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PetBreed Plan

Sources & Method

Every number on PetBreed Plan comes from a published veterinary or scientific source. None of it replaces your vet, who knows your animal.

Pregnancy and heat-cycle figures

  • Merck Veterinary Manual (Pet Owner Version): "Management of Reproduction in Dogs" and "Management of Reproduction of Cats". Dog cycle interval (average 7 months, range 4–13), proestrus and estrus lengths, dog pregnancy of about 62–64 days, cat pregnancy of 60–65 days with delivery 64–66 days after breeding, detection times, X-ray after day 55, signs of prolonged labor.
  • American Kennel Club: "Gestation Period: How Long Are Dogs Pregnant?". Due dates by anchor: 65–66 days from the LH surge, 63 days from ovulation, 64–66 days from the first progesterone rise, 58–72 days from first breeding.
  • VCA Animal Hospitals: "Breeding for Pet Owners: Pregnancy in Dogs", "Whelping in Dogs", "Estrous Cycles in Dogs", "Estrous Cycles in Cats", "Raising Kittens" and "Caring for Newborn Puppies". Dog gestation 57–65 days, feeding guidance by trimester, temperature drop before labor, cat estrus about 7 days (1–21) and interestrus about 7 days (2–19), newborn weight checks.
  • Cornell University College of Veterinary Medicine, Riney Canine Health Center: "Dog estrous cycles". The four stages and timing of a spay after a heat.
  • Axnér E., "Catteries: Reproductive Performance and Problems", in August's Consultations in Feline Internal Medicine. Induced ovulation thresholds and pseudopregnancy in cats.

Growth data

  • Salt C, Morris PJ, German AJ, Wilson D, Lund EM, Cole TJ, Butterwick RF (2017). "Growth standard charts for monitoring bodyweight in dogs of different sizes." PLOS ONE 12(9): e0182064. Supporting data: University of Liverpool DataCat, record 377.
  • Salt C, et al. (2022). "Growth standard charts for monitoring bodyweight in intact domestic shorthair kittens from the USA." PLOS ONE 17(11): e0277531. Supporting data: University of Liverpool DataCat, record 1456.

How we used the growth data

Puppies. From the 2017 open dataset we kept visits of dogs aged about 5 weeks to 2 years, excluding visits recorded as thin or heavy. Using each record's breed-average adult weight, we grouped dogs into six sizes (under 6.5, 6.5–9, 9–15, 15–30 and 30–40 kg, matching the paper's categories, plus over 40 kg). For each size and 4-week age bin we took the 10th, 50th and 90th percentiles of weight as a share of breed-average adult weight, then rescaled so the median at about 2 years equals 100%. This is our own simplified summary, not the paper's GAMLSS centile model, and it is less precise than the published WALTHAM charts.

Kittens. From the 2022 "Modelling" subset (healthy kittens in ideal condition) we took the 9th, 25th, 50th, 75th and 91st percentiles of weight by sex in 2- to 4-week age bins, keeping bins with at least 60 kittens.

AI answers

The optional "Ask" boxes send your question and the dates or weights on screen to a language model (OpenAI GPT-6 Luna via Vercel AI Gateway). It is told to stay on breeding-planning topics, rely on the published sources above, never give medical, medication or dosing advice, and send anything clinical to a vet. AI can make mistakes, so check anything important with your vet.

Why we explain things interactively

Several pages include small interactive explainers: dragging the mating day, stepping through heat stages, toggling induced ovulation. Each one teaches a single mechanism from the sources above in a simplified form, and its caption says what it leaves out.