Nitrogen metabolism and protein requirements for maintenance of growing Red Norte bulls
T.R. Amorim,
A.L. Silva,
M.M. Ladeira,
M.L. Chizzotti,
C.S. Cunha,
O.R. Machado Neto,
J.R.R. Carvalho,
R.R.P.S. Corte,
L.F. Mueller,
A.S.C. Pereira,
M.I. Marcondes
Affiliations
T.R. Amorim
Faculty of Animal Science and Food Engineering, Universidade de São Paulo, Av. Duque de Caxias Norte, 225 – Zona Rural, Pirassununga, São Paulo 13635-900, Brazil; Department of Animal Science, Universidade Federal de Lavras, Avenida Sul UFLA – Aquenta Sol, Lavras, Minas Gerais 37200-000, Brazil
A.L. Silva
Department of Animal Science, Universidade Federal de Viçosa, Avenida PH Rolfs, s/n, Viçosa, Minas Gerais 36570-900, Brazil
M.M. Ladeira
Department of Animal Science, Universidade Federal de Lavras, Avenida Sul UFLA – Aquenta Sol, Lavras, Minas Gerais 37200-000, Brazil
M.L. Chizzotti
Department of Animal Science, Universidade Federal de Viçosa, Avenida PH Rolfs, s/n, Viçosa, Minas Gerais 36570-900, Brazil
C.S. Cunha
Department of Animal Science, Universidade Federal de Viçosa, Avenida PH Rolfs, s/n, Viçosa, Minas Gerais 36570-900, Brazil
O.R. Machado Neto
College of Veterinary Medicine and Animal Science, Universidade Estadual Paulista ‘Júlio de Mesquita Filho’, Rua Prof. Dr. Walter Mauricio Corrêa, s/n – Rubião Junior, Botucatu, São Paulo 18610-307, Brazil;
J.R.R. Carvalho
Department of Animal Science, Universidade Federal de Lavras, Avenida Sul UFLA – Aquenta Sol, Lavras, Minas Gerais 37200-000, Brazil
R.R.P.S. Corte
Faculty of Animal Science and Food Engineering, Universidade de São Paulo, Av. Duque de Caxias Norte, 225 – Zona Rural, Pirassununga, São Paulo 13635-900, Brazil
L.F. Mueller
Faculty of Animal Science and Food Engineering, Universidade de São Paulo, Av. Duque de Caxias Norte, 225 – Zona Rural, Pirassununga, São Paulo 13635-900, Brazil
A.S.C. Pereira
Faculty of Animal Science and Food Engineering, Universidade de São Paulo, Av. Duque de Caxias Norte, 225 – Zona Rural, Pirassununga, São Paulo 13635-900, Brazil
M.I. Marcondes
Department of Animal Science, Universidade Federal de Viçosa, Avenida PH Rolfs, s/n, Viçosa, Minas Gerais 36570-900, Brazil
Dietary protein adjustments can reduce environmental impact and economic losses in production systems. However, we lack information regarding nitrogen (N) metabolism and protein requirements for maintenance of crossbred animals such as Red Norte breed, precluding a precise dietary management. The objective was to evaluate the effect of increasing dietary CP levels (9%, 11%, 13%, 15% and 17%) on intake, digestibility and N balance, as well as to estimate the metabolizable protein requirements for maintenance (MPm) of growing Red Norte bulls. Thirty five animals averaging 280 ± 4.0 kg BW were fed during 45 days in a 60 : 40 forage : concentrate ratio diet in which the last 5 days were used for the digestibility trial. Intakes of CP and non-fibrous carbohydrates (NFCs) and feed efficiency linearly increased (P 0.05). Digestibilities of DM, organic matter, ether extract, NFC and CP as well as metabolizable energy intake linearly increased (P 0.05) by treatments. Urinary N and retained N linearly increased (P < 0.05) with the increase in dietary N. The MPm were estimated as 4.46 g/BW0.75 and the efficiency of use of MPm was 0.673. In conclusion, obtained MPm requirements of growing Red Norte bulls are greater than the values reported in literature for Zebu cattle and dietary CP levels of 15% and 17% exhibited great responses for growing Red Norte cattle. However, a cost-benefit evaluation should be done before its use.