Oestrus
Age at first conception and parturition
Parturition interval
Fertility, prolificacy and fecundity
Reproductivity wastage
Male-female ratios
Information on the reproductive performance of sheep and goats in the humid zone of West Africa is very limited and largely refers to experience under research conditions. Technical data derived from traditional production systems are virtually non-existent. Although some authors have distinguished different types or breeds of small ruminants in terms of different levels of reproductive performance, these traits generally have a low heritability. Differences in performance are more likely to be due to differences in feeding and management, and efforts to increase reproduction rates should probably focus on these factors rather than on genetic improvement through selection.
Both rams and bucks exhibit high libido, high fertility and early sexual maturity. In an experimental herd of West African Dwarf goats from Cameroon kept in the United States, Rogers et al. (1969) observed male sexual maturity at three months, and it proved necessary to separate the sexes prior to that age to prevent indiscriminate breeding. It should be remembered, however, that these observations were made under a high level of management and feeding. In West Africa, Ginisty (in CNRZ, 1977) recorded conception rates among sheep at first service at 73% in January/February and 87% in July/August. He attributed the lower figure to low fertility in one ram, but a seasonal effect on fertility in rams or ewes cannot be completely excluded.
In goats, the lowest age reported for the onset of oestrus was about three months (Rogers et al., 1969), though this was under excellent conditions in the temperate zone. Vohradsky and Sada (1973) recorded the onset of oestrus at around four months among goats in Ghana under experimental conditions. Rombaut and van Vlaenderen (1976) recorded a range of 4.5 to 6.5 months for the onset of oestrus among sheep, and Ginisty (in CNRZ, 1977) observed an average of 8.6 months, with a range of 6.9 to 10.7 in a flock of 437 sheep. From these observations, it would appear that efforts to lower the age of puberty among dwarf sheep and goats should not be given priority.
The duration of oestrus and the timing of ovulation are not of great importance at the present level of production. The duration of oestrus in goats was recorded by Otchere and Nimo (1975) at 17.0 ± 9.7 hours, while Jarosz et al. (1971) estimated 2.82 days for 'pure' dwarf goats and 4.2 days for seven-eighths pure dwarf goats, using cytological methods in the temperate zone at different times of the year. Ginisty (in CNRZ, 1977) recorded a mean of 36 hours oestrus in sheep, ranging from 12 to 60 hours. There is very little information on the timing of ovulation, though Jarosz et al. (1971) reported ovulation at 4.25 days after the first signs of oestrus among Toggenburg goats and at 3.10 days among West African Dwarf x Toggenburg crosses.
An average cycle length for goats of 24 days was recorded by Jarosz et al. (1971), with a range from 16 to 31. Otchere and Nimo (1975) reported an average cycle of 24 days, ranging from 14 to 34, and detected a significant effect of season on cycle length, though their observations were only over five months. These very large ranges in cycle length are not explained by the authors. For sheep, Ginisty (in CNRZ, 1977) recorded an average cycle of 17.7 days, ranging from 16 to 19 days only. This range is surprisingly narrow, and may be indicative of a regular feed supply for this research station flock. Jollans (1960a), however, recorded a cycle ranging from 6 to 24 days for a flock of West African Dwarf sheep kept on a research station in Ghana's forest zone, with a 'fair number' of ewes cycling only every 32 to 37 days.
In the humid tropics, most research workers have observed dwarf sheep and goats breeding throughout the year. The seasonal peaks which do occur are more likely the result of fluctuations in feed availability, rather than changes in photo-intensity. Vohradsky and Sada (1973) observed a peak in kidding around April and a smaller peak around September at an experimental station on the Accra plains in Ghana, which would imply conception peaks in November and April. Although these peaks were likely due to levels of nutrition, this cannot be proven as the feeding regime was not reported. Seasonal birth peaks may also be due to previous seasonal peaks in mortality, though Ragan et al. (1966) and Rogers et al. (1969) suggest that differences in photointensity at different times of year may affect the occurrence of oestrus. Montsma (personal communication) reports that oestrus occurs among dwarf goats in the Netherlands in early spring, while Devendra and Burns (1970) state that oestrus among dwarf goats in Europe occurs year round.
Orji (1977) simulated traditional management conditions with a flock of West African Dwarf sheep, fed only roughage or roughage with some supplementation. He found no significant effect of season or nutritional status on the oestrus period or cycle, which continued throughout the year. Hill (1960) observed a flock of dwarf sheep from 1950 to 1959 under traditional management conditions at the University of Ibadan in Nigeria with a minimum of supplementary feeding. The ewes bred throughout the year, though lambs born during the dry season from November to March were slightly heavier, averaging 8.1 kg at birth, than lambs born during the wet season from April to October, who averaged 6.9 kg. As the ewes averaged three lambings over two years, it was originally decided to synchronize breeding so lambing would occur in December, August and February/March, but subsequent work suggested that a year-round breeding programme would be more productive because many ewes would lamb twice in one year.
The gestation period for dwarf sheep and goats is approximately five months. For goats, various authors in Ghana and Nigeria give a range of 133 to 153 days, while Ginisty (in CNRZ, 1977) recorded an average of 149.3 days for sheep with a range of 145 to 152 days. The gestation period for twin births averages about 1.2 days less than for singles. Variations in gestation period are usually associated with such factors as multiple births, weight of offspring and age and parity status of the dam, though the underlying causes are largely hormonal.
Rombaut and van Vlaenderen (1976) observed an average age at first lambing of 11.5 months among sheep kept under traditional management, with a range of 9.5 to 14.0 months. This implies an average age at first conception of 6.5 months, ranging from 4.5 to 9.0. These average ages are probably not optimal, however, because only 11% of the lambs born to ewes mated between four and eight months survived to one year (see also Table 3). Dettmers et al. (1976) found an average age at first lambing of 20.5 months, ranging from 8 to 72 months; 37% of these ewes lambed again within one year and 66% within 13.3 months. Ngere (1977) studied a flock of West African Dwarf sheep kept under experimental conditions to determine the optimum age at first mating. His findings are shown in Table 3.
Table 3. Pregnancy and birth rates and average lamb weights for first-lamb ewes at various ages
|
Age in Months |
Number Exposed |
% Pregnant |
% Live Births |
Average Birth Weights (kg) |
|
8 |
12 |
42 |
17 |
1.6 ± 0.3 |
|
9 |
13 |
77 |
54 |
1.7 ± 0.2 |
|
10 |
8 |
75 |
38 |
1.7 ± 0.4 |
|
11 |
9 |
100 |
100 |
2.0 ± 0.4 |
|
12 and over |
9 |
100 |
100 |
2.0 ± 0.4 |
Source: Ngere (1977).
It appears from Table 3 that, under the conditions of the experiment, the optimal age at first mating for West African Dwarf ewes is about 11 months. Data are not presented on ewe body weights, however, and it is likely that the best criterion for age at first mating would be derived from a consideration of age and body weight combined.
Among goats, Vohradsky and Sada (1973) recorded an average age at first parturition of 12.1 months, ranging from 9.3 to 16.2, giving an average age at first conception of around 5.5 months. Kid mortality averaged 21.9% up to three months, with a seasonal peak of 46 to 60% in the cooler months of June/July, mainly due to cases of acute pneumonia. These relationships are illustrated in Figure 2.
Research indicates that dwarf sheep and goats tend to have a short reproduction cycle. Matthewman (1977) observed ewes suckling their young for 70 to 98 days or more and suggested that the onset of oestrus might be delayed by lactation. Orji (1977) recorded postpartum anoestrus averaging 54.91 days and also hypothesized that lactation might delay oestrus. Others, however, have reported that oestrus occurs among dwarf goats shortly after parturition in spite of lactation. Ginisty (in CNRZ, 1977) reported that oestrus occurred within 43 days for 95% of a flock of 44 suckling ewes, with a range of 22 to 66 days.
Parturition intervals averaging 258 days were recorded by Vohradsky and Sada (1973) for dwarf goats kept under research conditions in Ghana, with a range of 175 to 310 days. Otchere and Nimo (1976) reported an average of 254 days, ranging from 119 to 499. Matthewman (1977), Vallerand and Branckaert (1975) and others consider the optimum interval to be three parturitions in two years.
In measuring reproductive performance, fertility refers to the number of parturitions per annum, prolificacy to the average number of young in each litter and fecundity to the number of young produced per year. Data on these parameters for West African Dwarf sheep and goats are limited and somewhat conflicting, but it seems likely that cases of infertility are associated with nutritional deficiencies or debilitating disease.
Among goats kept at the Agricultural Research Station, Nungua in Ghana, Vohradsky and Sada (1973) found a kidding interval of 285 days, as already mentioned, which implies a fertility rate of 124%. Of all births recorded, 32.1% were singles, 52.9% twins, 13.7% triplets and 1.3% quadruplets, giving an average prolificacy rate of 184% which leads to a fecundity rate of 260%, meaning that on average each doe produced 2.6 kids a year. Otchere and Nimo (1976) calculated an average fecundity rate of 267% for their sample.
Mecha (1978) attempted to classify the goats of southern Nigeria according to body size. He found that the medium size, or pituitary dwarf type, was the most fertile: 'The kidding interval is short and twin, triplet and quadruplet births occur many times in their life span'. The smaller achondroplastic dwarfs, on the other hand, were characterized by ' a long kidding interval with one kid per birth throughout most of the period ...'. Among the larger types, twin births were common. This work might usefully be extended to include calculations of fertility and fecundity as well as prolificacy.
Production parameters of sheep and goats have been recorded at the University of Science and Technology in Kumasi, Ghana for more than ten years; the final analysis of these data should be available soon. Fertility rates observed among goats have been calculated by Buadu (1972), averaging 154%, and prolificacy rates 184%, which gives an average fecundity rate of 293%.
Figure 2. Percentage of does kidding from total number of does on hand, percentage of kids dying and mean monthly rainfall in mm
Source: Vohradsky and Sada (1973).
Turning to sheep, Ginisty (in CNRZ, 1977) observed a number of flocks in Ivory Coast maintained under both traditional and commercial conditions. He reported an average fertility rate of more than 160% under traditional conditions but a. prolificacy of only about 110%, meaning that only about 10% of the births were twins. This resulted in a fecundity rate of about 175%, though approximately 50% of the lambs died before the age of four months, resulting in a net fecundity rate of 87.5%. At the Agricultural Research Station, Nungua, a prolificacy rate of 143% was recorded for West African Dwarf sheep, together with a lamb mortality rate of 16.7% (University of Ghana, 1976). Prolificacy in Nungua Blackheads was found to be lower, at 100%. Dettmers et al. (1976) found a fertility rate of 145% and a prolificacy rate of 172%, giving an annual fecundity rate of 249%. Comparing sheep and goats, Matthewman (1977) observed fertility rates of 155% for goats and 115% for sheep in two villages in southern Nigeria. Survey data from the humid zone in Nigeria gathered in 1972 confirm these results. Records of reproductive performance are also being maintained by the Société de Développement de la Production Animale (SODEPRA) in Ivory Coast and by Bennet and Bonniwell in a forest-zone village in Ghana, but the results have not yet been published.
Rather than increasing production in every case, early maturity, high prolificacy and short parturition intervals may lead to substantial reproductive losses. Rombaut and van Vlaenderen (1976) found a strong positive correlation between length of parturition interval and survival of lambs under simulated traditional production conditions. Their findings are summarized in Table 4.
Table 4. Influence of parturition interval on survival rate of lambs: Percentage of losses
|
Deaths |
Period Between Lambings |
|
|
under 7 months |
over 7 months |
|
|
Abortions and perinatal |
22 |
0 |
|
Up to 1 month |
30 |
20 |
|
1-6 months |
41 |
40 |
|
Surviving at 6 months |
7 |
40 |
Source: Rombaut and van Vlaenderen (1976).
They also found significantly higher mortality rates among the offspring of ewes which were first mated between four and eight months, compared with the offspring of ewes which were not mated until maturity.
These two authors described the condition resulting from a rapid succession of pregnancies as 'fatigue des mères', Not only do the ewes lose weight, but there is a steady deterioration in the health of the young over successive lambings: 86% of the lambs born to non-fatigued ewes survived to four months and 81% to seven months, while only 53% of the lambs of fatigued ewes survived to four months and 24% to seven months. These lambs were less robust and more susceptible to the effects of disease and poor nutrition. Lamb mortality reached a peak at four months, corresponding with reduced lactation, and at seven months, corresponding with subsequent parturition. It should be pointed out, however, that work with sheep in Ghana did not reveal a similar correlation between lamb survival rates and parturition interval. More research on optimum parturition interval and age at first mating is called for, taking into account the role of nutrition levels, to serve as a basis for improved management strategies.
Reproductive wastage might also be reduced if breeding were controlled on a seasonal basis to reduce the incidence of helminthiasis, most prevalent in the form of parasitic gastro-enteritis and most damaging to the young. Through the year there are wide fluctuations in parasitic larval challenge. Young animal who are weaned and begin grazing during the wet season are exposed more intensely to infective larvae at a susceptible age than others who are weaned during the dry season and are not exposed until they are older and better able to withstand damaging infestations.
The experience of research institutes and commercial sheep farms has indicated that male to female ratios ranging between 1 : 20 and 1 : 60 are sufficient to ensure efficient conception rates. However, much higher proportions of males tend to be kept in flocks under traditional husbandry systems.
In a survey conducted in southwestern Nigeria, Sellers et al. (1974) found that 120 rural households kept a total of 118 adult rams and 327 adult ewes, giving a ratio of 1 : 2.8. In 745 rural households, 381 adult bucks were kept and 1 635 does, or a ratio of 1 : 4.3. Matthewman (1977) found 11 adult bucks kept with 153 does, or a ratio of 1 : 17, and he reported that sires were usually under one year old. Van Vlaenderen (personal communication) found 130 adult rams and 663 adult ewes over five months old in a survey of 20 villages in Ivory Coast. Differences in the ratios cited may reflect differences in the definition of maturity in both males and females or a slower growth rate in males which leads to slaughter or sale at a later age.
