Substituição do farelo de soja por uréia de liberação lenta em dietas de terminação para bovinos de corte

• Autor(a) principal: Benedeti, Pedro Del Bianco
• Data de Publicação: 2012
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5722
• topic: Amônia ruminal; Crescimento microbiano; Proteína; Ruminantes; Ruminal ammonia; Microbial growth; Protein; Ruminants; CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::NUTRICAO E ALIMENTACAO ANIMAL

This study evaluated the effects of replacing soybean meal (SBM) by slow-release urea (SRU) in beef cattle diets containing two concentrate levels on intake, partial and total digestibility, nutrients flow, ruminal parameters, microbial protein production, protein efficiency and nitrogen balance in finishing beef steers. Eight crossbred steers were used (average BW of 418 kg) fitted with ruminal and abomasal cannulae. The animals were distributed in two groups of four steers, each group received one of the two levels of the concentrate (40 or 80% of the total DM). The experiment was designed as a Latin square in 2 x 4 factorial scheme, with two energy levels in the diet, and within each square, four levels of replacement of soybean meal protein by slow-release urea: 0, 33, 66 and 100 %. The interaction of concentrate level x SRU levels was not significant (P>0.05) for any variables measure. Thus, the effects of concentrate level and SRU inclusion will be discussed independently. Dry matter (DM) intake, as well as organic matter (OM) intake and crude protein (CP) intake decreased linearly (P<0,05) as SBM was replaced by SRU. For each percentage unit of SRU added to the diet there was a reduction of 5.80, 5.17 and 0.58 g in DMI, OMI and CPI. The intake of non-fiber carbohydrates (NFC) was higher (P <0.05) in the diet containing 80% concentrate when compared to the 40 % concentrate diet, whereas neutral detergent fiber (NDF) intake was greater (P <0.05) on the low concentrate diet when compared to the high concentrate diet. Ruminal digestibility coefficient of OM tented to be greater (P <0.074) for the 40 % concentrate diet, whereas all other ruminal, intestinal and total digestibility parameters evaluated were not statistically different (P> 0.10) among treatments. DM and OM passage rates (kp) were greater (P<0.05) on the 80% concentrate diet than on the 40 % concentrate diet, with averages of 4.37 and 4.35%. Replacing SBM by SRU up to 100 % on the diet did not lead to any modification (P>0.05) on DM, OM, CP and NDF passage rate. Digestion rates (kd) were also not affected by any of the treatments (P>0.05). The average kd for DM, OM, CP and NDF were 3.82, 4.21, 1.13 and 2.20%. A cubic effect (P <0.10) of SBM replacement by SRU on ruminal ammonia (N-NH3) concentration in relation to the hours of collection was detected. A quadratic effect was observed (P <0.10) by replacing SBM with SRU on pH and on the excretion of urea N in urine, expressed both as g/day or mg/kg of BW. The animals had higher (P <0.10) total N excretion in urine, in g/day, as the slow-release urea levels were increased in the diet, but no significant effects were observed (P>0.10) for total N in urine in mg/kgBW (average of 148.56 mg/kgBW) and in the concentrations of urea N in the serum (average value of 11.53 mg/dL). Nitrogen intake, N excreted in the feces, nitrogen balance and efficiency of nitrogen use decreased linearly (P <0.10) as the levels of SRU increased in the diet, whereas the amount of nitrogen compounds excreted in urine increased linearly (P <0.10) as SRU replaced SBM in the diet. The production of microbial nitrogen and microbial efficiency were not significantly affected by the experimental treatment (P> 0.10) obtaining average values of 152.02 g/day and 120.18 g/kg TDN, respectively.