No animal from any rescue or shelter should be adopted without being spade or neutered prior to going to a new home. The hundreds of thousands of animals, purebred and mixed are euthanized yearly at shelters around the world. The numbers are astounding and beyond sad here in the US when it's so preventable. I only know of one veterinarian, Dr. Jeff in Colorado, also known as Rocky mountain vet on Animal Planet who works hard to promote spaying and neutering ( I'm sure there may be more - hopefully), often going outside of the US with his team in poor areas to round up and spay and neuter all pets that are either feral or owned by the people who simply have no money to do so.
The problems that can evolve in these animals without spaying and neutering includes uterine cancer, testicular cancer, and in a beautiful German Shorthaired pointer I had ( incidentally belonged to my father but lived with me because he didn't believe in containing a dog properly) developed a perianal hernia at age nine. He was in such intense pain because of it and emergency surgery had to be performed and not by just any vet, it had to be a specialist which was located three hours away. Because he wasn't neutered. Here's some information on this:
https://www.google.com/search?q=Perineal+hernias+in+dogs&client=firefox-b-1-ab&tbm=isch&source=iu&ictx=1&fir=lGASBPVSZyEVFM%253A%252C9ukbLBC_bSyRVM%252C_&vet=1&usg=AI4_-kTZxDG0a57-LKaXR1s-jpIa1Im_Yg&sa=X&ved=2ahUKEwiV6J2b6I7oAhXmRd8KHYjzCRMQ9QEwAHoECAUQAw#imgrc=lGASBPVSZyEVFM:
A
perineal hernia is a condition seen in
dogs and cats in which the pelvic diaphragm becomes weakened. This results in displacement of pelvic and abdominal organs (rectum, prostate, bladder, or fat) into the region surrounding the anus. ... The vast majority of cases occur in intact male
dogs that are middle-aged or older.
Since then, all of my dogs have been spayed or neutered before they reached six months of age. I've done my part to prevent adding to the growing population of dogs and to prevent my dogs from having any cancer related to their reproductive organs.
Birds, if not cared for properly prior to breeding can have a host of issues.... many which can cause death if untreated. Anyone remotely interested in breeding and raising birds should gather all the information they can about proper housing ( spacious enclosure/cage and quality nestbox/ including substrate appropriate for the species, quality husbandry practices, diet prior to, during and after, tests for wellness prior to, do you have a reliable avian vet, could your birds be related, purchase all equipment needed for weighing, all utensils and reliable thermometers for feeding chicks should need be, a quality brooder including a heating source and thermometer/hygrometer should it be needed for chicks that may have problems ( likely), should a chick need supportive care because it's rejected by the parents or any other reason there should already be knowledge on how to hand feed instructed by someone knowledgeable. What will you do if your pair continues to mate and lay... even if you removed the nest box. Some hens can be chronic egg layers which is very detrimental their health. Would you be prepared to separate the pair. Know what source you may need to purchase formula from, which brand you will use. Be prepared when chicks mature to house them separately if you are keeping them, if not, have planned homes for them, start them on a varied diet in preparation for new owners if you are selling them. You must be prepared to spend money for any incurring costs and be prepared for those people who want a cheap bird... because, in some instances, in their minds those babies were free to you since your birds had babies so they shouldn't have to spend a fortune for a bird coming direct from a breeder and not a pet store. More often than not, we see people here who stuck a nest box in the cage to see what would happen and are at a complete loss as to what to do when a problem rises as they weren't prepared. Knowledge, is power... read all you can about every potential problem and just try to prepare for anything...with a savings account for possible vet bills. You may also want to know within a 200 mile radius how many breeders of your species there are, and if there are rescues or fosters that have an abundance of your species waiting on a new home. Chances of rescues and fosters being adopted when there are available babies lessens the opportunity for them to have a forever home. I've covered a few things to consider should anyone still have an interest in breeding.