Resumo

RODRIGUEZ G, Yuliska Y  e  MARTINEZ G, Gonzalo E. Effect of Age at First Calving, Breed Group and Some Environmental Factors in Milk Production and First Calving Interval in Dual Purpose Cows. Rev. Fac. Cienc. Vet. [online]. 2010, vol.51, n.2, pp.079-091. ISSN 0258-6576.

The aim of this study was to evaluate the effect of age at first calving (AFC), some non-genetic factors, and breed group on milk production, adjusted to 244 d (P244) in the first (PL1) and second (PL2) lactations, and the first calving interval (FCI), in dual purpose cows. A total of 2471 observations for PL1, 1589 for PL2, and 1491 for FCI, from two commercial farms located in the tropical humid forest life zone, in the State of Trujillo, Venezuela, were analyzed. All the animals were grazing and received salts and minerals ad libitum, with reproductive and sanitary management, adequate to the conditions of each farm. An analysis of variance was used for the three variables studied. This included the fixed effects: Farm (F: Agrounica; Valle Verde); Year of Calving (YC: 2000-2007); Season of Calving (SC: Jan-Mar; Apr-May; Jun-Aug; Sep-Dec); Breed Group (BG: 50% Zebu, 50% European; mainly Zebu, milking crossbred); AFC (24, 30, 36, and 42 m). The following interactions were included for PL1 and PL2: FxYC; FxBG; and YCxSC. The results show that the average for PL1 and PL2 was 1430.9 and 1579.8 kg, respectively. All main effects included in the model significantly affected PL1 and PL2 (P<0.05), with the exception of AFC and SC (P>0.05). For the FCI, all the effects included in the model were statistically significant (P<0.05), except for AFC and SC (P>0.05). The dissimilarity for extreme SC was 51.4 kg in PL1, 39.2 kg in PL2, and 23.4 d for FCI, correspondingly. The difference between farms was 146.5 kg for PL1, 267.4 kg for PL2, and 16.3 d for FCI, respectively. The difference in YC was 294.0 kg 183.7 kg, and 83 d in PL1, Pl2, and FCI, in that order. Neither AFC nor FCI affected milk production in PL1 and PL2. 

Palavras-chave : Calving interval; Environmental factors; Milk production; Reproduction, Lactation.

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