Effect of Introduction of Female and Male Urine Pheromones on Estrous Cycle Length and Progestogen and Testosterone Metabolite Concentration in Captive Red River Hogs (Potamochoerus Porcus) in North American Zoos

Abstract

Captive red river hogs (RRH) have variable reproductive success yet potential causes are unknown. We hypothesized that non-breeding females would cycle or cycle more regularly and non-breeding males with low libido would increase concentrations of fecal testosterone metabolites in response to urine pheromone exposure. Female estrous cycles and progestogen metabolite (P4) concentrations and male testosterone metabolite (T) concentrations were compared between: 1) proven-breeder pairs (control(C); male n=3; female n=4), 2) new pairs (new male(NM); male n=4; female n=4), and 3) pairs exposed to pheromones (pheromone(P); male n=3; female n=3). Fecal samples were collected 3-5 times per week for a year. P animals had baseline sampling (6 months), followed by 2.5 month exposure to sow urine, 2-4 week wash-out, and 2.5 month exposure to boar urine. Fecals were extracted and assayed for P4 and T with ELISAs. Results were assessed for normality with PROC GLM (SAS, Cary, N.C.) and non-normal data transformed with repeated measures ANOVA (P4/T) or one-way ANOVA (cycles). There was a trend for P female’s estrous cycle length to elongate (P baseline: 15.7 ± 1.5 days; P post-male: 19.3 ± 3.1 days; p=0.07) and for P male T concentrations to increase (+336.1±1.4 ng/g feces) in response to male urine pheromones. Pregnancies occurred in 2/3 C, 1/4 NM, with pseudopregnancy/pregnancy loss noted in 1/3 C and 2/3 NM females. The luteal phase P4 concentration for non-pregnant females was highest in P females and lowest in NM females (P: 3945.6 ± 158.3 ng/g feces; C: 3291.6 ± 196.3 ng/g feces; NM: 2884.5 ± 144.1 ng/g feces). Overall T concentration for males was highest in P males and lowest in NM males (P: 909.6 ± 365.3 ng/g feces; C: 427.5 ± 353.8 ng/g feces; NM: 325.4 ± 283.2 ng/g feces). A season and treatment interaction (p<0.0001) for males and females, and acyclicity of females from August-December suggest that season confounded the results. Females housed with pregnant females were acyclic or experienced pseudopregnancy/pregnancy loss, suggestive of female reproductive suppression. In conclusion, urine pheromones may manipulate reproduction in captive RRH and consideration of the number of female RRH in housing is warranted.