Effects of heights of Marandu pastures and sources of energy supplements on the intake, digestibility of nutrients by young Nellore bulls during the rainy season
The study was conducted to evaluate the sward heights, and energy supplementation with different sources effects on the forage nutritive value, total DM intake, and digestibility of nutrients by young Nellore bull yearling in pastures of Urochloa brizantha Marandu in continuous stocking grazing system during the rainy season. Effects of three sward heights (15, 25 and 35 cm) and three supplements (mineral mixture and two protein-energy supplements, based on corn and other on citrus pulp), were studied. Both energy/protein supplements contained 19.0% of crude protein were supplied at 0.3% of body weight/day. Forage mass, and animal body weight were determined monthly to calculate the forage allowance and the amount of supplement. Experiment was conducted from January to April, at this time forage was sampling by hand plucking methodology to evaluate the nutritive value. Fecal production was estimated using an external marker LIPE®; (Eucalyptus grandis lignin isolated, purified and enriched). Individual supplement intake was estimated using titanium dioxide (TiO2) as external marker. Experiment was conducted according to a randomized completely design whit a combination of three pasture heights and three supplements. The average value of NFC was 20.0, 20.0, and 18.9% in pastures of 15, 25 and 35 cm height. There was a linear increase in the levels of NDFap (52.9%, 53.6% and 55.9%), and a reduction on the CP levels (16.3, 15.3%, and 14.7 %) in response to the pasture heights (15, 25 and 35 cm, respectively). Pasture maintained at 15 cm presented highest NPN of total nitrogen, and with 35 cm, showed highest values of N associated to NDF fraction. Intake of DM, OM, and NDF increased linearly in response to sward heights, however diet digestibility decreased. Citrus pulp supplementation as an energy source provided a greatest intake of DM, OM, CP, TDN and also increased the digestibility of DM, OM and CP compared to the others treatments. There was a reduction of NDF digestibility in response to corn supplementation. Swards grazed in lowest height, resulted in lower dry matter intake, but the CP and no fiber carbohydrate intake did not differ among heights, due to the greater proportion of these nutrients in the lowest pastures. It was concluded that swards grazed at lowest height provided forage with better nutritive value. Citrus pulp utilization as a source of energy of supplement increased the intake and digestibility of nutrients.
Keywords: Beef cattle, citrus pulp, digestibility, tropical grass