The effect of rapeseed meal on the energy metabolism of laying hens

[Rapeseed and rapeseed meal as components in diets of laying hens]

In an experiment with 405 Hisex white hens rations with 5-20% low glucosinolate rapeseed (RS) or rapeseed meal (RSM) of 00 quality were used. Feed intake, egg production, individual egg weight and live weight gain were reduced in hens fed 5-20% RS and 10-20% RSM. There was a positive correlation between the RS proportion in the ration and the thyroid weight as well as the iodine content of the thyroid. The relation between the iodine content related to one gram of thyroid and the RS proportion was not significant. There were not any significant differences between the RSM groups and the iodine content of the thyroid. The T3 and T4 concentrations in the blood plasma was independent of the RS- or RSM-proportion in the diet. The outward egg quality was not influenced by feeding. The Haugh units were lower when RS or RSM were offered. The fatty acid pattern of the yolk was changed by RS or RSM feeding, particularly the proportion of oleic acid increased. We concluded from the results, RS cannot be recommended for feeding white hens and only a maximum of 5% RSM should be administered.

Thyroid function in relation to trimethylamine oxidation in immature domestic fowl fed on rapeseed meal

1. Two groups of 12-week-old female chicks were selected for their ability to oxidise 14C-trimethylamine (TMA) after being fed on a diet containing 100 g high-glucosinolate rapeseed meal (RSM)/kg for 14 d. A third group (control) was fed on a rapeseed-free diet. Measurements of thyroid activity and hepatic TMA activity were made after a further week on the diets. 2. After feeding RSM, hepatic TMA oxidase oxidase was very low (P less than 0.001) in one group (sensitive) but was unaffected in the other group (resistant). Thyroid size was increased in both groups receiving RSM but was larger (P less than 0.001) in sensitive birds. 3. Plasma half life of thyroxine (T4) and its metabolite clearance rate were not affected by feeding RSM; thyroidal secretion was reduced (P less than 0.05) to the same extent in both groups. 4. Plasma concentration of triiodothyronine was decreased in both groups after feeding RSM (P less than 0.05); plasma T4 concentration was increased (P less than 0.05) only in sensitive birds. 5. The results indicate that the short-term depression of TMA oxidation in birds sensitive to RSM is not mediated by the thyroid.