Non-genetic factors influencing post-weaning growth and reproductive performances of Arsi-Bale goats

Year of birth had a significant effect (P <0.05 and P <0.001) on all traits studied except for 18MW. Live weights tended to increase from 1999 to 2001 and decreased thereafter. Differences observed in weights between years may be a reflection of differences in feed availability among years, caused by variation in total annual precipitation and the distribution of rainfall. Mid Rift Valley area of the country is subjected to shortage of rain with limited feed availability. Total rainfall recorded at the center was 780, 784, 777, 669 and 602 mm for the years 1999, 2000, 2001, 2002 and 2003, respectively. Similar results of the effects of year on post-weaning growth performances are well documented (Wilson 1987; Das et al 1996).

Season of birth had a significant influence (P <0.001) only on 3MW and had no influence on the rest of live weights, average daily gains and reproductive performances. Kids born in the dry season had 0.8kg heavier liveweight at 3-months of age than those born in wet season though feed availability is relatively better in wet season. Thus, from the results of this study it is evident that kids born in the dry season perform better than those born in the other seasons do. Hailu et al (2004) also reported that season had a significant effect on pre-weaning growth performances of Arsi Bale goat breed. However, Mourad et al (2000) reported that season had no significant effect on liveweight of kids. Generally, lower weaning weight was recorded in early-dry season than in dry season. A possible explanation for this is that, in the wet season the forages are succulent. Though, the current study was conducted on station, sheep and goats are usually tethered or confined in the wet season to prevent crop damage (Solomon et al 2005) and may have limited intake and selectivity of forages. Further more, disease challenge is high in wet season (Mboera and Kitalyi 1994; Gemeda et al 2005) contributing further to lower liveweight at weaning. Actually, since the present study was conducted in semi arid area, disease challenges could be less pronounced in wet season as compared to humid areas of the country and succulence of forages is for a very short period. In fact, forages are extremely scarce in dry season compared to humid and highland areas. The reason for the existence of differences in live weight among seasons in the present study could not be clearly identified and needs further investigation.

Least squares means (±SE) for 3-to 6-months growth rate of kids (ADG1), 6- to 12-months daily weight gain of kids (ADG2) and 12- to 18-months daily gain (ADG3) are presented in Table 4.

The overall mean growth rates of 24.5, 29.3 and 30.4g/day were recorded for ADG1, ADG2 and ADG3, respectively. The estimated value of 24.5g/day obtained at 6-months for Arsi-Bale goats was lower than the overall mean of 41.7g/day reported for East African goats at 180 days of age by Ndlovu et al (1996). In this study, no seasonal effect on the growth rate and live weight of the kids was observed except at weaning age. However, it was reported that seasonal effects on growth rate and liveweight are common features of extensively managed flocks (Hale 1986; Karua 1989; Mourad et al 2000).

The effect of parity was significant for 3MW (P <0.001), 6MW (P <0.01), ADG2 (P <0.05) and litter size (P <0.001). Its effect increased with increasing parity until the maximum of 8.7, 10.6kg liveweight was recorded for 3MW and 6MW, respectively and 2.1 kids/doe at parity 6. The influence of parity on live weight of kids was greatest at 3MW and 6MW, but decreased, as the kids grew older to yearling and above. Kids of first parity were lighter at 3-, 6- and 12-months of age than those of the rest parity. This might be explained by the fact that young does that had not reached adult size continued to grow during pregnancy and thus competed with the fetus for the available nutrients. Moreover, does as first-time kidders may produce less milk than average. Thus, the gradual kids' live weight increment may be associated with a greater milk yield produced by mature does. Moreover, physiologically matured does had a tendency of producing heavier kids than younger dams. It is generally known that mothering ability, such as milk yield gradually increase with parity, older dams are larger in body size and produce better milk yield (Wright et al 1975; Stobart et al 1986). Therefore, influence of the maternal ability is expected to be high for 3MW, and it is not surprising that post weaning weights at 12 and 18 months were not significantly affected by parity. Post-natal factors account for 75 % of the maternal influence on weaning weight and are largely mediated through milk production (Bradford 1972). It is generally agreed that post weaning growth of goats is partly determined by the direct genetic effect of the goat and the level of non-genetic factors.

As expected, sex had a highly significant (P <0.001) influence on post weaning live weights and growth rates. Several similar results were also reported in the literature (Wilson 1987; Das and Sendalo 1992; Safari et al 2005). The influence of sex on liveweight difference increased with age from 10.8% (0.8kg) at 3-months of age to 20.4% (4.2kg) at 18-months of age (Table 3). This might be attributed to different physiological processes in the two sexes.

Nevertheless, no significant sex influence was observed in East African goats (Ndlovu and Simela 1996) and West African dwarf goats (Mourad et al 2000) at 90, 150 and 180 days of age. In the present study, males grew approximately 11.5% (2.4kg), 27.3% (7.3kg) and 29.2% (10.6g) faster than their female counter parts from 3- to 6-months, 6- to 12-months and 12- to 18-months, respectively. Their differences in growth rate increased with age implying that sex effects are more pronounced with age after puberty. In general, Arsi-Bale goats have slow growth rate but with large individual variations. This calls for a need to conduct selection within the breed or/and introduce better genes to improve the trait under consideration while considering not to adversely affect the good traits of Arsi-Bale goats.

Litter size also had a significant effect (P <0.001) on 3MW, 6MW and 12MW. Single born kids were heaviest at 3-, 6- and 12- months of age than twins and triplets. Nevertheless, they did not grow fastest than their twins and triplets contemporaries (Table 4). The effect of litter size decreased with the increase in age of the kids. Part of the litter size differences on liveweight might be due to the carry-over effect of the heavier weight of singles at birth. Liveweight differences in litter size were also observed in pasture grazed goats in Tanzania (Das et al 1996), Egypt (Marzouk et al 2000), Guinea (Mourad et al 2000) and Ethiopia (Gizaw et al 1991). Nevertheless, this difference was not detected between single and twins born goats when kept under artificial rearing system (Norton and Banda 1993) indicating that growth differences between single and twin/triplets could be resulted from competition of kids at young age for limited supply of milk produced by the does.

The phenotypic correlations among the different growth traits are tabulated in Table 5.

Weaning weight was highly and positively correlated with 6MW and moderately correlated with 12MW and 18MW. Similarly, 6MW had medium to high phenotypic correlations both with 12MW and 18MW. Weaning weight would be a better predictor of the subsequent liveweight of the goats under this production system since it is highly and positively correlated with 6MW. In Ethiopia goats are invariably marketed at younger age usually less than a year of age.

Least squares means for AFK, KI and litter size performances of Arsi-Bale Does are presented in Table 6.

The overall means for AFK, KI and litter size were 28.5 months, 293.2 days and 1.6kids, respectively. Year significantly influenced (P <0.001) AFK, KI and Litter size. Mavrogenis et al (1984) also reported effects of year on litter size and KI in Red Sokoto does. Longer kidding intervals of about 342 and 326 days were recorded in years 2005 and 2004 while the shortest kidding interval (243 days) was recorded in year 2003. This may be due to management differences in the different years or due to differences in rainfall that could affect feed availability. The trend of length of KI gradually decreased with increasing parity. This may calls for preferential treatments of young does to shorten their kidding interval.

The average AFK (853.8days) is large as compared to 543 days reported for West African dwarf goats (Tuah et al 1992) and 810.8 days for small East African goats and their crosses (Mtenga et al 1994).

Overall mean of KI for Arsi-Bale goats is 293.2 days, indicating that this goat breed is not, therefore, capable of three kiddings in 2 years. The mean KI found in this study was slightly shorter than that reported by Wilson and Light (1986), but longer than those survey results reported for goats in western part of Oromia by Solomon et al (2005). Here, it calls for management intervention to decrease the long KI found in this study to at least less than 250 days, which would increase productivity of this goat breed. Season did not have significant effect on KI. However, does which kidded in the short rainy season had non-significantly longer KI than those kidded in early-dry season (Table 6). They had 49.2 more days of kidding interval than those born in the dry season, whose variation largely appears to reflect the effects of nutrition. Kidding interval could be affected by change in the quality and quantity of forages, which occur during the various seasons of the year, as these forages are the main sources of goats’ diet. Inadequate nutrition is a major limiting factor to small ruminant production in the arid and semi-arid areas of Africa. In general, there is no proper culling of poor producer animals in the center, thus perhaps if culling of unproductive animals were carried out regularly, kidding interval would have been shortened.

Parity exerted a significant influence (P <0.001) on litter size with largest litter sizes of 2.1±0.10 being achieved at about sixth parity. Mean litter size obtained in the present study was 1.6 and it is larger than those reported by Wilson and Light (1986) for traditionally managed goats in semi-arid agro pastoral system in central Mali. Still there might possibly be some potential for increasing litter size by selection, as there are variations among individual does.

Dam age exerted a significant influence (P <0.001) on AFK. Generally, AFK, KI and litter size showed a general trend of gradual increase as the age of does increase. The probability of getting more than one kid increased with increased dame age up to 54 months of age and decreased thereafter.

Conclusions

• In this study, several non-genetic factors were observed with significant influence on both the growth and reproductive traits considered. Year of birth has an effect on post growth and reproductive traits which is a reflection of differences in feed availability among years due to variation in total annual precipitation and the distribution of rainfall. Season of birth affected only the weaning weight of kids indicating its more effect on the pre-weaning growth than post weaning growth and reproductive performances. Kids born in dry season performs better than wet season.

  
  

• Both live weight and litter sizes increased with increasing parity until the maximum parity of six considered in the current study. Male kids grow faster than female counterparts indicating that sex has an effect on the post weaning growth performance. Similarly litter size also has a significant effect on growth performance of Arsi Bale kids. Overall mean of KI for Arsi-Bale goats is 293.2 days, indicating that there is a need for management intervention to decrease the long KI found in this study to at least less than 250 days, which would increase productivity of this goat breed. Though, some of the factors (for example, sex and year) exerted great influence on flock productivity, unfortunately least control can be exerted on them by management. Here, data used in the present study did not permit to determine the maximum parity where both production and reproduction decline that could enable to make proper culling. The probability of getting more than one kid increased with increased dame age up to 54 months of age and decreased thereafter. Generally, the effects of non-genetic factors on both growth and reproductive traits considered were significant and hence will need to be considered in goat breed improvement program.

Acknowledgements 

We would like to extend our great thanks to Merga Wakjira, Jarso Wakeyo, Meseret Tilaye and Meseret Terefe for data collection and typing the manuscript. We are also thankful to the Ethiopian Agricultural Research Organization for funding this study.

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Received 22 October 2006; Accepted 13 May 2008; Published 3 July 2008

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