Genetic Analysis of Fitness Traits of Kashmir Merino Sheep at Organized Farms of Kashmir

Sheep are reared in Jammu and Kashmir from the time immemorial by mankind owing to its multifaceted utility. The region (J&K) possesses rich repository of ovine genetic resources. However, the production potential of native sheep breeds of J&K was poor. Therefore, crossbreeding was adopted to improve the performance of native nondescript sheep population by using Kashmir Merino (a synthetic breed) to improve the production potential of native sheep breeds of Kashmir. Many sheep breeding farm were established in J&K by state Government for production of improved and superior quality Kashmir Merino breeding rams. These high-quality breeding rams, produced at government sheep breeding farms were distributed among progressive farmers for up gradations of nondescript sheep population. The breeding policy so adopted resulted in increased production of quality wool per animal, increased growth rate and profitability of sheep farmers. The contribution off springs to the next generation by an individual is called its fitness. Fitness or life-history traits include measures of reproductive efficiency and survivability of an individual. Improvement in reproductive efficiency has significant impact on sheep husbandry. However, the reproduction traits are not considered while selecting an animal (Gowane et al., 2014). The possible reason for not including reproduction traits in selection programs include large environmental influences, low heritability, late expression, non-availability of reliable data and these traits are usually threshold in expression. The components of fitness traits of sheep breed decide its performance and adaptability to particular environmental conditions. Although the genetic studies on the breed in past have been carried by researchers (Das et al., 2014; Rather et al., 2019a; b; c; Rather et al., 2020a; b; c; Rather et al., 2021a; b) but information regarding fitness traits of Kashmir Merino sheep is scanty. Hence the present study was undertaken with objectives to estimate number of lambs born per ewe (NLBE), number of lambs weaned per ewe (NLWE), litter size (LS) and sex ratio (SR) of Kashmir Merino sheep.
 

Data recording
 
The data spanning over 21 years pertaining to Kashmir Merino sheep maintained at Government Sheep Breeding Farm Kralpathri and Goabal were collected from flock books. For estimation of number lambs born per ewe (NLBE) and number of lambs weaned per ewe (NLWE) data spraining over 13 years (1997 to 2009) were classified in 4 periods as reflected in Table 1, whereas for estimation of litter size and sex ratio the data were classified into 7 periods each period consisting of 3 years. However, for estimation of the latter 2 traits the data were also classified as pleuriparous and primiparous (based on parity), single and multiple born (based on birth type) and Kralpathri and Goabal (based on place of birth of lamb). Sex ratio (male to female) was calculated as the ratio of number of males versus females born. The analysis was carried out by using mixed model least-squares maximum likelihood (LSMLMW) computer (PC-2) programme designed by Harvey (1990). The mathematical model used for estimation of number of lambs born per ewe and number of lambs weaned per ewe was
   
Where:
Y_ijk = Observation of kth lamb, born in jth period to ith sire.
µ = Overall mean.
R_i = Random effect of ith sire.
P_J = Fixed effect of jth period of birth.
e_ijkl = Random error, N (0, σ²_e).
 
For estimation of litter size and sex ratio following mathematical model used for
   
Where:
Y_ijklmn = Observation of nth lamb, born in mth birth type to dam in lth parity, inkth period, present in jth farm of birth and born to ith sire.
µ = Overall mean.
R_i = Random effect of ith sire.
F_k = Fixed effect of kth farmof birth.
Y_l =  Fixed effect of lth period of birth.
P_m = Fixed effect of mth parity of dam.
T_n = Fixed effect of nth type of birth.
e_ijklmn = Random error, N (0, σ²_e ).
 
Heritability estimates for different traits were obtained from sire component of variances using paternal half-sib correlation method (Becker, 1975). The sires with three or more than three progeny were included for the estimation of heritability. The model used to estimate the heritability was:
   
Where: 
Y_ij = Observation of the jth progeny of the ith sire.
µ = Overall mean.
s_i = Effect of the ith sire, NID (0, σ²_s).
e_ij = Random error NID (0, σ²_e).

The least square means along with non-genetic factors affecting number of lambs born per ewe (NLBE) and number of lambs weaned per ewe (NLWE) are presented in Table 1. The overall means for NLBE, NLWE were 3.56±0.11 and 3.20±0.10, respectively. The effect of sire was significant (P<0.05) on NLWE, LS and SR whereas effect of all the non-genetic factors included was non-significant on all the traits under study. Contradictory to the results the present study higher estimates of 3.85±0.05 and 3.37±0.05 for NLBE and NLWE, respectively in Malpura sheep were observed by Gowane et al (2014). Overall number of 4.80 ± 0.11 lambs per ewe in life time was reported by Nabi et al., (2020) in Corriedale sheep. The traits were statistically significantly influenced by the period of birth and sire. Significant effect of period of birth on NLBE and NLWE in Malpora sheep and on NLBE in Corriedale sheep was observed by Gowane et al. (2014)  and Nabi et al., (2020), respectively. Vatankhah et al., (2018) in Lori Bakhtiari breed of sheep also reported significant effect of period of birth on TNLB. However, Babar and Javed (2009) in Rambouillet sheep observed a non-significant effect of period of birth on NLBE. Both the traits presented constant decreasing trend from first to last period in Kashmir Merino sheep in the present study. The constant decreasing trend may be attributed to increase rate of culling of ewes at younger age forced by increased sero-prevalence of Brucellosis at the farm. TLBE per ewe ranged from 1 to 11whereas TLWE ranged from 0-9. More or less similar findings were reported in Malpora sheep by Gowane et al (2014).
       
The least square means along with non-genetic factors affecting litter size (LS) and sex ratio (SR) are presented in Table 2. The overall means for LS and SR were 48.32±0.04 and 1.06±0.01, respectively. More or less similar average litter size of 1.04 in Malpura sheep at birth and 1.07±0.01 in Corriedale sheep was observed by Gowane et al. (2014) and Nabi et al., (2020), respectively. Nabi et al., (2020) reported average litter size of 1.07±0.01 and sex ratio of 80.90±1.92 in Corriedale sheep. Kumar et al., (2001) in Marwari goats reported LS and SR of 54.7% and 1.15, respectively. Tomar et al., (1995 and) Kumar et al., (2001) in Marwari goats also reported similar values. However, higher estimates of 1.08±0.03 and 1.40±0.04 for LS in Kashmir Merino and Fec-B gene Introgressed Kashmir Merino sheep was found by Rather et al., (2019). Gavojdian et al., (2015) reported LS of 1.40±0.05, 1.21±0.08 and 1.45±0.03 in Dorper sheep, White Dorper sheep and Tsigai sheep, respectively. The effect of all the non-genetic factors was non-significant on SR and LS. Contradictory to the results of present study Nabi et al., (2020) in Corriedale sheep and Rather et al., (2019) in Kashmir Merino reported significant effect of period of birth on LS. As we the sex is determined at the union of gamete and it is irrelevant that any factor actually affects the sex of the lamb. Kumar et al (2021) reported SR of 50.43±0.28 in Malpura and 51.05±0.32 in Avikalin sheep. Kumar et al (2021) also reported non-significant effect of birth type, parity and period of birth on SR. The variation among periods may be caused sampling variances in lambs born to a particular sex. Lowest SR was observed in first period 1997-2000 and highest SR was observed in third period (2004-2006) 55.49±0.06.


       
The genetic parameters the fitness traits are presented in Table 3. The heritability estimates were low for all the traits under study. The low estimate of h2 indicated the presence of lower additive genetic variance as the traits were largely influenced by environmental factors. Low heritability estimates for NLB and NLW were also observed by Gowane et al., (2014) in Malpura sheep. However, Nabi et al., (2020) In Corriedale sheep reported moderate h2 of 0.40±0.04 for LS and 0.29±0.07 for TLBE. Kumar et al., (2021) found h² of 0.019±0.003 and 0.04±0.01 in Avikalin and Malpura, respectively. Low heritability estimates of 0.032 for SR were also observed by Mohan (2016) in Malpura sheep. Positive and very high genetic and phenotypic correlations between NLBE and NLWE were observed in the present study.

Constant decrease in number of lambs born and number of lambs weaned per ewe indicated that the overall reproductive has decrease over the years. Similarly, low heritability estimates for the traits indicated role of management in improving all the traits except SR over which breeders have minimum control as sex of lamb is fixed at zygote formation.