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Four Holstein steers (297 ± 56 kg of body weight (BW)) fitted with duodenal cannula and rumen catheter, were housed in metabolism cages and used in a 4 × 4 Latin Square trial to evaluate the effect of both protein source and Acacia mearnsii tannin extract on digestibility, ruminal fermentation, rumen microbial protein synthesis, N utilization and on duodenal flow of individual amino acids. The diet was offered at restricted amount of 25 g of dry matter (DM)/kg BW and consisted of maize silage plus concentrate, in a proportion of 0·7:0·3 (DM basis) respectively. Concentrate was formulated with either soybean meal or canola meal as protein source, with or without 50 g/ kg of A. mearnsii tannin extract (i.e. 15 g/kg of total dietary DM). There was no effect of protein source on most variables. The apparent and true organic matter (OM) digestibilities, as well as neutral detergent fibre (NDF) digestibility were negatively affected by tannin extract inclusion without, however, affecting digestible OM intake. The amount of nitrogen (N) excreted in faeces increased whereas the urinary N excretion decreased in tannin extract treatments. No interaction time × treatment was detected for any rumen variable and no treatment effect was observed for rumen fluid pH and reducing sugars concentration. Rumen fluid concentration of ammonia N was lower for the canola meal plus tannin extract treatment. Rumen concentration of α-amino compounds was not affected by tannin extract but was higher when canola meal was the protein source. The duodenal flow of OM, total N, α-amino N and non-ammonia non-microbial N increased with tannin extract inclusion, whereas the duodenal flow of microbial N was not affected by treatment. For both protein sources, the amount of most individual amino acids flowing to the duodenum increased due to tannin extract addition. In conclusion, the dietary inclusion of 15 g/kg DM of tannin extract from A. mearnsii improved the amino acid supply independently of whether the protein source was canola meal or soybean meal, without affecting the amino acid profile, to steers fed maize silage plus concentrate, with a minor but significant impact on OM digestibility.

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This study was carried out to evaluate the impact of including Acacia mearnsii tannin extract (TA) as a feed additive on nutrition and productive performance of dairy cows grazing a high-quality temperate pasture and receiving supplementation with a concentrate feedstuff. Fourteen multiparous Holstein cows were assigned to either of the following treatments: concentrate without or with 20 g TA/kg dry matter (DM). Concentrate intake accounted for 32% of the total DM intake. Tannin addition increased the herbage DM intake by 22% (p < .05). There was no effect of TA inclusion on milk yield, milk composition, milk nitrogen (N) excretion, milk and plasma urea-N concentration, urinary excretion of total N, urea-N, and purine derivatives. However, TA inclusion increased the N intake and retention, total N excretion in manure, fecal N to urine N ratio, and decreased the dietary N efficiency for milk production and the percentage of ingested N excreted in urine (p < .05). In conclusion, supplementing dairy cows grazing a high-quality temperate pasture with a concentrate containing 20 g TA/kg DM showed the potential of decreasing the proportion of ingested N excreted in urine without affecting the productive performance.

Context Tannin extracts have been investigated as natural feed additives with the potential to decrease the enteric emission of methane and urinary N and to improve the productive performance of ruminants. However, the impact of this additive in dairy cattle grazing tropical grass pastures has not been extensively evaluated. Aims To evaluate the impact of the Acacia mearnsii bark extract (TA) on productive and nutritional variables in dairy cows grazing a Cynodon dactylon pasture and receiving supplementary corn silage and concentrate. Methods Fourteen multiparous Holstein dairy cows were assigned in a randomised block design to either of the following two treatments: concentrate without TA (control) or with 10 g of TA/kg dry matter (DM). The concentrate and corn silage accounted for ~0.30 and 0.30 of total DM intake respectively. Key results The dietary concentration of TA was 2.9 g/kg DM and it did not affect nutrients intake, milk production and composition, rumen microbial protein synthesis, plasma urea concentration or faecal N excretion. Total N and urea N excreted in urine were higher, whereas total N excreted in manure tended to be higher in TA treatment. Conclusions No productive advantage was obtained by including TA in the diet of dairy cows grazing Cynodon dactylon pasture. Instead, it increased the excretion of labile urinary N. Implications The effect of the use of TA as a feed additive for cows fed tropical grass-based diets is negative from the environmental point of view.

ResultsOnly cystine and methionine were significantly influenced by dietary methionine level but not with phytase level. This confirms the interrelationship between the cystine and methionine in the metabolism of the two amino acids. Also, threonine was significantly affected by only dietary methionine levels. There was no significant interaction between methoinine and phytase level. Though not significant, phytase addition led to numerical improvement in most of the amino acid digestibility. ConclusionThese results show that when methionine is marginally deficient in the diet of laying hens, addition of phytase could bring about numerical improvement in the AA digestibility which is not significant. This suggests that the inclusion level of methionine must be met even when phytase is to be used. AcknowledgementThe authors gratefully acknowledge the funding received from Alexander von Humboldt, Bonn, Germany. References IntroductionContinual growth of the biodiesel industry in Brazil has increased the availability of byproducts, such as canola meal (CM), for use in livestock feeding. However, the nutritional effects of CM supplementation for ruminants fed tropical grass based-diets need to be evaluated. This study evaluated the effect of offering canola meal as a supplementary feed on digestible organic matter intake, microbial protein synthesis, duodenal flux of amino acids and N retention in wethers fed a tropical grass based-diet. Materials and methodsEight Polwarth 3 Texel crossbreed wethers (31.1 6 3.8 kg live weight) housed in metabolism cages were used in a replicated 4 3 4 Latin Square experiment. Four of them were implanted with duodenal cannulae. Each experimental period was conducted over 15 d, with a 10 d adaptation and a 5 d measurement period. Wethers were fed a basal diet consisting of Sudangrass (Sorghum sudanense) ad libitum (100 to 200 g/kg of orts) and treatments were not supplementation (control) or supplementation with CM at a rate of 5, 10 or 15 g/Kg live weight. Forage and supplements were offered separately, in two daily meals, at 0800 and 1700 h. Cracked corn grain was added to CM (1:9) to improve palatability. Feed, refusals, urine and fecal output were recorded and sampled daily on days 10 to 15 of each experimental period. Duodenal sub-samples (100 mL) were taken on day 15 of each collection period in three hour intervals during a 24-h period. All samples were composited by animal and period. Feed, refusals, duodenal and feces samples were analysed for dry matter (DM), organic matter (OM), N and acid detergent lignin (ADL). Duodenal samples were also analysed for purines and a-amino N. Urine samples were analysed for N concentration. Duodenal flux of DM was estimated based on ADL concentration in duodenal digesta and feces as follows: Duodenal DM (g/day) 5 [fecal DM (g/day) 3 fecal ADL (g/kg of DM)]/duodenal ADL (g/kg of DM) (Porter & Singleton 1971). The amount of microbial N supplied to the small intestine (g/d) was calculated considering a ratio of purine N/microbial N of 0.116 (C...