Relationship between milk odd and branched-chain fatty acids and urinary purine derivatives in dairy cows supplemented with quebracho tannins—A study to test milk fatty acids as predictors of rumen microbial protein synthesis

Relationship of Milk Odd- and Branched-Chain Fatty Acids with Urine Parameters and Ruminal Microbial Protein Synthesis in Dairy Cows Fed Different Proportions of Maize Silage and Red Clover Silage

“…However, the correlations obtained in this study show weak to moderate relationships of the proportions and yields of individual OBCFA in milk with the urine variables (N, uric acid, allantoin, and total PD). This is in agreement with results reported by Castro-Montoya et al [12], who found relationships with r between −0.42 and 0.37. Yields of individual OBCFA and yields of total BCFA, OCFA, or OBCFA correlated positively (r = 0.21 to 0.55) with the estimated MCPME and MCPdOM.…”

“…Fatty acid methyl esters (FAME) were obtained from the extracted milk fat by transesterification [20]. Subsequently, the FA composition was determined by the gas chromatography procedure [21] as described by Castro-Montoya et al [12]. Analyses of FAME were performed with an Agilent 7890A gas chromatograph equipped with a 60-m fused silica capillary column (i.d.…”

“…Succinctly, spot urine samples (~600 mL) were obtained from all cows once daily on days 14, 16, 18, and 20 at 07:30, 19:30, 15:30, and 11:30 h, respectively, by manual stimulation of the region around the vulva. This sampling design was applied to account for possible diurnal and day-to-day variations in the urinary excretion of PD and N [12]. Immediately after collection, urine was acidified to pH < 3 using 20% (vol/vol) H 2 SO 4 to avoid the volatilization of N compounds, then stored at −20 • C. At the end of the experiment, urine samples were thawed at room temperature, pooled on an equal-volume basis by cows and periods, and stored at −20 • C for N analysis.…”

“…Conversely, Dewhurst et al [11] did not find any relationship between milk OBCFA and the duodenal flow of purine bases or to the duodenal flow of OBCFA. Additionally, Castro-Montoya et al [12] found a weak relationship between milk OBCFA and PD in urine. In general, studies related to the use of OBCFA as a biomarker for MCP have shown contrasting results and indicate that more research is needed on this matter.…”

Empirical Attributes and Limitations of Methodologies for Predicting the Degradability of Ruminal Protein

“…Under such conditions, the ruminal epithelium would generate N homeostasis between the ruminal medium and the plasma level by absorbing the excess N (principally in the form of ammonium) not fixed by the microorganisms to maintain the nitrogen equilibrium in the ruminal medium. Additionally, this absorption of ammonium would have metabolic consequences for the kidneys, liver and mammary glands (Kornegay, 1996;Van Duinkerken et al, 2005;Castro-Montoya et al, 2016). It is also important to have as accurate information as possible on the degradability of polypeptides in the rumen to establish balanced diets, thus optimizing the efficient use of N. Thus, the accuracy and representativeness of the methods used for predicting protein degradability in the rumen play a fundamental role in optimizing the use of nitrogenous resources through the formulation of diets for productive ruminants (Givens et al, 2000;Benninghoff et al, 2015).…”