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On this page, the information will explain the reproductive cycle starting right after copulation all the way to parturition.
Movement of Sperm Through the Female Tract
Movement of Sperm Through the Female Tract
There are two phases of sperm transport, the first is the rapid phase. The sperm in this phase is from the initial part of the toms ejaculate, and these sperm reach the oviduct within minutes but are unable to fertilize the oocyte. The sustained phase of transport occurs with the rest of the ejaculate, and is a slow transport of sperm to the oviduct. The sustained phase has sperm docking in the isthmus, which is vital for sperm survival and for successful fertilization. Sperm reservoirs after copulation occur in the cat, at the uterotubual junction (UTJ), uterine crypts and the lower isthmus (2). These reservoirs are released after induced ovulation occurs, and continue on in the process of movement through the female tract from where they were stored (2). The major steps in sperm transport are deposition, passing through the cervix, passing through the uterus, and reaching the oviduct where fertilization can occur.
Image (above): Diagram of the female reproductive tract, color coated to show the movement of sperm through the tract after copulation until the site of fertilization
Image Source: Modified from Normal feline reproduction: The queen
1. Deposition
In cats, the semen is deposited in the cranial vagina after copulation. At this point, some sperm are lost due to retrograde loss, phagocytosis and when attempting to enter the cervix. Semen is seen as a foreign substance, which causes neutrophils from the female tract to come into play and phagocytosis of the sperm to occur.
2. Cervix
The sperm transverse the cervix after being deposited in the cranial vagina. Movement of the sperm is driven by high estrogen levels, which increases myometrium tone and contractions. In the cervix, there is increased mucus production which is another barrier sperm must be able to pass to continue through the female tract toward the oocyte. In the cat, the capacitation reaction (explained in greater detail below) begins within the cervix. Not all sperm make it through the cervix to continue to the uterus.
3. Uterus
The sperm that pass through the cervix, continue on to pass through the uterus. Again, the movement of the sperm is driven by high estrogen levels and prostaglandins, which increases myometrium tone and contractions. During sperm transport in the uterus, the capacitation reaction continues to occur and more sperm is lost due to phagocytosis.
4. Oviduct
The sperm that reach the oviduct from the sustained transport phase, dock into the oviduct epithelium near the UTJ which is necessary for the ability of the sperm to survive. Without sperm docking into the oviduct epithelium, the sperm would die off and be unable to fertilize the oocyte. By the time the sperm reach the isthmus of the oviduct, capacitation should be complete. After capacitation is complete, the sperm change from moving in a linear fashion to hyper-motility. Hyper-motility causes the sperm to move quickly in different patterns and this hyper-motility increases the likelihood it will come into contact with the zona pellucida of the oocyte. Once one sperm comes into contact with the zona pellucida of the ovulated oocyte in the ampulla of the oviduct, the process of fertilization can occur which is explained below.
Capacitation Reaction
Capacitation Reaction
Capacitation of sperm occurs starting in the cervix of the queen and should be complete once the sperm reaches the isthmus of the oviduct. Capacitation is a reaction that is necessary for the process of fertilization to be able to occur. In the epididymus, sperm mixes with seminal plasma, which coats them with proteins and carbohydrates. The process of capacitation is where luminal fluid from the female tract causes the seminal plasma coating and other molecules to be removed, which leaves areas for the sperm to be able to bind to the zona pellucida of the oocyte and start the fertilization process.
All information in sperm movement through the female tract are from source 1 unless otherwise noted
Image (above): Diagram showing the process of capacitation, from sperm in the epididymus until sperm in the female tract after capacitation
Image Source: Pathways to Parturition pg. 259
References for movement of sperm through the female tract
1. Senger, P.L. (2012) Pathways to Pregnancy and Parturition. 3rd ed. Current Conceptions, Inc.
2. Chatdarong K. (2003) Reproductive Physiology of the Female Cat Swedish University Uppsala https://pub.epsilon.slu.se/364/1/Veterinaria162.pdf
Once the sperm comes into contact with the zona pellucida the following steps occur:
Binding between the oocyte and sperm occurs
The oocyte contains a Zona Pellucida 3 protein (ZP3) which is where the primary zona binding region (ZBR) on the sperm head binds too.
The acrosome reaction:
The acrosome reaction is initiated when the acrosome reaction promoting ligand (ARPR) on the sperm head binds to ZP3.
This binding causes an influx of calcium through the membrane
The calcium influx leads to vesiculation of the sperm head which is when the outer plasma membrane fuses with the outer acrosomal membrane, creating small vesicles.
These vesicles allow for acrosome enzymes to be released
The vesicles and the outer sperm membrane slough off after the reaction has occured, leaving the sperm with an inner acrosomal membrane
Penetration of the zona pellucida: With the help of acrosome enzymes, the sperm penetrates the zona pellucida and the oocyte plasma membrane fuses with the middle section of the sperm.
The cortical reaction: This reaction occurs while the oocyte plasma membrane is binding to the sperm and it ensures only one sperm can fertilize the oocyte.
The cortical reaction occurs when cortical granules from the oocyte go through exocytosis, and then change the biochemical structure of the zona pellucida which stops other sperm from binding to it.
Decondensation and the formation of the male pronucleus: After the sperm head is engulfed into the oocyte cytoplasm, its genetic material decondenses. Decondesation of the genetic material allows for the female and male pronucleus chromosomes to interact later on. After this decondensation, it forms the male pronucleus.
Ootid: At this stage, the male and female pronuclei are inside of the zona pellucida and it is known as an ootid.
Syngamy: At this point, the oocyte will finish meiosis 2. The final step of fertilization is referred to as syngamy, which is when the male and female pronucleus fuse together which creates a diploid nucleus.
All information in the fertilization section is from source 1
Image (above): Showing transition from a morula (image on far left) to a blastocyst (image on far right) during feline early embryogenesis
Early Embryogenesis
Early Embryogenesis
After fertilization has occurred, the steps of early embryogenesis can occur. As the beginning stages of mitotic divisions are occurring, the embryo is moving towards the uterus from the site of fertilization in the oviduct.
Zygote- After syngamy occurs, it is known as a zygote. The zygote undergoes mitotic divisions which continues the development of the embryo.
Blastomere: The first mitotic division gives rise to a 2 celled embryo which is known as the blastomere. The blastomere continues to divide through mitosis, giving rise to a 4 and then 8 cell embryo.
Morula: As mitotic divisions of the blastomere increase the number of daughter cells it becomes a mass of cells that cant be distinguished from one another. At this point, it is known as a morula. In the queen, the morula is developed by day 5 after ovulation and it is located in the uterus.
Blastocyst: The morula continues to grow, developing an inner cell mass with gap junctions and outer cell mass (trophoblast cells) with tight junctions. The tight junctions allow for an active sodium pump which causes fluid accumulation flowing towards the embryo. This fluid accumulates and forms a cavity known as a blastocoele. In the queen, the blastocyst develops by day 8.
Blastocyst Hatching: As the blastocyst continues to grow and accumulate fluid, the pressure increases and the trophoblast cells release enzymes that break down the zona pellucida. Both of these factors coupled with blastocyst contractions, allow the blastocyst to slip out of the zona pellucida into the uterine lumen as a free floating embryo. In the queen this occurs by day 10-12.
Extra-embryonic Membrane Development: As the blastocyst continues to grow outside of the confines of the zona pellucida, 4 membranes develop. The yolk sac develops from primitive endoderm and provides primitive germ cells. The chorion and the amnion develop from trophoblast cells, primitive endoderm and mesoderm. The chorion surrounds the amnion, and the amnion surrounds the embryo as a fluid filled sac. The allantois, collects waste from the embryo and eventually fuses with the chorion, creating the allantochorion.
Implantation: The free floating embryo implants into the uterine endometrium on day 14 in the domestic cat (3)
All information in early embryogenesis section is source 1 unless otherwise noted
Maternal Recognition of Pregnancy
Maternal Recognition of Pregnancy
Maternal recognition of pregnancy occurs when a signal is sent out by the conceptus that allows the body to recognize that it is pregnant. This signal ensures the CL, which produces progesterone for maintenance of pregnancy, is not lysed. In many species, the CL would be lysed before the entire length of gestation was complete without the process of MROP which is why it is so important that MROP occurs. However, in the queen maternal recognition of pregnancy is not required. The CL of the cat remains for approximately 60 days after induced ovulation occurs, which is the length of gestation. This allows for plenty of time for the body to establish and carry out the entire pregnancy without the risk of the CL being lysed. Therefore, no signal from the conceptus is needed to establish pregnancy after fertilization.
All information in MROP is section is source 1
The Placenta
The Placenta
The placenta begins to develop during day 12-14 of pregnancy in the queen and serves many functions including (2):
Metabolic exchange of products: Oxygen/gasses, nutrients, waste are exchanged through simple diffusion, facilitated diffusion and active transport between the dam and fetus.
Hormone production: Hormones are secreted to maintain pregnancy, help with the growth of the mammary gland and fetus, and for parturition. Hormones secreted are progesterone, estrogen, relaxin, and PGF2alpha.
Chemical barrier: The placenta allows for toxins to be kept away from the fetus
Physical protection: shock absorption
The fetal contribution to the placenta is from the chorion membrane and the maternal part of the placenta is from her uterine endometrium. Queens have a zonary placenta, which is characterized by a large band of chorionic villi near the center of the fetus, which is where the fetal and maternal regions connect and metabolic exchange occurs. In the cat, the band is complete and fully encircles the fetus (2). Zonary placentas also contain a highly vascularized area for iron exchange and an area without vasculature, which serves as a site of absorption. The dam-fetal barrier is characterized as endothelial-chorial, which means it has 5 layers. These 5 layers are made from the maternal side which has the endothelium and some connective tissue present, and the fetal side which has the epithelium, connective tissue, and endothelium present.
All information in The placenta section is from source 1 unless otherwise noted
Figure 1- Cartoon depicting zonary placenta type
Figure 2- Diagram showing layers of the endotheliochorial placenta.
Image Source: Adapted from Placenta
References for fertilization, MROP, & Placenta
Senger, P.L. (2012) Pathways to Pregnancy and Parturition. 3rd ed. Current Conceptions, Inc.
Benirsc K (2002) Comparative Placentation: Domestic Cat UCSD http://placentation.ucsd.edu/cat.html#:~:text=The%20cat%20has%20a%20zonary,but%20not%20into%20the%20myometrium.
In Utero Development
In Utero Development
First Trimester (Day 1 to Day 20)
Early embryogenesis as previously described
Development of the placenta
Early development of organs and primitive GI and genital tract
Head and tail are prominent
By day 19 limbs should be seen
At the end of trimester 1, the conceptus is approx. 20 mm long
Second Trimester (Day 20-Day 40)
Further development of genitalia, organs, limbs, eyes
Development of distinct toes, important glands including the pituitary gland and salivary glands
Development and calcification of the skeletal system
Rapid growth and development is occurring during the second trimester and by day 40 the fetus is around 50-60 mm
Third Trimester (Day 40- Parturition)
Final development and differentiation occurs
Development of alveoli in the lungs, villi in the intestines
Further growth of head, ears, tail, limbs takes place
Fetus is is viable and is anywhere from 90-180 mm by day 55-65
All information from Source 1
Image (above): Showing length of gestation broken up into trimesters
References for In utero Development
Leipoldt A. (2023) Embryology of the domestic cat PawPeds https://www.pawpeds.com/cms/index.php/en/education/articles/reproduction/embryology-of-the-domestic-cat
Physiological Aspects of Pregnancy
Physiological Aspects of Pregnancy
Litter Size: The average litter size in cats is 4.0 kittens, but it varies among breeds and is not correlated with the number of mating’s (1).
Gestation Length: The average gestation length is 65.6 days, with a range of 52–74 days. Gestation lengths less than 60 days are associated with decreased viability of offspring (2).
Super-fecundation and Superfetation: Super-fecundation (offspring from more than one sire in a single litter) is common in cats. Superfetation (simultaneous presence of offspring of differing gestational ages) has not been definitively demonstrated in domestic cats (1).
Endocrine Profile: Pregnancy and Parturition
Endocrine Profile: Pregnancy and Parturition
Estrogen (Estradiol-17b): Serum concentrations of estradiol-17b and luteinizing hormone fluctuate around the baseline during the first half of gestation. Approximately one week before parturition, about half of the queens show a significant rise in estradiol-17b levels (1).
Luteinizing Hormone (LH): After the LH surge prior to ovulation, LH levels remain low until the time of parturition (1).
Progesterone: Progesterone levels rise after ovulation and must be present throughout gestation. The peak serum values reported are 11–60 ng/ml after the first mating. However, unlike in dogs, cats can progress into active labor with serum progesterone concentrations greater than 1 ng/ml (3).
Prolactin: Prolactin, a luteotropic hormone, plays a role in maintaining progesterone levels. Administration of a prolactin-inhibiting drug has been shown to cause a decrease in progesterone levels and subsequent abortion in treated queens (3).
References for Endocrine Profile and Physiological Aspects of Pregnancy
Johnson, A. (2022) Normal Feline Reproduction: The Queen. Journal of Feline Medicine and Surgery. Volume 24, Issue 3, p. 204-211.
Kustritz, M.V.R. (2006). Clinical management of pregnancy in cats. Theriogenology 66 (2006) 145–150.
Parturition
Parturition is the process of giving birth. In domestic felines, it is called queening.
The first stage is initiated by fetus (kittens) (4).
Relaxation of vagina and cervix happens (1).
Intermittent uterine contractions start but are not straining yet (1).
Pelvic muscles also relax (1).
Perineum, which is the area between anus and vulva, loosens and elongates (1).
Movement of kittens may be felt, due to it repositioning (1).
This phases lasts between 6-12 hours (3).
The cervix is fully dilated by the end of this stage (3).
Uterine contractions pick up in strength and frequency which make them visibly straining on the queen (1).
Abdominal contractions also start during this phases (1).
The first kitten should be queened within 1-2 hours of the start of this stage (3).
The resting phase, which is the time in between kittens being queened, has an average of 30 mins but can last as long as 4 hours (3).
The amnion ruptures (4) when kitten starts to enter the pelvis (1).
Image (above): A queen eating her placenta which is normal behavior.
Stage III: Expulsion of Placenta
Stage III: Expulsion of Placenta
The placentas are passed after each kitten (1).
If two kitten are born quickly after one another, their placentas may be passed together (1).
This phases lasts between 5-15 mins after each kitten (3).
Dystocia
Dystocia is any difficulties giving birth.
Common Causes of Dystocia:
pelvic opening is too small
kitten is too large
death of kitten
lack of dilation of cervix
primary inertia - leak or no uterine contractions or uterine exhaustion
malpresentation - not as common as other species due to kitten being born tail-first
*all information was from source 2
References for Parturition and Dystocia
References for Parturition and Dystocia
Cat Birth. International Cat Care. (2018a, July 31). https://icatcare.org/advice/cat-birth/
Difficult cat birth: when to wait and when to worry. International Cat Care. (2018b, July 31). https://icatcare.org/advice/difficult-cat-birth/
Normal Labor and Delivery in the Cat. Auburn Animal Hospital. (n.d.). https://www.rochesterhillsvet.com/articles/normal_labor_and_delivery_in_the_cat.php
VanKlompenberg, M. (2023) Parturition and Puerperium period
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