Information on the breeds and types of dwarf sheep and goats in West and Central Africa is largely limited to descriptions of size, colour and conformation (see Mason, 1951; Epstein, 1953). Little information is available on production parameters.
A major characteristic of these breeds is their small size and body weight. A number of reasons for this small size are cited in the literature, including limited feed supply, metabolic efficiency and reduced heat loss, but none of them appears completely convincing. It is perhaps worth asking whether these dwarf types are in fact unusually small or whether other types are unusually large. In Western Europe, for example, the body weight of sheep and cattle has increased by about 200% over the past two centuries, primarily as a result of improved feeding plus selection. Selection for higher meat production per animal obviously leads to increased size, and it would also appear that selection for individual high milk production leads to larger animals with bigger appetites.
Improved feeding and management plus effective selection might well lead to larger and therefore faster growing animals over a century or so, though this might not be the best strategy if productivity per unit of body weight is considered rather than productivity per animal. At any rate, these three factors have largely been absent in West Africa until recently. A further consideration is that maintaining a small flock of large animals entails higher risks than maintaining a large flock of small animals, especially in a situation where disease is the main production constraint. Up to a point, high fecundity can lead to higher survival rates than larger size or body weight. High fecundity can also be manipulated to increase production by taking advantage of early growth, though if fecundity is too high maternal stress can lead to increased mortality among the young. Selection goals can therefore be defined only after careful scrutiny of the entire production environment.
The most suitable approach at this stage would be to classify the dwarf sheep and goats of the region into two populations, one larger and one smaller, each with different local types resulting from seclusion or importation. Mecha (1978) has attempted to distinguish different breeds among the goats of southern Nigeria on the basis of size. He divided the goat population arbitrarily into three groups according to height at withers, and found that about 27% measured 40 cm or less, 67% measured 41 to 50 cm, and only 6% measured over 50 cm. He made a further subdivision of the dwarf types into pituitary dwarfs, which were small but with regular proportions, and achondroplastic dwarfs, which had irregular proportions with short legs. As the achondroplastic type forms a very small proportion of the population, attention for the present can be focussed on the pituitary type.
Specific conformational differences are sometimes striking. In Nigeria, for instance, many goats with wattles were observed, while virtually all the goats in Ghana were wattle free. More important differences in genetic makeup with regard to physiological functions, such as appetite, digestive capacity, fat deposition and innate immunity, are likely to be less striking, however. One reason for the variations in breed types and characteristics is that there has hitherto been very little control over breeding or selection within the populations, and breeds have been crossed, such as West African Dwarf and Red Sokoto, indiscriminately. Just as more information is needed on the production environment before specifying goals for genetic improvement, more needs to be known about the genetic characteristics of existing populations.
Birth Weight
Growth Rates
Lactation Rates and Milk Composition
Weaning Weights
Carcass Quality
Fibre Production
Little information is available on production characteristics such as weights at birth, weaning and maturity, growth curves and lactation yields. Some of the data which have been recorded will be presented here. Data on reproductive performance will be presented in a separate section.
For goats in Ghana, Sada and Vohradsky (1973) recorded a mean birth weight of 1.40 kg. with a range of 0.54 to 2.48. This average birth weight is about 6% of the average mature female weight, recorded at 25 kg, which is roughly similar to percentages recorded for other small and large breeds (see Devendra and Burns, 1970). The ILCA village survey under way in southern Nigeria has given a preliminary average birth weight for all goats of 1.2 kg. If the weights of individual young are much less for multiple births, then the proportion which survive to weaning is likely to become less with increased prolificacy. Devendra and Burns (1970) recorded an overall kid mortality of 20% but did not relate this to litter size or birth weight.
Turning to sheep, the ILCA village survey found an average birth weight of 1.8 kg. Dettmers et al. (1976) recorded birth weights of individual males in a flock of West African Dwarf sheep in southern Nigeria and calculated average weights of 1.9 kg for singles, 1.6 kg for twins and 1.5 kg for triplets. They also found a much higher mortality rate of 35 to 47% among triplets than among twins and singles, at 12 to 22%. At the Agricultural Research Station. Nungua in Ghana (University of Ghana, 1976), the average birth weight for Nungua Blackheads, a cross between West African Dwarf and Blackhead Persian, was approximately 2.25 kg, compared with 1.13 kg for the local type. As the prolificacy rate was 100% for the Nungua Blackhead and 144% for the local type, the total birth weights were 2.25 and 1.62 kg respectively.
Ngere (1973) compared the birth and mature weights of West African Dwarfs (which he refers to as 'forest type') and Nungua Blackheads with data for Suffolk sheep recorded in the United Kingdom. He obtained averages as shown in Table 2.
Table 2. Comparison of birth and mature weights for three breeds of sheep
|
|
West African Dwarf |
Nungua Blackhead |
Suffolk |
|
birth weight (kg) |
1.66 |
2.56 |
5.26 |
|
mature weight (kg) |
21.00 |
32.00 |
76.00 |
|
birth weight as % mature weight |
8% |
8% |
7% |
Source: Ngere (1973).
These calculations show that the relative birth weights of the two small breeds compare favourably with the figures obtained in Britain.
As in the case of birth weights, it is important to consider growth rates in relation to prolificacy and mature weights. For single lambs in Ivory Coast, Ginisty (1978) recorded growth rates of 55 to 60 g per day among Djallonké sheep, a West African Dwarf type, compared with 100 g for crossbreds with the larger Sahelian types.1 As with birth weights, Ngere's study in Ghana (1973) indicated that absolute daily weight gains were higher for Nungua crosses than for local sheep, but relative weight gains compared with mature weights were similar.
1. Average birth weights of 2.3 to 2.8 kg for the dwarf types and 2. 0 for the crossbreds were also constructed by subtracting the sum of daily weight gains from the weights at four months, but these estimates are probably inaccurate. More precise data may be available soon.
For West African Dwarf goats, Sada and Vohradsky (1973) recorded average daily growth rates of 53 g among male and female twins up to three months, resulting in a relative body weight at that age of 25% of mature weight. At one year, body weights averaged 12.85 kg, or 50% of mature weight, but the range was from 10 to 19 kg, or 40 to 80% of mature weight. It is difficult to compare these figures with others, however, because of the substantial effects of differences in birth and mature weights and levels of nutrition. Among mixed dwarf goats in the Netherlands, daily growth rates of 90 ± 22 g were recorded for the first 100 days (ranging from 50 to 140 days) under an excellent feeding regime (Montsma, personal communication) .
Notwithstanding their early sexual maturity, it appears that goats mature late in terms of growth. Sada and Vohradsky (1973) observed that females were still growing at three years, in terms of both weight and size. However, a sharp drop in the growth rate was observed between three and four months, so that late growth may result partly from improved nutrition. Wilson (1958) found that nutritional levels affected the growth rates of East African Dwarf goats by 50% in males and 57% in females.
Nonetheless, the considerable variations in birth weights and growth rates recorded in the humid zone, especially for goats, suggest that substantial improvements could be achieved by selection, since a fair proportion of the variation is likely to be due to genetic factors. The wide variability also indicates that fairly large samples will be required to achieve statistical significance in research work.
Under present production conditions, lactation in dwarf sheep and goats in the humid zone is important primarily in terms of the nutrition of the young, especially when prolificacy is high. For goats, the only data on milk yields and composition have been recorded by Akinsoyinu et al. (1977) in Nigeria. Milk yields of about 40 kg over an 18-week lactation were recorded for six mature goats over 12 lactations. This would result in an overall average daily yield of 317 g, though in fact more than 90% of the milk was produced in the first 12 weeks, with a peak of 5 kg per week, or 714 g per day, around the fifth week. These yields were obtained by hand milking; it is likely that yields are higher with suckling.
As regards milk composition, Akinsoyinu et al. (1977) reported an energy content of 455 kJ/100 g for goat milk, which is very high, mainly due to the high lactose content (6.3%) and the high fat content (6.9%). Protein content was 3.91%. In another trial carried out at Ibadan in Nigeria, Mba et al. (1975) compared the milk composition of nine goats, three each of the Saanen, Sokoto Bed and West African Dwarf breeds, over a lactation period of 12 weeks. Daily milk yields averaged from 500 to 1 000 g, with the Saanen ranking highest and the West African Dwarf goats lowest, but the order was reversed in terms of milk composition. The West African Dwarf goat milk contained approximately 70% more energy and protein than the Saanen milk. Furthermore, the yields for the West African Dwarf and Saanen goats were similar in terms of kg of body weight, though the yields recorded for the Saanen goats were low for the breed, especially considering the fact that they are accustomed to hand milking.
Rombaut and van Vlaenderen (1976) recorded milk yields of 40 kg per lactation for Djallonké sheep under village conditions, and 90 kg under improved feeding.
In efforts at genetic improvement, it would seem more practicable to select for high preweaning growth rates, rather than trying to measure milk yields directly. Converting the milk yields obtained by Akinsoyinu et al. (1977) and Mba et al. (1975) into estimated daily weight gains at a ratio of approximately 8 : 1, growth rates of 65 g per day are obtained for West African Dwarf kids. Assuming that suckling would produce 25% more milk than the yields obtained in hand milking trials, the projected daily growth rate would rise to about 80 g. Growth rates derived in this way are expressed in terms of litters rather than individual animals; the growth rate of individual animals would also depend on fecundity and survival rates. The data available at present are not sufficient to determine whether milk yield is an important factor limiting kid survival and growth.
Hill (1960) reported an average weight at three months of 8 kg for male and female West African Dwarf lambs at Ibadan, Nigeria. Out of a group of 306 lambs, losses to 18 months were 38%, with over 40% of these occurring from one week to three months. Given a flock fertility rate of 150%, the net weaning weight at three months was 7.08 kg per ewe. At Nungua (University of Ghana, 1976), weaning weights for Nungua Blackheads averaged 12.6 kg, compared with 8.1 kg for West African Dwarf lambs. Prolificacy was 100% and 143% and mortality to weaning 59% and 16% respectively, giving net weaning weights per parturition of 5.2 and 9.7 kg. Net weaning weights could also be expressed in terms of 100 kg of ewe body weight. Expressed in these terms, the net weaning weight for the Nungua Blackhead was 10 kg compared with 40 kg for the West African Dwarf.
Ginisty (1978) reported an average body weight for Djallonké sheep in Ivory Coast at four months of 9.5 kg compared with an average weight of 14 kg for crossbreds with the larger Sahelian types. The weaning weights for the Djallonké averaged 40% of their mature body weights. Prolificacy averaged 110% among the Djallonké and a similar rate was assumed for the crossbreds, giving net weaning weights per parturition of 9.5 kg for the Djallonké and 9.8 for the crossbreds. Assuming annual fertility at 150%, the weight of weaned lamb produced by the Djallonké was 13.75 kg per ewe per year, compared with 14.7 kg for the crossbreds. As at Nungua, the West African Dwarf breed produced a greater weight of weaned lamb per 100 kg of ewe body weight than the crossbreed.
Turning to goats, Sada and Vohradsky (1973) and Vohradsky and Sada (1973) found average prolificacy rates of 184%, average weaning weights at four months of 6.26 kg and average mortality up to three months of 21.4%. This results in a net weight at weaning of 9.1 kg per parturition. With a fertility rate of 141%, the annual production of weaned kid per 100 kg of doe body weight was 51 kg, which compares with levels of production achieved by typical mutton breeds in the temperate zone. It is better than the typical levels achieved by beef cattle, which average 20 to 30 kg of weaned calf annually per 100 kg of cow body weight.
Under a traditional production system, carcass quality is not of great significance because most of the animal is consumed, including the skin. Under a commercial system, dressing out percentages, meat-to-bone and meat-to-fat ratios are likely to become more important. These characteristics depend to some extent on genetic traits, but far more on levels of nutrition and age at slaughter. Because a variety of factors are involved, comparisons in different situations have limited value. For goats, Akinsoyinu et al. (1975) recorded an average dressing out ratio of 50 to 51% among 12 castrates used in a feeding experiment. Body weights ranged from 14. 5 to 17 kg. Ginisty (1978) recorded an average dressing out ratio of 49. 6% among nine wethers fattened before slaughter with an average body weight of 25 kg. These figures suggest that both West African Dwarf sheep and goats achieve satisfactory dressing out ratios.
For the goats recorded by Akinsoyinu et al. (1975), the ratio of fat in the lean meat was just under 10%, which is adequate for cooking but a bare minimum for roasting or processing. However, these animals were immature and had not been finished. Ginisty (1978) found an average of 64% muscle tissue for the nine wethers, 20% fat and 16% bone. These animals had been fattened but they were not mature; they were probably between 1. 0 and 1. 5 years old.
Most West African Dwarf sheep and goats have short, sleek coats. In sheep, coats with longer hair sometimes occur and some young lambs display mixed coats which pad and are shed later on. Present knowledge indicates that wool growth would be undesirable in the humid tropics, for both physiological and technical reasons, but further research on coat and skin characteristics from a physiological and climatic point of view would be desirable.
Variations in production parameters among sheep and goats of the West African humid tropics appear to be substantial, probably due to variations in production conditions and the absence of deliberate selection strategies. Before major efforts are expended towards genetic improvement, the goals should be clearly defined in terms of the relevant production environment, which may vary in different parts of the region and among different producers.
Projects undertaken in the region so far aimed at the genetic improvement of sheep, and to a lesser extent of goats, have largely focussed on increasing size and body weight by introducing exotic northern types, such as the Blackhead Persian in Ghana. The reason for this emphasis on increased size is not clear, as a larger, longer-legged animal may have an advantage under ranch conditions but not necessarily under village conditions.
The major drawback of the northern breeds is a greater susceptibility to disease, especially haemonchosis and trypanosomiasis. For example, the Nungua Blackhead in Ghana is not well adapted to the high levels of worm infestation which accompany year-round humidity, and consequently prolificacy is low and lamb mortality high, even with frequent deworming. According to Ginisty (1978) the mortality rate among crossbreds between Djallonké and Sahelian sheep averages 29.8%, compared with 10% for the Djallonké.
Improvements in animal production in the temperate regions have, by and large, been achieved by maintaining an equilibrium between the animals' genetic potential and the environment in which this potential has to be realized. If priority is given to improving such environmental factors as animal health and feeding, genetic improvement will occur automatically because of the shift in survival values. However, this process can be substantially accelerated by selective breeding programmes carefully tuned to existing and anticipated environmental conditions.
