The Biology of Dairy Animals

The average American consumes almost 68 gallons of cow milk in the form of fluid milk and milk products, and milk ranks amongst their top four consumed beverages (not including tap water). These and other statistics show that milk is a ubiquitous part of our cultural diet. How cultural, how-ever, is knowledge about the average dairy cow’s life? Recently, while visiting at a neighbor’s house following evening milking chores, I was amused by their four-year-old son’s response to learning that I had spent the last few hours milking cows. “Milking the….cows!?”, he replied in shocked amazement. I’ll chalk this one up to being a four-year-old, but must also acknowledge a study published in the U.K. in 2012 by LEAF (Linking Environment and Farming). In their study only 6 out of ten participants between the ages of 16-23 were able to successfully link milk to a photo of a dairy cow. Knowing the cow (or goat or sheep) as the origin of milk is an important first step in agricultural literacy. In promoting agri-cultural literacy and consumers that are actively making conscious food decisions, however, we must also be educating about the concepts of animal welfare, behavior and nutrition, as well as the daily routines and management decisions of farmers. It is an easy step to be a part of a culture that embraces a product but it is a vital step to be a part of a culture that knows the story of the product’s origins.

Evolution of the domestic ruminant

Throughout different cultures in history the cow has been (and in some cultures still is) celebrated as sacred. Modern insights into Indian culture, where the cow remains sacred for many, have suggested that this status in religion and culture is perhaps rooted in the essential contributions that the cow offers in exchange for relatively little inputs. The cow in India is a major contributor of physical labor, dairy products, and nutrients from excrement (manure and urine). Observers note that the typical cow in India is given freedom to graze road-sides and cropland after the harvests have been taken off, essentially what is otherwise wasteland and has a very low cost of production. De-spite this low input demand, the cow is still productive and fruitful. She produces valuable offspring, which are either raised as cows or if male are trained as oxen to be used for labor; she also produces nutrient dense milk which humans consume, and manure which can be used as a fuel source for cooking and heating as well as a vital fertilizer for crop fields. Given this relationship, the sacred cow is a symbol of care, compassion, sustainability and equity within the Indian culture.

Archaeologists estimate that the domestication of ruminant animals began roughly 11 thousand years ago (ruminants are animals with a unique four-chamber stomach and include cows, sheep and goats amongst others). This theory of domestication is supported with bone remains and other evidence, which show a gradual spread of domesticated ruminants from the Middle East through modern-day Turkey and eventually into Europe. At a number of these sites archaeologists have found pottery shards and other vessels that are reminiscent of modern day cheese-making or yogurt fermenting technology. It is theorized that fermentation techniques were utilized by these early cultures to allow digestibility of the milk.

DNA research has allowed scientists to pinpoint a genetic mutation that encourages the production and presence of an enzyme that allows for the digestion of unfermented milk beyond the weaning years and throughout adulthood. Roughly 35% of today’s human population has this mutation and is thus able to digest unfermented dairy products beyond the age of 7-8 years old. It is thought that this mutation first occurred in Europe roughly 7,000 years ago. Those with the genetic mutation are suggested to have had a reproductive advantage during this period of history, likely due to improved quality and availability of food supply in the form of unfermented dairy. This advantage promoted the spread and migration of the human populations with the enzyme gene mutation. Due to the mutually beneficial relationship between humans and dairy animals, dairy animals also experienced a population and migration increase following the development of the genetic mutation in humans. This genetic mutation is traced as the major contributor of modern dairy digestibility in individuals of European descent. Several other isolated pockets of populations that have evolved to digest raw dairy, however, have since been found in West Africa, the Middle East and south Asia. These ‘hot spots’ are all linked to different genetic mutations.

During the European colonization of the United States in the 1600s, immigrants brought cattle with them from Europe. These colonists continued the migration of cattle for the observed benefits of food production (meat and dairy) and labor in the form of draft power. Records show that it wasn’t until the late 1800’s that cattle in America began to be bred specifically for dairy purposes alone, and even during this period cows were primarily kept for home or local needs. As people in the US increasingly began to populate cities through the turn of the century, the demand for systemized milk production grew and innovations such as milking machines, commercial milk bottles, pasteurization and homogenization techniques and equipment, refrigerated trucks, automated bottling machines, advances in crop production for animal feed, and advances in veterinary medicine came about. By the mid-1920s, government regulations began to be established to improve milk price stability and to ensure the availability of a sufficient quantity of safe (or unadulterated) milk. In 1946 the US government passed the National School Lunch Act, which mandated that each school lunch include between ½ to 2 pints of whole milk.

Today, dairy is one of the top five agricultural commodities in the United States. It is estimated that there were over 9 million mature milk cows in the US in 2013 with an average annual production of 2,450 gallons (or 21,805 lbs.) of milk per cow. These numbers are evidence of the influence that the dairy industry continues to plays within our culture; however, they do little to reveal the intricacies of the true player – today’s dairy animal.

What is a ruminant?

Our most common domesticated dairy animals, cows, sheep and goats, are all mammals classified (by their digestive system) as ruminants. Ruminants are herbivores (consume plant materials) and have evolved to digest a diet composed primarily of fibrous plants such as grasses. This is unique from mammals with a single stomach (or a monogastric) digestive system, such as humans. In the human diet, the fiber from plant material, such as leafy vegetables, is beneficial but does not provide actual nutrition. Our stomachs lack the necessary enzymes to digest and absorb proteins and other nutrients from grasses and similar fibrous vegetation. The digestive system of ruminant animals is distinctive because, as suggested previously, they have a unique digestive feature: a four-compartment stomach. The four parts of their stomach are known as the rumen, reticulum, omasum and abomasum. When a ruminant animal swallows a chewed mouthful of food that has been mixed with saliva, it travels through the esophagus to the rumen and reticulum (also known as the reticulorumen). The reticulorumen is essentially a fermentation vat; it plays host to a variety of microbes that are essential for the fermentation and breakdown of the consumed plant materials. In the fermentation vat (or rumen), solids are clumped together to form a bolus or cud. The bolus of partially digested plant material is then regurgitated by the animal for further chewing and particle breakdown. This is where the common phrase of ‘to ruminate on a thought’ or ‘to chew something over’ originated.

During the rumination process of swallowing, regurgitating, chewing, swallowing again and further fermentation in the reticulorumen, volatile fatty acids (a main source of energy for the ruminant animal), vitamins, and other by-products of fermentation microbes are absorbed into the animal’s bloodstream through the rumen wall. Other materials of fermentation, such as methane gases, are released from the rumen via belching (or eructation). When thoroughly broken down, plant materials are transported from the reticulorumen to the omasum. In the omasum the digested water and minerals are absorbed into the animal’s bloodstream. Any remaining materials are then transported to the abomasum. Of the four chambers, the abomasum is the most comparable to the digestive stomach of a non-ruminant mammal. In the abomasum, further digestion of the food materials is facilitated by the presence of acids and enzymes. These contents continue to the small intestine where nutrients such as fats and proteins are absorbed by the animal. Finally, undigested feedstuffs pass through the large intestine and are excreted by the animal.

Milk production

After learning what makes a cow’s digestion (or goat, sheep, etc.) unique from other mammals as a ruminant, the next defining characteristic to understand about the dairy animal is how (and why) they produce milk. Like most mammals, lactation for the female ruminant animal begins with parturition (or the birthing of offspring) and the natural release of the oxytocin hormone. The start of milk production for a dairy animal is also known as freshening. Following parturition, all mammals produce colostrum for approximately 3-4 days. Colostrum is similar to milk but is composed of antibodies to be ingested by the newborn ruminant animal; the consumption of colostrum, particularly within the first 24 hours of age, is vital for the oral transfer of immunity to the newborn because immune system traits are not transferred to the offspring through the placenta.

Today, most commercial dairy operations separate newborns from the dairy cow within the first 24 hours of birth. This practice stems from the business end of dairy operations, which is milk production and collection for commercial sales. Arguably, the practice of separation also allows for farm management to have more specialized attention on the mother’s milk quality and health following birthing as well as the calf’s milk intake and growth. Recent research has observed the potential impacts that separation at birth has on calf development and lifetime production versus alternative management methods for calf-cow relationships that still promote herd health and milk quality. Once such study from the University of Veterinary Medicine in Vienna showed an increase in the sociability of adult cows that had been raised with a herd and their mother. It is not yet clear how the sociability of a cow translates to milk production or the ease of adopting new management practices on farm. Continued research and on-farm trials of raising calves with their mother will improve the chance of adopting any of these practices on commercial operations.

Though they are separated from their mothers, it is common practice in the dairy industry to deliver the colostrum to newborns and continue to provide them milk (or milk replacer) for at least 2-3 months. Milk consumed by nursing young stock bypasses the rumen and is sent to the abomasum for digestion.

Mammal’s milk is roughly composed of 2-8% (by weight) lactose, though this proportion varies depending on the species. Lactose is a carbohydrate, or sugar, that is essentially unique to the mammary gland of mammals. Mammals are born with the ability to digest the lactose in their mother’s milk (and consequently that of other mammals) due to the presence of an enzyme known as lactase. The lactase enzyme, along with other cells, forms what is commonly called the brush border. The brush border is the area of small intestine where nutrients are absorbed into the blood stream. As lactose sugars from milk approach the brush border, lactase enzymes housed in the brush border activate the breakdown of lactose sugars into simple sugars. One of these simple sugars, glucose, is a key energy source for the mammalian body. During maturation and the weaning process, the presence of lactase in the digestive system lessens for most mammals including our earliest ancestors. The evolution of the genetic mutation in humans, as noted previously, allows for the persistence of lactase enzyme production and therefore the digestion of milk throughout adulthood.

Rumen development begins with the introduction of forages and/or grain to the calf diet. Under a less intensively managed though still domesticated setting, we can predict that calves would self-wean from their dam (or cow mother) at approximately 8 months of age. This estimate is based on a comparison of cow calf relationships in domesticated beef cows where the average age of weaning pasture-raised beef is approximately 8 months of age. Healthy beef and dairy cows begin showing signs of heat (or the ability to be bred) at approximately 15 months of age. Breeding occurs on today’s farm in two manners: 1) with the help of a bull, or 2) using artificial insemination. After being bred, gestation periods vary by species; similar to humans, a dairy cow carries her young for approximately 9 months (this period is shorter for goats and sheep).

Cows have evolved in an annual cycle that follows the availability of abundant forages. When observing wild ruminant populations, it is notable that they freshen (or give birth) at the onset of the growing season (or spring). This allows for maximum food intake for the animals to support the high energy demand associated with producing milk for their offspring. To remain on this evolved cyclical pattern, and due to their relatively long gestation period, healthy cows are able to be rebred only 2-3 months following parturition (or birthing). When managed on this cycle, an average dairy cow will be milked for approximately 9 months following parturition. At the end of this period she is dried off, which essentially means that her milk production ceases. Similarly, wild ruminant populations would be self-weaning at approximately a similar time. This dry period evolved to occur during the non-growing season. The cow’s energy demand is lower without needing to produce milk and her energy is directed to the growing fetus during this period.

Animal welfare

The average dairy cow can live to be 12-15 years old. At 10 years of age, a dairy cow would have had a maximum of 8 lactation cycles and an estimated lifetime milk production of at least 20,000 gallons of milk. The average age of dairy cows in today’s agriculture tends to be closer to 5-6 years of age. If a cow is injured or ill and unable to maintain milk productivity, the farmer must often cull the cow from the herd in order to maintain financial productivity. Good management techniques can improve the health and welfare of the dairy animals, promoting their production and prolonging their life span.

In the past decade, researchers have observed that, given freedom of movement, the average lactating dairy cow has a relatively routine expenditure of her daily activities. The cow spends roughly 12-14 hours of her day lying down and resting. The remaining hours of the day are spent eating and drinking (2-3.5 hours), socializing or standing (2-3 hours) and milking and other herd management activities. Additionally, it’s estimated that approximately 7-10 hours are spent ruminating; these hours overlap with time spent lying down and standing. These numbers are essentially a cow’s internal time management system. It is suggested that by providing appropriate housing and animal management routines that allow for animals to maintain this natural schedule farmers can promote cow welfare, health and performance.

Organic dairy information

The emergence of the organic movement and local food awareness has bolstered consumer interest and awareness about the dairy industry. The implementation of a national set of standards for organic dairy production, which accounts for animal welfare, animal feed and healthcare treatments, has improved the transparency of organic milk production practices for consumers. It has been suggested by some retail data that organic milk is a gateway product for consumers into the organic marketplace.

Overall, milk production trends in the US, even for organic dairy operations, show a shift away from small family-owned farms and towards larger commercial operations. The number of dairy farmers is decreasing and in our communities small working dairy farms are becoming less prevalent. Given this trend, it is less likely that today’s youth will have gleaned a knowledge of food production from childhood experiences on or near farms. It is important to highlight the work of farms and to educate our communities about them. With an awareness of our food production systems, consumers will be empowered to promote animal health and welfare as well as the rights of farmers. This begins with young generations being able to identify a dairy cow and know the basics of how and why a dairy cow produces milk.

Ashley Green currently works as a Dairy and Livestock Certification Specialist for Vermont Organic Farmers (VOF), the certification body of NOFA-VT. She enjoys the exposure that the job provides to the hardworking and talented farmers and researchers in VT and neighboring states. Ashley grew up in a region surrounded by agriculture, but her involvement was limited until she became employed as a student relief milker at the University of New Hampshire’s organic dairy research facility. She quickly bonded with the routine of the dairy cow and, since completing her B.S. and M.S at UNH, she has continued to pursue a career that supports and contributes to the future of sustainable livestock agriculture.