Reproductive failure can be defined as either sterility or infertility. Sterility occurs when there is a permanent problem preventing kid production, while infertility, or temporary sterility, is the inability to produce live young within a specific time period. There are a number of factors that can cause reproductive failure including physiological, toxicological and psychological factors. Please see the links below for specific information on these causes.
In addition, there can be causes of reproduction problems that are inherited (passed on from parents). For example, females might have malformed reproductive tracts like incomplete oviducts, an abnormal uterus or a blind cervix or vagina. These problems may not detected without slaughter because the female may cycle (come in heat) regularly, but cannot get pregnant. Males may also have inherited abnormal problems as well.
More problems with reproductive anatomy might be the case of hermaphrodites. They are usually classified as true hermaphrodites or pseudohermaphrodytes. The true hermaphrodite will have both male and female reproductive gonads (ovaries and testis) while a pseudohermaphrodite will have either testis or ovaries, but have other parts representing both male and female.
Cryptorchidism is another condition that might lead to reproductive failure in males. This is a condition in which the testes do not pass through the inguinal canal into the scrotom, so they stay up in the body cavity. A male will be fertile in cases where one testis descends (unilateral cryptorchid), or even if part of one testicle is outside the body cavity, but if both testicles are still inside the body (bilateral cryptorchid), the male will be sterile. This condition is heritable (passed on from parents), so bucks with this condition should not be used for breeding.
Injury can also cause reproductive failure in both males and females. For instance, a female can be injured during kidding and a tear in the uterus may heal but may not allow the female to get or stay pregnant in the future. Injuries to the vagina, cervix or even vulva may also happen during kidding, such as if too much force is used to pull kids during a difficult birth. Injuries to the buck include inflammation of the scrotum/testes or injuries to the penis during natural mating or semen collection for artificial insemination (AI).
For more information on reproductive problems: Maryland Small Ruminant Page