Some preslaughter feeding and other environmental effects on aspects of gut microbiology of cattle and chickens : a thesis presented in partial fulfillment of the requirements for the degree of Master of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
Controlling microorganisms, especially pathogenic bacteria, in meat-producing animals destined for slaughter is important for reasons of consumer food safety, profitability and animal welfare. It is difficult for the consumer to accurately assess the safety of meat products, which means that meat must be provided with some form of assurance that it will be safe to eat. The overall objective of this work was to investigate approaches to improving food safety through preslaughter manipulation of gut microorganisms in cattle and chickens. The preslaughter feeding treatment of cattle, which offered the most advantages in the first study, was the provision of hay for 48 hours before despatch to slaughter. This method helped to reduce the gut burden and excretion of Escherichia coli (E. coli) and it helped keep the animals clean. Cattle that were transported directly from pasture had runny faeces and ended up with more surface soiling on the hide. Fasted animals produced less effluent during transport, but they had high levels of E. coli in their rumens and faeces at slaughter. The way the cattle were fed before slaughter had little effect on the amount of weight they lost. These results were confirmed in the second study involving eight preslaughter feeding regimes, with cattle fed red clover hay for 48 hours prior to transport to slaughter having reduced E. coli counts in the rumen to less than 1 log count g−¹ It is recommended that preslaughter fasting of cattle be reduced to 18 hours or less, including transport, to minimize gastrointestinal E. coli counts at slaughter and to minimize losses in carcass weight. The addition of commercial additives (a pre- and a syn-biotic) to the diet of chicks in their growing environment improved the chick growth rates and weights, however it also caused increased Eimeria tenella infection, following a challenge, resulting in significantly higher lesion scores. The presence of hens imparted partial resistance to infection to the chicks, but negatively affected their growth rates compared to chicks raised without hens.