Effects of Prepartum Dried Distillers Supplementation on the Performance of Fescue Grazed Fall-Calving Cows and Subsequent Steer Feedlot Performance

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1 Effects of Prepartum Dried Distillers Supplementation on the Performance of Fescue Grazed Fall-Calving Cows and Subsequent Steer Feedlot Performance T.B. Wilson, D.W. Shike, D.B. Faulkner, A.R. Schroeder, T.G. Nash, F.A. Ireland Background As a result of the ethanol boom, dried distillers grains with solubles (DDGS) have become readily available and offer an excellent source of protein. Supplementation with a protein-based supplement is a management tool frequently used to maintain beef cows grazing low quality standing forage. One instance of when this supplementation may become necessary is for fall-calving pregnant or lactating cows grazing established, toxic endophyte infected fescue pastures. This supplementation can serve as a means to maintain cow body condition during the mid to late summer, or what is commonly referred to as the summer slump. This is the period of time when forage quality sharply declines and the negative effects of fescue toxicity are heightened. In some supplementation studies conducted in the western United States, improvements in carcass characteristics of progeny from cows supplemented during late gestation have been observed when compared to non-supplemented cows. These studies have utilized spring-calving cows grazing dormant, low quality native forages when cows are susceptible to loses in body condition; with body condition scores (BCS) likely to fall below 5.0. The goal of this study was to evaluate the efficacy of distillers grains supplementation on maintaining pregnant cow performance through the summer slump period, as well as evaluating any log lasting effects of protein supplementation on subsequent feedlot progeny. Methods Mature, fall-calving Angus and Angus X Simmental cows (n=260) were blocked by breed, then randomly allotted to six groups; resulting in 12 groups total. Cows were placed on one of two dietary treatments: control (CON) cows not offered prepartum supplement or prepartum supplementation (SUP) of 5 lbs. DM/head/d dried distillers grains plus solubles (DDGS) offered daily. For SUP cows, the supplementation period was 60d prepartum to calving. Both treatments were grazed on mixed tall fescue/red

2 clover pastures of similar size and forage availability. Following calving, cows of both treatments were comingled in pastures without supplementation. Cows calving more than 30d after expected calving date were removed from study. At rebreeding, cows were artificially inseminated (A.I.) once using a timed breeding protocol. Cows were then serviced by clean-up bulls for two subsequent cycles. Subsequent steer progeny (n=81; 41 CON, 41 SUP) were weaned at an average of 82d +/- 14d of age and transitioned to a common feedlot diet with individual feed intake monitored using GrowSafe. During the feedlot phase, compositional ultrasound was used to target final 12 th rib fat thickness at 1.1 cm; resulting in steers being harvested at a commercial facility in three groups with equal treatment representation in each group. Results

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4 Conclusions Supplementation of 5 lbs. of DDGS resulted in increased cow average daily gain during the supplementation period. Cow body weight and BCS also tended to be higher when cows were offered DDGS supplement. Resulting A.I. conception rates were relatively low due to technician error that was equal across both treatments; however, supplemented cows tended to have higher conception rates. Along with this, cows offered protein supplementation had significantly higher overall conception rates. Prepartum supplementation had no lasting effects on subsequent steer feedlot performance of carcass characteristics. This may be due to the relatively low level of DDGS that were supplemented. It also thought that the cows utilized in this study were

5 in adequate condition during the supplementation period; and as a result, an adequate nutrient supply was available to the growing fetus.