Left to their own devices mares are long day cycling animals....their heat cycles and fertility are tied to the length of the daylight in the area in which they live. For most mares this means that they are actually more fertile, with better cycles from about late April to early May to early to mid August...the longest day of the year being June 20 or 21 (depending on the year). This puts foals on the ground when the weather has warmed up and spring/early summer grass is available for the mare to gain pre-natally and support lots of milk production post delivery.
Costs vary widely throughout the country and depending on what you have done....a simple culture, cytology and pre-breeding exam here is around $100. I have my own stallions and live cover so there is no stud fee and no chute fee, collection or insemination fees for me to deal with. If you do AI with collection and shipping costs on top of stud fees there will be ultrasound costs, possible hormone injections etc with your vet. Increased feed costs (and supplements if used) plus "normal" vaccinations for pregnant mares (again, I do my own so don't have vet costs for those either) and treating for worms if needed....depends again on local costs and how much you do yourself. Any complications can throw any estimates completely out the window. Best bet...talk with your vet for his prices for routine stuff and then discuss potential problems (taking several cycles to get her pregnant for instance, pinching off a twin, things like placentitis).
how much? Varies widely from sending your mare to a live cover stallion for a week at 15 bucks a day board at an inexpensive farm to a fortune if you go to a top repro center to breed by frozen and need a whole lotta ultrasounds. Your board situation will vary widely from stall board to pasture board. I don't up the grain until the last trimester for the mare...so at the end the grain bill goes up a little but other than that your normal feed costs.Pneumabort vacccines at months 5/7/9 are pretty cheap....especially if you give it yourself. If all goes well with the delivery and you foal out at home them you have a vet call for an IGG....under a hundred bucks. If you send her out to New Bolton to foal out....$$$$$.
Here in PA I have found the mares to be most fertile (best conception rates) in May/June/July but some mares will cycle into October and the latest foal we had born here so far was August....so was a September bred. (That was a surprise baby for hubby.....mare was not known to be in foal when hubby bought her as a riding horse that spring....bought from a QH feedlot. Mare had papers but daddy-o was "some unknown colt").
How late in the summer is it reasonable to breed my mare. btw, total newbie to breeding here?
Also, what is a reasonable cost estimate for vet bills for the entire pregnancy (getting her pregnant and everything)
Most PA breeders I know (in southeast PA) try to be done by about now. Most aim for foaling to be April-early June. Too early and we have snow and ice still...too late and it is stinking hot, humid and buggy.
Costs vary...I'd talk with your vet.
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