Efficacy, persistence and presence of Synergistes jonesii in cattle grazing leucaena in Queensland: on-farm observations pre- and post-inoculation

Abstract

A study of eight commercial cattle herds grazing leucaena (Leucaena leucocephala subsp. glabrata) pastures was undertaken to determine (1) the efficacy of in vitro Synergistes jonesii inoculum (produced in an anaerobic fermenter) in degrading the dihydroxypyridone (DHP) isomers produced during digestion of leucaena forage; and (2) the persistence of the inoculum in the rumen of cattle following a period grazing non-leucaena pastures. Cattle were introduced to the leucaena pastures for an initial period varying from 17 to 71 days. Fourteen to fifteen animals were then sampled for (1) urine and blood plasma to determine toxicity status as indicated by concentration of DHP; (2) faeces for estimation of diet composition; and (3) rumen fluid for detection of S. jonesii by nested polymerase PCR analysis. After a further 42–56 days, animals were resampled as before to confirm toxicity status and inoculated with the in vitro S. jonesii inoculum; the herds were then sampled a third time (42–60 days after inoculation) to test the effectiveness of the inoculum in degrading DHP. Five of the herds were then removed from leucaena pastures for periods ranging from 80 to 120 days and returned to leucaena pastures for 21 days to check persistence of the inoculum as indicated by retention of capacity to degrade DHP. The data indicated (1) a very slow build up of capacity to degrade DHP isomers on some properties before inoculation; (2) frequent occurrence of high levels of 2,3-DHP in urine indicating partial toxin degradation, both before and after inoculation; (3) a low incidence of detection of S. jonesii in rumen fluid after inoculation based on nested PCR analysis; (4) failure of inoculation to degrade DHP on one of two properties tested; and (5) loss of capacity to degrade DHP on some properties after <4 months on alternative non-leucaena pastures. It was concluded that while most herds showed some capability to degrade DHP due to some residual capability from previous exposure, they did not achieve the same rapid and complete DHP degradation reported in the 1980s. Nevertheless, it was concluded that the in vitro inoculum was at least partially effective and should continue to be used by graziers until improved sources of inoculum and/or inoculation methodologies are demonstrated.

Ovarian activity and estrus behavior in early postpartum cows grazing Leucaena leucocephala in the tropics

“…Plasma concentration of 2,3-DHP in the SS treatment was higher than reported by Phaikaew et al (2012), who observed that concentrations from 142 to 182 μg/mL in urine are indicative of subclinical toxicity in cows. Given the strong correlation between DHP levels in urine and blood (Graham et al 2013), it is reasonable to suggest that cows in the SS treatment had subclinical toxic levels of 2,3-DHP.…”

Unravelling Leucaena leucocephala toxicity: ruminant studies in eastern Indonesia and Australia

“…However, recent findings worldwide have indicated the frequent occurrence of high levels of DHP in animals, which were otherwise considered protected by S. jonesii. Concerns regarding the efficacy of the inoculum were initially raised in 2004, following a survey of Queensland cattle which revealed high DHP levels in urine of animals grazing leucaena (Dalzell et al 2012;Graham et al 2013). Similar findings were subsequently recorded in ruminants in Thailand (Phaikaew et al 2012), Mexico (Contreras-Hernández et al 2013Ruz-Ruiz et al 2013), and Indonesia (Halliday et al 2013;Halliday et al 2014b) (Chapter 4), where animals were often fed high levels of leucaena in diet, up to 100%.…”

“…Since their animals fed leucaena may still be performing better than those without legume, there is understandable denial that toxicity is an issue. Another highly anomalous situation is that many ruminants in the tropical world are consuming large amounts of leucaena for prolonged periods and excreting high concentrations of urinary DHP without any apparent clinical symptoms of toxicity (Phaikaew et al 2012;Graham et al 2013;Halliday et al 2014c), including no indication of goitre (Palmer et al 2010). The reasons for this are not understood, but may be due to alternative detoxification pathways such as chemical conjugation of the toxins, discussed later in this review.…”

“…The isomer 2,3-DHP was originally thought to be transitory, and indicative of incipient ruminal colonization of S. jonesii (Ford et al 1984;Jones et al 2009). Much recent data from Australia, Thailand and Indonesia contradict the notion of 2,3-DHP being transitory (Dalzell et al 2012;Phaikaew et al 2012;Graham et al 2013;Halliday et al 2014c) and…”

Genetic control of methane emission, feed efficiency and metagenomics in dairy cattle

“…Recent work with repeated inoculation of beef heifers with bison rumen contents altered the rumen microbiome and metabolic activity eliciting increased protein and nitrogen retention on a nutritionally poor straw diet (Ribeiro et al, 2017). Another example is the discovery of Synergistes jonesii in goats which conveys the ability of the host to degrade the otherwise toxic pyridinediol compounds from the fodder plant Leucaena leucocephala, which was successfully conveyed to Australian beef cattle and sheep (Graham et al, 2013). Both of these examples demonstrate the rapid adaption of host to dietary changes acquired through the incorporation of beneficial microbes into the rumen community.…”