There are many factors affecting profitability in dairy production; one of the most important factors is milk yield during the first lactation since it has been related to the future performance traits or the longevity of the animal. The aim of this study was to determine the relation between normalized yield in the first lactation of dairy heifers and traits from the heifer (birth season, genetic value for milk production, age at first calving, calving difficulty and sex of the calf) and their dam (calving number when the dam calved this heifer and calving difficulty along with gestation length, milk production at drying-off and duration of the dry period prior to calving). For this purpose, data were obtained from 12,029 Friesian heifers that finished their first lactation in 2015. Regression was used to identify factors related to normalized milk yield. Of the analyzed parameters, those that seem to have more influence on this trait were the birth season and the calving difficulty of the heifer along with its genetic value for milk production, besides the calving difficulty and production at drying‑off of the dam.

Sánchez MJ, Fouz R, Yus E, Camino F, Diéguez FJ (2019). Efecto de los factores zootécnicos en la producción en primera lactación de vacas Frisonas en N.O. de España. ITEA‑Información Técnica Económica Agraria 115(1): 52‑61. https://doi.org/10.12706/itea.2018.026