A female dog is usually diestrous (goes into heat typically twice per year), although some breeds typically have one or three cycles per year. The proestrus is relatively long at 5 to 9 days, while the estrus may last 4 to 13 days, with a diestrus of 60 days followed by about 90 to 150 days of anestrus. Female dogs bleed during estrus, which usually lasts from 7–13 days, depending on the size and maturity of the dog. Ovulation occurs 24–48 hours after the luteinizing hormone peak, which is about somewhere around the fourth day of estrus; therefore, this is the best time to begin breeding. Proestrus bleeding in dogs is common and is believed to be caused by diapedesis of red blood cells from the blood vessels due to the increase of the estradiol-17β hormone . 
Each person is called to love as friendship and self-giving. Each person is freed from the tendency to selfishness by the love of others, in the first place by parents or those who take their place and, definitively, by God, from whom all true love proceeds and in whose love alone does man discover to what extent he is loved. Here we find the root of the educative power of Christianity: " Humanity is loved by God! This very simple yet profound proclamation is owed to humanity by the Church". In this way Christ has revealed his true identity to man: "Christ the new Adam, in the very revelation of the mystery of the Father and of his love, fully reveals man to himself and brings to light his most high calling".
The American Medical Association has estimated that several million US women suffer from a female sexual arousal disorder , though arousal is not at all synonymous with desire, so this finding is of limited relevance to the discussion of libido.  Some specialists claim that women may experience low libido due to some hormonal abnormalities such as lack of luteinising hormone or androgenic hormones, although these theories are still controversial. Also, women commonly lack sexual desire in the period immediately after giving birth . Moreover, any condition affecting the genital area can make women reject the idea of having intercourse . It has been estimated that half of women experience different health problems in the area of the vagina and vulva , such as thinning, tightening, dryness or atrophy . Frustration may appear as a result of these issues and because many of them lead to painful sexual intercourse, many women prefer not having sex at all. Surgery or major health conditions such as arthritis , cancer , diabetes , high blood pressure , coronary artery disease or infertility may have the same effect in women.  Surgery that affects the hormonal levels in women include oophrectomies .