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

Table 6

Summary of incidence rate ratio (IRR) 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	IRR ( value)
	Age group/pasture
Group 1 heifers, pasture C	3.06 (0.048)
Group 2 heifers, pasture A^†	4.12 (0.012)
Group 2 heifers, pasture B^‡	Reference
Cows, pasture C	2.00 (0.052)

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.
Relative risk significantly greater for these groups at the 95% confidence level.