Relationships between postruminal casein infusion and milk production, and concentrations of plasma amino acids and blood urea in dairy cows: A multilevel mixed-effects meta-analysis

Abstract

The relationships between postruminal casein infusion and production variables and concentrations of plasma AA and blood urea were evaluated using multilevel mixed-effects models derived from literature data collected in dairy cows. The data set contained 147 treatment means [i.e., 66 controls (CTL) and 81 casein-infused (CAS) means]. Each CAS mean was paired with its corresponding CTL mean to create 81 mean differences (CAS minus CTL), which were analyzed as absolute and percentage-based units (i.e., percentage increase or decrease in CAS relative to CTL). The primary variable of interest was the difference in estimated metabolizable protein (MP) supply (ΔMP) between CAS and CTL. The other explanatory variables were based on levels in CTL: MP supply, MP balance, the ratio of duodenal microbial protein (MCP) to MP supply (MCPMP), the stage of lactation (early or mid/late) and the type of forage (grass/legume- or corn silage-based). The MP supply and MP balance influenced negatively the relationship between ΔMP and the response of true protein yield. Responses of milk urea, blood urea, and plasma urea cycle AA concentrations were associated positively with ΔMP, indicating that a large amount of infused AA was catabolized to urea. Responses of plasma essential AA concentrations were related positively to ΔMP. The relative effect of ΔMP was highest for responses of plasma His concentration in cows fed grass/legume-based diets and at high MCPMP ratios. This relationship suggests that positive responses of plasma His concentrations are associated with diets relying heavily on microbial protein synthesis (high MCP), low in crude protein (low estimated MP supply), or both. The relationship between ΔMP and responses of plasma group 2 AA (Ile, Leu, Lys, and Val) concentrations was approximately 2 times greater than that for group 1 AA (His, Met, and Phe+Tyr) at mean MCPMP and MP supply. This could reflect the low hepatic removal group 2 AA compared with group 1 AA in dairy cows. Collectively, these results provide novel information on how dietary and cow conditions may alter responses to protein supplementation.

Plasma essential amino acid concentrations in response to casein infusion or ration change in dairy cows: A multilevel, mixed-effects meta-analysis

“…A large collection of studies reporting p[AA] and milk true protein yield (MTPY) in dairy cows was assembled by merging 141 treatment means from Martineau et al (2014Martineau et al ( , 2017 and 526 treatment means from Patton et al (2015). Data from Schwab et al (1992) and Larsen et al (2014) were removed from the data set because control cows were infused with dl-Met, l-Lys, or both and cows were in early postpartum period, respectively.…”

“…The data set was updated in June 2017 using the Scopus online database to include 40 new treatment means from dairy cow studies published since 2012 in the Journal of Dairy Science. Note that the data sets from Martineau et al (2014Martineau et al ( , 2017 were updated on regular basis by the first author to include canola meal feeding and casein infusion studies with no restraint to the Journal of Dairy Science.…”

“…In the third analysis, the influence of each moderator on linear relationships was tested only in FT studies because moderators related to the diet were constant on a within-study basis in CN studies (refer to Supplemental Figure S1; https: / / doi .org/ 10 .3168/ jds .2018 -15218). More details on the statistical model can be found in Martineau et al (2017).…”

“…However, the corresponding relationships for CN studies have not been yet evaluated to our knowledge. Martineau et al (2017) reviewed the response of p[AA] to incremental MP but not to incremental AADuo in CN studies.…”

“…The current study was undertaken because notable differences were observed between results reported in Patton et al (2015) and responses in p[AA] to incremental AADuo in CN studies using the data set used by Martineau et al (2017; refer to Supplemental File S1 and Table S1 for additional information, https: / / doi .org/ 10 .3168/ jds .2018 -15218). For example, the linear terms of Ile, Leu, and Val were about 2-fold lower in FT versus CN studies; this indicated that, for a same ΔBCAADuo, Δp [BCAA] in FT studies was half that in CN studies.…”