Abstract: The aim of the present study was to estimate ME requirements for maintenance (MEm) and Energetic Efficiency of Weight Gain (EEWG), in four Zebu (Bos indicus) and four Brown Swiss (Bos taurus) cows from cattle farms producing weaners in the tropical area of South Mexico. Cows were fed three levels of ME (low 120 kcal kg-0.75, medium 180 kcal kg-0.75 and ad libitum) during three periods of 28 days each, with an experimental ration consisting of 53% ground hay of Pennisetum purpureum CT-115 and 47% of a concentrate based on grains, containing 2.1 Mcal kg-1 DM of ME and 11.0% CP. Feed intake was measured by weighing food offered and that refused and cows were weighed at the beginning and every 14 days thereafter to assess average Changes in Live Weight (CLW). Requirement of EMm was estimated by regressing values of CLW against ME intake (Y= B0 + B1* x). Average dry matter digestibility was 68.7±4.6 and 66.7±4.4%, whereas gross energy digestibility was 66.3±4.6 and 64.3±4.3%, for the Zebu and Brown Swiss cows, respectively. Significant differences (p<0.05) were found in dry matter and gross energy digestibilities due to breed of cow. No significant differences were found (p>0.05) for requirements of EMm among Zebu and Brown Swiss cows (113.4±19.7 vs. 125.6±12.5 kcal/kg0.75/d1), although the values of EMm of Zebu cows were 9.7% lower compared to those found for Brown Swiss. Efficiency of utilization of ME for maintenance (km) was similar (p>0.05) in both breeds of cows (0.62±0.1 and 0.74±0.1, for Zebu and Brown Swiss, respectively), although Brown Swiss cows showed a higher (19.4%) value for km. EEWG was similar among breeds, but Zebu cows showed greater (22.4%) values (80.2±24.6 and 65.5±4.7, for Zebu and Brown Swiss, respectively). Results from this research confirm that Bos indicus breeds of cattle have lower (10%) energy requirements for maintenance than Bos taurus breeds, an observation that may become an opportunity for beef ranching in Yucatan, for the development of cow genotypes based on crosses of B. indicus x B. taurus, which may allow an increase in energetic efficiency of beef production.
Jose Valentin Cardenas-Medina, Juan Carlos Ku-Vera and Juan Gabriel Magana-Monforte, 2010. Estimation of Metabolizable Energy Requirements for Maintenance and Energetic Efficiency of Weight Gain in Bos taurus and Bos indicus Cows in Tropical Mexico. Journal of Animal and Veterinary Advances, 9: 421-428.