Effect of Complete Replacement of Dry-Rolled Corn with Unprocessed Rye on Growth Performance, Efficiency of Dietary Net Energy Use, and Carcass Traits of Finishing Heifers

SIMPLE SUMMARY: Crop rotation diversity has many benefits for integrated crop–livestock production systems. Cereal rye deserves consideration for use as a component of an integrated crop–livestock system as rye is a multi-use crop than can be grazed, harvested for forage, or harvested for grain and straw. Previous research from this research center has indicated that processed rye (processed to a processing index of 78.8%) is a suitable ingredient (84% of the net energy value of dry-rolled corn) for use in cattle-finishing diets. Processing grains prior to feeding is proven to enhance growth performance in feedlot cattle. A major impediment to the use of rye in finishing diets is that the rye should be processed prior to feeding, and processing rye requires different equipment settings than for processing dry-rolled corn. The objectives of the present study were to evaluate the impact of the complete substitution of dry-rolled corn with unprocessed rye in finishing diets fed to feedlot heifers on growth performance, dietary net energy use, and carcass traits. ABSTRACT: Continental crossbred beef heifers were used in a randomized complete block design experiment to evaluate the effects of replacement of dry-rolled corn with unprocessed rye on the finishing-phase growth performance and efficiency of dietary net energy (NE) use. Fifty-six heifers (433 ± 34.0 kg) were transported 241 km from a sale barn in North Central South Dakota to the Ruminant Nutrition Center in Brookings, SD. Heifers were blocked by weight grouping and allotted to treatment pens (n = 7 heifers/pen and 4 pens/treatment). Treatments included a finishing diet that contained 60% grain (diet dry matter basis) as dry-rolled corn (DRC) or unprocessed rye grain (RYE). On study day 14, all heifers were consuming the final diet and were implanted with 200 mg of trenbolone acetate and 28 mg of estradiol benzoate (Synovex-Plus, Zoetis, Parsippany, NJ, USA). The RYE heifers had decreased (p ≤ 0.01) final body weight, average daily gain, and gain efficiency; however, they tended (p = 0.08) to have a greater dry matter intake compared to DRC heifers. RYE heifers had decreased (p ≤ 0.01) observed dietary NE and decreased (p ≤ 0.01) observed-to-expected dietary NE ratio for maintenance and gain compared to DRC heifers. The dressing percentage, 12th rib fat thickness, ribeye area, and the distribution of yield and quality grades were not altered (p ≥ 0.12) by dietary treatment. The hot carcass weight, calculated yield grade, estimated empty body fat (EBF), and body weight at 28% EBF decreased (p ≤ 0.02) and retail yield increased (p = 0.01) in RYE compared to DRC heifers. These data indicate that unprocessed rye is a palatable feed ingredient for inclusion in finishing diets for beef cattle and that rye inclusion only minimally influences the carcass quality grade. The feeding value of unprocessed rye is considerably less (21.4%) than that of dry-rolled corn using current standards and approximately 91% of the NE value of processed rye (processing index = 78.8%). Rye grain fed as processed or unprocessed grain has an NE value that is less than 90% of that of dry-rolled corn.