Rumen microbial protein synthesis in total mixed ration vs. component fed high-producing dairy cows

Abstract Text: The objective was to determine effects of total mixed ration (TMR) delivery vs. component feeding of forage and concentrate (CFC) on rumen microbial protein synthesis in high-producing lactating cows in a noncompetitive environment. Four multiparous (665 ± 65 kg body weight; 67 ± 20 days in milk; mean ± SD) and four primiparous (583 ± 43 kg body weight; 85 ± 36 days in milk) lactating Holstein cows housed in free individual boxes (4 ×3 m) were used in a cross-over design experiment with two 25-d periods. Each period had 20-d of adaptation. Cows received a diet, based on barley grain and a mixture of corn silage and alfalfa hay, prepared and presented as either TMR or CFC. The forage to concentrate ratio was 50:50 (dry matter basis), permitting 5-10% daily orts. Two ml of urine sample was taken daily for the last 5 days of each period, diluted 5 times in distilled water, and stored at -20°C for later analysis of purine derivatives (allantoin and uric acid) to estimate duodenal microbial protein flow. Cows were experimented under thermoneutral conditions. Cows were milked twice daily at 0500 and 1700 h. Data were analyzed using Mixed Models with fixed effects of treatment, parity and their interaction, and random effects of period and cow within parity. Least square means were estimated with Restricted Maximum Likelihood method, and degrees of freedom were calculated using Satterthwaite method. Daily urinary excretion of allantoin (411 vs. 421 mmol/d), uric acid (47 vs. 49 mmol/d), and total purine derivatives (458 vs. 470 mmol/d) were not influenced (P>0.10) by feeding system (TMR vs. CFC, respectively). As a result, daily estimates of duodenal microbial protein flow were not different for cows fed TMR vs. CFC, respectively (2202 vs. 2260 g/d, P>0.10). Neither parity nor its interaction with feeding system affected urinary purine derivatives and microbial protein flow estimates. The results suggest that feeding high-producing dairy cows TMR vs. CFC did not influence the factors contributing to rumen microbial protein synthesis, indicating that rumen conditions and function were not affected by feeding system in a non-competitive environment. Findings have important economical, managemental and health implications for commercial dairy enterprises.

Keywords: Feeding system, Microbial protein, Dairy cow