New Phenotypes & Infrastructure for Genetic Improvement

Summary

​Heritability and genetics of sperm chromatin integrity and protamine deficiency were studied in Brahman (n = 592) and Tropical Composites (n = 538) bulls using flow cytometry. Frozen sperm samples and fertility phenotypes of Beef CRC bulls were used. Sperm chromatin integrity was measured by the sperm chromatin structure assay (SCSA) and reported as two DNA fragmentation indexes (DFI3 and DFI4). Sperm protamine deficiency was measured using the newly developed sperm protamine deficiency assay (SPDA) and reported as low, medium or high CMA3 binding levels (LCB, MCB and HCB). Heritabilities estimated for these sperm phenotypes using genomics ranged from 0.21 to 0.40. The genetic correlations between DFI3, DFI4 and PNS were estimated as -0.20 and -0.43 in Brahman bulls and -0.32 and -0.36 in Tropical Composites. The genetic correlations between sperm protamine deficiency and percentage of normal sperm (PNS) were estimated as -0.10 (HCB) and -0.22 (MCB) in Brahmans. In Tropical Composites, correlations with PNS were -0.26 (HCB) and -0.34 (MCB). Sperm chromatin integrity and protamine deficiency were genetically correlated traits (r2 ~ 0.33 to 0.51) in both breeds. Genome-wide studies identified regions of chromosome X that were associated with sperm chromatin integrity, protamine deficiency and PNS.