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Even cows need more than 90 minutes in the sun each day – Feb 2012

25-Hydroxycholecalciferol status in plasma is linearly correlated to daily summer pasture time in cattle at 56°N.

Br J Nutr. 2012 Feb 6:1-6.
Hymøller L, Jensen SK.
Department of Animal Science, Aarhus University, Blichers Allé 20, Box 50, DK-8830 Tjele, Denmark.

In vitro studies with skin samples or pure precursors of cholecalciferol indicated that cholecalciferol synthesis during UV light exposure is a non-linear process. However, in vitro studies indicate nothing about the relationship between sunlight exposure and physiological cholecalciferol status of living organisms. Due to the lack of cholecalciferol in plant material, this relationship is important for herbivores including domestic cattle, particularly in organic agriculture, because the use of synthetic additives, like cholecalciferol, is restricted in order to fulfil the principles of sustainable organic production. The major physiological metabolite of cholecalciferol is the liver-derived 25-hydroxycholecalciferol (25(OH)D3). The purpose of the present study was to determine the relationship between sunlight exposure and 25(OH)D3 status in vivo in large herbivores during mid-summer at 56°N.

Five groups of cows were given access to pasture during 15, 30, 75, 150 or 300 min daily for 28 d in June and plasma analysed for 25(OH)D3.

Animals allowed 15, 30 or 75 min of daily access to pasture showed a declining linear relationship between plasma 25(OH)D3 and sampling day in contrast to animals allowed 150 or 300 min of pasture access which showed linear increasing plasma 25(OH)D3 status.

Determined from the slopes of 25(OH)D3 concentration curves within treatments, breakeven for maintaining the initial 25(OH)D3 status of 45 nmol/l was 90 min pasture access per d during summer at 56°N.

PMID: 22309951


Northern cows (56 degree latitude) in June needed 90 minutes to maintain 18 ng
Most cows get vitamin D in their feed. Did these cows get any vitamin D in their feed?

See also VitaminDWiki

See also web

  • Do Blanketed Horses Get Enough Vitamin D? June 2015
    NZ horses do not have reduced vitamin D levels when they wear blankets
    Note that chickens get > 100X as much vitamin D from their legs as from their feathered body.
    Perhaps horses get vitamin D from sun on their legs as well - much less hair to get in the way.
    The study did not investigate the amount of vitamin D horses get from their hay - which is quite large.
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