Maintenance energy needs of goats: predictions based on observations of heat and recovered energy

J. Luo¹, A. L. Goetsch¹, I.V. Nsahlai^1,2, Z. B. Johnson³, T. Sahlu¹, J. E. Moore⁴, C. L. Ferrell⁵, M. L. Galyean⁶, and F. N. Owens⁷

¹E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK
²Department of Animal and Poultry Science, University of Natal, Scottsville, R. South Africa
³Department of Animal Science, University of Arkansas, Fayetteville, AR
⁴Department of Animal Science, University of Florida, Gainesville, FL
⁵US Meat Animal Research Center, Clay Center, NE
⁶Department of Animal Science and Food Technology, Texas Tech University, Lubbock, TX
⁷Pioneer Hi-Bred International, Crop Genetics Research and Development, Johnston, IA

A database including 80 treatment means based on energy balance publications was constructed and analyzed to estimate fasting heat production (FHP) and ME required for maintenance (ME_m) of goats. Experiments entailed comparative slaughter, respiration calorimetry, or CO₂ entry rate techniques. Goats were of eight breeds and five physiological states (preweaning, growing, mature and nonlactating, early and mid-pregnancy, and lactating). Assuming that heat increment was 40% of total heat energy, unweighted and weighted (number of observations per treatment mean) log-log regressions (n = 74 following removal of outliers) of FHP against BW resulted in FHP (kJ) = 299 x BW^0.762 (R² = 0.82) and 244 x BW^0.826 (R² = 0.75), respectively. The 0.762 and 0.826 BW scaling factors did not differ (P > 0.17) from 0.75. Consequently, equivalent expressions based on mean BW were 311 to 314 kJ/kg BW^0.75 and from regressions with a fixed BW exponent of 0.75 were 330 - 332 kJ/kg BW^0.75. The slope and intercept of a regression of recovered energy (RE) against ME intake (MEI) for preweaning goats differed (P < 0.01) from those for other physiological states. A linear regression analysis of RE on MEI (both kJ/kg BW^0.75) was conducted for the remaining 71 observations, after removing two observations with greater than 2.5 residual SD. The resultant equation was: RE = -298.0 (SE = 22.38) + (0.691 (SE = 0.028) x MEI) [n = 69; R² = 0.90]. These estimates of FHP and efficiency of ME use yielded an estimate of ME_m of 431 kJ/kg BW^0.75. In summary, BW^0.75 appeared acceptable as a scaler for expressing goat energy requirements, and FHP and ME_m of 298 and 431 kJ/kg BW^0.75, respectively, appear appropriate as general descriptors of the maintenance energy need of goats.