undergo a number of metabolic, endocrine, physiologic, and immune adaptations during the transition into lactation. Metabolically, the increase in mobilization of adipose depots as parturition approaches not only increases liver triacylglycerol accumulation, but also could trigger inflammation, oxidative stress, immune dysfunction, and reductions in liver function. The degree and length of time during which these systems remain out of balance could render cows more susceptible to disease, poor reproductive outcomes and less efficient. Thus, there continues to be interest on approaches that might synergistically help cows modulate metabolism and immune responses during the periparturient period. In the context of “immunometabolism”, varying the post-ruminal supply of micronutrients [e.g. B vitamins, folic acid, choline, trace minerals, amino acids (AA)] has been a focus of research. Classical studies in non-ruminants established a crucial role for Glu and Gln in immune cell metabolism and function. At the cellular level these AA along with essential (e.g. Met, His, Thr), semi-essential (Arg), and non- essential (Ser, Gly) AA not only interact through common biochemical pathways to help immune cells meet energy needs, but also are important for synthesis of nucleotides, antioxidants, and polyamines. From a nutritional standpoint, the 1-carbon metabolism pathway represents an example of an interconnected route through which AA could impact molecular events such as epigenetic regulation. An important “nutrient sensor” sensitive to AA supply is the mechanistic target of rapamycin (MTOR). Although MTOR has been primarily studied in the context of bovine milk protein synthesis, a growing body of literature in non-ruminants underscores its involvement in the immunometabolic response. The objective of this review is to provide an overview of immune system responses in the periparturient cow followed by more specific discussion of the immunometabolic role of specific AA. Available molecular data on immune cells and immune-responsive organs in dairy cows are discussed in the context of AA transport, cellular sensors, and signalling mechanisms that might impact responses to increases in the supply of specific AA. With nutritional management during the periparturient period continuing to be an active area of research, it is important to develop a systems understanding the potential immunometabolic role that dietary AA may play during this period.