Methionine is one of the most limiting amino acids in lactating dairy cow diets. Methionine hydroxy analogues as 2-hydroxy-4-(methylthio)butanoate are synthetic amino acids in which the amino group has been replaced with a hydroxyl group in order to protect methionine from ruminal degradation.
Methionine and lysine are the main limiting amino acids in lactating dairy cow diets. However, recent research shows histidine may be a limiting amino acid as well. A series of three studies (2015, 2016, 2017) conducted at The Pennsylvania State University’s Dairy Teaching and Research Center reported greater intake and milk protein yield in high-production cows fed low-protein diets supplemented with rumen-protected (RP) histidine.