Effect of wheat and corn on the proliferation of Clostridium perfringens type A and the prevalence and importance of Clostridium perfringens in broiler chickens in Saskatchewan.

摘要

This work was carried out in two phases. The first was to examine the effect that the cereals, wheat and corn and their major components have on the in vitro proliferation and alpha toxin production by Clostridium perfringens type A (CP). The second phase was to determine the prevalence of CP in broiler chickens in Saskatchewan and finally, what factors may be involved for the increased susceptibility of broilers on farms to CP, and what consequences to the production cycle affected flocks may have when infected with CP. In the first experiment, CP was grown in vitro in thioglycollate media (TG) alone, TG plus pancreatin and pepsin (TGE) or TG plus in vitro digested corn (C) or wheat (W) supernatant in a 2:1 ratio. Colony forming units (CFU) were counted and alpha toxin activity (U) was measured from each group using a commercially available kit. There was significantly more proliferation when CPA was grown in W compared to C, TG, or TGE. Alpha toxin production was significantly higher in C compared to W or TGE but no significant differences were found in U/CFU between TG and TGE, C or W. To further isolate the specific component in the corn and wheat that made the difference in the proliferation and alpha toxin production, a second experiment was conducted to examine this in vitro phenomena in either the digested or non-digested protein, fat or carbohydrate fractions of each. In vitro proliferation of CP was reduced when this bacterium was grown in digested corn gluten meal (CGM) compared to non-digested CGM, as well as digested or non-digested wheat gluten (WG) and the control media, thioglycollate (TG). Digestion of wheat and corn oil and starch reduced proliferation significantly, when compared to the non-digested components of these cereals. Alpha toxin production was increased when proliferation was inhibited in all cases. A dipeptide that has been identified in CGM hydrolysate, Alanine-Glutamine, was shown to reduce CPA proliferation when mixed with TG at 0.5%. The second phase of this study involved examining the prevalence of CP in broiler chickens over the span of a full year. There were two sampling periods involving up to 41 barns per period. Prevalences of CP and anti-alpha toxin antibodies were evaluated in the birds at hatch and at slaughter. CP prevalence in the flock was also determined at mid-production and in starter feed samples. CP was present in 178/1440 (12.4%) of birds (57/738 (7.7%) for winter/spring and 121/702 (17.2%) summer/fall) between 18 -- 28 days of age and occurred in 534/3000 (17.8%) of birds (208/1520 (13.7%) for winter/spring and 326/1480 (22%) for summer/fall) at slaughter. CP was not isolated from chicks at hatch. CP could be isolated from 76% of feed samples. Although not all birds had titres, 175/769 (22.8%) of hatched chicks and 303/1392 (21.8%) of broilers tested at slaughter peaked at an anti-alpha toxin antibody titre of 1:64. Finally, an evaluation of the influence of management practices on the occurrence of CP in broiler chicken production in the province of Saskatchewan was conducted over the same full year. Using a multilevel mixed model to account for unmeasured factors associated with the breeder flock, the broiler producer and the barn where the flock was raised, factors associated with the isolation of CP included anti-alpha toxin antibody (AATA) titres at hatch and at slaughter. Barn factors that influenced the frequency of CP isolation included relative humidity, CO2, floor type and barn type. Feed form, feed supplier, contamination of starter feed and in feed antimicrobials also affected CP isolation. In addition there was a difference in CP isolation when bird strain was compared. There was a positive correlation between isolating CP from feces during mid-cycle production and isolating CP at slaughter. The effects of CP infection included an increase in lesion score with decreasing isolation of CP. There were no significant effects of CP infection on whole carcass or liver condemnations, total flock mortality or birds arriving dead at the plant, nor was there an effect on total weight gain or feed conversion. It is concluded that corn gluten can have an effect on the proliferation and alpha toxin production of CP and that this component could explain the reduced incidence of necrotic enteritis (NE) in broiler chickens in the field.