An investigation into the effects of different starts to the grazing season on sward structure and sward dynamics and dairy cow performance during the grazing season.

Abstract

Summary and Implications •Cows outdoors from mid February to early April offered an 80:20 grazed grass concentrate diet produced similar milk yield with higher protein yield and content compared to cows offered a 40:60 grass silage concentrate diet. •The improvement in animal performance is attributed to a higher energy, protein and total DM intake. •In the carryover period when both groups were grazing fulltime, the cows with early turnout had higher milk protein concentrations and higher grass DM intakes (1kg DM/cow/day) •An early grazed sward had a similar grass growth potential as a late grazed sward. •Herbage from early grazed swards have higher grass digestibility (OMD and UFL) value than late grazed swards •A lower daily herbage allowance can be tolerated with early grazed swards to achieve similar milk production performance as from late grazed swards. Up to 5-6 kg grass DM of late grazed swards will achieve the same level of milk production from early grazed swards. •With late turnout allocating high daily herbage allowance with large pre -grazing herbage mass is wasteful and compounds the effects of poor grass utilisation and undergrazing. •Early grazing is recommended when conditions allow even on heavy soil types. •From mid April onwards the optimum-stocking rate on early grazed swards is between 4.0 - 4.5 cows/ha. At this stocking rate a balance is found between feeding the cow adequately at pasture and achieving the correct post - grazing residuals. •Grass dry matter intake was significantly higher for the early grazed medium stocked cows in both studies, which clearly shows that the improvements in sward quality with early grazed swards can be converted to higher dairy cow performance. •Cows grazing the early grazed sward at a medium stocking rate had higher milk production performance which persisted in subsequent grazing rotations. This was due to the higher quality herbage available with the lower herbage mass swards. •When modelled to the whole farm system the reduced feed cost and higher performance achieved with early grazing, resulted in each extra day at grass increasing cow profitability by €2.70 cow/day