Association between the lactation curve shape and calving interval in Holstein dairy cows of Iran

Document Type: Full paper (Original article)


1 Department of Animal Science, College of Agriculture, Shiraz University, Shiraz, Iran

2 Animal Breeding Center of Iran, Karaj, Iran

3 Department of Animal Science, College of Agriculture, Razi University, Kermanshah, Iran


This study was carried out to investigate the relationship between early lactation curve parameters and
calving interval in Holstein cows of Iran. In order to describe the lactation curve, the incomplete gamma
function was fitted to 5,754,428 test-day milk records corresponding to 766,108 lactations on 315,634 cows
in 2,448 herds. Cows with higher milk yield during early lactation had shorter calving intervals; however,
longer calving intervals increased the 305-d milk production (P<0.01). Cows with higher yield at the
beginning of lactation, steeper ascending, and steeper descending slope had shorter calving intervals
(P<0.01). Calving interval was increased by 2.73 (±0.12) d for every extra kg of milk at peak lactation
(P<0.01). The calving interval was directly impacted by the persistency of milk yield, but milk yield
persistency was reduced in cows with shorter calving intervals (P<0.01).