Diestrus is a term used in veterinary medicine to describe the stage in the reproductive cycle of female animals. This phase is characterized by the absence of ovulation and a decrease in reproductive hormones. Some synonyms for diestrus include the luteal phase, non-fertile period, and the interoestrous interval. The luteal phase is named for the presence of the corpus luteum, a hormone-secreting structure that forms after ovulation. The non-fertile period is a term used to describe the phase in which the female is not receptive to mating. The interoestrous interval is the time between periods of sexual receptivity. Understanding the different synonyms for diestrus is important for veterinarians to accurately assess and manage reproductive health in animals.