Control de intensidad de defoliación sobre la producción de forraje estacional y total en sistemas lecheros

This study aimed to determine the effect of controlling the intensity of defoliation (ID) on forage production and herbage disappearance in eight commercial farms, in a complete randomized block design. Two blocks were selected in each farm to compare, the grazing management routine of the farm (T0) vs. controlled management (T1, pre grazing height 15-20 cm and post grazing height 5-7 cm). Pre grazing sward height (SH), herbage mass (HM, kg DM ha-1) and daily growth rate (GR, kg DM ha-1 d-1) were determined. In average, SH was lower (p <0.05) in autumn (A) and winter (W) (15.5 ± 1.2 and 16.9 ± 1 cm) than in spring (Sp) and summer (Su) (19.8 ± 1.0 and 21.1 ± 1.2 cm). The same trend (p <0.05) followed HM (A: 1250 ± 164; W: 1476 ± 145; Sp: 1914 ± 140; Su: 2564 ± 167 kg DM ha-1). Average GR was 26.5% higher in T1 than in T0 (p <0.05), and significant differences remained throughout the seasons (A: 19.3 ± 4.3 vs 7.0 ± 3.9; W: 21.3 ± 3.4 vs 17.0 ± 3.0; Sp: 39.6 ± 9.0 vs 33.4 ± 2.5 Su: 43.5 ± 4.2 vs 39.7 ± 4, 0 kg DM ha-1 d-1; p <0.05, for T1 and T0 respectively). In average, T1 yielded 2336 kg DM ha-1 extra when compared to T0, 52% of that was produced in A (p<0.05). Herbage allowance (HA), HM, length of the grazing and SH explained most of the variation (R2 =0.75) of the disappeared forage per hectare (offered - rejected). Controlled grazing management increased herbage production and utilization by dairy cows.