In situ starch and crude protein degradation in the rumen and in vitro gas production kinetics of wheat genotypes†

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Almost half of the wheat production in Germany is used as animal feed. However, only approximately 8% of the cultivated wheat genotypes are registered as fodder wheat, whereas at least 79% of these accessions are listed according to the food quality classes A, B or E (BMELV, 2014). Thus, many wheat genotypes with potentially different nutritional characteristics are available for animal feeding. To optimize wheat grain use in diet formulation, its nutritive value, particularly degradation characteristics of starch (ST) and crude protein (CP) in the rumen, must be known. Moreover, in the plant breeding and feeding industries, easily measurable characteristics are necessary to select genotypes with the targeted phenotypic and nutritive values. Grain quality measures currently used include thousand seed weight, test weight (TW) and falling number. However, these characteristics appear not well suited to evaluate the nutritive value of wheat grains for ruminants (Wilkinson et al., 2003).
Several in situ experiments have studied the ruminal degradation of wheat grain, either in comparison with other grain types or as influenced by different growing and/or processing methods (Arieli et al., 1995; Givens et al., 1997; Michalet‐Doreau et al., 1997; Philippeau et al., 1999; Turgut et al., 2004; de Campeneere et al., 2006; Lund et al., 2008; Arroyo et al., 2009). To our knowledge, only three studies compared the in situ degradation of different wheat grain genotypes (Garnsworthy and Wiseman, 2000; Swan et al., 2006; McAllister and Sultana, 2011), and only two studies investigated the gas production (GP) kinetics of a set of different genotypes of wheat grains (Lanzas et al., 2007; Pozdíšek and Vaculová, 2008). Furthermore, only Hindle et al. (2005) compared in situ ST degradation and in vitro GP profiles of wheat grain (a single sample) and determined ruminal degradation in vivo. The advantage of the in vitro GP technique is that fermentation characteristics can be compared against many samples simultaneously within a maximum time of 96 h and without need for additional chemical analyses. It is therefore a very quick and cheap method to study the fermentation characteristics of feedstuffs in the rumen. N. Seifried, H. Steingaß, W. Schipprack and M. Rodehutscord (submitted) showed that the in situ degradation characteristics of ST and CP of maize grains could be described by their in vitro GP profiles and that the effective degradation (ED) of those nutrients in the rumen could be predicted from GP values in combination with physical and chemical characteristics with high accuracy.
The primary aim of the present study was to determine the variation of in situ ruminal degradation parameters of dry matter (DM), CP and ST and ED of these nutrients based on a wide range of wheat grain genotypes. The secondary aim was to evaluate the relationships among in situ degradation kinetics, in vitro GP kinetics and physical and chemical characteristics. Our objective was to investigate how these characteristics alone or in combination with other properties are useful in screening large sample sets of wheat grains to predict the degradation parameters and ED of CP and ST in the rumen.
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