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Gonadotropin-releasing hormone is intermittently released from the hypothalamus in consistent patterns from before birth to final maturation of the hypothalamic-pituitary-gonadal axis at puberty. Disruption of this signaling via GnRH vaccination during the neonatal period can alter reproduction at maturity. The objective of this study was to investigate the long-term effects of GnRH-antibody exposure on reproductive maturation and function in elk calves passively exposed to high concentrations of GnRH antibodies immediately after birth. Fifteen elk calves (eight males and seven females) born to females treated with GnRH vaccine or sham vaccine during midgestation were divided into two groups based on the concentration of serum GnRH antibodies measured during the neonatal period. Those with robust (>15 pmol (125)I-GnRH bound per mL of serum) titers (N = 10; four females and six males) were designated as the exposed group, whereas those with undetectable titers (N = 5; three females and two males) were the unexposed group. Onset of puberty, reproductive development, and endocrine function in antibody-exposed and unexposed male and female elk calves were compared. Neonatal exposure to high concentrations of GnRH antibodies had no effect on body weight (P = 0.968), endocrine profiles (P > 0.05), or gametogenesis in either sex. Likewise, there were no differences between groups in gross or histologic structure of the hypothalamus, pituitary, testes, or ovaries. Pituitary stimulation with a GnRH analog before the second potential reproductive season induced substantial LH secretion in all experimental elk. All females became pregnant during their second reproductive season and all males exhibited similar mature secondary sexual characteristics. There were no differences between exposure groups in hypothalamic GnRH content (P = 0.979), pituitary gonadotropin content (P > 0.05) or gonadal structure. We concluded that suppressing GnRH signaling through immunoneutralization during the neonatal period likely does not alter long-term reproductive function in this species., (Published by Elsevier Inc.)

Fertility control offers a potential alternative to traditional methods for regulating the growth of overabundant wild ungulate populations. However, current technology is limited due to practical treatment application, undesirable side-effects and economic considerations. A promising non-steroidal, non-immunological approach to contraception involves the use of a potent GnRH agonist. Two experiments were conducted to evaluate the effectiveness of a GnRH agonist (leuprolide) for controlling fertility in captive female wapiti and to assess physiological and behavioural side-effects of the treatment. In Expt 1, the optimum dose of agonist treatment was determined by measuring serum LH response of eight female wapiti to four formulations of leuprolide (0, 45, 90 and 180 mg) administered as a subcutaneous (s.c.) bioimplant. In Expt 2, the effects of leuprolide on wapiti pregnancy rates, duration of suppression of serum LH and progesterone secretion, and short-term behavioural and physiological side-effects were evaluated. All concentrations of leuprolide in Expt 1 were equally effective in reducing serum LH to non-detectable values throughout the 130 day trial. In Expt 2, leuprolide administered before the breeding season was 100% effective at preventing pregnancy in treated females. Serum LH and progesterone were reduced to baseline values by day 92 and remained at this concentration for 195-251 days after treatment, and returned to pretreatment concentrations in the following breeding season. Reproductive behaviour rates were similar for treated and untreated wapiti for all behaviour categories for both the breeding and post-breeding seasons. Haematology and blood chemistry parameters of treated and un-treated females were similar, and seasonal intake and body weight dynamics appeared normal. In conclusion, leuprolide is a safe, effective contraceptive agent and can potentially suppress fertility in female wapiti for one breeding season.

Diseased animals may exhibit behavioral shifts that increase or decrease their probability of being randomly sampled. In harvest-based sampling approaches, animal movements, changes in habitat utilization, changes in breeding behaviors during harvest periods, or differential susceptibility to harvest via behaviors like hiding or decreased sensitivity to stimuli may result in a non-random sample that biases prevalence estimates. We present a method that can be used to determine whether bias exists in prevalence estimates from harvest samples. Using data from harvested mule deer (Odocoileus hemionus) sampled in northcentral Colorado (USA) during fall hunting seasons 1996-98 and Akaike's information criterion (AIC) model selection, we detected within-yr trends indicating potential bias in harvest-based prevalence estimates for chronic wasting disease (CWD). The proportion of CWD-positive deer harvested slightly increased through time within a yr. We speculate that differential susceptibility to harvest or breeding season movements may explain the positive trend in proportion of CWD-positive deer harvested during fall hunting seasons. Detection of bias may provide information about temporal patterns of a disease, suggest biological hypotheses that could further understanding of a disease, or provide wildlife managers with information about when diseased animals are more or less likely to be harvested. Although AIC model selection can be useful for detecting bias in data, it has limited utility in determining underlying causes of bias. In cases where bias is detected in data using such model selection methods, then design-based methods (i.e., experimental manipulation) may be necessary to assign causality.