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Published online by Cambridge University Press: 27 March 2009
The first lactation records of 684 Sahiwal, 157 Brown Swiss × Sahiwal (BS × S) and 255 Friesian × Sahiwal (F × S) constituted the data for this study. The 300-day yield was estimated from part lactation yields of 13, 17, 21, 26 and 30 weeks post partum by four methods, namely, regression, ratio, gamma and inverse polynomial functions. The duration of the part record and the method of estimation were evaluated for their reliability in estimating the 300-day yield and sire evaluation.
The correlations between part records and 300-day yield ranged from 0·76 to 0·95, thecorrelations being higher in F × S. The error, absolute error and standard deviation of error weresmaller for ratio and regression methods than for the gamma and inverse polynomial functions. The part records of 30 weeks or more were found to be necessary to estimate 300-day yield within 15% of the actual yield with regression or ratio methods.
The rank correlations and product moment correlations between sire indices calculated with part records and 300-day yield were found to be highly significant. The part records of 17 weeks or more extended by ratio or regression could be used to evaluate sires as accurately as with 300-day yield by increasing the progeny group size by 7–10% in Sahiwal and by about 20% in F × S. Theloss of efficiency in sire evaluation amounted to about 10–15% with part records of 17 weeks or more compared with 300-day yield.
