here is an article from the canadian cattlemen mag
I also googled and gastro problems came up
Reasons for hair loss Dr. Ken Linde | Back to Vet Advice
A Cattlemen subscriber recently wrote: We have had a calf born and after only two weeks he has lost 80 per cent of his hair, mostly along his spine and head and legs. It is very sad. None of the other cows or calves is suffering from this. Someone mentioned there is a rare allergy to the sun. Have you ever heard of this? What is it called?
Human hair is hardly indispensable, seen more as a cosmetic advantage than environmental protection. In contrast, for an animal to become permanently bald, it is indeed a sad situation since hair provides many functions for the animal, the most important of which is insulation against cold, wind, wet, and sunlight. A hairless animal doesn't survive long.
Fortunately, most cases of extreme hair loss in calves are temporary.
Hair loss due to sickness
In the situation that the writer describes, the hair loss was quite possibly a sequel of an unnoticed high fever due to illness. For example, it isn't unusual for a calf that has just recovered from a bad case of the scours (diarrhea) to subsequently lose a large amount of its coat.
Hair has a lifecycle of its own that can be divided into various phases, one of which is called the resting phase. Under the stress of a high fever and dehydration, the hair follicles go into the resting phase, and stop producing hair. Without new growth the hair falls out and the animal quickly becomes bald. Often by the time the hair loss appears the calf is over the fever and appears to be normal other than the baldness. Characteristically there is no itchiness associated with the baldness, and only individual animals are affected.
Treatment consists of treating the underlying cause of the fever and then keeping the animal from being exposed to excessive cold, dampness or sun. Within three to four weeks the calf grows a new hair coat and goes on to live a normal life with a luxuriant covering.
Photosensitivity
The writer suspects an allergy to the sun may have caused her calf's condition. Although skin reactions to the sun (photosensitivity) do occur in cattle, I have never seen this occur in a very young calf and have not read any reports of inherited photosensitivity in cattle. In older cattle photosensitivity usually occurs if the liver is not functioning properly (for instance, due to liver abscesses). Plant pigments are not metabolized and excreted properly, and end up being activated in the skin tissue by sunlight. Certain weeds can also be a primary cause of this condition.
In these cases hair loss is the least of the animal's worries. This is not just sunburn. Typically the skin is severely blistered particularly around the muzzle and eyes, even to the point of the skin sloughing off of the animal. A high fever and severe pain cause the animal to be anorexic, and without treatment many of the affected animals will die. With treatment (shade, anti-inflammatory/pain relief medication, and antibiotics) the skin can recover, and the hair grows back.
Inherited defects
In rare cases, hairlessness in young calves can also be present as a birth defect. Some six known forms of congenital hairlessness occur in cattle, and often are associated with other defects, many of which are fatal. There are reports, mostly in the dairy breeds of calves born without hair, yet with normal, supple skin. Kept out of the sunlight these calves survive, but are not thrifty. I also have seen two cases of inherited hair loss in Holsteins that shows up two to three months after birth as a gradual loss of hair, while the animal is otherwise completely normal. In Herefords, there is an inherited condition in which the hair is very poorly developed but the animal doesn’t go completely bald.
External parasites
Always think of skin parasites anytime you see hair loss in cattle, because the majority of the time lice and mites are the most common culprits. The difference is of course that these bugs are associated with itchiness and rubbing. It is also a group problem, not just an individual animal condition.
