Felis catus, domestic cat at GeoChemBio: life cycle, developmental stages, embryology

Felis catus, cat life cycle & development

Unfertilized egg Also ovum. Unfertilized mature eggs are usually not released from the ovaries until mating. Read about cat reproductive cycle (mating, estrous cycle).
Prenatal Gestation period lasts from 53-67 (about 9 weeks) ranging from less than 54 to more than 74 days. There are very little data on development of cat embryo in vivo. The following are data from two studies (see Cat main page for references).
- Pre-implantation embryo
  - Fertilized egg Also, zygote, is about 0.13 mm in diameter. The fertilized ovum is surrounded by tough transparent membrane called zona pellucida. It is penetrated by the sperm during fertilization. Ovulation and fertilization occurs in about
    24 - 30 hours after mating. In one study
    natural multiple mating resulted in 73.1%
    fertility in cats (38 of 52). The remaining
    non-fertile cats had either ovulatory or
    fertilization failure. Fertilized egg is
    located in the oviduct. The following time
    intervals are given in hours after first
    copulation (because exact moment when
    fertilization occurs is almost impossible
    to determine).
  - Cleavage Fertilized egg mitotic division starts in the oviduct. Each cleavage yields two blastomeres of about half size of the parent cell. The cell division occurs every 10-14 hours (slower in cats then in other mammals, for example, rabbit).
    - 2-8 cell embryo In 64 hours after copulation.
    - 8-16 cell embryo In 76-100 hours after copulation. The cytoplasm of 8-celled embryos contains copious lipid vacuoles, which are typical for the feline egg. The presence of these vacuoles makes analysis of cytological details difficult.
  - Morula An early embryo that is a compact mass
    of about 16 cells (blastomeres), which
    differentiated into two types of cells,
    outer cells and inner cells. Morulae and
    compact morulae appear in about 124
    hours post-copulation in cats. They are
    still in the oviduct.
    - Compact morula By 148 hour post-copulation most
      morulae are compacted and migrated
      into uterus.
  - Blastocyst A post-morula preimplantation mammalian embryo that develops from a 32-cell stage into a fluid-filled hollow ball of over a hundred cells. A blastocyst has two distinctive tissues. The outer layer of trophoblasts gives rise to extra-embryonic tissues. The inner cell mass gives rise to the embryonic disc and eventual embryo proper. First blastocysts were found in 148 (~6 days) hours after copulation.
    - Early blastocyst Five-days embryos (24-48 cell stage) exhibit marked differences between two groups of blastomeres: 1. a knot-like group of lightly stained (HgBPB) cells, and 2. a cap of more intensely stained blastomeres which form a single layer at the periphery of the first group. At the 6-days stage (60-100 cells), the cap-like structure of outer bastomeres closes over the inner blastomeres (ectoderm) and fluid begins to accumulate in the intracellular spaces. At this time, a number of lipid vacuoles in the blastomeres markedly decreases and by 10^th day after coitus, almost completely disappear. Between 6^th and 7^th day after coitus the blastocysts undergo intrauterine migration and become equally spaced in the uterus.
    - Expanded blastocyst At day 8, the blastocyst becomes ovoid by extending inside the zona pellucida.
  - Gastrula Gastrulation is a process of complicated morphogenetic cell movements that reorganizes a bilayer embryo into one with three layers and specific orientation (dorsal/ventral; anterior/posterior).
    - Endoderm
      formation At 8.5-10.5 days after coitus, the gastrula is about 1.5 x 1 mm, egg-shaped, formation of endoderm occurs.
    - Mesoderm
      formation At 10.5-12 days post coitus, invagination of embryo leads to the formation of the mesoderm and appearance of primitive streak. Primitive streak is a linear band of rapidly proliferating cells that begins near the posterior end of an embryo and grows cranially. Primitive streak is formed by the convergent migration of primary ectodermal cells (epiblast). The knot at the tip of the streak is called Hensen node. No zona pellucida is found at the surface of these blastocysts flushed from uterus at 12^th day post coitus.
  - Neurula The neurulation is a is characterized by morphogenic movements of ectoderm resulting in the formation of the neural plate, theneural crest and the neural tube (structures that give rise to a future nervious system). At this time, paraxial mesoderm start developing first somites. Somites are paired, segmented masses of mesoderm located on either side of the developing spinal cord (neural tube). Somites continue to increase in number during organogenesis. Somites give rise to skeleton, muscles and dermis.
- Implantation Attachment of tropoblasts to uterine lining is believed to begin between 13^th and 14^th day after coitus. Total size of embryo is about 2 x 3 mm. Triphasic implantation involves apposition, adhesion, and intrusion.
- Post-implantation
  embryo
  - 14-15 days Six to eight somites. Formation of head and tail folds. Size is ~6 x 5.5 mm
  - 15-17 days Closing of neural tube. 15-18 somites.
  - 16-18 days 25-30 somites. Size is ~7 x 15 mm
  - 18-19 days Forelimb and hind limb buds make their appearance. Somites are still recognized but are already in differentiation.
  - 19-21 days Size it about 10-24 mm. Formation of vertebrae. Organogenesis.
  - 21-28 days Size it about 21-40 mm. The organs further differentiate.
  - Fetus
    - 28-38 days Size it about 25-50 mm. Toes separated; tongue is visible; hair follicles in development; formation of the claws, genital differentiation.
    - 38-44 days Rapid growth of all body parts. The skin thickens and becomes wrinkled. Size is about 45-70 mm and weight is ~14 g.
    - 44-48 days Size is about 81-100 mm and weight is 21.9-34.5 g.
    - Until birth
      (~66 days) Pigmentation, bone ossification, coat development. Final growth and preparation of organism to change of environment.

Post natal

Neonate Parturition (queening) lasts from 2 to 6 hours in majority of cats. Two to three days before partuition, mammary glands enlarge.
Labor stages:
1. The first stage is characterized by nesting behavior and may last 1-24 hours. The queen appears restless, may pace, posture to defecate, vocalize, groom excessively, refuse food, and paw or dig at the ground. Uterine contractions and cervical dilation occur.
2. Delivery of the kittens. During this time, queen may appear uncomfortable and frequently squat, scratch, circle, or rearrange their bedding. Kittens are quickly delivered in head-first or posterior-first (breech) orientation.
3. Expulsion of placenta. Other kittens may be born before the placenta of a previous kitten is expelled. The queen usually eats the placenta.
Litter size varies from 1 to as much as 13 kittens with average of about 3-5 kittens, one stillborn per litter is considered normal. Kittens are born with underdeveloped brains and sensory organs: eyes and external auditory canals are closed; mean weight is about 70-110 grams ranging from 30 and up to 170 depending on the breed. Diet is entierly milk. Unlike homeothermic adults, neonates are poikilothermic (lack an internal temperature regulating mechanism); however, they have well developed behavioral heat-seeking responses. Neonatal period lasts approximately 3-4 weeks after birth.
Developing cat
- Sensory development:
  visual and auditory Eyes usually start opening gradually and symmetrically at about 6-10 (5-14) days of age; the cornea appears slightly cloudy for the first 3-4 weeks of life because of increased water content, and the iris is typically bluish-gray because of low pigmentation; palpebral and blink reflex appear shortly after birth (blink response is getting dulled with age and may be absent by 15-43 days of age especially if the cat is fully awakened). By about 8-17 days of age both eyes are completely open; opening of auditory canals occurs at 4-17 days of age; at this time first startle responses on sharp noises are observed. By end of the first week weight of healthy kitten is nearly doubles.
- Locomotor development and weaning
  - Uncoordinated
    walking and learning
    to lap (milk, water) At about 3 weeks of age.
  - Starting to play
    and weaning to
    solid food. At about 4 to 7 weeks of age.
Juvenile Relatively independent and actively growing animal until age of sexual maturity (6-12 months). Independence is achieved at about 10 to 12 weeks of age. About this time, social kittens become more solitary. Plays with peers continue but take on more aggressive character. At about 14 weeks of age social play is almost completely replaced with object play.

Adult After attainment of sexual maturity. Age of first estrus in female cats ranges from 180 days to 560 days and may depend on date of the birth. On average male and female kittens reach puberty at about 1 year of age. Well-cared for animals can live for 16 years and more.
Cats Age Conversion Chart

Dog age	Human age
0.5	10
1	15
2	24
3	28
4	32
5	36
6	40
7	44
8	48
9	52
10	56
11	60
12	64
13	68
14	70.5
15	73
16	75.5
17	78
18	80.5
19	83
20	85.5

A recent study suggest that 28% of pet cats aged 11 to 14 years develop at least one geriatric onset behavioral problem, and this increases to over 50% for cats of 15 years of age and older.
Behavioral problems in geriatric cats:
-- house soiling (elimination and marking) ~70%;
-- excessive vocalization ~60% (night vocal ~30%);
-- disorientation ~20%;
-- restlessness ~20%.
Potential causes of changes in behavior in geriatric cats:
-- Arthritis -- Hypertension;
-- Hyperthyroidism;
-- Chronic renal failure;
-- Diabetes;
-- Urinary tract infection;
-- Gastrointestinal disease;
-- Liver disease;
-- Neurological defects (sensory or motor deficits);
-- Reduced vision or hearing;
-- Brain tumors;
-- Infectious disease
-- Dental or periodontal disease;
-- General inflammatory disease;
-- Pain in general;
-- Cognitive dysfunction syndrome (CDS).
To correlate with humans in dogs: in humans dementia is seen in 1-3% of 65-70 years old, and increases to ~50% of people older over 85 years of age. In dogs, 28% aged 11-12 years showed sign of CDS, compared with 68% of those over 15 years of age.

Aged A cat over 10 years old.
A recent study suggest that 28% of pet cats aged 11 to 14 years develop at least one geriatric onset behavioral problem, and this increases to over 50% for cats of 15 years of age and older.
Behavioral problems in geriatric cats:
-- house soiling (elimination and marking) ~70%;
-- excessive vocalization ~60% (night vocal ~30%);
-- disorientation ~20%;
-- restlessness ~20%.
Potential causes of changes in behavior in geriatric cats:
-- Arthritis -- Hypertension;
-- Hyperthyroidism;
-- Chronic renal failure;
-- Diabetes;
-- Urinary tract infection;
-- Gastrointestinal disease;
-- Liver disease;
-- Neurological defects (sensory or motor deficits);
-- Reduced vision or hearing;
-- Brain tumors;
-- Infectious disease<
-- Dental or periodontal disease;
-- General inflammatory disease;
-- Pain in general;
-- Cognitive dysfunction syndrome (CDS).
To correlate with humans in dogs: in humans dementia is seen in 1-3% of 65-70 years old, and increases to ~50% of people older over 85 years of age. In dogs, 28% aged 11-12 years showed sign of CDS, compared with 68% of those over 15 years of age.

Illustrating photo credit: http://kotomatrix.ru/

juvenile cat, 4.5 months

References

Leiser R, Koob B. Development and characteristics of placentation in a carnivore, the domestic cat. J Exp Zool. 1993 Sep 1;266(6):642-56.
Swanson WF et al. In vivo embryogenesis, embryo migration, and embryonic mortality in the domestic cat. Biol Reprod. 1994 Sep;51(3):452-64.
Beaver BV. Sensory development of Felis catus. Lab Anim. 1980 Jul;14(3):199-201.
DENKER H-W et al. Studies on the Early Development and Implantation in the Cat: 1. Cleavage and ßlastocyst Formation. Anat. Anz. 144 (1978) 457-468. (.pdf)
Miglino MA et al. The carnivore pregnancy: the development of the embryo and fetal membranes. Theriogenology. 2006 Oct;66(6-7):1699-702.
C. Knopse. Periods and Stages of the prenatal development of the domestic cat. Anat. Histol. Embryol. 31,37-51, 2002 Blackwell Wissenschafts-Verlag, Berlin, ISSN 0340-2096.
Gunn-Moore D, Moffat K, Christie LA, Head E. Cognitive dysfunction and the neurobiology of ageing in cats.J Small Anim Pract. 2007 Oct;48(10):546-53.
Landsberg GM, Denenberg S, Araujo JA. Cognitive dysfunction in cats: a syndrome we used to dismiss as 'old age'.J Feline Med Surg. 2010 Nov;12(11):837-48.
Griffin B. Prolific Cats: The Impact of Their Fertility on the Welfare of the Species. Vol. 23, No. 12 December 2001. (.pdf)