L.R. Ndlovu and L. HoveDepartment of Animal Science
University of Zimbabwe
P.O. Box MP 167
Mount Pleasant
Harare
Zimbabwe
Summary
Resume
Introduction
Materials and methods
Results and discussion
Conclusions
References
Five rumen-cannulated mature does were used to measure intake and rumen parameters in a trial to investigate the potential of groundnut hay as a supplement for goats fed on mature veld hay. Another 5 does were used to measure intake and digestibility. Groundnut hay was offered at 135 g/hd/d, 270 g/hd/d, 405 g/hd/d or 900 g/hd/d in addition to a 75/25 mixture of veld hay/dried poultry manure at 900 g/hd/d (control) for all treatments. Groundnut hay increased total dry matter intake (P < 0.05) but reduced intake of basal diet. Apparent digestibilities increased (P < 0.05) with increased levels of groundnut hay. Rumen pH and NH3-N increased to the 405 g treatment. The reasons for the drop at the higher level are unclear but could be related to volatile fatty acid production. A level of groundnut hay of 400 g/hd/d is recommended as optimal.
Cinq chèvres adultes équipées des cannules du rumen étaient utilisées pour mesurer les quantités ingérées et les paramètres du rumen afin d'évaluer le potentiel des fanes d'arachide utilisées comme suppléments pour des chèvres alimentées sur le foin de prairie naturelle mûre. Cinq autres chèvres ont été utilisées pour mesurer les quantités ingérées et la digestibilité. Les fanes d'arachide étaient offertes à 135 g/tête/j, 270 g/tête/j, 405 g/tête/j ou 900 g/tête/j alors que le foin de prairie naturelle mélangé avec 25 p.cent de fiante de poule séchée était offert à 900 g/tête/j pour l'ensemble des traitements. Les fanes d'arachide séchées augmentent l'ingestion de la matière sèche totale (P < 0,05) mais réduisent l'ingestion de la ration de base. La digestibilité apparente augmente (P < 0,05) avec l'augmentation du niveau de fane d'arachide. Les pH du rumen et l'azote ammoniacal n'augmentent qu'au-dessus de 405 g de fane d'arachide et ensuite diminuent. Cela pourrait être en relation avec la production des acides gras volatiles. Un niveau de fane d'arachide de 400 g/tête/j peut être recommandé comme ration optimale.
It has been estimated (AGRITEX, 1986) that more than 70% of Zimbabwe's meat goats are kept in dry mopani and acacia areas, the remaining 30% being in grassland areas where crop residues are also available (Central Statistics Office, 1986). In winter, the veld in Zimbabwe deteriorates in quality to less than 3% crude protein (Elliot and Fokkema, 1961). Protein supplementation increases veld intake by cattle (Elliot, 1967; Sibanda, 1989) and sheep (Elliot and Topps, 1963; Sibanda, 1989).
This experiment evaluates the potential of groundnut hay as a supplement for goats fed on veld hay and attempts to determine possible interactions between it and groundnut hay.
Experimental design and diets
Mature (3 yr) indigenous goats of about 31 kg were used in 2 trials. In Trial 1, 5 does fitted with permanent rumen cannulae were used for measuring intake, rumen parameters, rumen degradability and rate of passage from the rumen of veld hay. Intake and digestibility studies were made on 5 other does in Trial 2.
Both trials were run as 5 x 5 Latin squares. Basal diets (mature veld hay/dried poultry manure at 75/25 w/w) were offered at 900 g/doe/d throughout the experiment. Groundnut tops were supplied at 135 g/doe/d, 270 g/doe/d, 405 g/doe/d and 900 g/doe/d in addition to the control with no supplementation. The chemical composition of veld hay, veld hay mixed with dried poultry manure and groundnut tops is shown in Table 1.
Experimental protocol
In Trial 1, intake was monitored during 17 d but only days 11-16 were used to calculate the intake. On day 17 rumen fluid was collected every 3 hr for 24 hr. The pH was measured immediately after sampling and the fluid was strained through 4 layers of cheesecloth and stored at -20°C for further analysis. In Trial 2, goats were placed in metal metabolism crates. The first 10 d were used to adjust animals to the diets and the remaining 7 d to measure intake and faecal and urine outputs.
Table 1. Chemical composition of the main ingredients of the diets fed to goats in Trials 1 and 2.
|
Constituent¹) |
Veld hay |
Groundnut hay |
Veld hay/ poultry manure 75/25 w/w |
|
Dry matter |
88.0 |
89.0 |
89.0 |
|
Organic matter |
87.0 |
92.0 |
83.0 |
|
Neutral-detergent fibre |
64.5 |
44.0 |
61.0 |
|
Crude protein |
4.3 |
7.4 |
6.4 |
Note: 1. Dry matter as % of wet weight, other constituents as % DM.
Chemical analysis
Feed, orts and faeces were analysed for dry matter (DM) and neutral-detergent fibre (NDF). Feed and orts were also analysed for crude protein (CP) and organic matter (AOAC, 1975). Rumen NH3-N was assayed for by the indophenol-blue method (Novezamsky et al, 1974) and pH measured using a pH meter (Precise Instruments, Harare).
Intake
Total dry matter intake increased with the amount of groundnut hay offered (Figure 1), with the intake at the highest level being twice that of the control. The increase in intake was due to substitution rather than supplementation. A supplement has been defined as a feed that will increase total intake whilst maintaining or increasing intake of the basal diet (Kempton, 1982). The current experiments showed that the intake of the basal diet decreased with increased groundnut hay. Similar results have been reported using alfalfa hay as a supplement (Ndlovu and Buchanan-Smith, 1987). The preference for the groundnut hay was probably due to palatability and NDF content. The cell wall (NDF) of legumes is more fragile than that of grasses (Seoane, 1982) and would thus require less chewing per bolus (Welch, 1982). Total NDF intake did not differ greatly among treatment (Figure 2) and only the highest level of groundnut hay intake resulted in significantly higher NDF intakes. These results seem to support the theory of constant cell wall mass intake (van Soest, 1982). Organic matter intake followed the same pattern as total dry matter intake.
Figure 2. Intake of cell wall (NDF) and organic matter by Zimbabwe goats offered different levels of groundnut hay.
Digestibility
Apparent digestibility, as expected, increased with the level of groundnut hay supplied (Table 2), as the goats preferentially selected groundnut over veld hay and increasingly ate a diet better than that offered.
Rumen environment
Ruminal pH and NH3-N are important determinants of fibre digestion. High levels of both tend to favour digestion of fibre. A steady increase occurred in rumen pH and NH3-N as groundnut supplement increased from 0 g to 405 g but this was followed by a sudden drop at 900 g (Table 3). The reason for this is unclear, particularly as it is not reflected in intake and apparent digestibility. It is possible that when groundnut hay makes up over 80% of total dry matter intake, production of volatile fatty acids is increased sufficiently to result in a drop in pH. The drop, while statistically significant, does not result in a rumen pH that is detrimental to cellulolytic microbes (Hespell, 1979) and therefore would not affect intake and apparent digestibility.
Table 2. Apparent digestibility (%) of veld hay diets consumed by goats given graded levels of groundnut hay in Zimbabwe.
|
Groundnut hay level (g/hd/d) |
Digestibility |
|
|
Dry matter |
Organic matter |
|
|
0 |
36.6a |
39.6a |
|
135 |
42.4ab |
44.7ab |
|
270 |
45.2bc |
46.6bc |
|
405 |
50.3c |
51.6c |
|
900 |
54.8c |
56.6c |
In the same column, values without a suffix letter in common differ (P < 0.05).
Table 3. Mean rumen pH and NH3-N levels (ma N/100 ml of rumen fluid) of goats offered different levels of groundnut hay in Zimbabwe.
|
Groundnut hay level (g/hd/d) |
pH level |
NH3-N level |
|
0 |
6.423a |
2.60a |
|
135 |
6.564b |
3.80b |
|
270 |
6.681e |
4.67b |
|
405 |
6.731e |
6.06c |
|
900 |
6.521b |
3.98b |
In the same column, values without a suffix letter in common differ (P < 0.05).
Groundnut hay improved total dry matter intake but reduced intake of basal feed, particularly at high levels. There was no evidence of the synergism between veld hay and groundnut hay in intake and apparent digestibility which has been reported elsewhere (Heavens, 1978; Klopfenstein and Owen, 1981; Preston and Leng, 1984). It would appear that best benefits from groundnut hay as a supplement are achieved at levels below 400 g/hd/d.
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Central Statistics Office 1986. Agriculture and livestock survey of communal lands. Report AL3. Zimbabwe National Household Survey Capability Programme, Government Printers, Harare, Zimbabwe.
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Sibanda S. 1989. Effects of protein source on rumen degradability of nitrogen from protein for ruminants available in Zimbabwe and the performance of growing sheep and cattle. Ph.D Thesis. University of Zimbabwe, Harare, Zimbabwe.
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Indigenous Meshona goat on tether in Zimbabwe
