New functions to estimate 305-days milk production of Gir cows : Novas Funções para Estimar a Produção de Leite, em 305 Dias de Lactação, de Vacas da Raça Gir
2008
Reboucas, G.F. | Moraes Goncalves, de, T. | Martines, M.L. | Azevedo Junior, J. | Koops, W.J.
This study aimed to calculate new accumulated and daily functions based on the Michaelis-Menten equation to estimate the 305-days production of Gir cows using test day milk yields. Data consisted of 7,412 lactation records of 3,416 Gir cows (Bos indicus) collected from 1987 to 2004 in 51 herds assisted by the National Breeding Program of the Dairy Gir, coordinated by the Dairy Cattle National Research Center (EMBRAPA) and the Brazilian Association of Dairy Gir Breeders (ABCGIL). The models included the effects of herd milk production (High and Low), calving season (dry e rainy) and parity order (OP 1 to 5 and > 5). Residual Standard Deviation values ranged from 0.131 to 0.z984. Estimates for the Coefficient of Determination (R²) were close to one and for the Durbin-Watson coefficient were close to two. Values of statistics of Theil (U) were close to zero for UM and UV and close to one for UC suggesting a good fitting for the function. The persistency of milk yield is related to the parameter d and the time of the pick yield is related to both parameters d and n. The new functions are characterized by simplicity of the fitting procedure, biological interpretability of the parameters and flexibility to convert the daily function to the accumulated function. The new functions are an alternative to project lactations with records in progress to estimate the production required in genetic evaluation systems based on 305-day milk production records.
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