Condensed tannins (CTs) account for up to 20% of the dry matter in forage legumes used as ruminant feeds. Beneficial animal responses to CTs have included improved growth, milk and wool production, fertility, and reduced methane emissions and ammonia volatilization from dung or urine. Most important is the ability of such forages to combat the effects of gastrointestinal parasitic nematodes. Inconsistent animal responses to CTs were initially attributed to concentration in the diet, but recent research has highlighted the importance of their molecular structures, as well as concentration, and also the composition of the diet containing the CTs. The importance of CT structural traits cannot be underestimated. Interdisciplinary research is the key to unraveling the relationships between CT traits and bioactivities and will enable future on‐farm exploitation of these natural plant compounds. Research is also needed to provide plant breeders with guidelines and screening tools to optimize CT traits, in both the forage and the whole diet. In addition, improvements are needed in the competitiveness and agronomic traits of CT‐containing legumes and our understanding of options for their inclusion in ruminant diets. Farmers need varieties that are competitive in mixed swards and have predictable bioactivities. This review covers recent results from multidisciplinary research on sainfoin (Onobrychis Mill. spp.) and provides an overview of current developments with several other tanniniferous forages. Tannin chemistry is now being linked with agronomy, plant breeding, animal nutrition, and parasitology. The past decade has yielded considerable progress but also generated more questions—an enviable consequence of new knowledge!

Forage legumes that contain secondary compounds are considered to be less susceptible to proteolysis than other legumes, with improved silage quality and possibly improved animal performance. This was investigated feeding five groups of growing lambs for 10 weeks, five silages composed of pure timothy (T; Phleum pratense), mixtures of T with red clover (Trifolium pratense; T‐RC, 50/50 on DM basis), sainfoin (Onobrychis viciifolia; T‐SF), or both (T‐RC‐SF, 50/25/25), or a mixture of the two legumes (RC‐SF). Including SF and/or RC in silages improved silage fermentation as shown by higher lactic acid and lower soluble N and NH3 contents than in T silage. Voluntary intakes were higher with all the RC‐containing silages than with T and T‐SF. The T‐SF silage had the lowest, and RC‐containing silages the highest average values for daily gain, feed conversion efficiency, live weight and carcass weight. The differing effects of these silages cannot be totally explained by differences in their nutritive value and so may be due to their bioactive compounds impacting differently on feeding motivation and digestive efficiency. These results suggest that including RC in silages is a promising strategy to combine improved animal performance with reduced environmental pressure.

Little information exists on the effects of ensiling on condensed tannins or proanthocyanidins. The acetone-butanol-HCl assay is suitable for measuring proanthocyanidin contents in a wide range of samples, silages included, but provides limited information on proanthocyanidin composition, which is of interest for deciphering the relationships between tannins and their bioactivities in terms of animal nutrition or health. Degradation with benzyl mercaptan (thiolysis) provides information on proanthocyanidin composition, but proanthocyanidins in several sainfoin silages have proved resistant to thiolysis. We now report that a pretreatment step with sodium hydroxide prior to thiolysis was needed to enable their analysis. This alkaline treatment increased their extractability from ensiled sainfoin and facilitated especially the release of larger proanthocyanidins. Ensiling reduced assayable proanthocyanidins by 29%, but the composition of the remaining proanthocyanidins in silage resembled that of the fresh plants.

This work investigated the effects of feeding silage mixtures of a plant containing polyphenol oxidase (PPO; red clover [; RC]), a plant containing tannins (sainfoin [; SF]), and a grass species not containing these compounds (timothy [; 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 ( cv. Perly; 50:50 [T-SF]), 3) a binary mixture of timothy and PPO-containing red clover ( 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 ( < 0.001) and 1esser concentrations of MUFA ( < 0.001). The inclusion of forage legumes in the silage favored the accumulation of 18:3 -3 ( < 0.001), with the greatest concentrations being observed in SF-RC. This latter diet also led to the greatest percentage of 18:2 -6 ( < 0.001). Forage legumes decreased the -11 18:1 to 30% of T in rumen digesta ( < 0.001). Forage legumes decreased the total concentration of branched-chain fatty acids in the rumen digesta (on average, -28%; < 0.001), this effect being less marked (-17%; = 0.014) in T-RC in comparison with T. The dietary treatment tended to affect the proportion of MUFA ( = 0.081) and of PUFA ( = 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 -3 fatty acids was less in the T and T-SF groups compared with the mixture of legumes without T (SF-RC; < 0.001 and < 0.008, respectively). The latter group had also a lesser -6-to--3 ratio than the T-SF group ( = 0.01). -11 18:1 was greater ( < 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 (-9 -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 ( = 0.004). Contrarily, -9 -12 -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 ( < 0.001). Furthermore, the T-RC group showed a greater proportion of α-linolenic acid than the T group ( = 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.

Two experiments evaluated the effects of a Bacillus-based direct-fed microbial on in vitro dry matter (DM) and neutral detergent fiber (NDF; Exp. 1), and starch (Exp. 2) digestibility of a variety of ruminant feedstuffs. In Exp. 1, ten forage sources were evaluated: ryegrass, alfalfa hay, leucaena, corn silage, spinifex, buffel grass, flinders grass, Mitchell grass, rhodes grass hay, and Queensland bluegrass. Experimental treatments were a Control, forages with no probiotic inoculation; CON) or forages sources inoculated with a mixture containing Bacillus licheniformis and B. subtilis (3.2 × 10 9 CFU/g; DFM). In vitro DM and NDF digestibility were evaluated at 24- and 48-hours post-treatment inoculation. Treatment × hour interactions were noted for IVDMD and IVNDFD (P ≤ 0.05). More specifically, DFM inoculation increased (P ≤ 0.03) IVDMD at 24 hours in four forages and increased 48-hour IVDMD (P ≤ 0.02) in alfalfa hay, ryegrass, leucaena, and Mitchell grass hay, but opposite results were observed for Queensland bluegrass (P &lt; 0.01). Twenty-four and 48-hour IVNDFD increased following DFM inoculation (P ≤ 0.02) in five forage sources, but reduced for Queensland bluegrass (P &lt; 0.01). When the forages were classified according to their quality, main treatment effects were detected for IVDMD (P ≤ 0.02) and IVNDFD (P &lt; 0.01). In Exp. 2, five common cereal grains were evaluated [high-density barley (82 g/100 mL), low-density barley (69 g/100 mL), corn, sorghum, and wheat] under the same treatments as in Exp. 1. In vitro starch digestibility was evaluated at 6- and 12-hours following treatment inoculation. Treatment × hour interactions were observed for starch digestibility in 3 out of 5 concentrate sources (P ≤ 0.001). Inoculation of DFM yielded greater 24-hour starch digestibility for high-, low-density barley, and wheat (P ≤ 0.02), but also greater at 48 hours in wheat (P &lt; 0.0001). Moreover, mean starch digestibility improved for corn and sorghum inoculated with DFM (P &lt; 0.01). Using a Bacillus-based DFM (B. licheniformis and B. subtilis) improved mean in vitro DM and NDF digestibility of different forage sources of varying qualities (based on CP content). Similarly, in vitro starch digestibility was also greater following DFM inoculation, highlighting the potential of this probiotic to improve nutrient digestibility and utilization into the beef and dairy cattle herd.

The use of forage legumes as a source of protein for ruminants is a sustainable strategy to reduce the use of inorganic-nitrogen fertiliser. In addition, some legumes species contain naturally bioactive secondary compounds, which could improve silage quality and digestive processes in ruminants. The aim of this study is to investigate the effects of bioactive legumes containing condensed tannins or polyphenol oxidase, ensiled alone or in mixture with a grass, on silage quality and conservation characteristics. Six mini-silos were prepared in triplicate as follows: 100% red clover (RC), 100% sainfoin (SF), 100% Timothy (T, control without bioactive compounds), binary mixtures 50% T + 50% RC, 50% T + 50% SF and ternary mixture 50% T + 25% RC + 25% SF. Condensed tannins remain unaltered during the silage-making process in terms of quantity and chemical structures, while polyphenol oxidase is activated during this process. All the silages that contained bioactive legumes were better conserved than the pure grass silo. In addition bioactive legumes were able to preserve protein from their degradation during the silage process. Inclusion of bioactive legumes can improve silage quality, and polyphenol oxidase may be more efficient than condensed tannins to improve the nitrogen value of silage.

Generalist herbivores typically grow better on mixed- than on single-component diets. This response has been attributed to food complementarities that either enhance the utilization of nutrients or dilute the negative impacts of plant secondary compounds (PSC). For instance, when animals choose between foods that contain diverse PSC, they eat more than animals offered a food that contains just one PSC. In addition to their negative impacts on herbivore fitness, recent evidence suggests that at appropriate doses PSC may provide beneficial effects to herbivores (i.e., by reducing parasitic infections). Thus, complementarities among diverse PSC may not only influence an herbivore's ability to consume food but also reduce the incidence of disease. We assessed the complementary effects of two PSC by offering sheep (Ovis aries) a choice of foods containing condensed tannins and saponins while challenged with a parasitic (Haemonchus contortus) infection. Animals offered a choice ate more than animals just offered tannins or saponins in single rations. However, sheep offered choices displayed greater fecal egg counts (an indirect measurement of parasitic burdens) than sheep offered single rations. Thus, saponin- and tannin-containing foods were complementary resources regarding nutrient intake but antagonistic regarding effects on parasitic loads. The nature of the relationship among PSC may depend on the dimension (i.e., nutrient intake, disease) where the interaction occurs. A unifying currency such as growth or reproductive output may help understand the trade-offs between costs (disease) and benefits (nutrient and medicine intake) for herbivores grazing multiple PSC.

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