Browsing by Subject "Additivität"

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Investigations on ruminal degradation of nutrients and feeding values of single feeds and compound feeds for cattle
(2020) Grubjesic, Goran; Rodehutscord, Markus
The environmental impact of intensive animal farming has been steadily increasing. Cattle can contribute to environmental pollution due to relatively low nitrogen (N) and phosphorus (P) utilisation, leading to their excess excretion. High-yielding dairy cows are commonly fed concentrate compound feed, in mash or pelleted form, to satisfy high protein and energy requirements. Main source of energy in concentrate compound feeds is starch (ST). For the accurate formulation of compound feeds, comprehensive insight into nutritive values of single feeds as well as their potential interactions (associative effects) when mixed is needed. Typically, the nutritive values of single feeds are considered to be additive, assuming that no associative effects exist. However, data supporting such assumption for concentrate feed are scarce. The present thesis had two aims: evaluation of additivity of ruminal degradation of nutrients and feeding values of single concentrate feeds in compound feeds, and evaluation of effects of pelleting on ruminal degradation of nutrients and feeding values of compound feeds. Twelve single feeds were used to formulate eight compound feeds in different combinations, targeting crude protein (CP) concentrations from 16 to 30% in dry matter (DM). Compound feeds were prepared both, in mash and pellet form in a commercial feed mill using standard industrial conditions. Ruminal degradation of single and compound feeds was evaluated using in situ and different in vitro techniques. The in situ incubations were conducted by incubating samples of all single and compound feeds in polyester bags for 2, 4, 6, 8, 16, 24, 48, and 72 hours in three ruminally fistulated dairy cows. Bag residues were analysed and the ruminal effective degradability (EDIN_SITU) of CP and ST, was calculated for passage rates of 5 and 8%/h. Phosphorus is located in plants as phytate (InsP6), and for some feed samples the EDIN_SITU of InsP6 was also determined. The in vitro gas production (GP), digestibility of organic matter (dOM), metabolisable energy (ME), and utilisable CP at the duodenum (uCP) were evaluated using Hohenheim Gas Test and extended HGT. Intestinal digestibility (IDRUP) of ruminally undegraded protein (RUP) was determined using a three-step enzymatic method through incubation with pepsin and pancreatin. Chemical fractionation of CP was performed according to the Cornell Net Carbohydrate and Protein System (CNCPS) The CP fractions can be also used to predict EDIN_SITU. Assessment of additivity was performed by comparing the observed values of compound feeds with values for compound feeds calculated from single feeds. It was concluded that additivity of single feeds in mash compound feeds was given for EDCPIN_SITU, EDSTIN_SITU (Manuscript 1), uCP, CP fractions, GP, and dOM (Manuscript 2). Here, associative effects among single feeds were considered to be small and should not affect formulation of concentrate compound feeds. The GP and proximate nutrients are necessary to estimate ME using appropriate equations, often specific for feed or feed type. The additivity of ME was given only when same ME equation for single and compound feeds was used. Additivity was not given for IDRUP (Manuscript 2). Pelleting had overall small effects on feeding values of compound feeds determined in situ and in vitro (Manuscripts 1 and 2). Presumably, the relatively low intensity of heating (up to 80–90°C) during the pelleting process was not sufficient to significantly affect nutritive value of compound feeds, with the exception of decreased IDRUP. Overall, it was concluded that additivity of ruminal degradation of nutrients and feeding values of single feeds in mash and pelleted compound feeds can be assumed for practical feed formulation. While some associative effects were detected, they might be related to methodological causes in most of the cases.