VIABILITY OF CRYPTOSPORIDIUM-PARVUM DURING ENSILAGE OF PERENNIAL RYEGRASS

The survival of Cryptosporidium parvum during ensilage of perennial ry egrass was examined in laboratory silos with herbage prepared in one o f three different ways; either untreated, inoculated with a strain of Lactobacillus plantarum or by direct acidification with formic acid. T he pH values of all silages initially fell below 4 . 5, but only formi c acid-treated silage remained stable at less than pH 4 after 106 d, w ith the pH of the untreated and inoculant-treated silages rising to ab ove 6. The formic acid-treated silage had a high lactic acid concentra tion (109 g kg(-1) dry matter (DM)) and low concentrations of propioni c and butyric acids after 106 d. However, the untreated and inoculant- treated silages showed an inverse relationship, with low lactic acid c oncentrations and high concentrations of acetic, propionic and butyric acids. These silages also contained ammonia-N concentrations in exces s of 9 g kg(-1) DM. In terms of the viability of Cryptosporidium parvu m oocysts very few differences were seen after 14 d of ensilage with c a 50% remaining viable, irrespective of treatment and total numbers ha d declined from the initial level of 5 . 9 x 10(4) to 1 x 10(4) g(-1) fresh matter. Total oocyst numbers remained approximately the same unt il the end of the ensiling period, with the percentage of viable oocys ts declining to 46, 41 and 32% respectively for formic acid, inoculant and untreated silages. The results are discussed in terms of changes occurring during the silage fermentation, in particular the products w hich may influence the survival of Cryptosporidium and implications fo r agricultural practice and the health of silage fed livestock.