The effects of supplementation with cobalt, and method of administration, on ewe reproduction and offspring performance to weaning

•Ewes in grass-based system supplemented with Co from pre joining to late pregnancy.•Cobalt supplementation increased plasma concentrations of Co and vitamin B12.•Supplementation reduced the incidence of ewes classed as marginal/low for Co status.•Ewes on fortnightly Co drench had higher plasma B12 than those with a Co bolus.•Cobalt supplementation had no effect on ewe productivity or progeny performance.