Using compositional mixed-effects models to evaluate responses to amino acid supplementation in milk replacers for calves

摘要

The consequences of supplementing Lys, Met, andThr in milk replacers (MR) for calves have been widelystudied, but scarce information exists about potentialroles of other AA (whether essential or not). The effectson growth performance of supplementation of 4different AA combinations in a mixed ration (25.4%crude protein and 20.3% fat) based on skim milk powderand whey protein concentrate were evaluated in 76Holstein male calves (3 ± 1.7 d old). The 4 MR wereas follows: CTRL with no AA supplementation; PG,supplying additional 0.3% Pro and 0.1% Gly; FY, supplyingadditional 0.2% Phe and 0.2% Tyr; and KMT,providing additional 0.62% Lys, 0.22% Met, and 0.61%Thr. All calves were fed the same milk allowance programand were weaned at 56 d of study. Concentrateintake was limited to minimize interference of potentialdifferences in solid feed intake among treatments. Animalswere weighed weekly, intakes recorded daily, andblood samples obtained at 2, 5, and 7 wk of study todetermine serum urea and plasma AA concentrations.Plasma AA concentrations were explored using compositionaldata analysis, and their isometric log-ratiotransformations were used to analyze their potential influenceon ADG and serum urea concentration using alinear mixed-effects model. We detected no differencesin calf performance and feed intake. Plasma relativeconcentration of the AA supplemented in the KMT andPG treatments increased in their respective treatments,and, in PG calves, a slight increase in the proportion ofplasma Gly, Glu, and branched-chain AA was also observed.The proportions of plasma branched-chain AA,His, and Gln increased, and those of Thr, Arg, Lys, andGlu decreased with calves’ age. A specific log-contrastbalance formed by Arg, Thr, and Lys was found to bethe main driver for lowering serum urea concentrationsand increasing calf growth. The use of compositionalmixed-effects models identified a cluster formed by thecombination of Arg, Thr, and Lys, as a potential AA tooptimize calf growth.