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W. R. Burris, B. Knight, J. D. Patterson, J. C. Matthews, 013 Form of Se in free-choice mineral mix tends to affect individual ad libitum intake by grazing beef cows and affects cow and suckling calf blood Se levels, Journal of Animal Science, Volume 94, Issue suppl_1, February 2016, Pages 6–7, https://doi.org/10.2527/ssasas2015-013
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Abstract
Previous controlled-mineral intake feeding trials have demonstrated that intake of 3 mg Se per day (the maximal FDA inclusion amount) from mineral mixes (85 g/d) that contained different sources of Se differentially affected Se assimilation by liver and blood Se concentrations of maturing beef heifers. To transfer this knowledge to formulation of free-choice mineral mixes, the amount of Se likely to be consumed by cows needs to be determined. However, individual intake of free-choice mineral mixes by cows managed under commercial forage-based cow-calf regimens has not been adequately characterized. The objectives of this study were to determine (1) individual ad libitum intake of mineral mix by beef cows managed under a year-long, fall-calving, forage-based production regimen and (2) if Se form in mineral mix affected blood Se levels of cows and suckling calves, and calf performance. Twenty-four late-gestation (6 to 8 mos) Angus-cross cows (3.5 ± 0.9 yr; BW = 607 ± 70 kg) were assigned (n = 8) to a mineral supplement treatment (TRT) containing 35 ppm Se as either inorganic (ISe; sodium selenite), organic (OSe; SEL-PLEX), or a 1:1 combination of ISe:OSe (MIX). Cows commonly grazed a 10.1 ha predominately tall fescue pasture and had individual ad libitum access to TRT using in-pasture Calan gates. Cows calved from August to November and calves had common ad libitum access to creep feed and a mineral supplement that lacked Se. Cow jugular blood was taken at 28-d intervals (13 periods). Calf blood was taken within 48 h of birth and then at same time period as dam's until weaning. Mean individual cow mineral mix intake was affected by Period (P < 0.001) and tended to be affected (P = 0.096) by cow TRT (90 ± 37, 87 ± 0.34, 64 ± 21 g/d, respectively for ISe, OSe, and MIX). Mean individual cow Se intakes also tended to differ by TRT (P = 0.078) and were 3.00 ± 1.23, 3.02 ± 1.20, and 2.15 ± 0.71 mg/d, respectively. Mean cow blood Se levels were affected (P < 0.001) by Period and TRT and were 0.27 ± 0.01, 0.20 ± 0.01, and 0.22 ± 0.01 µg/mL, respectively. Calf blood Se was correlated (P < 0.001) with cow blood Se and affected (P< 0.002) by Period and cow Se TRT and was 0.10 ± 0.01, 0.23 ± 0.01, and 0.16 ± 0.01 µg/mL, respectively.
