Energy and protein requirements for growth and maintenance of F1 Nellore x Red Angus bulls, steers, and heifers

¹ Department of Animal Science, Universidade Federal de Viçosa, Viçosa, MG 36571, Brazil; Department of Animal Science, Texas A&M University, College Station, TX 77843-2471
² Department of Animal Science, Universidade Federal de Viçosa, Viçosa, MG 36571, Brazil
³ Department of Animal Science, Texas A&M University, College Station, TX 77843-2471

^* To whom correspondence should be addressed. E-mail: luis.tedeschi{at}tamu.edu.

	Abstract

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. Three animals from each gender 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 NE and net protein (MRNE and MRNP, respectively) and the growth requirement for NE and net protein (GRNE and GRNP, 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. There were no differences in MRNE (P = 0.06) among genders. The combined data indicated a MRNE 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 GRNE for steers and heifers were similar (P = 0.15) but were 18.7% greater (P = 0.03) for steers and heifers than for bulls. The MRNP did not differ among genders and averaged 2.53 g CP·kg^-0.75 of EBW·d^-1. Likewise, GRNP was not different among genders. The percentage of retained energy deposited as protein (RE_p) increased as the content of retained energy in the gain (RE_c, Mcal/kg of empty body gain) decreased. The RE_p equation of the pooled data was 46.5 x e^-0.2463xREc. We conclude that the energy requirement of crossbred Bos indicus x Bos taurus for maintenance might be less than that of pure Bos taurus and that RE_p is nonlinearly, negatively correlated with RE_c. The GRNE was less for bulls than for steers and heifers. However, we found no differences in MRNE, MRNP, and GRNP for bulls, steers, and heifers of Nellore x Red Angus crossbreds.

Key Words: beef cattle, Bos indicus, comparative slaughter, digestible energy, net energy, net protein

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				M. L. Chizzotti, L. O. Tedeschi, and S. C. Valadares Filho A meta-analysis of energy and protein requirements for maintenance and growth of Nellore cattle J Anim Sci, July 1, 2008; 86(7): 1588 - 1597. [Abstract] [Full Text] [PDF]