Determination of tylosin concentration in sow's milk after intramuscular administration.

Introduction: Tylosin's pharmacokinetics has been defined in different species of animals. Despite the description to date of multiple analytical protocols for the determination of tylosin in a variety of biological matrices, research evaluating the antibiotic concentration in sow's milk cannot be found in scientific literature. This study aimed to conduct such an evaluation.

Material and methods: The study was carried out on five lactating sows reared on a farm located in Poland. The animals were given intramuscular injections of tylosin at 10 mg per kg of body weight for three consecutive days. Milk samples were collected 3 h and 1, 2, 5, 7, 14 and 21 d after the first administration. The determination of tylosin was carried out using ultra-high performance liquid chromatography with tandem mass spectrometry.

Results: The highest mean concentration of the substance (1,802 μg/L) was found in the samples collected 3 h after the injection. The mean levels of tylosin in the samples collected on day 1 and day 2 were 744 μg/L and 482 μg/L, respectively. The mean concentration on day 5 was lower, falling to 97 μg/L. The value of 6 μg/L in the samples collected on day 7 was the lowest noted. The samples obtained 14 and 21 d after the first administration were below the limit of quantification.

Conclusion: Tylosin easily passes the blood-milk barrier in sows, reaching its maximum concentration in a short time. To the best of our knowledge, this is the first report describing the excretion of tylosin into sow milk.