Some aspects of outdoor pig production in Argentina
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 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.