Resumen Se compararon terneros braford machos enteros y castrados, con diferentes edades de esterilización, con el objetivo de evaluar este efecto en el crecimiento mediante la ganancia total y diaria de peso. Se utilizaron 28 terneros al pie de madre en campo natural. Se dividieron aleatoriamente en grupos de 7 individuos: C45: castrados a los 45 días de edad; E45: enteros con 45 días de edad; C90: castrados a los 90 días de edad y E90: enteros con 90 días de edad. Los pesos se registraron individualmente el día 0 (día de la castración) y posteriormente los días 15, 30 y 45. La técnica de castración se realizó por cirugía cruenta. Las variables estudiadas para el peso vivo fueron: ganancia total (GT, kg) y ganancia media diaria (GMD, kg/día). Se obtuvieron estadísticas descriptivas, análisis de varianza (ANOVA) y test de Duncan (p<0,05), tomándose como efecto principal la edad de castración (45 y 90 días), obrando los enteros como testigos. Las medias para GT fueron: C45: 34,86 kg; E45: 37,29 kg; C90: 51,14 kg y E90: 44,29 kg. Para GMD fueron: C45: 0,58 kg; E45: 0,62 kg; C90: 0,85 kg y E90: 0,74 kg. El ANOVA arrojó diferencias significativas para ambas variables: GT (p=0,0156) y GMD (p=0,0157), siendo C90 superior al resto de los grupos. Por su parte, E90 obtuvo valores intermedios entre C90 y los terneros de 45 días. Entre C45 y E45 no se hallaron diferencias significativas en ambas variables. Se concluye que el momento elegido para la castración debe ser cercano a los tres meses, ya que a los 45 días el peso vivo resultó más afectado por la cirugía.

Abstract We compared entire versus castrated male Braford calves, at different ages of castration, with the objective to evaluate this effect on growth by means of the total and daily weight gain. Twenty-eight Braford male suckling calves, were used. Animals were randomly divided into groups of 7 individuals: C45: castrated at 45 days of age; E45: entire, with 45 days of age; C90: castrated at 90 days of age and E90: entire, with 90 days of age. Individual weights were recorded on day 0 (castration’s day) and then on days 15, 30 and 45. Castration was performed by means of surgery. The studied variables were total gain (GT, kg of live weight) and average daily gain (GMD, kg/day). Descriptive statistics, analysis of variance (ANOVA) and Duncan’s test (p<0.05) were performed, considering as the main effect the age of castration (45 and 90 days), with the intact males as controls. The means for GT were: C45: 34.86 kg; E45: 37.29 kg; C90: 51.14 kg and E90: 44.29 kg. For GMD, they were: C45: 0.58 kg; E45: 0.62 kg; C90: 0.85 kg and E90: 0.74 kg. The ANOVA test showed significant differences for both variables, GT (p=0.0156) and GMD (p=0.0157), with C90 being the higher, considering the other groups. In particular, E90 group obtained intermediate values between C90 and calves of 45 days. Between C45 and E45, no significant differences were found for both variables. We conclude that a recommended castration time should be close to three months of age, since at 45 days of age live weight was more affected by the surgical technique.

The aquatic grasshopper Cornops aquaticum (Bruner) is native to South America and inhabits lowlands from southern Mexico to Central Argentina and Uruguay. This grasshopper is host-specific to aquatic plants of the genera Eichhornia and Pontederia. The objectives of this study were to analyze the feeding patterns of the aquatic grasshopper C. aquaticum in relationship to development stages and sex and to determine the food consumption rate in their host plant, Eichhornia crassipes. Samples were collected from April 2006 to May 2007 in different floodplain lakes of the Middle Parana River. The average consumption was greater in the females (0.127 g food/day ± 0.051) than in the males (0.060 g food/day ± 0.025). The feces of 361 nymphs and adults of this locust were examined and the most common tissue fragments found were of the water hyacinth (E. crassipes). In the initial nymphal stages (I, II and III), an exclusive consumption of E. crassipes was registered, while in the IV and V stages the choice included also other macrophytes. In summary, C. aquaticum presents polyphagy in the field, feeding on six macrophytes of different classes and families.