Abstract
The effects of fixed non-genetic factors (farm, season of birth, year of birth, total number of lactations) and a continuous non-genetic factor (age at first conception) on the expression and variability of longevity traits such as age at culling, length of productive life, days in milk and cow efficiency index were investigated in 2548 Simmental cows in three farming areas. Based on the model used for the analysis of the effects of non-genetic factors, including the environment and cow age at first conception, on the expression and variability of longevity traits, the overall means for age at culling, length of productive life, days in milk and cow efficiency index were 2445.21?17.49 days, 1562.55?17.71 days, 1094.17?12.28 days and 58.68?0.32%, respectively. The effect of farming area, year of birth and lactation group on longevity traits was very significant (P<0.01), whereas the effect of season of birth was significant (P<0.05). Age at first conception had a highly significant (P<0.01) effect on age at culling, length of productive life and cow efficiency index, and no significant effect on days in milk (P>0.05). Based on the model used, the coefficients of determination (R2) were very significant (P<0.01) for all longevity traits, and ranged from 0.898 for age at culling to 0.959 for days in milk.
Highlights
IntroductionSelection work in dairy herds in the last 50 years has strongly focused on milk performance traits
Research into phenotypic and genetic variability of production traits has an immense practical importance as this variability underlies annual and generational selection effects.Selection work in dairy herds in the last 50 years has strongly focused on milk performance traits
The effects of fixed non-genetic factors and a continuous non-genetic factor on the expression and variability of longevity traits such as age at culling, length of productive life, days in milk and cow efficiency index were investigated in 2548 Simmental cows in three farming areas
Summary
Selection work in dairy herds in the last 50 years has strongly focused on milk performance traits. This directselection based on milk performance traits has led to deterioration of fertility, longevity and immunity traits, which have a critical role in profitable milk production. In terms of milk production, functional traits have today become crucial in defining modern breeding programmes aimed at obtaining productive cost-efficient animals. Their basic effect on the economic efficiency of milk production is not achieved through direct increase in animal productivity, but is evidencedby production cost reduction through animal health, resistance, vitality and ability to last a number of lactations (Bogdanović et al, 2012)
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