183 EFFECTS OF LONG-TERM NUTRITIONAL RESTRICTION ON PREOVULATORY LUTEINIZING HORMONE SURGE, LEPTIN, AND LUTEAL PHASE IN LLAMAS (LAMA GLAMA)

Abstract

The aim of the study was to determine the effect of long-term energy restriction on preovulatory LH surge and luteal phase in llamas. Mature nonlactating, nonpregnant, female llamas (n = 16) were assigned randomly to the following groups: (1) llamas received Ballica sp. hay ad libitum and 300 g d^–1 of commercial concentrate (control group, n = 8, BCS = 3.9) or (2) llamas were fed the same feed but the amount was progressively reduced from 70% to 40% of their maintenance energy requirement (MER) for a period of 87 days, until the final BCS was 2.5 (restricted group, n = 8). After 2 months and 21 days of 40% MER diet, ovarian follicular wave emergence was synchronized by transvaginal ultrasound-guided ablation of follicles ≥5 mm in diameter using a 17-ga needle attached to a 5-MHz convex-array transducer. Ten days after follicle ablation (Day 0), llamas were given an i.m. dose of 50 µg of gonadorelin acetate to induce ovulation. Frequent blood samples were taken every 30 min for 6 h and every 15 min for 1 h for plasma LH and leptin concentration measurements, respectively, immediately after treatment. Llamas were examined daily by transrectal ultrasonography for 20 days to record serial changes in the CL diameter. In addition, blood samples were taken every 2 days from Day 0 to 16 to determine plasma concentrations of leptin and progesterone. Discrete dependent variables were compared between groups by Student t-tests and continuous dependent variables were analysed by analyses of variance with repeated-measures. There was an effect of time on plasma LH concentration (P ≤ 0.001), but not an effect of group (P = 0.1) or interaction (P = 0.6) after gonadorelin acetate treatment. Plasma leptin concentration was lower in llamas from the restricted than that of the control group after gonadorelin treatment [effect of time, group (P ≤ 0.01), and interaction (P ≤ 0.01)]. The maximum diameter of the CL and plasma progesterone concentration were lower in the restricted than in the control group, and both variables were affected by group (P ≤ 0.01, P ≤ 0.02), and day (P ≤ 0.001, P ≤ 0.001, respectively). Plasma leptin concentration was lower in the restricted than that of the control group during the entire experiment. In conclusion, long-term nutritional restriction affected negatively CL diameter, progesterone secretion, and leptin plasma concentration in llamas. The differential response of leptin to gonadorelin acetate treatment could reflect a subfertlity-nutritional induced problem related with steroidogenesis, oocyte quality, ovulation, and early embryo development processes.

Research supported by Postdoctoral Fondecyt N° 3110095.