Bovine embryo development after IVF with spermatozoa having abnormal morphology
Introduction
Elevation of testicular temperature, either by exposure to high ambient temperatures or by thermal insulation of the scrotum, disrupts spermatogenesis with a consequent decrease in semen quality and possibly sperm production, depending upon temperature elevation. The application of the scrotal insulation model to determine the effects of increased testicular temperature on sperm production and semen quality was reviewed by Setchell [1]. It has become a useful tool to study possible causes for differences in fertility rates among bulls and to provide insight into compensable and uncompensable factors [2], [3], [4], [5].
Defective sperm–zona interaction was a major cause for low fertilization rates in human IVF, and was associated with defects of the spermatozoa rather than defects of the oocytes [6]. Liu and Baker [7] reported that the proportion of spermatozoa that penetrated the zona pellucida (ZP), number of spermatozoa that bound to the ZP, and the percentage of sperm with normal morphology were strongly related to fertilization rates in vitro. Krzanowska and Lorenc [8] and Kot and Handel [9] have shown that in mice, spermatozoa with abnormal head shape can bind and penetrate the ZP; while, in domestic cats, the ability for spermatozoa with a deformed head shape to bind to the ZP is severely impaired [10]. Pyriform head shapes were associated with sub-fertility in cattle [11], and Dresdner and Katz [12] suggested that sperm morphology was related to hydrodynamic differences that may impair sperm motility. Therefore, the reduced ability of spermatozoa to bind to the ZP based on morphology may be due to aberrant patterns of motility or hyperactivated motility [2]. In contrast, Roussa et al. [13] reported a positive correlation between the percentage of spermatozoa with pyriform heads and other abnormalities present, and implied that sub-fertility was associated with a specific type of abnormality.
Bovine spermatozoa with abnormal head shapes were excluded from the accessory sperm population and, depending on the severity of the deformity, had a greater chance for exclusion [3], [14]. The ability of spermatozoa to bind and penetrate the ZP was dependent upon the severity of the defect, but spermatozoa with flattened and indented acrosomes were unable to bind the ZP [15]. Although the ZP is selective for binding spermatozoa with normal morphology, some spermatozoa with abnormal morphology are capable of binding to and penetrating the ZP [16], [17], leading to low fertilization rates, because of defects that occur later in the fertilization process such as sperm fusion with the oolemma, nuclear decondensation, or formation of the male pronucleus [6], [18].
Abnormal sperm morphology is highly correlated with the nuclear immaturity, based upon the degree of chromatin condensation assessed with flow cytometry [6], [19], [20]. However, the effects of sperm morphology on fertilization and embryonic development are largely influenced by characteristics of individual bulls, including their response to in vitro capacitation, fertilization rate, and subsequent embryonic development [21], [22], [23], [24]. There are marked differences among bulls in their response to scrotal insulation, with resultant variation in the type and percentage of morphologically abnormal spermatozoa produced, despite a chronological order of appearance in ejaculates [25]. Therefore, the application of a scrotal insulation model is a useful tool to obtain semen samples from individual bulls prior to and after scrotal insult, allowing within-bull comparisons, to investigate the effect of morphologically abnormal spermatozoa on embryonic development. Thus, the objective of this study was to evaluate the effect of semen samples collected from bulls subjected to scrotal insult and producing variable levels and types of abnormal sperm on embryonic development after IVF.
Section snippets
Materials and methods
Six Holstein bulls were subjected to a 48-h scrotal insulation period to obtain semen samples with high percentages of morphologically abnormal spermatozoa. The scrotal insult provided a mild interference with testicular thermoregulation. Briefly, for each bull, two ejaculates were collected twice weekly prior to and through 34 d after the scrotal insult (Day 0), and cryopreserved at a concentration of 50 × 106 sperm/mL [26]. Pre-insult collections (Days 8, 5 and 1) served as within-bull control
Sperm evaluation
The percentages of morphologically abnormal spermatozoa for each of the four bulls following the post-thaw evaluation are presented in Table 1. There was an overall decrease (P < 0.01) in the percentage of normal spermatozoa between the pre-insult ejaculates and the 3-week PI ejaculates for Bulls I–III, while no apparent changes were recorded for Bull IV, and no differences were found between replicates. For Bull I, the percentage of normal spermatozoa decreased from 74.2% pre-insult to 22.3% at
Discussion
This study provides compelling evidence that morphologically abnormal spermatozoa have a detrimental impact upon fertilization in vitro and subsequent embryonic development. A significant increase in the percentage of morphologically abnormal spermatozoa in the semen samples, more specific pyriform head shapes in combination with apical vacuoles (Table 1; Bull I) and diadems (Table 1; Bull III), was associated with a decrease in the percentage of embryos that cleaved (Table 3), leading to a
References (42)
- et al.
Can spermatozoa with abnormal heads gain access to the ovum in artificially inseminated super- and single-ovulating cattle?
Theriogenology
(1998) - et al.
Relationship of seminal traits and insemination time to fertilization rate and embryo quality
Anim Reprod Sci
(2000) - et al.
Effect of the knobbed acrosome defect in bovine sperm on IVF and embryo production
Theriogenology
(2000) - et al.
Variation in bovine embryo development in vitro due to bulls
Theriogenology
(1989) - et al.
Relationship between embryo development in vitro and 56-day nonreturn rate of cows inseminated with frozen-thawed semen from dairy bulls
Theriogenology
(1997) - et al.
Effects of elevated testicular temperature on morphology characteristics of ejaculated spermatozoa in the bovine
Theriogenology
(1993) - et al.
Effect of delayed supplementation of fetal calf serum to culture medium on bovine embryo development in vitro and following transfer
Theriogenology
(1998) - et al.
Bovine in vitro fertilization with frozen-thawed semen
Theriogenology
(1986) - et al.
Effects of bovine sperm by either swim-up or Percoll method on success of in vitro fertilization and early embryonic development
Theriogenology
(1995) - et al.
An investigation of the fertilization characteristics of pyriform-shaped bovine spermatozoa
Anim Reprod Sci
(1999)