190 Impact of post-weaning feeding management during the growing phase on growth performance of Holstein steers, and beef × Holstein steers and heifers.

Abstract Feed intake, growth, carcass characteristics, and time to finish are expected to differ between Holstein and beef × Holstein cattle. However, the effects of dietary strategy on these outcomes are not well established. This study compared the effects of dietary energy density during the growing phase (until body weight [BW] = 350 kg) on dry matter intake [DMI] and efficiency, growth, average daily gain [ADG], hip height, body length, and days on feed [DOF] of Holstein steers, beef × Holstein (B×H) steers, and B×H heifers. One hundred and nineteen individually housed calves (n = 40 Holstein steers, 40 B×H steers, 39 B×H heifers) were used in a randomized complete block design with a 3 × 2 factorial structure. After a 15-d receiving phase, calves were paired by initial BW (205 ± 23 kg) and randomly assigned to either a rapid growth (RG; 1.9 kg/d) or moderate growth (MG: 1.2 kg/d) program. To target RG, calves received a diet containing 48% starch and 15% crude protein [CP], while MG calves received a diet containing 28% starch and 15% CP. Feed intake was recorded weekly through collection of orts and adjusted for dry matter, while BW, hip height, and body length were measured every 28-d. Data were analyzed using the mixed model procedure of SAS with the fixed effects of program, breed/sex, and the 2-way interaction, with initial BW as a covariate. The total DOF until 70% of each treatment reached 350 kg BW was 78-d, 91-d, 104-d, 91-d, 113-d, and 113-d for RG B×H steers, RG B×H heifers, RG Holstein steers, MG B×H steers, MG B×H heifers, and MG Holstein steers, respectively. A breed/sex × program interaction was observed for DMI, such that the average DMI (10.2 kg/d) for the MG B×H steers during the growth phase was 23 to 30% greater than all other treatments (P < 0.01). However, the increased DMI did not result in improved ADG; rather, RG B×H steers grew 15 to 24% faster than all other treatments (Breed/sex × program, P = 0.03). The RG B×H steers had the greatest gain to feed ratio (G:F; 0.233 kg/kg), while MG B×H steers had the lowest (0.165 kg/kg). During the growing phase, hip heights were higher (P < 0.01) for Holstein and B×H steers compared to B×H heifers regardless of feeding program; while body lengths were shortest for RG B×H steers and longest for RG Holstein steers (Breed/sex × program, P < 0.01). Overall, feeding a high-energy diet (RG program) reduced DOF during the growth phase; however, further evaluation of performance in the finishing period is required. Crossbred steers had greater feed efficiency than Holstein steers, while crossbred heifers were similar to both groups of steers.