[The early or late administration of Paratect Flex bolus in heifers].

The effect of the time of administration of the Paratect Flex -Bolus (PF-Bolus) on the course of infections with gastrointestinal nematodes was investigated in a field experiment with three groups of 9 first year grazing heifers in the Swiss midland region. The heifers of groups A and B received the PF-Bolus at turnout on May 7 (early season application) and on July 16 (late season application), respectively. The heifers of group C remained untreated. All heifers were grazed together throughout the experiment. The mean egg excretion of the heifers of group A remained very low for a period of 70 days and peaked at the end of September reaching a mean value of 167 eggs per gram of faeces (epg). After the administration of the PF-Bolus to the heifers of group B, the egg excretion was reduced by 97% and remained below 50 epg for the rest of the season. While the mean serum pepsinogen values of the heifers of groups A and B only reflected subclinical infections, the mean values of the heifers of group C exceeded 4400 mU tyrosine and 4 heifers exhibited signs of parasitic gastroenteritis. At the end of the experiment (Oct 8) heifers of group A were 14 kg heavier than the controls (not significant) whereas the heifers of group B outperformed the control heifers by 20 kg (significant, p > 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)