Our objective was to evaluate production, nutritive value and carrying capacity of piatã grass (Brachiaria brizantha cv. BRS Piatã), and performance of Nellore heifers in agrosilvopastoral systems (ASPS) with three eucalyptus (Eucalyptus urograndis) tree densities, during winter, spring, summer, and fall. Three integrated systems were evaluated: ASPS-1 (357 trees ha(-1)), ASPS-2 (227 trees ha(-1)), and CON (5 trees ha(-1)). In each system, two sward heights were evaluated: short and tall. A total of 80 11-month-old Nellore heifers were randomly allocated in a randomized split-plot block, 3 × 2 factorial. Greater dry matter availability was observed on CON pastures during the fall season. Greater percentage of leaf lamina was detected on ASPS-1 with short sward height and greater during summer, compared with other seasons. A greater forage production was observed between tree rows and for tall sward height. Spring was the season with less forage nutritive value. Average daily gain was greater during summer and fall. Gain per hectare and stocking rate were greater on CON system and on ASPS-2. Pastures with short sward height had greater gain per hectare and stocking rate. Agrosilvopastoral systems with intermediate tree density seem to be a good choice for producers willing to diversify their revenue sources without decreasing animal production.
The objective was to evaluate vaginal temperature as a thermoregulatory response of Nellore heifers under different microclimatic conditions. The study was conducted during one year in an experimental area located at 54°37′W, 20°27′S, and 530 m of altitude in Brazil. Twenty-four Nellore females were reared in integrated crop-livestock-forestry systems with different shading patterns. The randomized complete block experimental design was utilized with a sub subdivided plots scheme, with plot corresponding to the production systems, the subplot to the season of the year, and the sub subplot, the hours of the day. To characterize the microclimate, data regarding air and black globe temperatures, and air relative humidity were collected and from them, temperature-humidity index was calculated. Vaginal temperature was obtained by using a bottom-type temperature logger (i-button) attached to an adapted intravaginal device. The black-globe temperature explained the variation on vaginal temperature. Increases on vaginal temperature were only observed, on average, two hours after the increase of black-globe temperature. The microclimatic conditions found in the systems, resulting from the various tree densities, modify the vaginal temperature in different degrees, demonstrating that the shading effect is not always accompanied by improvements in thermal comfort. The system with intermediate density showed a better microclimatic condition and, consequently, a lower increase in vaginal temperature. The interaction between air temperature, humidity and solar radiation resulted in adverse environmental conditions, however, Nellore heifers showed good adaptation to the environment. In conclusion, vaginal temperature is a good indicator to evaluate the thermoregulatory response in Nellore heifers.
Foram avaliados os principais indicadores zootécnicos, os componentes do custo de produção e os principais indicadores econômicos em fazendas produtoras de leite da região Norte de Minas Gerais, com diferentes estratos de tamanho. A discretização dos dados foi realizada pelo método não supervisionado de acordo com o número total de vacas no rebanho. Foram determinados os coeficientes de correlação linear entre os indicadores zootécnicos, os indicadores econômicos e os custos de produção, assim como parâmetros de regressão das variáveis com correlação significativa com a rentabilidade. Quanto à correlação os indicadores zootécnicos com maior influência nos custos unitários de produção foram a porcentagem de vacas em lactação, o número médio de dias em lactação, a produtividade média do rebanho, a eficiência de utilização da mão de obra e a produtividade por área. Somente o intervalo de partos apresentou correlação significativa com as margens bruta e líquida por litro de leite virtual. A porcentagem de vacas em lactação, a produtividade de animais em lactação e a produtividade por área apresentaram maior coeficiente de correlação com a rentabilidade. Na regressão, os indicadores zootécnicos porcentagem de vacas em lactação e a produtividade de vacas em lactação apresentaram valores negativos para o ponto de intercepto da variável dependente rentabilidade. Conclui-se que estratos com maior produtividade apresentaram menor custo operacional e menor margem líquida, o que não influenciou a obtenção de valores consideráveis de rentabilidade.
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