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ThesisItem Open Access GENETIC STUDIES ON THE PERFORMANCE OF HD-K75 PIGS(College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati, 2022-02) BAYAN, JYOTISHREE; Zaman, Galib UzPig farming in India is primarily a small scale unorganized rural activity and is an integral part of diversified agriculture particularly in the tribal belt of the country and have been contributing to improve the livelihood of poor and socially weaker section of the society including the tribal people of India. Pig farming in Assam is rapidly gaining momentum in recent years as the farmers are finding it a profitable enterprise. The present investigation was carried out on HD-K75 pigs (75% Hampshire inheritance and 25 % indigenous inheritance) that are bred and maintained in the All India Coordinated Research Project (AICRP) on pigs, ICAR, located at College of Veterinary Science, Assam Agricultural University, Khanapara, Guwahati-781022. The data were collected and compiled from the progenies of 44 sires and 114 dams maintained over a period of 6 years from 2012 to 2018. The objective of the investigation were to study some important traits of growth and reproduction and the effect of various non-genetic factors influencing these traits, determine heritability, genetic correlation and phenotypic correlation of some important growth and reproduction traits, to construct linear, partial and multiple regression equations and to predict adult body weights based on early body weights. Traits included in the study were body weights at birth, weaning, 1st, 2nd, 3rd, 4th, 6thand 8th months of ages, and daily body weight gains during pre-weaning (birth to weaning) and post-weaning periods (from weaning to 4th, 6th and 8th month of ages), age at sexual maturity, gestation period, farrowing interval, litter size at birth, litter weight at birth, litter size at weaning and litter weight at weaning. The overall mean body weight in HD-K75 pigs at birth, 1 month, weaning, 2 months, 3 months, 4 months, 6 months and 8 months of age were 1.001 ± 0.001 kg, 6.912 ± 0.011 kg, 9.666 ± 0.013 kg, 12.207 ± 0.007 kg, 18.324 ± 0.001 kg, 28.349 ± 0.052 kg, 51.177 ± 0.091 kg and 71.229 ± 0.110 kg respectively. The average daily body weight gains (ADG) in g during birth to weaning, weaning to 4th month, weaning to 6th month and weaning to 8th month of ages were 206.299 ± 0.311, 237.294 ± 0.773, 299541 ± 0.700 and 311.206 ± 0.557 respectively. Least-squares analysis of variance revealed highly significant effect of season of birth, parity and sex on body weight at all ages and daily body weight gains at various stages of growth. Piglets born during winter season had higher body weight at birth, 1 month, 42 days, whereas piglets born during post-monsoon season had higher body weight at 2 months, 3 months, 4 months and 6 months of age and piglets born during monsoon season had higher body weight at 8 months of age. Pre-weaning ADG was higher in piglets born during monsoon season and lowest in animals born during pre-monsoon season. The ADG during 42 days to 4th month and 42 days to 6th month were found to be higher in piglets born during post-monsoon season and lowest in piglets born during pre-monsoon season. Piglets born in second parity had higher body weight at 3 months, 4 months, 6 months and 8 months whereas piglets born in third parity had higher body weight at birth and 1 month and piglets born in first parity had higher body weight at weaning and 2 months of age. Significantly higher ADG was found during pre-weaning period of growth in animals born in first parity. Further, the ADG from 42 days to 4th month, 42 days to 6th month and 42 days to 8th months of age were found to be higher in animals born in second parity and revealed significant difference with the animals of first and third parities. Males showed higher body weight and higher ADG than females in all stages of growth. ii The h2 estimates for body weight and ADG at various stages of growth in the present study were moderate to high in most of the cases which indicated that the population under study possess good amount of additive genetic variance and there is scope of genetic improvement of the herd in terms of growth traits and ADG at various stages using adequate methods of selection by incorporating these estimates. The phenotypic correlations among body weights at various ages were moderate and positive in some cases and negative in some cases. The phenotypic correlations among ADG at various stages of growth were moderate and positive in some cases and negative in some cases. The genetic correlations among body weights at various ages of growth were low to high and positive in some cases and negative in some cases. The genetic correlations among ADG at various stages of growth were moderate and positive in some cases and negative in some cases. The overall means for age at sexual maturity, gestation length and farrowing interval were found to be 205.294 ± 1.054, 112.70 ± 0.119 and 216.781 ± 2.565 days respectively. Effect of season of birth on age at sexual maturity was found to be non-significant as indicated by least square analysis of variance. Non-significant effect of season of birth and parity on gestation period was observed in the present study in HD-K75 pigs. Least-squares analysis of variance revealed significant difference between the various seasons under study in respect of farrowing interval. Sows that farrowed during post-monsoon season had significantly longer farrowing interval and differed significantly with other seasons and the shortest farrowing interval was observed in sows that farrowed during monsoon season. Least square analysis of variance revealed that the effect of parity on farrowing interval in the present study was non-significant. The h2 estimates of age at sexual maturity, gestation length and farrowing interval for HD-K75 pigs was low to moderate in magnitude. The phenotypic correlation among the reproduction traits were found to be low and positive in most cases. The genetic correlation among the reproduction traits were found to be moderate and positive in most cases. The overall means for litter size at birth, litter size at weaning, litter weight at birth and litter weight at weaning were found to be 7.747 ± 0.088, 7.556 ± 0.093 numbers and 7.804 ± 0.084 and 74.644 ± 0.0886 kg respectively. Least-squares analysis of variance revealed significant effect of season of birth on litter size at birth, litter size at weaning, litter weight at birth and litter weight at weaning. Piglets born during pre-monsoon season showed highest litter size at birth and weaning. Piglets born during post-monsoon season and winter season showed highest litter weight at birth and litter weight at weaning. Further, litter size at birth, litter size at weaning, litter weight at birth and litter weight at weaning were found lowest during monsoon season. Least-squares analysis of variance revealed that parity had significant effect on litter size at birth, litter size at weaning, litter weight at birth and litter weight at weaning. Piglets born in third parity showed highest and piglets born in first parity showed lowest litter size at birth, litter size at weaning, litter weight at birth and litter weight at weaning respectively. The h2 estimates of litter size at birth and litter size at weaning in HD-K75 pigs in the present study were found to be low in magnitude. The h2 estimates of litter weight at birth and litter weight at weaning were found to be medium in magnitude. The phenotypic correlations among the litter traits were found to be high and positive in most cases. The genetic correlations among the litter traits were found to be moderate to high and positive in most cases. Prediction equations were developed using post-weaning body weights at 6 months (Y1) and 8 months (Y2) of ages as dependent variables based on pre-weaning body weights at birth (X1), 1 month (X2), 42 days (X3), 2 months (X4) and 3 months (X5) of age as independent variables in various combinations. For prediction of adult body weights on the basis of body weights at early ages in HD-K75 pigs, linear, partial and multiple regression equations were developed. The linear regression equations for predicting body weights at 6 months of age had comparatively higher R2 values than 8 months of age in HD-K75 pigs, but were not found to be reliable as the R2 values were less than 60 %. The partial regression equations for predicting body weights at 8 months of age had comparatively higher R2 values than 6 months of age and were found to be more reliable. All the multiple regression equations developed to predict the adult body weight at 8 months of age can be reliably used when 3-5 independent variables are considered. Multiple regression equations developed to predict 8 month body weight showed highest reliability with R2 values ranging from 70.87 to 90.56 %. High R2 values indicates that the 8 month body weight can be predicted more efficiently than 6 month body weight. The multiple regression equations for predicting body weight at 8 months using 3 independent variables viz. body weight at birth, 1 month and weaning showed high R2 value of 90.21 % which was found to be highly reliable and the best combination, though higher R2 values were obtained in multiple regression equations using 4 and 5 independent variables.
