Rumen microbial protein synthesis in cows fed dried whey.
Two rumen-fistulated Holstein cows, weighing approximately 550 kg, were in an experiment with switchback design to evaluate effects of consuming large amounts (38% of total ration dry matter) of dried whole whey on synthesis of microbial protein in the rumen. Cows were fed total mixed rations of (dry matter) 45% corn silage, 10% alfalfa hay, and 45% concentrate mix. The concentrate mix was primarily corn and soybean meal (control) or 85% dried whole whey. Dry matter intakes averaged 16.4 and 15.3 kg/day for control and whey diets. Diaminopimelic acid nitrogen as percent of bacterial nitrogen was similar for both diets (.61 and .63% for control and whey diets). Likewise, aminoethylphosphonic acid nitrogen as percent of protozoal nitrogen was similar for both diets (.17 and .19% for control and whey diets). For the control diet, total ruminal nitrogen was estimated to be 45% bacterial and 27% protozoal. Bacteria and protozoa accounted for 52 and 22% of the total ruminal nitrogen in the cows fed the whey diet. Ruminal fluid volume (33.8 and 39.2 liters for control and dried whey diets) and dilution rates (10.2 and 12.8% h) were higher for dried whey. Ruminal ammonia (5.0 and 3.4 mg/dl) was lower for dried whey. Butyrate (16.5 and 24.4 moles/100 moles total volatile fatty acids) was higher, whereas propionate was lower (32.4 and 23.2 moles/100 moles total volatile fatty acids) when cows were fed dried whey. Bacterial synthesis appeared to be increased when cows were fed a diet containing large amounts of dried whey.