an epidemiological study of listeriosis in dairy cattle

5. 2. 1. Study design :
This pilot study was carried out over a 12 month period, between September 1994
and August 1995 and involved a dairy herd of 99 Holstein cows on the University of
Bristol’s farm.
The herd was housed between October, 24th 1994 and April, 12th 1995. Silage
was fed to animals from the beginning of September 1994 to 12th April 1995.
The herd was visited monthly with the exception of February 1995. Rectal faeces
samples were collected from the animals available at the time of each visit using
lubricated (Lubrel, Arnolds, UK) rectal gloves. The first visit was made on 5th
September, 1994 and the last visit was made on 16th August 1995. Samples of silage
were also taken from the cutting face of the clamp on four occasions. The dates of the
visits and the number of samples collected are shown in Table 5. 1.
Table 5. 1. Date of visits and number of samples collected
a) Indoor period b) Outdoor period
Month Date N Month Date N
November 17/11/1994 69 May 17/5/1995 77
December 15/12/1994 74 June 13/6/1995 75
January* 31/1/1995 77 July 18/7/1995 67
February* ND ND August 16/81995 57
March* 7/3/1995 79
April* 12/4/1995 74
Total 373 Total 276
ND not done, N number of animals sampled, * silage samples were also collected
On the 12th of April 1995 the milking cows present on the farm were bled. A total
of 77 sera were prepared and held at -20 0 C until use.
133