Mean herd prevalence of clinical lameness was 15% (range = 2.5 46%).
Data were available from 14,572 herds with mean herd size of 17.9 cow years.
The mean herd occurrence of cubicle refusal was 6%, but showed great variation (range 0 55%).
The mean herd occurrence of cubicle refusal was found to be 6% (Table 1), and the range was wide (0 55%).
Mean herd size of the selected herds was 679 (standard deviation (SD) = 334), which was comparable to the sampling frame (Student's t-test, P = 0.22).
The mean herd size of case and control herds was 41.1 (SD = 19.1) and 34.4 (SD = 16.1) lactating cows, respectively (P = 0.26).
The mean herd size of the study farms (409 sows) was larger than the mean herd size (220 sows) of farms fitting the selection criteria in the national herd in 2003 (DEFRA June 2003 statistics, personal communication) but this might reflect the fact that herd sizes were increasing in Britain during this period [ 18].
The difference in mean herd size of the herds with only one viral agent detected by serology versus those with several viral agents was analysed with a One-way analysis of variance.
The arithmetic mean herd size of these herds was 92 cows (50% central range (CR): 45 - 117 cows, n = 223) and the majority of farms (83%, n = 222) had conventional milking systems (parlor or tie-stall systems) while 17% had robotic milking or a combination of robotic milking and conventional milking on the farm.
The absence, or very low prevalence, of Cp. abortus in Swedish dairy cows could be due to the small mean herd size of 44 animals (year 2005) and that most are kept tethered during a nine-month stable period, with little contact within the herd.
