Heritability and genetic correlations between milk composition and milk coagulation traits in Bulgarian Brown cattle
Teodora Angelova, Jivko Krastanov, Daniela Yordanova
Abstract: The aim of the present study was to determine the heritability and to evaluate genetic correlations
between milk composition traits and milk coagulation properties in Bulgarian Brown cattle. The
analysis included 155 cows from 4 herds in different regions of the country regardless of lactation
number and days in milk. Heritability coefficients and genetic correlations describing milk quality
and milk coagulation properties were determined on the basis of records for animals’ origin from
herdbooks. The analysis of milk composition was done in the lab of the Agriculture Institute – Stara
Zagora on Lactoscan ultrasound milk analyzer, whereas coagulaiton properties of individual milk
samples were evaluated on a Computerized Renneting Metter – Polo Trade, Italy. For unbiased estimation
of additive and environmental variance and co-variance components, fir calculation of heritability
and genetic correlations between production / milk composition / traits and milk coagulation
traits, a Random Regression Test day model was used. Coefficients of heritability of traits for milk
quality composition – daily milk yield, fat and protein contents were 0.29, 0.39 and 0.33, respectively.
The traits characterizing milk coagulation properties (RCT, A30 and K20) were outlined with medium
and low heritability coefficients: 0.34, 0.15 and 0.04. Daily milk yield correlated negatively with milk
fat (-0.394) but positively with milk protein (0.253). The three studied traits describing the qualitative
composition of milk – daily milk yield, fat and protein substances have a negative correlation with the
rennet coagulation time (-0.027, -0.294 and -0.104) and a positive correlation with the curd firmness
(0.231, 0.356 and 0.208) respectively.
between milk composition traits and milk coagulation properties in Bulgarian Brown cattle. The
analysis included 155 cows from 4 herds in different regions of the country regardless of lactation
number and days in milk. Heritability coefficients and genetic correlations describing milk quality
and milk coagulation properties were determined on the basis of records for animals’ origin from
herdbooks. The analysis of milk composition was done in the lab of the Agriculture Institute – Stara
Zagora on Lactoscan ultrasound milk analyzer, whereas coagulaiton properties of individual milk
samples were evaluated on a Computerized Renneting Metter – Polo Trade, Italy. For unbiased estimation
of additive and environmental variance and co-variance components, fir calculation of heritability
and genetic correlations between production / milk composition / traits and milk coagulation
traits, a Random Regression Test day model was used. Coefficients of heritability of traits for milk
quality composition – daily milk yield, fat and protein contents were 0.29, 0.39 and 0.33, respectively.
The traits characterizing milk coagulation properties (RCT, A30 and K20) were outlined with medium
and low heritability coefficients: 0.34, 0.15 and 0.04. Daily milk yield correlated negatively with milk
fat (-0.394) but positively with milk protein (0.253). The three studied traits describing the qualitative
composition of milk – daily milk yield, fat and protein substances have a negative correlation with the
rennet coagulation time (-0.027, -0.294 and -0.104) and a positive correlation with the curd firmness
(0.231, 0.356 and 0.208) respectively.
Keywords: Brown cattle; coagulation properties; Heritability and genetic correlations; milk production
Date published: 2021-10-27
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