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Figure 1.
Mean live weight changes for control and Dicrostachys cinerea
group in relation to Dicrostachys cinerea intake. |
| Livestock Research for Rural Development 20 (5) 2008 | Guide for preparation of papers | LRRD News | Citation of this paper |
Poor weight gain and low conception rate of cattle is mainly a result of poor nutrition. The conventional protein supplements are usually too expensive for farmers. Browse plants could be an alternative source of crude protein and/or indirect microbial protein. The objective of this study was to determine the effects of dry season supplementation with Dicrostachys cinerea on weight gain and rumen protozoa in cattle.
The study was conducted for one year in yearling Friesian bulls with average weight of 105 kg. Four were randomly allocated to Dicrostachys cinerea group and five to the control group. All animals grazed together up to 14:00 hours but supplemented in individual pens from 14:00 hours to 08:30 hours the following morning. Ciliate protozoa from each group were counted before and after the commencement of feeding.
The daily weight gains for the Dicrostachys cinerea group in August–November, December, January-February, March-April, May, June, July and August, were 393, 414, 892, 655, 635, 360, 200 and 114 g/day respectively. Weight gains for the control group during the same periods were, 39, 428, 1846, 500, 384, 120, 54 and 23 g/day. In January and February, the control group exhibited compensatory gain. However, the compensatory period was too short for the group to gain its original status of being heavier than the Dicrostachys cinerea group. The population of ciliate protozoa in the Dicrostachys cinerea group decreased by 55% while there was no change in the control group.
Dicrostachys cinerea supplementation significantly increased daily weight gain in cattle. The weight gain was the same for daily or weekly supplementation and could not be offset by compensatory gain in the control group. The defaunating ability of Dicrostachys cinerea in addition to its crude protein played a significant role in increasing weight gain. However, more studies are required for optimising Dicrostachys cinerea supplementation.
Key words: Bacteria, defaunation, protein, tree foliage
Most cattle in Zambia exhibit poor condition for a period of about half a year in the dry season. This poor condition of animals results in low market weights hence less income for the farmer as well as poor reproductive performance of cows, hence small herd sizes. The poor performance of animals at this time of the year is mainly a result of low nutritive value of dry pastures. In addition the presence of a large number of rumen protozoa reduces the protein to energy ratio in the absorbed nutrients (Bird 1991). The reduction in protein to energy ratio is through:
(a) the protozoa engulfing rumen bacteria thereby reducing their availability for intestinal digestion (Coleman 1975)
(b) the retention of about 70% of protozoa in the rumen making them unavailable for intestinal digestion (Weller and Pilgrim 1974; Leng 1982)
(c) the ability of protozoa to digest particulate protein in the rumen and converting the protein and amino acids to volatile fatty acids with a net loss of dietary protein (Ushida and Jouany 1986).
Bird (1991) reviewed the beneficial effects of removing protozoa and maintaining a defaunated rumen and summarised them as: (a) increased use of protein nitrogen in the rumen, (b) increased availability of dietary protein for intestinal digestion, (c) increased production of microbial protein and (d) increased proportion of the rumen microbes flowing to the intestines.
Elimination (defaunation) or reduction of ciliate protozoa numbers from the rumen improves productivity of ruminants fed on fibre or fibre with soluble sugars. This is due to an improvement of the protein to energy ratio in the nutrients absorbed by increasing the amount of bacterial and sometimes dietary amino acids available for absorption at the small intestines. The increased ratio of amino acids to volatile fatty acids in the absorbed nutrients leads to a better performance in defaunated animals (Bird et al 1990; Bird 1991). Despite the benefits to be gained from defaunation the only technique available at farm level is the use of a single drench of vegetable oil, traditionally used by cattle farmers in Vietnam and recently studied in detail by Nuguyen Thi Hong Nhan et al (2001) in Vietnam and Seng et al (2001) in Cambodia.
The objective of this study was to determine the effects of dry season supplementation with Dicrostachys cinerea on live weight gain and rumen protozoa in cattle.
The experiment consisted of five and four yearling Friesian bulls in the control and Dicrostachys cinerea groups respectively. The average live weight of the animals at the beginning of the experiment was 105 kg and they were randomly allocated to the groups. All animals were housed individually in pens from 14:00 hours to 08:30 hours the following morning. During that period, animals in the Dicrostachys cinerea group were given 5kg of supplement consisting of 67% coarsely ground pods of Dicrostachys cinerea, combined with 19.8% of maize bran and 13.2% of maize meal. During the same period each animal in the control group was given 5kg of 67% coarsely ground dry Digitaria grass, combined with 19.8% of maize bran and 13.2% of maize meal. Between 08:30 and 14:00 hours all animals were allowed to graze together in the paddocks with natural grass. Clean fresh water was provided ad libitum through out the period. All feed remaining and all animals were weighed every morning at 08:30 hours. The supplements were given daily in August and September and weekly in October and November of 2006 (see Figure 1). In 2007, no supplements were given.
Protozoa numbers were counted before the beginning of supplementation and on day 1, day 4, day 15 and day 39 of experimentation. Approximately 3 ml of rumen fluid were collected from each animal at 08:30 hours in the morning using a canula and plastic tubing attached to a syringe. A drop of fresh rumen fluid was put on a glass slide and examined under a microscope for determining ciliate protozoa motility. An aliquot of 1ml of well-mixed rumen fluid was added to 1ml of formal saline (10% (v/v) formaldehyde; 0.9% (w/v) NaCl), with a few drops of iodine solution. Fixed protozoa were counted using a haemocytometer and a microscope.
During the period of supplementation the number of ciliate protozoa (193 000±2600/ml) in the Dicrostachys cinerea group was significantly lower than the number before supplementation (423 500±3300/ml). This was a decrease of about 55%. In the control group, there was no significant change in protozoa numbers at any point in time (440 000±3800/ml). Dicrostachys cinerea pod particles in rumen fluid liberated mucilage that either trapped or slowed down the movement of ciliate protozoa.
Figure 1 shows a plot of live weights for the Dicrostachys cinerea and control groups and that of pod intake as a percentage of the live weight of the Dicrostachys cinerea group. Daily fluctuations in live weights were mainly due to fluctuations in gut and bladder fill. The rate of weight gain during the period of daily Dicrostachys cinerea supplementation was the same as the rate of weight gain during the period of Dicrostachys cinerea supplementation at weekly intervals.
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Figure 1.
Mean live weight changes for control and Dicrostachys cinerea
group in relation to Dicrostachys cinerea intake. |
In January and February the daily weight gain in the control group was higher than that of the Dicrostachys cinerea group, exhibiting the phenomena of compensatory gain (Figure 2).
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This study was conducted in yearling Friesian bulls for a period of one year. It was observed that the control group had a growth pattern that showed a significant daily weight gain, only for a period of about six months from December to May inclusive. On the other hand, supplementation with Dicrostachys cinerea pods daily in August and September and weekly, in October and November significantly improved their daily live weight gain in the dry season, through the rain season to June, giving a total period of weight gain of eleven months. Compensatory gain was observed in the control group in January and February. However, the period of compensatory gain was too short to allow the control group gain its original status of being heavier than the Dicrostachys cinerea group. This meant that dry season Dicrostachys cinerea supplementation of cattle in Zambia was beneficial because of the long 8 month dry season and short 4 month rain season that had only 2 months of compensatory gain.
There are various reports of beneficial effects resulting from supplementing ruminants with Dicrostachys cinerea. For example, Smith et al (2005) reported improved performance of goats resulting from supplementation with Dicrostachys cinerea fruits. The beneficial effect of feeding ruminants with shrub or tree forages can be attributed to either high crude protein content, defaunating effects of the forages or both. Various plants species, especially those containing saponins have been shown to decrease or eliminate ciliate protozoa in ruminants resulting in improved weight gains (Leng et al 1992). However, there are no reports of effects of Dicrostachys cinerea on rumen ciliate protozoa in addition to its crude protein content. In this study, daily crude protein intake for Dicrostachys cinerea group was 291g/day and 288g/day for the control group. This level of crude protein intake was below the daily requirement of 427g/day for growing Friesian bulls of 100 kg live weight (Merck 1986). There was no significant difference between the two groups in supplemented total crude protein intake, however, the Dicrostachys cinerea group had a second source, which was due to defaunation, enabling the group meet the daily requirement and even gain significant weight during the dry season. The control group still had a protein deficit in the dry season, hence the compensatory gain in the rain season when protein content in grass had increased.
This study was allowed to continue for eight months without supplementation in order to know how long the benefit of supplementation would last after supplementation had been stopped. In spite of the two months of compensatory gain in the control, Dicrostachys cinerea group had attained much higher live weights after one year. The weekly supplementation from October to November showed that there was some residual daily weight gain in the Dicrostachys cinerea group. Defaunation has been shown to produce a residual weight gain effect because of a gradual increase in bacterial population that apparently is the main protein source for the ruminant. A single drench of cattle with cooking oil reduced protozoa numbers (Seng et al 2001; Nguyen Thi Hong Nhan et al 2001) resulting in a sustained increase in bacterial population (Nguyen Thi Hong Nhan et al 2007) and weight gain for up to 84 days (Seng et al 2001). This type of residual weight gain is not associated with a single dietary crude protein intake of either rumen digestible or rumen by-pass protein because excess dietary protein given at any one time is not stored. In order to maintain a given weight gain, daily requirements of dietary protein must be met on a daily basis, certainly not on a weekly or longer interval.
In this study Dicrostachys cinerea pod supplementation significantly reduced the protozoa numbers in the rumen especially those of the genera Isotricha and Dasytricha. The mechanism responsible for the reduction in protozoa numbers was not investigated in this study. However, it was observed that Dicrostachys cinerea pod particles when soaked in rumen fluid, released mucilage that was seen under the microscope to trap a large number of ciliate protozoa. The protozoa trapped in mucilage were unable to move into a direction of their choice. Protozoa were more effectively immobilised at concentration of 2.5% w/v and above. This meant that in vivo, trapped protozoa would eventually die within the mucilage or would flow together with the digesta to the abomasum where they would be killed by the acidic pH. Therefore, this process would decrease their predatory effect on bacteria in the rumen resulting in an increase in microbial protein available to the animal. Under normal circumstances only 30% of the protozoal cells actually move to the intestines for digestion (Weller and Pilgrim 1974; Leng 1982). It is well established that many factors in the feed can affect ciliate protozoa ecology, in ways that may not be well understood. For example, bentonite, a clay mineral, had an overall effect similar to defaunation when it was added to the diet of sheep in small quantities of 15–20g/d (Fenn and Leng 1990).
Every year 73-81% of leaves fall during the winter season (Singh 1992). Large quantities of nutritious frost killed leaves and fruits from browse plants including Dicrostachys cinerea, are later destroyed by bush fires before animals can consume them. If these valuable crude protein resources that also have the added advantage of reducing protozoa numbers were harvested and safely stored for feeding cattle in the dry season at weekly or longer intervals, they would significantly improve livestock productivity and help to alleviate poverty among the resource poor farmers.
We would like to thank the University of Zambia Directorate of Research and Graduate Studies, the Government of the Republic of Zambia and co-operating partners for funding this study through the GRZ Sector Pool Funding. We also thank Mr M. Chabota for allowing us to use some of his animals in the study.
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Received 14 November 2007; Accepted 29 February 2008; Published 1 May 2008
