Reproductive Performance of Beef Cattle Heifers Associated with Molecular Markers Related to the Fertility

Background: The marker assisted selection (MAS) is indicated as an auxiliary strategy to increase the productive performance in cattle. The principle consists in the identification and selection of molecular markers associated with genes involved directly or indirectly with the expression of a desired trait, usually multifactorial and polygenic. The pregnancy rate is a form of expression fertility, with great economic importance in cattle production systems. The pregnancy rate is a multifactorial trait, which is influence by genetics, environment and their interactions. In the current study was search for an association between the reproductive response, expressed by pregnancy rate at insemination and pregnancy rate at the end of the mating season, and molecular markers of genes related to IGF-1 receptor, LH beta, Leptin, receptors of FSH and LH. Materials, Methods & Results: Data were evaluated from 249 beef heifers of British breeds, Angus, Devon and crosses. The animals at fourteen or twenty seven months were subjected to different protocols for artificial insemination (AI) and fixed-time artificial insemination (TAI), followed by clean up bulls. The protocols AI and TAI, called AI/TAI, were: Group 1 -Ovsynch protocol (27th months). At day zero the animals received an injection of a GnRH at a dose of 10 mu g buserelin, at seventh day received 500 mu g of cloprostenol sodium, at ninth day the animals received another dose of 10 mu g of buserelin. TAI was performed 10 h after the application of buserelin; Group 2 - Protocol Crestar (R) with 1/2 dose of estradiol valerate injectable (27th months). At eighth day the implant was removed, followed by 375 mu g of cloprostenol sodium. At ninth day, was administered 1 mg of estradiol benzoate. TAI was performed in tenth day, 52 h after implant removal; Group 3 - Control group (27th months), with AI 12 h after estrus during the first seven days. Seventh day, was applied 375 mu g of cloprostenol sodium on all heifers not inseminated, followed by AI for five days more; Group 4 (14th months) - Same protocol of the Group 2; Group 5 (14th months) - Same protocol of the Group 3. During the group formation, blood samples for extraction of DNA were obtained individually from all experimental animals. Microsatellite markers (short tandem repeats, STR) and/ or single nucleotide polymorphisms (SNPs) were investigated by means of polymerase chain reaction (PCR). The STR investigated were the AFZ-1, HEL5, ILST002, IDVGA51, FSHR and LHR. We considered the effects of the treatment groups, age, body condition score (BCS), reproductive tract score (RTS), weight at the beginning of the breeding season, daily weight gain on pregnancy rate to AI/ TAI and pregnancy rate to final. Molecular markers investigated did not show association with pregnancy rate. The mean pregnancy rate at insemination was 41.0% and the pregnancy rate final was 91.6%. There were no differences in pregnancy between the age of the animals. The average weight at the beginning of the mating was 313 kg without differentiate between animal that become pregnant or empty during the reproductive season. The RTS influenced the pregnancy rate after insemination in respectively 0%, 32.1% and 49.5% (P < 0.05) for RTS 1, 2 and 3. Discussion: Molecular markers AFZ-1, HEL5, ILST002, IDVGA51, FSHR and LHR could not be associated with pregnancy rate at insemination and pregnancy in beef heifers, perhaps because the high degree of reproductive selection that these animals are subjected. The nutritional status of the herd, expressed by weight and body condition score at mating of animals contributed to the achievement of significant pregnancy rates. The reproductive tract score can be considered as a predictor of fertility in herds of beef heifers.