Investigation of Anaplasma marginale Seroprevalence in a Traditionally Managed Large California Beef Herd

Table 5

Summary of incidence density rate (IDR) per 1000 cow-days for three cohorts of California beef cattle followed up for A. marginale infection by age group/pasture exposure, age group, and stage of maturity.

Age group	IDR	95% CI
Group 1 heifers, pasture C	7.26	(4.30, 11.47)
Group 2 heifers, pasture A^†	10.04	(6.56, 14.76)
Group 2 heifers, pasture B^‡	2.44	(0.50, 7.12)
Group 2 heifers, pasture A + pasture B	9.29	(5.58, 12.00)
Combined heifer groups	8.39	(6.16, 11.18)
Group 2 heifers, pasture A and group 1 heifers	8.68	(5.81, 12.50)
Cows, pasture C	5.00	(0.61, 18.05)
Combined heifers and cows	8.17	(6.04, 10.81)

Cows and group 1 heifers were maintained on pasture C throughout their study period.
^†Group 2 heifers were maintained on pasture A from study day 0 to day 70.
^‡Group 2 heifers were maintained on pasture B from study day 71 to day 193.
Incident cases and at-risk time combined for all of the group 2 study period.
Incident cases and at-risk time combined for all of groups 1 and 2 study period.
Incident cases and at-risk time combined for all study animals throughout the study period.