Effects of Late Gestational Cow Tall Fescue Forage System on Steer Offspring Carcass Characteristics

Abstract Text: We hypothesized that cows grazing stockpiled tall fescue (STF) during late gestation would have greater nutrient intake than cows fed summer-baled hay, which would result in increased prenatal nutrient supply and ultimately improved fetal development and subsequent carcass characteristics. Forty-eight multiparous, spring-calving crossbred beef cows (683 + 16 kg BW) were allocated to either strip-graze STF (59.7% NDF, 12.3% CP; DM basis; n = 4 pastures) or consume ad libitum tall fescue hay in uncovered drylots (64.9% NDF, 6.2% CP; DM basis; n = 4 pens) beginning on d 188 ± 2 of gestation. Treatments were terminated within a week post-calving (average calving date: February 18, 2014), and all cow-calf pairs were managed as a single group until weaning. Post-weaning, steer offspring (n = 17) were placed under common management and fed growing and finishing diets. Steers were slaughtered in 4 groups based on degree of finish, and samples were collected from the longissimus dorsi, semimembranosus, and supraspinatus. Data were analyzed with maternal forage system as a fixed effect, and dam pasture or pen was considered the experimental unit. It has been previously reported that birth weight was reduced in calves born to cows fed hay during late gestation, suggesting impaired fetal growth due to low forage nutrient availability. Despite this, there was no effect (P > 0.23) of maternal forage system on carcass weight, yield grade, marbling score, backfat thickness, ribeye area, KPH, or dressing percent. Additionally, Warner Bratzler shear force, cook loss, percent moisture, and percent fat of the 3 muscles sampled were not impacted by maternal forage system (P > 0.16). Longissimus dorsi b* value was greater (P = 0.03) for steers born to cows grazing STF compared with steers from hay-fed cows, but there were no other differences (P > 0.16) in L*, a*, or b* for the 3 muscles samples. Supraspinatus from steers born to cows grazing STF also tended to have greater (P = 0.12) deoxymyoglobin and less (P = 0.12) oxymyoglobin. No other differences (P> 0.25) were observed for metmyoglobin, oxymyoglobin, or metmyoglobin concentrations due to maternal forage system. In conclusion, maternal forage system did not impact steer offspring carcass yield or quality in the current study but may impact product color.

Keywords: carcass, developmental programming, meat color