# Occurrence and Genetic Parameters Estimation of Blood and Meat Spots in Brown-Shelled Eggs During the Extended Laying Period

## TL;DR

This study examines blood and meat spots in brown-shelled eggs from older hens, finding that meat spots are more common and can be improved through breeding, while blood spots are less heritable and may require other management strategies.

## Contribution

The study provides new genetic insights into blood and meat spots in brown-shelled eggs during extended laying periods, showing their differing heritability and potential for improvement.

## Key findings

- Meat spots are more common and have moderate heritability, making them suitable for selective breeding.
- Blood spots are rare, small, and have low heritability, suggesting management strategies are more effective for improvement.
- Both defects are genetically linked and negatively correlated with egg quality traits like albumen height and shell strength.

## Abstract

Blood and meat spots are visible inner defects in eggs that reduce consumer acceptance and economic value, particularly in aged laying hens producing brown-shelled eggs. With modern laying cycles extended to later ages, understanding why these defects occur and whether they can be reduced through breeding is important. In this study, a total of 392 eggs from Rhode Island Red hens were included in the analysis and examined for the presence, number, size, and location of blood and meat spots. Blood spots were few, very small, and mainly located on the yolk, while meat spots were common, often multiple, and mostly found in the egg white and chalaza. Genetic analysis showed a strong relationship between blood and meat spots, but their potential for improvement differs: meat spots had moderate heritability and could be reduced through selective breeding, whereas blood spots showed low heritability, suggesting that nutrition and management strategies may be more effective. These defects were linked to poorer internal egg quality, highlighting the importance of managing meat spots to improve egg quality, reduce economic losses, and support sustainable egg production.

Blood and meat spots are key internal egg quality indicators, and clarifying their genetic characteristics in late laying periods is critical for quality improvement via selective breeding. This study collected 392 eggs from 421 96-week-old Rhode Island Red hens across 69 families, analyzing 10 traits including blood/meat spots and standard egg quality traits. Heritability, genetic and phenotypic correlations were estimated using the DMU package. The incidences of blood and meat spots were 15.8% and 64.8%, respectively. Blood spots were yolk-localized, single and <1 mm in diameter, while meat spots mostly occurred on chalazae (83.5%) and thick albumen (33.1%), mostly multiple (56.1% with 2–5 spots) and 1.80 ± 1.53 mm in diameter (30% >2 mm). Blood spots had low heritability (0.05), meat spots moderate heritability (0.20). The two traits showed high positive genetic correlation (rG = 0.93), and strong negative genetic correlations with albumen height and eggshell strength. In conclusion, blood and meat spots in late-laying hens differ in distribution, size and number, and meat spots are amenable to genetic selection for internal egg quality enhancement.