Abstract
Lactation records of 2 567 Holstein-Friesian (HF) cows in Egypt (subtropical area) and Hungary (rainy area) were used to determine the effect of drought on changes in genetic parameters. The traits studied were udder length and depth, teat length, attachment and placement and milk production traits (total milk, fat and protein yield). Variations in all studied traits due to random effects of sire groups were much higher in the rainy area than in the subtropical one. Changes of all genetic (co)variances with an advancing order of lactation were greater for subtropical animals. In subtropical area heritability estimates of udder traits for HF were higher than estimates for milk production and their differences were also larger than the corresponding estimates of cold rainy area. Low heritability estimate was computed for mastitis infection for Hungarian HF. Highest genetic and phenotypic correlations (-0.67 and -0.87, respectively) for mastitis with udder depth were recorded in subtropical area. Many details concerning genetic parameters which could be taken into consideration during planning and carrying out phenotypic and genetic selection to increase the total economic benefit of dairy farms were tabulated and discussed.