Effect of intramammary treatment on primiparous heifers and investigation of antimicrobial residues in postpartum milk

Abstract


 The aims of the present study were to investigate the occurrence of intramammary infections in primiparous heifers treated and not with antibiotics in the prepartum, postpartum and subsequent lactation periods and to verify the occurrence of antibiotic residues in the milk released for consumption. A total of 188 mammary glands from 47 Black and White Holstein and crossbred heifers belonging to two experimental dairy farms located in the state of São Paulo, Brazil, were evaluated. Animals were randomly distributed into four groups, treated and untreated (control). In the prepartum period, mammary gland secretion samples were collected from all mammary quarters for microbiological examinations. Then, animals in the treated group received intramammary infusion with antibiotics. Milk samples were collected immediately after calving, ten days after and monthly throughout lactation for microbiological assays, milk composition determination, somatic cell count and investigation of antimicrobial residues using Delvotest®SP. It was observed that about 20% of animals already had intramammary infections sixty days before calving, and around 40% at calving. The dry cow therapy had no significant effect on controlling infections. Staphylococcus spp. was the main isolated bacterial genus. Antimicrobial residues were detected in 5.43% of milk samples from treated heifers. The dry cow therapy should be administered in primiparous heifers at the prepartum period with caution and accompanied by a veterinarian.