Turkish Journal of Veterinary and Animal Sciences

Abstract: In this study, lactation curves traits of Simmental cows in raised at regional in Experimental Farm of Kazova were determined the shape and type of lactation curve were described by Gamma curve parameters of Yt = A.t^b e^-ct. The 42% percent of lactation curve were atypical. The distribution of typical and atypical lactation curves were depended upon the calving season (P<0.01), and weren't significant (P>0.05) depended upon the lactation number. Effect of calving year on B and C values was highly significant (P<0.01) or significant (P<0.05). Effect of calving season on the B values was significant (P<0.05). Effect of breeding type was highly significant (P<0.01) for the A, S (persistency) and Y_max (maximum daily peak yield). Least squares means were found to be 13.00±0.9 kg, 0.154±0.022, 0.00345±0.00042, 6.628±0.105,19.95±1.4 kg and 36.55±4.4 days for A (beginning yield), B (coefficient of rising), C (coefficient of decreasing), S (persistency), Y_max (Average of maximum daily peak yield), T_max (Average of daily peak yield length).

Key Words: Lactation Curve, Lactation persistency, Holstein cattle