Estimates of Duodenal Microbial Protein in Free Housed Dairy Cows fed Total Mixed Ration vs. Component Diet

Abstract Text: The objective was to determine effects of total mixed ration (TMR) delivery vs. component feeding of forage and concentrate (CF) in lactating dairy cows in a competitive housing environment. Twelve multiparous (650 ± 55 kg body weight; 45 ± 20 days in milk; mean ± SD) and twelve primiparous (579 ± 49 kg body weight; 59 ± 36 days in milk) lactating Holstein cows in free houses were monitored continuously in a completely randomized design experiment for three months. A 10-d pre-trial adaptation period was allowed before data collection. Cows were offered an experimental diet (barley grain and corn silage-alfalfa hay based) as either TMR or CF of forage and concentrate for the entire experiment. The forage to concentrate ratio (dry matter based) was 50:50, allowing 5-10% daily orts. Cows were fed 3 times daily at 0530, 1330, and 2130 h. The daily TMR was divided to three equal portions and each portion was fed at each feed delivery. The CF was divided to one portion of forage fed at 0530 h, and two equal portions of concentrate fed at 1330 and 2130 h. Cows were milked 3 times daily at 0500, 1300, and 2100 h. Statistical data analysis was conducted with Mixed Models. Two ml of urine sample was taken, diluted 5 times in distilled water, and stored at -20°C for analysis of purine derivatives (allantoin and uric acid) to estimate duodenal microbial protein flow. Daily urinary excretion of allantoin (401 vs. 429 mmol/d), uric acid (43 vs. 48 mmol/d), and total purine derivatives (444 vs. 477 mmol/d) were not affected (P>0.15) by feeding TMR vs. CF, respectively. Daily estimates of duodenal microbial protein were thus not different. Parity interaction with feeding system did not affect microbial protein flow estimates. The data suggest that feeding high-producing dairy cows TMR vs. CF did not any positive impact on rumen microbial protein estimates, suggesting that rumen conditions were not impacted by feeding system in a competitive environment.

Key words: Total Mixed Ration, Microbial Protein, Component Feeding