A programme of study was undertaken to asses the antimicrobial and potential immunological properties of fermented liquid feed fed to sows in late gestation period. A liquid feed fermented with Lactobacillus plantarum fed to the pregnant sow in late gestation had the potential to beneficially modify the microflora the lactating sows introduces into the environment, which was consequently reflected in beneficial changes in the gut microflora of their litters. In addition, colostrum from sows fed FLF had a significantly greater mitogenic activity on both intestinal ce11s (79326 ± 3069 CPM) and blood lymphocytes (1903 ± 204 CPM) compared with colostrum from dry feed fed sows (53433 ± 1568 CPM and 1231 ± 61.4 CPM respectively). The combined effects of higher milk quality and the reduction in the level of environmental contamination with faecal pathogens, achieved by FLF, may be important in achieving improved health status for both sows and piglets. A series of in vitro experiments were conducted in order to select a suitable new starter culture from LAB of porcine origin, which would have similar fermentative abilities to Lactobacillus plantarum, but could exert possible 'probiotic' effects on the host (pregnant sow). From a total of 87 faecal Lactobacillus strains, a homofermentative aggregating Lactobacillus salivarius, was selected for further in vivo studies as it was able to resist bile and acid conditions, had good adherence abilities to a11 intestinal compartments (mucus, epithelial cells, collagen), as well as being a potent stimulator of interleukin (IL)-12. In addition, it had comparable fermentation properties to the Lactobacillus plantarum that has been widely used to ferment FLF in this laboratory. In vivo experiments with porcine Lactobacillus salivarius strongly indicated that this bacterial strain is an effective inoculant for FLF, with a potential double role: the role of the starter culture and the role of probiotic. This could help sows to overcome disorders due to the stress associated with farrowing, enhance immunity of newborn piglets through better immunological quality of colostrum and control pathogen challenge for both sows and their newborn piglets.

A programme of study was undertaken to assess the safety and palatability of fermented liquid feed. A series of laboratory experiments was conducted to select an inoculant capable of fermenting liquid feed at 20°C. Whilst combinations of cultures dropped the pH the most rapidly, the Lb. plantarum (PC) strain decreased the pH the lowest. A series of trials were conducted using a rifampicin mutant of Lb. plantarum (PC) to examine the fate of the starter culture. In an experiment using liquid milled wheat the addition of the starter culture resulted in an improvement in the inhibition of coliforms over the control (no inoculant). A series of fermentations prepared using Lb. plantarum (PC) were challenged with potential porcine pathogens at three temperatures (20°, 30° and 37°C) and after the feed had been fermented for different periods of time (24, 48, 72 and 96h). This study demonstrated that fermentation is an effective mechanism for eliminating potential porcine pathogens from liquid feed, However, the rate at which these pathogens are inactivated is dependent on temperature, duration of fermentation and challenge strain. The effect of temperature on the ability of E. coli and Salmonella spp. to survive in fermented liquid feed has implications for the management of liquid feeding systems. A study was conducted to examine the effect of feed form on the microbiology of the young piglets' gut. The benefits of feeding a FLF diet compared with a non-fermented liquid feed (NFLF), a conventional pelleted dry feed (DF) and leaving the piglet to continue to suckle the dam (S) for two weeks post-weaning were assessed. No coliforms bacteria (< 3.0 log10 cfu gˉ¹) were detected at the terminal ileum section of pigs fed FLF compared with 8.5, 8.1 and 6.0 log10 cfu gˉ¹ digesta in DF, NFLF and S pigs respectively. These results have implications in terms of .piglet health and dietary prevention of enteric diseases.

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The thesis presents work evaluating performance of an Argentinian outdoor pig production system based on later weaning, induction of lactational oestrus and rearing of growing and finishing pigs at pasture. In experiment 1 the effect of hut type (straw bale huts or conventional corrugated metal huts) and season (summer and winter), on the extent of, and factors affecting, pre-weaning piglet mortality, piglet growth, sow lactational feed intake and weight loss were evaluated. Straw bales huts had lower levels of piglet mortality than control huts from birth to weaning probably due to lower summer temperatures and a larger area of floor space for the sow. High summer temperatures reduced piglet growth probably due to reduced milk production in the sow. Sow feed intake and sow weight loss during lactation were not different between seasons probably because of the availability of wallows during summer. Neonatal competition within litters for teats and colostrum/milk was the primary cause of a high proportion of outdoor piglet deaths. In experiment 1<I> </I>the effect of sow mixing, boar presence and season (summer or winter) on the occurrence of lactational oestrus in outdoor sows was evaluated. Sow mixing (groups of 2) had no effect on lactational oestrus induction probably due to a low suckling disruption in mixed sows and litters. Sows exposed to the boar (either with full physical or fence-line contact), farrowing during winter and losing little weight between farrowing and weaning were more likely to show oestrus before weaning. In experiment 3, pasture intake, pig growth, concentrate intake, concentrate feed conversion rate and pneumonic lesions of outdoor protein restricted growing and finishing pigs with or without access to an alfalfa + fescue based pasture were evaluated in spring and summer. Pasture can improve growth during spring in protein restricted pigs, especially in pigs of higher body weight, but can have a detrimental effect on concentrate intake and FCR during summer due to its low digestibility, especially if composed of highly mature grass. FCR can deteriorate in outdoor growing pigs during winter-spring due to a climate penalty associated with higher heat loss. However, this appears not to impair their health status. In conclusion, the results of these studies indicate the potential under Argentinian conditions for benefits from outdoor pig production systems involving simple straw bale farrowing huts, extended lactations, lactational breeding and deployment of pasture as part of the feeding regime for growing-finishing pigs. These potential benefits relate to pig welfare aspects as well as economic considerations.

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