Abstract
Simple SummarySuboptimal fertility in males accounts for about two-thirds of infertility cases, thus being of serious concern for the dairy industry, where optimal fertility is fundamental for farm profitability. Although genetic defects responsible for subfertility have been identified, the role of seminal compounds on fertility remain unclear. Feeding rumen-protected isomers of conjugated linoleic acid (CLA) to dairy cows reportedly enhances circulating insulin-like growth factor I (IGF-I) levels. In breeding bulls, the IGF-I concentration in seminal plasma has been positively correlated with fertility rates. Therefore, the objective of the study was to evaluate the effect of dietary CLA supplementation and of their inclusion to the semen extender on bovine semen quality and freezability.Isomers of conjugated linoleic acid (CLA) enhances circulating insulin-like growth factor I (IGF-I) levels. Furthermore, fertility rate of breeding bulls is positively correlated to seminal plasma IGF-I concentration. Our objective was to evaluate the effect of dietary CLA supplementation and inclusion to the semen extender on bovine semen quality and freezability. Fourteen bulls, randomly assigned to control (CTL) and CLA (50 g/day) groups, were supplemented for 10 weeks. Samples were collected at Weeks −2 (before supplementation), 0, 4, 6 (during supplementation), 10, and 11 (after supplementation). Blood and seminal plasma were analyzed for IGF-I; the ejaculates were frozen in the following subgroups: CTL (no addition to semen extender), CLA c9, t11 (50 µM), CLA c9, t11 (100 µM), CLA t10, c12 (50 µM), CLA t10, c12 (100 µM), and CLA mix (50 µM each of CLA c9, t11 and CLA t10, c12). Sperm motility, morphology, viability, mitochondrial membrane potential, and reactive oxidative species were assessed. CLA supplementation decreased ejaculates’ total volume, increased sperm concentration, beat cross frequency, and decreased oxidative stress; it also increased plasma and seminal plasma IGF-I levels compared to the CTL. The inclusion of CLA c9, t11 100 µM and CLA mixture in the extender increased live spermatozoa percentage post-thawing compared to other groups. Our results show a beneficial effect of CLA supplementation on semen quality; however, further studies evaluating fertilization rates are necessary to corroborate the results.
Highlights
In the cattle industry, suboptimal fertility in males accounts for about two-thirds of infertility cases, being of serious concern for the livestock industry [1,2,3]
To the best of our knowledge, no other studies evaluated the effect of dietary conjugated linoleic acid (CLA) supplementation on circulating insulin-like growth factor I (IGF-I) levels in bulls, our results are in line with what has been observed in dairy cows [23,24]
Studies conducted on male growth hormone (GH) deficient dwarf rats proved that treating the rats with exogenous GH resulted in higher concentrations of IGF-I in blood plasma and seminal vesicle fluid compared with non-dwarf control rats [40]
Summary
Suboptimal fertility in males accounts for about two-thirds of infertility cases, being of serious concern for the livestock industry [1,2,3]. In vitro studies proved that the addition of IGF-I stimulates spermatozoa motility in bovine samples [14] This is achieved by the activity of tyrosine kinase of the insulin-like growth factor I receptor (IGF-IR) and its ligand IGF-I present in the seminal plasma. By supplementing the isomers cis-9, trans-11 and trans-10, cis-12 of the conjugated linoleic acid to the bulls, plasma and seminal plasma IGF-I levels might increase, improving sperm quality. The objectives of our study were: (1) to evaluate the effect of dietary CLA supplementation in bulls, on blood plasma and seminal plasma IGF-I levels and on post-thaw sperm quality; (2) to evaluate the effect of the inclusion of the isomers of the CLA at different concentration on post-thaw sperm quality; and (3) to evaluate a possible interaction between treatments and which approach is the more performing
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