Anaplasma marginale is a rickettsial pathogen that causes the disease anaplasmosis in cattle (25). Feeding ticks effect biological transmission of this obligate intraerythrocytic organism, while mechanical transmission occurs when infected blood is transferred to susceptible cattle by biting flies or blood-contaminated fomites (for a review, see the report by Ewing [13]). Many A. marginale geographic isolates which differ in biology, morphology, protein sequence, and antigenic characteristics have been identified and have been characterized by the major surface protein 1a (MSP1a), which varies in sequence and molecular weight due to different numbers of tandem 28-to 29-amino-acid repeats (for a review, see reference 5). The MSP1a tandem repeats are located after a conserved decapeptide in the amino-terminal region of the protein and are exposed extracellularly for interaction with host cell receptors (11). The frequency of variable amino acid positions in geographic isolates is higher in this region than in the rest of the protein (for a review, see reference 5).The organisms in the order Rickettsiales have been reclassified into two families, the Anaplasmataceae and Rickettsiaceae, on the basis of genetic analyses of the 16S rRNA, groesl, and surface protein genes (12). Recent research has focused on MSPs that are involved in interactions with vertebrate and invertebrate host cells (7,8,20,21) and have been used to elucidate the phylogeographic patterns of A. marginale (5,6,9,16,19). These MSPs are involved in host-pathogen interactions and may evolve more rapidly than other nuclear genes because of selective pressures exerted by host immune systems. Of the six A. marginale MSPs that have been identified and characterized, only three (MSP1a, MSP4, and MSP5) are encoded by single genes. Because these MSPs do not appear to undergo antigenic variation in cattle or ticks (4), they were posited to be more stable genes for phylogenetic studies. MSP1a, encoded by msp1␣, has been reported to be an adhesin for bovine erythrocytes and tick cells and to effect adhesion, infection, and transmission of A. marginale by ticks of the genus Dermacentor

Estrous behavior and time of ovulation relative to the onset of estrus were determined in mature Angus x Hereford cows (n = 17 to 21 each season) during summer, winter, and spring for 2 yr. Estrous behavior was evaluated during the first of two consecutive estrous periods, and time of ovulation was determined during the second estrus. Concentrations of progesterone were quantified in twice weekly blood samples to ensure all cows had normal estrous cycles. The HeatWatch system was used to measure the duration of estrus, number of mounts received per estrus, and duration of the longest interval between mounts received. Commencing 16 h after the onset of the second estrus, transrectal ultrasonography was performed every 4 h until the dominant follicle was no longer present on the ovary, and time of ovulation was defined as 2 h preceding the absence of the dominant follicle. There was a seasonal effect on the duration of estrus; cows were estrus longer in summer (17.6 +/- 0.8 h) than in winter (15.5 +/- 0.8 h; P = 0.07) or spring (13.9 +/- 0.9 h; P < 0.05). Cows were mounted more times per estrus (P < 0.05) in winter (59.0 +/- 5.3) than in summer (43.6 +/- 5.3) or spring (38.2 +/- 5.8). Intervals between mounts of estrous cows were longer (P < 0.05) in summer (4.1 +/- 0.4 h) than in spring or winter (2.7 +/- 0.4 h). During all seasons, cows were mounted more times (P < 0.01) between 0600 to 1200 (3.2 +/- 0.2 mounts received/h of estrus) than during other times of the day (2.1 +/- 0.2 mounts received/h of estrus). Cows ovulated 31.1 +/- 0.6 h after the onset of estrus, and time of ovulation was not influenced by season. We conclude that season influences estrous behavior of beef cows; cows are mounted more times per estrus in winter than in summer or spring. Time of ovulation relative to the onset of estrus is constant during all seasons and averages 31.1 h.

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Sedation or changes in heart and respiratory rates were not detected with any treatment before administration of TZ. Acepromazine alone and acepromazine with butorphanol (0.1 mg/kg) prolonged the duration of antinociception in TZ-treated llamas.