No studies have been conducted to assess the effects of a blend of grains naturally contaminated with 'Fusarium' mycotoxins to sows in late gestation and lactation. Experiments were conducted, therefore, to assess the effects on reproduction and metabolism of sows fed a blend of grains naturally contaminated with 'Fusarium' mycotoxins. The efficacy of a polymeric glucomannan mycotoxin adsorbent (GMA) in preventing the adverse effects of mycotoxins was also tested. The experimental diets contained uncontaminated corn and wheat, contaminated corn and wheat, and contaminated corn and wheat supplemented with GMA. The feeding of contaminated grains to sows in late gestation resulted in increased frequency of stillborn piglets, and supplementation with GMA prevented this effect. The feeding of contaminated grains to sows resulted in a reduction in feed intake and increased loss of body weight in lactation, and the supplementation with GMA could not prevent this effect. The feeding of contaminated grains to sows tended to increase the weaning-to-estrus interval and GMA was not efficacious in preventing this effect. The feeding of diets containing contaminated grains to sows also resulted in liver damage, which was not prevented by GMA. It was hypothesized that sows fed contaminated grains in lactation had higher muscle protein mobilization and higher serum ammonia concentrations than controls. In late gestation, sows fed contaminated grains and restricted fed sows had higher serum ammonia concentrations compared to sows fed contaminated grains + GMA. The capacity for muscle protein synthesis was not reduced in sows fed contaminated grain. The capacity for protein synthesis was increased in sows fed the contaminated diet + GMA. Reduction in skeletal muscle protein was observed as the result of lactation. These was no a direct effect of mycotoxin, but it was an indirect effect of reductions in feed intake. It was concluded that the feeding of contaminated grains to sows resulted in reductions of reproductive performance and that GMA could prevent some of these adverse effects. The feeding of contaminated grains to sows did not alter the capacity for protein synthesis in muscle, or the cellular protein content.