Blood prolactin depression in growing pigs fed sorghum ergot (Claviceps africana)

The toxicity of sorghum ergot (Claviceps africana) was assessed in young pigs over 28 days. Fortyeight pigs of both sexes and 2 breeds (Large White and Duroc) were allocated across 6 grower diets, balanced for fibre and predicted digestible energy, and containing 0, 0.3, 0.6, 1.3, 2.5, or 5% ergot sclerotia [the 5% sclerotia diet contained 70 mg alkaloids/kg (>90% dihydroergosine)]. Blood samples taken on Days 0 and 28 were analysed for prolactin and clinical, biochemical, and haematological indices of health. Feed consumption and liveweight were individually monitored. There were no clinical signs of illness attributable to ergotism in the pigs. Blood prolactin concentrations were significantly depressed in pigs receiving 9 mg alkaloids/kg (0.6% sclerotia) and by >80% in pigs receiving 35 and 70 mg alkaloids/kg, clearly indicating a potential to interfere with lactation in sows. Reductions in feed intake and poor feed conversion were observed over the first 7 days with >9 mg alkaloids/kg, but some tolerance developed later. Feed refusal was more pronounced for pigs of the Duroc breed. Over the full trial period, growth was reduced by about 30% in pigs receiving 70 mg alkaloids/kg, as a result of poor feed intake and feed conversion. Digestible energy of diets containing ergot was later found to be lower than predicted, which contributed to this result. Additional keywords: mycotoxin, fungus. © CSIRO 2000 Introduction Sorghum ergot (Claviceps africana) was first identified in Australia in April 1996, and within 6 months had been found in all sorghum-producing regions in Queensland and New South Wales. It has also recently entered South and North America (Bandyopadhyay et al. 1996). Ergot fungi infect the plant during flowering and after a growth cycle characterised by release of modified plant sap (honeydew) and release of spores, the infected florets develop hard sclerotia (ergots), which either fall to earth or are harvested with the grain. C. africana sclerotia are small, grey/white, and elongated, about half the size of sorghum grain and with a rough surface. Sclerotia are a mass of simple fungal cells, composed largely of chitin, and containing alkaloids. Sorghum ergot produces a different range of alkaloids than the ergot of rye (C. purpurea) (Mantle 1977). Alkaloids of rye ergot interfere with milk production in sows (Nordskog and Clark 1945) by inhibiting release of prolactin, and reduce pig growth (Whittemore et al. 1977). However, pigs appear to be relatively resistant to the impaired peripheral circulation that can produce gangrene of the extremities in cattle and other species. In contrast to rye ergot alkaloids, several published reports have suggested that the main alkaloid of sorghum ergot (dihydroergosine) was much less toxic and did not affect lactation (Frederickson et al. 1991). Indeed, there were no reports of disease in livestock caused by sorghum ergot anywhere in the world (Mantle 1977) until recent cases of agalactia in sows and cows in central Queensland (Blaney et al. 2000b). In these cases, apart from agalactia, severe feed refusal and poor growth of pigs was reported. The objective of this study was to test whether sorghum ergot was toxic or in any way detrimental to pigs growing from 20 kg to 40 kg. Some of the preliminary results have been presented at conferences (Blaney 1997; Blaney and Kopinski 1998). B. J. Blaney et al. 786 Materials and methods