Performance of lactating dairy cows fed alfalfa silage or perennial ryegrass silage.

The nutrient contents of perennial ryegrass (Lolium perenne L.) and alfalfa (Medicago sativa L.) are reasonably similar. Despite similarities, the lactation performance of dairy cows fed perennial ryegrass has not been compared with the lactation performance of dairy cows fed alfalfa. The present study was implemented to compare the performance of lactating cows fed alfalfa or perennial ryegrass silage. Alfalfa and perennial ryegrass were harvested at late bud and boot stages of maturity, respectively, and ensiled in separate 4.9- x 18.3-m concrete silos. The experimental silages were supplemented with a concentrate mix at 31.1% of dietary dry matter and fed to 18 multiparous Holstein cows in early lactation in a crossover experimental design with 28-d periods. Digestibility and rate of passage of experimental diets were also measured using rare earth markers. The perennial ryegrass contained 3.0 percentage units more neutral detergent fiber than did alfalfa, but in vitro digestibility of neutral detergent fiber was 8.8 percentage units higher for perennial ryegrass. In vitro digestibility of dry matter was also higher for perennial ryegrass. Cows fed alfalfa silage produced more milk (31.8 kg/d) than did cows fed perennial ryegrass silage (30.2 kg/d). Cows fed perennial ryegrass silage ate less feed (2.2 kg/d) than did cows fed alfalfa. Because dry matter intake was lower, diet digestibilities were higher, and rate of passage was slower, for cows consuming perennial ryegrass. Based on laboratory evaluations, perennial ryegrass silage has high nutritional quality, but performance of lactating cows indicated that the forage was suboptimal for supporting high milk production when compared with alfalfa. The perennial ryegrass silage was suboptimal because it did not stimulate high amounts of dry matter intake in lactating cows.