John J Ozoga on fawn puberty

Successful Deer Management Starts With Large Healthy Fawns: Fawns Achieving Puberty

By John J Ozoga

Whether a fawn (male or female) reaches puberty and breeds in its first year might depend upon many poorly understood factors. Birth date, genetics, day length, nutrition, climate and social pressure are just a few factors likely involved in this poorly understood phenomenon. Even within the same population, the sexes seem to differ in their chances of achieving puberty.

Clearly, before any fawn can achieve puberty it must first be skeletally large and fat. A high incidence of pregnant fawns and buck fawns carrying small “infant” antlers (nubs that shed velvet, revealing small spikes, generally less than half inch long) indicates good range conditions where healthy herds are maintained below carrying capacity. This doesn’t necessarily mean that all such physically-fit individuals breed in their first year.

The highest fawn pregnancy rates occur in the Midwest farmland, where more than half of them commonly breed. Whereas only 10 percent to 40 percent reportedly breed in the Southeast. On Northern range, fewer than 10 percent of doe fawns normally breed. However, pregnancy rates may be highly variable because of climate and range quality can vary greatly over relatively short distances.

Based on our studies at Cusino, we concluded that doe fawns must achieve a certain critical fat to lean body composition to achieve puberty. Reduced photoperiod (amount of daylight in a 24 hour period) tends to trigger such important seasonal events as pelage (hair coat) change and fattening. On Northern range, body weights of doe fawns essentially become stable in midautumn because of marginal nutrition and the onset of harsh weather.

Generally, as little as a 10 percent reduction in caloric intake for fawns in autumn seriously curbs their fattening and skeletal growth. Therefore, on Northern range a natural decrease in high-energy foods, rather than decreasing daylight probably halts the doe fawn’s sexual development.

Early-born doe fawns that grow to be fat and skeletally large by autumn have the best chance of breeding, if herd density is low. However, weather, social factors, genetics, and other unknown factors can come into play and interrupt breeding.

Under certain conditions, buck fawns also can achieve puberty, but they respond to certain environmental factors differently than female fawns.

Some bucks may grow, polish and cast small “button” antlers before 1 year old. Usually, these so called “infant” antlers, which are generally less than one-half inch long, are only grown by early-born, well-nourished and otherwise healthy animals. Since high levels of the male hormone testosterone are necessary to induce “infant” antler formation, mineralization, and polishing, they are sure signs of puberty.

Most biologists contend that fewer than 10 percent of buck fawns grow infant antlers. However, Harry Jacobson reported a 20 percent rate among buck fawns in his research facilities in Mississippi, while I documented an 84 percent incidence among supplementally-fed buck fawns in northern Michigan’s Cusino enclosure.

I found that most buck fawns “rubbed out” their tiny antlers during December, after nearly all deer harvest seasons were completed. Likewise, Jacobson observed that buck fawns in Mississippi polished their infant antlers during February and March. As a result, this phenomenon may be overlooked in most free-ranging deer populations.

Interestingly, despite the high incidence of “infant” antlers recorded in the Cusino enclosure, only 7 percent of the doe fawns bred during this same time period – likely due to high deer density.

Therefore, a high incidence of “infant” antlers among buck fawns may not indicate frequent breeding among doe fawns in the same population, regardless of nutrition, as it seems the young sexes respond differently to social and density stress. Apparently, such stress can suppress breeding among young subordinate females, as in yearling does, but not necessarily the attainment of puberty among buck fawns.

Literature Cited

Ozoga, J. J. 1988. Incidence of “infant” antlers among supplementally-fed white-tailed deer. Journal of Mammalogy 69: 393-395.

Ozoga, J. J. and L. J. Verma. 1982. Physical and reproductive characteristics of a supplementally-fed white-tailed deer herd. Journal of Wildlife Management 46:281-301.

Ozoga, J. J. and L. J. Verma. 1984. Effects of family-bond deprivation on reproductive performance of female white-tailed deer. Journal of Wildlife Management 48:1326-1334.

Ozoga, J. J., L. J. Verma and C. S. Bienz. 1982. Parturition behavior and territoriality in white-tailed deer: impact on neonatal mortality. Journal of Wildlife Management 46:1-11.

Verma, L. J. 1988. Lipogenesis in buck fawn white-tailed deer: photoperiod effects. Journal of Mammalogy 69:67-70.

Verma, L. J. and J. J. Ozoga. 1980. Influence of protein-energy intake of deer fawns in autumn. Journal of Wildlife Management 44:305-314.

Verma, L. J. and J. J. Ozoga. 1980. Effects of diet on growth and lipogenesis in deer fawns. Journal of Wildlife Management 44:315-324.

Verma, L. J. and J. J. Ozoga. 1987. Relationship of photoperiod to puberty in doe fawn white-tailed deer. Journal of Wildlife Mammalogy 68:107-110.

Image IMG_1554.JPG Caption: Fawns achieving puberty before the end of their first winter is a strong indication of quality habitat.