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

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.

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.

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.

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.