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 (P value)
	Age group/pasture
Group 1 heifers, pasture C∗	3.06 (0.048)a
Group 2 heifers, pasture A†	4.12 (0.012)a
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.

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