Vitamin D(3) synthesis in the entire skin surface of dairy cows despite hair coverage.
Level 5 - mechanism / opinion, no new human data
Animal study without human clinical data (CEBM Level 5).
PubMed 20412916 · doi:10.3168/jds.2009-2991
What was done
Sixteen Danish Holstein dairy cows were assigned to four body-coverage treatments designed to block cutaneous sunlight exposure: no cover (natural), udder cover, horse blanket, or horse blanket plus udder cover. Cows were turned out to pasture daily from 10:00 to 15:00 for 4 weeks in July and August 2009. Blood was sampled 15 times over the 28-day study to evaluate plasma 25-hydroxyvitamin D3 [25(OH)D3] concentrations.
What was found
The abstract reports no exact numerical values, effect sizes, or p-values. Uncovered cows had higher plasma 25(OH)D3 concentrations after 28 days compared to covered cows, with plasma concentrations strongly inversely correlated with covered body surface area. Large differences among coverage groups also contradicted the hypothesis that vitamin D3 is primarily acquired through grooming sebum from hair.
Why it matters
This trial demonstrates that bovine hair does not block cutaneous vitamin D3 synthesis in the way clothing does in humans, indicating that cows synthesize vitamin D3 across their entire skin surface.
Limits
The study had a very small sample size (n = 16 cows across 4 treatment groups, ~4 per arm). The abstract lacks numerical metrics, confidence intervals, and exact statistics. Findings in Danish Holsteins under summer grazing may not extrapolate directly to other breeds, coat types, or seasons.
Cited by
- contradicts Furred animals obtain vitamin D by licking their fur where it is synthesized, whereas humans and domesticated pigs synthesize and absorb it directly through skin.