Rams sometimes fail to mate the ewes, even when the ewes are in estrus, or mating can occur but pregnancy does not ensue.
The many reasons for failure to mate include the following:
The ewes are being bred, but the marking harness or crayon is not functioning properly.
The ram lacks libido because it is ill with another disease, too thin, or too old; mating is happening during the anovulatory period; or the weather is too hot.
The ram is reluctant to breed, perhaps because of the pain of infectious balanoposthitis (pizzle rot), because of contagious ecthyma of the penis or prepuce, or because it is lame and cannot mount comfortably.
The ram might be inexperienced and has not been “taught” how to breed by observing a more experienced ram.
The ram might not be able to cope properly with the environment (eg, a barn-raised ram turned out to mountainous pasture).
Too few rams are available to breed the ewes (ram:ewe ratio) for the type of ram (age, experience), conditions (paddock versus range), time of year (ovulatory versus anovulatory), or synchronization programs.
Rams might have behavioral issues such as inter-ram aggression, shy rams, or rams preferring or disliking specific ewes.
Mating not followed by pregnancy can present as ewes being marked repeatedly, a spread-out lambing period, or poor prolificacy in the ewes. Many of the reasons for failure to mate can also influence failure to achieve pregnancy. Additional reasons for lack of pregnancy after mating include the following:
impaired fertility caused by one or more factors:
diseases such as Brucella ovis infection, chorioptic mange of the scrotum, infertility after a fever, or other causes of orchitis and/or epididymitis
mechanical reasons, such as excessive heat or cold, inguinal hernia, or injury from fighting
environmental hormone disrupters (eg, phytoestrogenic plants)
inadequate testicular circumference because of age, season, genetics, or disease
abnormalities of the penis due to a congenital defect or trauma
sperm abnormalities
