Unit Animal Science

Problem Area Animal Reproduction

Lesson Sperm Motility

Student Learning Objectives 1. Describe the importance of animal reproduction. 2. Explain how sperm are formed and how they differ from the female gamete. 3. Explain the three factors that are used to evaluate semen.

Terms acrosome artificial insemination cumulus egg extenders fertilization gametogenesis insemination morphology natural insemination oogenesis reproduction semen sexual reproduction sperm spermatogenesis sperm mobility zona pellucida

Why is reproduction important? Reproduction is the process by which animals produce offspring. Reproductive decisions are some of the most critical management decisions that a producer makes. Whether someone is managing a 400 cow beef herd or raising guinea pigs for a local pet supply store lack of understanding the reproductive process can cost producers a significant amount of time, money, and other resources. The ability to reproduce is one of the basic characteristics of a living thing; in order for a species to continue they must be able to produce viable offspring.

A. Only animals within a species can produce fertile offspring. Offspring have similar traits of their parents. A horse and a donkey are two different species that can reproduce. However, they produce a mule which is sterile.  1. Parents are selected and mated to achieve certain goals with offspring such as producing offspring with high milk productivity, large litters, or meaty carcasses.  2. Reproduction results in new animals that are raised for the products they produce. Examples of products include meat, eggs, milk, wool, and pets.

B. Most animals are produced with sexual reproduction. Sexual reproduction is the union of the sperm and the egg. Two parents are required. Asexual reproduction requires only one parent; offspring are genetically identical to the parent. Bacteria and other one-celled organisms reproduce through asexual reproduction.  1. Sperm is the sex cell of male animals. They are produced in the testes. Semen is the fluid that is ejaculated by males and contains the sperm.  2. The egg or ovum is the sex cell of female animals. They are produced in the ovaries.

C. Fertilization is the process by which the union of a sperm and an egg occurs. It is also known as conception. Conception takes place in the female’s reproductive tract for dogs, cattle, hogs, and many other animals. Fertilization occurs outside of the body for organisms such as fish.  1. The process of placing sperm in the reproductive tract of the female is known as insemination.  2. Natural insemination occurs when a male of a species mates with a female of the same species. Sperm are placed in the female reproductive tract by the male during copulation.

3. Artificial insemination (AI) is used in some situations, such as with dairy and beef cows, horses, and others. Artificial insemination involves placing semen collected from a male in the female reproductive tract using equipment designed for the purpose. AI is a key management tool for producers that allows them to have greater choices in selecting beneficial traits for improved genetic performance.

How are sperm formed and how do they differ from the female gamete? Gametogenesis is a series of transformations that result in the formation of the egg and sperm cells or gametes. A. Spermatogenesis is the production of sperm and oogenesis is the production of egg cells. B. During spermatogenesis spermatogonia are found along the outside wall of the seminiferous tubules and have increased in number due to mitosis. Each increases in size developing into primary spermatocytes. Two secondary spermatocytes are developed when each primary spermatocyte undergoes the first meiotic division.

 1. Four spermatids are then developed after the second meiotic division.  2. Each spermatid contains the haploid number of chromosomes. For example, human sperm cells contain 23 chromosomes, swine have 19 chromosomes, sheep have 27 chromosomes, cattle have 30 chromosomes, dogs have 39 chromosomes, cats have 19 chromosomes, and chickens have 39 chromosomes.  3. As the spermatid develops into mature sperm they lose a large amount of cytoplasm. The nucleus is condensed into a head, and a whip-like flagella tail is developed.

C. In oogenesis the early germ cells, called oogonia, grow into primary oocytes. The pri-mary oocyte will divide into one polar body and one secondary oocyte. The majority of the cytoplasm goes to the secondary oocyte and the polar body is rather small. Each contains the same number of chromosomes. The secondary oocyte divides again resulting in an ootid and another polar body. Sometimes the first polar body will divide into two polar bodies.

 1. Oogenesis results in one large ootid that contains the haploid number of chromosomes and most of the cytoplasm and three polar bodies. These polar bodies will disintegrate since they are nonfunctional.  2. The large ootid then grows into a functioning ovum.  3. The large size is needed to provide food for the embryo until it can receive nourishment from its mother.  4. Oogenesis differs from spermatogenesis in that only one sex cell is created versus four sperm cells. D. Both the spermatid and ootid possess either all maternal chromosomes, paternal chromosomes, or a combination of chromosomes from the mother and father.

What factors are used to evaluate semen? A. The volume of semen that is ejaculated varies greatly between species. One bull can ejaculate enough sperm to inseminate hundreds of cows while a stallion only has enough for about 17 mares.  1. Because of this, semen is extended or diluted before it is frozen. Nutrients, pH adjustment, and protection from freezing are benefits of adding extenders. Dehydration results when glycerol is added helping to prevent ice crystal damage.  2. After the semen is diluted, it is placed in a small plastic straw and slowly cooled. After the semen reaches 0° C, it is rapidly cooled to -320° F using liquid nitrogen. a. The metabolism of the sperm cell is stopped. b. Constant temperatures and easy transport are benefits of using liquid nitrogen.

 3. Only 50–65% of sperm cells will survive freezing in an excellent sample.  4. Refreezing of semen significantly reduces the survivability of the sperm. B. Morphology is the structure of an organism or of any of its parts, in this case a sperm cell.  1. A microscope is used to view the sperm after they have been stained to identify any morphological problems.  2. A sperm consists of a head, mid-piece or body, and tail. A membrane cap covers the head and is called the acrosome.  3. Frequent morphological problems include: abnormal shaped head or tail, multiple tails or heads, ruffled acrosome, incomplete acrosome, etc.

C. Sperm motility or movement of the sperm is very important and is evaluated by looking at the sperm under a microscope. The tail is primarily responsible for motility. Sperm must be healthy in order to meet the challenges of each step of the fertilization process; several different tasks are required.  1. At least 30% of the sperm should be normal and highly motile.  2. After ejaculation, the sperm must swim out of the semen. In order to do so, they must swim quickly and in a straight line. This is known as “rapid and linear.” If they swim in circles, slowly, or in a curved manner, few of them will make it out of the semen and be able to continue on to fertilization.

 3. Next, the sperm must travel to the egg which is in the upper part of the fallopian tube or oviduct. Tiny hairs called cilia and contractions in the uterine wall help the sperm travel to the egg.  4. Once the sperm reaches the egg, it must pass through two layers. a. The first layer is called cumulus and is made up of cells and non-cellular material. Sperm must swim in a fast spiraling path in order to penetrate the cumulus. This is known as “capacitating motility pattern.” b. The second layer is called the zona pellucida and is the non-living cover. When the sperm gets to the zona pellucida, enzymes from the acrosome must digest a small hole allowing the sperm to enter. Next, the sperm must swim in a “hyperactivation” manner. The head bends sharply back and forth in a rapid and random manner. The whip-like movements of the tail cause it to finally enter the egg.

D. There are many causes of poor sperm health.  1. Abnormal development or poor genetics  2. Heat  3. Stress  4. Illness (fever)  5. Poor nutrition  6. Extreme or lasting cold temperatures  7. Insufficient levels of ATP for the flagella to move quickly and in the appropriate manner  8. Salinity

Review/Summary Why is reproduction important? How are sperm formed and how do they differ from the female gamete? What factors are used to evaluate semen?