The effects of glucosinolates in canola meal feeding regiments on liver and thyroid physiological responses and productive performance parameters in the laying hen
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Long-term (4-8 months) experiments were conducted to evaluate the feeding value of a new low-glucosinolate canola meal for laying hens and to investigate the physiological responses in the liver and the thyroid to diet glucosinolate levels in various canola meal feeding regimens. An experiment was conducted to investigate the effects of glucosinolates on fertility and hatchability in breeder laying hens and to assess the possible influence of iodine supplementation. The importance of glucosinolate hydrolysis products in the physiological response of laying hens to dietary glucosinolates was exemplified by the observations that hepatic glutathione and thyroid weight showed more pronounced response in birds fed diets designed to produce a maximum amount of glucosinolate hydrolysis products. A significant linear relationship between diet glucosinolate levels and hepatic glutathione content was observed. These data along with the data that a high rate of egg production and no mortality due to liver hemorrhage were noted in laying hens fed meal produced from the new low-glucosinolate cultivar indicate that the glucosinolate content should be reduced in future canola varieties. The corresponding meals could then be used in laying hen diets based on their nutritive value with no need for an upper-limit constraint. An increase in T3 and a decrease in T4 in response to the increasing glucosinolate levels were noted from the regression analyses indicating that the biological active hormone form, T3, rather than T4 tended to be produced as a compensatory response to ingested glucosinolates. No adverse effects were noted on hatchability and fertility of laying hens in canola meal feeding regimens indicating that canola meal can be used as a protein supplement in breeder laying hen diets. However, a reduction in body weight and plasma T4 of day-old chicks were noted although the latter response could be alleviated by adding supplemental iodine to the canola meal diet.