The Use of 120 Day Milk Production for Sire and Cow Genetic Evaluation in Libyan Dairy Cattle

Abstract

This study was carried out using 1298 first lactation production records of Holstien Fresian Dairy cattle at Al-Nasir project. These records included total milk production (TMP), adjusted 305 day milk production (305DMP), 120 day milk production (120 DMP), and length of lactation. In order to assess the effect of year and season and the interaction of these two factors, one subclass was intiated and coded in the data. The year was devided into two seasons; hot season included the months (from May to October), and cold season included (from November to April). Breeding values of cows and sires were estimated for 120 DMP and 305 DMP using contemporary comparison. The analysis of variance with unequal subclass numbers indicated significant effect of year and season on all production traits (P<.01). Correlations between 120DMP,and 305DMP with TMP were 0.78 and 0.77 respectively. Breeding values of sires using 305DMP ranged from -315 to +414 kgs with a weighted mean of +36 kg, while for 120DMP the estimates ranged from –94.7 to 144.7 kg, and their weighted mean was +9.8 kg. The frequency distribution of breeding values showed that more than 51% of sires were of negative values. Correlation between 120DMP, and 305DMP expressed as contemporary deviations of cows and sire daughters averages were 0.76 for cows and 0.86 for sires. Correlations between breeding values of cows and sires for 120DMP and 305DMP were 0.76 and 0.86. All estimates were significant(P<.01) indicating large association between breeding values of 120DMP and 305DMP for the same animals. Rank correlations between 120DMP and 305DMP expressed for the same animals as cow contemporary deviations, sire average daughters deviations, cow and sire breeding values were: 0.87, 0.87, 0.87 and 0.74 respectively. These estimates indicate that cows and sires rank similarly when ranked according to their breeding values estimated using 120DMP and 305DMP. 120DMP could be used for genetic evaluation of sires and cows, And its adoption will be benificial to Libyan dairy industry through reduction of generation interval, and early decision making in culling, and selection of sires and cows especially in the absence of adequate correction factors to 305 days milk production.The accurate evaluation and proper use of sires is very important due to their large contribution and effect on population production. This study indicates that low production of imported cows is not only due to environment, but also due to breeding policies specialy in sires which contribute the most to this effect.