Effect of nematode infections on growth performance of calves during winter housing on dairy farms.

Growth performance of calves was estimated by means of heart girth measurements on 48 farms during winter housing (from December to the end of March). Level of exposure to nematode infection was measured by antibody titres, pepsinogen values, and faecal examinations. Half of each herd was treated with albendazole after housing. All infection parameters measured in March were significantly lower in the treated groups than in the untreated control groups. Treatment increased growth rate by an average of +0.007 cm day-1 (N.S.), i.e. +0.036 kg day-1. Effect of treatment varied from -0.075 to +0.100 cm day-1 among herds. This effect of treatment on the growth performance was significantly correlated positively to pepsinogen value (r = 0.321, P less than 0.05 measured in October; r = 0.265, P less than 0.10 measured in December). Control groups showed very different growth rates among herds, ranging from 0.023 to 0.170 cm day-1, i.e. 0.112-0.874 kg day-1. This variation was strongly related to several infection parameters, particularly those measured in October. The most pronounced correlation was found between the average daily gain of the control groups and the mean herd antibody titre against Ostertagia spp. measured in October (r = -0.413, P less than 0.01). These results were consistent with those of a similar study conducted on commercial dairy farms a year earlier.