Sperm abnormality traits can contribute to the genetic evaluation for male and female reproduction in tropical beef genotypes

Genetic parameters for traits describing the incidence of sperm cell abnormalities (proximal droplets (PD), abnormalities of the sperm cell mid-piece and tails and heads) were estimated for 1,234 Brahman (BRAH) and 1,914 Tropical Composite (TCOMP) bulls at 12, 18 and 24 months of age. At 12 months, only 8.3% of BRAH bulls were sufficiently mature to produce an analysable sample, compared to 50.4% for TCOMP. PD, associated with samples from peripubertal bulls, were the most common abnormality, with highest incidence for BRAH at 18 months (24.6%) and TCOMP at 12 months (22.6%) of age. Heritabilities for PD tended to be higher than for other abnormalities, at 0.39 for BRAH at 24 months, and 0.45 for TCOMP bulls at 12 months. Genetic correlations of PD with female age at puberty (AP) and lactation anoestrous interval (LAI) were moderate for BRAH bulls at 18 (rg = 0.51 and 0.35 respectively) and 24 months (rg = 0.22 and 0.49 respectively). These relationships were generally weaker for TCOMP, though PD at 12 months showed a comparable genetic correlation with LAI of 0.51. AP and LAI are difficult and expensive to measure for genetic evaluation. The potential for PD to be exploited as a direct and early descriptor of male puberty, and an indicator trait for female reproductive performance, presents new opportunities to apply selection to improve reproductive performance in tropical beef breeds.