Estimation of Microbial Nitrogen Flow to the Duodenum of Cattle Based on Dry Matter Intake and Diet Composition

Abstract

The objectives of this study were: 1) to evaluate the National Research Council equation used to predict microbial N flow to the duodenum in lactating cows, and 2) to determine whether improved equations could be developed by using dietary parameters used in the field. Treatment means from 55 trials with lactating and nonlactating cattle with duodenal cannulas were subjected to the backward elimination procedure of multiple regression. Variation within and among trials was accounted for by weighting the observations and including trial effects in all models. The equations to predict microbial N flow based on net energy for lactation (NEL) intake were different from the equation based on NEL intake used by the dairy National Research Council. Dry matter intake (DMI) estimated microbial N flow as well as did NEL intake, indicating that DMI drives predictions based on NEL intake. When multiple dietary factors [i.e., DMI; dietary percentages of crude protein, forage, and neutral detergent fiber; and all two-way interactions] were included, the resulting equation [microbial N (grams per day) = 16.1 + 22.9 x DMI (kilograms per day) - 0.365 x DMI2 - 1.74 x dietary neutral detergent fiber (percentage of dry matter)] tended to fit the data better than the equations based on NEL intake but not better than the equation based on DMI alone. The multiple-factor equation appeared to be the best overall equation for prediction; in contrast to the equation based on DMI, this equation is sensitive to diet composition. An asymptotic multiple-factor equation was developed, which may be more appropriate when extrapolating beyond the data range.

Milk Odd- and Branched-Chain Fatty Acids in Relation to the Rumen Fermentation Pattern

“…However, an integrated comparison between the different models (mechanistic models vs. models based on milk odd-and branched-chain fatty acids) is hindered because of the different sets of data used. In addition, validations based on data from a few trials only may result in particularly favorable or unfavorable valida-tions if trials near or far from the average trial used to define the model are used, respectively (Oldick et al, 1999).…”

Impacts of the Source and Amount of Crude Protein on the Intestinal Supply of Nitrogen Fractions and Performance of Dairy Cows

“…A mixed model approach was used based on the assumption of random variation in the effect of study (St-Pierre, 2001). Treatment means were weighted by the reciprocal of the variance of the means (i.e., n/s 2 scaled using the average weight) to account for unequal replications and heterogeneous variances across studies (Oldick et al, 1999). The best-fit model (Milk yield, kg/d = 1.04 [SE 8.91, P < 0.91] + 2.92 × CP% in the diet [SE 1.00, P < 0.004] − 0.064 × CP% 2 in the diet [SE 0.028, P < 0.02]; R 2 = 0.19) was estimated using the Mixed procedure of SAS (SAS Inst., Inc., Cary, NC).…”

Fontes de carboidratos e ionóforo em dietas contendo óleo vegetal para ovinos: digestibilidade, balanço de nitrogênio e fluxo portal de nutrientes

“…Van Nevel & Demeyer (1995), em estudos in Tabela 3 -Balanço de nitrogênio Tabela 4 -Médias do fluxo plasmático portal (FPP), concentração portal e arterial, diferença venosa-arterial (V-A) e fluxo plasmático portal de glicose, N α-amino, amônia e uréia Os nutrientes que desaparecem no trato digestivo não necessariamente atingem o sistema porta. Parâmetros relacionados à utilização dos carboidratos (Tabela 2) que poderiam interferir na síntese de proteína microbiana, como a digestibilidade da MO e dos CNF (Oldick et al, 1999) e outros relacionados à utilização da PB (Tabela 3), não foram influenciados pela utilização de monensina, que, no entanto, afetou diretamente as concentrações plasmáticas de aminoácidos.…”