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Genetic and Genomic Characterization of Composite Beef Breeds with an Insight into the Canadian ‘Hays Converter’
- Author / Creator
- Khorshidi, Razie
Crossbreeding is a widely used strategy in animal breeding to benefit from complementarity and heterosis. Composite breeds are one of the products of crossbreeding in which animals maintain a stabilized combination of genetic characteristics of two or more pure breeds. Hays Converter (HC), the first registered Canadian beef breed, developed by Harry Hays in the late 1950’s is defined as a composite of beef and dairy breeds. The breed is well adapted to the Western Canadian climate, calves reach market weight early, convert feed to gain efficiently, and possess qualified carcass.
My first study investigated key concepts in developing composite cattle using simulation to look at improvement of indigenous Afrikaner cattle by crossing with exotic terminal sires like Charolais. The composite dams were fitter producing 7.8% more calves and their progeny performance was improved by reducing feed intake (−24.4%) and increasing meat production (+11.7%).
Subsequent studies focused on the genetic characterization of the Hays Converter. First I estimated genetic parameters and trends in birth, weaning and yearling weights of HC through comparison of different multiple trait models (MTM) with a random regression model (RRM) and use of contemporary groups (CG). The results indicated similar changes along the growth trajectory for estimates of variance components, heritability and genetic correlations from the two approaches and fixed CG were preferred. Although there was a considerable reduction in genetic trends from 2004 to 2008 due to weak sire selection, trends generally increased through 2016.
HC is a mixture of primarily Hereford (HER), Holstein (HOL) and Brown Swiss (BSW) with a later introgression of Angus (AN). Therefore, the third study was conducted to estimate the genomic breed composition of HC based on the entirety of its genome and chromosomal segments of equal intervals. Overall, HC genomic composition was predicted as approximately 8% AN, 51% HER, 15% BSW and 26% HOL. Diversity of breed proportions in chromosomal segments relative to whole genome was used to imply signatures of selection from HC founders.
HC was developed to capture benefits from fertility and carcass traits (HER), milk production and growth potential (HOL) and strong feet and udders (BSW). AN was used to control calving difficulty in first calf heifers and it was not a foundation breed. The fourth study explored indicators of selection across the genome using Fst and runs of homozygosity (ROH). Twenty eight chromosomal segments showing over-representation of ancestral breeds relative to the entire genome were identified using Grubbs’ test. Only three were detected to be under positive trend for ROH length from 1973 to 2015. Several regions of HOL, BSW or AN origin were found in these chromosomal segments through Fst ranking. These overlapped with QTLs associated with traits of body weight and milk production. However, the effects of such trends may not be meaningful as for the remaining 25 chromosomal segments, they still showed a lower Fst with HER. The use of Fst, ROH, the analysis of breed proportions and the AnimalQTL database help to interpret signatures of selection of breeds contributing to composite animals.
- Subjects / Keywords
- Graduation date
- Fall 2022
- Type of Item
- Doctor of Philosophy
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