Desempenho produtivo de novilhos Nelore, na recria e na engorda, recebendo dietas com diferentes níveis de concentrado e proteína

Abstract

Foram utilizados 36 novilhos Nelore inteiros, com peso vivo médio inicial de 240 kg, sendo quatro novilhos de referência e o restante distribuído em oito tratamentos, com quatro diferentes níveis de concentrado nas dietas (20, 40, 60 e 80%) e dois níveis de proteína bruta (PB) (15 e 18%), expressos na MS. Avaliaram-se os consumos de matéria seca (MS), matéria orgânica (MO), PB, fibra em detergente neutro (FDN) e nutrientes digestíveis totais (NDT), os ganhos médios diários de peso vivo (GMD), de peso de corpo vazio (GMPVZ) e de carcaça (GC) e a conversão alimentar (CA). O consumo de MS não foi influenciado pelo nível de concentrado, na fase de recria, apresentando média de 7,06 kg/dia, porém, quando expresso em porcentagem do peso vivo (% PV) e em gramas por unidade de tamanho metabólico (g/kg0,75), estimaram-se consumos máximos de 2,59% PV e 107,32 g/kg0,75, com 42,60 e 42,52 % de concentrado, respectivamente. Na fase de engorda, os níveis de concentrado não influenciaram o consumo de MS, observando-se valores médios de 7,16 kg/dia; 1,80% PV e 80,64 g/kg0,75. O aumento do teor de proteína bruta da dieta, de 15 para 18%, elevou o consumo de MS, na fase de recria, mas não influenciou o consumo na fase de engorda. Os níveis de concentrado das dietas não influenciaram os consumos de MO, PB e NDT, nas fases de recria e engorda, cujos valores médios, expressos em kg/dia, foram 6,50; 1,18; e 5,52, respectivamente, na recria; e 6,89; 1,20; e 5,59, respectivamente, na engorda. O consumo de FDN, expresso em kg/dia e % PV, reduziu linearmente com o aumento do nível de concentrado. Os GMD, GMPCVZ, GC e CA não foram influenciados pelos níveis de concentrado da dieta, independentemente da fase estudada, cujas respectivas médias foram 1,15; 1,13 e 0,75 kg/dia e 6,29, na recria, e 1,05; 1,00 e 0,71 kg/dia e 8,02, na engorda. O teor de PB da dieta influenciou positivamente o GMD nas duas fases. A dieta com 18% de PB propiciou, aos novilhos, 22 e 22,6% a mais de ganho de peso na recria e na engorda, respectivamente, comparada à dieta com 15% de PB. Os níveis mais altos de concentrado apresentaram os menores custo de produção por arroba, durante a fase de recria, e os níveis com 40 e 60% de concentrado apresentaram os menores custos por arroba, na engorda.

Thirty six Nellore bulls, with 240 kg initial live weight (LW), were used. Four were reference bulls and the remaining were distributed in eight treatments, with four different concentrate levels in the diets (20; 40; 60 and 80%) and two crude protein (CP) levels (15 and 18%), in dry matter basis. The dry matter (DMI), organic matter (OM), CP, neutral detergent fiber (NDF) and total digestible nutrients (TDN) intakes were determined, as well as the average LW gain (LWG), empty body weight gain (EBWG), carcass gain (CG) and the feed conversion (FC). The DMI in the growing phase, expressed in kg/day, was not influenced by the concentrate level, presenting mean value of 7.06. But the DMI, expressed as a percentage of the LW (% LW) and in grams for unit of metabolic size (g/kg0.75), in this phase, demonstrated a quadratic behavior in relation to the concentrate level, with maximum consumptions of 2.59% LW and 107.32 g/kg0.75, with 42.60 and 42.52% of concentrate, respectively. In the fattening phase, the concentrate levels did not influence the DMI, in any of the expressed ways, with mean values of 7.16 kg/day; 1.80% LW and 80.64 g/kg0.75. The increase in the diet CP level, from 15 to 18%, caused a significant increase in the growing phase DMI, but it did not influence the consumption in the fattening phase. The diets concentrate levels did not influence the OM, CP and TND intakes, in the growing and fattening phases. The average values of OM, CP and TND intake, expressed in kg/day, were 6.50; 1.18 and 5.52, respectively, during the growing phase; and 6.89; 1.20 and 5.59, respectively, during the fattening phase. The NDF consumption, expressed in kg/day and in % LW, had a decreasing linear behavior with the concentrate level increase. LWG, EBWG, CG and FC were not influenced by the concentrate levels of the diet, independently of the studied phase. In the growing phase, the mean values for LWG, EBWG, CG and FC were 1.15; 1.13 and 0.75 kg/day and 6.29, respectively; and, in the fattening phase, they were 1.05; 1.00 and 0.71 kg/day and 8.02, respectively. The diet CP level had a positive influence on the LWG in both phases. The diet with 18% of CP provided, to the bulls, 22 and 22.6% more LWG in the growing and in the fattening phases, respectively, compared to the diet with 15% CP. The highest concentrate levels presented the smallest production cost during the growing phase, and the levels of 40 and 60% of concentrate presented the smallest cost in the fattening