Elsevier

Theriogenology

Volume 63, Issue 7, 15 April 2005, Pages 1925-1937
Theriogenology

Bovine embryo development after IVF with spermatozoa having abnormal morphology

https://doi.org/10.1016/j.theriogenology.2004.09.001Get rights and content

Abstract

The study was conducted to evaluate the effects of scrotal insulation on semen samples collected from bulls on embryonic development after IVF. Semen samples were obtained and cryopreserved from four Holstein bulls before and after a scrotal insulation period of 48 h (Day 0). Three types of samples were used for IVF: (1) semen from the test bulls collected 5 d prior to scrotal insulation (pre-insult); (2) semen from Day 13 (2-week post-insult; 2-week PI); and (3) semen from Day 20 (3-week PI). After 18 h of sperm–oocyte co-incubation, the zygotes were cultured for 8 d when a developmental score (0 = degenerate, 1 = 2-cell embryo through 5 = blastocyst) was assigned to each embryo. The post-thaw morphological evaluation of sperm samples revealed a decrease (P < 0.01) in the percentages of normal spermatozoa in the 3-week PI samples in comparison with the pre-insult samples for Bulls I and III (74–22.3% and 67.7–0.5 %, respectively). The percentage of vacuolated spermatozoa increased significantly for Bull II. The cleavage and blastocyst formation rates and embryo development scores were affected (P < 0.01) by the interaction of bull by sample collection time. For Bulls I and III (severe responders) the scrotal insulation effects persisted from the time of cleavage through blastocyst formation. In contrast, the cleavage and blastocyst formation rates for Bulls II and IV were unaffected, despite high percentages of vacuolated spermatozoa present in the post-insult samples for Bull II. In conclusion, the use of scrotal insulation to elevate scrotal temperature was an effective method to obtain semen samples with high percentages of abnormal spermatozoa. The decrease in embryonic development after IVF when using spermatozoa with morphological abnormalities seemed to be multifaceted and related to changes in head 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)

  • D.R. Franken et al.

    The hemizona assay:its role in identifying male factor infertility in assistant reproduction

    Fertil Steril

    (1993)
  • J.R. Correa et al.

    Preparation and recovery of frozen-thawed bovine spermatozoa via various sperm selection techniques employed in assisted reproductive technologies

    Theriogenology

    (1996)
  • B.P. Setchell

    Heat and the testis

    J Reprod Fertil

    (1998)
  • R.G. Saacke et al.

    Accessory sperm evaluation and bull fertility: an update

  • J.M. De Jarnette et al.

    Accessory sperm: their importance to fertility and embryo quality, and attempts to alter their numbers in artificially inseminated cattle

    J Anim Sci

    (1992)
  • D.Y. Liu et al.

    Defective sperm-zona pellucida interaction: a major cause of failure of fertilization in clinical in vitro fertilization

    Hum Reprod

    (2000)
  • D.Y. Liu et al.

    Evaluation and assessment of semen for IVF/ICSI

    Asian J Androl

    (2002)
  • H. Krzanowska et al.

    Influence of egg investments on in vitro penetration of mouse eggs by misshapen spermatozoa

    J Reprod Fertil

    (1983)
  • M.C. Kot et al.

    Binding of morphologically abnormal sperm to mouse egg zona pellucidae in vitro

    Gamete Res

    (1987)
  • J. Howard et al.

    Zona pellucida filtration of structurally abnormal spermatozoa and reduced fertilization in teratospermic cats

    Biol Reprod

    (1993)
  • E. Blom

    The ultrastructure of some characteristic sperm defects and a proposal of the bull spermiogram

    Nord Vet Med

    (1973)
  • Cited by (0)

    View full text