Cattle derive vitamin D from both dietary sources and from the ultraviolet light conversion of 7-dehydrocholesterol in the skin. One of the three major target tissues of vitamin D is the intestine, where it stimulates transport of Ca and P across the intestinal brush border. Vitamin D, also known as the “sunshine vitamin”, is higher in the serum of cattle during the summer months. The seasonal increase in serum vitamin D concentrations taken together with its presence and active role in the intestine, led us to hypothesize that vitamin D may play a role in the seasonal prevalence of E. coli O157:H7.
The objective of the current research was to examine the effect of supplemental vitamin D on fecal shedding of E. coli O157:H7 in naturally colonized cattle.
Two experiments were conducted in which beef and Holstein steers were administered oral doses of vitamin D. In Experiment I, 14 crossbred beef steers (avg. BW = 225 kg) and 12 Holstein steers (avg. BW = 454 kg) were randomly assigned to control or vitamin D treatments. Fecal samples were collected daily for 6 d prior to, and during the 10-d period of vitamin D administration. Experiment II utilized 14 Holstein steers that were administered vitamin D daily in three successive doses: 2400, 4800, and 9600 IU/d each administered for 14 d. Fecal samples were collected daily and blood samples weekly throughout the 42-d study.
In Experiment I, no differences in the percentage of Holsteins or beef calves shedding E. coli O157:H7 were observed prior to vitamin D treatment. However, during treatment administration, more calves in the vitamin D treatment tended (P = 0.11) to shed E. coli O157:H7 compared to controls (6.5 versus 14.3% for control and vitamin D treatments, respectively). Serum concentrations of vitamin D were markedly higher (P < 0.0001) in treated (782 nMol/L) versus control (258 nMol/L) calves. In Experiment II, no differences in fecal prevalence or serum vitamin D concentrations were observed for any of the vitamin D dosages. Differences in fecal shedding among the Holsteins and the beef calves in Experiment I are likely due to the difference in the vitamin D dose administered per unit of BW, as reflected in the serum concentrations of vitamin D.
The long-term goal of this research is to determine if the complete removal of vitamin D from the ration in feedlot cattle in the summer could have a beneficial effect on E. coli O157:H7 populations or prevalence. As serum vitamin D concentrations are reported to be higher in the summer due to increased day-length and light intensity, we speculated that the removal of supplementary vitamin D would be offset by the seasonal increase and there would not be any adverse effects on performance or carcass quality. If our hypothesis that the summer elevation in vitamin D concentration is involved in the increased prevalence of E. coli O157:H7, then any change in E. coli prevalence should be associated with a change in serum vitamin D concentrations. This was observed in the first but not second experiment, supporting our hypothesis and further research in this area.