Browsing by Author "Neethling, Kathleen Elizabeth"

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    The effect of different energy and nitrogen sources on in vitro fibre digestion and gas production kinetics of high and low quality forages.
    (Stellenbosch : Stellenbosch University, 2016-12) Neethling, Kathleen Elizabeth; Cruywagen, C. W.; Stellenbosch University. Faculty of Agrisciences. Dept. of Animal Sciences.
    ENGLISH ABSTRACT: Digestibility of fibre from the roughage component of total mixed rations for dairy cows can be influenced by the source of supplemental energy and nitrogen included in the ration. By optimizing the digestion of fibre in the rumen, dairy cows can utilize the potential nutrients in roughages to its best, and thereby obtain more substrates for optimal production. This thesis reports on two in vitro studies aimed to improve forage digestion. In the first study, a high quality forage (lucerne hay) and a poor quality forage (wheat straw) were incubated in vitro with the filter bag method with an energy source, being either maize, citrus pulp or molasses syrup and a nitrogen source, being either soybean meal, urea or no added N. The forage samples were weighed out to provide 125 mg NDF and transferred to Ankom filter bags. Bags were heat sealed and incubated in Erlenmeyer flasks for six and 30 hours at 39ºC. Energy sources were added to the incubation medium in the respective flasks and amounts were calculated to supply a metabolisable energy equivalent of 125 mg of pure starch. The amounts of the respective N sources were calculated to provide 21 mg of N per flask. Dry matter and NDF disappearance values were calculated. There was no treatment that increased DM disappearance significantly in either of the two forage sources after six or 30 hours of fermentation. The highest NDF disappearance values for LH treatments were observed in the LHCU and LHCSB treatments, after six and 30 hours, respectively. With WS as substrate, the highest NDFD values were observed in the WSCSB and WSSSB, at six and 30 hours, respectively. In the second study, the same sources were used as in the first study. Total mixed rations were simulated in which roughage was included at 229 g DM, energy sources at 188 g DM and nitrogen sources calculated to supply 21 mg N. The sample diets were incubated in sealed flasks with rumen fluid and incubation medium for 30 hours. During the incubation period, gas production was measured at regular intervals. After termination of the incubation the same digestion parameters were measured as in the first study. The highest DM disappearance was seen in LHMU and WSSSB for the two forage sources respectively. The combinations that showed the highest NDF disappearance values were M*U and S*U for lucerne hay, and S*SB for wheat straw. In both LH and WS, the highest amount of gas produced was present when M served as energy source and U as nitrogen source. It was concluded that the various combinations of forages, energy and nitrogen sources affected forage digestibility differently and knowledge thereof can be of value in formulating ruminant total mixed rations.