Randomized field trial to determine the effects of oral selenium supplementation on milk production and reproductive performance of Holstein heifers

A field trial was conducted to measure differences in performance between selenium-supplemented and nonsupplemented heifers on a 1200-cow California dairy. 117 19- to 27-month-old Holstein heifers were randomly assigned to treatment (n = 59) and control (n = 58) groups. A federally approved, commercially available, sustained-release intraruminal selenium bolus was administered to each heifer in the treatment group. Blood samples were taken from treated and control animals to assess Se values before and after bolus administration and again after introduction to the milking ration. Production data were obtained from an on-farm computerised record system for each heifer during her first lactation. Mean blood Se concn in treated heifers were higher than those in control heifers from posttreatment day 30 until after calving. Data analysed in midlactation and late lactation indicated no significant differences between treated and control groups in somatic cell count, days not pregnant, total milk production, or times bred.