Features of the Reproductive Cycle
Species Age at puberty Cycle Type Cycle Length Duration of Estrus Best Breeding Time First Estrus After Parturition Remarks
Cattle 4-18 (12) mo, usually first bred ~15 mo Polyestrous, all year 21 days (18-24) 18 hr (10-24) Insemination from mid-estrus until 6 hr after end Varies,* best to breed at 60-90 days Ovulation 10-12 hr after end of estrus. Uterine bleeding ~24 hr after ovulation in most but may require vaginal exam for detection.
Horse 10-24 (18) mo Seasonally polyestrous early spring on. Very variable, ~21 days 6 days (2-10) Last few days; should be bred at (19-26) 4-14 days (9) 2-day intervals Double ovulation occurs in ~20% of estrous periods, but twins rarely progress to term.
Sheep 7-12 (9) mo Seasonally polyestrous, early fall to winter. Prolonged seasons in Dorsets & Merinos. 16½ days (14-20) 24-48 hr 18-20 hr after onset of estrus Next fall Ovulation near end of estrus.
Pig 4-9 (7) mo Polyestrous, all year.21 days (16-24) 2-3 days ~24 hr after onset of estrus 4-10 days after weaning Ovulation usually ~40 hr after beginning of estrus.
Goat 4-8 (5) mo Seasonally polyestrous, early fall to late winter. 18-21 days (19) 2-3 days Daily during estrus Next fall Many intersexes born in hornless strains.
Dog 5-24 mo; earlier in smaller breeds later in larger breeds Unseasonally monestrous. 3½ - 13 mo 2-21 days (6-12 av) From day 2 of estrus, and on alternate days thereafter until end of estrus Few 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.
Cat 4-12 (10) mo; 12-18 mo in Persians Provoked ovulation seasonally polyestrous spring and early fall. 14-21 days6-7 days Daily from day 2 of estrus 4-6 wk Ovulation 24-48 hr after coitus. Pseudopregnancy lasts 36 days.Infertile matings prolong onset of next cycle ~45 days.
Rhesus monkey (Macaca mulatta) 3 yr Polyestrous all year, tendency to anovulatory cycles in summer in USA. 27-28 days (23-33) ~3 days Near ovulation, day 10-13 of cycle After weaning of previous young Menstruation 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. (2014). Medicomm Pacific, Inc.