Fertilization, Pregnancy, and Birth Flashcards

Fertilization Mechanics and Sperm Physiology

  • Definition of Fertilization: Fertilization is the union of an egg (ovum) and a sperm cell. This process typically occurs in the uterine tubes (also known as fallopian tubes or oviducts) after the ovum moves from the ovary.

  • Sperm Transport and Survival:

    • During breeding, millions to billions of sperm are ejaculated into the female reproductive tract.

    • Sperm travel from the vagina into the cervical mucus, through the cervix, into the uterus, and finally into the uterine tubes.

    • Uterine Contractions: These help propel sperm toward the site of fertilization.

    • Viability: In most species, spermatozoa remain viable (alive) for approximately 24 hours24\,\text{hours} in the female genital tract. The dog is a notable exception, where sperm can remain viable for 55 to 6 days6\,\text{days}.

  • The Fertilization Process:

    • Timing: Fertilization usually happens within a few hours of ovulation, provided viable sperm are present.

    • Capacitation: In some species, sperm must undergo a maturation process within the uterus or fallopian tubes called capacitation to gain the ability to fertilize the egg.

    • Penetration: Once one sperm penetrates the egg, the egg membrane closes to prevent polyspermy (entry of more than one sperm).

    • Developmental Migration: The fertilized ovum develops and is transported to the uterus within 33 to 8 days8\,\text{days}, depending on the species.

  • Sperm Anatomy and Motility:

    • Head: Carries the genetic material.

    • Tail: Propels the sperm.

    • Motility: The ability of the sperm to move, which is critical for traveling the long distance to the oviduct within the short lifespan of the ovum (which survives only a few hours).

Pregnancy Diagnosis Methods

  • Importance: Early diagnosis is essential for successful breeding programs across all species (dogs, cats, horses, cows, etc.).

  • Methods of Diagnosis:

    • Observation of Outward Signs: In polyestrous species (cow, mare, ewe, sow), the first sign is the cessation of estrous cycles, though this is not always accurate.

    • Internal Examination (Rectal Palpation): Used by veterinarians in cows and mares to detect changes in reproductive organs before the fetus is palpable.

    • Ultrasonography: Uses sound waves to outline internal structures. It is highly accurate and used in:

      • Mares: For early detection.

      • Ewes: To determine multiple pregnancies (twins/triplets) for specialized lambing care.

      • Bitches and Queens: Performed at mid-gestation for better accuracy and fetal well-being assessment than palpation alone.

    • Biologic or Chemical Assays (Mares):

      • Equine Chorionic Gonadotropin (eCG): Produced by the placenta between day 4040 and day 120120 of gestation.

      • Fetal Estrogen: A form of estrogen produced by the fetus, indicating fetal health.

    • Abdominal Palpation: Used in bitches and queens at mid-gestation.

    • Radiographs (X-rays): Taken late in pregnancy for bitches and queens to count the exact number of fetuses for delivery management.

Gestation and Parturition Periods

  • Gestation: The period of offspring development from fertilization until birth.

  • Duration of Gestation by Species:

    • Cow: 273−296 days273-296\,\text{days}

    • Mare: 327−357 days327-357\,\text{days}

    • Ewe: 140−155 days140-155\,\text{days}

    • Swine: 111−116 days111-116\,\text{days}

    • Goat: 148−156 days148-156\,\text{days}

    • Bitch: 60−63 days60-63\,\text{days}

    • Queen: 56−65 days56-65\,\text{days}

  • Parturition: The act of giving birth. Breeders calculate the expected date by adding the gestation length to the breeding date.

Stages and Physiology of Labor

  • Pre-Parturition Signs:

    • Behavior: Separation from the herd; nesting behavior in sows, queens, and bitches; nervousness, pacing, and restlessness.

    • Physical Changes: Relaxation of pelvic ligaments and the cervix; milk production in mammary glands.

  • Hormonal Triggers:

    • As the placenta ages, the fetus becomes stressed and releases cortisone.

    • Cortisone and estrogen work together to decrease progesterone levels, ending gestation.

    • Oxytocin release stimulates labor.

  • The Three Stages of Labor:

    • Stage 1: Uterine contractions begin and the cervix dilates (widens). Straining is typically absent.

    • Stage 2: The fetus enters the birth canal, fetal membranes rupture, abdominal contractions occur, and the fetus is expelled through the vulva.

    • Stage 3: Expulsion of fetal membranes (placenta) and uterine involution.

  • Involution of the Uterus: The process where the uterus returns to its non-pregnant state, which can take several months.

Birth Complications: Dystocia

  • Definition of Dystocia: A condition where the female cannot deliver her offspring without external assistance.

  • Causes of Dystocia:

    • Hereditary Factors: Small pelvic size (common in Bulldogs) or "double muscling" in cattle (producing excessively large fetuses).

    • Nutritional/Management Factors: Breeding females that are too young or underfed.

    • Positional Factors: Abnormal presentation or position of the fetus prevents passage through the vagina despite a healthy uterus and fetus.

    • Other: Infections, trauma, or parasites.

Mammary Glands and Lactation

  • Function: Accessory reproductive glands that produce milk, providing nutrition and maternal antibodies for disease resistance in newborns.

  • Anatomical Locations:

    • Inguinal Region (Mare, Cow, Ewe, Goat): Underside near the rear.

      • Mare, Ewe, Goat: Two halves opening into two separate teats.

      • Cow: Udder divided into four quarters, each with its own teat. Supernumerary teats (extra glands/teats) are common.

    • Under Surface (Sow, Bitch, Queen): Arranged in pairs, usually between 44 and 99 pairs.

  • Hormonal Control of Lactation:

    • Development: Estrogen and progesterone (from ovaries/placenta) cause gland growth.

    • Secretory Onset: Triggered by a drop in progesterone and estrogen at the end of gestation, combined with the release of prolactin from the pituitary gland.

Reproductive Failure

  • Congenital (Inherited) Causes:

    • Hypoplasia: Incomplete formation of parts of the reproductive tract.

    • Other: Anatomical defects, chromosomal abnormalities, inherited disease tendencies, or behavioral problems that prevent breeding.

  • Physiological and Psychological Causes:

    • Acquired Abnormalities: Tumors or trauma-induced damage to organs.

    • Hormonal Failure: Improper timing or quantity of hormone release.

    • Behavioral Lack of Conception: Failure of the female to show receptive behavior or failure of the male to detect the fertile period or perform copulation.

  • Infectious Diseases:

    • Systemic Diseases: Affect the whole body, including reproduction (e.g., tuberculosis in cattle, distemper in dogs).

    • Venereal Diseases: Sexually transmitted during breeding (e.g., trichomoniasis, brucellosis).

    • Brucellosis Transmission: Can also occur through consuming food contaminated with infected birth fluids.

    • Abortion: The expulsion of conception products before the fetus is viable, often caused by trichomoniasis or brucellosis.