Parenteral administration of l-arginine to twin-bearing Romney ewes during late pregnancy is associated with reduced milk somatic cell count during early lactation

Background: L-arginine has been shown to improve mammary gland function and development in a number of species through potential regulation of mechanistic target of rapamycin (mTOR) signaling. Objective: We examined whether parenteral administration of L-arginine to twin-bearing ewes during mid-late-pregnancy influences mammary gland development and function, the abundance of mechanistic target of rapamycin (mTOR) protein, and improves lactation performance in the early postpartum period (14 days). Methods: Cohort 1 was administered L-arginine from d 100 of pregnancy until d 140. At d 140 ewes were euthanized and maternal mammary tissue collected for analysis of total DNA, RNA, protein and the abundance of mTOR and mTORSer2448 protein. Cohort 2 was administered L-arginine from d 100 until parturition. At parturition, treatment ceased and ewes allowed to lamb naturally. Milk was collected over a 14 day period (d 1, 4, 7, 10 and 14) to assess milk yield and composition. Results: In cohort 1, total mammary DNA content tended to be higher (P = 0.07) in L-arginine ewes, with no change in mTOR protein abundance or phosphorylation. In cohort 2, milk composition analysis from L-arginine ewes showed decreased milk somatic cell counts (d 4 to 14), higher crude protein percentage from d 7 to 10, but lower at d 14 and altered absolute concentrations of some free amino acids (d 7 and 14), compared to controls. Conclusion: Parenteral administration of L-arginine is associated with increased maternal mammary DNA content (d 100 to 140), improved mammary gland health and function (d 100 to parturition).