y Decoding HF crossbred bull fertility: Candidate gene markers contributing significantly to the phenotypes

Bull fertility is an important trait determining conception in cows and subsequently, influencing other economic traits. Sire conception rate has been used as a reliable predictor of bull fertility and is often considered as a pseudophenotype for selection. However, in order to make substantial genetic improvements in the trait, information related to genetic markers for major candidate genes associated with bull fertility is indispensible. Based on a candidate gene approach, this study aimed to identify SNP markers in AKR1B1 and INCENP genes having a major role in determining bull fertility using Sire Conception Rate (SCR) as a pseudo-phenotype. A total of 3308 artificial insemination records of 40 HF crossbred bulls belonging to the different sets of progeny testing programme were utilized for estimating SCR. Seminal parameter traits were also recorded for all the bulls. The polymorphisms detected in AKR1B1 and INCENP genes was then associated with SCR and seminal traits. The estimated SCR ranged from -16.0 to +17.4. The least-squares mean estimates for post thaw motility (PTM), acrosomal integrity, percent live spermatozoa and plasma membrane integrity of frozen thawed semen samples were estimated as 49.68 +/- 0.50, 62.43 +/- 0.50 and 57.91 +/- 0.42, 51.11 +/- 1.10% respectively. As far as PCR-RFLP and sequencing studies were concerned, AKR1B1 gene exhibited a polymorphism in the intron 7 with A>G change at position 333 while promoter region of INCENP gene showed change T>G at position 79. Association analysis revealed a significant association of the genotypes of AKR1B1 gene with SCR and those of INCENP gene with PTM. Breeding HF crossbred bulls with AA genotype for AKR1B1 gene and GG genotype for INCENP gene were desirable in the herd for higher bull fertility. SNP markers associated with bull fertility identified in this study may be included in markerbased selection for the trait after proper validation in future.