Partial replacement of a total mixed ration with annual ryegrass herbage: effects on dairy cow dry matter intake and milk production

ABSTRACT Studies with dairy cows receiving mixed ration and grazing annual pastures, which have low tiller density, are scarce. This study examined the effect of partial replacement of a total mixed ration (TMR) with annual temperate pasture. Treatments were ad libitum TMR (TMR100), 75% ad libitum TMR + ryegrass (Lolium multiflorum ‘Maximus’) (pTMR75), and 50% ad libitum TMR + ryegrass (pTMR50). Twelve multiparous Holstein and F1 Jersey × Holstein cows were divided into six groups (experimental units), taking account of milk production (26.6 ± 4.55 kg/day), days-in-milk (129 ± 50.8) and body weight (546 ± 30.6 kg). Treatments were compared using two 3 × 3 Latin square arangements, comprising three 21-day periods (measurements during final 5 days). Herbage DM intake increased from 4.8 kg/day with pTMR75 to 6.7 kg/day with pTMR50. Total DM intake decreased from 19.4 kg/day (TMR100), to 18.1 and 15.8 kg/day (pTMR75 and pTMR50, respectively). Milk production, energy corrected milk production (ECM), and milk fat content were similar between treatments, averaging 25.6, 28.4 kg/day and 44.6 g/kg, respectively. Ryegrass pastures were able to replace up to 50% of TMR offered to mid lactation dairy cows with no adverse effects on ECM production.