Wheat middlings in high concentrate rations: digestibility and ruminal metabolism

Six medium-framed steers, fitted with ruminal cannulae were used in a 6 x 6 Latin square design and fed the following six high concentrat e (90%) rations: control; 5, 10, or 15% pelleted wheat middlings (WM) replacing the concentrate (dry rolled corn); and 5 or 10% pelleted WM replacing the roughage (chopped alfalfa hay). Dry matter (DM), organic matter (OM), and starch digestibilities decreased linearly when increasing levels of WM replaced the concentrate , but replacing the roughage increased DM and OM digestibilities linearly. WM could replace only up to 5 % of the concentrate without reducing nutrient digestibilities, but complete (10% WM) replacement of the roughage increased nutrient digestibilities.

The pelleted wheat middlings were provided by ADM Milling Co., Shawnee Mission, Kansas.

Summary
Six medium-framed steers, fitted with rumin al cannulae were used in a 6 × 6 Latin square design and fed the following six high concentrat e (90%) rations: control; 5, 10, or 15% pelleted wheat middlings (WM) replacing the conce ntrate (dry rolled corn); and 5 or 10% pellete d WM replacing the roughage (chopped alfalfa hay). Dry matter (DM), organic matter (OM), and starch digestibilities decreased linearly when i ncreasing levels of WM replaced the concentrate , but replacing the roughage increased DM and OM digestibilities linearly. WM could replace only up to 5 % of the concentrate without reducing nutrient digestibilities, but complete (10% WM) replacement of the roughage increased nutrient digestibilities.

Introduction
Wheat middlings (WM) are byproducts of flour milling and comprise a mixture of small particles of bran, germ, and the aleurone layer of the wheat kernel. The nutrient content of WM can be highly variable, but NRC publication s indicate that they contain (dry basis) approximately .73 Mcal of N E /lb, .45 m Mcal of NE /lb, 18.0% crude protein (CP), and g high levels of rapidly degradable fiber.
Although WM commonly are us e d as a feed ingredient , little information is available concernin g their nutritive value in high concentrate rations. Cattle performance results indicat e that pelleted WM were more effective as a replacement of roughage than of concentrate in feedlot rations (page 19, this report).
Our objectives were to determin e the effects of WM fed as a replacement for either the concentrat e or roughage components in finishing rations on nutrient digestibilities and ruminal metabolism in feedlot steers.

Experimental Procedures
Six medium-framed stee r s, averaging 1,060 lb, were fitted with ruminal cannulae and utilize d in a 6 × 6 Latin square design. They were fed the following six high concentrate rations (81.5% dry rolled corn, 10% chopped alfalfa, 6% supplement, and 2.5% molasses on a DM basis): control (0); 5, 10, or 15% pelleted ( .25 inch) WM replacing the dry rolled corn; and 5 or 10% pelleted WM replacing the roughage. The rations were formulated to be isonitrogenous , supplied equal amounts monensin and tylosin, and were fed ad libitum, twice daily (8:0 0 AM and 3:3 0 PM) for the duration of the experimental periods. On day 1 of each period, the steers were allocated randomly to one of the six rations.
The experimenta l periods were 14 days and consisted of a 9-day adaptation, a 4-day total fecal collection, and a 1-day rumen sampling. Rumina l digesta samples were collected before the first feeding (0 hour) an d at 2, 4, 6, and 10 hours after the first feeding. The samples consisted of subsamples from the dorsal blind sac, mid-dorsa l region, mid-ventral region, and the reticulum.
Data were analyzed using the SAS GLM procedure. Fermentation profile s were analyzed as a split-plot in time 6 × 6 Latin square design using contrasts (linea r , quadratic, and cubic) for treatment comparisons. Terms in the fixed effects model included the main effects of ration, period, steer, ration × period × steer, time, an d time × ration. Digestibility data were analyze d as a 6 × 6 Latin square design using contrasts (linear, quadratic, and cubic) for specific treatment comparisons. Terms in the fixed effect s model included ration, period, and steer.
The effects of replacing concentrate with WM on DM intake, intake of digestible DM (DDM) , and nutrient digestibilities in the steers are presented in Table 1. Neither DM intake nor digestible DM intake were significantly influence d (P>.05) by replacing concentrate with WM. Dry matter, OM, and starch digestibilitie s decreased (P<.05) in a linear manner with increasing WM. Decreases of 5.7 and 5.3 percentage units in DM and starch digestibilities, respectively, were observed at the 15% level of WM addition.
The effect of replacing concentrate with WM on rumina l fermentation characteristics is summariz ed in Table 2. Ruminal pH increased (P<.05 ) linearly with increasing levels of WM. Acetat e and butyrate proportions increased (P<.05 ) and propionate proportions decreased (P<.05) as WM increased, resulting in a quadratic increase (P<.05) i n the acetate/propionate ratio. Total VFA concentratio n s decreased 25% at both the 10 and 15% leve l s of WM compared to the control.
The effects of replaci ng roughage with WM on DM intake, intake of DDM, and nutrient digestibilitie s in the steers are summarized in Table 1. Daily intakes of DM and DDM were not affected (P>.05) by WM replacement of roughage. However, DM and OM d i gestibilities increase d in a linear manner with increasing levels of WM.
The effects of replaci ng roughage with WM on ruminal fermentation characteristics is summarized i n Table 2. Total VFA and propionate concentratio n and pH were not influenced (P>.05 ) by WM replacement of roughage. Acetate proportions and acetate / propionate ratio were decreased and butyrate proportions were increased as WM replaced roughage.
In summary, WM could replace only 5% of the concentrate without reducing nutrient digestibili ties, but complete (10%) replacement of the roughage increased nutrient digestibilities.