The aim of the study was to investigate the effect of mixed grazing with first season heifers and pregnant sows on animal performance, gastro-intestinal helminths, pasture quality and sward structure during three grazing seasons. This presentation will focus on results from 1999, primarily regarding performance and parasitosis in heifers. There have been no earlier reports on such mixed grazing systems. Three grazing systems were studied in replicate: 1) Heifers grazing alone; 2) sows grazing alone; 3) heifers grazing together with sows. The heifers were inoculated with low doses of infective O.ostertagi larvae at turn-out. Continuous grazing was practised in paddocks regulated in size according to herbage allowance. Individual weight gain, faecal egg output and serum pepsinogen concentrations - as indicator of O.ostertagi infection - were measured fortnightly. The sward structure and quality were greatly influenced by the applied grazing system. The average daily gain of the heifers was significantly higher (P=0.0006) when grazing together with sows (1,121±45 g/day, n=16) than when grazing alone (869±48 g/day, n=14). The mean pepsinogen concentrations were elevated in the heifers grazing alone. It is concluded, that weight gains were significantly better and infection levels with O.ostertagi were significantly reduced in heifers grazing together with sows
