Exigências nutricionais de bovinos Nelore, puros e cruzados, de diferentes classes sexuais

• Ano de defesa: 2007
• Autor(a) principal: Chizzotti, Mario Luiz
• Orientador(a): Valadares Filho, Sebastião de Campos
• Banca de defesa: Tedeschi, Luis Orlindo , Paulino, Pedro Veiga Rodrigues
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Energia líquida; Proteína líquida; Abate comparativo; Zebu
• Palavras-chave em Inglês: Net energy; Net protein; Comparative slaughter; Nellore
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::NUTRICAO E ALIMENTACAO ANIMAL::EXIGENCIAS NUTRICIONAIS DOS ANIMAIS
• Link de acesso: http://locus.ufv.br/handle/123456789/1906

A comparative slaughter trial was conducted with 36 F1 Nellore x Red Angus calves (12 steers, 12 bulls, and 12 heifers), averaging 274 kg BW, to assess the net requirements of protein and energy for growth and maintenance and the net requirements of macro-minerals for growth. Three animals from each group (i.e., steers, bulls, and heifers) were slaughtered at the beginning of the trial to determine the initial body composition. The remaining calves were randomly assigned to 3 treatments: maintenance level (diet containing 70% of DM as corn silage fed at 1.2% of BW daily) or fed concentrate at 0.75 or 1.5% of BW daily with corn silage available for ad libitum consumption. The diets were isonitrogenous (2% N, DM basis). The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict the maintenance requirements for net energy and net protein (NEm and NPm, respectively) and the growth requirement for net energy and net protein (NEg and NPg, respectively). After 84 d of growth, cattle were slaughtered. The cleaned gastrointestinal tracts, organs, carcasses, heads, hides, tails, feet, blood, and tissues were weighed to measure empty BW (EBW). These parts were ground separately and sub-sampled for chemical analyses. For each animal within a period, DMI was measured daily and samples of feces were collected to determine diet digestibility. The antilog of the intercept of the linear regression between the log of heat production (HP) on metabolizable energy intake (MEI) was used to estimate the NEm (on a kcal/kg0.75 of EBW daily). The ME required for maintenance (MEm) was calculated by iteration, assuming that the maintenance requirement is the value at which HP is equal to MEI according to this equation: HP = β0 × e(β1 × MEI). The slope of the regression of retained energy (RE) on MEI was assumed to be the efficiency of energy utilization for growth (Kg). Alternatively, the intercept divided by the slope (Kg) was used to compute MEm. The NPm was assumed to be the intercept of the linear regression of the retained N on N intake. The NEg was calculated as a × EBW0.75 × EWGb, where EBW is empty BW; a and b are the antilog of the intercept and the slope of the linear regression of the log of the RE on the log of the empty body gain (EWG). The NPg was calculated as c + (d × EBW) + (e × RE) where c, d, and e are the intercept and slopes of the multiple regression of the retained protein on the EBW and RE, respectively. The log of the contents of each mineral in the EBW was regressed on the log of the EBW to estimate the net requirement for each mineral per kg of empty body gain (EBG). A meta-analysis was conducted to determine net energy and net protein requirements of growing bulls, steers, and heifers of Nellore purebred and Nellore × Bos taurus crossbreds. A database of 16 comparative slaughter studies (n = 389 animals) was gathered to provided enough information to develop equations to predict the NEm, NEg, NPm and NPg. The data were analyzed using a random coefficients model, considering studies as random effects, and genders (bulls, steers, and heifers; n = 262, 103 and 24, respectively) and breeds as fixed effects. For the experiment, there were no differences in NEm (P = 0.06) among genders for F1 Nellore x Red Angus cattle. The combined data indicated a NEm of 71.2 kcal·kg- 0.75 of EBW·d-1, with a partial efficiency of use of ME to NE for maintenance of 0.71. The partial efficiency of use of ME to NE for growth was 0.54 for bulls, 0.47 for steers, and 0.54 for heifers. The NEg for steers and heifers were similar but were 18.7% greater than for bulls. The NPm did not differ among genders and averaged 2.53 g NPm·kg-0.75 of EBW·d- 1. Likewise, NPg was not different among genders. The percentage of retained energy deposited as protein (%REp) increased as the content of retained energy in the gain (REc, Mcal/kg of EWG) decreased. There were no differences in the net requirements for growth of macrominerals among genders. The equations of the pooled data of the net requirements for growth (g/kg EWG) were: 0.3326 × EBW 0.6367 for Ca, 0.1121 × EBW -0.5615 for P, 0.0108 × EBW -0.3992 for Na, 0.004 × EBW -0.153 for K, and 0.0036 × EBW -0.462 for Mg. For the meta-analisys study, there were no differences in NEm among genders and breeds. The combined data indicated a NEm requirement of 75 kcal/kg0.75 of EBW with a partial efficiency of use of ME to NEm of 0.67. The NEg requirement was different (P = 0.009) among genders and tended (P = 0.06) to be different among breeds. The equation for NEg for bulls was 0.0514 × EBW0.75 × EWG1.070, for steers it was 0.0700 × EBW0.75 × EWG1.070; and for heifers it was 0.0771 × EBW0.75 × EWG1.070. The partial efficiency of use of ME to NEg was not different among genders and breeds, and averaged 0.44. There were no differences in NPm requirement among genders and breeds; the overall NPm requirement was 1.74 g of NP·kg-0.75 EBW·d-1. The overall MP requirement for maintenance was 2.59 g of MP·kg-0.75 EBW·d-1. The NPg requirement, g/d, was not different among genders and breeds; the overall equation was EWG × (217 - 12.8 × RE/EWG), where RE is Mcal/d. %REp decreased exponentially as the REc incresead. Because no study effect was observed, we pooled the data across studies and the overall equation to predict %REp was 0.101 + 1.667 × e(-0.660 × REc ). Our results do not support the hypothesis that bulls have greater NEm requirements than steers and heifers. Likewise, no significant differences in the NPm requirements among bulls, steers, and heifers were detected. Nonetheless, the NEg requirement of steers was greater than for bulls and lesser than for heifers. Even though the %REp was negatively correlated with REc, our findings indicated no differences in NPg requirement for bulls, steers, and heifers.