Winter Q&A With Seth Nagy

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Last week we had frigid temperatures. The freezing conditions sparked two interesting questions.

Question: What are the two trees growing next to highway 321 just north of Lenoir? They look like lemon trees. orange tree They have big, bright yellow fruit hanging from the limbs and on the ground.

Answer: These trees are not lemon trees. The trees are hardy oranges or trifoliate oranges. The scientific name is Poncirus trifoliata. These trees are native to Central and Northern China. They can survive extremely cold temperatures.

Although the trifoliate orange is not in the Rutaceae, or citrus, family, they are a close relative. In fact, the trifoliate orange can be grafted to members of the citrus family. Many commercial citrus trees – grapefruit, orange, lime, and lemon – are grafted onto trifoliate orange rootstock. It is recommended that citrus trees planted north of Gainesville, FL be grafted to trifoliate orange rootstock. Using the trifoliate rootstock imparts some cold hardiness to the entire plant. However, it will not survive freezing temperatures.

Besides the bright yellow fruit, trifoliate orange trees also have very, very sharp thorns. There are several named cultivars and hybrids of the trifoliate orange. Some of the cultivars were developed strictly as rootstock for the citrus industry, some for ornamental value, and some for fruit quality.

The more popular varieties of these trees for home owners are dwarfed species. Most of these have interesting, curved thorns which look very intimidating. These trees can be planted as a hedge or planted singly. Although these trees are interesting, some consider them to be an invasive plant. Sales of trifoliate orange are restricted in California, Texas, Florida, Arizona, Puerto Rico, and Europe.

Question: How do calves survive when born in freezing weather?

Answer: Calves are able to survive, and even thrive, in cold temperatures because they possess something called brown fat. Brown fat, or brown adipose tissue, is a special type of fat cell. These cells are actually reddish brown in color rather than the typical white fat cell. Brown fat is located inside the body cavity around the kidneys. The tissue is colored because of the blood vessels surrounding the fat cells and the mitochondria that are packed inside the cells. The unique thing about brown fat is its ability to produce heat. This process is called non-shivering thermogenesis. And this is why calves can survive when born into freezing conditions.

A healthy 65 pound calf has about one pound of brown fat when it is born. The fat is burned to help the calf maintain its body temperature when air temperatures drop below 56 degrees. In freezing weather, the brown fat is quickly consumed when the calf is working hard to maintain its body temperature at 100 degrees.

Ideally, the calf should nurse within the first 30 minutes of being born. When the calf initially nurses the cow, it is consuming milk called colostrum. Colostrum is sometimes called first milk. nursingcowThis first milk is thick and yellowish-brownish. It typically has higher levels of protein and fat, as well as special antibodies. These antibodies help the calf’s immune system fight diseases for the first few months of life.

Fat that is in the colostrum is absorbed into the calf’s body and is metabolized directly by the  brown fat cells to produce heat. The energy that is burned in the brown fat cells is replaced when the calf nurses. If the calf does not nurse, then the brown fat energy reserves can be depleted and the calf may not be able to maintain its body temperature.

Soon, newborn calves may not be the only ones benefiting from brown fat. Scientists at Purdue University have been experimenting with nanoparticle-drugs that stimulate the body to create brown fat. Brown fat has the potential to increase metabolism and lower body weight. This could ultimately be a way to use cellular reprogramming to combat obesity and type II diabetes in humans.

For answers to your agriculture questions, call the Caldwell County Extension Center at 828-757-1290 or visit us online anytime at