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Causes terminating lactation records in holstein-friesian x guzera crosses

Fernando E. Madalena^I; Alvaro Mattos Lemos^II; Roberto L. Teodoro^II; João B. Neves Monteiro^II; Rogério T. Barbosa^III

^IR. Teodoro Coelho, 365, 36050 Juiz de Fora, MG, Brasil. Send correspondence to F.E.M.
^IIEMBRAPA, Centro Nacional de Pesquisa - Gado de Leite, 36155 Coronel Pacheco, MG, Brasil
^IIIEMBRAPA, UEPAE Säo Carlos, 13560 Säo Carlos, SP, Brasil

ABSTRACT

Causes terminating lactation records (CTR) were studied using 921 records of six Holstein-Friesian (HF) x Guzera crossbred groups kept in farms with high (HML) and low (LML) management levels. In the HML, percentages of lactations terminated because of "normal" reasons, because of calf loss or because of cow illness, injury or death, were, for groups with 1/4, 1/2, 5/8, 3/4, 7/8 and - 31/32 HF gene fraction, respectively: 95.0, 2.5, 2.5; 97.0, 1.2, 5.8; 85.4, 4.2, 10.4; 98.1, 0, 1.9; 90.7, 0, 9.3 and 98.0, 0, 2.0. Corresponding percentages in the LML were: 87.2, 11.7, 1.1; 90.8, 6.7, 2.5; 89.9, 2.9, 7.2; 85.4, 8.3, 6.3; 84.6, 3.8, 11.5 and 84.1, 3.2, 12.7. Chi-square for heterogeneity of the latter distribution among crossbred groups was highly significant (P <0.005). Since "abnormal" CTRs are likely to affect milk yield, it was concluded that unbiased comparisons of breeds and crosses and estimates of inter-population genetic parameters for milk yield should be based on all available records and not only on those with "normal" CTRs.

Keywords: terminating; lactation; holstein-friesian.

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