Recognizing the Signs of a Heat Cycle & When To Breed

Whether you’ve been a dog breeder for a couple of years or for 10 years, you know that you can only breed a female dog when she is in season, or during her heat cycle. However, not all breeders realize that individual variations in the timing of a female dog’s reproductive cycle could throw off the breeding schedule and cause failure to conceive. 

In general, female dogs have two heat cycles a year that are about six to seven months apart and that last about two to three weeks. The estrous cycle consists of four phases: proestrus, estrus, diestrus and anestrus. Proestrus and estrus are the phases most familiar to breeders because this is when a female dog is swollen, bleeding and other dogs are interested in her.  

“Not all females have a regular cycle,” explains Cheryl Lopate, MS, DVM, DACT, a board-certified small-animal reproduction specialist at Reproductive Revolutions in Wilsonville, Oregon. “Sometimes there is little bleeding or swelling in the first days of proestrus, making it easy for a breeder to miss the signs, or sometimes a female dog’s proestrus is shorter than normal. Both could affect the ability to determine the beginning of the fertile period. 

“On the other hand, some female dogs may have a prolonged proestrus or prolonged estrus that lasts up to three to four weeks. Breeding these females too early will result in failure to conceive.” 

In contrast, “some female dogs have a prolonged anestrus, in which they fail to enter estrus at all,” she says. “This can be caused by many things, including prior spay, delayed puberty, parasites, nutrition, ovarian hypoplasia, immune-mediated ovarian inflammation and progesterone-secreting cysts. It also may be caused by silent heat or failure of a novice breeder to notice a heat cycle because the female is fastidiously clean or not bleeding much.” 

The hormonal changes that occur in female dogs during their reproductive stages relate to their ability to get pregnant. In the female dog, progesterone is a reproductive hormone that increases in the bloodstream just before ovulation. Progesterone rises due to luteinizing hormone being released from the pituitary gland, first in lower amounts and finally in a big surge that induces ovulation. 

Thus, progesterone testing is key to knowing the appropriate time to breed. If you know when the female dog is ovulating, or when the eggs are released from the follicles, this tells you the fertile window to optimize the chance of pregnancy and having a full-size litter. It also allows for the calculation of an accurate due date. 

The fertile period occurs during estrus. Before estrus is proestrus, on average a nine-day signal of the start of the heat cycle. During proestrus, the female dog has a blood-tinged vaginal discharge, and the vulva is enlarged and swollen. As estrus begins, the bloody discharge diminishes, changing to pink or straw-colored and eventually becoming watery, though the vulva remains swollen. 

“The luteinizing hormone surge happens at the end of proestrus, and then estrus occurs for seven to nine days,” Dr. Lopate says. “The fertile period is the last four to five days of estrus.” 

Although a female dog is not typically receptive to breeding during proestrus, this changes during estrus. Her receptive, passive behavior during estrus encourages males to mate. 

Receptive behavior, however, is not a rule of thumb on when to breed all female dogs. 

“Breeding based on receptive behavior or a set day of the cycle may result in breeding outside the female dog’s fertile period,” Dr. Lopate says. “It also may result in decreased litter size or failure to conceive. Receptive behavior is a result of the change in the estrogen to progesterone ratio and doesn’t always correlate with ovulation.  

“At the very end of estrus, or day one of diestrus, the cervix will close to sperm, so natural breeding or vaginal artificial insemination will not result in pregnancy,” Dr. Lopate says. “However, surgical artificial insemination or transcervical insemination in which the sperm goes directly into the uterus by-passing the cervix will allow eggs to be fertilized for another two to three days.” 

If a female dog is successfully bred, pregnancy occurs during the two-month diestrus stage. Whelping occurs around 64 to 66 days after the luteinizing hormone surge. The anestrus stage of reproduction, with no significant hormonal activity, follows diestrus.  

“The period of anestrus is important for the uterine epithelium to recover from the prolonged hormone exposure that occurs during estrus and diestrus,” Dr. Lopate says. “If this period is too short, the endometrium, or lining of the uterus, may not be compatible with embryo survival.” 

Some dogs have shorter interestrous intervals, the period from ovulation to ovulation, than is considered normal, though it does not hinder their reproductive ability.  

“A few breeds, such as Akitas, Basset Hounds, Cocker Spaniels, Labrador Retrievers and Rottweilers, tend to have shorter interestrous intervals with normal fertility,” Dr. Lopate says. “Some breeds, such as Basenjis and Tibetan Mastiffs, cycle only one time a year. 

“We know that some female dogs can conceive with a short interestrous interval, but others cannot. If the interestrous interval is under four months, less than 30 percent of female dogs will conceive, yet if the interval is over five months, over 70 percent will conceive. In some cases, a short interestrous interval can be treated by medications to suppress estrus and provide a normal interval.” 

Recognizing the signs of a heat cycle and understanding the stages of the female reproductive cycle can help improve breeding management. Importantly, it can help you achieve successful conception and produce healthy litters of puppies. 

The Role of Nutrition in Breeding

The relationship between nutrition management and reproductive efficiency is key in dog breeding. Experts advise breeders to practice proper nutrition management for reproducing female dogs before mating, as a female dog should be in her best physical condition to help ensure a successful pregnancy and ease whelping her litter. 

Inadequate nutrition management, either deficiencies or excesses, may have a detrimental effect in pregnancy. They also have been shown to have negative effects on fertilization rate and number of fetuses. 

“It is important to feed reproducing female dogs a highly digestible food that has at least 24 to 26 percent protein and at least 16 percent fat,” says Arleigh Reynolds, DVM, PhD, DACVN, Purina Senior Research Nutritionist, a board-certified veterinary nutritionistÒ. “A complete and balanced food that is approved for all life stages or a puppy food that has nutrients to support females through growth and development will provide the nutrition needed during pregnancy and whelping.  

“If you switch from a lower protein and fat maintenance diet prior to breeding, there is a lag time of two to three months to get the full benefit of the diet. Besides the nutritional benefits of feeding a higher protein and fat food year-round, you can adjust the amount of food fed based on a dog’s body condition and metabolic energy needs.”