181 Effect of systemic administration of β-nerve growth factor during the periovulatory stage on corpus luteum development and function in dairy heifers

There is evidence that the β-nerve growth factor (β-NGF) present in seminal plasma in llamas and alpacas exerts a luteotrophic effect in camelids and other species after systemic administration. The main goal of this study was to determine whether systemic administration of purified llama β-NGF before or after the preovulatory LH peak induced by oestradiol affects corpus luteum (CL) function in dairy heifers. Semen was collected from adult llamas using an ovine artificial vagina. Seminal plasma β-NGF was purified using a combination of hydroxylapatite and gel filtration chromatography. Holstein-Friesian heifers (n = 24) weighing between 320 and 330 kg received 2 mg of oestradiol benzoate (EB) plus an intravaginal progesterone device (DIB^®, Zoetis, Day = 0). On Day 8, the device was removed along with an intramuscular (i.m) dose of 500 µg of cloprostenol (Boviprost^®, Anasac), and 1 mg of EB was given i.m at Day 9 and then heifers (n = 8/per group) were randomly given an i.m. injection of either: (i) phosphate-buffered saline ([PBS] Control), (ii) 1 mg of purified β-NGF at the time of EB treatment (Pre-LH group), or (iii) 36 h after EB treatment (Post-LH group). Ovaries were examined daily by B-Mode ultrasonography from DIB removal to ovulation (disappearance of dominant follicles) and then by Power Doppler at days 2, 4, 6, 8, 10, 12, 14, 16, and 18 after ovulation to determine CL vascularisation. Blood samples were collected every 4 h from DIB removal until ovulation to determine plasma LH concentration and during the luteal phase for plasma progesterone concentration. Non-serial data were analysed using one-way ANOVA; CL profile development, vascularisation area, and hormone concentrations were analysed using PROC MIXED procedure in SAS. All females ovulated (100%, 24/24) after oestrus synchronisation. There was no significant difference in follicular diameter (P = 0.65) at the time of treatment nor in the maximum CL diameter (P = 0.35) after treatment. Plasma LH concentration was higher (P < 0.001) in females given β-NGF along with the dose of EB at Day 9 of the synchronisation protocol. Although the day-by-day profile CL diameter did not differ among groups (P = 0.84), heifers treated with purified β-NGF showed a significant increase in CL vascular area (P = 0.04) and plasma progesterone concentration (P = 0.001) at Day 12 and 14 after ovulation. Hence, administration of systemic heterologous β-NGF given before or after the LH peak induced by oestradiol benzoate enhances CL function.

This study was supported by Agencia Nacional de Investigación y Desarrollo (ANID) of Chile, grant Fondecyt Regular 1190980.