GonaConTrial in Heifers and bull calves (R12/3145)

Summary

The nature of beef production in northern Australia often makes it difficult to keep different classes of cattle (e.g. breeding and non-breeding heifers and cows) as separate herds and it is also difficult to tightly control the dispersal of bulls, both within and between properties. This creates problems with the prevention of pregnancies in heifers and cows that are surplus to breeding requirements and are deemed ‘turn-off’ animals. The solution has been surgical intervention (spaying) to prevent pregnancies and it is estimated that 400,000 to 500,000 animals, or potentially more, are spayed each year in northern Australia. All spaying techniques are invasive and can have unintended production and welfare outcomes. Accordingly, the beef industry is seeking to identify and introduce practical and cost effective technology to replace spaying.
Gonadotrophin releasing hormone (GnRH) has a fundamental role in reproduction both in females and males and the neutralisation of GnRH in blood has received considerable attention as an alternative to spaying and castration.
This project investigated the utility of the immunocontraceptive vaccine GonaCon™ to induce neutralising anti-GnRH antibodies in heifers and thereby suppress ovarian activity long-term. It was found that double vaccination with GnRH was required to induce significant anti-GnRH antibody titres and achieve long-term suppression of ovarian activity (330 days and potentially longer) in heifers.
The GonaCon™ vaccine incorporates attenuated Mycobacterium avium (M. avium) cell wall components which is important in generating an immune response. Mycobacterium avium and closely related organisms are endemic in many regions globally and the GonaCon™ vaccine relies on pre-expose to M. avium and/or related organisms so that immune memory is evoked when individuals are vaccinated with GonaCon™. The ensuing immune response to M. avium is accompanied by an immune response to a GnRH conjugate also in the vaccine, which results in the generation of anti-GnRH antibodies. This rationale for the formulation of GonaCon™ has resulted in strong immunocontraceptive responses in wildlife, domestic and production animals, primarily in North America but also in southern Australia (Canberra) in kangaroos, after single vaccination with GonaCon™. Mycobacterium avium paratuberculosis is the causative agent for Johne’s Disease which occurs in southern Australia and the failure of heifers in southern Queensland to show a response to single vaccination with GonaCon™ confirmed that the Johne’s organism is not prevalent in northern Australia.
The response to double vaccination with GonaCon™ in heifers was not consistent and 6/9 heifers had significant anti-GnRH antibody titres after secondary vaccination and 5/9 showed long-term suppression of ovarian activity. It was concluded that the doses of GonaCon™ used for primary and secondary vaccination were likely marginal for a consistent and repeatable response in cattle.
Therefore, the recommendation from the project is that higher doses of GonaCon™ are investigated. GonaCon™ should be further investigated in cattle given that the evidence from the project is that a long-term immunocontraceptive response can be evoked in cattle if significant anti-GnRH antibodies are induced.
Also, the neutralisation of GnRH with a vaccine is not a gender-specific approach and the same technology would have application in both female and male cattle.