Constraints to milk production in grazing dairy cows in Brazil and management strategies for improving their productivity

Productivity in most Brazilian dairy herds is low and depends exclusively o n pasture. To study the productive potential of pastures and to devise stra tegies to further improve pasture and animal productivity in this productio n system, studies were carried out to obtain basic on-farm information. The constraints which affect productivity and reproductive performance of dair y cows, the effects of restrictions in suckling time of calves, and strateg ic supplementation during the dry season upon animal production were the ev aluated parameters. From March 1992 through February 1997, studies were car ried out on four private farms in the northern region of the State of Sao P aulo. Between March 1992 and February 1994 (Study 1 - survey phase), 142 co ws (parity=1-6) grazed pasture which consisted of signal grass (Brachiaria decumbens and Brachiaria brizanta). Once-a-month data were collected on bod y weight, body condition, and milk production. Reproduction parameters were assessed by milk progesterone profiles. From March 1996 to February 1997 ( Study 2 - intervention phase), 45 lactating dairy cows from two farms were hand-milked once a day and the calf suckling was restricted to two hours af ter milking. Data were collected on milk production and cow body weight. In Study 1, cows were grouped by calving date for the analysis of the reprodu ctive and production data. Concentrations of blood metabolites, hemoglobin, and hematocrit were compared among randomly selected cows (n=69) from all farms. Estimated pasture available per hectare (ha) at any time, crude prot ein (CP), and dry matter digestibility (DMD) of pasture available for grazi ng differed (p<0.05) between seasons [pasture available=1.2, 1.4, 1.8 and 2 .2 t/ha (SE=0.70); CP=42, 60, 48 and 57 g/kg (DM) (SE=10.1); DMD=399, 468, 401 and 457 g/kg (DM) (SE=21), respectively, for dry season 1992 (D92), wet season 1992 (W92), dry season 1993 (D93), and wet season 1993 (W93)]. The proportion of animals showing ovarian activity at 90 days postpartum (DPP) was higher for cows which calved in the wet season than cows which calved i n the dry season. In Study 2, milli production tended to the higher (7.3 an d 6.5 kg/day, respectively, fur the intervention and survey studies: p=0.08 ) The data suggest that milk production is being limited by pasture availab ility, the quality of pasture, and the lack of supplementation. We suggest that, although supplementing cows in the dry period may have an economic ad vantage, better pasture management needs to be introduced. Stocking rate mu st be adapted to pasture productivity and pasture quality throughout the ye ar. (C) 1999 Elsevier Science B.V. All rights reserved.