Efecto de la cobertura arbórea sobre la ganancia de peso y el desempeño reproductivo de vacas brahman en trópico bajo

Abstract

RESUMEN: Este trabajo evaluó el efecto de la cobertura arbórea en el desempeño reproductivo de hembras bovinas de la raza Brahman, su ganancia de peso y la de sus crías, en una ganadería de carne del corregimiento La Sierra, municipio de Puerto Nare, Antioquia, situado bajo las coordenadas Latitud 6° 15′ 0″ N y Longitud 74° 33′ 0″ W, con una altura de 125 m.s.n.m., una temperatura promedio de 27°C, una humedad relativa de 81% y una precipitación anual promedio de 2487 mm, características que corresponden a una zona de vida Bosque húmedo Tropical (BhT), según la clasificación de Holdridge (1967). El pasto introducido dominante es el Angleton (Dichantium aristatum) y los árboles predominantes son Melina (Gmelina arborea Roxb), Dinde (Chloropholia tinctoria) y Samán (Samanea saman). En esta ganadería se tomó un grupo experimental de 40 hembras entre 1 y 9 partos, clínicamente libres de problemas sanitarios y que tuvieran programado su parto entre los meses de marzo y abril de 2013. Se conformaron dos grupos: uno de 20 vacas manejadas con sombrío superior al 22% e intercepción de la luz entre el 50 y 80% (tratamiento A) y un grupo control de 20 vacas en condiciones de manejo tradicional, en potreros con bajo sombrío, inferior al 7%, con intercepción de la luz entre el 50 y 80% (tratamiento B). A cada hembra se le evaluó el desempeño reproductivo con ayuda de ultrasonido para determinar reactivación ovárica y ovulación postparto, mediante el hallazgo de cuerpos lúteos. Igualmente se determinaron el número de días abiertos y la tasa de gestación; la ganancia de peso se obtuvo realizando pesajes mensuales en la báscula, tanto a vacas como a crías.

ABSTRACT: This work evaluated the effect of tree cover on reproductive performance and weight gain of female cattle of Brahman race and the weight gain of their calves, beef cattle in the village of La Sierra, municipality of Puerto Nare, Antioquia located under the Latitude 6 ° 15 '0 "N and Longitude 74 ° 33' 0" W coordinates, with a height of 125 m, an average temperature of 27 ° C, relative humidity of 81% and a average annual rainfall of 2487 mm, corresponding to a life zone Tropical moist forest (TMF), as classified by Holdridge (1967).The dominant grass is Angleton (Dichanthium aristatum) and the dominant trees are Melina (Gmelina arborea Roxb) Dinde (Chloropholia tinctoria) and Saman (Samanea saman). In this study an experimental group of 40 females who were between 1 and 9 births, clinically free of health problems and who were scheduled for delivery between March and April 2013 was selected. Two groups were formed: one of 20 cows managed in pastures with shadow more than 22% and light interception between 50 and 80% (treatment A) and 20 control cows in traditional management conditions in pastures with low coverage of shadow, lower 7%, with light interception between 50 and 80% (treatment B). The reproductive performance of each female was evaluated using ultrasound in order to determine recovery and postpartum ovarian ovulation by finding corpora lutea. Similarly , the number of open days and pregnancy rates were determined; weight gain was obtained by performing monthly weighings of cows and calves on the scale.. Additionally, in each group, some physiological variables were measured to correlate with reproductive performance and weight gain, such as respiratory environmental rate and body condition, ethological variables (grazing behavior and dry matter intake), environmental variables (availability forage, temperature and relative humidity in the shade and out of it) and other meteorological variables such as precipitation and sunshine. Statistical analysis was performed using SAS system (Statistical Analysis System), working with a generalized design of randomized blocks; statistical methods used were: analysis of variance, repeated measures assessment over time, binomial proportions using Chi square test and Student's t test. The results showed no significant difference in recovery and weight gain in cows but in weight gain of calves being higher for treatment A (P=0.05); there was a tendency for sooner return to estrus in cows of treatment A (P=0.07); faster return to pregnancy in cows of treatment A thus finding that cows grazing under proper tree cover between 90 and 120 postpartum had greater number of pregnancy (P = 0.05). In conclusion, according to this study, silvopastoral arrangements that provide appropriate shady in the pasture improve reproductive performance in Brahman cows and weight gain in their calves.