The effect of supplementary protein on the performance of pigs given swedes (Brassica napus) as a replacement for barley in the diet

A feeding trial was carried out to examine the effect of supplementary protein on the performance of pigs, when swede dry matter replaced 40% of the dry matter supplied by barley in two diets providing different amounts of protein. One hundred and twenty pigs of about 60 kg initial live weight were given one of four diets, each of which provided a constant amount of dry matter daily for 42 days, after which the pigs were slaughtered at about 90 kg live weight. The two basal diets were, on a dry matter basis; barley 2.0 kg plus either 0.2 or 0.4 kg soya bean meal. A mineral and vitamin supplement was given with each diet. There was no significant interaction between the effects of the inclusion of swedes or additional soya bean meal in the diet. The averaged results for pairs of diets showed that the use of swedes decreased carcass-weight gain from 0.62 to 0.51 kg/day and that the increment of soya bean meal increased it from 0.54 to 0.59 kg/day (P < 0.001 for both). It is suggested that the failure of swede dry matter to give an equivalent response to that of barley is not due to the nutritional value of its crude protein component per se but to other physical and chemical factors which may affect its utilization as an energy feed-source for pigs.