Timing of Gelding

Q. Is there any loss of body size or development from early gelding? One of our local veterinarians will not geld before the horse is at least a year old. I have a 7-year-old who was gelded prior to weaning and is the same size as his fully grown genetic siblings. I thought that early gelding was proven to be no problem and that waiting for them to mature is an old wives' tale. Any research on this topic?

Phyllis, via e-mail

A. The age at which a stallion is castrated depends on many factors, but managerial convenience usually is the determining factor. Most stallions are castrated shortly after they reach puberty, when the owner finds masculine behavior of the stallion to be intolerable. The effect that castration and its timing have on behavior, physical appearance, and the incidence of various diseases has been studied extensively in cats and dogs, but the same is not true of horses.

Although I am not aware of any studies examining the effect of castrating stallions before or after puberty on growth and development, studies performed on cattle and goats have shown that early castration prolongs growth because castration delays closure of the long bone growth plates. The same may be true for stallions castrated before puberty or at least before the long bone growth plates have closed. The age at which colts reach puberty varies considerably between and within breeds. One study found that the mean age at which American Quarter Horse colts reached puberty was about 68.68 ± 12.7 weeks and ranged between 55 and 101 weeks (Cornwell et al., 1973). The growth plates of the long bones that have the most influence on the horse's growth close at various times, and these times probably vary among breeds. In another study, growth from the distal (bottom) end of the cannon bones and pasterns of Thoroughbred-Quarter Horse crosses ceased when the horses were 10 weeks old, but growth from the distal end of the radius (forearm bone) was continuous, though declining, until the horses were about 60 weeks old (Fretz et al., 1984). Castrating a horse before growth from the distal aspect of the radius or tibia (the long bone above the hock) begins to slow is likely to increase his height, but whether this increase is likely to be substantial is unknown.


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