The efficacy of a cultured Synergistes jonesii inoculum to control hydroxypyridone toxicity in Bos indicus steers fed leucaena/grass diets

Abstract

An experiment was conducted to investigate the efficacy of a cultured Synergistes jonesii inoculum in degrading the Leucaena leucocephala (leucaena) toxins: 3-hydroxy-4(1H)-pyridone and 3-hydroxy-2(1H)-pyridone (3,4- and 2,3-DHP). Sixteen stall-housed Bos indicus steers naïve to leucaena were fed varying combinations of forage-harvested leucaena and Chloris gayana (Rhodes grass). Dietary treatments, offered at 25 g dry matter/kg LW.day, were: 25% leucaena; 50% leucaena; 100% leucaena; and 50% leucaena, switched to 50% Medicago sativa (lucerne) after 6 weeks at time of inoculation. The experiment was 10 weeks in duration, consisting of a 6-week pre-inoculation period, followed by inoculation with cultured S. jonesii, and a 4-week post-inoculation period. Mean daily dry matter intake was recorded. Twenty-four-hour urine collections and rumen fluid samples were obtained weekly for estimation of total urinary DHP, and detection of S. jonesii using nested polymerase chain reaction analysis including presence of single nucleotide polymorphisms (SNP), respectively. In the pre-inoculation period, total urinary DHP increased quickly to high levels, then gradually declined after Week 3 with 2,3-DHP the dominant isomer through to Week 6. Indigenous strains of S. jonesii were sporadically detected by PCR analysis, indicating S. jonesii was present before inoculation but at the lower limits of detection. After inoculation there was no change in the rate of total DHP degradation or the frequency of detection of S. jonesii, although there was increased rate of degradation of 2,3-DHP. SNP indicated the presence of different strains of S. jonesii in both indigenous and cultured S. jonesii. DMI was low, especially in the 100% treatment, due in part to the high stem content of the forage-harvested leucaena and probable DHP toxicosis. It was concluded that the cultured S. jonesii inoculum did not fully protect animals against leucaena toxicity.