Developing an understanding of basic genetics helps when you’re raising animals, and also comes easier when you’re applying it on a farm than it does when you’re trying to understand it in a high school biology class. As Ken said when he saw me reviewing some papers on Mendel for this chapter, “I never ‘got’ genetics in school, but once I started to raise animals it began to make sense.”
Biology 101
If you struggled with the concept in school, or avoided it at all costs, a condensed biology lesson may be helpful. Mendel worked with peas and demonstrated that observable traits — such as flower position, pod color, and stem length — could be passed from parents to their offspring. He surmised that there was some type of a hereditary unit — now called a gene — that passed information along from both parents. Mendel hypothesized that each gene could come in different forms. In the pea experiment, for example, there were two forms for pod color — green and yellow. These gene forms are called alleles, and the offspring actually receives one allele from each parent for each of its genes.
Mendel also demonstrated that some of these alleles were dominant and others were recessive. In the case of Mendel’s peas, the green allele was dominant (Figure 5.3). If a plant or an animal has received a dominant allele from one parent and a recessive allele from the other parent, it will always show the dominant trait. Recessive traits only show up when the recessive allele has been received from both parents. Our German shepherd, Kima, is solid white. White is a recessive color in German shepherds (black patterned with tan is the dominant color for the breed), so Kima received the white allele from both of her parents.
Figure 5.3. Mendel’s experiment. (A.) All offspring will show the green trait, as G is the dominant allele. (B.) If one of these offspring are crossed with the yellow pea (YY); one-half would show the green trait, and one-half would show the yellow.
Some traits are passed along on a single gene, but most traits are actually passed along on more than one gene. As an example, scientists have so far determined seven genes that are responsible for color in horses, and they think there are probably still more to be found. When multiple genes are responsible for a single trait, one gene may be dominant, or epistatic, over the others. An epistatic gene simply obscures the expression of other genes. In horses, the white gene is such a gene; if its dominant allele is present, the horse lacks any pigment in its skin and hair, like an albino.
Geneticists use letters to represent the alleles for each gene. Convention has established that a capital letter is used for the dominant allele and a lowercase letter is used for the recessive allele. For the white gene in horses, the letter used is W. There are three possible combinations:
1. WW. A horse with a WW set of alleles received the dominant allele W from each parent; however, this particular allele combination is lethal before birth.
2. Ww. This set shows a horse that received the dominant W allele from one parent and the recessive w from another parent. Any horse with this combination exhibits albino characteristics. In the mating of two albino horses, approximately one-fourth the time their offspring would receive the lethal WW form, one-quarter would receive the ww combination, and one-half would receive the Ww combination (Table 5.1).
3. ww. This final combination of white alleles in horses is also the most common. It means the horse received the recessive w from each parent.
Table 5.2 describes the best current knowledge of color inheritance in horses.
You may have heard of the Human Genome Project. A genome is simply the full complement of genetic material for any living thing. All living creatures, from single-celled organisms to humans, have a unique genome that repeats itself in every single cell. Take a brain cell, a blood cell, a skin cell, or any of the other seven trillion cells in your body; in each one, basically the exact same set of genetic data is found. The Human Genome Project’s goal is to map all 100,000 human genes (which are located on 23 chromosomes). Recently, veterinary geneticists have begun genome-mapping projects on most major livestock species. Mapping genes is another technological two-edged sword; it may be of great benefit, but it could be highly abused. The ethical debate over gene mapping and genetic engineering is one that we small-scale farmers need to follow.
Traits such as hair color and eye color — or in the case of Mendel’s peas, pod color — are completely based on heredity; they’re traits that are in the genes.
But some traits, including temperament, intelligence, and size, are based in part on heredity and in part on environment, and are affected by the attention an animal received after birth. Proper handling and training can make a naturally high-strung animal pleasant to work with: improper handling and training can make a monster out of a naturally docile and calm animal. An animal can have the genetic potential for quick growth, but if it isn’t receiving adequate nutrition or if it is carrying an excessive parasite load, it won’t realize its full growth potential.
Table 5.1
GENETICS OF HORSE COLORS
Table 5.2
COLOR DEFINITION IN HORSES
Emotions and Senses
Speak of an animal’s emotions and some people get kind of testy (especially people with PhDs who study animal behavior): Referring to an animal’s emotions is viewed as being anthropomorphic (attributing human characteristics to nonhuman beings). In his book When Elephants Weep, Jeffrey Moussaieff Masson tells the story of a trainer who says that animals don’t get angry. I don’t know what that trainer trains, but I do know that I’ve seen animals angry, happy, scared, contented, and loving. Shauna, our mare, was plain mad at us when we sold two of her colts, and she displayed that anger for weeks. Calves playing “king of the hill” on a pile of dirt in our barnyard were obviously having great fun and were quite happy, at least until Leona decided that her calf, Les, should be the winner of the game. She began bashing the other calves angrily off the hill until Les was on top.
Then there are the people who say this or that type of animal is stupid — not just that a single animal isn’t so bright, but that the entire species is dumb. Sheep, cows, and turkeys are especially vulnerable to this assessment, but even horses are occasionally accused of stupidity, which is far from the truth — horses are intelligent animals. Animals respond to certain stimuli differently than we do, and react based on long-standing genetic programming. These responses and reactions are sometimes taken as signs of stupidity. Learning to understand these patterns of behavior, and learning to “read” an animal’s emotional state, makes working with animals much easier and less dangerous for you and the animal.
The emotion that animals are usually evincing when people accuse them of being stupid (or dangerous) is fear. I once heard an old rancher say that a critter remembers the worst thing that ever happened to it and the most recent bad thing that has happened to it. Now scientists have proven him right. Fear memories, they’ve discovered, are stored, basically forever, in a portion of the animal’s brain that isn’t very well developed. An animal that has had an extremely bad fright — say, on entering a trailer — will continue to be afraid of trailers until brain centers that are more highly developed learn to block the fear. Overcoming an animal’s fears can be a time-consuming process, and requires patience on the part of handlers and trainers.
Understanding how your animals use their senses (sight, sound, smell, taste, and touch) will help you understand why fear reactions can happen so quickly. Remember that livestock species are primarily prey animals, so their senses have developed to help them find food and shelter, for navigation, and, most importantly, to avoid predators.
Vision
As prey species, livestock have a wide field of vision (Figure 5.4). This allows them to see predators moving in on them from almost any direction, and is made possible by the biological design of the animals’ eyes: large relative to their head size and located toward the sides of the face. Predators’ eyes are smaller in proportion to head size and located to the front of the face, providing predators
with a narrower field of vision, but the centered eye placement enhances depth perception through bifocal vision.
Bifocal vision occurs when both eyes can independently focus on the same thing at the same time. To put these differences in perspective, a prey animal can see a predator well on the horizon in almost any direction, but it has trouble seeing a stationary bug sitting on a leaf. Most predators don’t see as well at a long distance, and they can only see in the direction they’re facing; still, they can make out even slight movements within their field of vision and can differentiate three dimensions well. Horses and pigs have more bifocal vision than cattle or sheep, because their eyes are located more forward on their heads than are the eyes of cattle and sheep (Figure 5.5).
Despite their wide field of vision, livestock species have a very narrow blind spot right in front of their noses, and a slightly larger blind spot directly behind them. When you work with animals that are secured (tied or stanchioned), you learn (sometimes the painful way) to talk to them before approaching them directly from behind. One day Ken walked up behind one of our milk cows, Libby, to take the milking unit off her while she was in her stanchion. She hadn’t heard him coming, so when he kneeled to remove the unit she kicked out; Ken went flying and she stomped his glasses. Libby was a fairly even-tempered girl, but she reacted out of fear.
Figure 5.4. Cows (and other prey species) have monofocal vision; that is, they only can see something with one eye at a time. Because their eyes are situated more to the sides of their heads than to the front, their depth perception is not very good. Still, though they may lack depth perception, their blind spots are minimal, which allows them to see almost all the way around themselves. In fact, the field of vision for cows is almost 330 degrees. Most prey species have a small blind spot right in front of their noses and a slightly larger blind spot behind themselves.
Figure 5.5. Horses, with eyes situated more to the front than cows’ eyes but more offset than predators’ eyes, share the same large field of vision as cows, but they have the added advantage of a small area of bifocal vision.
Visual frights are responsible for the majority of difficulties that arise when working animals. If an animal is acting skittish, look around the area for items that may be causing it stress. Shadows or reflections off water; something out of its regular place, even something as simple as a jacket hung over a shovel handle; bright-colored objects; or an object flapping in the wind can spook an animal. The play of light can also affect animals. They are most comfortable in a diffusely lit area; extremely bright lights will cause them to balk.
Hearing
In most land animals, hearing is controlled by a three-part ear system. The external ear acts as a gathering device and canal for sound waves, moving them into the middle ear. Sound waves are basically just air particles, jostling each other at various pressures and speeds.
The size and shape of the external ear was, in many ways, a product of the environment in which the animal developed. Asses have the largest external ears of any of the domestic equines, and horses have the smallest. Mules’ ears, as a cross between asses’ and horses’, are between the two. Asses evolved in a desert environment, which forced the animals to spread out over large geographical areas to find adequate feed. Big areas required big voices, and ears that were capable of hearing them. This was the only way they could find each other for companionship, support, or mating. In comparison, horses evolved in a grassy and lush savanna. In this environment, the land supported larger communities of animals. The horses could “talk” to each other without raising their voices, and they didn’t need as large an external ear to hear each other.
The middle ear transmits the vibrations, which are created when sound waves strike the eardrum, into the inner ear. The inner ear acts as a messenger service, translating the vibrations for the brain and nervous system to interpret.
After sight, hearing is the second most critical sense for those of us who handle animals to understand. Low-pitched, rumbling sounds don’t tend to bother livestock, but any kind of high-pitched whine will scare them. This is due to the range of sounds that their ears are most sensitive to: Human ears are most sensitive to sounds in the 1,000 to 3,000 Hz range, but livestock are most sensitive to the higher sounds of the 7,000 to 8,000 Hz range. The difference in sensitivities is due to the size and shape of the eardrum.
Although high-pitched, loud, or novel sounds can cause fear reactions, not all sounds are bad. Animals do well when a variety of sounds are part of their normal environment. We always played a radio in the barn while we were milking. We noticed that most of the time this didn’t bother the animals at all, but sometimes a very loud commercial would come on and really get a reaction out of the girls. We switched over to a cheap CD player, and the cows did better. It didn’t seem to matter what we played — Garth Brooks, Jimi Hendrix, or Mozart — so long as the volume was consistent and changes were made incrementally.
Touch and Smell
Livestock use their noses both for smelling things and for touching them. Notice how an animal approaches something new that’s been placed in its environment: It lowers its head and approaches with its neck stuck out, first sniffing and then, slowly, touching the article with its nose. The nose has large bundles of nerve endings, making it the organ of choice for “feeling” new things.
The sense of smell is stronger in most animals than in humans and the other primates. A horse that spots something moving on the horizon will put its nose into the wind and begin sniffing the air. The sniffing action brings more air through the nasal cavity, increasing the likelihood that it will pick up the scent of what it sees.
Males of most species use their sense of smell to detect females that are coming into heat or are ready to breed. The male smells and licks the female’s vulva; then he holds his head out and curls his lip up, in a behavior known as a Flehmen response. What he is sensing is a chemical attractant the female releases called a pheromone.
The sense of smell also allows mother animals to identify their own offspring. Mothers detect their own odor on a newborn animal, allowing them to identify it as their own; later, they detect their own milk odor. One method of “grafting” an orphan onto a mother animal is to feed the orphan her milk for a few days prior to introducing it. Then place Mom, her own baby, and the orphan together in a small pen. Mom smells her own milk on the orphan and figures the little guy must be hers. Sheep farmers also use this approach to graft a lamb from a large litter onto a sheep that lost a lamb at birth; they skin the dead lamb and place its skin over the “extra” lamb. The ewe smells her own smell and allows the lamb to nurse. After two or three days, the skin is taken off, but by this time the mother smells her own milk.
FARMER PROFILE
Kevin and Marcia Powell
Mulefoot hogs are an almost extinct minor breed. Developed in the Midwest in the middle of the nineteenth century, they were used by farmers along the Mississippi and Missouri Rivers to forage on river islands during the summer months. Today, to the best of Kevin Powell’s knowledge, there are only seven breeding herds left — but Kevin is on a mission to change that.
Kevin grew up on a family farm near Strawberry Point, Iowa, and like many Iowa farm kids he attended Iowa State University’s College of Agriculture. But unlike many of his peers, Kevin was accepted into the Biotechnology Scholars Program, which puts ten incoming freshmen onto an advanced track for their four years of school.
“The Biotechnology Scholars Program emphasizes studies of biotechnology and genetics. The more I learned about genetics, the more I became concerned about the loss of genetic diversity. I started to realize that we were losing genes that couldn’t be replaced — and that someday a lost gene could be crucial to saving an entire segment of agriculture. My concern for both plant and animal genetic diversity grew proportionally to what I learned.”
When Kevin returned to the farm from college, he and Marcia farmed full time. “We raised corn and alfalfa hay, hogs and cattl
e; but poor markets and high debt did us in. We tried to diversify with dairy goats, and the dairy goats paid pretty well, but the existing debt from our conventional operation was just too much.”
Kevin gave up full-time farming and went to work as a quality engineer for the Square-D Company (manufacturers of electrical system components). “I still wanted to farm part time, so I took over 40 acres of my parents’ farm. And I decided to do something about my concern for genetic diversity.”
Kevin and Marcia contacted a group called the Institute for Agricultural Biodiversity in Decorah, Iowa. The institute ran a farm that maintained a number of minor breeds. “We went to visit in 1995. The director of the farm explained to us that they had a ‘nucleus herd-lending program.’”
The lending program was designed to loan out breeding herds to farmers interested in helping maintain the breeds. The idea was that a farmer would keep a small breeding herd for a year or two then send it on to another farmer, but keep back some of the young stock for his or her own use. Kevin and Marcia took a breeding herd of Mulefoot hogs (eight sows and two boars), but during the time that they had the herd on loan the institute ran into financial trouble. “We ended up purchasing the herd,” Kevin says.
Small-Scale Livestock Farming Page 9
