Novel function describing dairy cow lactation of Holstein breed

Abstract Text: The generalized Michaelis-Menten (GMM) function was fitted to the rainy and dry seasons, and parity order (PO 1, 2, 3 and ≥4). In both calving seasons the 305 days yields (Y₃₀₅) were similar. Highest yield peak (Y_m), lowest lactation persistence (h) and shortest time of occurrence of peak (t_m) for dry season-calved cows. The Y₃₀₅ of PO1 and PO≥4 cows was similar, the h value at PO1 being higher. For both POs 2 and 3 the animals showed same Y₃₀₅ and similar curve shape. For PO1 calved in the months of October to March had higher t_m and more persistent curves than calving between months of April to September. The same occurred for PO≥4 cows. it is necessary the fitting of lactation curves for both heifers and mature cows, because effect on the shape of lactation curve.

Keywords: Projection of lactation, enviroment factors, persistency of lactation, genetic evaluation.