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Genetic Evaluation Of Growth Performance Of Farmbred Nilagiri And Sandyno Sheep

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Title Genetic Evaluation Of Growth Performance Of Farmbred Nilagiri And Sandyno Sheep
 
Creator Venkataramanan, R.
 
Contributor Subramanian, A.
Sivaselvam, S.N.
Sivakumar, T.
Sreekumar, C.
 
Subject Sheep
Nilagiri
Sandyno
Growth
Genetic parameters
 
Description Nilagiri and Sandyno sheep were evaluated for growth performance. Data
on pedigree information for 48 years (1965-2012) and growth for 21 years (1992-
2012), collected from records maintained at the Sheep Breeding Research Station,
Sandynallah, The Nilgiris were utilised for the study. The different growth traits
studied were body weights at birth (BW), weaning (WW), 6-months (6W), 9-
months (9W), 12-months (YW) and 18-months (18W) of age and absolute growth
rate (AGR), relative growth rate (RGR) and Kleiber ratio (KR) estimated on a
daily basis at different age intervals from birth to 12 months.
The various traits were analysed using least-squares method for effect of
breed, contemporary groups of year-season, sex, type of birth, age of dam at
lambing and inbreeding. The inbreeding parameters calculated were Wright’s
Inbreeding coefficient and equivalent inbreeding coefficient. (Co)Variance
components were estimated through restricted maximum likelihood technique
(REML) using an Animal model. The fixed effects found to be significant from
the least-squares analyses were fitted for each trait.
The mean BW, WW, 6W, 9W, 12W and 18W for Nilagiri and Sandyno
sheep were 2.29, 9.47, 13.10, 15.99, 19.22 and 24.45 kg and 2.57, 10.24, 14.46,
17.55, 21.00 and 27.49 kg respectively. The pre- and post-weaning (3-12 m) AGR
in Nilagiri sheep were 79.76 and 36.00 g, respectively and corresponding values
in Sandyno sheep were 85.15 and 38.92 g.
The mean generation interval (GI), inbreeding coefficient (F), proportion of
population inbred, equivalent no. of generations (EqGi), equivalent inbreeding
coefficient (EF) and effective population size (Ne) for Nilagiri sheep were 3.36
years, 2.17 per cent, 100 per cent, 3.75, 2.05 per cent and 90.34 respectively. The
corresponding values for Sandyno sheep were 3.73 years, 0.83 per cent, 95 per
cent, 2.52, 0.90 per cent and 134.86 respectively. EF was found to correct for
inbreeding coefficient in the Sandyno population, in which ancestral knowledge
was comparatively less. The regression of most of the traits on F and EF were
negative. In Nilagiri sheep, significant effects of F was observed for WW (-0.048
kg), YW (-0.062 kg), pre-weaning AGR (-0.470 kg) and pre-weaning KR (-
0.029). In addition to these traits 6W (-0.031 kg), 9W (-0.046 kg) and 18W (-
0.076 g) were found to be influenced by EF. In Sandyno sheep, YW(-0.100 g) and
post-weaning AGR (3-12 m) with a regression of -0.263 g were influenced by F,
while EF had significant influence on YW (-0.098), post-weaning AGR for the
periods from 6 to 9 m (-0.420g) and 3-12 m (-0.273g). Post-weaning KR for the
same periods were also affected by EF in Sandyno sheep, with regression values
of -0.039 and -0.016 respectively.
The direct heritability for BW, WW, 6W, 9W, YW and 18W estimated from
the best model in Nilagiri sheep were 0.140, 0.130, 0.074, 0.168, 0.129 and 0.166
respectively. In Sandyno sheep, the respective values were 0.147, 0.114, 0.098,
0.141, 0.144 and 0.115. Maternal genetic influence was important up to 9W in
Nilagiri sheep. In Sandyno sheep, in addition to the other traits, 18W was also
affected.
The genetic correlations among body weight traits were positive and high,
and higher than the phenotypic correlations. Genetic correlations between most of
the body weight traits and pre-weaning AGR, RGR and KR were high and
positive. Early body weights had negative or positive, negligible genetic
correlation with post-weaning AGR and RGR. Correlated responses to selection
were higher in body weight traits, when selection was based on 9W and 6W in
Nilagiri and Sandyno sheep respectively. The direct genetic trends for BW, WW,
6W, 9W, YW and 18W were 0.000, 0.011, 0.006, 0.016, 0.011 and 0.015
respectively in Nilagiri sheep and for Sandyno sheep, the values were 0.001,
0.013, 0.011, 0.017, 0.017 and 0.022 respectively.
In general, the moderate values for heritability, positive genetic
correlations and positive genetic trends for different growth traits are indicative of
good scope for genetic improvement. The BLUP estimates of breeding value
showed an accuracy of selection almost equal to unity and could be effective in
ranking of superior animals. The individual inbreeding coefficient also must be
considered, when ranking is based on breeding values. The traits with best
correlated responses identified through this study could be explored. Especially
9W even though available at a later age, could be added as a last stage selection
criterion for better responses in other economically important body weights. In
Sandyno, 6W could be continued as an effective means to bring about overall
improvement in growth.
 
Date 2016-05-23T17:04:55Z
2016-05-23T17:04:55Z
2013
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/66238
 
Language en
 
Format application/pdf
 
Publisher Tamil Nadu Veterinary and Animal Sciences University