Supplementation of organic and inorganic selenium to late gestation and early lactation beef cows effect on cow and preweaning calf performance.

Angus × Simmental cows ( = 48; BW = 595 ± 17.4 kg, BCS = 5.26 ± 0.05, and age = 2.3 ± 0.07 yr), pregnant with male fetuses, were used to determine the effect of Se source during the last 80 d of gestation and first 108 d of lactation on cow and calf performance. At 203 d in gestation, cows were blocked by BW, breed composition, age, and calf sire and randomly allotted to organic Se, inorganic Se, or no Se treatments. Diets contained corn silage, corn stover, haylage, dried distillers' grains with solubles, and minerals and 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. Diets were fed daily as a total mixed ration and none, 3 mg/d Se as sodium selenite, or 3 mg/d Se as Sel-Plex were top-dressed daily. At 68 d postpartum (DPP), milk production was calculated using the weigh-suckle-weigh procedure and a milk sample was collected to determine composition. At 108 DPP, cow-calf pairs were commingled until weaning at 210 DPP. Cow BW and BCS ( ≥ 0.56) did not differ between treatments at any time point during the study. Milk production, milk fat, and total solids ( ≥ 0.38) did not differ among treatments. Milk protein tended to increase in cows fed inorganic Se compared with cows fed organic Se ( = 0.07) and milk lactose tended to be greatest in cows fed organic Se ( = 0.10). Conception to AI and overall pregnancy rates did not differ between treatments ( ≥ 0.39). Calf weights and ADG did not differ through 108 DPP ( ≥ 0.77) or for the preweaning period ( ≥ 0.33). Plasma Se concentration was adequate for all cows and did not differ among treatments for cows ( ≥ 0.37) or calves ( ≥ 0.90). Liver Se concentrations in cows fed inorganic or organic Se were greater than in control cows ( < 0.01). Longissimus muscles biopsies taken from progeny at 108 DPP also did not differ between treatments ( = 0.45). In conclusion, dietary Se source did not affect cow performance, milk production, or reproductive efficiency. Organic Se decreased milk protein and increased milk lactose but did not alter preweaning performance of progeny from Se-adequate cows.