PERFORMANCE OF LACTATING DAIRY-COWS FED ALFALFA SILAGE OR PERENNIAL RYEGRASS SILAGE

The nutrient contents of perennial ryegrass (Lolium perenne L.) and al falfa (Medicago sativa L.) are reasonably similar. Despite similaritie s, the lactation performance of dairy cows fed perennial ryegrass has not been compared with the lactation performance of dairy cows fed alf alfa. The present study was implemented to compare the performance of lactating cows fed alfalfa or perennial ryegrass silage. Alfalfa and p erennial ryegrass were harvested at late bud and boot stages of maturi ty, 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 i n early lactation in a crossover experimental design with 28-d periods . Digestibility and rate of passage of experimental diets were also me asured 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 uni ts higher for perennial ryegrass. In vitro digestibility of dry matter was also higher for perennial ryegrass. Cows fed alfalfa silage produ ced 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, die t digestibilities were higher, and rate of passage was slower, for cow s consuming perennial ryegrass. Based on laboratory evaluations, peren nial 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 ryegra ss silage was suboptimal because it did not stimulate high amounts of dry matter intake in lactating cows.