Potencial forrageiro e desempenho de bovinos de corte em pastagem de Hemarthria allISSIma cv. Flórida pastejada em quatro alturas sob lotação contínua

Abstract

The animal production system on pasture is the most economical form of production, however, a good forage planning is necessary. The lack of autumnal forage is common in the Brazilian subtropics. Hemarthria altissima has relative tolerance to cold and less sensitivity to photoperiod, being an alternative in such periods, in addition to good production under limited fertilization conditions. However, the different cultivars have morphological differences between them, requiring specific studies to determine the ideal management height. The main goal of the present study was to determine the management height for H. altissima cv. Florida that maximizes animal performance and forage production. The experiment was conducted at IDR-Paraná, in Ponta Grossa-PR, from October 2019 to April 2020. The experimental area was divided into 12 experimental units with variable area according to the treatment, which were 10, 20, 30 and 40 cm height of pasture management. Purunã heifers with an initial average age of 15 months were used under continuous grazing with stocking rate. There were no significant differences (P>0.05) between treatments for the parameters tiller density (1312 ± 83.42 tillers/m²), phyllochron (67 ± 0.86 degree days), leaf lifespan (623 ± 21.97 degree days), accumulation rate (55.1 ± 5.24 kg DM/ha/day), proportion of senescent material (20.2 ± 1.24%) and total forage production (12428 ± 1323 .1 kg MS/ha). The number of expanded leaves varied significantly (P<0.05) from 8.5 (10 cm) to 10.6 (40 cm) leaves. The percentage of leaves was significantly higher in treatments 10 and 20 cm, with 42,7 ± 1,32 and 34,7 ± 3,54 % respectively. For each centimeter of increase in pasture height, there was an increase of 118.9 kg of DM/ha. When the period effect was included in the analysis of variance (i.e. 28-day period), a higher average daily gain (ADG) was observed in spring and summer (0,632 ± 0,0548 kg/animal/day), due to higher values of forage supply (14,4 ± 3,18 %), supply of blades (5,1 ± 0,96%) and accumulation rate (80,7 ± 14,82 kg MS/ha/day) in the same period, while the gain per area was higher in the summer (3,5 ± 0,30 kg/ha/day) due to a higher stocking rate (2426 ± 297,5 kg/ha), regardless of the treatment, as no significant interactions were observed between these two factors (i.e. period x treatment). A higher ADG ( 0.660 ± 0.0108 kg/animal/day) was observed in the 40 cm treatment, but also a lower gain per area (351 ± 5.5 kg BW/ha) due to a lower stocking rate. (1056.9 ± 7.11 kg PV/ha). Regression analysis showed maximum values for ADG with height around 32 cm (0.61 kg/animal/day). A significant quadratic relationship was also observed between pasture height and gain per area, with maximum values around 21 cm (433.8 kg BW/ha in 177 days of grazing). Therefore, this range of pasture height (21-30 cm), which is equivalent to moderate grazing, can be considered for the management of cv. Florida.