School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemEffect of hardness on intake and storage quality of urea molasses block by sheep( 1990)This thesis presents a research programme undertaken to examine the possibility to develop a suitable composition for urea molasses block ideal for Bangladesh climatic conditions, using locally available ingredients. The investigations were carried out within the general context of using rice husk ash (RHA) as a binding agent for urea molasses block and to replace a reasonable proportion of lime in the block. Attention was focussed on the extent of tooth wear and possible causes of variability in intake of urea molasses block and effects of long-term feeding of such blocks on animal performance. A review of literature enabled the presentation in chapter 2 of the various factors affecting intake of urea molasses block, properties of rice husk ash and its opportunity of uses for different purposes and finally the major causes of tooth wear with possible consequences on animals. Reported effects of the level of urea, essential mineral elements, sources of phosphorus in block, climatic conditions and placement of block, animal's previous experience with such food and hardness or compressive strength of urea molasses block are reviewed. It is concluded that increasing the level of urea from 5-10% in the block tends to stimulate intake. A very high level of calcium and low phosphorus or any mineral imbalances tend to decrease its intake through its effects in long-term. Pre-weaning experience and other management strategies have also been found to increase intake of urea molasses block. Supplementation of poor quality cereal straw diets with urea molasses blocks has given variable responses in the reviewed reports. The reasons for this variability are numerous and can be attributed in part to the characteristics of basal diet being supplemented, to animal factors such as species, physiological state and health and to the conditions under which measurements have been made. No studies have been made on the efficacy of use of rice husk ash as binding agent for urea molasses. Chapters 3 and 4 report on experiment in which six different types of urea molasses blocks with varying levels of lime and rice husk ash were prepared and their hardness was measured in terms of compressive strength (kg) both under normal environmental conditions and after placing these blocks in a hot room for 5 days at temperatures and relative humidity of 25- 35C and 50-80% respectively. It is found that 40% rice husk ash and 60% lime (out of total 8% binding agents) is the best ratio in terms of compressive strength. Blocks with more than 8% binding agent have better strength when both rice husk ash and lime are in equal proportion. After compressive strength test four different types of urea molasses blocks were selected for a feeding experiment lasting 13 weeks including two weeks of adjustment period. Barley straw and urea molasses block were offered ad libitum to sheep along with 30 g of lupin/day/sheep. The blocks and straw together constituted four different dietary treatments and three sheep received each dietary treatment. The average initial liveweight was 41.4 kg (range33-59). The organic matter contents of urea molasses blocks were 739-802 g/kg DM. The nitrogen content of straw was 7.1 g/kg DM. The nitrogen contents of blocks ranged from 54.4 to 56.3 g/kg DM. The in vitro organic matter digestibility of straw was 51.8% and of the urea molasses blocks ranged from 92-97%. Comparisons of straw offered with that refused indicated no difference in organic matter, nitrogen and acid detergent fibre content. However, there was a highly significant (P<0.001) difference in neutral detergent fibre (NDF) and silica content between straw offered and refused. The mean daily intake of straw among four different groups of sheep ranged from 31.6 to 40 g DM/kg W0.75. The highest being observed in the group consuming block with 6% rice husk ash and 6% lime. Mean daily intake of urea molasses block was also highest in that group and the range of intake among four different groups was 9.8- 15.2 g DM/kg W0.75. The ratio of intake of block: straw was highest for group D (0.44: 1), followed by blocks A, C and B. The overall correlation between straw and block intake was 0.70. There was no significant difference between intakes of straw and block among the four groups. However, some animals were found to reduce feed intake drastically at the beginning and at the end of the experiment. This reduction in feed intake was much frequently observed with group D consuming the lime only (8%) block. Two out of three animals in this group reduced feed intake during the last three weeks of the experiment. This reduction in feed intake was highly significant (P<0.01) compared to previous intake by the same group or others. There was no significant difference in mean daily liveweight change over the experimental period. Reduction in feed intake in group D during the last three weeks resulted in a highly significant (P<0.01) loss in liveweight compared to liveweight changes of the previous weeks of the same group or other groups of sheep. There was no significant difference in tooth wear among four groups of sheep. Addition of rice hush ash at higher level (10%) will not cause tooth wear. There was no significant difference in nitrogen balance of the four groups of sheep. The highest N balance was observed with group A. Three out of four groups of sheep were in positive nitrogen balance, but positive nitrogen balance was not reflected in liveweight gain, probably due to error in faeces and urine collection, sampling or nitrogen loss during analysis of sample. Alternatively nitrogen balance trial week may not be truly representative of the whole period. There was significant (P<0.05) difference in water consumption between group of animals. The level of silica excreted in faeces was related to silica level in urea molasses block (r=0.94). It is concluded that urea molasses block intake is related to straw intake, factors likely to increase straw intake will also increase block intake. Blocks with high level of lime (8% or more) has harmful effect on animal performance in long-term feeding probably due to mineral imbalances. The effect most likely to affect animal performance is severe reduction in feed intake. Urea molasses blocks containing rice husk ash have not been found to cause any such effect in long-term feeding and better compressive strength can also be obtained with rice husk ash. It is found that at least 40% of lime (out of total 8%) could be replaced with rice husk ash without altering the compressive strength (storage quality) and a better quality block could be made with 12% binding agent, 6% rice husk ash and 6% lime. So the use of rice husk ash as binding agent for urea molasses block could be recommended.