Evaluación de pasturas de Brachiaria decumbens solas o asociadas con Centrosema acutifolium con ganado de doble propósito: II. Evaluación de la productividad animal

En la segunda parte de esta investigación se evaluaron el cambio de peso de las vacas, y sus crías; la producción de leche; y los índices de preñez al finalizar el ensayo. Se utilizaron 4 praderas de 4 ha cada una, dos establecidas con B. decumbens solo, y dos con B. decumbens asociado, las cuales fueron pastoreados en forma alterna cada 21 días, asignándose una carga fija de 1.5 animales/ha. Se emplearon 24 vacas con sus crías (15 de tipo racial Hartón del Valle y 9 del tipo racial Mestizo), divididas aleatoriamente en 2 grupos en un ensayo de tipo "continuo", en el cual los animales pastorearon siempre en la misma pastura  (tratamiento). La producción total de leche, ajustada (incluyendo los días de no ordeño) y corregida por covarianza de la producción acumulada durante los tres primeros días de ordeño, fue significativamente mayor (24% de mayor producción al 5.6% de probabilidad), en la pastura asociada (680 kg, lactancia media de 236 días), que en la pastura sola (550 kg, lactancia media de 241 días). El cambio de peso vivo posparto de las vacas, medido después de 210 días de lactancia y corregido por covarianza del peso inicial, indicó una diferencia altamente significativa (P < 0.003) a favor de la pastura asociada, (466 vs 429 kg). El cambio de peso vivo de las crías, no presentó diferencias significativas. En la pastura asociada las vacas presentaron mayor porcentaje de preñez (58.3% vs 33.3%) y la totalidad de las vacas no preñadas presentaban actividad ovárica. Se estimó una diferencia de tres meses adicionales de intervalo entre partos en las vacas que pastorearon la pastura sola. Trabajo de investigación realizado dentro del programa colaborativo entre el Fondo Ganadero del Valle del Cauca y el Centro Internacional de Agricultura Tropical CIAT. La investigación, se hizo acreedora al Premio Nacional a la "Mejor Investigación en Bovinos", otorgado por el Bando Ganadero en el 18° Congreso Nacional de Medicina Veterinaria y de Zootecnia, realizado en agosto de 1992.

In the second part of this research were evaluated the influence of pastures on the animal production productivity in a dual purpose cattle. Four fields of 4 ha. each one were used; two of them had B. decumbens alone and the other two B. decumbens plus C. acutifolium CIAT 5568. Each pasture was grazed in alternating way, using 21 days of occupation and 21 days of rest There was a fixed animal charge of 1,5 animal units per ha. At the beginning of the experiment there were 24 cows with their calves from the dual-prupose type: 15 from the Native "Harton of Valley" breed and 9 from "Mestizo" racial type (Creole and Zebu cattle crossed with european milking cows). Animals were split random in 2 groups in a "continuous" type of assay in which the animals always were located m the same pasture (treatment). The total milk production analysis was made by mean of an adjustment (including the no milking days). With those data adjusted and corrected by covariance analysis, in which the covariable was the sum of the milk production obtained during the first three days of milking, there was a statistical significant difference (P > 0.056) favoring the associate pasture with a milk production (680 kg, 236 days of lactation), in relation with the pasture alone (550 kg, 241 days of lactation), having a 24% of difference the cows grazed in the associate pasture. The body weight change in cows after birth corrected by covariance analysis (was made closer to the 210 days of lactation) taking as co-variable the cows initial weight. There was a highly significant difference (P > 0.003) favoring the associate pasture (466 vs. 429 kg). In body weight change in calves there was no statistical difference. The cows located in the associate pasture, besides of having a greater pregnancy percentage in relation to the cows in the pure pasture (58.3 vs. 33.3%) and met ovarian activity in alls non pregnant cows. Also was estimated a difference in a larger calving intervals near of three aditional months with the cows grazed in pure pasture.