The Effect of Inbreeding on Lactation Performance in Holstein Cows of Iran

The objective of this study was to investigate the effect of inbreeding on lactation performance in Holstein cows of Iran.The pedigree file contained information of 1,025,281 animals born between 1965 and 2007.Lactation performance records from March 2000 to April 2009 comprising 193,501calving events on 123,751 cows in 85 dairy herds were included in the data set. The potential consequent effects of inbreeding on lactation traits were analyzed through mixed linear model using the MIXED procedure of the SAS. The mean level of inbreeding was shown to be 0.7%. Less than 37% of all animals were inbred, and a small proportion, 3.45%, of inbreed animals had inbreeding coefficients greater than 5%, with a maximum inbreeding coefficient of 38%. Overall mean (±SD) of 305-d milk, fat and protein yields were estimated to be 7812 (±1780), 252.5 (±64.5), and 247.8 (±50.6) kg, respectively. The 305-d milk, fat and protein yields decreased by -19 (±3.7), -0.7 (±0.13), and -0.43 (±0.13) kg per lactation for each 1% increase in inbreeding, respectively. Inbreeding showed no significant impact on fat and protein percentages.