Evaluation of Supplemental Energy Source for Grazing Stocker Evaluation of Supplemental Energy Source for Grazing Stocker Cattle Cattle

Summary A total of 144 steers grazing smooth bromegrass pastures were used to evaluate the effects of supplemental energy sources on available forage, grazing gains, subsequent finishing gains, and carcass characteristics in 2014, 2015, 2016, and 2017. Supplementation treatments evaluated were: no supplement, a supplement with starch as the primary source of energy, and a supplement with fat as the primary source of energy. Supplements were formulated to provide the same quantity of protein and energy per head daily. Supplementation with the starch-based or fat-based supplement during the grazing phase resulted in higher ( P < 0.05) grazing gains than feeding no supplement during all four years. In 2014, 2016, and 2017, grazing gains of steers supplemented with the starch-based or fat-based supplement were similar ( P > 0.05). In 2015, steers supplemented with the fat-based supplement had greater ( P < 0.05) grazing gains than those that received the starch-based supplement. In 2014, supplementation during the grazing phase had no effect ( P > 0.05) on finishing gain, feed intake, and feed:gain. Steers supplemented with the starch-based supplement had greater ( P < 0.05) final finishing liveweight, and greater ( P < 0.05) hot carcass weight than those that received no supplement. In 2015, steers fed the fat-based supplement had higher ( P < 0.05) final finishing liveweight, greater ( P < 0.05) hot carcass weight, and lower ( P < 0.05) finishing gain than those supplemented with the starch-based supplement or fed no supplement. In 2016, steers fed the starch-based or fat-based supplement had greater ( P < 0.05) hot carcass weight and higher ( P < 0.05) marbling scores than those fed no supplement. Supplementation had no effect ( P > 0.05) on finishing gains.


Agricultural Research
Kansas State University Agricultural Experiment Station and Cooperative Extension Service 1 Evaluation of Supplemental Energy Source for Grazing Stocker Cattle L.W. Lomas, J.K. Farney, and J.L. Moyer Summary Seventy-two steers grazing smooth bromegrass pastures were used to evaluate the effects of supplemental energy source on available forage, grazing gains, subsequent finishing gains, and carcass characteristics in 2014 and 2015. Supplementation treatments evaluated were: no supplement, a supplement with starch as the primary source of energy, and a supplement with fat as the primary source of energy. Supplements were formulated to provide the same quantity of protein and energy per head daily. Supplementation with the starch-based or fat-based supplement during the grazing phase resulted in higher (P < 0.05) grazing gains than feeding no supplement during both years. In 2015, steers supplemented with the fat-based supplement had greater (P < 0.05) grazing gains than those that received the starch-based supplement. In 2014, supplementation during the grazing phase had no effect (P > 0.05) on finishing gain, feed intake, and feed:gain. Steers supplemented with the starch-based supplement had greater (P < 0.05) final finishing liveweight, and greater (P < 0.05) hot carcass weight than those that received no supplement. In 2015, steers supplemented with the fat-based supplement had higher (P < 0.05) final finishing liveweight and hot carcass weight and lower (P < 0.05) finishing gain than those supplemented with the starch-based supplement or fed no supplement.

Introduction
Supplementation of grazing cattle is most economically feasible when cattle prices are high relative to the price of grain. Energy supplementation of grazing ruminants may reduce forage intake and digestibility, but energy supplementation at low levels (less than 0.4% bodyweight) has been shown to have little effect on forage intake when crude protein was not limiting. Several studies have evaluated the effect of supplementation on stocker cattle gains and forage utilization during the grazing phase, but few have evaluated the effects of supplementation during the grazing phase on subsequent finishing performance and carcass traits. This research seeks to obtain a more thorough understanding of the interactions among grazing nutrition and management, finishing performance, and carcass traits to facilitate greater economic utilization of these relationships.

Experimental Procedures
Seventy-two steers of predominately Angus breeding were weighed on two consecutive days, stratified by weight, and randomly allotted to nine 5-acre smooth bromegrass pastures on April 9, 2014 (446 lb) and April 7, 2015 (488 lb). Three pastures of steers were randomly assigned to one of three supplementation treatments (3 replicates per treatment) and were grazed for 181 and 224 days in 2014 and 2015, respectively. Supplementation treatments were: no supplement, 4.25 lb per head daily of a starchbased supplement, or 4.5 lb per head daily of a fat-based supplement. Supplements were formulated to provide the same amount of protein (0.7 lb) and energy (3.3 lb of TDN) per head daily. Pastures were fertilized with 100 lb/a N on February 24, 2014 and February 12, 2015. Pastures were stocked with 0.8 steers/a and grazed continuously until October 7, 2014 (181 days) and November 10, 2015 (224 days); when steers were weighed on two consecutive days and grazing was terminated.
Cattle in each pasture were group-fed supplement in meal form on a daily basis in metal feed bunks, and pasture was the experimental unit. No implants or feed additives were used during the grazing phase. Weight gain was the primary measurement. Cattle were weighed every 28 days. Cattle were treated for internal and external parasites before being turned out to pasture and later were vaccinated for protection from pinkeye. Cattle had free access to commercial mineral blocks that contained 12% calcium, 12% phosphorus, and 12% salt. Forage availability was measured approximately every 28 days with a disk meter calibrated for smooth bromegrass.
After the grazing period, cattle were shipped to a finishing facility, implanted with Synovex S, and fed a diet of 80% whole-shelled corn, 15% corn silage, and 5% supplement (dry matter basis) for 125 days and 97 days in 2014 and 2015, respectively. All cattle were slaughtered in a commercial facility at the end of the finishing period, and carcass data were collected.

Results and Discussion
Average available forage for the smooth bromegrass pastures during the grazing phase and grazing and subsequent finishing performance of grazing steers are presented by supplementation treatment for 2014 and 2015 in Tables 1 and 2, respectively. Supplementation treatment had no effect (P > 0.05) on the quantity of forage available for grazing in either year. Pastures grazed by supplemented steers would be expected to have greater available forage DM as consumption of supplement by steers grazing these pastures would likely reduce forage intake thereby resulting in more residual forage.
Supplemented steers had greater (P < 0.05) weight gain, daily gain, and steer gain/a than those that received no supplement in both years. In 2014, grazing weight gain, daily gain, and gain/a were not different (P > 0.05) between steers that were supplemented with the starch-based or fat-based supplement. Steers fed the starch-based supplement had greater (P < 0.05) final finishing liveweight, greater (P < 0.05) hot carcass weight, greater (P < 0.05) overall (grazing + finishing) gain, and greater (P < 0.05) overall daily gain than those that received no supplement. Supplementation during the grazing phase had no effect (P >0.05) on finishing weight gain, feed intake, feed:gain, backfat, ribeye area, yield grade, or marbling score.
In 2015, steers supplemented with the fat-based supplement had greater (P < 0.05) grazing gains than those that received the starch-based supplement. Steers supple-mented with the fat-based supplement had higher (P < 0.05) slaughter weight and hot carcass weight and lower (P < 0.05) finishing gain than those fed no supplement or supplemented with the starch-based supplement.
Under the conditions of this study, supplementation of stocker cattle grazing smooth bromegrass pasture improved grazing performance and increased slaughter weight and carcass weight. Most of the increase in slaughter weight and carcass weight can be attributed to greater gains of supplemented cattle during the grazing phase. Supplemental energy source while grazing had no effect on carcass quality.