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Lactation length is a very important trait of dairy animals directly affecting the milk yield. Shorter or extended lactation lengths are not desirable as it affects the milk yield. Therefore the study of factors affecting lactation length is of most important. The present study was conducted on data of 9094 lactations collected from 3425 Frieswal lactating cattle (Holstein Friesian x Sahiwal cattle) born to 239 sires maintained at Military Farm, Pimpri, Pune, Maharashtra from the year 1983 to 2018 to quantify effect of certain non genetic factors on lactation length. The normalized data were analyzed using PROC GLM procedure of SAS to study the effect of various genetic (sire) and non genetic (period, season and parity) factors on lactation length. The age at first calving was used as a covariate. The effect of period of calving was found to be highly significant ( less than 0.001) on lactation length. The season, parity and age at first calving were significantly affecting the lactation length. Parity two to six does not differ significantly in lactation length. Among the genetic factors effect of sire was significant on lactation length.

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