Fatty acid composition of ruminal digesta and longissimus muscle from lambs fed silage mixtures including red clover, sainfoin, and timothy

This work investigated the effects of feeding silage mixtures of a plant containing polyphenol oxidase (PPO; red clover [Trifolium pratense; RC]), a plant containing tannins (sainfoin [Onobrychis viciifolia; SF]), and a grass species not containing these compounds (timothy [Phleum pratense; T]) on ruminal and intramuscular (i.m.) fatty acids of lambs. Forty 4-mo-old castrated male Romane lambs, divided into 5 groups, received 1 of the following silages: 1) T (100%), 2) a binary mixture of timothy and tannin-containing sainfoin (Onobrychis viciifolia cv. Perly; 50:50 [T-SF]), 3) a binary mixture of timothy and PPO-containing red clover (Trifolium pratense cv. Mervius; 50:50 [T-RC]), 4) a ternary mixture of timothy, sainfoin, and red clover containing both tannins and PPO (50:25:25, respectively [T-SF-RC]), and 5) a binary mixture of tannin-containing sainfoin and PPO-containing red clover (50:50 [SF-RC]). In the rumen digesta, the partial or total replacement of T with forage legumes was associated with greater concentrations of PUFA (P < 0.001) and 1esser concentrations of MUFA (P < 0.001). The inclusion of forage legumes in the silage favored the accumulation of 18: 3 n-3 (P < 0.001), with the greatest concentrations being observed in SF-RC. This latter diet also led to the greatest percentage of 18: 2 n-6 (P < 0.001). Forage legumes decreased the trans-11 18: 1 to 30% of T in rumen digesta (P < 0.001). Forage legumes decreased the total concentration of branched-chain fatty acids in the rumen digesta (on average, -28%; P < 0.001), this effect being less marked (-17%; P = 0.014) in T-RC in comparison with T. The dietary treatment tended to affect the proportion of MUFA (P = 0.081) and of PUFA (P = 0.079) in the i. m. fat of the LM, respectively, at the highest and lowest numerical value in the T group. The sum of n-3 fatty acids was less in the T and T-SF groups compared with the mixture of legumes without T (SF-RC; P < 0.001 and P < 0.008, respectively). The latter group had also a lesser n-6-to-n-3 ratio than the T-SF group (P = 0.01). Trans-11 18: 1 was greater (P < 0.03) in lambs given T as the sole silage in comparison with lambs given T-RC, T-SF-RC, and SF-RC. Rumenic acid (cis-9 trans-11 CLA) was detected at a greater percentage in the LM from the animals fed the T silage compared with animals fed the T-SF-RC treatment (P = 0.004). Contrarily, cis-9 cis-12 cis-15 18:3 was found at a greater concentration in the muscle from lambs in the SF-RC treatment compared with lambs in the other treatments (P < 0.001). Furthermore, the T-RC group showed a greater proportion of a-linolenic acid than the T group (P = 0.03). In conclusion, the effects of the 2 active compounds (PPO and tannins) appear to be similar and additive. Moreover, a silage composed of a mixture of RC and SF is an excellent forage for growing lambs in terms of i. m. fatty acid composition.