Physiological limit of the daily endogenous cholecalciferol synthesis from UV light in cattle

Abstract

The link between UV light (sunlight) and endogenous cholecalciferol (vitamin D ) synthesis in the skin of humans has been known for more than a 100 years, since doctors for the first time successfully used UV light to cure rickets in children. Years later, it was shown that UV light also had a significant effect on the cholecalciferol status in the body of cattle. The cholecalciferol status in the body is measured as the plasma concentration of 25-hydroxycholecalciferol, which in cattle and humans is the major circulating metabolite of cholecalciferol. Very little is, however, known about the quantitative efficiency of UV light as a source of cholecalciferol in cattle nutrition and physiology. Hence, the aim of this study was to determine the efficiency of using UV light for increasing the plasma 25-hydroxycholecalciferol concentration in cholecalciferol-deprived cattle. Twelve cows deprived of cholecalciferol for 6 months were divided into three treatment groups and exposed to UV light for 30, 90 or 120 min/day during 28 days. UV-light wavelengths ranged from 280 to 415 nm and 30-min exposure to the UV light was equivalent to 60-min average summer-sunlight exposure at 56 °N. Blood samples were collected every 3-4 days and analysed for 25-hydroxycholecalciferol and cholecalciferol. Results showed that increasing the exposure time from 90-120 min/day did not change the slope of the daily increase in plasma 25-hydroxycholecalciferol. Hence, it appears that cholecalciferol-deprived dairy cattle are able to increase their plasma 25-hydroxycholecalciferol concentration by a maximum of 1 ng/ml/day from UV-light exposure.

Vitamin D status in growing dairy goats and sheep: Influence of ultraviolet B radiation on bone metabolism and calcium homeostasis

“…Considering therefore that the difference in 25vitD status between the groups was not caused by a different degradation and the husbandry conditions and the feeding were identical for all groups, the difference must have been caused by the production with irradiation of the skin. These findings are in line with previous studies that showed a better vitD status in sheep exposed to UVB irradiation (Quarterman et al, 1964;Smith and Wright, 1980;Hidiroglou and Karpinski, 1989;Kovács et al, 2015) and show evidence of the parallelism to the endogenous vitD production in dairy cows (Hymøller et al, 2009;Jensen, 2010, 2012;Hymøller et al, 2017). Also, the lower content of 7DHC in the skin of the irradiated animals compared with the control group supports our hypothesis.…”

“…The animals in this study had a normal initial vitD status thanks to the high vitD intake due to the vitD content in the normal concentrate fed before starting the experiment and the vitD intake via milk before weaning. Indeed, for newborn ruminants, in contrast to other species, milk can be an adequate source of vitD under the condition of a high vitD status in combination with a moderate milk yield of the dam (Kohler et al, 2013;Weiss et al, 2015;Hymøller et al, 2017). The 25vitD can then be stored in the body tissue (primary fat, muscle, and liver) to help prevent a fast drop of vitD status (Hidiroglou, 1987;Hidiroglou and Karpinski, 1989).…”

Associations between bone and energy metabolism in cows fed diets differing in level of dietary cation-anion difference and supplemented with cholecalciferol or calcidiol

“…Cows produce vitamin D 3 in the skin in response to UV exposure, as was recently shown in cows not supplemented with cholecalciferol for 6 mo and exposed to UV light for 30, 90, or 120 min/d for 28 d (Hymøller et al, 2017). Exposure to UV light increased plasma concentrations of 25-hydroxyvitamin D 3 linearly from approximately 5 ng/mL on experiment d 0 to almost 40 ng/mL on d 28 in cows receiving either 90 or 120 min/d of light exposure (Hymøller et al, 2017). Therefore, some background concentration of vitamin D metabolites was expected in cows from endogenous synthesis or from previous supplementation before initiation of the experiment.…”

Low serum vitamin D concentrations in Spring-born dairy calves are associated with elevated peripheral leukocytes

“…Multiple factors are known to regulate Vit D 3 skin synthesis, including latitude, altitude, and time of exposition to sunlight 23 . As in humans, seasonal variation in the Vit D status on grazing calves (with minimal or null Vit D 3 supplementation) has been reported, with low 25OHD concentration in winter and early spring 21 , 24 .…”