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The objective of this study was to estimate the amount of post-rumen crude protein (prCP), a precursor to metabolisable protein for ruminants, of feeds and feed mixtures using an in situ and in vitro method, and to contrast the results of both approaches. For this, 34 samples were examined: 9 feeds, 13 feed mixtures made thereof and 12 feed mixtures provided by commercial dairy farms. As a minor aspect, additivity of protein values from feeds was evaluated by comparing measured and calculated values of feed mixtures. Effective prCP was calculated for assumed rumen passage rates (k) of 0.05 h−1 (prCP5) and 0.08 h−1 (prCP8) by in situ measurements of rumen undegraded CP and fermented organic matter (FOM) assuming an efficiency of 181 g microbial CP/kg FOM. Additionally, effective prCP in vitro was estimated using the modified Hohenheim gas test (modHGT) through incubation in rumen-fluid buffer solution for 8 and 24 h followed by ammonia distillation. In vitro estimations were highly correlated with in situ values for both passage rates (k = 0.05 h−1: p < 0.001, R2 = 0.68; k = 0.08 h−1: p < 0.001, R2 = 0.76). The in vitro method yielded higher values for effective prCP than the in situ approach with 29 g/kg OM (k = 0.05 h−1) and 37 g/kg OM (k = 0.08 h−1) on average for all samples. Small positive associative effects – reflecting non-additivity – were found, averaging at 2.2 g prCP8/kg OM (p < 0.05) for the in situ and 10.7 g prCP8/kg OM (p < 0.001) for the in vitro approach. Due to the need of an assumption of a certain value for microbial efficiency in situ, effective prCP might be more accurately estimated in vitro, accounting for nutrient-specific efficiencies as well as interactions between carbohydrate and protein degradation by rumen microbes. Furthermore, the modHGT highlighted associative effects more pronounced and seems suitable as a routine method due to the comparably low effort and high sample throughput. The potential of the modHGT to determine the protein value of feeds could be demonstrated by our study. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effects of dietary Quebracho tannin extract (QTE) on feed intake, apparent total tract digestibility (ATTD), excretion of urinary purine derivatives (PD) and milk composition and yield in dairy cows. Fifty Holstein cows were divided into two groups. To reach a similar performance of both groups, cows were divided according to their milk yield, body weight, days in milk and number of lactations at the start of the experiment averaging 33.2 ± 8.2 kg/d, 637 ± 58 kg, 114 ± 73 d and 2.3 ± 1.6 lactations, respectively. The cows were fed a basal diet as total mixed ration containing on dry matter (DM) basis 34% grass silage, 32% maize silage and 34% concentrate feeds. Three dietary treatments were tested, the control (CON, basal diet without QTE), QTE15(basal diet with QTE at 15 g/kg DM) and QTE30(basal diet with QTE at 30 g/kg DM). Two treatments were arranged along six periods each 21 d (13 d adaptation phase and 8 d sampling phase). The ATTD of DM and organic matter were reduced only in Diet QTE30, whereas both QTE treatments reduced ATTD of fibre and nitrogen (N), indicating that QTE impaired rumen fermentation. Nevertheless, feed intake was unaffected by QTE. In Diet CON, urinary N excretion accounted for 29.8% of N intake and decreased in treatments QTE15and QTE30to 27.5% and 17.9%, respectively. Daily faecal N excretion increased in treatments CON, QTE15and QTE30from 211 to 237 and 273 g/d, respectively, which amounted to 39.0%, 42.4% and 51.7% of the N intake, respectively. Hence, QTE shifted N excretion from urine to faeces, whereas the proportion of ingested N appearing in milk was not affected by QTE (average 30.7% of N intake). Daily PD excretion as indicator for microbial crude protein (CP) flow at the duodenum decreased in treatment QTE30compared with Diet CON from 413 to 280 mmol/d. The ratios of total PD to creatinine suggest that urinary PD excretion was already lower when feeding Diet QTE15. While there was no effect of Diet QTE15, treatment QTE30reduced milk yield, milk fat and protein. Both QTE treatments reduced milk urea concentration, which suggest that ruminal degradation of dietary CP was reduced. In summary, adding QTE at dosages of 15 and 30 g/kg DM to diets of lactating dairy cows to improve feed and protein use efficiency is not recommended. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterise the variation of utilisable crude protein at the duodenum (uCP) of dried distillers’ grains with solubles (DDGS) for ruminants using a modified gas test and to predict the uCP in DDGS based on chemical composition. Thirteen samples originating from wheat, maize, barley or blends of different substrates were studied. Thein vitrouCP was estimated using the modified Hohenheim gas test (moHGT). Samples were incubated in rumen fluid for 8 h, 24 h and 48 h followed by ammonia distillation. The obtained values were compared to reference values of uCP (based on the contents of crude protein (CP),in situundegraded CP and metabolisable energy). The reference andin vitrovalues of uCP were calculated according to passage rates of 2, 5 and 8%/h (i.e., uCP2, uCP5and uCP8, respectively). The in vitrouCP8ranged from 214 to 320 g/kg DM and reference values from 158 to 302 g/kg DM. The in vitrouCP2was on average lower (by 7 g/kg DM) andin vitrouCP8was higher (by 56 g/kg DM) than their respective reference values. Thein vitrouCP5and uCP8were correlated with reference values and the correlations were improved with increasing passage rates. When the differences of uCP content betweenin vitroand reference values were related to CP fractions, they increased with increasing content of CP fraction A and decreasing content of CP fraction B3 for uCP8. The prediction of uCP values from chemical composition was not reliable. It was concluded that uCP can be predicted on the basis of the moHGT method and CP fractions. The accuracy of prediction improved upon the inclusion of CP fractions and neutral-detergent insoluble nitrogen. The present study revealed a significant variation in the uCP content of DDGS, which should be considered when formulating rations for dairy cows. [ABSTRACT FROM AUTHOR]

The objective of this study was to characterise variations in the composition and nutritive value of dried distillers’ grains with solubles (DDGS) for ruminants, and to estimate the undegradable crude protein (UDP) in DDGS. Thirteen samples originating from wheat, corn, barley and blends of different substrates were studied. The rumen degradation of crude protein (CP) was determined using the nylon bag technique. Samples were incubated for 0, 1, 2, 4, 8, 16, 32 and 72 h, and in situ degradation kinetics were determined. The UDP was estimated using a passage rate of 8%/h. In vitro gas production was measured to estimate the metabolisable energy (ME), net energy for lactation (NEL) and in vitro digestibility of organic matter (IVDOM). Chemical profiles varied among samples [in g/kg dry matter (DM) ± standard deviation]; the values were 310 ± 33 CP, 86 ± 37 ether extract, 89 ± 18 crude fibre, 408 ± 39 neutral detergent fibre, 151 ± 39 acid detergent fibre and 62 ± 31 acid detergent lignin, as well as in protein fractions according to the Cornell Net Carbohydrate and Protein System [in g/kg CP]; the values were for fractions A, 161 ± 82; B1, 24 ± 11; B2, 404 ± 105; B3, 242 ± 61; and C, 170 ± 87. The ME, NEL [MJ/kg DM] and IVDOM [%] also varied among samples: 12.1 ± 0.59, 7.3 ± 0.39 and 72.5 ± 4.30, respectively. The in situ rapidly degradable CP fraction (a) varied from 10.2% to 30.6%, and the potentially degradable fraction (b) averaged to 66.8%. The UDP varied from 8.6% to 62.6% of CP. The present study suggests significant variations in composition and nutritive value among different sources of DDGS. The UDP could be predicted on the basis of analysed CP fractions, but the accuracy of UDP prediction improved upon the inclusion of neutral-detergent insoluble nitrogen, explaining 94% of the variation in the UDP values. We conclude that chemical protein fractions may be used to predict the UDP values of DDGS and that the variability in the protein fractions of DDGS should be considered when formulating diets for dairy cows. [ABSTRACT FROM AUTHOR]