Effect of partial substitution of concentrate feed by grazing with Leucaena leucocephala on the production and characteristics of milk, and liveweight change of crossbred cows

At "La Esperanza" farm of the University of Zulia, located in Zulia state, Venezuela, 24 non-pregnant predominantly Holstein crossbred cows in the first 45 to 60 days of their third or fourth lactation were used to evaluate the effect of substituting 50 to 75% of concentrate feed (C) with 17% crude protein by grazing of a leucaena bank during 2 h/day (LB) on milk production and properties and liveweight (LW) gain. There were used 12 cows in the dry (DS) and wet (WS) season, respectively. The treatments during DS were: T1: 1 kg of C/cow/day + LB; T2: 2 kg of C/cow/day + LB, and T3: 4 kg of C/cow/day. An additional treatment T4, 2 kg of C/cow/day + LB during 2 h on alternate days, was evaluated during WS. A switch-back design was used in both seasons, with four (DS) and three (WS) cows per treatment and three 4-week periods. Basal diets were Brachiaria humidicola hay (DS) and grazing on Panicum maximum (WS) plus water and minerals ad libitum. Milk productions (kg/cow/d) for T2 (10.5 and 10.8) and T3 (10.8 and 11.1) were higher (P≤0.05) than those for T1 (9.9 and 9.7) in DS and WS, respectively. During WS, T4 (10.2 kg/cow/d) was higher than T1, but similar to T2 and T3. Treatments were similar (P>0.05) for LW gain (360 and 423 g/cow/d), milk fat (3.5 and 3.6%), and protein content (3.3 and 3.4%), acidity (16.5 and 16.6 mL NaOH 0.1N/100 mL) nor density (1.030 and 1.029 g/mL) during DS and WS, respectively. En la finca "La Esperanza" de La Universidad del Zulia, estado Zulia, Venezuela, se seleccionaron 24 vacas mestizas predominantes Holstein, no gestantes y en los primeros 45 a 60 días de su tercera o cuarta lactancia, para evaluar el efecto de sustituir el 50 a 75% de un alimento concentrado (C) con 17% de proteína cruda por pastoreo en bancos de leucaena durante dos horas diarias (BL) sobre la producción, características de la leche y variación de peso vivo. Se utilizaron 12 vacas en las épocas seca (S) y lluviosa (LL), respectivamente. Los tratamientos durante S fueron: T1: 1 kg de C/vaca/día + BL; T2: 2 kg de C/vaca/día + BL y T3: 4 kg de C/vaca/ día; durante LL, se evaluó también T4 : 2 kg de C/vaca/día + BL en días alternos. La alimentación base fue heno de Brachiaria humidicola (S) y pastoreo en Panicum maximum (LL) además de agua y minerales ad libitum. El diseño experimental de reversión doble, con tres periodos de cuatro semanas cada uno. La producción de leche (kg/vaca/día) para T2 (10,5 y 10,8) y T3 (10,7 y 11,1) fue mayor (P≤0,05) que para T1 (9,