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Use of whole sunflower seeds and urea as supplements to crop-residue-based diets for goats

A R Warambwa 1 and L R Ndlovu 2

1 Henderson Research Station
Private Bag 2004, Mazowe, Zimbabwe

2 Department of Animal Science
University of Zimbabwe
PO Box MP 167, Mount Pleasant, Harare, Zimbabwe

ABSTRACT

The potential use of diets based on maize stover and groundnut bay with either urea or sunflower seed as a supplement was investigated using indigenous Small East African goats. Four female goats fitted with permanent rumen cannulae were randomly assigned to a 2 x 2 change-over design to determine dry-matter loss using the nylon-bag technique. The sunflower-supplemented diet contained more readily degradable fraction than the urea-supplemented diet (11.45 vs 4.64%) but had a lower dry-matter degradation (45.08 vs 56.02%). In another trial, 33 female goats were balanced for weight and assigned to two groups and given one of the two diets for 16 weeks. Intake and liveweight changes were not different between the two diets. Both diets were adequate to maintain weight.

RESUME

Utilisation de graines entières de tournesol et d'urée comme compléments de rations à base de résidus de récolte chez les caprins

Des rations à base de paille de maïs et de fourrage d'arachide complémentés avec de l'urée ou des graines de tournesol ont été évaluées sur des petites chèvres d'Afrique de l'Est. Quatre femelles dans le rumen desquelles avaient été en permanence fixées des canules ont été réparties au hasard selon un modèle croisé en vue de déterminer les pertes de matière sèche par la méthode des sachets en nylon. Il ressort des résultats enregistrés que la fraction facilement dégradable était plus importante avec les graines de tournesol qu'avec l'urée (11,45% contre 4,64%). Par ailleurs, le taux de la dégradation de la matière sèche était plus faible avec le premier (45,08%) qu'avec le second type de complément (56,02%). Dans un autre essai, 33 chèvres avaient été divisées en deux groupes de poids homogène soumis chacun à l'une ou l'autre de ces deux rations pendant 16 semaines. Ces deux régimes alimentaires permettaient en outre aux animaux de maintenir leur poids et n'étaient différents ni en ce qui concerne la consommation, ni en ce qui concerne les variations de poids des animaux.

INTRODUCTION

Nutrition is the main constraint to goat production in Zimbabwe (Manyuchi and Sibanda, 1989) and stocking rates may be as high as 15 times the recommended levels. As pressure on land continues to increase with the increasing population (3.6% per year), especially in the crop-livestock areas, overgrazing in the wet season does not allow sufficient weight carry-over for the dry season, leading to weight loss and general low productivity. Results from the University of Zimbabwe (Nyamangara and Ndlovu, 1991) show that goats lose weight even in the wet season, especially when continuous rain restricts grazing time.

One possible solution is to provide supplementary feed. The resources available in communal areas are mainly crop residues (maize and sorghum stover and groundout tops). Cereal stovers have high fibre and low nitrogen contents and thus low degradabilities in the rumen, and so are generally low in nutritive value. Groundnut hay has higher nutritive value and has been found to improve utilisation of stovers (Ndlovu and Hove, 1989). However, low nitrogen diets supplemented with legume still need a source of readily fermentable nitrogen to ensure adequate concentration of ammonia in the rumen (Preston, 1986). Urea used as a feed supplement, even in small amounts, can increase fermentable nitrogen. There may also be a need to supply animals with "by-pass" energy in the form of lipids. Most farmers in the communal areas grow some sunflowers. Sunflower seed contains about 20% crude protein and 40% oil and its use in crop-residue-based diets could be beneficial.

The aim of this study was to characterise diets based on crop residues supplemented with small amounts of urea or sunflower seed.

MATERIALS AND METHODS

Animals and diets

The experimental animals were indigenous female Small East African goats.

Two experimental diets, based on maize stover and groundnut hay, were investigated; one (diet A) contained urea as a supplement, the other (diet B) sunflower seed (Table 1).

Table 1. As-fed composition and chemical analysis of diets


Diet A

Diet B

As-fed composition (%)

Groundnut hay

28.2

25.9

Maize stover

65.9

60.2

Urea

1.9

-

Sunflower seed

-

10.3

Ground limestone

1.2

1.1

Salt

2.6

2.4

Vitamin/mineral mix

0.2

0.2

Chemical analysis (g/kg DM)

Dry matter

95.78

95.89

Crude protein

7.17

8.45

Neutral detergent fibre

73.05

69.35

Acid detergent fibre

52.72

48.49

Ash

1.09

8.33

Fat

1.31

3.49

Dry-matter degradability

Dry-matter degradabilities of the diets were determined using four female goats fitted with rumen cannulae and randomly assigned to a 2 x 2 change-over design. Feed samples were milled to pass through either a 3-mm or a 1-mm screen to assess the effect of particle size on degradability. Nylon bags (195 x 90 mm; pore size, 38 m m) containing 3 g of feed were incubated in the rumen of each goat. Bags were withdrawn at 3, 6, 9, 12, 24, 48 and 72 hours, washed under running tap water and dried at 60°C to constant weight. Dry matter was analysed at each sampling time. Degradability was described using a derivation of the equation described by Ørskov and McDonald (1979):

Amount degraded in time t = a + be-ct

where:

a = readily degradable fraction (%)
b = extent of degradation (%)
c = rate of degradation
t = time (hours)

Intake and growth of goats

A total of 33 young indigenous female goats were stratified according to weight and then randomly assigned to two groups. Goats with a liveweight less than 15.5 kg at the start of the trial were classified as light, the others as heavy. The goats were housed in individual pens with concrete floors and received either diet A or diet B for 16 weeks. Feed intake was recorded daily. Liveweight changes were recorded fortnightly.

RESULTS

Dry-matter degradability

Results of the dry-matter degradability studies are shown in Table 2.

Diet B had a significantly (P<0.001) higher readily degradable fraction than diet A. Screen size had an effect on degradability of diet B. but not of diet A. There were significant diet and screen interactions (P<0.05). Within the 1-mm screen size, diet B had higher (P<0.05) readily degradable values than diet A. There were no such differences with between samples milled through the 3-mm screen.

Diet A had a higher extent of degradation than diet B (P<0.001). Within diet A, samples milled through a 1-mm screen had a higher extent of degradation (P<0.05) than those milled through a 3-mm screen. Diet B was not affected by screen size. Within both screens diet A had a higher extent of degradation (P<0.05) than diet B.

Rate of degradation was similar for both diets and was not affected by screen size.

Table 2. Dry-matter degradability values of crop-residue-based diets supplemented with either urea (diets) or sunflower seed (diet B); feed samples milled through 1-mm or 3-mm screen



Degradability value (%)

1-mm screen

3-mm screen

Readily degradable fraction (%) a

Diet A

3.42

5.85

Diet B

14.37

8.54

Extent of degradation (%) a

Diet A

58.97

53.08

Diet B

46.06

44.10

Rate of degradation a

Diet A

0.041

0.045

Diet B

0.044

0.051

a In the equation (amount degraded in time t = a + be-ct), a = readily degradable fraction; b = extent of degradation; c = rate of degradation; t = time

Table 3. Effect of diet and weight category of goats on liveweight change, feed intake and efficiency of production for goats fed crop-residue-based diets supplemented with either urea (diet A) or sunflower seed (diet B)


Total liveweight change (kg)

Total intake (kg)

Feed efficiency (liveweight gain/feed intake)

Diet A

0.70

49.6

0.014

Diet B

0.66

50.7

0.013

SE

0.35

1.21

0.007

Light goats

0.84

48.3

0.017

Heavy goats

0.52

52.1

0.010

SE

0.35

1.21

0.007

Animal responses

Feed intake and growth responses of the animals fed the experimental diets are shown in Table 3. There were no differences in liveweight changes within diet groups or weight categories. There were no differences in daily intake between diets but, as expected, heavier animals consumed more than light animals (P<0.01). Feed efficiency did not differ within diet or weight groups.

DISCUSSION

Dry matter degradabilities

The inclusion of sunflower seed in diet B was meant to increase both energy and protein content of the diet. This was, however, not achieved as the diets were similar in terms of chemical composition. Adding a source of oil to diets based on maize stover is supposed to alter the glucogenic ratio in volatile fatty acids in favour of propionate (Preston and Leng, 1987) thus leading to higher gains of goats on such diets. However, the maximum recommended level of oil inclusion is 5%, as higher values tend to depress intake and reduce microbial activity (Jenkins and Palmquist, 1984). Adding 12% unprocessed sunflower seeds supplied 3.5% oil inclusion. As this was less than the maximum recommended level, the lack of response by the goats was probably due to poor degradation of the unprocessed sunflower seed. Sunflower seed has a thick seed coat which might be resistant to degradation by rumen bacteria. It is also possible that the fat in the sunflower seed reduced hydrophility of feed particle surfaces and prevented further microbial adhesion and digestion (Lindberg, 1985).

According to Preston (1986), if extent of degradation of roughage after 48 hours is less than 40 50%, then it is not worth feeding. Degradability of both diets A and B had exceeded 40% by 48 hours; these diets thus appear to be promising feeds.

Effect screen size

Milling samples through a 3-mm screen decreased the readily degradable fraction in diet B and the extent of degradation in diet A compared with the 1-mm screen. Decreasing screen (feed particle) size increases the surface area exposed to microbial activity and hence results in higher degradation values (Ørskov, 1975). However, in other instances screen size had no effect. Lindberg (1984) postulated that lack of effect due to particle size could be due to reduced inflow of rumen liquor and microbes into the nylon bags. Other workers (van Keuren and Heinemann, 1962) also found no significant effects due to screen size. Differences in dry-matter disappearance due to screen size may be noticeable at short incubation times, but prolonged incubation reduces the magnitude of differences in digestibility (McLeod and Minson, 1969).

Animal responses

Goats on both diet A and B managed to maintain weight throughout the 16-week experimental period. The results obtained are in contrast to work done by Prasad and Mandebvu (Makoholi Research Station, Masvingo, Zimbabwe) who reported weight loses (-14 and -11 g/d) when groundnut and siratro hay, respectively, were fed with maize stover. However, Banda and Ayoade (1986) reported that groundnut haulms significantly improved liveweight gains in goats fed maize bran.

CONCLUSIONS

Although neither diet could support goat production, both were adequate to meet the maintenance requirements, and this is a positive step in improving goat productivity in critical periods (hot wet and cold dry seasons) when the goats lose weight.

REFERENCES

Banda J L L and Ayoade J A. 1986. Leucaena leaf hay (Leucaena leucocephala cv Peru) as protein supplement for Malawian goats fed chopped maize stover. In: Preston T R and Nuwanyakpa M Y (eds), Towards optimal feeding of agricultural byproducts to livestock in Africa. Proceedings of a workshop held at the University of Alexandria, Egypt, October 1985. ARNAB (African Research Network for Agricultural By-products). ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 124-128.

Jenkins T C and Palmquist D L. 1984. Effect of fatty acids or calcium soaps on rumen and total nutrient digestibility of dairy rations. Journal of Dairy Science 67:978-986.

van Keuren R W and Heinemann W W. 1962. Study of the nylon bag technique for in vivo estimation of forage digestibility. Journal of Animal Science 21:340-345.

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Manyuchi B and Sibanda S. 1989. Research on crop residues and agro-industrial byproducts as livestock feed in Zimbabwe. A review. ARNAB Newsletter 9(2):1-11. ARNAB (African Research Network for Agricultural By-products). ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia.

McLeod M N and Minson D J. 1969. Sources of variation in the in vitro digestibility of tropical grasses. Journal of the British Grassland Society 24:244-249.

Ndlovu L R and Hove L. 1989. Effects of feeding graded levels of groundnut hay on the utilization of veld hay by goats in Zimbabwe. In: Wilson R T and Azeb Melaku (eds), African small ruminant research and development. Proceedings of a conference held at Bamenda, Cameroon, 18-25 January 1989. African Small Ruminant Research Network. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. pp. 192-203.

Nyamangara M E and Ndlovu L R. 1991. Feeding behaviour, feed intake and characteristics of the diets of indigenous goats grazed on natural vegetation in a high rainfall area of Zimbabwe. Zimbabwe Journal of Agricultural Research (accepted, in press).

Ørskov E R. 1975. Manipulation of rumen fermentation for maximum food utilization. World Review of Nutrition and Dietetics 22:152-182.

Ørskov E R and McDonald I. 1979. The estimate of protein degradability in rumen from incubation measurements weighted according to the rate of passage. Journal of Agricultural Science, Cambridge 92:499-503.

Preston T R. 1986. Better utilization of crop residues and by-products in animal feeding Research guidelines. 2 A practical manual for research workers. FAO Animal Production and Health Paper 50/2. FAO (Food and Agriculture Organization of the United Nations), Rome, Italy. 154 pp.

Preston T R and Leng R A. 1987. Matching ruminant production systems with available resources in the tropics and subtropics. Penambul Books, Armidale, New South Wales, Australia. 245 pp.


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