Environmental influences on pre-weaning growth performances and mortality rates of extensively managed Somali goats in Eastern Ethiopia

Zeleke Mekuriaw Zeleke

Bahir Dar University, PO Box 1866, Bahir Dar, Ethiopia
Zeleke_Mekuriaw@yahoo.co.uk

Abstract

Records of 326 Somali goats born from 1994 to 2004 in eastern Ethiopia were used to assess effects of major environmental factors on growth and survival traits. Year of birth had significant effect (P<0.01) on birth weight, pre-weaning daily weight gain and weaning weight of kids.

Male kids had higher (P<0.01) birth weight (3.35±0.18kg vs. 3.04±0.18kg), pre-weaning daily weight gain (61.60±7.06g vs. 55.87±7.15g) and weaning weight (12.27±0.89kg vs. 11.10±0.91kg) than female kids. Kids born from fifth parity dams had the least birth weight (2.98±0.23kg) and the highest pre-weaning mortality rate (33.33%) than those born from dams younger than fifth parity. Similarly, single born kids had heavier birth weight (3.17±0.06kg vs. 2.30± 0.20kg), higher pre-weaning daily weight gain (55.80±2.22g vs. 47.31±7.92g), higher weaning weight (11.47±0.28kg vs. 9.50±1.00kg) and less pre-weaning mortality rate (8.78 vs. 42.86%) than twin born kids. Similarly, mortality rate was found to be the highest (75%) in kids weighing <1.5kg. Improving feeding management for pregnant and lactating dams to assure moderate birth weight and adequate quantity of milk for twin born kids, and stringent culling practice of dams beyond fourth parity can be suggested to improve the productivity of Somali goats.

Key words: birth weight; birth type; parity; season; sex; weaning weight

Introduction

Goats are known to be potential genetic resources for meat, milk, skin and fiber throughout tropical and developing countries. Goats play an important role in generating employment, income, capital storage and improving household nutrition. Being small in size, they may not require large housing space per head compared to cattle and can easily be handled and managed by women and children. Goats in Ethiopia with the estimated total population of 18.5 million (CSA 2007) make a major contribution towards meat, milk and skin production. They are more dominant in lowland areas of Ethiopia, which encompasses more than 60% of the total landmass of the country. In these lowland areas, Somali goats are one of the known breeds reared by pastoral and agro-pastoral societies for meat and milk production purposes (FARM-Africa 1996). In these areas, goats are the most important species for milk next to camels. It was also reported that goats are the most common animals sold by pastoral households for immediate cash income such as for purchase of food items. They are also the major species slaughtered at home to be consumed by the family (FARM-Africa 1996; Baars 2000), which indicates their significant role in household nutrition and food security of the pastoral society.

Even though growth performance and survival rates are the most important production traits for successful animal production for whatever purpose, very little is known about these traits for Somali goat under extensive management conditions of Ethiopia. Therefore, the current study is intended to assess the effect of some environmental factors on pre-weaning growth performance and mortality rates of Somali goats.
 

Material and methods

The study was conducted at Alemaya University, Eastern Ethiopia. The University is located at 9⁰24”N latitude and 41⁰5”E longitude, and at an altitude of 1980m above sea level. According to Alemaya University’s meteorological data of 12 years (1992-2004), the area enjoys a moderate average temperature of 16ºC, and the mean maximum and minimum annual temperatures of 24.02 and 9.73 ºC, respectively. The annual rainfall, which fluctuates from year to year, ranges between 507.30-995.40mm. The pattern of rainfall is bimodal type consisting of short rainy season occurring from end of April to end of June and main rainy season from July to beginning of October. The dominant pasture types consist of Hyparrhenia species, Cyndon dactylon, Sporobulus africanus and Pennisetun species (Mengestu and Asnakeh 1986).

The Somali goat breed is found in Somalia, Ethiopia and North-east Kenya (Mason 1996). The breed is used primarily for meat production. These goats are predominantly white in colour, but some individuals have colored spots or patches; the males are horned and the females are either horned or polled.

The goats used for this study were managed at extensive conditions. The animals were allowed to graze 8 hours a day (8h00-12h00 and 14h00-18h00) on legume-grass-mixed natural pasture. In addition to grazing, lactating goats were occasionally provided with less than half a kilogram of brewer’s grain per head per day in the afternoon after grazing. When brewer’s grain is not available, they are given approximately 200-300 g of wheat bran per head per day. Mineral lick and water were available ad libitum. All the goats were provided with shelter during night. Kids were allowed to suckle their dams up to the age of four months. 

Records of 326 goats born from 1994 to 2004 were used for the study. Birth date, birth weight, litter size, sex of kids and age of dams were recorded for each kid during this period. Furthermore, body weight of kids was measured fortnightly using weighing balance. Death of kids was also recorded as it occurred. 

The effects of environmental factors on birth weight, average pre-weaning daily weight gain, and weaning weight of kids were analyzed using General Linear Model (GLM) procedures of SAS (SAS 1999) whereas mortality rates were analyzed using CATMOD procedures of the same software.
 

Results and discussion 

Birth weight

The overall mean birth weight of Somali goats obtained in the present study was 3.19 kg, which is inline with the report of Abebe (1996), who indicated the birth weight of the same breed of goats in Awasa University, Ethiopia, to be 3.05 kg. However, lower birth weights than the present finding had been documented by Das et al (1994) for Tanzanian goats and Liu et al (2005) for Angora goats.

The effects of year of birth, sex of kids, parity of dams and litter size on birth weight are indicated in Table 1.

Year of birth had significant (P<0.01) effect on birth weight of kids. The significant influence of year of birth on birth weight of kids was also reported in previous studies (Gifford et al 1990; Liu et al 2005). As birth year is a complex variable encompassing conditions of climate, feeding and management, the variation in birth weights may be related to the variation of natural environments, feed availability, management methods and body conditions of dams. The poor body condition of dams may be a factor responsible for a reduced birth weight of kids in some years. Even though the effect of year of birth on kid weight at birth is not persistent, the general trend indicates that kids born in later years have the least birth weights as compared to kids born in earlier years. This may be due to deterioration of grazing land of the farm as the flock size increases without proportionate increment in farmland or improved productivity per unit of land.

Season of birth had no statistically significant effect (P>0.05) on birth weight. The possible reason for lack of significant influence of season on birth weight of kids may be availability of hay and concentrate supplement to the dams during the dearth of browse.

The other non-genetic factor which significantly (P<0.01) affected birth weight was sex of kids. In this study, males had significantly (P<0.01) heavier birth weights than female kids. This is in agreement with reports of Gerstmayr and Horst (1995), Bhoite et al (1996), Husein et al (1996) and Liu et al (2005).

Similarly, the parity of dams had significant (P<0.01) effect on birth weight of kids. Kids born from dams of fifth parity had lighter (P<0.01) weights at birth compared to kids born from dams of first to fourth parities. Kids born from fourth parity of dams also had significantly (P<0.01) lighter weights at birth as compared to kids born from second and third parity groups. In general, there is an increasing trend in birth weight of kids as the parity of does advances from the first to third. Thereafter, the birth weights of kids declined.  Similar results were reported by previous workers (Gifford et al 1990; Liu et al 2005) concerning the effect of parity of dams on birth weight of kids. The reason for the decline of the birth weight beyond third parity groups of dams may be due to wear of teeth and consequent loss of body condition of dams and hence retarded growth rate of fetus. Based on the result of this finding, culling of dams beyond fourth parity can be suggested.

Birth type was also found to have significant (P<0.01) effect on birth weight of kids. In this case, single born kids had heavier birth weights as compared to twins. The heavier birth weights recorded for single born kids as compared to twins is in agreement with reports of Gifford et al (1990) and Husein et al (1996). The probable reason for heavier birth weights of single born kids is due to absence of intra-uterine nutritional and space competition in single born kids unlike that of twin born kids. Robinson et al (1977) reported that for lambs in utero, as the number of fetuses increase, the number of caruncles attached to each foetus decreases, thus reducing the feed supply to the foetus and hence reduction in the birth weight of the lambs.

Pre-weaning growth rate

The overall mean pre-weaning daily weight gain of Somali goats was 61.25g (Table 2).

The pre-weaning weight gain obtained in this study was lower than the one reported by Abebe (1996) for the same breed of goat (76 g/day). Lower pre-weaning daily weight gains than the present study was also reported by Husein et al (1996) for Black Bengal goats (39.50±1.91 g/day). The variation in pre-weaning weight gain might have been emanated from management difference of both dams and kids at early age.

Year of birth, sex and birth type of kids had significant (P<0.01) effect on pre-weaning daily weight gain. There was a declining trend in pre-weaning daily weight gain of kids from year 1994 to 2004; the least mean daily weight gain being in year 2004. This indicates that there is deterioration in feeding management of the flock in later years. Formerly, the goat farm had been managed by FARM Africa, which is non-governmental organization. Later on, it was handed over to Alemaya University. The overall input of production invested on the same farm, even if difficult to quantify, differs between these to institutions. The significant effect of year on weight gain of kids was reported by Gifford et al (1990) and Liu et al (2005).   

In this study, male kids gained significantly (P<0.01) higher daily weights as compared to female kids. The pattern of live weight change of male and female kids is indicated in figure 1.

The higher daily weight gains in male kids than in females is in agreement with the reports of Husein et al (1996). This is a natural phenomenon that male kids grow faster than females, as their mature weight is also heavier.

Although there is a tendency of relatively higher daily weight gains in kids born during rainy seasons as compared to dry season (figure 2), the difference was not statistically significant.

Parity of dams had significant (P<0.01) influence on pre-weaning daily weight gain of kids. As the parity of dams advanced the pre-weaning daily weight gain of kids declined. The significant influence of parity of dam on pre-weaning daily weight gain of kids is in compliance with the findings of Husein et al (1996) and Liu et al (2005). The likely reason for the decline of pre-weaning daily weight gain of kids as the parity of their dams advanced is due to a reduction in milk production performance of their dams.

Single born kids gained significantly (P<0.01) higher daily weights as compared to twins, which is inline with the findings of Husein et al (1996). The higher daily weight gains attained in single born kids is due to relatively higher amount of milk consumed per kid as there is no competition for dam’s milk. To improve weight gain in twin born kids, provision of special feeding management such as creep feeding may be required. The growth pattern of single born and twin kids is indicated in figure 3.

The overall mean weight at weaning (end of forth month of age) was 11.67 kg. The value for live weight at weaning in this study is inline with the reports of Das et al (1994), who reported 11.14±0.15 kg in Tanzania.

Year of kidding, sex of kids and birth type had significant (P<0.01) effects on weaning weight (Table 3).

There are inconsistent variations in weaning weight of kids between years; the highest and the least weaning weight being recorded in 1994 (15kg) and 2002 (9.65), respectively. This may be due to variations in feed availability between years as distribution and amount of rainfall also varies among years. 

In this study males attained significantly (P<0.01) heavier weights at weaning than female kids, implying that sex effects exist even before the age of puberty. This is a natural phenomenon that males do have faster growth rate and heavier weights at maturity than female animals. Similar influences of age of animals on growth rates had also been reported by Bell et al (1970) and Das et al (1994). 

Similarly, single born kids weighed significantly (P<0.01) higher than twins for the reason that the former consume dam’s milk alone whereas the latter ones shared limited amount of milk between two kids. 

Pre-weaning mortality rate

The overall mean pre-weaning mortality rate of Somali goat kids and factors affecting it are indicated in Table 4.

The overall pre-weaning mortality rate of kids in the present study was 11.52% (31/269). Out of 31 deaths encountered before four months of age, 11 deaths occurred within two weeks of age. It seems that the first two weeks post kidding are critical periods which determinately affect the survival rate of kids. The mortality rate encountered in the present study is lower than the values reported by Awemu et al (1999) for Red Sokoto goats in Nigeria (38%) and Husein et al (1995) for Black Bengal kids in Bangladesh (28.3%). 

Season of birth kids did not demonstrate any significant effect on pre-weaning mortality rate contrary to findings of Husein et al (1995), who reported significantly higher survival rates of kids born in rainy season compared to those born during dry season. Absence of significant difference in pre-weaning mortality rate due to season in the present study may be due to provision of supplementary feed and shelter for goats which minimizes nutritional variations and direct influence of weather factors such as ambient temperature and humidity among seasons.

In this study, sex of kids did not show any significant influence on pre-weaning mortality rate of kids which is inline with the findings of Awemu et al (1999). Other previous findings (Husein et al 1995; Alexandre et al 1999), however, indicated higher mortality rates in male kids as compared to female kids. Ebozoje and Ngere (1995) also reported that females had higher mortality rate than males in West African dwarf goats. Absence of significant difference in mortality rate due to sex of kids in the present study indicates lack of preferential management for female kids, as production objective of Somali goats is both for milk and meat production.

Parity of dam and birth weight of kids had significant (P<0.01) effects on pre-weaning mortality rates of kids. Significantly (P<0.01) fewer number of kids born from dams of first and second parities died before weaning  age compared to kids born from the later parities. The pre-weaning mortality rates of kids born from third and fourth parity groups of dams were intermediate. The highest (P<0.01) number of pre-weaning mortality was encountered in kids born from dams of fifth parity. The occurrence of higher pre-weaning mortality rates in kids born from fifth parity dams in this study is contrary to the findings of Husein et al (1995), who reported absence of significant effect of parity on survival rates in Black Bengal kids. Awemu et al (1999) also reported higher survival rate in Sokoto kids born from sixth parity dams. The possible reason for the increased incidence of pre-weaning mortality rates in kids born from fifth parity dams in the present finding may be due to unsuitable uterine environment for the proper growth of the fetus and /or reduced milk yield post-kidding due to old age.

Birth weight of kids affected (P<0.01) mortality rate. The maximum mortality rate (75%) was recorded from kids weighing 1.5 kg or less at birth followed by kids weighing 1.5-2kg. The least mortality rate was recorded in kids with 3-4 kg at birth. Though not statistically significant, there is a tendency of increasing in mortality rate when birth weight exceeds 4 kg (figure 4).

The occurrence of increased incidence of mortality in kids born with lower birth weights is in compliance with the findings of Husein et al (1995). The probable reason for higher rate of pre-weaning mortality of kids with lighter birth weights is due to inadequate body reserves at birth to withstand environmental stress. Again the scaling up of mortality rate in kids heavier than 4 kg at birth may be due to difficulty during birth and/or inadequacy of milk from their dams to satisfy their demand to maintain their higher body mass. Improved management conditions which would help maintain optimum body condition of dams to obtain kids with reasonable birth weights could be suggested.  

In the present study, the type of birth significantly (P<0.01) affected pre-weaning mortality rates of kids.  Significantly higher number of twin born kids died before weaning as compared to single born kids. The higher incidence of mortality in twin born than single born kids is inline with previous findings (Wilson and Light 1986; Awemu et al 1999). The competition for limited nutrients in the uterus and for milk after birth may be reasons for higher incidence of pre-weaning mortality in twin born kids.

Conclusion

• Environmental factors had significant influence on birth weight, pre-weaning growth rate, weaning weight and pre-weaning mortality rate.
  
  
•  Strategic feeding of dams to improve their body condition during the dearth of natural pasture may mitigate problems of fluctuating body weight of kids at birth among years.
  
  
• Furthermore, stringent culling procedure should be followed, especially for goats older than fourth parity as kids born from these groups of dams had lighter birth weights, poor pre-weaning daily weight gains, lighter body weights at weaning and higher pre-weaning mortality rates.
  
  
• Preferential feeding care should be given to twins and their dams in order to mitigate inferior birth weights, pre-weaning growth rates, weaning weights and higher pre-weaning mortality rates observed in twin born kids as compared to single born kids.

Acknowledgements

The author is thankful to Haramaya University’s Goat Farm workers for recording valuable information.

Reference

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Received 3 February 2007; Accepted 26 September 2007; Published 12 December 2007

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