Enhancing evaluation of bull fertility through multivariate analysis of sperm

H C Azevedo; H D Blackburn; E A Lozada-Soto; S F Spiller; P H Purdy

doi:10.3168/jds.2024-25163

Enhancing evaluation of bull fertility through multivariate analysis of sperm

J Dairy Sci. 2024 Sep 27:S0022-0302(24)01157-3. doi: 10.3168/jds.2024-25163. Online ahead of print.

Authors

H C Azevedo¹, H D Blackburn², E A Lozada-Soto³, S F Spiller³, P H Purdy³

Affiliations

¹ Brazilian Agricultural Research Corporation (Embrapa), Aracaju 49025-040, SE, Brazil. Electronic address: hymerson.azevedo@embrapa.br.
² U.S. Department of Agriculture - Agricultural Research Service (USDA ARS), National Animal Germplasm Program, 1111 S. Mason St., Fort Collins, CO 80521-4500, USA Tel: +1-970-492-7511. Electronic address: harvey.blackburn@usda.gov.
³ U.S. Department of Agriculture - Agricultural Research Service (USDA ARS), National Animal Germplasm Program, 1111 S. Mason St., Fort Collins, CO 80521-4500, USA Tel: +1-970-492-7511.

PMID: 39343204
DOI: 10.3168/jds.2024-25163

Abstract

Computer-assisted sperm analysis (CASA) has become the predominant tool for assessing bull semen in artificial insemination programs. Despite such popularity CASA's ability to predict fertility has been limited, especially when emphasis is based upon single motion characteristics. Our hypothesis is that numerical sets of CASA measures provide a more effective method to differentiate the potential fertilization capacity of bulls and that bulls can be clustered based upon sets of CASA measures. Therefore, we used CASA to evaluate frozen-thawed semen samples from 307 Holstein and 152 Jersey bulls sourced from USDA-ARS's National Animal Germplasm Program gene bank. Sperm was evaluated immediately after thawing and 30 min later. We evaluated sperm kinetic and morphometric means and variances to capture the structure of CASA data in relation to various sources of variation. These data were subjected to univariate and multivariate statistical methods to investigate animal and management factors affecting sperm characteristics measured by CASA. Clustering with K-means identified 4 clusters of bulls based upon each cluster's set of CASA parameters after thawing. There was little overlap among clusters for sets of CASA measures. At the extremes, bull cluster 1 (BC1, n = 180) and BC3 (n = 101) had different sire conception rates (SCR) -0.07 vs -1.29, respectively and sets of CASA measures. Interestingly, BC2 had CASA measures that could be perceived as negative, e.g., cell size at 8.18mm² vs 6.37mm² for BC4 and total motility of 29.7% vs 48.7% for BC3, but SCR for BC2 was higher (-0.79) than BC3 (-1.29). Despite such discrepancies for some BC2 CASA values it appears the potentially negative effects were offset by the levels of other CASA values. Our findings suggest improved approaches for using CASA could lie in evaluating multiple CASA measures as sets within specific numerical ranges rather than as independent measures.

Keywords: Cattle; Cryopreserved semen; Post-thaw evaluation.

The Authors. Published by Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).