Einfluss verschiedener Faktoren der Stickstoffversorgung auf den Stickstoff‐ und Energieumsatz sowie die Methanproduktion beim Wiederkäuer (English shop)

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The focus of this work lies in examining nutritive modifications of N supply with regard to N source, N amount, ruminal degradability of N as well as the amino acid composition of the undegraded crude protein (UDP) with respect to the efficiency of N utilisation, as well as their potential for reducing N and methane emissions.

The N requirement of methanogenic archaea in the rumen has so far only been rudimentarily described in the literature. Therefore, an in vitro study was intended to examine whether a reduction of N supply in the rumen offers the possibility of lowering methane production without impairing the remaining fermentation performance. Furthermore, by using different N sources, possible preferences of the methanogens in N utilisation were to be investigated. Using the in vitro method of the Hohenheim gas test, the carbohydrates (CHO) starch and cellulose (Cell) were incubated with the N sources casein (Cas) and NH4HCO3 (NPN). The N supplementation comprised four levels with 0/1.68/3.37 and 6.74 mg N per syringe. At the same time, the ratio of buffer solution to rumen fluid was varied (2:1/5:1/11:1) in order to induce an even broader N spectrum. After 24 h of incubation, gas and methane formation were determined. CHO and N source as well as N amount exerted a significant effect on gas and methane formation. Overall, both gas and methane production correlated with the amount of available N, which was defined as N supplementation plus NH3-N of the rumen fluid blank after 24 h. Thus, all CHO/N combinations reached a plateau of maximum production performance with increasing N supply. The transition to this plateau corresponds to the minimum N requirement for optimal fermentation or methanogenesis and was determined by fitting a segmented quadratic function. The minimum N requirement for the methanogens turned out to be considerably lower than for gas formation in the combinations Cell-NPN, starch-NPN and starch-casein, whereas in the combination Cell-Cas the minimum N requirement was at the same level. From this it can be concluded that a reduction of N supply is initially accompanied by a depression of digestibility (gas formation) and that a depression of methanogenesis is only to be expected later. Therefore, a reduction of N supply in the rumen cannot be recommended as an adequate measure for reducing methane emissions.

Microbial protein usually represents the main source of utilisable crude protein at the duodenum. For the efficiency of microbial protein synthesis, in addition to the amount and quality of the CHO and N sources, their simultaneous (synchronous) availability in the rumen also plays an important role. By means of a synchronous ration design, this work was intended to examine whether N excretions as well as methane production can be lowered as a result of an improved N supply. In C/N balance and respiration trials, feed rations based on the CHO source maize (low degradation rate) or pea-starch-sugar (high degradation rate) and the protein carriers whey protein, lupin and urea were administered to 36 lambs (mean live weight (LW) 25 kg) divided into six groups. Using the modified Hohenheim gas test, a synchronous N release of the protein carrier mixture corresponding to the ruminal degradation of the CHO mixture was determined. A cross-over exchange of the protein mixtures with the respective other CHO carrier yielded the asynchronous rations. The synchronous ration design led neither to an increased microbial protein synthesis nor to an improved N retention. In contrast, the protein mixture with the lowest ruminal degradation rate achieved the highest N retention (0.74 and 0.76 g/kg metabolic LW, respectively) irrespective of the CHO source, and thus the lowest N excretion. It can be assumed that with a slow degradation rate of the protein source additional amino acids (AA) are available post-ruminally, whereby N deposition is improved. In the energy balance, synchronisation brought about an improvement of the energy supply of the lambs as a result of a higher utilisation of ME, which was based on a higher fat deposition. Methane production of the lambs was at a very low level, at 11.4-20.3 l per animal and day or 3.3-5.9 % of digestible energy. Slowly degradable CHO sources with a high CHO bypass lowered methane production by up to 45 % compared to rations with a rapid CHO degradation rate, whereas slowly degradable protein sources did not bring about any reduction of methane production. Asynchronous rations numerically led to lower methane emissions than synchronous rations, especially in the rations based on CHO with a rapid degradation rate. On the basis of these results, a synchronous ration design is not suitable for reducing methane production.

Particularly for animals with a high performance level, the contribution of UDP or of the protein bypass to meeting the AA requirement is important. Therefore, this work aimed to investigate in growing lambs the influence of the degradability and AA composition of four protein or N carriers on parameters of fattening and slaughter performance. In each case 20 male and 20 female lambs of the Merinolandschaf breed (mean LW 24 kg) received a feed ration consisting of 25 % hay and 75 % concentrate. The concentrate was based on barley, supplemented by N carriers with decreasing contents of UDP (corn gluten > potato protein > field beans > urea) and was available to the animals ad libitum. A reduced bypass proportion had a performance-reducing effect in the form of significantly lower daily gains (347 g/310 g/281 g/209 g), which likewise resulted in significant differences in the fattening period of up to one month between the best and the poorest group. Feed conversion was also impaired in rations with a low protein bypass. Beyond this, no significant influences of the N carriers on parameters of slaughter performance or on the nutrient composition of the M. longissimus dorsi could be observed. The protein quality of the UDP remained without significant effects on fattening and slaughter performance. From this it is concluded that the lambs used the UDP not only as an AA source but also as an additional energy source for growth. The performance-enhancing effect of a higher bypass protein proportion in the ration possesses a high potential for lowering N and methane excretions per animal and can be implemented in agricultural practice comparatively easily.