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

Table 4

Summary of population at risk, incident cases, and time at risk of Anaplasma marginale infection for cattle followed up to determine rate of A. marginale infection.

Age group	Group 1 heifers	Group 2 heifers		Cows
Pasture	C	A^†	B^‡	C
Population at risk	31	37	10	5
Incident cases	18	26	3	2
Days at risk	80	70	123	80

Group 2 heifers were grazed on pasture A for the first 70 study days and on pasture B for the remaining 123 study days.
^†Annual rangeland pasture, approximately 160 m elevation, Tehama County, CA.
^‡Valley irrigated pasture, approximately 120 m elevation, Tehama County, CA.
Mountain meadow irrigated pasture, approximately 1060 m elevation, Plumas County, CA.