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Context: High concentrations of crude protein in ruminant diets may lead to excessive production of ruminal ammonia, which may stress the animal's metabolism and impact nitrogen efficiency. This may become a problem in zero-concentrate feeding systems when pasture grass is rich in crude protein. Polyphenols such as tannins may protect part of dietary protein from ruminal degradation and thus inhibit ammonia formation. Aims: The present study screened mature herbs for their potential to mitigate ruminal ammonia formation in cattle, when provided as a supplement to a forage diet. Methods: Thirty-five temperate-climate, herbaceous meadow plant species (including three legumes) that appear in biodiverse natural and sown pastures were investigated for their effects on ruminal ammonia production. Aboveground material was harvested during ripening of the seeds and analysed for nutrient and phenol concentrations. Net energy and protein absorbable at the duodenum were calculated. Incubations (24 h) with cattle rumen fluid following the in vitro Hohenheim Gas Test protocol were performed to compare the effects of the test plants on ruminal gas and ammonia formation. Test plants replaced one-third of a basal mixture consisting of 57% Lolium perenne L. and 43% Medicago sativa L. (air-dry-matter basis). Results were compared with those obtained with the basal mixture alone. Key results: According to regression analysis, ammonia concentration after incubation was negatively related to concentrations of total extractable phenols and total tannins in feed mixtures, whereas the relationship was weakly positive with dietary crude protein. In 23 and 19 of the test diets, respectively, in vitro gas production (indicating ruminal organic matter digestibility) and ammonia concentrations in the incubation medium after 24 h were significantly lower than with the basal mixture alone. Incubations containing Galium verum L., Leontodon hispidus L., Lotus corniculatus L., Onobrychis viciifolia Scop., Plantago lanceolata L., Sanguisorba minor Scop. and Scabiosa columbaria L. maintained gas production and estimated in vitro organic matter digestibility while at the same time lowering ammonia concentrations. Conclusions: Seven mature herbs of a screening of 35 proved to have potential for positive effects on ruminal protein utilisation without impairing fermentation. Implications: These herbs are of particular interest as dietary supplements for dairy cows grazing protein-rich pastures. In pasture-based feeding systems for dairy cows, dietary protein excess may cause high levels of ammonia formation during digestion, which is a burden for the animal's metabolism and to the environment. We tested the potential of 35 herbaceous meadow species to mitigate this problem and found seven promising temperate herbs that are candidates as dietary supplements. This outcome can be used to develop herb-based dietary supplements that will benefit protein efficiency, lower nitrogen emissions and improve animal health in grassland-based dairy production. [ABSTRACT FROM AUTHOR]

The potential use of tannin extracts from quebracho (QCT), grape (GCT), chestnut (CHT) and oak (OHT) included at 10, 20 or 30 mg/g to modulate rumen fermentation of concentrates was studied in three 24-h in vitro incubation runs, with barley grain as reference substrate and simulating high concentrate feeding conditions by adjusting pH at 6.2. Incubation pH at 8 and 24 h ranged from 6.14 to 6.18 and from 5.94 to 6.00, respectively. Gas production from barley alone (CTL) was linearly reduced with CHT (P < 0.05 up to 6 h; P < 0.10 from 8 to 18 h), OHT (P < 0.05 up to 12 h; P < 0.10 from 18 h), GCT (P < 0.05 from 2 to 24 h) and QCT (P < 0.10 up to 6 h), but a quadratic trend (P < 0.10) was also detected on GCT. The effect of GCT was highest and that of CHT lowest. Similarly, dry matter disappearance after 24 h showed a linear decrease with all tannin sources (P < 0.05), being lower with GCT than with QCT and CHT (P < 0.05). All tannin sources linearly increased (P < 0.05) molar butyrate proportion from CTL, at the expense of propionate proportion in GCT (P < 0.01) and CHT (P < 0.10). Except for the linear effect of chestnut on barley fermentation, all sources already reached their maximum level of response at their first level of inclusion (10 mg/g), especially with GCT. Qualitatively, tannins did not largely affect pH or other environmental parameters, except for an increase in butyrate proportion. Ruminants given high-concentrate diets are at risk of acidosis. Use of tannin extracts as dietary additives may slow down the fermentation rate, thus reducing the pH drop. The magnitude of the effect depends on the type of tannin but is not related to its chemical classification. Effect on fermentation is not dose related. [ABSTRACT FROM AUTHOR]