Pregnancy Calendar (Species-Specific)

Companion Animal Embryology, Organogenesis, and Fetal Developmental Milestones

Canine and feline gestation is an accelerated biological process lasting an average of 63 days (range: 58 to 68 days) calculated from the day of ovulation (progesterone 5.0 ng/mL) or initial breeding. During this brief 9-week window, fertilized blastocysts undergo rapid cleavage, uterine implantation, organogenesis, and skeletal calcification.

Under veterinary developmental theriogenology standards from the Society for Theriogenology and the Merck Veterinary Manual:

Trimester Developmental Roadmap:
- Trimester 1 (Days 1–21): Cleavage, blastocyst migration into uterine horns, implantation at Days 17–21
- Trimester 2 (Days 22–42): Organogenesis (heartbeats at Day 25, limb buds, ultrasound confirmation at Days 25–30)
- Trimester 3 (Days 43–63): Rapid fetal mass expansion (75% of fetal weight gained), skeletal mineralization (X-ray at Day 55+)
Maternal Caloric Transition: Transition mother to 30% protein / 20% fat puppy/kitten food at Day 42 (increase portions by 30–50%)

Critical Third-Trimester Nutritional Management

During the final 3 weeks of pregnancy, developing fetuses physically compress the mother's stomach while demanding massive energy and calcium:

• Feed Frequent, Concentrated Meals: Divide high-energy, nutrient-dense growth kibble into 3 to 4 smaller meals daily.
• NEVER Supplement Calcium During Pregnancy: Supplementing calcium before birth shuts down the mother's parathyroid gland. When lactation begins, her body cannot mobilize bone calcium, triggering fatal Eclampsia (Puerperal Hypocalcemia / Milk Fever).

Track whelping labor with Whelping & Kittening Checklist, predict litter size via Litter Size Predictor, monitor growth using Puppy & Kitten Weight Chart, and explore theriogenology at the Society for Theriogenology.