Abstract #T360

# T360
Effect of rumen protected carbohydrate supplementation on performance in feedlot finishing steers during heat stress.
Juan P. Russi*1,3, Patricio Davies4, Nicolas DiLorenzo2, Alejandro E. Relling1, 1Facultad de Cs Veterinarias, UNLP, La Plata, Buenos Aires, Argentina, 2University of Florida, Mariana, FL, 3RUPCA LLC, Merced, CA, 4INTA, Gral Villegas, Buenos Aires, Argentina.

Finishing steers during the summer can be challenging due to the effects of high temperatures and humidity on DMI. The objective of this study was to evaluate the inclusion of a rumen-protected carbohydrate (RUPCA; US Patent # 8,507,025) on performance of finishing steers during heat stress. Temperature-humidity index average measured every day during the experiment was 72 ± 4.9. Crossbred steers (n = 135; 355 ± 20kg) were used in a 62-d experiment. Steers were blocked by initial BW and placed into 15 pens. Steers within blocks were randomly assigned to 3 treatments: T0 = fed 91.4% of a basal diet (% DM), 22.3% corn silage, 65.9% dry corn, 0.6% sunflower meal, 0.5% urea, 2% minerals and vitamins and 8.6% of a supplement containing (% DM) 58.1% soybean meal, 38.9% soluble carbohydrates, 2% urea and 1% minerals salts; T1 = fed the basal diet plus 4.3% supplement and 4.3% RUPCA; and T2 = fed basal diet plus 8.6% RUPCA. The supplement and RUPCA consisted of the same ingredients, differing on the processing of the carbohydrate (i.e., protected or not from ruminal degradation). Body weight was measured on d 0, 15, 39 and 62 relative to the beginning of treatments feeding (d 0). Pen DMI was measured on d 10, 18, 25, 31, 35, 46, 51, 56, 60 and 62. Back-fat on the 12th rib (BF) and LM area were measured on d 1 and 62. Data were analyzed as a randomized complete block design with repeated measures using a mixed model of SAS. Initial BW was used as a covariate. There were no differences between treatments on final BW, BF or LM area on d 62 (P > 0.10). Treatment × day interactions were observed for G:F, ADG and DMI (P < 0.05) suggesting a different response to treatments during periods of heat stress (Table 1). Feeding RUPCA may be beneficial for finishing steers under heat stress. Table 1.
T0T1T2TrtDayTrt × Day
DMI, kg/d9.9ab9.8a10.0b0.070.04<0.0010.001
Initial BW, kg2872852850.60.23
Final BW, kg3523573533.10.51
ADG, kg1.<0.0010.039
Backfat 12th rib (62 d), mm0.580.610.600.0170.68
LM area (62 d), cm257.654.956.10.970.30
abMeans without common superscript differ (P < 0.05).

Key Words: carbohydrate, rumen, bypass energy