Evaluation of Stress Accompanying Immunocontraceptive Vaccination in Donkeys

Abstract

The overpopulation of donkeys is recognized as a problem in many parts of the world. The main concerns with uncontrolled donkey populations are habitat degradation and competition for feed resources between donkeys and other species. One of the most effective and humane solutions is the use of immunocontraception. Therefore, this study sought to evaluate the stress imposed by the use of two formulations of a zona pellucida (ZP) vaccine, a recombinant (reZP) and a native porcine (pZP) vaccine, both formulated with a Freund's adjuvant. The stress was objectively measured using fecal cortisol concentrations and physical examination parameters at fixed points before and after vaccination. We hypothesized that fewer changes in physical exam parameters and lower fecal cortisol concentrations would be stimulated in jennies treated with the reZP vaccine due to the selection of specific proteins. Twenty-five reproductively sound jennies were randomly assigned to reZP (n = 9), pZP (n = 8) or control (n = 8) groups. The vaccines were administered at five-week intervals. Physical exam parameters and body wall thickness of injection sites were recorded for each jenny for four days post-injections. Fecal samples were obtained every other day from day 0 (first vaccination) through day 6 and on days 35 to 41 after booster. Injection site reactions were common in all groups with the reZP and pZP groups being overrepresented. Lameness was observed in the pZP and reZP groups that were affected by injection site reactions and open abscesses. The present study showed an increase in fecal cortisol concentrations within 4 days after the first vaccination with ZP vaccines and, thereafter, a decrease in cortisol 35 days later after the second vaccination, especially in donkeys with open abscesses. Our results suggest that acute stress (increased cortisol) was induced after the first vaccination, and chronic stress (decreased cortisol) occurred thereafter in association with open abscesses. In conclusion, reZP and pZP formulated with Freund's adjuvant induced local inflammatory reactions with a differential degree of acute and chronic stress in donkeys.

Keywords: Equus asinus; animal welfare; contraceptive; feral; overpopulation.

Figure 1

A fecal sample from a control male donkey was extracted and subsequently diluted (1×, 2×, 4×) with assay buffer and analyzed. Visually, various dilutions paralleled the cortisol reference standard curve with an overall CV of 21.2% that encompassed the range of dilutions.

Figure 2

Body wall thickness (cm) of the injection site measured by an ultrasonographic image of donkeys after vaccination with recombinant zona pellucida (reZP, n = 9), porcine zona pellucida (pZP, n = 8), or Freund’s adjuvant (Control, n = 8). (A) body wall after the first vaccination. (B) Body wall after the booster. Day 0, day of vaccination. Data are expressed as the mean (±SEM). Different superscripts denote effects of time (^a,b,c) (p < 0.05).

Figure 3

Changes in fecal cortisol concentrations (pg/g) in donkeys after the first vaccination (day 0) and the booster (day 35) with recombinant zona pellucida (reZP, n = 9), porcine zona pellucida (pZP, n = 8), or Freund’s adjuvant (Control, n = 8). Cortisol concentrations from each day were compared with the cortisol concentration at day 0. Different letters denote effects of time (^A,B) and differences between groups within each time point (^a,b) (p < 0.05).

Figure 4

Mean (±SEM) changes in fecal cortisol concentrations (pg/g) in donkeys that did not develop or had a closed abscess after the first (day 0) or second (day 35) injection of zona pellucida vaccine (n = 17) or Freund’s adjuvant (n = 8). Different letters denote effects of time (^A,B) and differences between groups within each time point (^a,b) (p < 05).