Mastite subclínica reduz a ovulação e a qualidade de oócitos em vacas produtoras de leite

Abstract

The aim was to evaluate the association between of mastitis by somatic cell count (SCC) on follicular dynamics, ovulation, quality of oocytes and cumulus cells, concentration and size of exosomes in milk producing cows submitted to synchronization of ovulation. Cross cows (Bos taurus¬ – Holstein x Bos indicus ¬– Gir) were distributed in a control group (SCC<200.000 cells/mL milk) and the mastitis group (SCC>400.000 cells/mL milk). In the experiment 1 (follicular dynamics), the cows (n=57) were submitted to ultrasonographic evaluations every 24 hours, after the removal of the progesterone intravaginal device (D8) up to 48 hours later (D10). From the D10, evaluations were performed every 12 hours until ovulation, or up to 96 hours after withdrawal of the progesterone device, aiming at monitoring the final growth of the dominant follicle and the ovulation. In experiment 2 (Evaluation of oocytes, cumulus cells and follicular fluid), cows (n=23) were submitted to follicular aspiration, preceded by synchronization of the emergence of follicular growth wave. The levels of target genes in cumulus cells (BCL2, BAX, PI3K, PTEN, FOXO3) were evaluated by the Real Time Polymerase Chain Reaction assay. In the follicular fluid, exosomes were isolated to evaluate the concentration and size of the particles. The ovulation rate (P =0,09) and viable oocytes rate (P=0,01) were higher in control animals, [control 77,42% (24/31) and mastitis 57,69% (15/26)] and [control 59,1% (130/220) and mastitis 41,9% (125/298)], respectively. The follicular growth dynamics did not differ between the groups. There was a higher number of degenerate oocytes (P=0,001) were observed in animals from the mastitis group. In the evaluation of gene expression in cumulus cells, the greater abundance of BAX transcripts (P=0,003) was observed in cows in the mastitis group. Also, cows with mastitis had exosomes diameter with lower mean (P=0,03) and lower mode (P=0,02). In conclusion, there was effect of mastitis on ovulation, oocyte quality and diameter of exosomes of follicular fluid.