Avaliação dos fatores oficiais de correção da produção até o primeiro controle leiteiro em vacas holandesas

Abstract

The official dairy control performed on Holstein cows in Brazil is intended to enhance the productive potential of the breed, collect amount of data for progeny testing and genetic breeding and spread update results for the economical and scientific community. In the calculation of the lactation, correction factors a reutilized to estimate yield till the first control,proposed by Everett & Carter (1968). Aiming to evaluate these factors, 262 lactations as daily Yield controls of two herds of Holstein cattle participating in the service of the officiai dairy control of the Holstein Cattle Breeders of Minas Gerais Association were utilized. The data were divided into different classes of age at calving (CAC); CAC 1 (till 3 years), CAC2 (between 3 and 4 years),CAC3 (between 4 and 5 years), CAC 4(between 5 and 6 years) and CAC 5 (over 6 years) with 104, 56, 44, 18 and 40 lactations, respectively. The cumulated yields calculated by utilizing the official factors with the accumulated actual yields were compared, by taking into consideration the 6th, 20th, 34th, 48th, 62th and 75th day of lactation as days of the first control. In all the age at calving classes, the official factors over estimate the cumulated milk yield till the first control (P<0.05) with the relative overestimate error (%) to decreasing with the advance of the day of the first control. Although with alower relative error, the overestimate in terms of kg of milk was greater with the advance of the day of the first control, with values ranging from 13.9 to 87.1 kg of milk in CAC 1, class of the lowest overestimate and of 20.6 to 196.3 kg of milk in CAC 2, class of the greatest overestimate. Following the same behavior, age at calving classes 3, 4 and 5 presented intermediary values. Following the same methodology Utilized by Everett & Carter (1968), new factors were generated foreach day from the 6th to 75th the day of lactation, in the five ages at calving classes studied. It was found that those factors were lower and provided estimates closer to the actual values than those officially used to estimate milk yield till the first control.