Bharat Merino Sheep Research Articles

(CO)Variance components and genetic parameters of pre- weaning growth traits and Kleiber ratio in Bharat Merino sheep

(CO)Variance components and genetic parameters of pre- weaning growth traits and Kleiber ratio in Bharat Merino sheep

Genetic Variability of Bharat Merino Sheep Derived from Pedigree Information

Background: The genetic variability in a population is the raw material for selection, because the estimation of genetic parameters depends on the variability present within the population. The pedigree analysis is a method to assess population genetic variability. An increase in the level of inbreeding disturbs the production performance of the animals. Hence, it is essential to assess the effect of inbreeding on production performance of the animals at regular intervals. The present study was conducted on data of Bharat Merino (BM) sheep with twin objectives of evaluating the population structure by pedigree analysis and possible effect of inbreeding on lamb growth and heritability estimates. Methods: The study was conducted on data consisting of a total of 9688 pedigree records of BM sheep born from 1975 to 2018 (43 years), out of which 9050 formed population reference (with both the parents known). ENDOG ver 4.8 program was used to generate different measures of genetic diversity. General Linear Model of SPSS 25.0 was used to ascertain the effect of inbreeding (Fi) or change in inbreeding (ÄFi) on the lamb live weights. Using animal model with software WOMBAT, single trait linear mixed model analyses were performed. The heritability estimates and breeding values were obtained by including or excluding the inbreeding coefficient in the model to observe how the estimates of heritability varied with inclusion or exclusion of the inbreeding coefficient. Result: Effective number of founders (fe) was 56, constituting 11.39% founders in the population reference, while the effective number of ancestors (fa) was 43.The genetic contribution of the 15 most influent ancestors explained 50% of the genetic variability in the dataset. The ratio fe/fa, representing the effect of population bottleneck, was 1.302. The average inbreeding coefficients for the whole pedigree was 2.36%, while it was 3.84% for inbred animals. It was found that the inbreeding coefficient (Fi) increased with the addition of each generation to the pedigree. The average relatedness coefficient was 4.53% between members of the population.The effect of individual inbreeding (Fi) or the change in inbreeding (DFi) was not significant on the lamb live weights, except the effect of individual inbreeding (Fi) on three-month body weight and average daily gain (0-3month) and of change in inbreeding (DFi) on three-month body weight. From the analysis of the pedigree data of Bharat Merino sheep, it was found that the most of the measures of genetic diversity were within acceptable limits and the pedigree data was reasonably well maintained. When inbreeding was accounted for in the model, there were reductions in h2 estimates as well as the estimates of breeding values for both 3WT and ADG1 and consequently there were changes in ranking of animals for both 3WT and ADG1.

Average daily gain and kleiber ratio in Bharat merino sheep

To investigate the effect of non-genetic factors on average daily gain (ADG) and Kleiber ratio (KR) and to estimate their genetic parameters in Bharat Merino flock, a study was conducted using records of 6931 animals (from 1986 to 2015) maintained in semi-arid region at ICAR-Central Sheep and Wool Research Institute, Avikanagar (Rajasthan) and in sub-temperate region at Southern Regional Research Centre, Mannavanur (Tamil Nadu). The overall least squares means of ADG from 0–3M (ADG1), 3–6M (ADG2) and 6–12M (ADG3) were 158.19±0.53, 68.91±0.55 and 40.95±0.44 g, respectively. Kleiber ratios from 0–3M (3WTKR) and 3–6 months (6WTKR) were 17.97±0.02 and 6.19±0.04, respectively. Location, year, season and sex of birth had significant effect (P<0.01) on all the traits. The effect of ewe's weight was significant (P<0.01) on ADG1, 3WTKR and 6WTKR. The heritability estimates for ADGs and corresponding KRs ranged from 0.14 to 0.18. The estimates of genetic and phenotypic correlations among the traits ranged between-0.28 (ADG2 and ADG3) to 0.96 (ADG2 and 6WTKR) and-0.31 (ADG1 and 6WTKR) to 0.95 (ADG2 and 6WTKR) respectively. Selection for any of the studied traits of Bharat, Merino sheep would be expected to have a large effect on the other growth traits as a result of their moderately positive genetic correlations.

Population structure and effect of inbreeding on lamb growth in a closed flock of bharat merino sheep

Population structure and effect of inbreeding on lamb growth in a closed flock of bharat merino sheep

Decline in Additive Genetic Variance for Live Weight and Greasy Fleece Weight in Bharat Merino Sheep

Impact of selection and other environmental determinants on the additive genetic variance was studied for traits under selection, viz. live weight at 6 month (6WT) and first greasy fleece weight (GFW). Data on 3067 Bharat Merino sheep for 19 years (1988–2006) were divided in four periods P1 (1988–1992), P2 (1993–1997), P3 (1998–2002) and P4 (2003–2006). Estimates for inbreeding ranged from 2.32 to 3.12 % in four periods. Least squares means for 6WT in four periods were 25.53, 23.79, 20.77 and 21.92 kg, respectively; corresponding estimates for GFW were 1.008, 0.843, 0.659 and 0.673 kg. Heritability estimate (h2 ± SE) for 6WT was 0.135 ± 0.077, 0.148 ± 0.059, 0.063 ± 0.051 and 0.020 ± 0.065 for the periods P1, P2, P3 and P4, respectively. Corresponding estimates for GFW were 0.192 ± 0.086, 0.135 ± 0.058, 0.275 ± 0.081 and 0.055 ± 0.068. The estimates of breeding value (BV ± SE) for 6WT in four periods were 22.29 ± 0.01, 22.36 ± 0.01, 22.45 ± 0.01 and 22.51 ± 0.00, whereas corresponding figures for GFW were 0.798 ± 0.002, 0.813 ± 0.002, 0.837 ± 0.002 and 0.839 ± 0.002. Phenotypic trend over 19 years revealed sudden drop in the phenotypic expression of traits. Positive genetic trend for 6WT and GFW was observed; however, the magnitude of the trend was small. Bharat Merino being a synthetic strain had limited variation that declined due to selection.

Influence of genetic and non genetic factors on growth traits of Bharat Merino sheep in sub-temperate climate of Kodai hills of Tamil Nadu, India

In the present study, the data on 1649 Bharat Merino (BM) lambs; progeny of 144 sires over the year from 2000 to 2014 available at Southern Regional Research Centre (SRRC), Central Sheep and Wool Research Institute, Mannavanur were considered for the analysis. The different economic growth traits used for the analysis were birth weight (BWT), weaning weight (3MWT), 6 month weight (6MWT), 12 month weight (12MWT) and greasy fleece yield (GFY). The overall least-square means for weights (in kg) were 3.28±0.02, 19.08±0.23, 25.00±0.35, 34.79±0.59 and 2.13±0.07 for BWT, 3MWT, 6MWT, 12MWT and GFY respectively. Different non genetic factors such as year, sex, type of birth and dam's age had significant (P&lt;0.01) influence on BWT and 3MWT. Season influenced the BWT (P&lt;0.05) while it had no significant effect on 3MWT. Six month weight was also significantly (P&lt;0.05) influenced by all non-genetic factors taken under present study. Twelve month weight was significantly affected by year (P&lt;0.01), sex and season (P&lt;0.05). Similarly, analysis of variance showed that the year, sex of the lambs (P&lt;0.01) and season (P&lt;0.05) were important sources of variation on GFY of Bharat Merino sheep. Lambs born single had higher values of BWT and 3MWT than that of the lambs born as twins. The trend of the increase in BWT and 3MWT of the lambs is being observed up to the period when the age of their corresponding dams is 4-5 years. The findings of the present study showed that non - genetic factors play an important role in the expression of genetic potential in the lambs as well as growth performance of Bharat Merino sheep under sub temperate conditions of Kodai hills of Tamil Nadu, India. The genetic parameters estimated of 6MWT indicate that it is most suitable for use as selection criterion. Improvement of body weight of BM sheep seems feasible in selection programs, as some of the related traits are moderately heritable and those traits specially are well correlated, which could suggest that these traits are useful in selection programs.

Genetic trend for growth and wool performance in a closed flock of Bharat Merino sheep at sub temperate region of Kodai hills, Tamil Nadu.

Aim:The study was conducted at Southern Regional Research Center, ICAR-Central Sheep and Wool Research Institute (CSWRI), Mannavanur, Kodaikanal, Tamil Nadu to estimate genetic trends for birth weight (BWT), weaning weight (3WT), 6 months weight (6WT), and greasy fleece weight (GFY) in a Bharat Merino (BM) flock, where selection was practiced for 6WT and GFY.Materials and Methods:The data for this study represents a total of 1652 BM lambs; progeny of 144 sires spread over 15 years starting from 2000 to 2014, obtained from the BM flock of ICAR-SRRC (CSWRI), Mannavanur, Kodaikanal, Tamil Nadu, India. The genetic trends were calculated by regression of average predicted breeding values using software WOMBAT for the traits BWT, 3WT, 6WT and GFY versus the animal’s birth year.Results:The least square means were 3.28±0.02 kg, 19.08±0.23 kg, 25.00±0.35 kg and 2.13±0.07 kg for BWT, 3WT, 6WT and GFY, respectively. Genetic trends were positive and highly significant (p<0.01) for BWT, while the values for 3WT, 6WT and GFY though positive, were not significant. The estimates of genetic trends in BWT, 3WT, 6WT and GFY were 5 g, 0.8 g, 7 g and 0.3 g/year gain and the fit of the regression shows 55%, 22%, 42% and 12% coefficient of determination with the regressed value, respectively. In this study, estimated mean predicted breeding value (kg) in BWT and 3WT, 6WT and GFY were 0.067, 0.008, 0.036 and −0.003, respectively.Conclusion:Estimates of genetic trends indicated that there was a positive genetic improvement in all studied traits and selection would be effective for the improvement of body weight traits and GFY of BM sheep.

Effect of time and depth of insemination on fertility of Bharat Merino sheep inseminated trans-cervical with frozen-thawed semen.

BackgroundArtificial insemination (AI) can serve as a powerful tool to the sheep owners for making rapid genetic progress of their flock. The AI in sheep is mostly performed using fresh semen with two reasons i) lambing rate following trans-cervical AI with frozen semen is limited by the inability of frozen-thawed sperm to transit the cervix and ii) the need of circumventing the cervical barrier through laparoscope aided intrauterine AI. Therefore, AI with frozen-thawed semen is not as widespread in sheep as it is in other domestic species. However, to get maximum benefits through the use of AI, frozen-thawed semen is a prerequisite because instead of high fertility, the short shelf life of fresh semen coupled with a limitation on the number of insemination doses achievable per unit time restricts the widespread use of individual sires. Therefore, in order to enhance lambing rate, a total of 240 trans-cervical artificial inseminations with frozen-thawed semen were performed in Bharat Merino ewes during autumn season either once in the evening (G-I, 10 h after onset of estrus, n = 100) or twice (G-II, 14 h and 22 h after onset of estrus, n = 140) i.e. once in the morning and again in the evening.ResultsThe pregnancy rate (proportion of pregnant ewes confirmed by ultrasonography at day 40) and lambing rate (proportion of ewes lambed) were higher in G-II as compared to G-I (26.4 vs 20% and 19.3 vs 10%, respectively). The difference in lambing rates was statistically (P < 0.05) significant. The depth of insemination within cervico-uterine tract had no significant effect on pregnancy and lambing rates.ConclusionsThe results indicate that lambing rate in sheep following TCAI with frozen-thawed semen was significantly influenced by time of inseminations. Two inseminations after 14 and 22 h of onset of estrus enhanced the lambing rates of Bharat Merino sheep as compare to single insemination after 10 h of onset of estrus. The TCAI technique with frozen-thawed ram semen is promising and may serve as a valuable tool for genetic improvement of sheep breeds. Research efforts are going on worldwide to overcome the poor fertility following TCAI with frozen-thawed semen.

Population structure and effect of inbreeding on lamb growth in Bharat Merino sheep

The objective of present study was to evaluate the population structure and genetic variability in the Bharat Merino, a synthetic sheep evolved and maintained under standard farm management conditions and also to observe any possible effect of inbreeding on lamb growth and heritability estimate. The pedigree of 5723 animals born between 1975 and 2006 was available, out of which 5115 were in the population reference for which estimates were obtained. Effective number of founders (fe) was 55, representing 12.79% of the potential number of founders in population reference. The effective number of ancestors (fa) was 40 and the genetic contribution of the 14 most influent ancestors explained 50% of the genetic variability. The realized effective population size of the flock was 89.29±2.13. The ratio fe/fa which expresses the effect of population bottlenecks was 1.375. The average inbreeding coefficient for the whole analyzed pedigree and for inbred animals was 2.32% and 4.8%, respectively. The average relatedness coefficient between individuals of the population was estimated to be 4.23%. The inbreeding coefficient increased with the addition of each generation to the pedigree. In the reference population, 6.69% individuals had more than 6.25% Fi. Although the levels of inbreeding in the flock were under control, looking in to the closed structure of the flock, accumulation of higher inbreeding in some individuals was inevitable. Study revealed non-significant effect of individual inbreeding or change in inbreeding on the lamb live weights, except birth weight where every one percent increase in inbreeding (Fi) was found to negatively affect the birth weight in lambs by 0.019kg. Estimate of heritability for birth weight was little higher (0.27±0.03) when inbreeding was included in the model as compared to little lower estimate (0.26±0.03) where inbreeding was excluded.

Scope of Indirect Selection for Wool Traits in Bharat Merino Sheep in Semi Arid Region of Rajasthan

Gowane, G.R., Chopra, A., Prince, L.L.L. and Arora, A.L. 2010. Scope of indirect selection for wool traits in Bharat Merino sheep in semi arid region of Rajasthan. J. Appl. Anim. Res., 37: 97–100. Estimates of covariance components along with genetic, phenotypic and environmental correlation were obtained for different wool traits, viz. greasy fleece yield (GFY), staple length at six month (SL), medullation percentage (MED) and, fiber diameter (FD) in Bharat Merino Sheep developed and maintained at the Central Sheep & Wool Research Institute, Avikanagar, India. Twenty years data were analyzed by restricted maximum likelihood, (REML) fitting univariate and bivariate animal models. Additive genetic variability for all the traits was low except greasy fleece yield (h2 = 0.16). Permanent environmental variance as a proportion of phenotypic variance (c2) for GFY was 0.26. Genetic correlation between GFY and SL was 0.21, between SL and MED 0.19 and SL and FD 0.20. For further genetic improvement in this breed, MED and FD should be kept restricted at present level (MED: 18.08μ and FD: 1.25%) and emphasis should be given on GFY and SL, which are positively (favorably) associated with each other.

Estimates of (co)variance components and genetic parameters for body weights and first greasy fleece weight in Bharat Merino sheep

(Co)variance components and genetic parameters of weight at birth (BWT), weaning (3WT), 6, 9 and 12 months of age (6WT, 9WT and 12WT, respectively) and first greasy fleece weight (GFW) of Bharat Merino sheep, maintained at Central Sheep and Wool Research Institute, Avikanagar, Rajasthan, India, were estimated by restricted maximum likelihood, fitting six animal models with various combinations of direct and maternal effects. Data were collected over a period of 10 years (1998 to 2007). A log-likelihood ratio test was used to select the most appropriate univariate model for each trait, which was subsequently used in bivariate analysis. Heritability estimates for BWT, 3WT, 6WT, 9WT and 12WT and first GFW were 0.05 ± 0.03, 0.04 ± 0.02, 0.00, 0.03 ± 0.03, 0.09 ± 0.05 and 0.05 ± 0.03, respectively. There was no evidence for the maternal genetic effect on the traits under study. Maternal permanent environmental effect contributed 19% for BWT and 6% to 11% from 3WT to 9WT and 11% for first GFW. Maternal permanent environmental effect on the post-3WT was a carryover effect of maternal influences during pre-weaning age. A low rate of genetic progress seems possible in the flock through selection. Direct genetic correlations between body weight traits were positive and ranged from 0.36 between BWT and 6WT to 0.94 between 3WT and 6WT and between 6WT and 12WT. Genetic correlations of 3WT with 6WT, 9WT and 12WT were high and positive (0.94, 0.93 and 0.93, respectively), suggesting that genetic gain in post-3WT will be maintained if selection age is reduced to 3 months. The genetic correlations of GFW with live weights were 0.01, 0.16, 0.18, 0.40 and 0.32 for BWT, 3WT, 6WT, 9WT and 12WT, respectively. Correlations of permanent environmental effects of the dam across different traits were high and positive for all the traits (0.45 to 0.98).

The effect of thermal stress on superovulatory response and embryo production in Bharat Merino ewes

This experiment was conducted to observe the effect of thermal stress during estrous cycle on superovulatory response and subsequent embryo production in Bharat Merino ewes (fine wool crossbred developed for the tropical environment). Fourteen cycling, multiparous ewes were randomly allocated to two groups ( n=7/group). The animals in Group-I were maintained in a shed from 10.00 to 16.00 h while animals in Group-II were exposed to the elevated temperature for a period of 6 h (10.00–16.00 h) for 4 weeks. Animals grazed on natural pasture of Cenchrus ciliaris during the morning (7.00–10.00 h) and evening hours (16.30–19.30 h), and drinking water was offered once daily at 16.30 h. Daily meteorological observations were recorded during the trial. Superovulation was induced in all the ewes using FSH (ovagen 5.4 mg in eight injections) and PMSG (200 IU). Estrus in the ewes was synchronized with 2 doses of PGF2α (10 mg) 10 days apart. Ewes demonstrating estrus were hand mated with the aid of Bharat Merino rams. Ovarian examination and embryo/ova recovery were performed using laparoscopy on days 3–5 following mating. All the ewes exhibited estrus within 48 h after the second PGF2α injection. Ewes in Group-I exhibited estrus earlier (25.5±1.1 h) and the estrus period was longer (37.7±1.6 h) than ewes exposed to thermal stress, i.e. 30.6±1.2 and 31.7±3.6 h, respectively. No significant difference were observed for the two groups with respect to the superovulatory response and embryo/ova recovery rate. The ewes exposed to thermal stress yielded relatively poor quality embryos. The results indicate that thermal stress could adversely affected the quality of the embryos in Bharat Merino sheep during the preovulatory period.