Artificial Insemination in Cattle and Sheep

• Artificial insemination (AI) is a widely used reproductive technology in cattle and sheep breeding programs
• AI entails collecting semen from a male, preserving and storing it, and then placing it into the female reproductive tract when fertilization is most likely
• AI enhances genetic traits, manages disease, and boosts reproductive effectiveness
• Key AI steps: recognizing estrus, gathering and treating semen, and using proper insemination methods

Estrus Detection

• Precisely identifying estrus is essential for successful AI
• Estrus, also known as heat, is when the female is ready to mate
• Observing the animal is a typical way to identify estrus
• Estrus signs include willingness to be mounted, more activity, bellowing, and vaginal discharge
• Heat detection patches change color when mounted, helping to spot animals in estrus
• Electronic systems track activity to detect when an animal is likely in estrus
• Hormones greatly influence estrus
• Estradiol, from the developing follicle, causes behavioral changes during estrus
• Progesterone, from the corpus luteum, stops estrus behavior

Semen Collection and Processing

• Semen collection methods: artificial vagina, electroejaculation, and seminal vesicle massage
• The artificial vagina mimics natural mating conditions and is commonly used for collecting bull semen
• Electroejaculation involves using electrical stimulation on pelvic nerves to cause ejaculation
• Semen quality is judged by volume, concentration, motility, and morphology
• Semen is mixed with extenders to increase insemination doses and provide nutrients and protection during freezing
• Extenders usually contain buffers, energy sources (like glucose), antibiotics, and cryoprotectants (like glycerol)
• Semen is gradually cooled to 4°C for short-term storage or frozen in liquid nitrogen at -196°C for long-term storage
• Cryoprotectants protect sperm cells from damage during freezing and thawing
• Semen is stored and used for insemination in straws or ampules

Insemination Technique

• An insemination gun is typically used for AI
• The insemination gun places semen in the uterus or cervix
• Transcervical insemination is the most common method in cattle
• Transcervical insemination involves inserting the insemination gun through the cervix to deposit semen into the uterine body
• The recto-vaginal technique uses rectal manipulation to guide the insemination gun through the cervix
• In sheep, insemination depends on whether fresh or frozen semen is used
• Vaginal insemination can be used for fresh semen
• Laparoscopic insemination is often preferred for frozen semen, placing it directly into the uterus

Hormones and Drugs in AI

• Hormones and drugs are frequently combined with AI to regulate the estrous cycle and improve conception rates
• Prostaglandins (e.g., prostaglandin F2α) synchronize estrus by causing luteolysis (corpus luteum regression)
• Prostaglandins cause estrus within a predictable time
• Gonadotropin-releasing hormone (GnRH) induces ovulation or synchronizes follicular development
• GnRH stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland
• Progesterone synchronizes estrus or maintains pregnancy
• Progesterone is given through intravaginal devices like controlled internal drug release (CIDR) inserts or injections
• Estrogen induces estrus in anestrous animals, but its use is less common due to regulatory concerns
• Superovulation uses FSH to stimulate multiple follicular development
• Superovulation is commonly used in embryo transfer programs
• Antibiotics are sometimes added to semen extenders to prevent bacterial contamination and improve sperm survival

Advantages of AI

• Genetic improvement is achieved by using superior sires
• Disease control prevents the transmission of venereal diseases
• Increased reproductive efficiency allows more females to be bred to a single male
• Reduced risk of injury to both males and females
• Greater flexibility in breeding programs

Disadvantages of AI

• Requires skilled technicians and proper equipment
• Relies on accurate estrus detection
• Conception rates may be lower than with natural mating in some cases
• Labor intensive

Considerations Specific to Cattle

• Cattle AI is highly prevalent globally
• AI in cattle contributes significantly to genetic gain for traits like milk production, growth rate, and carcass quality
• Timed AI protocols combine hormonal treatments with fixed-time insemination, and are widely used to eliminate the need for estrus detection

Considerations Specific to Sheep

• AI is less common in sheep compared to cattle, but its use is increasing
• AI in sheep can improve genetic merit for traits like wool production, growth rate, and lambing percentage
• Laparoscopic AI is more common in sheep due to the complex anatomy of the ewe's reproductive tract
• Cervical insemination is also used, but can have lower success rates due to cervical structure

Artificial insemination (AI) is a common reproductive technology used in cattle and sheep breeding programs. AI involves semen collection, preservation, and deposition into the female reproductive tract. Accurate estrus detection is critical for successful AI, using visual observation, heat detection patches, or electronic monitoring systems.