Caracterização de perfis fisiológicos e marcadores moleculares em fêmeas Brangus-Ibagé com distintos graus de fertilidade

Abstract

The aim of the present study was to characterize physiological differences between animals of high and low fertility and to search for associations between molecular markers and reproductive performance, studding a population of Brangus-Ibagé cows (3/8 Nelore x 5/8 Abberdeen Angus). The cows were classified, in according to the average of the calving interval, in groups of high and low fertility. Cow weight at parturition (Pparturition), cow weight gain during the postpartum period (WGPP) and calf weight at weaning (CW205) were evaluated. The follicular population and the progesterone and estradiol levels were investigated during the postpartum period and the estrous cycle. It was not observed statistical differences among groups, in regarding to the Pparturition, WGPP and CW205. Heifers presented a low Pparturition (P<0.001) than cows but the WGPP was similar between groups. The effect year was significant (P<0.001) only on Pparturition and P205, but not on WGPP. In postpartum cows, the size of the largest follicle, the number of MF and the total number of follicles were higher in the high fertility group (P<0,05). In this cows, it was also observed the increase in estradiol production around 90 days postpartum, followed by increasing in the progesterone rate, with average values indicative of ovulation around 100 days postpartum. During the estrous cycle, the size and the number of LF were similar in high and low fertility cows; however the number of SF and the total number of follicles were higher in those animals classified as less fertile (P<0,05). Those finds are encouraging in the search of molecular markers related with factor which may influence the neuroendocrine regulation and the follicular wave for using in the selection of cows with higher fertility. From these results, an experiment was performed for searching association between reproductive performance and genetic markers, located in chromosomes where are present the estrogen receptor and the IGF-I receptor. A sample of 107 females was characterized for the ETH225 (D9S1), MM12E6 (D9S20), HEL5 (D21S15) and AFZ1 (D21S37) microsatellites. The associations between the genetic markers and reproductive efficiency were verified through analysis of variance using calving interval (CI), live weight at calving (LWC), live weight at first calving (LW1C) and live weight at second calving (LW2C) as dependent variables. The genotypes were classified according to allele sizes in homozygous for long alleles, homozygous for short alleles and heterozygous. A larger CI was verified in homozygous for long alleles at the HEL5 locus (P=0.022) while the other genotypes presented similar values. For the AFZ1 locus the two homozygous classes, demonstrated a significant association with the homozygous for long alleles presenting smaller CI (P=0.022). None of the studied systems presented significant association with LWC, LW1C and LW2C. The ETH225 and MM12E6 systems did not present any association with CI. The analysis of combined effects of the favorable genotypes in HEL5 and AFZ1, compared with the other genotypes, showed a significant association with CI (P=0.004). Individuals with unfavorable genotypes presented larger CI values (P=0.003), when compared with the other genotypes. The associations observed in this study indicate the possibility of use of the favorable genotypes of the microsatellites HEL5 and AFZ1 in the selection of this population as form of increment of the reproductive efficiency.