Investigation of relationship between vitamin D status and reproductive fitness in Scottish hill sheep

There is a growing interest in the influence of vitamin D on ovine non-skeletal health. The aim of this study was to explore the relationship between pre-mating vitamin D status, as assessed by serum concentrations of 25-Hydroxyvitamin D [25(OH) D; comprising D-2 and D-3] and subsequent reproductive performance of genetically unimproved Scottish Blackface (UBF), genetically improved Scottish Blackface (IBF) and Lleyn ewes kept under Scottish hill conditions. 25-Hydroxyvitamin D-2 (25(OH) D-2) and 25-Hydroxyvitamin D-3 (25(OH) D-3) concentrations were determined in serum samples harvested in November from ewes grazed outdoors. There were no significant differences in 25(OH) D-2 concentrations amongst the 3 genotypes. Lleyn ewes had significantly higher 25(OH) D-3 and 25(OH) D concentrations than both Scottish Blackface ewe genotypes, whereas these vitamin D parameters did not differ significantly between the UBF and IBF ewes. Concentrations of 25(OH) D-3 and 25(OH) D were positively associated with subsequent birth weights of singleton and of twin lamb litters. No significant associations between vitamin D status and number of lambs born or weaned per ewe were found. This study demonstrates that concentrations of cutaneously-derived 25(OH) D-3, but not of orally consumed 25(OH) D-2, differed between breeds. The positive association between ewe vitamin D status and offspring birth weight highlights the need for further investigations.