An Estimation of the Lactation Curve Parameters through Incomplete Gamma Function and a Determination of the Genetic Relationship between these Parameters and udder Traits, in Holstein Population of Iran

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The objective of the present study was to estimate the lactation curve parameters through incomplete gamma function and to genetically evaluate the relationship of these parameters and udder traits in Holstein population of Iran. Two data sets' including 117583 [(for lactation curve parameters) and 7351 (for determining genetic and phenotypic relationship between lactation curve parameters and udder type traits)], first lactation records on cows from 19303 and 1148 herd-year-season groups were respectively employed. Heritability estimates varied from 0.02 (a and b) to 0.22 (peak) and for udder type traits ranged from 0.11 (FU) to 0.21 (RTP).The genetic correlations among lactation curve parameters ranged from 0.99 (TTP and PERS) to -0.64 (a and b) and among udder type traits and lactation curve parameters ranged from 0.54 (RTP and a, RUW and PEAK) to -0.54 (RTP and b). Results suggested that the application of RUW for indirect selection of lactation curve parameters could be useful for genetic improvement of persistency in milk yield. With regard to the present study, cows with more udder width had a more M305, PEAK as well as PERS.

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