Features of the Reproductive Cycle
SpeciesAge at pubertyCycle TypeCycle LengthDuration of EstrusBest Breeding TimeFirst Estrus After ParturitionRemarks
Cattle4-18 (12) mo, usually first bred ~15 moPolyestrous, all year21 days (18-24)18 hr (10-24)Insemination from mid-estrus until 6 hr after endVaries,* best to breed at 60-90 daysOvulation 10-12 hr after end of estrus. Uterine bleeding ~24 hr after ovulation in most but may require vaginal exam for detection.
Horse10-24 (18) moSeasonally polyestrous early spring on.Very variable, ~21 days6 days (2-10)Last few days; should be bred at (19-26)4-14 days (9) 2-day intervalsDouble ovulation occurs in ~20% of estrous periods, but twins rarely progress to term.
Sheep7-12 (9) moSeasonally polyestrous, early fall to winter. Prolonged seasons in Dorsets & Merinos.16½ days (14-20)24-48 hr18-20 hr after onset of estrusNext fallOvulation near end of estrus.
Pig4-9 (7) moPolyestrous, all year.21 days (16-24)2-3 days~24 hr after onset of estrus4-10 days after weaningOvulation usually ~40 hr after beginning of estrus.
Goat4-8 (5) moSeasonally polyestrous, early fall to late winter.18-21 days (19)2-3 daysDaily during estrusNext fallMany intersexes born in hornless strains.
Dog5-24 mo; earlier in smaller breeds later in larger breedsUnseasonally monestrous.3½ - 13 mo2-21 days (6-12 av)From day 2 of estrus, and on alternate days thereafter until end of estrusFew months (2- to 3½-mo period of metestrus, followed by a highly variable period of anestrus)Proestrous bleeding 7-10 days. Ovulation usually 1-3 days after first acceptance. Ova shed before 1st polar body has been extruded.Pseudopregnancy usually ends between 60 and 70 days.
Cat4-12 (10) mo; 12-18 mo in PersiansProvoked ovulation seasonally polyestrous spring and early fall.14-21 days6-7 daysDaily from day 2 of estrus4-6 wkOvulation 24-48 hr after coitus. Pseudopregnancy lasts 36 days.Infertile matings prolong onset of next cycle ~45 days.
Rhesus monkey (Macaca mulatta)3 yrPolyestrous all year, tendency to anovulatory cycles in summer in USA.27-28 days (23-33)~3 daysNear ovulation, day 10-13 of cycleAfter weaning of previous youngMenstruation lasts 4-6 days. Ovulation usually ~13 days after onset.

* Many normal cows ovulate as early as 8-12 days after parturition, with or without detectable signs of estrus.

Philippine Veterinary Drug Directory (PVET) 16th Edition. (2022). Medicomm Pacific, Inc.