Effect of duration of linseed diet supplementation before slaughter on the performances, meat fatty acid composition and rumen bacterial community of fattening lambs

Linseed have been commonly used in diets to increase the content of alpha linolenic acid and conjugated linoleic acid in the milk and meat of ruminants; however, the time-dependent characteristics of these fatty acids (FAs) and rumen bacterial community in response to the linseed have not been examined in sheep. Thus, the aim of this study was to evaluate the effect of linseed feed duration (LFD) before slaughter on the performances, meat FA composition, and rumen bacterial community of lambs, which could provide a feasible linseed feeding length for lamb in consideration of FA profiles and cost effectiveness. A total of 100 male Hu lambs were randomly assigned to four treatments with different LFDs: animals were fed a diet without linseed (LFD0), an 8% linseed diet from 29 to 42 d (LFD14), the linseed diet from 15 to 42 d (LFD28), or the linseed diet from 1 to 42 d (LFD42). After 42 d of experimentation, 10 sheep from each treatment were slaughtered to collect samples. The daily gain of lambs in the LFD42 were greater than those in the LFD0. The proportions of n-3 PUFAs gradually increased as the LFD increased (P < 0.001). The n-6 PUFA to n-3 PUFA ratios in muscle (from 9.763 to 2.234) and the rumen digesta (from 17.169 to 2.795) decreased with increasing LFD. Compared to the lambs in the LFD0 group, the lambs fed a linseed diet (LFD14, LFD28 and LFD42) showed decreased amounts of ruminal Fibrobacter succinogenes. The amount of ruminal Butyrivibrio fibrisolvens in LFD14, LFD28 and LFD42 was higher than that in the LFD0. The ruminal bacteria Chao1 and Shannon indices were higher in the LFD14, LFD28 and LFD42 than in the LFD0. The bacterial community in LFD0 showed distinct clustering from the LFD14, LFD28 and LFD42. These results indicated that ruminal bacterial diversity and muscle FAs gradually changed as LFD increased, and intake of the linseed diet for 28 d was sufficient to obtain a desirable n-6 PUFA to n-3 PUFA ratio in the muscle of lambs.