Effect of ploidy and pasture mass on milk production and nitrogen use efficiency in late summer

Pre grazing mass and ploidy of perennial ryegrass pastures were investigated as immediate strategies that could be used to manipulate dry matter intake (DMI), milk production and nitrogen use efficiency (NUE) by reducing pasture crude protein (CP) content of the diet. Dry matter and N intake and milk production were compared using Friesian x Jersey dairy cows grazing diploid or tetraploid ryegrass at a high or low pasture mass. Dry matter intake was similar for all treatments (15.5 kg DM/cow/d). Crude protein content was affected by ploidy (18.7 vs 21.6% CP tetraploid and diploid respectively, P<0.05) and mass (18.2 vs 22.2% CP high and low mass respectively, P<0.05). There was a tendency for milk production to decrease with increasing pasture mass on diploid but not on tetraploid pastures (P<0.10). Pasture mass did not effect NUE but there was a trend for improved NUE on tetraploid compared with diploid pastures (0.23 and 0.19 respectively, P