Browsing by Subject "Cereal grains"

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Ruminal degradation characteristics of barley, rye, and triticale grains assayed in situ and in vitro, and by near-infrared spectroscopy
(2017) Krieg, Jochen; Rodehutscord, Markus
The milk yield of dairy cows and related energy and protein requirements have steadily increased in the last few decades. Since feed intake has not increased to the same extent as nutritional requirements, the concentration of nutrients in mixed rations had to be increased. An increase in energy concentration is often achieved by the inclusion of high levels of cereal grains. In the EU—apart from wheat—barley, rye, and triticale are widely cultivated cereal grains. Starch (ST), followed by crude protein (CP), is the main constituent of cereal grains. The rate and extent of ruminal CP and ST degradation can influence the performance and health of dairy cows, but data that can enable the comparison of ruminal degradation within and between barley, rye, and triticale grains are scarce. Commonly used techniques to explore ruminal degradation of feed are in situ and in vitro incubations. Both techniques require ruminal-fistulated animals, but alternative methods are being demanded by the community, in order to reduce the number of animal trials. An approach with the potential to estimate the nutritional value of various feeds is near-infrared spectroscopy (NIRS). The present thesis has two major parts. In the first part, ruminal degradation parameters and the effective degradability (ED) of DM, CP, and ST from barley, rye, and triticale grains are investigated using standardised in situ and in vitro incubation techniques. A total of 20 genotypes per grain species were used. In the second part, NIRS calibrations were developed with the aim of estimating the CP and ST concentrations of cereal grains and their incubation residues. Subsequently, data from in situ experiments were used to establish the calibrations for estimating the ruminal in situ degradation of cereal grains from their spectral data. In situ degradation studies have been conducted by ruminal incubation, utilising three lactating cows. Ruminal degradation parameters and ED (ruminal passage rate = 8%//h) were calculated. For in vitro incubations, the samples were incubated in a rumen fluid-buffer mixture (‘Hohenheim Gas Test’). The gas production was recorded for estimating gas production kinetics. In vitro gas production—in combination with crude nutrient concentrations—was used to estimate the metabolisable energy concentration (ME) and digestibility of organic matter (dOM). The degradation rates differed between and within the grain species for DM, CP, and ST. The variation within grain species was not reflected in the ED of CP and ST, due to the relatively fast and almost complete degradation of the grains. The ED of CP was 77% (69–80%) for barley, 85% (83–86%) for rye, and 82% (79–84%) for triticale. The corresponding ED of ST was 86% (82–88%), 95% (92–96%), and 94% (90–95%). Accordingly, the estimated ME (barley: 13.5 MJ/kg DM, rye: 13.9 MJ/kg DM, triticale: 13.5 MJ/ kg DM) showed only relatively minor variation within one grain species. The dOM was overall at a high level (barley: 91.3%, rye: 95.3%, triticale: 95.8%). The relatively small variation within one grain species could not be explained by the chemical and physical characteristics of the samples. Hence, it was concluded that it is feasible to use mean values for every species in feed formulation and ration planning. In the second part of this thesis, it was shown that it is possible to replace chemical CP and ST analyses of samples from in situ studies by NIRS without affecting the calculated ruminal degradation characteristics. NIRS could be used to estimate the ED of CP and ST from cereal grains. The sample set to establish the calibrations included barley, durum, maize, rye, triticale, and wheat grains. Calibrations for the CP and ST concentration were extended to pea samples. The calibrations with the best validation performance for CP and ST concentration were obtained by using the wavelength segment of 1250 to 2450 nm and the first derivative of the spectra (CP: R2 = 0.99; SEP = 0.46% DM. ST: R2 = 0.99; SEP = 2.10% DM). The results of in situ studies did not differ, irrespective of whether chemical or NIRS analysis was used. Like the CP and ST concentration, the ED was estimated with a high accuracy (ED8 CP: R2 = 0.95; SEP = 2.43%. ED8 ST: R2 = 0.97; SEP = 2.45%). However, calibrations need to be extended before they can be recommended for routine use. The present thesis demonstrates that the ED of CP and ST of barley, rye, and triticale grains differ between the species, but variation within one grain species is relatively small and not related to the chemical and physical characteristics of the grain. Hence, under the prevailing cultivation conditions, the mean values for each grain species in feed evaluation are deemed adequate. It was demonstrated that NIRS has the potential to facilitate the evaluation of the nutritive value of cereal grains for ruminants.