Genomic Analysis of Purebred and Crossbred Angus Cows Quantifies Heterozygosity, Breed, and Additive Effects on Components of Reproduction.

Wayne S Pitchford,Michelle L Hebart,Jena G Alexopoulos,Judith M Pitchford

doi:10.3390/ani12010061

Wayne S Pitchford, Michelle L Hebart + Show 2 more

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https://doi.org/10.3390/ani12010061

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Abstract

Simple SummaryThis study reports a genomic analysis of purebred Angus and Hereford × Angus maternal productivity, which is a key driver of sustainable systems. Heterozygosity effects quantify hybrid vigour or heterosis and were significant for growth and puberty. Breed differences were mostly due to heterosis, but there was an advantage of Hereford genes for reproductive performance. Days to calving was the most important Estimated Breeding Value (EBV) as a predictor of attainment of puberty and subsequent reproductive performance. Genomics offers a cheaper and faster strategy for the development of multi-breed EBVs in commercial herds.Multiple studies have quantified the production differences of Hereford Angus crossbreds compared to purebred Angus for a range of traits including growth, carcass, and reproductive traits. This study aims to quantify breed and heterosis effects on maternal performance using genomics. Thirty Hereford and thirty Angus sires were mated to 1100 Angus heifers and cows in a large commercial herd run on pasture at Musselroe Bay, Tasmania, Australia. Approximately 1650 calves were born. Heifers were weaned, scanned for attainment of puberty prior to joining at approximately 15 months of age, joined, and then recorded for status of pregnancy, calving, lactating, 2nd pregnancy, and weaning of second calf. Heterozygosity effects were significant for heifer pre-joining weight and height as well as proportion pubertal. Breed differences were significant for the same traits plus pregnancy rate at second joining and proportion rearing two calves. Genetic parameters were reported for 13 traits. On average, higher genetic merit (Estimated Breeding Value, EBV percentile) Hereford bulls were used than Angus for growth and puberty, but they were similar for fat and reproduction. Days to calving BREEDPLAN EBVs of the sires were related to puberty and reproduction. Scrotal size BREEDPLAN EBVs of the sires were related to attainment of puberty genomic EBVs calculated. In summary, breed differences in growth and puberty were due to heterosis, but there was an advantage of Hereford genes for reproductive performance. Ongoing emphasis on selection for reduced days to calving and estimation of multi-breed EBVs is important.

Highlights

Breeder herd or maternal productivity is important for the sustainability of beef cattle industries worldwide because of the large proportion of feed across the production system required for cow maintenance
Maternal productivity is key driver of sustainability due to the large feed requirement for the maintenance of breeder herds and the importance of weaning rate during periods of herd rebuilding after liquidation during drought. This project has quantified the differences in components of maternal productivity when using Hereford compared with Angus sires in an Angus cow herd
Using genomics allowed the separation of heterosis and additive genetic effects, enabling quantification of the effect of current BREEDPLAN EBVs on maternal traits

Summary

Introduction

Breeder herd or maternal productivity is important for the sustainability of beef cattle industries worldwide because of the large proportion of feed across the production system required for cow maintenance. In Australia, a large trial was conducted following concerns from beef cattle breeders that significant genetic improvement in feedlot and abattoir performance of cattle could have led to a decline in maternal productivity, especially manifest as low reproductive rates during poor pasture growth seasons. At second joining (maiden lactation), while the Low-Fat line had slightly lower pregnancy rates and were leaner, the differences from High-Fat were small [6]. There were negligible differences between lines in reproductive performance of mature cows [7], but Low-Fat cows continued to be leaner than High-Fat cows and were always those that triggered the initiation of supplementary feeding [8]. Economic modelling of a self-replacing herd concluded the reverse for gross margin [9]

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