Zinc supplementation within the reference ranges for zinc status in cattle improves sperm quality without modifying in vitro fertilization performance

Abstract

Zinc (Zn) has important functions in mammalian reproductive processes. In cattle, Zn status can be classified as deficient, marginal, and adequate, depending on the plasma Zn concentration. In addition, Zn deficiency can lead to reproductive failure. The aim of this study was to investigate the effect of maternal Zn status at the beginning of a fixed-time artificial insemination (FTAI) treatment regimen on pregnancy rate in cattle, and evaluate the effect of supplementing in vitro fertilization (IVF) medium with Zn concentrations within the reference range for Zn status on sperm quality and IVF performance. Pregnancy rates of animals with marginal and adequate Zn status did not differ, and there were no Zn-deficient animals detected. Supplementation of 0.8 μg/mL Zn to IVF medium enhanced progressive motility, sperm viability, functional sperm membrane integrity (HOST), acrosomal integrity and sperm-zona binding, without modifying pronuclear formation, or development of embryos to the cleavage or blastocyst stage after IVF. In conclusion, the present results indicate pregnancy rates are not associated with maternal Zn status at the beginning of the FTAI treatment regimen if Zn status is marginal or adequate. Furthermore, supplementation of IVF medium with Zn at concentrations which is considered adequate for Zn status in cattle led to improved sperm quality, without having effects on embryo development in cattle.

Introduction

Cattle require Zinc (Zn) for adequate growth and reproductive performance. Globally, Zn-deficient soils result in Zn-deficient pastures and crops, which in turn there is Zn deficiency in cattle (Underwood and Suttle, 1999; Nielsen, 2012). Cattle Zn status can be classified as deficient (< 0.4 μg/mL), marginal (0.4−0.8 μg/mL) and adequate (>0.8 μg/mL) based on plasma Zn concentrations (Underwood and Suttle, 1999; Kincaid, 2000). Zinc deficiency has been reported to contribute to reproductive disorders, including less than optimal fertility, long post-partum period to the initiation of estrous cycles, placental retention, increased number of services per conception, and pregnancy loss in cattle, mice, rats, women and monkeys (Swenerton and Hurley, 1980; Taneja and Kaur, 1990; Bedwal and Bahuguna, 1994; Graham et al., 1994; Underwood and Suttle, 1999; Enjalbert et al., 2006). To improve the genetic progress and reproductive performance of herds, beef cattle producers are utilizing fixed-time artificial insemination (FTAI) treatment regimens (Bó and Baruselli, 2014). The benefits of using FTAI include shortened calving season, earlier births during the calving season, increased calf uniformity and greater weight calves at weaning (Odde, 1990). To our knowledge, the effect of Zn status on pregnancy rate after FTAI in cattle has not yet been evaluated.

In mammals, fertilization and the first cell divisions of the developing embryo occur in the oviduct. The oviductal fluid results from specific secretions of oviductal epithelial cells and blood transudation (Pérez-Cerezales et al., 2018). Although the study of oviductal fluid components in cattle started in 1950 (Olds and Vandemark, 1957), Zn concentrations in these fluids have not yet been ascertained. The concentration of another trace mineral such as copper in the oviductal fluid of cattle is within the same range as blood plasma (Anchordoquy et al., 2017). Similar Zn concentrations have been recently reported in serum and oviductal fluid from dromedary camels (Swelum et al., 2020). The composition of oviductal fluid is important for sperm maturation, fertilization, and early embryo development (Grippo et al., 1992; Gardner et al., 1994; Bavister, 2000). There are many important functions of Zn on sperm physiology, including effects on viability, lipid metabolism and stabilization of sperm membrane and DNA structure (Fallah et al., 2018). Furthermore, extracellular Zn has been recently proposed as an important regulator of sperm capacitation and acrosome reaction (AR; Michailov et al., 2014). In rats, dietary Zn deficiency resulted in a rapid decrease in the Zn concentration of female reproductive fluid (Gallaher and Hurley, 1980). Less than optimal Zn concentrations in the oviduct of Zn-deficient females, therefore, might alter sperm viability and function, thereby reducing fertilization rates. Sperm-fertilizing capacity and details of the fertilization process itself can be evaluated conducting experiments of in vitro fertilization (IVF; Bavister, 1986). The addition of Zn within the reference range for Zn status in cattle to culture medium improved in vitro oocyte maturation (IVM; Picco et al., 2010; Anchordoquy et al., 2014). There, however, are no reports as to whether such supplementation to IVF medium affects sperm quality and subsequent embryo development in cattle.

The aim of the present study was to investigate the effect of plasma Zn concentration at the time of initiation of a FTAI treatment regimen on pregnancy rate in cattle and determine the relationship between maternal Zn status and pregnancy outcome. Furthermore, there was evaluation of the effect on sperm quality and efficacy of IVF when supplementing IVF medium with Zn concentrations within the reference range for Zn status in cattle.