No abstract

A study was made of the effects of adding 0.1 per cent myrosinase (a thioglucoside-splitting enzyme) to mouse diets containing Swedish or Polish type rapeseed oil meal and hot water-treated fractions of the meal. The latter were devoid of active enzyme but contained known quantities of the thioglucosides, precursors of the toxic isothiocyanates (I) and thiooxazolidones (T).Hot water extraction of the meals resulted in about 20 per cent of the dry matter being extracted and in significant alteration in the proportions and amounts of I and T.The addition of myrosinase to untreated rapeseed oil meals failed to increase the toxicity, presumably because there was already sufficient enzyme in the meals to reduce gains to about 25 per cent of normal. Addition of enzyme to the extracted residue (containing about one-third of the original thioglucosides of the meal) also failed to increase the toxicity. Enzyme addition to diets containing the water-soluble components resulted in significant growth depression but the full potential toxicity was not obtained.It is concluded that the enzyme myrosinase is an important factor affecting the toxicity of rapeseed oil meal in animal feeding, although conditions for its optimum activity were not achieved in this experiment where semi-purified enzyme was employed as a dietary supplement.

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A co-operative trial involving 10 swine units and 744 pigs examined the effects of adding 0.05 and 0.08% copper sulfate to diets fed, ad libitum, from approximately 11 to 90 kg liveweight. Supplementation resulted in weighted improvements of 2.2 and 1.7% in growth rate and 2.0 and 2.2% in the efficiency of feed conversion, respectively, for the overall period. Added copper had little effect upon carcass characteristics, but resulted in a marked increase in liver copper concentrations. Although 31 of the 500 livers analyzed contained levels in excess of the Canadian tolerance (150 mg Cu/kg fresh weight), 28 of these were from pigs fed the 0.08% copper supplement. Pigs fed the copper-supplemented diets tended to have a more unsaturated backfat, which contained a lower proportion of stearic acid, but more palmitoleic acid and a higher oleic:stearic ratio. There was evidence that both the composition of the unsupplemented diets and the sex of the pigs could also significantly influence the criteria measured in the carcass tissues. The level of dietary copper did not affect the eating quality of pork held for 4 or 8 mo frozen storage. The results indicate that under Canadian conditions, it would be preferable to limit the use of high levels of copper to diets for pigs under 50 kg liveweight.

Br.'rzu,n, R. J. eNo PorreurN, L. S. 1974. Effects of feeding soya flour on the performance of growing-furring mink. Can. J. Anim. Sci. 5, A trial for testing the replacement value of semipurified soya flour (SF) for raw meat was conducted with 30 male Pastel mink. The SF contained 72ok crtde protein and its amino acid composition revealed an inferior lysine and methionine content as compared to meat. Mink were fed wet diets containing zero,9.6, 17, 24.2 and 32% SF on a dry matter basis. Weight gain was significantly lower (P < 0.05) for the group fed i2Vo SF. Mink fed 24.2% SF had intermediate gains, although they had the highest feed intake (P < 0.05). Length