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Speer, H. F. Consequences of cow-calf production with limited perennial forage grazing.
Conversion of perennial grasslands to cropland and rising land prices prompts a need to evaluate alternative beef cow-calf production systems. A 3-yr study was conducted comparing beef cow-calf performance between two August-calving cow systems: perennial forage and corn residue grazing; or summer drylot, fall grazing of late-summer-planted cover crop, and corn residue grazing. Cow body condition score differed between systems, but condition of cows in both systems never fell below adequate. There were no differences in pregnancy rates between systems. Calf weaning weights differed between systems each year; differences are attributed to feedstuff quantity, quality, and type available to calves prior to weaning. Differences in time on green pastures between systems may impact cow supplemental vitamin A needs; therefore, two additional studies were conducted to understand maternal vitamin A supplementation needs in stored forage diets and its impacts on offspring vitamin A status. In the first study, beef cows in mid-gestation were provided supplemental vitamin A below current recommendations for 143 d. Mean cow liver retinol concentration 32 d post-calving was 482 µg/g DM and fell within current adequacy reference ranges, while both calf plasma and liver retinol were below adequate for calves 32 d of age. The second study evaluated the effect of 3 different supplemental vitamin A levels on cow and calf liver retinol concentrations: current recommendation (31,000 IU/d; 1X), 3 times (93,000 IU/d; 3X), or 5 times (155,000 IU/d; 5X) the current recommendation. Cows receiving 1X maintained liver retinol concentrations below adequate throughout the 165-d supplementation period, whereas cows on 3X and 5X were above adequate by d 81. Calves of 1X cows had lower liver retinol concentrations than 3X and 5X calves. Adequate liver retinol concentrations were only observed in 3X and 5X calves. Overall, cow liver retinol concentrations and dietary vitamin A intake will impact calf vitamin A status. Cows fed stored forage diets may require supplemental vitamin A above current recommendations to ensure adequate status of her and her calf.
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