When your border collie reaches 6 months of age, she will soon have her first oestrus, or "heat" cycle, which will occur approximately every seven months. Your dog's heat cycle is when she can conceive puppies, so it's helpful to be aware of the signs of heat to prevent unplanned pregnancies. All dogs have the strong instinct to reproduce during this cycle, and you will need to take measures to keep your female isolated from males. If your female border collie begins to show any of these signs, she is probably going into heat.
Swelling of the Vulva
One of the major signs of your border collie's heat cycle is the swelling of her vulva, which is the fleshy opening around her vagina. The border collie's vulva may normally be small and flesh-coloured, but during her heat cycle it will become swollen and red. According to Dr. Bruce E. Eilts, a dog's heat cycle begins with her ovaries growing follicles, which in turn produce oestrogen. Oestrogen is what causes the vaginal tissues to expand, which extends down to the vulva, the part that you can see externally.
A red or straw-coloured discharge coming from your border collie's vaginal opening is a significant sign that she is in heat. According to the Royal Canin Encyclopedia, the oestrogen released during the dog's heat causes expanded reproductive tissue, which result in these secretions. The scent of these secretions is a large part of the dog's reproductive cycle because it draws males to your female by signalling her fertility. If you see discharge on your border collie's bedding, fur or body, she is probably in heat.
According to the American Society for the Prevention of Cruelty to Animals website, a common sign of a dog in heat is a change in her behaviour. She may become clingy to you by seeking out constant attention. Some female border collies want to be by themselves since heat can make them feel tired or agitated. Your dog's hormonal changes make cause her to be possessive of toys and bedding, and she may react differently to other pets with behaviours such as mounting or growling. These changes are all related to the hormone imbalances created by her heat cycle. If your female border collie is behaving oddly, she may be in heat.
Reaction to Males
A female border collie tells male dogs that she's ready to mate with body postures and gestures. When not in heat, your border collie may interact with males and females normally, but according to Dr. Nicholas B. Carter of Border Collie Rescue Inc., when she goes into the second phase of heat, she will become "flirtatious" with males. Your dog may lift her tail and wave it like a flag, perform a "butt-bump" by nudging the male's hindquarters with her own or jumping on and off of them. She will also allow males to act this way toward her during this phase in her cycle. If your border collie is acting this way, she is probably in the fertile stage of her heat cycle.