Grazing dormant cool season forage
Does supplement type impact growing calves' performance?
By Adam McGee
Tall fescue (Festuca arundinacea) is the predominate forage across most of the southeastern United States. Tall fescue provides excellent forage for beef cattle during the spring and fall; however, as a cool season grass, its quality declines during the summer and winter resulting in decreased cattle performance during these seasons. Feeding supplemental feeds during these periods can help minimize the drop in performance of growing calves (McCollum and Horn, 1990; Kunkle et al., 2000).
The increasing availability of byproduct feeds has allowed for opportunities to decrease supplement costs and increase performance of cattle grazing forages. Dried distillers grains (DDG) is a by-product of ethanol production and has minimal starch (5.88%) and high crude protein (31%)(NAESM, 2016).
After reviewing several studies, McCollum and Horn (1990) summarized that supplementation with high protein diets produced better performance results compared to supplementing with high energy feeds on low quality forages. However, other studies (Bodine, 2001; Beck, 2006) found minimal differences in performance when grazing animals were fed high protein or high energy diets.
With the increasing prevalence of stocker operations in southwest Missouri, we designed this study to compare the effect of supplement type (starch vs protein) on the performance of growing beef cattle that were grazing dormant tall fescue dominated pastures in southwest Missouri.
Materials and methodsForty-two Hereford heifers (average wt 528 lbs) were sourced from the Journagan Ranch in Mountain Grove, Missouri, to be utilized in this 60- day supplementation study grazing dormant cool season pastures from 12/6/2022 to 01/30/2023.
Heifers were initially blocked by weight into three weight classes and randomly assigned within block to one of three supplement treatments: no supplemental feed (CON), high starch (STARCH), or high protein (DDG) (Table 1). Heifers were sorted into two head pens within treatment and block and were provided daily supplement at a rate of 0.75% of initial bodyweight.
Heifers were allowed to eat for 45 minutes before being returned to their pasture. Feed refusals were weighed and recorded daily by pen. All heifers shared a common pasture with free choice mineral and pasture rotation occurred based on forage availability. When snow or ice accumulation prevented feeding, hay previously baled from the same pastures was rolled out for the animals.
Body weights were recorded for all heifers prior to the start of feeding (initial), week 4 (intermediate), and end (final) of the study. Weights were taken on two consecutive days at both the start and end of the study and were averaged for the initial and final body weights respectively.
Results and discussionBody weight estimates and average gaily Gains (ADG) for the three treatments are reported in Table 2. Initial heifer body weights were statistically similar to each other (Trt x Block P = 0.94; Block P < 0.01; Trt P = 0.60) by design. Intermediate body weights and final body weights were statistically different (Trt x Block P ≥ 0.64; Block P < 0.01; Trt P < 0.01), with both supplemented groups being heavier at both time points than the control (P ≤ 0.05) and the DDG group being heavier than the STARCH group for final body weights (P ≤ 0.05).
Average daily gain was statistically significant at all three time points, Weeks 1-4 (First half), Weeks 5-8 (Second half) and Weeks 1-8 (Overall) (Trt x Block P ≥ 0.69; Block P ≥ 0.13; Trt P < 0.01). The ADG of the two supplemented treatments were greater at all three time points than the CON group (P ≤ 0.05). The ADG of STARCH and DDG were similar during the first half, but the ADG of heifers on the DDG treatment were heavier than those on the STARCH treatment for both the second half and the entire 60-day study (P ≤ 0.05).
During the first half of the study the weather was mild which likely allowed the forage to retain its nutritive value, resulting in similar performance between the two supplemented groups. During the second half of the study (weeks 4-8) the weather was colder with both snow and ice events, and the forage quality deteriorated quickly likely leading to the decrease in performance of all three groups.
Throughout the entire study, the heifers on the DDG diet had numerically higher gains that became statistically different from the STARCH treatment during the second half of the study. Our results suggest that providing supplemental feed in the form of DDG will improve the performance of growing cattle grazing dormant cool season pastures.
Literature citedBeck, P. A., S. A. Gunter, and J. M. Phillips. 2006. Evaluation of Supplementation Programs for Growing Cattle Grazing Tall Fescue. Prof. Anim. Sci. 22:325-333.
Bodine, T. N., H. T. Purvis and D. L. Lalman. 2001. Effects of supplement type on animal performance, forage intake, digestion, and ruminal measurements of growing beef cattle. J. Anim. Sci. 79:1041-1051.
Kunckle, W. E., J. T. Johns, M. H. Poore, and D. B. Herd. 2000. Designing Supplementation Programs for Beef Cattle Fed Forage Based Diets. J. Anim. Sci. 77:1-11.
McCollum, F. T. and G. W. Horn. 1990. Protein Supplementation of Grazing Livestock: A review. Prof. Anim. Sci. 6:1-16.
NASEM. Nutrient Requirements of Beef Cattle. 2016. 8th rev. ed. Natl. Acad. Press, Washington, DC.
McGee is an assistant professor in animal science in the William H. Darr College of Agriculture at Missouri State University.
