β-nerve growth factor is a major component of alpaca seminal plasma and induces ovulation in female alpacas

Ovulation in camelids is induced by an unidentified protein in the seminal plasma of the male termed 'ovulation-inducing factor'. This protein has been reported to be a 14-kDa protein under reducing conditions, which, when purified from seminal plasma, induces ovulation in llamas. The identification of this protein and investigation of its potential to induce ovulation in camelids may aid the development of protocols for the induction of ovulation. In the present study, alpaca seminal plasma proteins were separated using one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the most abundant protein of 14 kDa was identified as beta-nerve growth factor (beta-NGF) by liquid chromatography mass spectrometry. Female alpacas (n = 5 per group) were given intramuscular injections of: (1) 1mL of 0.9% saline; (2) 4 mu g buserelin, a gonadotrophin-releasing hormone agonist; (3) 2mL alpaca seminal plasma; or (4) 1mg human beta-NGF. Ovulation was detected by transrectal ultrasonography 8 days after treatment and confirmed by plasma progesterone concentrations. Ovulation occurred in 0%, 80%, 80% and 80% of animals treated with saline, buserelin, seminal plasma and beta-NGF, respectively. Treatment type did not affect the diameter of the corpus luteum, but plasma progesterone concentrations were lower in saline-treated animals than in the other treatment groups owing to the lack of a corpus luteum. The present study is the first to identify the ovulation-inducing factor protein in alpacas. beta-NGF successfully induces ovulation in alpacas and this finding may lead to new methods for the induction of ovulation in camelids