Derivation of the maintenance energy requirements in Jersey cows differing in body condition score

Research in a variety of species including cattle has suggested energy required for maintenance may be affected by body condition. The objective of this study was to use indirect calorimetry and total fecal and urine collections to estimate maintenance energy and fasting heat production (FHP) of cows differing in BCS. Twelve multiparous nonpregnant and nonlactating Jersey cows were randomly assigned to one of 2 treatment groups. To construct these groups, cows were fed 2 different TMR in a preexperimental period for 84 d resulting in a BCS of >5 (HiBCS) and a BCS <3 (LoBCS), and no difference was observed in initial BW or BCS between treatments, averaging 509 ± 26.0 kg and 4.1 ± 0.23. To begin the experiment all animals were fed at maintenance [NE_Lmaint, (Mcal/d) = 0.10 × metabolic BW (BW^0.75)] for 24 d followed by 4 d of data collection for energy balance, cows were then fasted of 96 h with data collection for energy balance once again taken over the final 24 h. During the maintenance collection period, differences in BW and BCS existed (439 and 566 ± 19.0 kg BW, and 3.0 and 5.0 ± 0.13 BCS) for LoBCS and HiBCS, respectively. Heat production increased with increasing BCS (13.1 to 16.2 ± 0.55 Mcal/d), but when expressed per unit of BW^0.75 no difference was observed (0.14 ± 0.002 Mcal/d per BW^0.75). When fasted, BW loss did not differ averaging 28.9 ± 0.181 kg. The FHP did not differ, averaging 0.10 ± 0.004 Mcal/d per BW^0.75 and resulted in the following representation of maintenance: [NE_Lmaint, (Mcal/d) = 0.10 ± 0.004 × BW^0.75]. During fasting the nitrogen free respiratory quotient tended to differ (0.69 and 0.73 ± 0.014) and O₂ consumption and CO₂ production for protein oxidation differed for LoBCS and HiBCS (5.44 and 2.35 ± 0.988 O₂ and 4.52 and 1.95 ± 0.821 CO₂ L/BW^0.75). Overall, FHP increased with increasing BCS, but FHP per unit of BW^0.75 did not differ. Although BW change was similar during fasting, differences O₂ consumption and CO₂ production per unit of BW^0.75 used for protein oxidation may indicate differences in the nature of body tissue utilization in cows differing in BCS.