Validation of an immunoassay system for progesterone dosage and physiological responses of postpartum cows treated with long-acting injectable progesterone

• Autor(a) principal: Silva, Taynara Jaqueline Barreiro da
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/11/11139/tde-14022022-131254/
• topic: Bos indicus; Bos indicus; Anestro; Anestrus; Chemiluminescence; Immulite; Immulite; Progesterona; Progesterone; Quimioluminescência

Studies were conducted to validate a kit for measuring P4 in cattle and to evaluate the circulating progesterone (P4) profile and ovarian dynamics after treatment with long-acting injectable progesterone (P4i) in postpartum cows. In the first study, tests were conducted to validate a commercial kit based on chemiluminescent technology, Immulite 1000 Progesterone (LKPW1), to measure P4 in cattle. For this purpose, standard curves were generated from plasma samples of steers enriched with known concentrations of P4, and the precision, accuracy, anticoagulant effect, and residual effect were evaluated. The method proved to be accurate for samples with a P4 concentration between 0.3 and 10.0 ng/mL and precise for samples between 0.5 and 20.0 ng/mL. In addition, the results provided by the equipment are reliable to the concentrations in the samples, whether using serum or plasma, and it is not necessary to analyze standard curves for each assay. In the second study, Nelore primiparous (n = 28) in postpartum anestrus were randomly assigned to receive 1 mL of oily vehicle (Con; n = 14) or 1 mL of oily vehicle with 150 mg of P4i (P4i; n = 14) on D0. Thereafter, for 21 d, blood samples and ovarian ultrasonography were performed in all animals, in addition to observation of expression of estrus between D8 and D15. In general, no cow expressed estrus, remaining anovulatory until D20. On D1, cows in the P4i group had a peak of circulating P4 (3.0 ng/mL), remaining above 0.5 ng/mL for 7 d, while in the Con group, circulating P4 remained below 0.2 ng/mL throughout the study. Cows in the P4i group had a larger diameter of the dominant follicle during the study (12.8 ± 0.5 vs. 10.6 ± 0.6 mm), a longer interval between waves (9.4 ± 1.0 vs. 6.5 ± 0.7 d) and more days with follicles with ovulatory capacity in the ovaries compared to the Con group (12.5 ± 0.5 vs. 8.3 ± 1.3 d). Thus, despite being inefficient in inducing cyclicity in postpartum cows, treatment with P4i promoted changes in ovarian dynamics and circulating profile of P4 that could serve as a basis for further studies and use strategies. Furthermore, the tested kit showed high potential for use in the quantification of circulating P4 in cattle. However, further tests and analyses of a larger number of samples are needed to confirm its robustness.