Associations between several aspects of heifer development and dairy cow survivability to second lactation

A data set from 7,768 Holstein heifers born between 2004 and 2006, including growth rates from birth until first calving; age and body weight at insemination; and incidence of diarrhea, navel infections, and bovine respiratory disease (BRD) was used to evaluate potential associations between these factors and the odds of completing the first lactation. All heifers were raised in a contract heifer operation (Rancho Las Nieves, Mallen, Spain) and returned to their herds of origin (133 herds in total) before calving. Dates of death were provided by the Subdirección General de Explotaciones y Sistemas de Trazabilidad de los Recursos Agrícolas y Ganaderos from the Ministry of Environment, and Rural and Marine Areas of the Spanish government. At the time of analysis, 2,571 (33.1%) animals out of the 7,768 considered had died. In total, 655 (8.4%) heifers did not finish first lactation, and 31.5% of these left the herd within the first 50 DIM. Also, 4.8% of heifers aborted and were rebred. Data were analyzed using a mixed-effects logistic regression and survival analysis for dichotomous variables and a mixed-effects model for continuous ones. Incidence of diarrhea or navel infection was not associated with the chances of finishing the first lactation. Heifers that completed first lactation had a lesser average age at first calving (724 ± 2 d) than those that did not (737 ± 3 d). Heifers that reached second lactation grew (0.8 ± 0.04 kg/d) more between 12 and 65 d of age than those that did not (0.7 ± 0.04 kg/d). As conception rate decreased, chances of leaving the herd before completing the first lactation increased. The number of AI services needed per conception as a nulliparous heifer was negatively associated with survivorship to second lactation. Heifers that experienced an abortion were 2.73 ± 0.52 times more likely to leave the herd before completing the first lactation (but also calved with a much older age at first calving). Heifers that experienced 4 or more BRD cases before first calving had 1.87 ± 0.14 greater odds of not completing the first lactation than those that never experienced BRD. These results show potential to forecast future heifer success in finishing the first lactation based on average daily gain early in life, incidence of BRD, reproductive performance (conception and abortion rates), and age at first calving.