Characterising the Influence of Genetics on Breast Muscle Myopathies in Broiler Chickens

Abstract

This report provides the first estimates of the genetic basis of all key breast muscle myopathies (BMM) in broiler chickens [Deep pectoral myopathy, wooden breast, white striping and spaghetti breast] and their relationship with body weight and breast yield. Data from a pure bred high yielding commercial broiler line were analysed to estimate the genetic parameters using a multivariate animal model with the appropriate fixed effects and permanent environmental effect of the dam. Heritabilities of the BMM ranged from 0.04 to 0.25 and the genetic correlation of the BMM with body weight and breast yield ranged from -0.06 to 0.41. Here we highlight that the genetic variance of BMM accounts for a low proportion of the phenotypic variance and the BMM have a low genetic relationship with performance traits. The large contribution of residual variance to the phenotypic variance for the BBM was >71.5% which indicates the importance of the non-genetic effects on BMM. The data presented also show that the moderate to low genetic influence for the development of BMM can be used, through balanced selection, to reduce the myopathy incidence in the long term. The impact of genetic selection against BMM was tested empirically by comparing the incidence of WB and % breast yield of a commercial broiler with a high generation (HG) broiler. The HG broiler used represents 2 years of genetic improvement compared to the commercial broiler; the HG broiler had an 18.4% relative decrease in WB and a 1.02% relative increase in breast yield compared to the commercial broiler. This paper describes the relationship between the genetic and non-genetic factors influencing BMM highlighting the importance of understanding the non-genetic effects on myopathy incidence. It also shows that the genetic component of BMM can be reduced whilst at the same time improving breast yield as part of balanced breeding goals.

Keywords: breast muscle; breeding; broiler; genetics; heritability; meat quality; myopathy.

FIGURE 1

Breast fillets showing the novel myopathies white striping (WS; left), wooden breast (WB; middle), and spaghetti breast (SB; right).

FIGURE 2

This venn diagram demonstrates the incidence of the myopathies in 995 myopathy affected fillets. It can be seen that the myopathies can occur individually or be comorbid with each other.

FIGURE 3

The commercial broiler is a four way cross of pure broiler lines (represented by A, B, C, and D) as demonstrated in this image. The movement of genetic material from the pedigree pure lines to the commercial broiler population takes around 4 years through great grandparent, grandparent, and parent multiplier flocks, i.e. the impact of any genetic selection made in 2020 will reach the broiler population in 2024.

FIGURE 4

In study 2 a high generation broiler was produced by using great grandparents as parent stock by crossing pedigree pure lines (right dashed box). The high generation broiler can then be compared to the current commercial broiler (left dashed box) to see the impact of genetic selection for a trait of interest such as wooden breast. The generational difference between the two broiler groups represents 2 years of genetic progress.

FIGURE 5

Relative results for wooden breast incidence (scores 1, 2 and 3) and breast yield of the high generation broiler compared to the current commercial broiler in study 2. Mean WB incidence and BY values are also given for all groups. An overall decrease in total wooden breast incidence can be seen as a result of genetic selection whilst simultaneously improvements in breast yield can be achieved.

FIGURE 6

The long term relationship between breast yield (%) and wooden breast (%) for the years 2011 to 2019 is displayed in this graph. The different coloured lines each represent the year long relationship between breeding values for each trait for each year. The broken arrow shows the movement of the mean breeding value for each trait from 2011 to 2019. It shows that there has been a yearly decrease in the mean breeding value for wooden breast whilst the mean breeding value for breast yield has increased.