Chemical changes and influences of rapeseed antinutritional factors on lamb physiology and performance: 1. Animal performance and thyroid histology

Sixty six Texel, Suffolk or crossbred lambs allocated to three groups were used. From the end of their first month of age till slaughtering, they were fed ad libitum with concentrates containing 0% (Control) or 25% of rapeseed meal obtained from either Samourai (Samourai) or Honk (Honk) variety. The Samourai and Honk concentrates contained 1.95 and 4.22 mmoles/g DM of glucosinolates, respectively. Lambs were weaned at 88 ± 8 days of age and 24 ± 5 kg of live weight and were slaughtered when their fattening state was estimated to be optimal. Apart from low concentrate intake for suckling lambs at the beginning of the experiment in the Honk, no negative effect of low glucosinolates (LG)-rapeseed meal was noted concerning animal performance. The quality of perirenal fat was better for lambs which received rapeseed meal since lower (P < 0.5) proportions of saturated fatty acids (C10 : 0, C12 : 0, C14 : 0) and higher contents (P < 0.05) of some unsaturated fatty acids (C18 : 1trans, C22 : 2) were determined. The thyroid weight was significantly higher (P < 0.05) for the Honk (3.04 ± 0.8 g) than in the Control (2.6 ± 0.5 g) and the Samourai (2.7 ± 0.6 g). Moreover, the percentages of small thyroid follicles were lower (P < 0.05) in the Honk than in the Control and Samourai groups. Conversely, the percentages of large thyroid follicles were higher (P < 0.05) in the Honk than in the two other groups. These results suggest that rapeseed meal can be used as the only protein supplement for fattening lambs despite the modification of thyroid histology by high glucosinolate content.