Milk production per cow and per hectare of spring-calving dairy cows grazing swards differing in Lolium perenne L. ploidy and Trifolium repens L. composition

摘要

Grazed grass is the cheapest feed available for dairycows in temperate regions; thus, to maximize profits,dairy farmers must optimize the use of this high-qualityfeed. Previous research has defined the benefits ofincluding white clover (Trifolium repens L.) in grassswards for milk production, usually at reduced nitrogenusage and stocking rate. The aim of this study was toquantify the responses in milk production of dairy cowsgrazing tetraploid or diploid perennial ryegrass (Loliumperenne L.; PRG) sown with and without white cloverbut without reducing stocking rate or nitrogen usage.We compared 4 grazing treatments in this study: tetraploidPRG-only swards, diploid PRG-only swards,tetraploid with white clover swards, and diploid withwhite clover swards. Thirty cows were assigned to eachtreatment, and swards were rotationally grazed at afarm-level stocking rate of 2.75 cows/ha and a nitrogenfertilizer rate of 250 kg/ha annually. Sward white clovercontent was 23.6 and 22.6% for tetraploid with whiteclover swards and diploid with white clover swards, respectively.Milk production did not differ between the2 ploidies during this 4-yr study, but cows grazing thePRG-white clover treatments had significantly greatermilk yields (+596 kg/cow per year) and milk solidyields (+48 kg/cow per year) compared with cows grazingthe PRG-only treatments. The PRG-white cloverswards also produced 1,205 kg of DM/ha per year moreherbage, which was available for conserving and bufferfeeding in spring when these swards were less productivethan PRG-only swards. Although white clover isgenerally combined with reduced nitrogen fertilizer use,this study provides evidence that including white cloverin either tetraploid or diploid PRG swards, combinedwith high levels of nitrogen fertilizer, can effectivelyincrease milk production per cow and per hectare.