Effects of rumen-protected carbohydrate supplementation on performance and blood metabolites in feedlot finishing steers during heat stress

Abstract

The objective of this experiment was to evaluate the inclusion of a rumen-protected carbohydrate (RPC) on growth performance and blood metabolites of finishing steers during the summer. A 62-d feedlot study was conducted using 135 Angus crossbred steers (body weight = 287 ± 13 kg). All animals were fed a basal diet (BD), then treatments were top-dressed. The treatments were the same composition and only varied in ruminal degradability. Treatments were 1) a BD with 1 kg/d of a control supplement (0RPC), 2) the BD plus 0.5 kg/d of the control supplement and 0.5 kg/d of RPC (0.5RCP), and 3) the BD with 1 kg/d of RPC supplement (1RPC). Temperature humidity index and cattle panting scores (CPS) were measured daily during the experiment. Growth performance, back-fat over the 12th rib (BF), LM area, blood glucose and plasma insulin, urea, and nonesterified fatty acid concentrations were measured. Data were statistically analyzed (PROC Mixed, SAS) using treatment, time, and their interaction as a fixed variable and pen as a random variable. There were no differences (P > 0.10) between the three treatments on CPS, BF, and LM area on day 62. There was a trend (P = 0.06) for treatment effect for a greater body weight on the 0.5RPC, and a treatment effect for dry matter intake (P = 0.05). Treatment × day interactions were observed for average daily gain (ADG, P =0.04), suggesting a different response to treatments during the different sampling periods. There was a treatment effect for blood glucose concentration (P = 0.03), having the 0RPC the greatest concentration. Treatment × day interactions were found for plasma insulin concentration (P = 0.01). The results suggest that the response to RPC supplementation depends in part on environment. The use of 0.5 kg/d of RPC tends to improve overall body weight; however, the response to RPC on ADG and plasma insulin concentration depend on the time of sampling.

Keywords: blood metabolites; glucose; heat stress; protected carbohydrate.

Figure 1.

THI across days on the experiment. Marked on the figure is the THI 70 and periods 1 to 3 organized to match sampling of performance and blood metabolites.

Figure 2.

Effects of increasing dose of RPC on ADG in finishing steers during heat stress. The dotted line represents the daily THI. 0RPC steers received the basal diet plus 1 kg/d of supplement top dressed (58.1% soybean meal, 38.9% dextrose, 2% urea, and 1% minerals salts DM basis, without the ruminal protection). 0.5RPC steers received the basal diet plus top dressed 0.5 kg/d of supplement and 0.5 kg/d of RPC (58.1% soybean meal, 38.9% dextrose, 2% urea, and 1% minerals salts DM basis, with ruminal protection). 1RPC steers received the basal diet plus 1 kg/d of RPC. Data are presented as least square means and SEM. P-value for the treatment by time interaction = 0.04.

Figure 3.

Effects of rumen-protected carbohydrate on plasma insulin concentration in finishing steers during heat stress. Steers on treatment 0RPC received the basal diet plus 1 kg/d of supplement top dressed (58.1% soybean meal, 38.9% dextrose, 2% urea, and 1% minerals salts DM basis, without the ruminal protection). Steers on treatment 0.5RPC received the basal diet plus top dressed 0.5 kg/d of supplement and 0.5 kg/d of RPC (58.1% soybean meal, 38.9% dextrose, 2% urea, and 1% minerals salts DM basis, with ruminal protection). Steers on treatment 1RPC received the basal diet plus 1 kg/d of RPC. Data are presented as least square means and SEM. P-value for the treatment by time interaction <0.01; *P < 0.05 using the SLICE option of SAS.