Productivity of Dairy Cows in Pastures of Tall Fescue or Dactylis

Abstract

The aim of this work was to study the milk production of dairy cows grazing Festuca arundinacea or Dactylis glomerata. The study was conducted at the Centro Regional Sur of the School of Agronomy (Progreso, Canelones) in 2008, on monospecific pastures sown in 2005. An herbage regrowth of 35 days was strip-grazed with a daily herbage allowance of 50 kg DM/cow. Twelve lactating Holstein cows were allotted to the two treatments on the basis of the pre-experimental milk production (26.6 ± 2.36 l/d milk, live weight (585 ± 23.3 kg) and lactation stage (194 ± 19.1 days). The production of milk and milk solids were analyzed using repeated measurements. Simultaneously to the trial with cows, voluntary intake and digestibility were determined using twelve Corriedale wethers. The pre-grazing biomass was greater in tall fescue (4034 kg DM/ha) than in orchardgrass (2965 kg DM/ha), but there were no differences above 5 cm (1641 kg DM/ha). No differences in voluntary intake (41.8 g MO/kg PV0.75) or digestibility (73.7% DMO) were observed between pastures above 5 cm. However, forage utilization above 5 cm tended to be higher on orchardgrass (+10%, P=0,0906), which might be explained by a higher proportion of leaves (67% , P=0.0304). In fact, milk production (21.2 vs 18.6 l/day P=0.0052) and protein production (P=0.0036) were higher for cows grazing orchardgrass, and fat production tended also to be higher (P=0.0984), which could be explained by an increased intake associated to higher herbage as green leaf mass above 5 cm for orchardgrass.