Abdalla A L, Louvandini H, Bueno I C, Vitti D M, Meirelles C F, Gennari S M
Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Brazil.
Prev Vet Med. 1999 Jan 27;38(2-3):217-30. doi: 10.1016/s0167-5877(98)00127-5.
Productivity in most Brazilian dairy herds is low and depends exclusively on pasture. To study the productive potential of pastures and to devise strategies to further improve pasture and animal productivity in this production system, studies were carried out to obtain basic on-farm information. The constraints which affect productivity and reproductive performance of dairy cows, the effects of restrictions in suckling time of calves, and strategic supplementation during the dry season upon animal production were the evaluated parameters. From March 1992 through February 1997, studies were carried out on four private farms in the northern region of the State of São Paulo. Between March 1992 and February 1994 (Study 1--survey phase), 142 cows (parity = 1-6) grazed pasture which consisted of signal grass (Brachiaria decumbens and Brachiaria brizanta). Once-a-month data were collected on body 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 after 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 reproductive 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 protein (CP), and dry matter digestibility (DMD) of pasture available for grazing 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 in the dry season. In Study 2, milk production tended to the higher (7.3 and 6.5 kg/day, respectively, for the intervention and survey studies; p = 0.08). The data suggest that milk production is being limited by pasture availability, the quality of pasture, and the lack of supplementation. We suggest that, although supplementing cows in the dry period may have an economic advantage, better pasture management needs to be introduced. Stocking rate must be adapted to pasture productivity and pasture quality throughout the year.
巴西大多数奶牛场的生产效率较低，且完全依赖牧场。为研究牧场的生产潜力，并制定策略以进一步提高该生产系统中牧场和动物的生产效率，开展了相关研究以获取农场的基础信息。评估的参数包括影响奶牛生产效率和繁殖性能的限制因素、犊牛哺乳时间限制的影响，以及旱季进行策略性补饲对动物生产的影响。1992年3月至1997年2月，在圣保罗州北部地区的四个私人农场开展了研究。1992年3月至1994年2月（研究1——调查阶段），142头奶牛（胎次=1 - 6）在由俯仰臂形草（臂形草和大黍）组成的牧场上放牧。每月收集一次体重、体况和产奶量数据。通过牛奶孕酮谱评估繁殖参数。1996年3月至1997年2月（研究2——干预阶段），对来自两个农场的45头泌乳奶牛每天手工挤奶一次，并将犊牛哺乳限制在挤奶后两小时。收集了产奶量和奶牛体重数据。在研究1中，按产犊日期对奶牛进行分组，以分析繁殖和生产数据。比较了从所有农场随机选取的奶牛（n = 69）的血液代谢物、血红蛋白和血细胞比容浓度。不同季节每公顷（ha）可利用的估计牧场、粗蛋白（CP）和可用于放牧的牧场干物质消化率（DMD）存在差异（p < 0.05）[可利用牧场分别为1.2、1.4、1.8和2.2吨/公顷（标准误=0.70）；CP分别为42、60、48和57克/千克（干物质）（标准误=10.1）；DMD分别为399、468、401和457克/千克（干物质）（标准误=21），对应1992年旱季（D92）、1992年雨季（W92）、1993年旱季（D93）和1993年雨季（W93）]。产后90天（DPP）表现出卵巢活动的动物比例，雨季产犊的奶牛高于旱季产犊的奶牛。在研究2中，产奶量有升高趋势（干预和调查研究分别为7.3和6.5千克/天；p = 0.08）。数据表明，产奶量受到牧场可利用性、牧场质量和缺乏补饲的限制。我们建议，尽管在干奶期对奶牛进行补饲可能具有经济优势，但需要引入更好的牧场管理措施。全年的载畜率必须适应牧场生产力和牧场质量。
