The determination at housing of exposure to gastrointestinal nematode infections in first-grazing season calves

Various parameter estimates were assessed at housing in calves that had bee n exposed to gastrointestinal nematodes during a first grazing season. The analysis involved 41 groups of first grazing season (FGS) calves on 15 diff erent farms in Belgium and comprised groups that had received chemoprophyla ctic treatment and untreated controls. Serum pepsinogen levels gave the dea rest division between chemoprophylactic-treated calf groups tall were <2.6 U tyr), and untreated calf groups in which sub-clinical (range: 2.0-4.1 U t yr) and clinical infections (range 3.7-6.3 U tyr) occurred. There was also a tight relationship between individual pepsinogen values and adult Osterta gia burdens obtained at slaughter. In chemoprophylactic-treated groups ther e was a significant negative relationship between mean serum pepsinogen lev els at housing and the proportion of the grazing season covered by differen t chemoprophylactic systems. Although only limited data on crude adult Oste rtagia antigen ELISA were available, a good relationship between optical de nsities and estimated exposure was also found. The parasitological paramete rs, faecal egg counts and pasture Ostertagia larval counts at housing, and weight gain per day, gave less clear divisions among the three categories ( chemoprophylaxis, sub-clinical and clinical). Distinguishing how much expos ure a calf group has experienced during a first grazing season could help i n designing more appropriate control measures for the FGS calves in the nex t year, assuring good protection and at the same time allowing sufficient e xposure far the development of acquired immunity to Ostertagia, and for thi s serum pepsinogen is recommended. (C) 1999 Elsevier Science B.V. All right s reserved.