Forage and shade type effects on stocker heifers' performance
In the Gulf Coast region, performance of young cattle is restricted by the nutritional value of perennial grasses and weather conditions (temperature and humidity). Natural shade is often limited because of grazing on reclaimed croplands or due to reduced number of trees in pasturelands. The objective of this experiment was to evaluate the performance of yearling heifers continuously stocked on alyceclover (Alysicarpus vaginalis L.) or pearl millet (Pennisetum glaucum) for 60 d-grazing periods (early-July to September) with artificial or natural shade. In two consecutive years, 36 crossbred heifers (BW= 323±15 kg) were randomly allotted to 12 paddocks (1.3 ha; 750 kg BW/ha) in a factorial arrangement of treatments with 3 replicates each. Portable shades were built with 6.25 cm pipe and welded into a 3 x 3.5 m frame which held a black woven polypropylene cloth providing 80% shade. These shades were available in half the paddocks while trees provide natural shade to the other half of the paddocks. Alycelover (12 kg/ha) and pearl millet (22 kg/ha) were no-till drilled after two applications of herbicide for weed control. Despite these applications, areas with some crabgrass and johnsongrass were present 30-40 d into the grazing season in all pastures. In July and August, THI (temperature humidity index, an indicator of heat load) was above 76 for the entire day and above 79 from 0600 to 2100. The latter indicates severe heat load which can adversely affect animal performance. Dry matter production of pearl millet (1800 kg DM/ha) was greater (P < 0.05) than alyceclover (1050 kg DM/ha). Alyceclover’s CP concentration (21%) was greater while NDF (53%), and ADF (41%) concentrations were lower (P < 0.05) than pearl millet (11, 63, and 53%, respectively), however, animal gains were not limited by forage mass and nutritional value of either forage. There was no interaction between forage and shade type on ADG (P=0.84). Forage type (P=0.029) affected animal performance. Heifers grazing alyceclover gained more (0.94 kg/d) than those grazing pearl millet (0.80 kg/d). No effect of shade was detected (P=0.19). Heifers with artificial shade gained 0.91 kg/d while those with natural shade gained 0.83 kg/d. As determined by our laboratory before and despite adverse environmental conditions, heifers grazing pearl millet or alyceclover performed better than those grazing bermudagrass (0.60 kg/d). Artificial shades like these are a viable alternative to improve animal welfare when natural shade is not available.
Keywords: alyceclover, pearl millet, shade