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

Abstract

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 α-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.