VGO 511: Veterinary Andrology and Reproductive Techniques (1+1)

MORPHOLOGY OF SPERMATOZOA

• An increased prevalence of abnormal sperm is associated with a decrease in fertility.

The sperm morphology is highly correlated with the fertility of the bull. There is considerable evidences are available that increased abnormalities will lead to poor conception rate.

• The appearance of an increased number of abnormal sperm in the ejaculate is a reflection of lesions of the testes and/or the excurrent duct system and provides a convenient clinical diagnostic aid.
• The prevalence of abnormal spermatozoa is usually determined by a stained semen smear examined under the light microscope or by a wet mount of spermatozoa preserved in formal saline solution and examined under a phase contrast microscope.
• Generally, abnormal sperm are categories and percentages recorded while counting a total of 200 sperm cells. An eosin-nigrosin stain is commonly used as a morphology stain.
• The eosin-nigrosin sperm smears prepared for live and dead count is satisfactory for assessing abnormal spermatozoa.
• Different areas of the smear are examined under oil immersion at a magnification of 1000X and the percentage of primary and secondary abnormalities as per Ball et al., (1983) is calculated by counting 200 spermatozoa.
• Phase contrast microscopy is preferred because certain types of sperm abnormalities cannot be detected when viewed under the light microscope.

TOP

Classification of sperm abnormalities

Primary Abnormalities

• Proximal droplets
• Head abnormalities
  • swollen, knobbed, beaded or ruffled acrosome
  • misshapen head
  • pyriform head
  • double head etc.,
• Midpiece abnormalities
  • proximally coiled tail involving midpiece
  • tightly coiled tail
  • mitochondrial bulge or swollen midpiece
  • mitochondrial loss
  • double midpiece and tail

Secondary abnormalities

• Tail abnormalities
  • Folded tail with or without droplet
  • Reversed tail with or without droplet
  • Kinked tail with or without droplet
  • Distally coiled tail
• Distal droplets
• Separated heads (including partially separated head)

TOP

• In addition to these there are many specific sperm abnormalities, which are associated with sub-fertility/sterility.
• These include, decapitated sperm defect, dag defect, knobbed sperm, tail stump defect, pseudodroplets, corkscrew defect etc.
• Abnormality counts of Jersey and Murrah bull semen are classified and scored (Ball et.al., 1983) as follows:

PRIMARY ABNORMALITIES(%)	<10	10 - 20	20 - 30	>30
TOTAL ABNORMALITIES (%)	<25	25-40	40-60	>60
SCORE	40	24	10	3

• The bulls used in AI programme should have both primary and total abnormalities within 10 and 25 per cent respectively.

TOP

Interpretation of spermiogram

• An increased prevalence of sperm with morphologic abnormalities such as head abnormalities and retained proximal droplets may be evidence of either sexual immaturity or degenerative changes in the seminiferous epithelium of the testes.
• Abnormal sperm will usually disappear from the ejaculated as the bull ages and, in some cases, as the testes become larger.
• A bull that does not exhibit a normal spermiogram by 18 month age is a poor risk as a future breeding animal.
• In case of matured bull, it has to be differentiated whether the degenerative changes are transient or permanent which is very difficult and is complicated by the fact that 49 days are required for sperm to complete the spermatogenic cycle plus an additional two weeks are required for passage of the sperm through the epididymis.
• The presence of more that 15% major abnormalities or more than 30% total abnormalities, especially when coupled with other findings such as palpable testicular or epididymal lesions or inadequate scrotal circumference, is sufficient reason to classify a bull as questionable or, depending upon severity, as an unsatisfactory potential breeder.However, interpretation of a spermiogram requires information concerning the bull’s breeding history and the results obtained from a through clinical examination of the bull.

TOP