VOLUME  55 (2) 2000

REPRODUCTIVE PERFORMANCE OF WEST AFRICAN DWARF GOATS IN THE HUMID TROPICAL ENVIRONMENT OF IBADAN.

Akusu, M.O. and Ajala, O.O.

Department of Veterinary Surgery and Reproduction, University of Ibadan, Ibadan, Nigeria

     Introduction      Materials and Methods      Results     Discussion

Introduction

Agricultural development in Nigeria has placed more emphasis on crop production although the rearing of cattle, sheep and goats have always formed an integral part of the domestic economy and source of wealth for Nigerians. The consequence of this imbalance is that most Nigerians consume far less animal protein daily than the minimum recommended level.

In the livestock sector some attention has been focused on non-ruminant farm animals, particularly poultry. Efforts have also been made to exploit the potential of cattle, whereas the goat has remained neglected and untapped. Various reports (1, 2) have shown that apart from poultry, the goat is the most numerous of the domestic livestock species in Nigeria. With goats numbering over 24,500,000 (3), it is estimated that there are 245 goats to 1000 Nigerians.

There are three main breeds of goats in Nigeria, the Red Sokoto, the Sahel and the West African dwarf goat (4). The West African dwarf goat is most prevalent in southern Nigeria. Its characteristics have been described earlier (4) while its relative trypanotolerance has singled it out as the breed of choice in southern Nigeria.

The West African dwarf goat is early maturing, prolific and a non-seasonal breeder (4,5). An average of 80.6% multiple births was recorded in one survey (6) and a total of 5 kidding in 3 years in another (7).

This present study is to investigate the effect of certain non-genetic factors on the prolificacy of the West African dwarf goat. It is hoped that the information generated will form part of a package required for profitable goat husbandry.

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Materials and Methods

Thirty adult West African dwarf goat aged between 1 and 4 years and 10- to 30 kg in weight were used for the study on fertility and prolificacy over a 4 year period. Following parturition, 9 does were assigned to a study on the variation of the post-partum period on oestrus cycle length. Another 8 does were used to study the effect of breeding at oestrus succeeding oestrus cycle lengths of short or long duration. The effect of the service period on the fertility and prolificacy of does was studied in 26 does; 13 were bred while suckling their kids (preweaning) while 13 were bred postweaning.

All animals were housed in roofed pens with concrete flooring and low wooden partitions. They were fed a corn-based concentrate ration (0.5 kg per day). Clean water and fresh giant star grass and centrosema were provided ad libitum while routine medication consisted of deworming with 10% Rintal (Bayer, Leverkusen) suspension and an ectoparasitic bath with Gamatox (Wellcome Coy, England).

Data were analysed by Chi square and Student’s t-test for the establishment of significance (8).

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Results

The fertility and prolificacy of the does were assessed from 77 services. Each doe became pregnant following breeding at each oestrus. Placentas were usually dropped within 10-30 minutes post partum.

The mean kid number per doe from the 77 services was 1.91±0.08. The male/female ratio of kids was 81/66 (i.e. 55.1% males). Male kids were heavier than female kids at birth (p>0.05). The mean birth-weight of the kids was 1.16±0.03 kg. Litter type had significant influence on kid birth-weight. The season of birth had no significant influence on birth-weight (Table 1).

Table 1: Effect of season, sex and litter size on birth weight

•  Number on the same vertical column differently superscripted differ significantly (p<0.05)
  

The mean gestation length for 68 observed parturitions was 144.9 days and was not significantly affected by season of birth. Does with singles had a longer gestation than those with twins or triplets. The mean gestation length in dams giving birth to only female kids was 1.13 days longer than in does with only male kids (Table 2).

Table 2: Effect of season, sex, litter size and parity on gestation

•  Number on the same vertical column differently superscripted differ significantly (p<0.05)
  

A total of 30 oestrus cycles were observed in 9 does post partum. The first observable post-partum oestrus occurred at 55.70±4.62 days.

The period was significantly longer (p<0.05) than subsequent cycles which were not significantly different from each other. The frequency distribution of oestrus cycle length is presented in Fig. 1 and Table 3. Table 4 summarises the influence of breeding during oestrus succeeding cycles of short and medium durations on some reproductive indices. The mean cycle lengths for short and medium oestrus cycles were 5.25±0.48 and 12.25±0.95 days (p<0.05) respectively. Oestrus duration and gestation lengths were not affected. Similarly, the mean kid birth-weights were not significantly influenced. However, prolificacy of does bred during cycles of medium duration was significantly superior (p<0.05) than their counterparts.

Fig 1.: Frequency distribution of oestrus cycle length in West African dwarf goats.

Table 3: Prevalence of oestrus cycle type (days) in West African dwarf goats

•  Number on the same vertical column differently superscripted differ significantly (p<0.05)

Table 4: Effect of breeding during short (A) and medium (B) oestrus cycle type (days) on some reproductive parameters of WAD goats (Mean ± SEM)

• N = Number of observations

  A,b,c,d = Number on the same row lettered differently differ significantly (p<0.05)

The effect of service period on fertility and prolificacy is depicted in Table 5. The service period in the pre-weaning does was 51.7±2.29 days while the corresponding value for post-weaning group was 355.69±22.63 days (p<0.05). Conception occurred in both groups of does following breeding at one oestrus. The gestation length in the does was not significantly affected by service period. Similarly, neither the litter size nor type was influenced significantly. However, the kidding interval was significantly longer (p<0.05) in the post-weaning than in the pre-weaning does.

Table 5: Effect of service period on the fertility and prolificacy of pluriparous WAD goats.

• * -- Indicate %

  A,b Number on the same row lettered differently differ significantly (p<0.05)

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Discussion

There is a general agreement (3,9) that litter type in West African dwarf goats tends towards multiple birth. The litter size of 1.91 kids observed in this  study was higher than in earlier reports (3,9,10).

The mean birth weight of 1.16 kg was lower than for European breeds which ranged between 2.6 — 4 kg (11). It was also lower than the 2.7 kg for the Norwegian dairy goats (12). This might be a reflection of the adult weight of these breeds (12,13). Sex influence on birth weights of goats have been reported (12,14,15) and the observation of the superiority of weights of males in this study is consistent with other reports (3,12). The results also agree with the report that individual birth-weight of kids was negatively correlated with litter size (4). The non-significant effect of season on birth-weight would suggest that breeding and kidding of West African dwarf goats can be performed all the year round.

The length of gestation of the West African dwarf goat was similar to earlier reports on this breed (15-18). Gestation length in goats is influenced by breed, with large breeds such as Angora, the Saanen, British Alpine and Toggenburg having longer gestation lengths (19,20). The non-significant effect of season, litter size, sex and parity on gestation length in the West African dwarf goat agreed with an earlier report (21). The effect of litter type on gestation length agree with reports in goats (22), sheep (23) and cattle (24). The decrease in gestation length as the litter size increases further supports the suggestion that uterine mass of the conceptus or optimal uterine stretch play a role in the initiation of parturition (5,9,15).

The mean length of oestrus cycle of 18.3±1.68 days in the West African dwarf goat is similar to other reports (25,26). There are however breed variations in cycle length in goats. Thus, while the Sinclair goat has an inter-oestrus interval of 8 days (27), the pygmy breed has a long cycle of 24 days (28). The long interval in the resumption of observable oestrus post-partum in the West African dwarf goat further confirms the general observation of lactational anoestrus in domestic animals (29,30). In the Criolo breed, it was observed that medium and short cycles accounted for 66% and 33%, respectively (31), while others reported 67% and 73.7% respectively, for normal cycles in the Barbari and Katjang breeds (26,32). Since it has low repeatability(26) and low correlation with either age or body weight ar body condition (33,34) it would appear that selection of goats based on cycle alone is not advisable. The observation of normal fertility following breeding during oestrus succeeding short or long cycles was at variance with one report (33) but concorded with another (32). Short or long cycles should therefore be regarded as normal in the West African dwarf goat as observed in Barbari breeds (34). The observation of superior prolificacy following breeding at oestrus succeeding normal cycles was similar to an earlier report (36). However, others reported that short or long cycles neither affected the reproductive efficiency of the goat, and ovulation rate when the corpus luteum is regressed at any stage after day 4 of the cycle (37). Direct relationship was observed between litter size and length of the service period (38). It is not obvious from this study if a similar effect occurs in the goat. There are contradictory reports on the effect of suckling intensity on service period. While some authors reported a prolonged service period consequent on suckling or milking (39), others did not observe a significant increase in the service period of beef cows suckled ad libitum nor in those suckled twice daily (40).

A mean kidding interval of 196.77 days was recorded for the preweaning group of does. This interval was shorter than the reports of 260 days and 240 days for the West African dwarf goat and Red Sokoto goats, respectively (3). It was also shorter than the 275.7 days reported for the West African dwarf goat (10) and 388.0 days for the Norwegian dairy goat (12). The improved reproductive efficiency in this study may be due to improved management, which is in agreement with the observation of earlier return to oestrus and shorter calving intervals in cows on higher nutritional status (41,42).

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