ARSBC 2018: Predicting and promoting fertility in bulls

Joe Dalton
University of Idaho

Sperm attributes necessary for fertilitization:

  • Acceptable morphology
  • Metabolism for production of energy
  • Progressive motility
  • Capacity for hyperactive motility
  • Stabilization of plasma and acrosomal membrane lipids
  • Acrosomal enzymes
  • Chromatin integrity


More is not always better. 1/2 cc straws are not better than 1/4 cc straws.
How many sperm cells are needed to get a female pregnant? It depends. Different bulls have different sperm fertility.

There are compensable semen traits, such as mis-shaped sperm, that compromise sperm quality. Increasing sperm number can compensate for this.

There are incompensable semen traits, such as genetic inviablity, that compromise sperm quality. Increasing sperm number cannont compensate for these traits.

They used Angus bulls on Nelore cows to look at the effect of sperm dose. They used 10 million, 20 million, 20 million, and 40 million sperm per straw. They put each of these treatments in different colored straws. There was no fertility differences between the number of sperm in a straw. By comparing the pregnancy outcomes between the two 20 million dose treatments they could show the random variation that happens in breeding programs.

They then looked at computer assisted sperm analysis (CASA) and flow cytometry at the bulls used in the study. There were differences between bulls in CASA and FC, but these differences did not explain fertility differences between bulls. There are things going on affecting fertility that we have not discovered yet.

We need to use Breeding Soundness Exams to promote fertility. Only 27% of producers are semen testing bulls. There is a difference between a BSE and a semen test. The spermatagenic cycle takes 60 days to create new sperm. BSE should be performed 60 days before the start of the breeding season.
BSE includes physical examination looking at eyes, feet, legs, testes, epididymides, penis, prepuce, seminal vesicles, etc. There is also a semen evaluation.
The minimum criteria for satisfactory potential breeder are scrotal circumference, sperm motility and morphology,and free of physical problems. There are unsatisfactory potential breeders and deferred breeders. Unsatisfactory breeders will not improve, deferred breeders may improve with time and a new spermatagenic cycle.

Based on reviews of BSEs, anywhere from 18% to 37% of bulls will fail a BSE. The BSE benefit to cost ratio is $20 for each $1 invested.

All sperm attributes necessary for fertilization and embryonic development are not known.

To reduce the risk of uncompensable seminal traits:

  • Use semen from AI studs where morphology is a routine part of quality control.
  • Use multiple sires.
  • Perform BSE on natural service sires.

Link to video of Dalton's presentation: https://www.facebook.com/AngusJournal/videos/242679089923465/

See ARSBC Newsroom for more information. http://www.appliedreprostrategies.com/2018/newsroom.html

Note: this post was live blogged and may contain errors.
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