Enhancing beef cow grazing productivity during summer: influence of tree density on beef cow and calf performance in natural grasslands

Abstract

Abstract To study the impact of tree density on the productivity of beef cows and their calves grazing natural grasslands during the summer, 29 cows (Brangus and their crossbreeds with British breeds) and their calves were randomly assigned to 3 treatments: 1) Full sun (0 trees/ha), 2) Low density (160 trees/ha), 3) High density (240 trees/ha). Grazing intensity was managed through its height at 7-10 cm in all treatments. Traits evaluated included live weight, body condition score, milk production, pregnancy rate and black globe temperature and humidity index (BGTHI), that were analysed using the SAS mixed and genmode procedures, being significant if P<0.05 and tendencies for P values >0.05 and <0.1. Each cm of forage height was equivalent to 168 kg DM/ha. The lowest BGTHI was recorded under the trees in the treatment 160 trees/ha (69.9±1.4), but the value in the alley of treatment 240 trees/ha (72.1±0.7) was similar to the control (72.2±0.7). Cow and calf productivity was similar among treatments (P>0.05). Cow in the high tree density tended to have a greater pregnancy rate (7/11) than cows in the full sun (2/9), with intermediate values for those in the low tree density (4/9; P<0.06). We conclude that in plantations of 160 and 240 trees/ha of 2 years of age, the cow-calf pair has the same productivity as the treeless group, when the natural grassland height is managed at 9±2 cm. However, pregnancy was positively related to tree density, advantage that was not associated to a lower BGTHI.