A preliminary trial established a subclinical level of infection with Oesophagostomum dentatum capable of affecting the performance of growing pigs. Thereafter a slightly higher level of infection (100 000 larvae) was administered to each of 24 individually- and scale-fed pigs to investigate the effect of O. dentatum on performance, digestibility and nitrogen retention over the live-weight range 32 to 64 kg. Worm-free but otherwise similar pigs served as controls. Infection reduced growth rate (12·9 %) and decreased efficiency of feed conversion to body weight (14·9%). There was no effect on killing-out percentage or area of eye muscle in cross-section, but infected pigs had relatively lower backfat depths (5·5 to 12·5 %). Infection did not influence nitrogen retention, but apparent digestibility of the dry matter, organic matter, nitrogen, gross energy and crude fibre was reduced. Possible explanations for these effects are discussed in relation to tissue changes associated with larval development in the large intestine.
Over a period of two years 180 pork pigs, 144 baconers and 144 sows from two slaughterhouses in northern England were examined for gastrointestinal parasites. Sows showed the highest level and intensity of infection, 85 per cent harbouring the dominant parasites Oesophagostomum dentatum and O quadrispinulatum; the highest worm burden recorded was 21,000. Hyostrongylus rubidus was present in 28.5 per cent of sows but virtually absent from younger pigs. Small numbers of Ascaris suum and Trichuris suis were recorded, 16 per cent and 23 per cent respectively in pork pigs and lower in older animals. Levels of parasitism appeared to be influenced by a number of management practices, in particular the housing system.
Ten sows were each infected with 300 000 larvae of Oesophagostomum dentatum after weaning their second litter, and subsequent performance over one parity was compared with that of 10 'worm free' controls. Mean worm burden in the sows when slaughtered immediately after weaning, was 13 480 ±2377. From service to weaning of the litter the mean body weight of worm-free sows increased (+11-3 kg) whereas that of infected sows declined (-13-1 kg) and at slaughter the carcasses of infected sows had lower depths of backfat. Worm-free sows averaged 12-8 pigs born of which 11-3 were born alive, corresponding values for infected sows being 12-4 and 9-5. Worm infection reduced birth weights by 15% but differences were not significant. Litters were equalized at eight pigs shortly after birth, and subsequent weaning weights were 10-5 % lower in those of infected sows despite a 29 % higher consumption of creep feed. Clinical disease was never observed in the infected sows, and no parasitic infection was found in the piglets. It is concluded that sub-clinical infections of O. dentatum in sows may be of economic significance.
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