| Summary: | This study was carried out to examine the effect of urea treatment on different roughages with respect to their degradation in the rumen. The effect of urea treatment of barley straw on dry matter intake, digestibility and weight gain was also studied.
The first experiment involved urea treatment of wheat straw and orchardgrass hay. Three urea levels were used; 2, 4 and 6 g/100 g DM and the samples ensiled for 3, 6 and 9 weeks. Samples were incubated in the rumen for 1, 12, 24, 36, 48, 72 and 96 hours. Degradation constants were derived using the equation
p = a + b(1 – e[sup –ct])
where 'p' represents the amount degraded at time 't'. 'a' represents the fraction which disappears rapidly, 'b' represents that fraction which will degrade in time and the rate of degradation of this fraction is represented by the 'c'. The fraction which is undegradable in the rumen can be derived as
100 - (a + b)
. Orchardgrass hay had significantly larger degradation constants than wheat straw (P<0.05). Treatment increased the rapidly disappearing-'a' fraction of wheat straw but reduced the same fraction of orchardgrass hay (P<0.05). The 'b' fraction of orchardgrass hay was increased significantly (P<0.05) by urea treatment; in the case of wheat straw, the increase was not significant (P>0.05). Crude protein content of both materials was increased by treatment (P<0.05). Rumen disappearance of CP did not show a consistent trend especially in the case of control samples and this was an indication of microbial contamination of the residue in the bags. In other words, part of dry matter that remained in the bags was contributed by microbial material. Such material also contributed to the nitrogen content of the residue thus masking some of the crude protein disappearance that may have occurred.
In the second experiment, some of the crop by-products that are fed to ruminants in Kenya, were treated. These included barley straw, maize stover, oat straw, rice straw, wheat straw and rhodesgrass hay which was considered to be of low quality. Water was added to raise the moisture content of the materials to 20%. Urea was applied at 6 g urea/100g DM and the materials were ensiled for 6 weeks. Samples of the ensiled materials and their controls were incubated in the rumen of a cannulated steer for 1, 12, 24, 36, 48 and 72 hours. Also incubated were untreated samples of napier grass, alfalfa hay and pyrethrum marc. Rhodesgrass hay had the largest degradation constants ('a', 'b' and :a+b') before treatment and barley had the least; 13.59, 61.63, 75.22 and 7.16, 37.71, 44.87% respectively. Treatment had the largest impact on rice straw; the 'a', 'b' and 'a+b' increased from 10.24, 46.27 and 56.51% to 22.11, 70.79 and 92.91% respectively. In the case of rhodesgrass hay, treatment had no significant effect (P>0.05). Urea treatment increased significantly (P<0.05) the CP content of all materials. Analysis of data for CP disappearance indicated microbial contamination and this was more evident in the control samples where 24 and 72 hours incubation left the samples with more CP than the unincubated samples. Most of the CP in low quality roughages is bound to the lignin and is therefore undegrable. As degradation proceeds, the CP progressively becomes a larger fraction of the total dry matter which undergraded, thus there is a concentrating effect.
In the final experiment sixteen calves weighing from 86 to 176 kg were divided into four weight categories. Animals within the same weight category were randomly allocated to four different diets; barley straw treated with 4 or 6 g urea/100g DM and ensiled for six weeks; or urea added to straw at feeding time to raise the crude protein to the levels in the ensiled straws. The straws were mixed with hay in 3:1 ratio (straw:hay) and offered ad libitum. In addition each calf received 1.5 kg of concentrate plus 20 g of a mineral mixture daily. A randomized complete block design was used and each group was on diet for four weeks after which the groups were randomly re-assigned to different diets. Treatment did not improve dry matter intake significantly (P>0.05). Acid insoluble ash (AIA) was used as an internal marker to calculate apparent digestibilities for DM, CP and ADF. Straw treated with 6 g urea/100g DM and ensiled had a higher dry matter digestibility (P<0.05) than the other straws; there was a 16.3% improvement over control. Ensiling reduced CP digestibility significantly (P<0.05). Acid detergent fibre digestibility was improved in the case of straw treated with 6 g urea/100g DM and ensiled compared to the control. There were no significant differences between the different diets in terms of average daily gain but there was a trend towards higher gain as the level of urea increased.
Urea as a source of ammonia for the treatment of low quality roughages has given encouraging results and is emerging as a viable treatment method. The method has some advantages over other chemicals in that it is safer to handle, cheaper, readily available and involves simple treatment procedures. === Land and Food Systems, Faculty of === Graduate
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