Population structure of the Japanese Brown breed

Area of Science:

• Animal Genetics
• Population Genetics
• Livestock Breeding

Background:

• The Japanese Brown cattle breed is economically significant in Japan.
• Understanding population structure is crucial for maintaining genetic diversity and breed health.
• Previous studies have not comprehensively analyzed the long-term population genetic trends in the Kumamoto Prefecture herd.

Purpose of the Study:

• To investigate the population structure and genetic parameters of the Japanese Brown cattle in Kumamoto Prefecture.
• To estimate key genetic metrics including F-statistics, index of subdivision, generation interval, effective population size, and effective number of sires.
• To assess the trends in inbreeding and genetic diversity over several decades.

Main Methods:

• Pedigree analysis of 200 randomly sampled heifers across four decades (1960, 1970, 1980, 1990).
• Estimation of population genetic parameters: F-statistics (F(IT), F(ST), F(IS)), index of diversity, generation interval, effective population size (N(e)), and effective number of sires.
• Longitudinal data analysis to track changes in genetic parameters over time.

Main Results:

• The effective number of sires significantly decreased, particularly between 1970 and 1980.
• Average inbreeding coefficient (F(IT)) increased from 0.64% in 1960 to 5.43% in 1990.
• F(ST) showed a parallel increase with F(IT), indicating rising irreversible inbreeding, while F(IS) remained low.
• The index of diversity decreased from 1960 to 1980 but showed a slight improvement by 1990.
• Effective population size (N(e)) decreased substantially from over 700 to 40.1.
• Generation interval increased, averaging 5.52 years between 1980-1990.

Conclusions:

• The current population structure of Japanese Brown cattle in Kumamoto is not immediately problematic regarding average inbreeding (F(IT)).
• However, the continuous increase in irreversible inbreeding (F(ST)) is a significant concern for long-term genetic health.
• Monitoring and potential interventions may be necessary to manage inbreeding and preserve genetic diversity in this important breed.