It's far from uncommon for me to field questions about how cattle can survive in the cold of winter without living in a barn with central heating. Perhaps unsurprisingly, I get this question mostly during the winter. In the summer I less frequently get rather the opposite question; how can cattle survive the awful heat without living in a barn with air conditioning.
Please don't think I'm poking fun at the questioners. Questions are good, asking about things we don't understand is a wonderful human characteristic.
Occasionally I get the question phrased as a personal attack. "How can you be so mean to those poor, innocent, wonderful, godlike creatures?!?" Those are actually pretty rare though and usually only come up on the koobecaf or other forums for antisocial intercourse.
"Ooh-ooh! He said intercourse!"
Yes I did. I have the heart of an eight year-old boy.
I keep it on my desk in a jar of formaldehyde.
Now quit that! I'm trying to be serious here.
If you read my post yesterday you know that I lost a calf. There's no way to know for certain whether it was an exposure death or some kind of a fatal congenital defect. Regardless, I have a responsibility to try to understand what happened and why, and to do what I can to prevent the same thing happening again. My responsibility is at the same time to the successful operation of the ranch business and to husband the animals in my care. The two are not mutually exclusive.
I also have a responsibility to you readers to explain what I do, why I do it, and how I do it. I'm not always so good at this, but I do try.
Anyway, cattle and cold.
Cattle are mammals, as are humans. Like humans, cattle are endothermic and homeothermic; that is, they regulate their body heat via internal metabolism and have to keep that level of body heat within a pretty narrow range to survive.
In mammals the autonomic nervous system is in charge of maintaining body heat, the process of which is called thremoregulation. To do this the ANS has clever sensors distributed everywhere in the body, measuring all kinds of parameters; temperature, blood pressure, heart rate, blood chemistry, and on and on.
When the body begins to lose heat, the hypothalamus (in charge of the ANS) recognizes the situation by "reading" the body's distributed sensors. It then coordinates a series of neural and hormonal commands which cause the body to do things to compensate for heat loss and to generate more heat.
Neurologically, it causes goosebumps and shivering. Goosebumps don't do much for people, but in most other mammals, who happen to have fur coats, goosebumps actually erect the hair to trap an insulating layer of warm air. Involuntary shivering generates muscle heat to help replace warmth lost to the cold.
At the same time hormonal commands cause enzyme cascades which ramp up cellular metabolism throughout the body. As the cells increase their activity they generate more heat. They also require more nutrients, so other hormonal/enzymatic cascades free up carbohydrates (sugars) and lipids (fats) to stoke the cellular fires.
Now if the body continues to cool, new neural signals are sent out which cause the blood vessels closest to the skin to constrict. This serves to keep warm blood away from the relatively colder surface of the body, and also conserves warmth around the vital organs in the core of the body.
A well nourished mammal can usually strike a balance between heat loss and heat manufacture/retention. Mammals are designed for this and we do it all the time. We can survive and thrive in very cold temperatures.
There can be complications though.
If a human's clothing gets soaked it loses much of it's ability to insulate. The same is true of a mammal's fur coat. Heat is lost that would otherwise be conserved. Add in some wind, and prodigious quantities of heat will be wicked away. This can be a recipe for disaster.
Even when cold and wet though, so long as the body can generate heat a bit faster than it's lost, all can be well in the end. Eventually body heat will dry clothing or fur, and things will return to a livable balance.
But for the body to generate heat, it must have enough stored energy to metabolize.
Mammals can survive remarkable extremes of cold. We humans usually don't have to do this because we have ways of keeping our immediate environment warm; furnaces, car heaters, etc. But lacking these, so long as we're properly nourished, clothed and sheltered from wind and wet we can easily survive extended exposure to sub-zero temperatures.
And that is, in a nutshell, how cattle survive the cold. My job as a rancher is to make sure they are nourished and have a way to shelter from extremes of wind and wet. In those situations where there is too much cold, wind and wet, and not enough nutrition, cattle will die. Fortunately, those situations are rare and cattle are incredibly tough and adapted to living in nature. It's seldom a big problem.
|Non-melting snow on these cows proves the efficacy of their hair coat insulation.|
Things are a little bit different when it comes to newborn mammals. I'm talking specifically about cattle, but there's really not a lot of difference between newborns of any mammalian species. We're accustomed to human babies being born in hospitals with incubators and fetal monitors and lots of staff rushing around, but there was a time, not so very long ago, when human babies were born at home with only the mother coordinating assistance. And not long before that, home might have been a tent or a cave or a clearing in the forest. The fact that humans survived as a species in the absence of hospital delivery tells us that there is probably something innately survivable about unassisted parturition!
When mammals are born they experience a huge environmental and metabolic change. In the womb thermoregulation is taken care of by the mother's body. Oxygen and nutrition are provided via the placenta and umbilicus, as is waste disposal. Many of the fetus' organs are functioning, such as the heart and circulatory system and brain and nervous system. But many of the organs are dormant, such as the respiratory system and the digestive tract.
At birth the newborn has to begin regulating its own body heat, begin breathing, begin metabolizing stored energy, and begin to take in and digest food to fuel the whole shebang.
When a calf is born in the cold it has to do all of these things pretty quickly.
It's born wet and begins to shed warmth immediately. The calf's autonomic nervous system immediately kicks into high gear. Muscles under the skin erect still-wet hairs (goosebumps) and deeper muscles begin to shiver. Its diaphragm begins to expand and contract, air rushes in and out, oxygen and carbon dioxide begin to be exchanged.
It takes a lot of energy to do these things. The first dose of energy comes from carbohydrates -- blood sugar already present and circulating. But that's a limited source. At the same time the calf's cells are burning glucose, hormonal and enzymatic cascades begin the process of metabolizing adipose tissue. Some of this is white fat, and some is brown fat. In very simple terms, white fat becomes ATP while brown fat is metabolized rather directly into heat. Metabolizing fat is far more complex than that, but it's a good first approximation.
Anyway, just as blood sugar is limited in the neonate, so is the quantity of available adipose tissue. Sooo...
The calf very quickly struggles to its feet, totters toward the udder, and begins to ingest colostrum. This is the first milk that the mother produces and it's loaded with sugar, fat and immune factors.
Once the calf gets dried off and begins digesting and metabolizing a belly full of colostrum it's in good shape. But it only has limited time and internal resources to accomplish this first, vital task.
|This calf is fine. He's dry and the crusted snow on his back proves that his hair coat is insulating him from the cold. A human wouldn't like this experience, but it's all part of being a mammal living in the great outdoors.|
If the calf doesn't get up and nurse, it will die. And even if it does get up and nurse, if it loses heat faster than it can make heat, it will die.
|This calf is not fine. He's wet. His hair coat isn't insulating. He's fixin' to die.|
Fortunately, there are things the rancher can do to help. Chief among these are to provide shelter, help the calf dry off, provide supplemental colostrum via a bottle or stomach tube, and if necessary, provide an external source of heat to slow or halt the rate of heat loss.
|But he didn't!|
Looking back to the calf I lost, he showed me all the signs I've learned to expect of a healthy newborn. He was breathing, shaking his head, and already working on getting to his feet. He should have got up, should have nursed, and should have been fine, just like the heifer who was born at roughly the same time.
I don't know for sure what happened, but if it was a simple matter of needing just a bit of help, I could have provided that. Therefore I should have checked on the little guy at least one more time instead of simply making the assumption.
So there you have it, a little peek at what I do and some of the things I have to consider.
Oh, and by the way...
We've been talking about mammals, which are endothermic/homeothermic. There are also creatures which are ectothermic/poikilothermic, deriving body heat from mostly external sources and having the ability to survive a wide range of body heat. Things like reptiles and amphibians. On a cool summer morning, reptiles, for instance, will slowly and lethargically make their way into the sunlight and bask until their body comes up to a warmer temperature. Once up to temperature their metabolism picks up and they become more active.
But endothems can also benefit from external sources of heat. I can put a chilled calf in the bathtub, for instance, and humans can turn up the furnace.
And on a cold, still day, cattle can stand in the sunshine, aligning themselves so as to expose the maximum body surface to the suns warming rays. Every little bit helps. This also answers the riddle of why my cows were all facing northeast or southwest yesterday morning. They were at it again this morning.