Effect of Grazing Pressure and Supplemental Level on Weight Gain in Dairy Heifers

An experiment designed to assess the effect of two grazing pressures (GP, expressed as kg MS/100 kg LW) and four levels of supplement (0, 0.25, 0.50 and 0.75 expressed as kg/100 kg LW) fed to yearling heifers (212 kg) on live weight gain, was carried out at the Dairy Unit of INIA La Estanzuela (Uruguay). The experiment consisted of 8 treatments. Forty animals were used in the experiment, 5 per treatment, each animal being a replication of the treatment. The animals were blocked by weight in 5 blocks of 8 animals each, and then randomly assigned to the different treatments. Field work was carried out in fall of 1993, starting on April 12 and finishing by July 15. Heifers were placed on a four year pasture composed originally of Tall Fescue (Festuca arundinacea L), White Clover (Trifolium repens L) and Lotus (Lotus corniculatus L). Wheat bran (16.2 % CP) was used as a supplement. No significant interaction was found between GP and supplement level. Nevertheless, supplement responses were only obtained at GP 2.5. The effect of GP on live weight gain was found as positive and very significant. As the amount of pasture offered was increased, the response in animal performance improved at a rate of 113 g/a/d of live weight gain per each unit of increment in GP (expressed as percentage of LW). A significant effect of the supplement on live weight gain was found, independently of the GP level. A linear response of 216 g/a/d of live weight gain per each unit of increment in supplement level (expressed as a percentage of LW) was obtained.