Forage and animal responses in pasture-based dairy production systems for lactating cows

In response to greater volatility in milk prices and higher costs of production, Florida's dairy producers have begun to consider use of grazed-pasture for their lactating cows. Insufficient research information is available to provide comprehensive grazing recommendations. During 1996 and 1997, research was conducted to quantify forage and animal production when lactating dairy cows grazed two cool-season forage systems (FS; N-fertilized rye [ Secale cereale L.]-ryegrass [Lolium multiflorum L.] pastures vs. rye-ryegrass-crimson clover [Trifolium incarnatum L.]-red clover [Trifolium pratense L.] pastures) at two stocking rates (SR; 5 vs. 2.5 cows ha-1) and two concentrate supplementation levels (CS; 1 kg [as-fed] per 2.5 kg of milk vs. 1 kg per 3.5 kg). Additionally, studies conducted in summer 1996 and winter 1997 evaluated management, season, and cows' coat color effects on grazing behavior. A further study compared the pulse dose marker and herbage disappearance techniques for estimating forage dry matter intake (DMI) vs. the energy requirement for animal performance method.;Stocking rate was the key factor affecting forage production and animal performance. Greater herbage mass occurred at low than high SR (1390 vs. 1020 kg DM ha-1) resulting in greater intake (17.6 vs 15.8 kg OM d-1) and milk production per animal (23.5 vs. 20.1 kg cow-1 d-1). Milk production per hectare was greater at high SR. Production based on high SR, however, may not be sustainable because of loss in body weight and condition. Animals fed at high CS had better energy balance and less body weight loss. Grass-N fertilizer systems were more adapted to intensive grazing than grass-clover systems in this environment.;Cows grazed for less time per day in summer (161 min) than winter (249 min) because of heat stress. In summer, animals on rhizoma. peanut pastures grazed less (179 vs. 143 min) but achieved greater forage intake (14.9 vs. 11.0 kg OM d-1) and milk production (17.2 vs. 14.9 kg cow-1 d-1) than cows grazing bermudagrass. In winter, cows on low SR grazed longer (494 vs. 419 min d-1 ) and achieved greater forage intake (12.5 vs. 10.2 kg OM d -1) and milk production (20.0 vs 16.2 kg cow-1 d-1) than those on high SR. Cows with predominantly white coats grazed on average 13 min d-1 longer than those with predominantly black coats, regardless of season, resulting in higher intake (12.5 vs. 11.2 kg d-1 and greater milk production (11.5 vs. 8.0 kg cow-1 d-1) in summer but not in winter. Forage DMI estimates obtained by the different techniques indicated that predictions by the herbage disappearance method more closely matched energy requirements compared to estimates by the pulse dose marker technique.