Genetic relationship between days open and days dry with milk yield in a herd of Holstein Friesian cattle
Abstract. A total of 2897 lactation records of Holstein Friesian cattle from the fields of Dena Farm in Egypt from 1987 to 1993 were used to study relationships of days open and days dry with milk production. The effect of month and year of calving, sire and cow within sires were also investigated.
Month of calving, year of calving, sire and cow within sires significantly influenced milk production.
Including DO and DP as a polynomial of second degree of production were significant. The partial linear and quadratic regression coefficients of 305 day milk yield on DO and DP were significant, being 7.59 ± 0.40 kg/d and −0.37 ± 0.00 kg/d2, respectively for DO and −9.37 ± 0.54 kg/d and 0.02 ± 0.00 kg/d2, respectively for DP. Therefore, reduction of DO and DP are a desirable goal of dairymen.
Heritability (h2) estimates for 305 day milk yield, DO, DP were 0.13 ± 0.05, 0.00 and 0.00, respectively.
Adjustment of lactation milk yield for DO will not involve genetic influence on milk yield.