24 EFFECT OF GNRH ON FIXED-TIMED ARTIFICIAL INSEMINATION PREGNANCY RATES OF WHITE-TAILED DEER

Abstract

During the fall 2008 breeding season in Louisiana, 2 synchronization protocols for fixed-timed artificial insemination (FTAI) in White-tailed deer were assessed. The objective was to determine if GnRH at FTAI improved pregnancy rates in White-tailed deer. White-tailed does (n = 35) with a mean body weight of 65.8 kg (range: 54.0 to 79.8 kg) and average age of 5.9 years (range: 1.5 to 9.5 years) were stratified by weight, age, and last fawning date into 2 groups. Treatment and control synchronization protocols were randomly assigned to each group. Does were synchronized with a CIDR-G device for 14 d and were then subjected to either FTAI 60 hpost-CIDR removal (control, n = 17) or 100 μg (i.m) injection of GnRH at FTAI 60 h post-CIDR removal (treated, n = 18). At insemination (AI), insemination pipette placement score (IP; 0 = at cervical os to 3 = within uterine body), mucous scores (clear/cloudy, viscous/nonviscous, or no secretions), vulva assessments (hyperemic/nonhyperemic and swollen/not swollen), and sperm progressive motility were recorded. Does were inseminated with frozen-thawed sperm (5 × 10⁷ progressively motile cells pre-freeze) from 2 fertile bucks stratified across each treatment group. Starting 28 d following AI, intact bucks (ITB) were introduced into both groups for natural mating. Pregnancy was determined via transrectal ultrasonography 73 or 80 d postinsemination. Does, confirmed pregnant via ultrasonography, had fawns within the reported gestation range of 187 to 222 days. Placentomes were visualized and measured in AI pregnancies (range: 32.7 to 56.2 mm in length), whereas pregnancies derived from ITB presented no identifiable placentomes. However, crown-rump measurements were obtainable from ITB pregnancies (range: 13.4 to 21.7 mm). Five does were not included in the final analyses as they were either lost to predators or removed because of illness. IP (1.4 ± 0.24 v. 1.3 ± 0.30; P = 0.671), mucous classifications (3.0 ± 0.35 v. 2.5 ± 0.39; P = 0.311), vulva assessments (2.1 ± 0.29, 1.7 ± 0.23; P = 0.223), and sperm motility (1.6 ± 0.16, 1.7 ± 0.22; P = 0.829) were not different for pregnant and nonpregnant AI does, respectively. Treatment did not affect AI pregnancy rates (53 v. 27%) or fecundity rates (1.6 v. 1.3 offspring/doe) for the GnRH treated and control groups, respectively. Addition of GnRH to a 14-day estrus synchronization protocol did not result in significantly higher pregnancy rates compared with controls. More studies are needed to determine the effect of GnRH on White-tailed pregnancies following FTAI protocols. We have demonstrated that differentiating pregnancies derived from AI and ITB could be accomplished by utilizing transrectal ultrasonography as early as 73 d postinsemination in White-tailed does.