Influences of Calcium Intake and Vitamin D Supplementation on Reproductive Performance of Dairy Cows

Reproductive performance of 37 2-to 6-year-old Holstein cows was observed, during 58 reproductive cycles, to compare effects of two calcium intakes, averaging 100 (A) and 200 g (B), fed in rations contributing 80 to 100 g of phosphorus daily, each with (+D) and without 300,000 IU vitamin D3 (--D) weekly. Alfalfa hay and concentrate mixtures were group fed to satiety. Uterine involution was completed eight days sooner (P < .05) in BTD than ATD with A--D and B--D equal and intermediate. First ovulation occurred six days earlier (P < .005) in cows fed Ration B than in those fed Ration A and was not influenced by supplemental vitamin D. First recognizable post-partum estrus occurred 16 days earlier (P < .06) and conception occurred 37 days earlier (P < .025) in the vitamin D supplemented than in the unsupplemented cows. Services per pregnancy and milk production did not vary significantly among treatments.