Conception Failure in Animals

Failure of conception is recognized by an increased number of regular returns to service (i.e., returns at 18–24 days after service). The conception rate (or non-return rate) in breeding herds should be at least 90%, and an incidence of return higher than 10% should be regarded as abnormal and unacceptable.

Conception failure suggests that viable ova did not come into contact with viable spermatozoa at the appropriate time. The result of this will be either total conception failure (i.e., regular return to service) or partial conception failure (i.e., reduction in litter size).

Assuming that ovulation has taken place, conception failure must be due to one or more of the following factors:

1. Timing of Service
2. Quality of Service
3. Semen Quality

Timing of Service

High embryonic survival rate and large litter size at birth can be ensured by a single mating at the appropriate stage of estrus, resulting in a high proportion of ova fertilized at the optimum time. However, identifying this ideal time is most difficult.

• The sow ovulates, on average, 36-44 hours after the onset of standing estrus
• Spermatozoa can survive for approximately 24 hours inside the sow’s reproductive tract
• A service regimen must take all these factors into account and aim to ensure that the uterus contains viable spermatozoa prior to the arrival of the ova
• Inappropriate timing of service results in conception failure

Keeping this in mind, the service management regimen should ensure that each sow is served on the day of the onset of standing estrus and at least once more, 18–24 hours later.

Quality of Service

Service pen design, particularly with reference to the floor surface, is of direct relevance to the quality of service. Young boars need to be trained for natural service and should be well supervised each time they mount a sow or gilt.

Semen Quality

Semen quality can be affected — in terms of ejaculate volume, sperm count, sperm motility, or morphology — by a wide range of factors such as age, environmental temperature, frequency of use, and disease.

Where boars are used for natural service, subfertile or infertile individuals may remain unidentified. The physical breeding soundness, with particular attention to the feet and leg conformation of the boar, should also be taken into account.