Utilisation of Leucaena leucocephala foliage, toxicity risk and management in ruminant breeding production systems

Abstract

<p>Leucaena has been shown to provide good nutritional value for ruminant fattening systems all over the world. However, there is still some debate concerning its suitability and safety for ruminant breeding stock despite the new paradigm regarding the detoxification mechanisms of leucaena toxicity that has been revealed recently. Therefore, the objectives of this thesis were to: 1) examine the application of this novel theory of detoxification in leucaena production systems, with special attention to breeding stock" 2) To clarify how breeding ruminants are susceptible to the effects of leucaena toxins" 3) to determine whether leucaena toxin effects on fertility could be mitigated by up-regulating detoxification processes, and 4) to identify methods for supporting or up-regulating detoxification mechanisms. One literature study, a survey and two controlled experiments were conducted to address these objectives.</p> <p>A literature review (Chapter 2) identified the effects of leucaena feeding, and also the possible mechanisms involved to obstruct the reproductive function of breeding ruminants. A survey (Chapter 3) clarified the role and the utilisation of leucaena in breeding enterprises as well as the impact of leucaena toxicity in breeders. Next, a trial with rams (Chapter 4) investigated the impact of leucaena toxins, mimosine and DHP on male fertility. Meanwhile, the cassava trial (Chapter 5) was conducted to test a potential strategy to deal with DHP toxicity and also to support the current paradigm of leucaena detoxification. </p> <p>The key findings of this thesis are: </p> <p>Leucaena is crucial to provide cattle in the tropics, particularly in eastern Indonesia, with a high-quality feed in order to improve performance and promote more intensive, productive, and profitable cattle enterprises. Leucaena was mostly used by farmers for breeding cattle as a strategic feed resource during the dry season and at particular periods of pregnancy, whereas the majority of their focus was on fattening cattle solely.</p> <p>Leucaena toxins can temporarily impair male fertility by adversely affecting sperm motility and proximal cytoplasmic droplet abnormalities for 5 - 7 weeks after exposure in leucaena-naive ruminants, but the mechanism is not 2,3-DHP. Two possible mechanisms are proposed as the cause of the leucaena-induced reduction in sperm quality observed in this thesis. Firstly, mimosine, which acts as an antimitotic agent by targeting germ cells involved in the mitotic proliferation of the sperm production cycle (spermatogenesis). Another mechanism could be the action of phytoestrogens in leucaena foliage, which can increase germ cell death or apoptosis, resulting in decreased sperm motility and testosterone levels. </p> <p>Glucuronic conjugation in the liver is essential for detoxifying leucaena toxins, and it can be upregulated very quickly even in the absence of highly digestible energy sources in the diet.</p> <p>Indigenous microbes in the rumen of animals naïve to leucaena cannot quickly and completely degrade mimosine and DHP into non-toxic substances. Therefore, before introducing leucaena for the first time, this thesis strongly suggests inoculating truly naive animals with leucaena-toxin-degrading bacteria to enhance the efficacy of mimosine/DHP-degrading bacterial populations to rapidly and thoroughly degrade mimosine into less toxic products for further detoxification in the liver.</p>