management of the brood mare 
41 
condition is also most readily noted at this season and too, they conceive 
more easily at this time. According to Youatt, 37 heat period usually 
comes early in the spring. Curryer 42 says: “Frequently, if the weather 
in this north latitude is warm in March or April, mares are very sure to 
come in heat; but our experience is that where one mare gets in foal, 3 
or 4 will fail when bred before the middle of May or June.” 
Mumford ‘ 0 states that in mares the ‘foal heat’ comes 7 to 9 days after 
foaling and oestrum ordinarily occur while the mares are nursing, al¬ 
though some do not show this indication during the same period. It is 
pointed out also that the tendency with some mares is to breed but once 
in 2 years. 
According to Carlson’s investigation, the period of heat comes every 
21 days, although variations from this are to be found with certain 
individuals. However, the mare that shows more or less constant ‘heat’ 
is an irregular breeder. The heat period lasts for 4 to 9 days, and ac¬ 
cording to his findings, in 85% of the animals under observation, the 
duration of the heat period was from 5 to 7 days. Here again variations 
were noted so that the duration of heat period in a few mares may ex¬ 
tend for only a few hours. Carlson advocates the breeding of the mares 
two days after the start of the heat period because the discharge of the 
ovum occurs after the heat period. 
Bergman 41 holds that the period of heat occurs every 21 days, each 
period lasting from 2 to 4 days. He points out that better success is ob¬ 
tained by breeding the mare on the second heat period after foaling. 
Marshall 80 places the foal heat 11 days after parturition but in some it 
occurs 17 days afterwards. 
Wallace 43 points out also that foal heat occurs 11 days after foaling 
when, he says, the mare gets settled most readily. The heat period lasts 
for 3 days. Later periods come every 3 weeks in spring and early sum¬ 
mer during which time each period extends for about a week. It is 
brought out that mares coming in heat in 4 weeks instead of the usual 
3 weeks do not ordinarily conceive. Wallace further says that mares that 
are not bred at the first indication of heat are likely not to conceive until 
after the foals are weaned, and even then they settle with difficulty. An 
explanation offered to this behavior is the fact that mares in their second 
season have a large flow of milk which to some degree affects the system 
and so makes conception difficult. 
Wallace 43 maintains also in accord with Carlson, that mares bred when 
going out of season are most likely to settle so he advocates the breeding 
of the mare in a day or two after the first service in case that she has 
been covered immediately after she comes in heat. 
According to Axe, 38 the period of heat lasts for 2 or 3 days at a time, 
occurring every 15 or 21 days. He believes that mares will be more suc¬ 
cessfully bred if service is made 9 days after foaling. 
Johnston 5 likewise maintains that mares will generally conceive if 
bred 9 days after parturition. He recommends the return of mares for 
three trials, as follows: About the 18th, 25th, and 32nd day. 
According to Curryer 42 the best time to breed the mare is at the height 
of the heat period. 
Quoting Axe, 38 the indications of heat period are as follows: “The 
animal is usually irritable or sluggish and less able to sustain severe 
exertion; the sensibility is increased, and the appetite is more or less in 
abeyance or capricious, and thirst is often present; there is a tendency 
to seek the company of other horses, especially males; attempts to pass 
urine are frequent, and there are spasmodic ejections of a whitish fluid, 
accompanied by movements of the vulva.” 
Smith 40 says: “The external signs of proestrum in all animals are a 
swelling of the vulva, more or less pronounced, with a slight flow of 
mucus, which may be blood-stained. There is excitement. The mare may 
