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Experiences in protein supplementary feeding of weaned lambs and goat kids in Tanzania: The issue of dietary energy - Etudes sur la complémentation protéique de la ration d'agneaux et de chevreaux sevrés en Tanzanie: le problème de l'énergie de la ration

Results and discussion

L.A. Mtenga and A. Madsen
Department of Animal Science and Production
Sokoine University of Agriculture
P O Box 3004, Chuo Kikuu, Morogoro, Tanzania


The prevailing idea, implied in previous studies on supplementary feeding of small ruminants in the tropics, has been that protein is the major limiting factor for growth. However, the low response to protein supplementation found in several studies at Sokoine University of Agriculture (SUA) cast some doubt on the validity of this idea.

This paper reviews past research work at SUA on supplementary feeding of lambs and goat kids. Intake of metabolisable energy and digestible crude protein were calculated from the original data. Growth rate was highly correlated to intake of metabolisable energy (r= 0.85) while the correlation to protein intake was poor (r= 0.67). It is concluded that the energy intake is the major limiting factor for growth of small ruminants under SUA conditions (tropical semi-arid region). It is also concluded that best effects on growth of weaned lambs and kids can be expected from supplements with high energy and moderate protein contents.


L'hypothèse dominante, sous-jacente aux études effectuées jusque-lá sur la complémentation alimentaire des petits ruminants dans les régions tropicales, veut que les protéines constituent le principal facteur limitant pour la croissance des ovins et des caprins. Cependant, compte tenu de la faible réponse à la complémentation protéique enregistrée dans des essais effectués à la Sokoine University of Agriculture (SUA), on est en droit de s'interroger sur le bien-fondé de cette assertion.

Cette étude fait le point des travaux effectués jusqu'ici à la SUA sur la complémentation alimentaire des agneaux et des chevreaux. Les quantités ingérées d'énergie métabolisable et de protéines brutes digestibles ont été calculées à partir des données initiales. Les analyses effectuées ont révélé qu'il existait une forte corrélation (r = 0,85) entre le rythme de croissance et la quantité d'énergie métabolisable ingérée, mais une faible corrélation r = 0,67) entre celui- ci et la consommation de protéines. Ces résultats amènent à conclure que la quantité d'énergie consommée constitue le principal facteur limitant de la croissance des petits ruminants dans les conditions de la SUA (région tropicale semi-aride). II est également conclu que les meilleures performances de croissance des agneaux et des chevreaux sevrés peuvent être obtenues avec des aliments complémentaires très riches en énergie mais seulement moyennement riches en protéines.


The major part of cattle as well as small ruminants in Tanzania are fed on arid or semi-arid grasslands. That the nutritive value of the pasture drops drastically during the dry season is well documented. The content of crude protein decreases while the content of crude fibre increases resulting in a decreased digestibility of all nutrients and hence a decreased energy content of the grass (Butterworth, 1967; Osbourn, 1976; Gohl, 1981; Butterworth, 1985). The low digestibility of grasses means that the amount taken up by the animal will be reduced due to the decreased rate of passage through the rumen. All together, K means that uptake of both protein and energy from pasture the animal decrease considerably during the dry season.

Therefore, supplementary feeding of livestock has been advocated and much research work has been devoted to trials using different compositions and amounts of supplements. The major idea has been that protein is the major limiting factor in the diet, and most trials have used supplements with protein-rich feeds. However, in many cases the response in terms of growth rate has been poor.

The present paper reviews the results of a total of eight research projects performed at Sokoine University of Agriculture, Tanzania as MSc thesis or special projects during the years 1981-1989 in search of an answer to the following questions:

Is intake of protein or energy the major limiting factor for ruminant growth on tropical grassland? and

What types of supplementary feeds are more likely to improve the performance of grazing small ruminants?


None of the reviewed papers estimated the of energy. For most of the works the animals were kept in metabolic cages and the intakes of dry matter as well as of the individual nutrients were measured. Moreover, the digestibilities of the individual nutrients were determined in the same experiments.

The available data therefore allowed us to calculate the intake of total digestible nutrients (TDN) or the intake of digestible organic matter (DOM) from which the intake of digestible energy (DE) or metabolisable energy (ME) was estimated using the following equations given by Devendra and McLeroy (1982):

DE (MJ) = 18.4 xTDN (kg)
DE (MJ) = 19.2 x DOM (kg)
ME (MJ) = 0.82 x DE (MJ)

Hence the metabolisable energies stated in this paper were calculated as follows:

1) ME (MJ) = 0.82x 18.4 x TDN = 15.1 x TDN (kg)
2) ME (MJ) = 0.82 x 19.2 x DOM = 15.7 x DOM (kg)

Results obtained from using equation (1) or (2) were not significantly different.

For some of the works reviewed the animals were grazed, so that the uptake of only the supplemented feed could be measured. For these cases we assumed that the uptake of dry matter from grazing was 0.45 kg/day for animals of 15-kg liveweight, and that the grass contained 9 MJ ME and 40 9 digestible crude protein (pop) per kg dry-matter (DM). These assumptions are in accordance with the findings of Shoo (1986) and Muhikambele (1990) using grass hay (Table 2). An uptake of 0.45 kg/day for a 15-kg animal corresponds to 3% of its liveweight. This agrees with a low-level uptake as stated by Devendra and McLeroy (1982).

The estimated intake of metabolisable energy and digestible crude protein (pop) as well as the growth rates observed in the reviewed works are shown in Tables 1, 2 and 3. Kitalyi (1982) is a typical example of an experiment using supplements increasing contents of protein. The results clearly demonstrate that supplementation of 200 9 concentrate with only 10% oil cake (11% CP) improved growth rate by two times. No further improvement was obtained by increasing the protein content of the mixture.

Table 1 Effect of supplement feeding on growth rate of hay-feed lambs and goat kids confined in metabolic cages.

Table 2. Effect of supplementary feeding on growth rate of grazing lambs And goat kids.

Table 3 Effect of supplementary feeding on growth. rate of grazing lambs and goat kids.

Nyaki (1981) and Massae (1984) observed about three-fold increase in growth rates by using 400 or 500 9 of supplement with moderate protein content.

The effect of high-protein allowance to low-energy diets was especially demonstrated by the works of Shoo (1986) and Muhikambele (1990) using supplements of Leucaena leucocephala or cottonseed cake, respectively (Table 2). In both cases, the supplement had no effect on the growth rate.

The relationship between growth and intake of energy or protein for all eight studies is illustrated in Figure 1a and 1b, respectively. The data show that growth rates are highly correlated with energy intake (r =0.85), while the correlation to protein intake (all points) is poor (r = 0.67). Figure 2 illustrates growth rates in relation to the amount of supplemented concentrate. The correlation is fairly high (r=0.77).

Results and discussion

The relationship between growth rates and intakes of protein and energy was already illustrated by ARC (Agricultural Research Council) in 1980 (Figure 3). The data presented in Figure 1b are in good agreement with the ARC illustration. Increase of protein intake on a low level of energy intake gives no improved growth. With increasing intakes of energy, growth rate increased and the requirement for protein increased. The encircled points in Figure 1b show protein intake vs the growth when energy is non-limiting. Under these conditions growth rate is highly correlated to protein intake (r = 0.94).

Thestippled lines in Figure 1a and 1b show feeding norms for a 15-kg goat kid according to Devendra and McLeory (1982). These feeding norms assume that protein and energy are fed in a ratio of 6 9 pop per MJ ME. Other feeding norms also give similar ratio for protein/energy, e.g. NRC (1976) stated 6.5 9 DCP/MJ ME. The protein/energy ratios of the supplemented diets referred to in the present review (Tables 1, 2 and 3) in most cases exceed that of feeding norms.

Table 4 summaries the data in Tables 1, 2 and 3, showing average values of intake, protein/energy ratio and growth rates for unsupplemented groups and for groups given concentrates with "moderate" or "high" protein content. The data show that unsupplemented diets have low intakes, low protein/energy ratio and low growth rate. Supplementation increased energy intakes by 50% in average (from 4 to 6 MJ) and increased intakes of digestible protein by 100 or 200%. The average effect on growth rates was about 100%, independent of the protein level. The data strongly point to the energy intake as the major limiting factor for growth under the conditions of the studies reviewed.

Figure 1. Growth rate of lambs and goat kids versus intakes of energy and protein.

Figure 2. Growth rate of lambs and goat kids versus daily allowance of concentrate feed.

Data from Tables 1, 2 and 3.

The importance of energy supplementation is emphasised by the findings of Hai (1988) and Susuma (1989) both using cassava chips to increase the energy content of the supplement without changing the protein content (Table 3). The minor increase in energy intake from the supplement can not explain the observed increase of growth rate (about 50%). However, K is most likely that the groups on the cassava based concentrates had a higher uptake of grasses. resulting from a positive effect of cassava starch on the digestibility of the grass.

The effect of energy on utilisation of protein is mainly due to the fact that protein synthesis is a very energy demanding process. The synthesis of microbial protein in the rumen requires the presents of digestible carbohydrate to provide energy. The synthesis of proteins in the animal body, for example muscle protein, require the supply of energy from combustion of nutrients like acetate and glucose. If the supply of energy rich nutrients is deficient, then an increased intake of protein will result in an increased transamination and deamination of amino acid. Increased amounts of ammonia are released, converted into urea in the liver and further excrete in the urine (Rids, 1983).

Figure 3. The response of growing ruminants to the combined effects of energy and protein (after ARC, 1980).

This explains that increased protein intake on low energy allowance results in increased excretion of urinary nitrogen (Shoo, 1986; Muhikambele, 1990). Such diets result in increased nitrogen intake and increased nitrogen excretion, but no significant improvement in nitrogen balance or growth.

Furthermore, the addition of high protein to low energy diets may have a negative effect as illustrated in Figure 3, lower curve. This is likely due to the energy expense of urea synthesis.

Table 4. Effects of supplementary feeding on growth rate of lambs and goat kids (average + SD of values from Tables 1, 2 and 3).


Total intake per day

Protein-energy ratio (gDCP/MJME),(g/d)

Growth rate

DM (kg)





0 44

3 9









"Moderate" protein







content (protein limiting²)






"High" protein content







(protein in excess³)






1. N = Number of experiments.
2. The supplement groups symbolized with (X) in Figure 1 and in the Tables 1, 2 and 3.
3. The groups are symbolised with X in Figure 1 and in the Tables 1, 2 and 3.
For abbreviations, see Table 1 footnote.


The present review allows us to conclude the following:

1. Energy intake is the major limiting factor for growth of ruminants on semi arid grasslands of Tanzania.

2. Protein supplement alone to low energy diet has no effect on growth rate.

3. Concentrate supplements should contain high energy and moderate amounts of protein to allow a content of about 6 g pop per MJ ME in the whole ration (concentrate + roughage).

4. The summarised data of this review (Table 4) indicate that the growth rates of grazing lambs or kids can be improved from 30 to 60 g/day by use of a daily supplement of 200 g concentrate containing 12 MJ ME/kg DM and 12-13% of pop. This corresponds to a mixture of maize bran with 30% cotton seed cake (CSC). A growth rate of 100 g/d requires total intake of 8.5 MJ ME and 55 g DC) (Fig. 1). Considering the supply from the basic diet (Table 4) the required content of the supplement is 4.6 MJ ME and 37 g pop. If 400 g concentrate is given it must contain 11.5 MJ ME/kg DM and 9% pop. This corresponds to maize bran mixed with only 15% CSC.

5. Improved suggestions for best supplements require growth studies using different amounts of concentrate mixture with different protein-energy ratios. Such trails would allow us to calculate the economical optimal composition and amount of mixture.

6. Future research on feeding must consider the intakes of both energy and protein, during the experimental design as well as in the conclusion of the work. Otherwise we shall continue to judge all beneficial effects as due to protein and all lacks of effect as due to experimental error!


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Hai M. 1988. Cassava as a source of high energy for weaner dairy goats kids and its effect on their growth rates. Special project. Sokoine University of Agriculture, - Morogoro, Tanzania.

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NRC (National Research Council).1976. Nutrient requirements of beef cattle. No. 4. Fifth revised edition. National Academy of Sciences, Washington, DC. USA. 56 pp.

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Osbourn D F. 1976. The utilization of natural grasslands in the tropics. In: Smith A J (ed), Beef cattle production in developing countries. Centre for Tropical Veterinary Medicine, University of Edinburgh, Edinburgh, UK. pp.184-203.

Riis P M. 1983. The pools of tissue constituents and products: proteins. In: Riis P M (ed), Dynamic biochemistry of animal production. Elsevier Science Publishers, Amsterdam, The Netherlands. pp. 75-108.

Shoo R A. 1986. A comparative study of roughage utilisation and growth performance between sheep and goats supplemented with different levels of Leucaena leucocephala. MSc thesis, Sokoine University of Agriculture, Morogoro, Tanzania.

Susuma K L. 1989. The effect of energy supplementation on the performance of genetically improved improved female goat kids at SUA. Special Special Project. Sokoine University of Agriculture, Morogoro, Tanzania.

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