Ostertagia ostertagi in calves: growth, nitrogen balance and digestibility studies conducted during winter feeding following different fenbendazole therapy programmes

Abstract

Observations of growth, nitrogen (N) balance and digestibility were made during the first winter housing period upon three groups of calves which had previously been naturally infected with Ostertagia ostertagi and which were left either untreated (A) or treated with fenbendazole on three occasions (B) or every two weeks during the entire grazing season (C). The diet given contained sufficient metabolisable energy but only about 60 per cent of the recommended crude protein to sustain a daily growth rate of 0.5 kg. Growth rates were only 50 per cent of that expected on a basis of metabolisable energy input with untreated calves A being poorest. Water intake and output was greatest in group A. There were no significant differences in digestibility between groups although group A had the lowest apparent crude protein digestibility. N balance was always lowest in group A and highest in group C but group B demonstrated a marked increase in N retention with time after housing. Differences in N retention were mainly accounted for by increased urinary N excretion. It is concluded that, under conditions of suboptimal protein intake, nematode infection in the growing calf can markedly affect production even after efficient anthelmintic treatment.