Gestation Lengths of Northern Versus Southern White-tailed Deer

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Mark K. JohnsonProducers and managers of deer work toward improved animal performance just as those who produce livestock. For deer, this can involve relocating animals from one part of the country to another in an effort to improve animal genetics and deer characteristics, such as size, antler development and reduced disease problems. During the last decade the problems associated with genetic mixing, controlled breeding and relocating northern deer to southern states have been the focus of a research program at the LSU AgCenter’s Idlewild Research Station. Because of the differences in weather patterns and seasons, researchers need to know whether gestation lengths of northern deer are similar enough to those of southern deer to avoid breeding problems.

To estimate peak rutting for white-tailed deer populations, biologists sample gravid does during late winter and spring to examine fetuses. They use of the length of the fetus to estimate age in days since conception. However, no data have been available for the population of northern deer being studied at Idlewild. Thus, LSU AgCenter researchers conducted an experiment to determine whether average gestation periods of white-tailed deer from different geographic regions differ significantly.

All deer in the experiment were acquired as fawns and donated by conservation officers from Missouri and Louisiana. Sixty-eight Missouri does, 27 Louisiana does and six Missouri bucks were used. Before breeding, all does were fitted with a Heat Watch system (DDx, Inc.), which was designed to record breeding in cattle remotely. This estrus detection system uses transmitters sewn into patches that are then secured to the rear of each doe with a contact adhesive. A remote computer records signals when a buck mounts a doe. When multiple mounts occur, it is assumed that the last mounting was the conception date. Gestation lengths were determined by observing all births for each bred, captive doe.

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Results of the study indicate that neither breeding dates nor gestation lengths were dramatically affected by age of the doe (yearling versus adult). Fawns occasionally breed, but fawns were not used in this experiment. The average Missouri doe bred a month or more earlier than the average doe from Louisiana. Missouri fawns were therefore born earlier than Louisiana fawns (Table 1). Gestation lengths were not affected by litter size or sex of fawn (Table 2). Origin of doe slightly affected gestation length, with the Louisiana deer gestating a few days longer than those from Missouri. However, Louisiana does also gestated during slightly warmer weather. Gestation in warmer weather could have reduced feed intake and subsequently slowed fetal development, increasing gestation length.

Even though sample sizes in many studies such as this one are small, the results of these studies indicate breeding periods and gestation lengths of northern and southern deer are very similar (193 to 205 days). Even though Louisiana does in this study bred nearly a month later (varies with herd) than Missouri does, bucks from either state will breed when the does are ready. Therefore, data, to date, indicate that producers who desire to improve the genetic performance of their white-tailed deer will not encounter breeding problems related to differences in breeding stocks. Mark K. Johnson, Professor, School of Renewable Natural Resources, LSU AgCenter, Baton Rouge, La.(This article was published in the spring 2002 issue of Louisiana Agriculture.)

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