D. Jotee
School of Agriculture, University of Mauritius
Reduit, Mauritius
Introduction
Materials and methods
Results
Discussion
Conclusions
References
Mauritius imports a substantial amount of its requirement for animal products thus negatively affecting its already strained balance of payment situation. This heavy dependence on imports is, no doubt, a phenomenon common to many developing countries. In recent years, the government has been promoting the animal production sector in order to rectify this situation and to create employment.
However, one of the major factors limiting increased animal production in Mauritius is the unavailability of land for feed production, due to the small size of the country and the high population density. There are, on the other hand, huge quantities of certain agro-industrial byproducts which, to date, have been little utilised as animal feed. Some 40% of the island's total area is devoted to sugar-cane production.
In non-disaster years, the average production of sugar-cane tops is estimated at 1.3 million t (UNDP, 1981). Of this, only 510% is utilised as feed during the crop season. Other byproducts include maize stover and cobs, obtained primarily from the interline growing of maize in the sugar-cane fields, and poultry litter/manure. Neither of these are used as animal feeds, despite their vast potential.
It is evident that in the future, agricultural waste products will play an increasing role in meeting the feed requirements of ruminants.
No doubt one of the reasons for the low level of utilisation of ligno-cellulosic wastes is their low protein content. This can, however, be overcome by supplementing the basal diet with locally produced, cheap leguminous forage. The forage which has been investigated so far, and which has proved to be a valuable protein supplement in ruminant diets, is Leucaena leucocephala.
The objectives of this investigation were to assess the nutritive value of Leucaena, to examine the effects of the mode of presentation of Leucaena with sugar-cane tops on animal performance, and to evaluate the effects of the various dietary treatments on carcass yield and composition.
Eighteen bucklings, each approximately 6-7 months old and similar in size and weight, were divided into three groups of six each. The animals were dewormed with Thibenzole and given 14 days to adjust to their new surroundings and feed before the experiment started. All animals were properly identified and weighed. During the experimental stage of 100 days, animals were weighed weekly after overnight fasting. After 60 days, half the animals from each treatment were slaughtered after overnight fasting and the carcass characteristics determined according to the procedure described by Owen and Norman (1977). The remaining animals were fed for a further 40 days and then slaughtered for carcass analysis. The experiment was replicated 6 months later with female goats of the same age but no carcass evaluation was carried out.
Diets
Three diets were formulated and one group of goats was assigned randomly to each diet. The diets were:
Diet A - Elephant grass (Pennisetum purpureum) + concentrate (control);
Diet B - Sugar-cane tops and Leucaena (1:1 w/w, fresh basis; offered separately);
Diet C - Sugar-cane tops and Leucaena (offered as a mixture).
All the fibrous feed components were chopped and offered ad libitum to the group-fed animals. The concentrate was a feed formulated for growing sheep and was given at the rate of 25 g/kg metabolic weight. A standard mineral-vitamin mixture and water were freely available. Daily feed intakes were recorded and weekly samples of fresh feed were processed for subsequent determination of dry matter intake and chemical composition.
Statistical analysis
An analysis of variance was carried out to determine the effect of the treatments. When the differences among the means were significant (P<0.05), the Duncan multiple range test (Steel and Torrie, 1960) was used to compare the means.
General observations
During the first experiment, two animals died, one on diet A and the other on diet C. In the second experiment, two animals on diet A and one on diet B. died. In some cases pneumonia caused the death but in other cases no proper cause could be established. Intoxication by mimosine did not apparently play a role. No clinical symptoms, such as profuse salivation or alopecia goitre, were observed. Examination of the tongue and oesophagus of the slaughtered bucklings did not reveal any ulceration, a common feature of Leucaena poisoning. The chemical composition of the various feed components used in the experiments is shown in Table 1. Table 2 presents the data on the dry matter intake, daily weight gain and efficiency of feed utilization for the various dietary treatment.
Table 1. Chemical composition (%) of feed components used.
|
Feed component |
Dry matter |
Expressed as % of dry matter |
||||
|
Crude protein |
Crude fibre |
Nitrogen-free extract |
Ether extract |
Ash |
||
|
Elephant grass |
20.8 |
8.5 |
35.4 |
45.1 |
1.4 |
9.5 |
|
Concentrate |
88.7 |
20.5 |
7.3 |
44.6 |
19.4 |
8.2 |
|
Sugar-cane tops |
31.3 |
4.6 |
36.8 |
49.2 |
1.4 |
8.1 |
|
Leucaena |
28.2 |
23.2 |
27.8 |
39.8 |
2.8 |
6.4 |
Table 2. Dry matter intake, daily weight gain and feed utilization.
|
|
Experiment I |
Experiment II |
||||
|
Diet |
Diet |
|||||
|
A |
B |
C |
A |
B |
C |
|
|
No. of animals |
6 |
6 |
6 |
6 |
6 |
6 |
|
Initial weight (kg) |
10.0 |
11.1 |
14.0 |
13.7 |
11.6 |
12.6 |
|
Duration of experiment (days) |
100 |
100 |
100 |
100 |
100 |
100 |
|
Total dry matter (kgW0.75/day) |
75±32a |
77±29a |
58±20b |
40±25a |
61±25b |
60±10b |
|
Dry matter intake kg feed/kg gain |
12.6 |
12.2 |
11.0 |
11.9 |
14.0 |
12.4 |
Treatment means with common superscripts are not statistically different at P<0.05.
Buckling feeding experiment
The effects of dietary treatment on daily weight gain and dry matter intake per kg metabolic bodyweight were very highly significant (P<0.001). Average daily gains of 38, 43 and 43 g were recorded for animals fed on diets A, B and C respectively. The difference in weight gain was not statistically significant (P>0.05), indicating that a diet of sugar-cane tops in combination with Leucaena was at least comparable to the control diet.
Animals fed diet C had the lowest dry-matter intake (kg W0.75), which was significantly lower (P<0.05) than the values of diets A and B. However, the best efficiency of feed utilization (kg feed dry matter per kg mass gain) was observed for diet C, implying that this diet, despite the low level of dry matter intake (g/kg W0.75), was more efficient. This could possibly be attributed to the more balanced nutrient intake in this treatment in which selection for the individual feed components was minimal. Selection of feed components in favour of Leucaena was more pronounced in diet B.
Female goat feeding experiment
Dietary treatment exerted a highly significant effect on dry matter intake/kg W0.75. Animals fed diets B and C consumed significantly (P<0.05) more dry matter than animals fed the control diet. However, the daily weight gain recorded indicated only a negligible difference among the various treatments. The poorest efficiency of feed utilization was noted for animals on diet B. while the values for animals on diets A and C were similar.
Carcass characteristics
The slaughter and dissection data are presented in Table 3. Dietary treatments exerted a significant influence (P<0.05) on most of the parameters investigated. On the other hand, the duration of feeding (60 or 100 day period) influenced only the dressing rate (P<0.01) and the weight of the loin (P<0.05) significantly. It must be noted that animals fed diet B yielded consistently higher values for all the parameters, which were, however, not significantly different. Significantly higher values (P<0.05) for all parameters were recorded for animals reared on diet C. This can be attributed not only to the dietary treatment but also the higher slaughter weight. The fact that few differences exist among the three dietary treatments is shown in Table 4.
Table 3. The effect of dietary treatments on carcass characteristics.
|
|
Dietary treatment |
||
|
A(n=5) |
B(n=6) |
C(n=5) |
|
|
Liveweight at slaughter (kg) |
11.6 |
12.7 |
15.9 |
|
Cold carcass weight (kg) |
4.6a |
4.8a |
6.6b |
|
Dressing rate (%) |
36.5a |
38.8a |
43.2b |
|
Neck (kg) |
0.4a |
0.5a |
0.7b |
|
Shoulder (kg) |
0.8a |
1.0a |
1.4b |
|
Thorax (kg) |
0.9a |
1.1a |
1.4b |
|
Loin (kg) |
1.0a |
1.2a |
1.7b |
|
Hind leg (kg) |
0.4a |
1.1a |
1.5b |
|
Meat (kg) |
2.7a |
3.1a |
4.5b |
|
Bone (kg) |
1.1a |
1.4ab |
1.7b |
|
Fat (kg) |
0.1a |
0.1a |
0.3b |
|
Meat: bone ratio:1 |
2.3 |
2.3 |
2.8 |
Treatment means with common superscripts are not statistically significant at P<0.05.
Table 4. Relative proportion of the carcass joints and tissues (% of cold carcass weight).
|
Cold carcass weight (kg) |
Dietary treatment |
|||
|
A |
B |
C |
||
|
4.05+0.3 |
4.76=1.09 |
6.63+1.2 |
||
|
Carcass joint |
|
|
|
|
|
|
Neck |
10.7 |
10.1 |
10.3 |
|
|
Shoulder |
19.3 |
20.4 |
20.4 |
|
|
Thorax |
22.0 |
22.3 |
21.0 |
|
|
Loin |
24.2 |
22.4 |
25.0 |
|
|
Hondles |
23.2 |
23.1 |
22.9 |
|
Carcass tissues (%) |
|
|
|
|
|
|
Meat |
65.7 |
65.3 |
68.3 |
|
|
Bone |
28.2 |
28.8 |
25.0 |
|
|
Fat |
3.2 |
2.7 |
3.9 |
The results of this study indicate that sugar-cane tops, a waste product of sugar-cane production, available in considerable quantities, could be used to formulate rations that sustain reasonable levels of growth in fattening goats. Sugar-cane tops are deficient in protein but can be successfully supplemented with the locally available legume, Leucaena leucocephala, to provide a balanced diet at a cost reasonable for economic production.
The dry-matter intake/kg W0.75 of the bucklings is in agreement with the data compiled by Devendra (1980) for tropical breeds, and other breeds introduced in the tropics, and those of Rekib (1979) for certain Indian breeds. The dry-matter intake was generally lower in comparison with other published values for temperature breeds and lactating animals. However, it is known that temperate breeds and lactating animals are capable of consuming higher levels of dry matter.
Average liveweight gains recorded are comparable to some data on tropical breeds (Singh and Senghor, 1970; Devendra and Chenost, 1973; Darbadaho et al, 1976; Fielding, 1977), but well below other published figures (Campbell, 1977; Naude and Hofmeyer, 1981). These depressed growth rates may be attributed partly to the inherent, relatively low, genetic growth potential, to some degree of inbreeding and to unfavourable climatic conditions prevailing during part of the experimental periods. The commonly observed depression in growth rate after weaning (from the fourth to the eighth month) as reported by McDowell and Bone (1977) could also have played a role.
The generally poorer efficiency of feed utilization of the female goats fed sugar-cane tops and Leucaena diets may, to some extent, be explained by the relatively lower levels of dry matter intake and/or growth rates. That high feed intake and high growth rate positively affect feed utilization efficiency is adequately supported by Fehr et al (1976) and Naude and Hofmeyer (1981). The feed conversion efficiency obtained in this study partly agrees with the findings of Devendra (1967) who recorded feed conversion ratios of 9.0, 10.5 and 16.7 for the Kambing Katjang breed fed a high, medium and low plane of nutrition.
Comparable efficiency of feed utilization was obtained by Wilson (1985) and more favourable data were reported by Ueckermann (1969) and Naude and Hofmeyer (1981) using improved breeds and better planes of nutrition.
The absence of any symptoms of Leucaena poisoning may be an indication that the animals possess certain micro-organisms in the rumen capable of degrading the toxic principle of the Leucaena, as reported by Jones (1981).
The results of the dressing rate are generally similar to the values obtained for tropical breeds by several authors (Ghanekar et al, 1973; Owen and Norman, 1977; Laor, 1978; Fielding, 1980). These results also agree with the fact that, to a certain extent, the dressing rate increases with increasing slaughter weight and age.
Jointing procedure, no doubt, has an effect on the percentage of the various joints in the cold carcass. The adoption of jointing procedures recommended by Owen and Norman (1977) yielded proportions of the various joints comparable with those of the authors. The percentage of meat in the cold carcass was found to be more favourable in animals fed sugarcane tops and Leucaena as a mixture. This is possibly due to a better energy/protein ratio, whereas the percentage of fat was slightly higher than the values for diets A and B. The published data (Owen, 1975; Fehr et al, 1976; Gall, 1982) on the percentage of carcass tissue in the cold carcass are in agreement with the results obtained in this study. However, the meat to bone ratio tended to be lower, probably due to the relatively poor body conformation of the animals.
It may be concluded that the use of sugar-cane tops, adequately supplemented with Leucaena, appears to be technically feasible as a feed for fattening goats, However, further investigations are required to assess its economic feasibility and to determine the most appropriate mode of presentation of the feed components to goats, given the particular feeding habits of these animals. Further research is required on processing methods, on the possibility of upgrading sugar-cane tops by micro-biological treatment, and on developing proper methods of preserving sugarcane tops for the inter-crop season.
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