Effects of grain level and protein source on yield, feed intake, and blood traits of lactating cows fed alfalfa silage

Multiparous Holstein cows (n = 27) averaging 590 kg BW were allotted at 3 wk postpartum to nine trios blocked on the basis of similar calving date. Animals were fed alfalfa silage for ad libitum intake and remained in the experiment until wk 11 of lactation. Cows within each trio were assigned randomly to either a medium level of concentrate fed at 1.8% BW containing soybean meal or a low level of concentrate fed at 1.3% BW containing either soybean meal or fish meal. The three treatments were designed to give similar CP intake as percentage of BW from the concentrate. Intake of DM and milk yield were measured daily, and BW and milk composition were recorded weekly. Blood was sampled during wk 7 of lactation. Total DMI was higher for cows fed concentrate at 1.8% BW than for those fed at 1.3% BW. Silage DMI was similar across treatments and averaged 2.17% BW. Milk production, 32.0 kg/d, and milk composition, 3.95% fat, 2.90% protein, and 5.07% lactose, were similar for all treatments. Cows fed at 1.8% BW gained 11.0 kg, whereas those fed at 1.3% BW lost 8.4 and 7.4 kg, respectively, when given soybean meal or fish meal, but these differences were not significant. Prefeeding plasma concentrations of NEFA were higher for cows fed fish meal, which was related to their greater weight lost at wk 7 of lactation compared with those fed soybean meal. Level of concentrate and protein of low or high rumen degradability resulted in similar milk production for cows averaging 32.0 kg/d during early lactation.