Maintenance energy requirements of beef cows grazing Campos grasslands

摘要

Energy expenditure of animals has been mainly determined under controlled confined conditions which would do not reflect always the conditions of rangelands cows. Multiparous beef cows (n=25) grazing on two herbage allowances (HA) of Campos grassland(average HA of 8 vs 12 kg dry matter/kg BW; LO vs HI) were used to estimate maintenance energy requirements (MEm) and efficiency use of consumed metabolizable energy (ME) for maintenance (km) in free-range beef cows grazing Campos. Along the annual production cycle, in four periods, cow BW (body weight) and BCS (body condition score), and calf birth weight or milk production and composition, as well as heat production (HP; by the 02 pulse technique) were recorded to estimate retained energy (RE) and MEintake (MEI). Data were expressed as kJ/kgBW0,75. Linear regressions of the dependency of HP on MEI (HP = b x MEI + a) for both, cows in negative and positive energy balance and MEm was calculated. Regressions of HP on MEI were high and significant (PO.001) for both, cows in positive (HP=323 + 0.43 MEI; r2=0.84) and negative (HP=176 + 0.61 MEI; r2=0.76) energy balance. Thus, MEm for rangeland beef cows varied from 444 to 567 kJ/kg of BW0,75 per d depending on their nutritional status. Nutritional statusas well as grazing management should be considered in order to adequate estimate nutritional demands of the suckler beef cow which would allow to improve productive efficiency and environmental sustainability of cow-calf systems.