Managing the Intake of Mineral Supplements that Contain Feed Additives for Beef Calves Grazing Flint Hills Native Grass Pasture is Important

Objective: The objective of this study was to determine the efficacy of mineral supplementation programs that provide a performance-enhancing antibiotic for improving growth of stocker calves grazing native grass pastures in the Flint Hills region of Kansas. Experimental Procedures: A 91-day grazing study was conducted at the Kansas State University Beef Stocker Unit starting in May 2020 utilizing 314 Brahman influenced crossbred steers (739.57 ± 10.54 lb) from Gorman, TX. Steers were randomized and allocated across 18 pastures and randomly assigned to three treatments groups with six replications (paddocks) per group. The treatments assessed consisted of standard free-choice mineral: 1) control, 2) Bambermycin, and 3) Monensin. Cattle were weighed individually on day 0 and day 90. Group pasture pen scale weights were taken and recorded on day 0, 45, and 90. Results: During the initial stages of the trial, the consumption of the Monensin treatment was significantly lower than the other two treatments (P < 0.05). However, by week seven the Monensin consumption was improved yet still lower than the other two treatments. There were no significant differences in average daily gain (P = 0.72) from the mineral supplement over the 91-day trial. The Bottom Line: Over the 91-day trial, there were no significant differences in average daily gain between the mineral treatments.


Introduction
For stocker cattle grazing in native Flint Hills pasture, optimizing growth rate is important in determining overall profitability. The use of feed additives as a part of a mineral supplementation program is a management practice that can be effectively used to help promote overall productivity during a grazing season. However, provision of mineral on pasture also requires a dedicated effort to manage for the intended level of consumption. The objective of this study was to manage the consumption of a mineral supplement containing two different types of feed additives that can improve the growth rate of stocker calves grazing native grass pastures in the Flint Hills region of Kansas.

Experimental Procedures
A 91-day grazing study was conducted at the Kansas State University Beef Stocker Unit, Manhattan, KS, starting in May 2020 utilizing 314 Brahman influenced crossbred steers (739.57 ± 10.54 lb) from Gorman, TX. Steers were randomized and allocated across 18 pastures at a targeted stocking density of 250 lb/acre. Pastures were randomly assigned to three treatment groups with six replications (paddocks) per group. Identical supplement feeders (Bullmaster; Mann Enterprises, Inc., Waterville, KS) were used in each pasture. The treatments assessed consisted of standard free-choice mineral: 1) control; 2) Bambermycin to be included in the supplement at 32 lb/ton on a dry matter basis to provide 20 mg/head/day, when consumed in 4 oz of supplement; and 3) Monensin to be included in the supplement at 26.67 lb/ton on a dry matter basis to provide 150 mg/head/day when consumed in 4 oz of supplement (see Table 1). Additionally, these treatments were randomly allocated with prescribed fire burn treatments (spring, summer, and fall). A common basal mineral supplement was used for all treatment groups throughout the study. In addition to the mineral supplement, cattle were provided free-choice salt blocks ad libitum.
After receiving the cattle, a 60 net energy for gain diet (mcal/lb) containing Amprolium 1.25% Medicated Pellets (Huvepharma, Peachtree, GA), was fed for 5 days in a limitfed fashion. Upon initiation of the study initial weights were recorded, and steers were randomly assigned to treatment. During this process, calves were given an individual Cattle were weighed individually on day 0 and day 91. Group pasture pen scale weights were taken and recorded on day 0, 45, and 91. On a weekly basis, mineral feeders were weighed to determine consumption. The data collected were used to calculate the previous week's intake of mineral. Mineral in the feeder of each paddock was checked daily for manure, water, or other foreign matter that could interfere with normal supplement consumption. To help cattle find the mineral, all rubber flap covers on all mineral feeders were opened at the beginning of the study. When inclement weather was forecasted, the flaps were closed and reopened as the threat passed. As consumption increased, flaps were closed permanently to minimize exposure to the environment. The initial targeted intake of mineral was 4 oz/head daily for all treatments.
A variety of management strategies were used to drive mineral intake to attain the targeted daily consumption. Because the calculated daily consumption of Monensin was significantly lower during the initial stages of the study, it was deemed necessary to add dried molasses to all treatments. Therefore, beginning week five, 1 lb of dried molasses was added and hand mixed per 50 lb of mineral for all 3 treatments. Because consumption was not increased, the amount of dried molasses was increased to 2 lb per every 50 lb of mineral for all treatments on week six. This concentration remained constant throughout the remainder of the trial for the control and Bambermycin treatments. Despite this increase, low levels of consumption for the Monensin treatment still persisted. On week nine, the level of dried molasses was increased to 3 lb per 50 lb of mineral for the remainder of the trial.
With the addition of dried molasses, the consumption of the control and Bambermycin treatments was vastly improved to the extent that the consumption of their calculated allotted levels was achieved within a 1-to 4-day timeframe over a one-week period. To slow the consumption of these two treatments, mineral feeders were checked daily and moved a distance from the water if mineral was being consumed too quickly. Free-choice salt blocks were also provided to slow the consumption of the control and Bambermycin treatments.

Results and Discussion
Manager attention to detail of the daily intake of mineral supplements is critical as feed additives need to be consumed regularly over several days to attain optimum performance. Figure 1 depicts the actual weekly intake of the mineral treatments over the 91-day grazing season. Daily intake for control and Bambermycin was at or above the target consumption for the first five weeks. During the initial stages of the trial, the consumption of the Monensin treatment was significantly lower than the other two treatments (P < 0.05). By week seven, Monensin consumption was improved but the dosage was below the intended optimum level required to demonstrate a response over control. Over the 91-day trial, there were no significant differences in average daily gain (P = 0.72) between the mineral treatments. The results in Table 3 show the forage quality at four time points of the experimental pastures during this study.

Implications
Continuous monitoring of mineral consumption in relation to its intended intake target is an important management practice that is often overlooked when using mineral supplements as a vehicle for delivery of feed additives. Strategic placement of mineral supplements in a pasture, use of salt blocks, and addition of flavor enhancers such as dried molasses to continuously adjust desired consumption may be used as needed based on intended intake levels.

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