232 S.Y. Huang et al. Animal Reproduction Science 63 2000 231–240
that the levels of HSP70 in boar spermatozoa are significantly lower during the hot season and might be associated with semen quality. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Heat shock protein 70; Semen quality; Season; Boar
1. Introduction
In most mammals, spermatogenesis deteriorates at an elevated testis temperature even only reaching as high as body temperature Chowdbury and Steinberger, 1964; Vandemark
and Free, 1970. This phenomenon implies that spermatogenetic cells are extremely sensi- tive to heat stress. Although not affecting semen volume or gel weight, heat stress decreases
sperm motility and percentage of normal sperm and increases the percentage of abnormal sperm and sperm with aged acrosome McNitt and First, 1970; Christenson et al., 1972;
Wettemann et al., 1976. Conception rates declined in sows that were either artificially in- seminated or were naturally mated with heat stressed boar Wettemann et al., 1976, 1979.
Wettemann and Desjardins 1979 indicated that heat stress suppressed maturation of sperm cell, subsequently decreasing the sperm output and semen quality. In the subtropical climate
of Taiwan, the semen quality of boars generally decrease during the summer, ultimately de- creasing reproductive performance Cheng and Wung, 1974; Liu et al., 1994; Kuo et al.,
1997.
Cells or multi-cell organisms respond to heat or other stresses by inducing or increasing the synthesis of a group of unique proteins commonly referred to as heat shock proteins
or HSPs Lindquist, 1986; Lindquist and Craig, 1988; Welch, 1992. Although the exact functions of HSPs are still unclear, one of their roles is to prevent the organisms from adverse
environmental impacts Li and Laszlo, 1985; Pelham, 1986; Welch, 1992. Many studies have demonstrated that HSPs, particularly the abundantly expressed 70 kDa HSP HSP70,
play important roles in acquired thermotolerance Li and Laszlo, 1985; Lindquist, 1986; Subjeck and Shyy, 1986; Sanchez and Lindquist, 1990; Nover, 1991; Sanchez et al., 1992,
and HSP70 has been suggested to function as an indicator of thermotolerance in cells Craig and Gross, 1991; Leung et al., 1996. According to recent vertebrate-related studies, HSP70
plays important roles in many stresses in multiple-cell organisms and protects lizards from heat stress Ulmasov et al., 1992; Lyashko et al., 1994; Malysheva et al., 1994; Marber et
al., 1995; Plumier et al., 1995. Whether or not HSP70 could function as an indicator of thermotolerance in livestock requires further study.
Raab et al. 1995 observed the presence of HSP70 in the ejaculated sperm of mammals including boars. Sarge 1995 indicated that the expression of HSP70 in male germ cells
could be induced at a lower temperature than that in somatic cells under in vitro culture conditions, implying that male germ cells are more heat sensitive than somatic cells. Owing
to the ability of HSP70 to protect cells against heat stress, this study attempts to determine whether or not the level of HSP70 increases during heat stress; if not, whether or not semen
quality decreases is also examined. Therefore, in addition to determining seasonal and breed effects on the levels of HSP70 in ejaculated boar spermatozoa, this work also investigates
the relationship between HSP70 level and semen quality.
S.Y. Huang et al. Animal Reproduction Science 63 2000 231–240 233
2. Materials and methods
