Date of Award

January 2015

Degree Type


Degree Name

Master of Science (MS)


Animal Science

First Advisor

Jon P. Schoonmaker

Committee Member 1

Kristen Brennan

Committee Member 2

Ron P. Lemenager


Angus x Simmental cows (n = 48, BW = 594 kg, BCS = 5.26, Age = 2.7), pregnant with male fetuses, were used to determine the effect selenium (Se) source during the last 80 d of gestation and first 108 d of lactation on progeny feedlot performance. At 203 d in gestation, cows were blocked by body weight, age, breed composition, and calf sire, and allotted to 1 of 3 treatments: no Se, inorganic Se, or organic Se. Maternal diets were formulated to contain 10.4% CP and 0.90 Mcal/kg NEg during gestation and 12.1% CP and 1.01 Mcal/kg NEg during lactation. Basal diets contained 0.07 and 0.11 mg/kg Se for gestation and lactation diets; respectively. Diets were fed daily as a total mixed ration and Se was provided in a top-dress containing 0, 0.30 mg/kg Se as sodium selenite, or 0.30 mg/kg Se as Sel-Plex®. Treatment diets were fed through 108 d post-partum (DPP). At 68 DPP milk production was calculated using the weigh-suckle-weigh procedure and a milk sample was collected was at 62 DPP to determine composition. At 108 DPP cow-calf pairs were commingled until weaning at 216 DPP. At 28 d post-weaning, steers (n = 47, BW = 301 kg) were placed in individual pens and fed a diet formulated to provide 13.9% CP, 1.24 Mcal/kg NEg, and 0.10 mg/kg Se. The diet was delivered as total mixed ration once daily. . Cow weight and BCS and calf birth weight did not differ at the beginning of the trial (P ≥ 0.55). Cow BW and BCS (P ≥ 0.85) did not differ between treatments at any time point during the study. Milk production, milk fat, and total solids (P ≥ 0.38) did not differ among treatments. Milk protein tended to increase in cows fed inorganic Se compared to cows fed organic Se (P = 0.07) and milk lactose tended to be greatest in cows fed organic Se (P = 0.10). Conception to AI and overall pregnancy rates did not differ between the diets (P ≥ 0.39). Calf weights and ADG did not differ for the 105 d experimental period (P ≥ 0.77) or for the entire pre-weaning period (P ≥ 0.33). Plasma Se concentration did not differ between treatments for the cows (P ≥ 0.37). Liver Se concentration in cows fed inorganic and organic Se treatment were significantly greater than that of cows from the control treatment (P < 0.01). There were no treatment effects on calf plasma Se concentration (P ≥ 0.90). Muscles biopsies taken at 105 DPP also were not different (P = 0.45). Steers from cows supplemented with organic Se diet entered the feedlot heavier (P = 0.02) and tended to be heavier on d 87 (P = 0.08) compared to steers from cows supplemented with inorganic Se. There was no difference in ADG among treatments (P ≥ 0.76), but steers from organic Se cows tended to spend fewer days on feed compared to steers from inorganic Se cows (P = 0.09). Steers from organic Se cows had a greater overall DMI compared to steers from inorganic Se cows (P = 0.04), but there was no difference in overall gain:feed ratio (P = 0.82). Dressing percentage was greater for steers from cows fed no Se compared with steers from cows fed either inorganic or organic Se (P = 0.03). Maternal Se source had no effect on hot carcass weight, back fat, %KPH, L. dorsi area, yield grade, marbling score, or quality grade distribution (P ≥ .17) of progeny. In conclusion, dietary Se source did not affect cow performance, milk production, or reproductive ability. Organic Se decreased milk protein and increased milk lactose, but did not alter pre-weaning performance of the progeny. Maternal supplementation with organic Se appears to have a long-term benefit on intake of steer progeny and may result in improvements in growth that decreases days in the feedlot.