Factors Affecting Pregnancy in Free-ranging Elk, Cervus elaphus nelsoni, in Michigan

Authors

  • Jessica R. Piasecke Department of Fisheries and Wildlife Sciences, New Mexico State University, Las Cruces, New Mexico 88003
  • Louis C. Bender Department of Extension Animal Sciences and Natural Resources, Department of Animal and Range Sciences, and Department of Fisheries and Wildlife Sciences, New Mexico State University, P.O. Box 30003MSC 4901, Las Cruces, New Mexico
  • Stephen M. Schmitt Wildlife Disease Laboratory, Michigan Department of Natural Resources, 4125 Beaumont Road, Lansing, Michigan

DOI:

https://doi.org/10.22621/cfn.v123i3.969

Keywords:

Elk, Cervus elaphus, age, pregnancy, mass, lactation, Michigan

Abstract

Uncertainty exists as to which factors are most closely related to probability of pregnancy in Elk (Cervus elaphus), which thresholds are key for managers who want to assess the potential productivity of free-ranging Elk herds, and whether these thresholds vary among populations. We examined relationships among pregnancy, age, and mass for 513 harvested free-ranging Elk in Michigan, and compared relationships with other published models and with thresholds derived from other free-ranging and penned populations to see if relationships were consistent among populations. Pregnancy rates varied (chi22 = 136.3; P < 0.0001) among yearling (0.30), prime-aged (2.5-11.5-year-olds; 0.88), and old (> 12.5-year-olds; 0.60) cows. Probability of pregnancy in adult cows was related to mass (chi2 = 7.4; P = 0.006), age (chi2 = 12.6; P = 0.0004) and age class (chi2 = 16.4; P < 0.0001), but not to lactation status (chi2 = 0.4; P = 0.515); pregnancy was also positively related (chi2 = 15.8; P < 0.0001) to mass in yearlings. Probability of pregnancy increased 1.02× and 1.04× for each 1 kg increase in body mass of adult and yearling cows, respectively, and prime-aged cows were 4.9× more likely to conceive than old cows. Compared to thresholds derived primarily from penned or farmed Elk, both adult and yearling free-ranging Elk in Michigan and elsewhere were able to achieve higher levels of pregnancy at lower body mass. Thresholds also varied among free-ranging Elk populations. Given variation among populations, managers should calibrate mass-pregnancy relationships for their respective populations to determine whether condition is potentially limiting pregnancy in their populations.

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