404 Energy balance and net energy for maintenance of beef × dairy crossbred steers.

Abstract Our objective was to determine the partitioning of energy in beef × dairy crossbred steers fed at 2 multiples of maintenance and to determine their net energy for maintenance (NEm) requirement. Beef × dairy crossbred cattle make up approximately 28% of the cattle on feed in the United States. Their NEm requirement and efficiency of metabolizable energy use is currently unknown but is hypothesized to be intermediate between beef steers and dairy steers. Seventeen beef × dairy steers with Holstein dams and Angus or Angus × Simmental sires were used in a crossover design (initial BW = 492 ± 21 kg). Steers were assigned randomly to either maintenance energy intake (1X; estimated at 84 kcal/kg of MBS) or 2-times maintenance energy intake (2X). Total fecal and urine collections were obtained over 6 d along with gas exchange over a 24-h period. After the collection period, steers were fasted, and fasting heat production (FHP) estimates were obtained using indirect respiration calorimeter headboxes (24 h). Body weight and DMI differed (P < 0.01) between treatments. On a megacalorie basis, digestible energy, fecal and urinary energy loss, metabolizable energy, heat production, and recovered energy were greater (P < 0.01) for the 2X steers. Total methane production tended (P = 0.06) to increase for 2X vs. 1X steers. Apparent DM digestibility was less (P = 0.02) in 1X than in 2X steers. As a percentage of intake energy (IE), urinary energy loss, metabolizable energy, heat production, and retained energy were greater (P = 0.02) for 2X than for 1X steers. Fecal energy loss tended to increase (P = 0.07) for 2X steers, which caused a tendency (P = 0.07) for digestible energy, as a percentage of IE, to decrease for 2X vs. 1X steers. As expected, enteric methane production, as a percentage of IE, was greater (P < 0.01) for 1X steers. Using metabolizable energy intake and recovered energy during FHP, 1X, and 2X measurements, the estimate of NEm was 117 kcal/kg BW0.75. Steers were outside of thermoneutral conditions for 41% of the study and were younger than the beef and dairy steers evaluated for previous NEm determinations both of which could have contributed to an increased NEm. The NEm requirement of beef x dairy steers deserves further research to determine whether the value we observed is repeatable and to directly compare it with purebred beef and dairy cattle in the United States.