title: Influence of milking frequency on genetic parameters associated with the milk production in the first and second lactations of Iranian Holstein dairy cows using random regression test day models.
abstract: BACKGROUND
  The milk yield can be affected by the frequency of milking per day, in dairy cows. Previous studies have shown that the milk yield is increased by 6-25 % per lactation when the milking frequency is increased from 2 to 3 times per day while the somatic cell count is decreased. To investigate the effect of milking frequency (3X vs. 4X) on milk yield and it's genetic parameters in the first and second lactations of the Iranian Holstein dairy cows, a total of 142,604 test day (TD) records of milk yield were measured on 20,762 cows.
  
  
  RESULTS
  Heritability estimates of milk yield were 0.25 and 0.19 for 3X milking frequency and 0.34 and 0.26 for 4X milking frequency throughout the first and second lactations, respectively. Repeatability estimates of milk yield were 0.70 and 0.71 for 3X milking frequency and 0.76 and 0.77 for 4X milking frequency, respectively. In comparison with 3X milking frequency, the milk yield of the first and second lactations was increased by 11.6 and 12.2 %, respectively when 4X was used (p < 0.01).
  
  
  CONCLUSIONS
  Results of this research demonstrated that increasing milking frequency led to an increase in heritability and repeatability of milk yield. The current investigation provided clear evidences for the benefits of using 4X milking frequency instead of 3X in Iranian Holstein dairy cows.
authors.affiliation: Department of Animal Science, Faculty of Agriculture, University of Jiroft, Jiroft, Iran.
authors.forename: Moslem Moghbeli
authors.initials: MM
authors.lastname: Damane
authors.affiliation: Department of Animal Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran.
authors.forename: Masood Asadi
authors.initials: MA
authors.lastname: Fozi
authors.affiliation: Department of Animal Science, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran.
authors.forename: Ahmad Ayatollahi
authors.initials: AA
authors.lastname: Mehrgardi
keywords: Genetic parameters; Iranian Holstein cows; Milk production; Milking frequency; Random regression
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