Substituição do farelo de algodão por uréia ou da silagem de milho pelo feno de capim-mombaça em dietas de bovinos de corte

• Autor(a) principal: Pereira, Dalton Henrique
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1691
• topic: Níveis de proteína bruta; Silagem de sorgo; Confinamento; Crude protein levels; Sorghum silage; Feedlot; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::PASTAGEM E FORRAGICULTURA

The present work was developed based on four experiments that were conducted at the experimental, research, and extension center (CEPET) of the Federal University of Viçosa, Brazil, during July to November of 2004. Experiments 1 and 2 were conducted aiming to evaluate the effects of different levels of crude protein (CP) and replacement of cottonseed meal for urea (U) on intake and total and partial apparent digestibility of nutrients, performance, ruminal characteristics, microbial efficiency and nitrogen balance (NB) in beef cattle. Experiment 1 was conducted with 30 Holstein x Zebu (HxZ) crossbred animals (357 ± 27.15 kg of BW), non castrated, distributed in five randomize blocks to evaluate intake and digestibility of nutrients and performance. The experiment were realized involving a 2 x 3 factorial arrangement, being two CP levels (10.5 and 12.5%) and three replacement levels of cottonseed meal for urea (0, 50 and 100%).The diets consisted of 65% sorghum silage and 35% concentrate, % in dry matter (DM). There were no effect of CP, urea and CP x urea levels in the daily intakes of all nutrients, excepted it of non-fiber carbohydrates (NFC), that was influenced by the CP levels, registering higher value with 10.5% CP. The 12.5% CP promoted greater digestibility of DM, organic matter (OM), CP, neutral detergent fiber (NDF) and NFC. Except for the CP digestibility, that was greater with 100% urea, the replacement of cottonseed meal for urea did not influence on digestibility of the other nutrients. There were no treatment differences in the average daily gain (ADG), carcass average daily gain (CADG), feed conversion (FC) and carcass yield (CY %), registering average values of 1.36 kg/day, 0.84 kg/day, 7.54 and 53.49%, respectively. In Experiment 2, four crossbred (HxZ) ruminally and abomasally cannulated steers (226 ± 24.56 kg of BW), castrated, were used in a 4 x 4 Latin square design and fed with the same diet described in Experiment 1, to evaluate the intake and total and partial apparent digestibility of nutrients, ruminal characteristics, microbial efficiency and NB. The experiment were realized involving a 2 x 2 factorial arrangement, being two CP levels (10.5 and 12.5%) and two replacement levels of cottonseed meal for urea (0 and 100%). Except for the daily intakes of CP, rumen degradable protein (RDP) and total digestible nutrients (TDN), which were higher with 12.5% CP, the CP levels did not influence on intakes of the other nutrients. The total replacement of cottonseed meal for urea promoted lower daily intakes of DM, OM, NDF and NFC. The total apparent digestibility of CP and NFC and ruminal apparent digestibility of CP were greater with 12.5% CP, while the total and apparent digestibility of the other nutrients were not influenced by the CP levels. Greater total and ruminal digestibility of CP and NDF with 100% urea were observed. Ruminal pH and NH3-N concentration (mg/dL) were affected by diets, by sampling times and by diet x sampling times interaction. The microbial efficiency was not influenced by diets, verifying average value of 123.05 g CPMic/kg TDN. The 12.5% CP and total replacement of cottonseed meal for urea caused higher serum urea N concentration (SUN), daily excretions of total urinary N (TUN) and urinary urea N (UUN), influencing negatively the NB. The 10.5% CP level and total replacement of cottonseed meal for urea can be used in diets for beef cattle, once do not influence the intake, performance and microbial efficiency, besides promoting greater N utilization efficiency. The third and fourth experiments were realized to evaluate the intake and total and partial apparent digestibility of nutrients, performance, ruminal characteristics, microbial efficiency and NB in beef cattle fed diets with corn silage (CS) and Mombaça hay (MH) in the following ratios on roughage (%): 100CS:0MH; 65CS:35MH; 35CS:65MH and 0CS:100MH. The diets consisted of 65% roughage and 35% concentrate, and were formulated to be isonitrogenous (12% CP, DM basis). Experiment 3 was conducted with 24 Nelore steers, castrated, averaging 334 ± 41.11 kg of BW, distributed in six randomized blocks to evaluate the intake and digestibility of nutrients and performance. The increase of hay level on roughage influenced quadractly the daily intakes of DM, OM, CP, ethereal extract (EE), NDF and TDN, independently in the expression form, registering maximum values of 8.28, 7.83, 1.10, 0.25, 3.74 and 5.50 kg/day, with hay level of 39.78, 39.15, 43.63, 10.50, 69.67 and 32.19%, respectively. However, NFC intake decreased linearly with increase of hay level. Total digestibility of DM, OM and NFC decreased, while CP total digestibility increased linearly with increase of hay level. Hay levels did not influence the total digestibility of EE and NDF, verifying average values of 75.93 and 53.16%, respectively. The ADG decreased starting from 65% level of replacement of corn silage for hay, while FC increased starting from 35% level of replacement. In Experiment 4, four crossbred (HxZ) ruminally and abomasally cannulated steers (226 ± 12,34 kg of BW), castrated, were used in a 4 x 4 Latin square design and fed with the same diet described in Experiment 3, to evaluate the intake and total and partial apparent digestibility of nutrients, ruminal characteristics, microbial efficiency and NB. Although NDF intake increased linearly, the daily intakes of DM, OM, CP, EE, NFC and TDN, independently in the expression form, decreased linearly with increase of hay level. Total apparent digestibility of DM, MO and NFC decreased linearly, while the total apparent digestibility of CP and NDF increased linearly with replacement of corn silage for hay. Except for the NFC ruminal apparent digestibility, that decreased and, the intestinal apparent digestibility of CP and NFC, which increased linearly, the partial apparent digestibility of the other nutrients were not influenced by hay levels. Models of response surface were adjusted for ruminal pH and NH3-N concentration (mg/dL), in function of hay levels and sampling times, being the suitable values for the growth of ruminal microorganisms, independently of diet or sampling time. There was no effect of diets in the microbial efficiency, verifying average value of 143.68 g CPMic/kg TDN. The N intake decreased linearly with increase of hay level on roughage. However, the increment of hay levels promoted linear increase in the SUN concentration and daily excretions of TUN and UUN, causing linear decrease on NB, in g N/day or % of ingested N. Poor quality Mombaça hay, replacing the corn silage, worsening the intake and digestibility of nutrients, microbial protein synthesis, besides promoting higher losses of ingested N. However, animal performance did not influenced until the 35% level of replacement of corn silage for hay, being recommended not to exceed it.