Predictions of ruminal outflow of essential amino acids in dairy cattle

Abstract

The objective of this work was to update and evaluate predictions of essential AA (EAA) outflows from the rumen. The model was constructed based on previously derived equations for rumen-undegradable (RUP), microbial (MiCP), and endogenous (EndCP) protein outflows from the rumen, and revised estimates of ingredient composition and EAA composition of the protein fractions. Corrections were adopted to account for incomplete recovery of EAA during 24-h acid hydrolysis. The predicted ruminal protein and EAA outflows were evaluated against a data set of observed values from the literature. Initial evaluations indicated a minor mean bias for non-ammonia, non-microbial nitrogen flow ([RUP + EndCP]/6.25) of 16 g of N per day. Root mean squared errors (RMSE) of EAA predictions ranged from 26.8 to 40.6% of observed mean values. Concordance correlation coefficients (CCC) of EAA predictions ranged from 0.34 to 0.55. Except for Leu, all ruminal EAA outflows were overpredicted by 3.0 to 32 g/d. In addition, small but significant slope biases were present for Arg [2.2% mean squared error (MSE)] and Lys (3.2% MSE). The overpredictions may suggest that the mean recovery of AA from acid hydrolysis across laboratories was less than estimates encompassed in the recovery factors. To test this hypothesis, several regression approaches were undertaken to identify potential causes of the bias. These included regressions of (1) residual errors for predicted EAA flows on each of the 3 protein-driven EA flows, (2) observed EAA flows on each protein-driven EAA flow, including an intercept, (3) observed EAA flows on the protein-driven EAA flows, excluding an intercept term, and (4) observed EAA flows on RUP and MiCP. However, these equations were deemed unsatisfactory for bias adjustment, as they generated biologically unfeasible predictions for some entities. Future work should focus on identifying the cause of the observed prediction bias.

Effects of rumen-protected lysine and histidine on milk production and energy and nitrogen utilization in diets containing hydrolyzed feather meal fed to lactating Jersey cows

“…Because the supply of Lys and His in the basal diets were only marginally below targets, it is plausible that supplies of Lys and His may have been adequate without the inclusion of either RP Lys or His. Variance in modelestimated supply of individual AA can be large (Fleming et al, 2019b); therefore, the true supply of Lys and His in the current study is unknown. Admittedly, the target for Lys and His supply are not well established, and suppling increasing amounts of Lys (Vyas and Erdman, 2009) or His (Zang et al, 2019) may increase milk production and milk component yield.…”

Effects of Different Parts on the Chemical Composition, Silage Fermentation Profile, In Vitro and In Situ Digestibility of Paper Mulberry

“…However, compared to other amino acids, the PM's histidine content (including leaf, stem, and whole plant) was relatively low, which should be taken into consideration when a PM-based diet is supplemented with concentrates for dairy cows. Among the top five amino acids in the leaf and whole plant, leucine and lysine were the essential amino acids for dairy cows, making up for the deficiency that cows cannot synthesize these amino acids by themselves [40,41]. In short, PM's amino acid composition does not entirely meet the ideal amino acid requirements of dairy cows.…”

Estimating degradation of individual essential amino acids in fish meal and blood meal by rumen microbes in a dual-flow continuous-culture system

“…Therefore, differential degradation of individual AA is likely related to the differences in the structure and AA profile of different proteins within feeds. Recently, Fleming et al (2019) developed prediction equations for the flow of AA to the small intestine and reported that the flow of EAA, with the exception of Leu, was consistently overestimated. They attributed this overestimation to methodological problems in the analysis of AA, citing the "under-reporting of true flows in the literature due to recovery problems."…”