The effect of pasture manganese concentrations on lamb growth

Abstract

A trial was laid down at Woodlands in Southland to investigate the effect of pasture manganese (Mn) on sheep performance. Pasture Mn concentrations were increased from background concentrations (82-98 mg/kg DM) to 192-354, 466-694 and 912-1178 mg/kg DM by the regular spray application of MnSO4. These pasture concentrations were replicated four times and grazed by mobs of 10 Coopworth x Texel ram lambs. Pasture growth, botanical composition and pasture Mn concentrations were monitored. Lamb liveweights were measured fortnightly and the lambs were slaughtered after 14 weeks with the livers of six animals from each treatment sampled for vitamin B12, copper (Cu), selenium (Se) and Mn concentration. Average clover content of the pastures declined throughout the trial, averaging 17%, 15% and 4% for the three grazing areas respectively. Animal growth rates averaged 180 g/day for the duration of the experiment but varied from 250 g/day during the first 2 weeks they grazed the pastures declining steadily for each 2 week period they remained on that group of paddocks to a low of <90 g/day after 6 weeks. The animal growth rates were only significantly influenced by extremely high initial Mn concentrations (>2000 mg/ kg DM) or where concentrations were above 1200 mg/ kg DM for the full 2 week grazing period. There was no effect of high Mn intake on liver B12, Se, Cu or Mn under these conditions. Keywords: sheep, manganese, lamb growth rates, pasture manganese concentration