Meta-analysis of feeding trials to estimate energy requirements of dairy cows under tropical condition

• B. taurus × B. indicus cows have lower energetic requirement for maintenance than B. taurus cows.
• B. taurus × B. indicus cows have lower net energetic efficiency for milk production than B. taurus cows.
• This study may contribute to adjustments in energy recommendations for dairy cows.

A meta-analysis of feeding trials was performed to determine the metabolizable energy requirement for maintenance (MEm) and efficiency of utilization of the metabolizable energy intake (MEI) for milk production (kL) of Bos taurus and Bos taurus × Bos indicus crossbreds dairy cows in the tropics. The database contained 231 treatment means (n = 148 Bos taurus and n = 83 Bos taurus × Bos indicus) from 60 feeding trial studies. A linear regression of MEI with milk energy output adjusted to a zero energy balance (EL(0), MJ/kg BW0.75/day) was fitted using a mixed model with the study as the random effect and the genotype (G) as dummy variable (Bos taurus = 0 and Bos taurus × Bos indicus = 1). The MEm was calculated as the intercept and kL as the reciprocal of the slope of the regression. The dairy cow genotype affected the MEm requirements (P = 0.05) and tended to affect kL (P = 0.08). The equation fitted was MEI (MJ/kg BW0.75/day) = 0.754 (±0.076) − 0.196 (±0.102) × G + [1.522 (±0.126) + 0.368 (±0.210) × G] × EL(0). Thus, Bos taurus × Bos indicus crossbred dairy cows have MEm requirement that was 26% lower (0.558 ± 0.103 vs. 0.754 ± 0.076 MJ/kg BW0.75/day) but kL tended to be 19% lower (0.53 ± 0.10 vs. 0.66 ± 0.05) than Bos taurus cows. These results support the hypothesis that Bos taurus × Bos indicus crossbred dairy cows have a lower MEm, but lower net energetic efficiency for milk production than Bos taurus dairy cows. This study may contribute to adjustments in feeding system energy recommendations for dairy cows under tropical condition.