The effect of different energy and nitrogen sources on in vitro fibre digestion of high and low quality roughages

[摘要] ENGLISH SUMMARY: Fibre digestion differs among roughages and it is also affected by the supplementation of different energy and nitrogen sources. Improving ruminal fibre digestion could increase the energy intake of ruminant animals and increase production. It is thus important to maximize forage utilization.This thesis reports on two in vitro studies aimed at the improvement of DM and NDF gestibility, as well as in vitro true digestibility (IVTD). In the first study, four levels of starch were chosen (0, 35, 80 and 125 mg hexose equivalents) to supplement 125 mg of NDF from either lucerne hay (good quality roughage) or wheat straw (poor quality roughage). The in vitro procedure was a combination of the filter bag and test tube (Tilley & Terry, 1963) methods, with slight modifications to the Goering & Van Soest (1970) incubation medium. Samples were incubated at 39 °C for six or 30 hours. No significant differences were observed among levels of starch supplementation regarding fibre digestion, thus the highest inclusion level (50:50 starch HE:NDF) was used in the second study. In the second study, different combinations of energy sources (starch, sucrose, pectin) and nitrogen sources (urea, soybean meal or no N) were studied with the two roughages. The same in vitro procedure was followed as in the first study, but the treatment combinations included an incubation medium that contained no nitrogen. The same digestibility parameters were measured as in the first study and pH was also recorded at the end of the fermentations. Regarding six hours DM digestibility, lucerne showed the best results with sucrose supplementation without any N. After 30 hours, sucrose with soybean meal proved to be the best combination. For wheat straw, treatments had no effect on six hours DM disappearance, but after 30 hours, pectin and soybean meal resulted in the highest digestion values. Similar results were observed for NDF digestibility and IVTD, where the sucrose and soybean meal combination gave the best results for lucerne hay after 30 hours of incubation. For wheat straw, the highest NDF digestibly and IVTD values were observed with the pectin and soybean meal combination at 30 hours. After six hours of fermentation, the highest pH values were observed for lucerne hay with starch and urea supplementation. After 30 hours, the same combination of starch and urea resulted in the highest pH values in both roughages.In the second study, it was shown that pectin and sucrose as energy sources resulted in the highestin vitrodigestibility values when supplemented to low quality (wheat straw) and high quality (lucerne hay) roughages, respectively. Soybean meal proved to be the best N supplement for both roughage sources. It was concluded that different energy sources affect in vitrodigestibility of different roughages in different ways. This may have practical implications in ration formulation for ruminant animals.

[发布机构] Stellenbosch University