13 EFFECTS OF NERVE GROWTH FACTOR-β, PURIFIED FROM BULL SEMINAL PLASMA, ON CORPUS LUTEUM FUNCTION AND CONCEPTUS DEVELOPMENT IN COWS

Nerve growth factor-β (NGF) has been identified in the seminal plasma of livestock and is required for the induction of ovulation in camelids. Until recently, it was thought to play a negligible role in species with spontaneous ovulation. On the contrary, recent studies have shown that systemic administration of NGF, purified from llama seminal plasma, was associated with larger corpus luteum (CL) diameter and higher concentrations of progesterone (P) following ovulation. The objective of the current project was to determine if systemic administration of NGF, purified from bovine seminal plasma, would improve CL formation and enhance embryonic development. Our hypothesis was that systemic administration of NGF at the time of artificial insemination in cows would lead to increased CL volume, increased P secretion, and improved expression of markers of conceptus development and maternal recognition of pregnancy. Seminal plasma was harvested from semen collected by electroejaculation in Angus cross bulls. Purification of NGF was performed using a combination of anion- and cation-exchange chromatography and gradient elution. Beef cows were randomly assigned to CONT (n = 30) or NGF (n = 30) groups and synchronized using a 7-day Co-Synch + CIDR program. At time of insemination (day 0), NGF cows received 296 µg of purified NGF, reconstituted in 12 mL of PBS, and CONT cows received 12 mL of PBS intramuscularly. Blood samples were collected from the coccygeal vein of each cow at days 0, 3, 7, 10, 14, 19, 21, 28, 31, 38, 45, and 66. Ultrasound was performed at each time point for determination of ovarian structures (day 0), corpus luteum volume (all time points), and fetus detection (day 28). Statistical analysis was performed using analysis of variance with repeated-measures in R (R version 3.2.2; https://www.r-project.org/). At day 28, 17/30 (57%) CONT cows and 21/30 (70%) NGF cows were diagnosed as pregnant (P = 0.15). At day 0, cows that later became pregnant had a larger follicular diameter (1.46 cm) than those diagnosed as open (1.16 cm; P < 0.01). Follicular diameter at day 0 did not differ significantly between CONT and NGF groups for either open (P = 0.35) or pregnant (P = 0.90) cows. CL volume in open cows was affected by day (P < 0.001) with no treatment (P = 0.84) or treatment by day (P = 0.42) interaction. CL volume in pregnant cows was affected by both day (P < 0.001) and treatment (P < 0.001), with CONT cows having a higher CL volume than NGF cows. Though NGF appeared to have an inhibitory effect on CL volume in pregnant cows, results are still pending for quantification of P, insulin-like growth factor 1, pregnancy-specific protein B, and interferon-stimulated genes, which will more accurately assess the effects that NGF may have on conceptus development. The results of this study will help us to better understand the role of the seminal plasma protein, NGF, at ovulation and determine if it can be utilised to enhance insemination programs in cattle.