OBJECTIVE To determine the concentration of tilmicosin in mammary gland secretions of dairy cows following administration of an experimental preparation once or twice during the dry period (45-day period immediately prior to calving during which cows are not milked) and to evaluate its efficacy for the treatment of cows with intramammary infections (IMIs) caused by Staphylococcus aureus at dry off (cessation of milking; first day of dry period), compared with that of an intramammary infusion of ceftiofur.
ANIMALS 172 cows.
PROCEDURES Milk samples were collected for microbiological culture 5 days before dry off and at calving and 15 and 30 days after calving. Cows with Staphylococcus IMIs were randomly assigned to receive an experimental preparation of tilmicosin (20 mg/kg, SC) once at dry off (n = 58) or at dry off and again 20 days later (56) or receive a long-acting intramammary preparation of ceftiofur (500 mg/mammary gland; 56) at dry off. Mammary gland secretions were collected from 5 cows in the tilmicosin-treated groups every 5 days after dry off until calving for determination of tilmicosin concentration.
RESULTS Mean maximum concentration of tilmicosin in mammary gland secretions ranged from 14.4 to 20.9 μg/mL after the first dose and was 17.1 μg/mL after the second dose. The bacteriologic cure rate was 100% for all 3 treatments. Tilmicosin was detectable for 0 and 18 days after calving in the milk of cows treated with 1 and 2 doses of tilmicosin, respectively.
CONCLUSIONS AND CLINICAL RELEVANCE Administration of an experimental preparation of tilmicosin (20 mg/kg, SC) once to dairy cows at dry off might be useful for the treatment of S aureus IMIs.
Objective—To evaluate chemotactic, phagocytic, and
bactericidal activities of bovine and porcine alveolar
macrophages (AM) exposed to tilmicosin.
Animals—12 healthy calves and 12 healthy pigs.
Procedure—Lungs were obtained immediately after
euthanasia; AM were collected by means of bronchoalveolar
lavage and density gradient centrifugation.
Chemotactic activity was evaluated by exposing
AM to lipopolysaccharide or macrophage inhibitory
peptide during incubation with tilmicosin. Phagocytic
activity was evaluated by incubating AM with tilmicosin
for 24 hours and then with tilmicosin-resistant
Salmonella serotype Typhimurium. Bactericidal activity
was evaluated by incubating AM with tilmicosin (0,
10, or 20 µg/ml for bovine AM; 0 or 10 µg/ml or 10
µg/ml but washed free of tilmicosin for porcine AM)
and then with Mannheimia haemolytica (bovine AM)
or with Actinobacillus pleuropneumoniae or
Pasteurella multocida(porcine AM).
Results—Tilmicosin had no significant effects on
chemotactic or phagocytic activities of bovine or
porcine AM. The time-course of bactericidal activity
was best described by polynomial equations. Time to
cessation of bacterial growth and area under the time
versus bacterial number curve were significantly
affected by incubation of AM with tilmicosin.
Conclusion and Clinical Relevance—Results show
that bactericidal activity of bovine and porcine AM
was enhanced by tilmicosin, but not in proportion to
the reported ability of AM to concentrate tilmicosin
intracellularly. With or without exposure to tilmicosin,
the time-course of bactericidal activity of bovine AM
against M haemolytica and of porcine AM against
A pleuropneumoniae or P multocida was too complex
to be reduced to a simple linear equation. (Am J Vet