Case Study: A comparison of 2 methionine sources for early lactation Holstein cows

The objective was to determine whether dl-Met supplied from metal specific AA complexes (MSAAC) of zinc and manganese could maintain milk yield and composition of multiparous Holstein cows in early lactation relative to a commonly used rumen-protected dl-Met source. Forty-seven multiparous Holstein cows were ranked by previous 305 ME milk and randomly assigned to 1 of 2 treatments delivered daily as gelcap boluses and fed a common basal diet predicted by Cornell Net Carbohydrate and Protein System v6.1 to be 4.9 g/d deficient in Met. Treatments were (1) 15.1 g/d of Zinpro 120 and 9.2 g/d of Manpro 160 (Zinpro Corporation, Eden Prairie, MN), which supplied 6.58 g/d of metabolizable Met (MSAAC:Met), and (2) 6.58 g/d of metabolizable Met supplied from 11.6 g of Smartamine M (Adisseo, Antony, France) and similar levels of Zn and Mn but supplied by zinc and manganese AA complexes (Availa Zn 120 and Availa Mn 80, Zinpro Corporation; AAC+SM). All cows were fed, milked, and housed together. Milk yield was collected daily, and milk composition was analyzed weekly. Treatment × time interactions were noted for milk yield and the yield of almost all milk components, largely due to cows treated with MSAAC:Met yielding 1.5 and 1.8 kg/d more milk at 35 and 42 DIM, respectively. The Met supplied as metal MSAAC is at least similar in availability as Met supplied from Smartamine M. Therefore, Met provided by MSAAC of zinc and manganese should be included in the summation of dietary metabolizable Met supply when balancing diets for AA in early lactation cows.