Selenium (Se) deficiency has been associated with lowered resistance to
mastitis in dairy cattle. However, little published data exists on the effect of Se supplementation before calving on udder health of pastured dairy heifers. Further, the relative efficacy of
injectable barium selenate and oral organic Se for improving udder health in cows has not previously been tested. The objectives of this study were to determine the effects of precalving Se supplementation and type of supplementation on the blood activity of
glutathione peroxidase and measures of udder health immediately after calving and during the first month of lactation in pastured dairy heifers. One hundred forty pregnant Chilean Holstein-Friesian heifers were fed a basal diet containing, on average, 0.15 mg of Se/kg of dry matter. One month before predicted calving, heifers were allocated to 1 of 3 groups. Group 1 (n=49) received no supplementary Se, group 2 (n=46) received a single
subcutaneous injection of Se (1 mg/kg of live weight, as
barium selenate), and group 3 (n=45) was fed Se yeast (3 mg/heifer/d until calving). Heifers supplemented with
barium selenate had a higher
glutathione peroxidase activity from 14 d in milk onwards.
Selenium supplementation, irrespective of source, tended to reduce the prevalence of intramammary
infection (IMI) and decrease the prevalence of quarters with high somatic cell count (SCC) at calving. Overall, Se supplementation did not result in a reduction of the incidence of new IMI or clinical
mastitis or in decreased SCC during the balance of the first month of lactation. However, in pasture-based heifers injected with
barium selenate before calving, and fed diets with 1.3 and 2.5 mg of Se/d precalving and during lactation, respectively, no cases of clinical
mastitis were observed in the first month of lactation.