Abstract
A total of 956 lactation records of Holstein cows kept at Kaa Albon station, Imuran Governorate, Yemen during the period from 1991 to 2003 were used to investigate the effect of some genetic and non-genetic factors (Sire, parity, season of calving, year of calving and age at first calving as covariate) on the Total Milk Yield (TMY), Lactation Length (LL), and Dry Period (DP). Components of variance for the random effects (mixed model) were estimated by Restricted Maximum Likelihood (REML) methodology. Sires were evaluated for the TMY by three methods, Best Linear Unbiased Prediction (BLUP) using Harvey program, Transmitting Ability (TA) according to the Least Square Means of sire progeny (TALSM) and according to Means (TAM). Results showed that TMY and DP were affected significantly (P < 0.01) by all factors except season of calving and age at first calving, while LL was affected significantly (P< 0.01) only by year of calving and parity. The averages of the TMY, LL, and DP were 3919.66 kg, 298.28 days, and 114.13 days respectively. The corresponding estimates of heritability (h²) were 0.35, 0.06, and 0.14 respectively. The highest and lowest BLUP values of sires for the TMY were – 542.44 kg and 402.14 kg, while the corresponding estimates for TALSM and TAM were – 470.38, 380.88 kg and – 370.12, 388.50 kg respectively. The Spearman rank correlation coefficients among BLUP, TALSM and TAM ranged from 0.81 to 0.67. These results provide evidence that the selection of sires will improve the TMY in this herd because of the wide differences in genetic poetical among sires, and a moderate estimation of heritability.

Key words: BLUP, Genetic evaluation, Heritability, Holstein cows.