Introduction

Sheep farming is an important component of rural economy particularly in the arid, semi-arid and mountainous areas of the country due to its multi-purpose utility for meat, wool, skin, milk and manure. Sheep are capable of living in all kind of environment and thrive well in hot and arid regions. The sheep is known for its adaptability to the harsh environment and potential for high meat production (Gowane et al., 2010). Munjal sheep is large in size, tall, rectangular and popular among the farmers of Haryana, Punjab and Rajasthan for their heavy weight. It has long head with Roman nose and narrow forehead.  Face is generally tan or brown in colour, which may extend up to middle of neck.

Development of breeding strategies and effective genetic improvement programme require knowledge of the genetic variation among important traits and accurate estimates of heritability and genetic correlations. Heritability estimates are useful for construction of selection indices, prediction of genetic response to selection and for deciding how much one can rely upon individual’s own phenotype for selection. The extent and direction of genetic correlations are essential to evaluate direct and correlated responses and net genetic gain, when simultaneous selection for several traits is practiced. The literature is dotted with conflicting and sporadic reports regarding genetic parameters of reproduction traits in sheep (Dey and Poonia (2005) in Nali sheep, Baber and Javed (2009) in Lohi sheep, Qureshi et al. (2010) in Kajli sheep, Chandar (2012) in Magra sheep and Gowane et al. (2014) in Malpura sheep and lalit et al. (2016) in Harnali sheep) but negligible research work is available for Munjal sheep. Therefore, the present investigation was carried out to estimate the genetic parameters of reproduction traits in Munjal sheep.

Materials and Methods

The data were collected over a period of 16 years (2001-2016)  pertaining to reproduction traits of 287 Munjal sheep maintained at Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar. The information were recorded on five reproduction traits namely age at first service (AFS), weight at first service (WFS), age at first lambing (AFL), weight at first lambing (WFL) and first lambing interval (FLI). The data were classified according to year of birth and age of dam at lambing to study the effect of these factors on traits under study. Whole duration of 16 years were divided into 8 groups each having two year duration on the basis of years of birth. For studying the effect of age of dam at lambing, the data were classified into different age groups (≤ 36 month, 36-48 month, 48 to 60 month, 60 to 72 month and ˃72 month of dam’s age at lambing). The effect of non-genetic factors viz. period of birth and dam’s age at lambing on various traits was studied by least squares technique by Harvey (1990) using the following mixed model-

Y_IJKLM = µ + S_I + P_J + D_L + EIJKLM

Where, Y_ijklm is observation on m^th animal belonging to l^thage group of dam, j^th period of birth and i^th sire. m is the overall mean; S_i is the random effect of i^th sire (i= 1 to 27); P_j is the fixed effect of j^th period of birth (j = 1 to 8); D_l is the fixed effect of l^thage group of dam (l = 1, 2,…5.); eijklm is the random error associated with each observation and assumed to be normality and independently distributed with mean zero and variance σ²_e . Modified Duncan’s multiple range test was used for comparing sub group means by Kramer (1957).

Heritability estimates for different reproduction traits were obtained from sire component of variances using paternal half-sib correlation method. The standard errors of heritability estimates were obtained using the formula given by Swiger et al. (1964). Genetic correlations among different traits were calculated from sire components of variances and co-variances and standard errors were estimated using the formula given by Robertson (1959). Phenotypic correlations among various traits were calculated from total variances and covariances and their standard error were computed using the formula given by Snedecor and Cocharan (1968).

Results and Discussion

The analysis of variance and least squares means along with standard error for the reproduction traits are presented in Table 1 and 2 respectively.

Table 1: Analysis of variance for reproduction traits in Munjal sheep   

 ** Significant at P≤0.01

Effect of Non-Genetic Factors

The period of birth had significant (P≤0.01) effect but the dam’s age at lambing had non-significant effect on all reproduction traits. The estimates for AFS, AFL and FLI in first period are lower than later periods which might be due to the reason that the selected ewes were purchased from field in 2001 and their lambs were heavier. The present finding were in close agreement with those reported by Qureshi et al. (2010) in Kajli sheep, Gowane et al. (2014) in Malpura sheep, Lakew et al. (2014) in  Dorper×Local crossbred, and Reddy (2015) in Nellore brown sheep. However, Dey and Poonia (2005) in Nali sheep, Baber and Javed (2009) in Lohi sheep and Das et al. (2014) in Kashmir Merino sheep found non-significant effect of period of birth on age at first service.

Table 2: Least squares means along with standard error for reproduction traits in Munjal sheep

Means with different superscript for an effect differed significantly (P<0.05)

Least Squares Means

The overall least squares means AFS, WFS, AFL, WFL and FLI were estimated  as 563.08±14.43days, 29.06±0.16 kg, 713.48±14.02 days, 31.30±0.16  kg and 351.82±1.12 days, respectively. The present findings are in close agreement with those reported by Dixit et al. (2002) in Bharat merino and Jahan et al. (2013) in Balochi sheep. The estimates obtained in the present study were on higher side than those reported by Dey and Poonia (2005) in Nali, Jahan et al. (2013) in Balochi, Poonia (2008) in Munjal, Panda et al. (2012) in Edka, Mane et al. (2014) in Decani and Lakew et al. (2014) in Dorper×Local crossbred sheep. The estimates obtained in the present study were on lower side than those reported by Baber and Javed (2009) in Lohi, Qureshi et al. (2010) in Kajli, Gowane et al. (2014) in Malpura and Kumar et al. (2016) in Harnali sheep. Poonia (2008) reported that the ewes lambing for the first time had longer lambing interval (287.39±10.14), which decreased in the subsequent lambings.

Genetic Parameters

Heritability estimates for AFS, WFS, AFL, WFL and FLI were estimated as 0.19±0.12, 0.24±0.15, 0.17±0.10, 0.27±0.15 and 0.05±0.01, respectively (Table 3). The heritability estimate for AFS in the present study was in close agreement with those reported by Dey and Poonia (2005) in Nali and Reddy (2015) in Nellore brown sheep and lower than those reported by Baber et al. (2008) in Lohi and Akhtar et al. (2008) in Hissardale sheep.

Table 3: Heritability (diagonal), genetic (above diagonal) and phenotypic (below diagonal) correlations along with standard error among reproduction traits

** Significant at P<0.01, * Significant at P<0.05

The heritability estimate for WFS in the present study was higher than those reported by Akhtar et al. (2008) in Hissardale and lower than those reported by Dey and Poonia (2005) in Nali, Baber (2008) in Lohi and Gowane et al. (2014) in Malpura sheep. The heritability estimate for AFL was in close agreement with those reported by Dixit et al. (2002) in Bharat Merino, Dey and Poonia (2005) in Nali and Gowane et al. (2014) in Malpura sheep and lower than those reported by Akhtar et al. (2008) in Hissardale and Kumar et al. (2016) in Harnali sheep. The heritability estimates for WFL in the present study were in close agreement with those reported by Gowane et al. (2014) in Malpura sheep, Khan et al. (2017) and higher than those reported by Akhtar et al. (2008) in Hissardale sheep and lower than those reported by Singh and Manuja (2000) in Gaddi and Dey and Poonia (2005) in Nali sheep. Low estimates of heritability for reproduction traits indicated that these traits are mostly influenced by environmental factors and can be improved by better managemental practices.

The genetic correlations of AFS with AFL (0.96±0.01) and WFS with WFL (0.94±0.03) were high and positive. The genetic correlation of AFS and AFL were found low and negative with WFS, WFL and FLI. Dey (2004) also reported high and positive genetic correlations of AFS with AFL. The phenotypic correlations of AFS with AFL (0.97±0.01) and WFS with WFL (0.94±0.01) were high, positive and significant. The phenotypic correlation of AFS and AFL were found low, positive and non significant with other reproduction traits. Dey (2004) reported moderate to high, positive and significant phenotypic correlations of AFS with AFL, WFS and WFL. The magnitude of association was more between AFS and AFL. The genetic correlations between traits pointed forward the conclusion that the early maturing ewes should be selected to have lower age at first lambing and more weight at lambing.

Conclusion

Development of breeding objectives and effective genetic improvement programme require knowledge of the genetic variation among reproduction traits and accurate estimates of heritability and genetic correlations of reproduction traits. Low estimates of heritability for reproduction traits indicated that these traits have low additive genetic variance and mostly influenced by environment. So, these traits can be improved by better managemental practices. Thus, identifying the source of variation and minimizing their effect is necessary for better reproductive health of Munjal sheep.

Acknowledgement

The authors are indebted to the Vice Chancellor, Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar, Haryana for providing the infrastructure facilities that enabled the successful completion of the project.

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