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A number of environmentally transmitted infectious diseases are characterized by intermittent infectiousness of infected hosts. However, it is unclear whether intermittent infectiousness must be explicitly accounted for in mathematical models for these diseases or if a simplified modelling approach is acceptable. To address this question we study the transmission of salmonellosis between penned pigs in a grower-finisher facility. The model considers indirect transmission, growth of free-living Salmonella within the environment, and environmental decontamination. The model is used to evaluate the role of intermittent fecal shedding by comparing the behaviour of the model with constant versus intermittent infectiousness. The basic reproduction number, [Formula: see text], is used to determine the long-term behaviour of the model regarding persistence or extinction of infection. The short-term behaviour of the model, relevant to swine production, is considered by examining the prevalence of infection at slaughter. Comparison of the two modelling approaches indicates that neglecting the intermittent pattern of infectiousness can result in biased estimates for [Formula: see text] and infection prevalence at slaughter. Therefore, models for salmonellosis or similar infections should explicitly account for the mechanism of intermittent infectiousness.

In a study of pigs slaughtered at British abattoirs, approximately 23% carried Salmonella in their cecal (large intestine) contents. The most frequent serotype was Salmonella Typhimurium (STM), which was the second most common cause of human salmonellosis in Great Britain. A pig industry-monitoring program was developed to reduce Salmonella infection on British farms. The control of STM infection on the farm requires an understanding of STM transmission dynamics within the herd, and a mathematical model has been developed for an infected grower-finisher farm. The model estimates the probability of a random pig being infected with STM. There are three broad categories of STM infection in pigs: pigs that are infected but unable to transmit the infection (latent); pigs that are infectious, i.e., able to transmit the infection (shedders); and pigs that have stopped shedding but harbor STM in their internal organs (carriers). The model estimates that 21.0% (5th and 95th percentiles, 0.05 to 77.5%) of slaughter-age pigs on an infected farm are likely to be shedding STM. Although this range is wide, it is biologically plausible. Sensitivity analysis of the total number of infected pigs revealed that the most significant input parameters are the probability of effective contact between a specific infectious and susceptible pig and the duration of shedding. The model predicted that 11.5% of pigs would be shedding STM at slaughter age. This value is close to the estimate obtained from a British abattoir survey that 11. 1% of pigs carried STM in their ceca, indicating that the model has reasonable validity.

The effects of health management strategy during rearing on subsequent growth performance and indicators of immune system stimulation in grower-finisher (G-F) pigs were evaluated. Pigs of approximately 25 kg body weight (BW) were sourced from three different management systems: (1) a farrow-to-finish unit with identified respiratory problems (Conventional), (2) segregated early weaned (SEW; piglets sourced from multiple sow herds), and (3) a minimal disease farrow-to-finish operation (MD). The pigs were of similar genetic background and were housed under similar conditions until slaughter. During the grower phase, MD had the highest average daily gain (ADG) (P < 0.05), while it was similar for SEW and Conventional (P > 0.10). Feed to gain (F:G) was similar for MD and SEW (P > 0.10), and poorest for Conventional (P < 0.05). During the finisher phase, SEW had the lowest ADG, and the poorest F:G (P < 0.05); these parameters were similar for Conventional and MD (P > 0.10). Over the entire G-F period, performance of MD pigs was better than that of Conventional and SEW pigs. Performance depressions appeared related to the degree of anterior-ventral lung atelectasis, antibody titers to porcine reproductive and respiratory syndrome (PRRS) virus and Mycoplasma hyopneumoniae, thymus size, plasma insulin-like growth factor levels, stomach ulceration, nasal turbinate damage, and microbial burden. The current study shows that the growth depressing effects of exposure to infectious organisms can be substantial in G-F pigs. Key words: Pigs, growth performance, disease, cytokines

One hundred and twenty-eight pigs were placed into four groups and each group was fed from approximately 32 to 97 kg liveweight one of four diets: a control corn-soy diet or one of three diets containing 30.0, 65.0 or 96.7% of Tibor naked oats. Total liveweight gains and carcass backfat and quality index values were not significantly different at the end of the 77-d growth period. Feed conversion of the oat diets was progressively improved as the amount of oats in the ration increased; probably because the energy content of the rations increased as the concentration of naked oat kernels with their 8–10% total lipid increased. Diets containing the higher levels of oats also produced a better carcass yield (or dressing percentage) than the control diet. Tibor naked oats are thus a suitable replacement for all or part of the grain corn and soybean meal in a grower-finisher pig ration. Key words: Pig, grower-finisher diets, naked oats, cultivar Tibor