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 blood metabolites 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).Blood samples were taken from jugular vein prior morning feeding on d 0, 15, 39, and 62 and analyzed for glucose, insulin, urea and NEFA concentrations. Data were analyzed as a randomized complete block design with repeated measures using a mixed model of SAS. Initial body weight was used as a covariate. Treatment × day interactions were found for insulin (P = 0.01) and urea (P = 0.02) plasma concentrations. There were no differences on plasma concentration of insulin, NEFA or urea among treatments (P > 0.10). T0 showed higher blood glucose concentration (P = 0.05). The results suggest that including RUPCA might help to mitigate the negative effects of heat stress on blood metabolites, potentially improving animal performance. Results are shown in Table 1. Table 1.

Item	T0	T1	T2	SEM	P-value
Trt	Day	Trt × day
Glucose, mg/dL	89.4a	81.9b	83.5b	2.73	0.05	<0.0001	0.35
Insulin, µg/dL	0.56	0.73	0.68	0.072	0.35	0.0014	0.01
NEFA mM	184.4	191.3	160.8	17.15	0.43	<0.0001	0.49
UREA, mg/dL	25.8	26.1	22.0	0.029	0.21	<0.0001	0.02

^a,bMeans without common superscript differ (P < 0.05).