increase until 2–3 days post copulation, then the level rises until day 21 post copulation where after it gradually declines to normal levels. Dogs Pseudopregnancy is a normal physiologic process that occurs in female dogs. It is seen 45–60 days after a normal estrous (heat) period. After ovulation, progesterone levels rise. Pseudopregnancy happens when the progesterone levels begin to fall as decreasing progesterone leads to an increase of the hormone prolactin. Prolactin is responsible for the behaviours seen during pseudopregnancy. Dogs may exhibit mothering of toys, nesting or aggression. Mammary development and milk production are common. Pseudopregnancy can also be acutely induced by spaying (removing of ovaries) a dog near the end of estrus. Spaying removes the source of progesterone and induces a rise in prolactin. Permanent prevention of pseudopregnancy is accomplished with spaying. Dogs become pseudopregnant following an estrus phase in which the female dog is not bred, or in which she is bred by an infertile male. Most species require signals from an embryo (such as IFN-τ in ruminants) to alert the female's body of a pregnancy. This maternal recognition of pregnancy will cause persistence of the corpus luteum and the development of characteristics and behaviors necessary to care for offspring. Limited research suggests that progesterone secretion is similar in pregnant and non-pregnant female dogs, so veterinary researchers hypothesize that they may not require molecular factors from the embryo for maternal recognition of pregnancy, and instead the corpus luteum persists regardless of pregnancy. Since the corpus luteum is not degraded, it will cause the development of maternal characteristics in the absence of pregnancy. Pseudopregnant dogs will develop their mammary glands, lactate, and build nests to varying degrees depending on breed. Although female dogs usually only cycle once or twice per year, pseudopregnancy is common. Swine Pseudopregnancy or "not-in-pig" is a condition that occurs when females exhibit physiological and behavioral signs associated with pregnancy, but there are no fetuses present. Pseudopregnancy can occur when all of the embryos are resorbed after the maternal recognition of pregnancy (days 10–15 postmating) and before fetal bone calcification (days 35–40 of gestation). The sow remains in anoestrus for prolonged periods, often as long as 115 days. These animals may exhibit varying degrees of udder development, but fail to deliver any pigs. The timely identification and removal of non-pregnant females from the breeding herd is important because it reduces both non-productive sow days and