Recording birth weight has no significance in village based genetic improvement programs of small ruminants

T Jembere, K Kebede¹, B Rischkowsky², A Haile², A Okeyo Mwai³ and T Dessie⁴

Bako Agricultural Research Center, P O Box 03, West Shoa, Ethiopia
tjbakara@yahoo.co.uk
¹ Schools of Animal and Range Sciences, Haramaya University, Haramaya, Ethiopia
² International Centre for Agricultural Research in the Dry Areas, Addis Ababa, Ethiopia
³ International Livestock Research Institute, Animal Science for Sustainable Productivity Program, Nairobi, Kenya
⁴ International Livestock Research Institute, Animal Science for Sustainable Productivity Program, Addis Ababa Ethiopia.

Abstract

The present study was conducted to justify that keeping birth weight (BWT) records have little or no significance in genetic improvements of market or adult weights of small ruminants while implementation of community based breeding program (CBBP). Analyses of Pearson correlations ("r") between BWT and six month (6MW), BWT and nine month weight (9MW), three month weight (3MW) and 6MW and 3MW and 9MW were conducted for three indigenous Ethiopian goat breeds, namely Abergelle (AB), Central Highland (CH) and Woyto-Guji (WG).

The records used for the trait combination ranged from 365 to 715 for BWT and 6MW, 271 to 543 for BWT and 9MW, 362 to 715 for 3MW and 6MW and 269 to 543 for 3MW and 9MW. The 6MW and 9MW were also regressed on BWT and 3MW for the three indigenous goat breeds. The "r" between BWT and 6MW, BWT and 9MW, 3MW and 6MW and 3MW and 9MW ranged from 0.099 to 0.176, 0.051 to 0.163, 0.598 to 0.706 and 0.370 to 0.546, respectively. The regression coefficients (" b") of 6MW on BWT, 9MW on BWT, 6MW on 3MW and 9MW on 3MW ranged from 0.494 to 0.999, 0.311 to 0.996, 0.706 to 0.927 and 0.415 to 0.669, respectively. In general, BWT had weak "r" with 6MW and 9MW in three indigenous goat breeds of Ethiopia. The adjusted R-squared (R²) for regressing 6MW and 9MW on BWT was less than three percent whereas the R² was in the range of 13 to 50% for the regression of the traits on 3MW. Literature reports also indicated weak "r" and genetic correlation (r_g) between BWT and adult or market weight in small ruminants. In addition, the direct heritability is smaller for BWT, compared to adult weights. For these factual, BWT could not be targeted for direct genetic improvement through selection and indirect improvement of other traits. Yet, recording BWT in the CBBP remained compulsory. We conclude that keeping BWT records under the village based breeding program of small ruminants has little or no significance.

Key words: correlation, goats, heritability, market weight, sheep

Introduction

Community based breeding program (CBBP) is said to be suitable for small stock keepers of small ruminants in developing countries (Mueller et al 2015a). It is presented as an alternative to the station or government based breeding program. These days, the CBBP is being implemented in many developing countries including Ethiopia (Duguma 2010; Duguma et al 2012; Haile et al 2011; Abegaz et al 2014; Wurzinger et al 2013; Mueller et al 2015b).

The approach required record keeping, among others, for which hiring enumerators is mandatory. Recording formats have been developed by breeders to be kept by enumerators for the CBBP implemented in Ethiopia. For instance, detailed recording formats developed and used in CBBP of sheep (Duguma 2010) and goat (Alemu 2015) in Ethiopia could be evidences. Growth traits at different ages including birth weight (BWT), three month weight (3MW), six month weight (6MW) and 12 month weight (12MW) in the CBBP of sheep (Duguma 2010) and BWT, 3MW, 6MW, nine month weight (9MW) and 12MW in the CBBP of goats (Alemu 2015) are being kept in Ethiopia.

Among the growth traits, we observed that keeping accurate BWT was not easy. Birth weights could be easily recorded within 24 hours after birth in station based breeding program. In the CBBP, however, it is not easy to record BWT within 24 hours after birth. Recording the BWT in CBBP rather depends on the feedback owners provide to enumerators or the activeness of the enumerators to round on all the member farmers participating in the CBBP and monitor new births. Unless special focus is given, for instance hiring as many enumerators as possible, accurate birth weight could not be recorded in the CBBP of small ruminants. Hiring numerous enumerators, on the other hand, could be associated with high variable costs leading to low discounted profitability of a breeding activity (Gizaw et al 2014; Mirkena et al 2012).

The paradox is embarking in the keeping of BWT records under village breeding program where it has little or no implication for the genetic improvement programs. Meta-analysis of literature review in sheep (Safari et al 2005) and in goats (Jembere et al unpublished) showed that birth weight had weak phenotypic and genetic (r_g) correlations with adult or market weights. On top, the BWT had smaller direct additive heritability and higher maternal heritability compared to the adult or market weights; which means it might not be appropriate selection criteria. We wanted to argue the importance of recording birth weight versus its significance in the CBBP of small ruminants. To reveal that, we analyzed correlation and regression coefficients BWT with adult or market weights. Growth data generated from three indigenous goat breeds namely, Abergelle, Central highland and Woyto-Guji were used. The work was also backstopped by reliable literature parameter estimates.

Materials and methods

Description of the study sites and breeds

The data used for the correlation and regression analysis in the present work were generated from CBBPs established for three indigenous goat breeds, namely Abergelle (AB), Central highland (CH) and Woyto-Guji (WG). There were two villages per breed. The data were pooled from the two villages and analysed by breed. The villages were where Biosciences for eastern and central Africa - International Livestock Research Institute (BecA-ILRI) goat project was implemented. Detailed information of the study sites were given in Table 1.

Description indigenous goat breeds

Abergelle goat breed is kept in arid production system whereas the Woyto-Guji goat breed is kept in the semi-arid production system. Central highland is suited to crop-livestock mixed production system (Tatek in press (Livestock sciences). The description of indigenous goat breeds is given in Table 2.

Phenotypic correlation and regression

Pearson correlation ("r") among growth traits in three indigenous goat breeds was made. Regression of adult or market weights on BWT and 3MW was also analyzed. The CORR and REG procedures in the SAS (2004) were used to calculate the correlation and regression coefficients, respectively. The statistical significances were tested for the coefficients. The phenotypic correlation of BWT and 3MW, BWT and 6MW, BWT and 9MW, 3MW and 6MW, 3MW and 9MW were investigated. In addition, 6mw and 9mw were regressed on BWT and 3MW and presented.

The present data analysis was reinforced by referring to the available weighted average genetic parameter estimates. The weighted average estimates included phenotypic and genetic correlations and direct genetic and direct maternal heritability estimates. The weighted average estimates are considered to be reliable and were presented based on pooled literature parameter estimates.

Results and discussion

The present study revealed that Pearson correlations ("r") of BWT with the market or adult weights were small or even equal to zero in some cases. The "r" between BWT and 6MW for WG and between BWT and 9MW for CH were not different from zero (Table 3). In general, "r" of BWT with both 6MW and 9MW from the three breeds were in the range of 0.051 to 0.176 and the "r" of 3MW with both 6MW and 9MW were in the range of 0.370 to 0.706 (Table 3).

Hither "r" between 3MW and 6MW was observed compared to the "r" between BWT and 6MW (Table 3). The "r" of 3MW and 6MW was higher than "r" of BWT and 6MW by more than three, five and six fold in the case of CH, AB and WG, respectively. In the same fashion, the 3MW and 9MW had higher "r" than BWT and 9MW where the superiority was by more than three, eight and two folds, for AB, CH and WG, respectively.

Adjacent weights had higher "r" than distant age weights. For instance, the "r" of 3MW and 6MW compared to "r" between 3MW and 9MW was higher for all the three breeds, the magnitude of superiority being 1.29, 1.40 and 1.86 folds for AB, CH and WG, respectively.

The present work indicated that BWT had weak "r" with both 6MW (0.099 to 0.176) and 9MW (0.051 to 0.163) regardless of the goat breeds. Rather, 3MW had higher "r" with the 6MW and 9MW traits. The "r" between 3MW and 6MW (0.598 to 0.706) was, however, higher than "r" of 3MW and 9MW (0.370 to 0.546). The weak association of birth weight with both 6MW and 9MW could be due to the fact BWT is affected by the maternal environments in the uterus compared to 3MW.

The regression of 6MW and 9MW on both BWT and 3MW resulted in high values of regression coefficient ("b") except regression of 9MW on BWT for CH and regression of 6MW on BWT for WG (Table 4). Regardless of their satisfactory " b" values (ranging from 0.311 to 0.996), the adjusted R-square for regressing 6MW and 9MW on BWT was considerably low, ranging from 0% to 3 %. This means some other factors contributed to the magnitude of "b" which lessens the reliability of regressing 6MW and 9MW on BWT which could indicate that BWT should not be used to predict both 6MW and 9MW.

The "b" of 6MW and 9MW on 3MW were not always higher than the "b" of 6MW and 9MW on BWT (Table 4). The adjusted R-Square for the regression of 6MW and 9MW on 3MW were considerably higher (13 to 50%) than adjusted R-Square of regressing 6MW and 9MW on BWT.

Weighted average phenotypic correlation among growth traits in goats, sheep and also in cattle was reported to be higher for adjacent age classes. Jembere et al (unpublished) reported weighted average "r" of 0.36 between BWT and 3MW and 0.27 between BWT and 12MW for goats; Safari et al (2005) reported weighted average "r" 0.37 and 0.26 between BWT and 3MW and BWT and adult weight, respectively in sheep. Lobo et al (2000) also reported weighted average "r", in cattle, 0.46 and 0.38, between BWT and 3MW and BWT and 12MW, respectively. In all the reports, the "r" of BWT and 12MW/adult weight was smaller than the "r" of BWT and 3MW the latter has less practical implication.

On the other hand, "r" between 3MW and 12MW was higher by 2.26, 2.15 and 1.77 folds than "r" between BWT and 12MW in goat (Jembere et al., unpublished), sheep (Safari et al 2005) and cattle (Lobo et al 2000), respectively. This may justify that; even based on the meta-analysis result, BWT had weak phenotypic correlation with adult age weights or market weights. The "r" is an estimate of the association between two visible characteristics and it contains genetic and environmental effects. The "r" could be similar with the genetic correlation (r_g) when estimates are made within the same environment (if estimates are made in similar environment, then the environmental covariance between the two traits become zero leading to equal genetic correlation with phenotypic correlation).

Since error variance could not be avoided, judging the genetic association of BWT with different adult weights could be more reliable than the phenotypic association of BWT with the different age weights. The weighted average r_g values in goats were 0.54, 0.32 and 0.31, between BWT and 3MW, BWT and 12MW and 3MW and 12MW, respectively in goats (Jembere et al unpublished). These values were 0.47, 0.22 and 0.75, for the trait combinations in sheep, respectively (Safari et al 2005). Lobo et al (2000) reported weighted average r_g values of 0.50, 0.55 and 0.81 between BWT and 3MW, BWT and 12MW and 3MW and 12MW, respectively in cattle.

In all the three reports, high r_g was reported between adjacent age classes; for instance between BWT and 3MW and between 3MW and 12MW. The weighted average r_g between BWT and 12MW or adult age weight was generally smaller than the r_g between 3MW and 12MW. This also, in addition to the "r", could indicate weak r_g between BWT and adult/market.

The BWT of goats, sheep and cattle had smaller direct heritability than 12MW whereas the maternal heritability of BWT for the species was higher than the maternal heritability of 12MW (Table 5). Comparing the direct heritability, same table, of BWT and 3MW, the latter had higher values in most cases. In the case of maternal heritability, it was BWT that had higher values compared to 3MW. The lower values of direct heritability of BWT or the higher values of maternal heritability of BWT might indicate the high influence of maternal environment on the trait. From the two heritability estimates, it is the direct heritability estimates that have more implication on genetic improvement through selection. Therefore, it could be concluded that BWT could not be targeted for selection.

Terefe et al (2013) says that the market weight of Afar goat is in the range of 25 - 30 kg. According to Shija et al (2013), slaughter age (years) and weight (kg) of indigenous sheep and goats in East Africa could be in the range 1.5 to 2 years and 20 to 25. Tibbo et al (2006) suggested market age and market weight for sheep in Ethiopia as 12 months of and 30 kg to be considered in designing the breeding program. The average marketing age (months), for indigenous goats in Ethiopia, was reported to be 11.67 and 12.33 for males and females, respectively (Asefa et al 2015). In the present study, we could not show favorable correlations between BWT and the market weights or adult weights. The direct heritability estimates from literature, were also small.

Conclusions

• Birth weight had weak phenotypic correlation with 6MWand 9MW in the three indigenous goat breeds in Ethiopia.
  
  
• The regression of 6MW and 9MW on BWT was not reliable because of low (less than three per cent) adjusted R-square.
  
  
• Literature reports indicate due to weak phenotypic and genetic correlation between BWT and adult or market weight and low direct heritability, BWT could not be targeted for genetic improvement through selection. Yet, recording BWT in the community based breeding program remained compulsory.
  
  
• We conclude that keeping BWT records under village based breeding program is not only of little or no significance, but also hardly practical.

Acknowledgment

We are grateful for the support we got from the smallholder farmers whose animals were monitored. We are also thankful to the partner research centers namely Tanqua Abergelle, Sekota Dry land, Gonder and Arbaminch for their close follow-up of data collection. The first author thanks ILRI and International Center for Agricultural Research in Dry Areas for supporting this work through the CGIAR Research Program Livestock and Fish, and a SIDA funded BecA-ILRI goat project and an International Fund for Agricultural Development (IFAD) funded SmaRT (Small Ruminant value chain Transformation in Ethiopia) project.

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Received 31 May 2016; Accepted 5 July 2016; Published 1 August 2016

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