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Title: Studies of the nutritive value of fresh and conserved grass, with special reference to silage
Author: McDonald, Peter
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1956
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1. Three different experiments in order to compare the nutritive value of 'good' and 'aid' silages made from the same material have been described. In the first experiment a comparison between top and bottom samples taken from a large farm silo showed that considerable variation in chemical composition can occur throughout the mass. In two experiments carried out using small experimental silos, silages with pH differences of 0.5 and 0.6 respectively were produced from similar grass material. There was little difference in nutritive value between the high and low pH products in either case. 2. Two experiments were carried out in order to compare wilted grass silage and ordinary grass silage. The wilted grass silages contained slightly more sugars than the ordinary materials and were of slightly higher pH. In the first experiment the digestibilities of the various constituents were similar in the wilted and non wilted silages but in the second experiment the wilted grass silage showed significantly higher digestibility values for all constituents. The dry matter losses which occurred during ensilage were of a similar order for both materials in spite of the absence of effluent from the wilted grass silo. 3. Results for the composition and digestibility of the constituents of a medium -protein grass- clover mixture and of molassed and unrnolassed silages derived from it indicated that there was little difference in nutritive value and both types compared favourably with the original grass when cut in both spring and autumn. The losses occurring in the silages made from spring grass were of a very low order whilst those obtained in the silages made from autumn grass showed losses of a greater magnitude; the unmolassed material showing the highest loss. The addition of molasses to the ordinary silage at the time of feeding did not markedly affect the digestibilities of the various constituents. The losses encountered during haymaking from the spring grass by two different methods illustrated the advantage that silage making had over haymaking in the efficiency of the conservation process. Tripoding had a distinct advantage over field curing in that a product of higher nutritive value was obtained. 4. In a comparison of the nutritive value of spring and autumn grass cut at a similar C.P. level, little difference could be detected in composition or digestibility although considerable variation occurred in the utilization of the total digestible nitrogen. The nitrogen in the spring grass was more efficiently utilized by growing sheep than that in the autumn grass. 5. An experiment designed to compare the digestibility and nitrogen utilization of dried grass when fed at two different seasons of the year to growing sheep showed that neither season nor age of the animal had much effect upon these values. The results showed there was a tendency for young lambs (aged 9 months) to digest slightly less crude fibre than adult animals although no significant difference in nitrogen utilization was detected. 6. A study of the results of 22 digestibility experiments on grass silages ranging in C.P. content from 9.9 to 23.1 have been made and two different methods of calculating the feed intake of animals on the 'self feed' system have been compared. The value of C calculated by Lancaster's method for animals consuming fresh pasture grass compared favourably with a similar value calculated for sheep on a silage diet. Equations have been derived for calculating dry matter intakes by Lancaster's method and by a method involving the use of the C.P. content of silage.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available