Small for Gestational Age Calves: Part I—Concept and Definition, Contributing Prenatal Factors and Neonatal Body Morphometrics in Holstein Friesian Calves.

Simple Summary: Low birth weight (BW) calves experience higher mortality, lower weights at calving, reduced milk yields in their first lactation, and longer intervals before first insemination. In human medicine, small for gestational age (SGA) babies are known to suffer from increased health risks. The aim of this study was to define SGA in Holstein Friesian (HF) calves, evaluate their body measurements, and identify prenatal risk factors for being born SGA. We used models to predict calf weight based on gestation length for male and female calves from nulli- and multiparous dams. Calves with a BW below the 10th percentile were classified as SGA. We then analyzed body measurements and identified associated risk factors. SGA calves had significantly smaller body measurements and different proportions compared to average and large calves. For nulliparous dams, a higher temperature–humidity index during the 2nd trimester and older age at birth increased the birth of SGA calves. For multiparous dams, both low and high milk production during pregnancy were linked to more SGA births. This study establishes SGA in HF calves and highlights the impact of prenatal factors on calf size at birth. Further research is needed to understand the long-term effects of being born SGA on growth, reproduction and productivity. Low birth weight (BW) calves exhibit higher mortality rates, reduced body weights at parturition, lower first-lactation milk yields, and longer parturition to first insemination intervals. In human medicine, small for gestational age (SGA) births are associated with increased perinatal morbidity and long-term metabolic risks. This study aimed to define SGA in Holstein Friesian (HF) calves, evaluate their body measurements and proportions, and identify its prenatal risk factors. Four linear regression models were built with weight as a function for gestation length for bull and heifer calves born from nulli- or multiparous dams. Calves with a BW below the 10th percentile were classified as SGA. Differences in body measurements were analyzed using ANOVA, and logistic regression models identified prenatal risk factors to be born SGA. Gestation length, calf sex, and dam parity were crucial variables in defining SGA. SGA calves had significantly smaller body measurements (p < 0.001) and larger body proportions (p < 0.001) compared to average and large calves. For nulliparous dams, a higher 2nd trimester temperature–humidity index (p = 0.032) and older age at parturition (>26 months, p = 0.026) significantly increased the birth of SGA calves. For multiparous dams, both low (<5800 kg, p = 0.049) and high (6700–8600 kg, p = 0.027) milk yields during gestation lead to more SGA births, although very high-yielding dams (>8600 kg) did not birth more SGA calves. This study establishes SGA in HF calves, suggests SGA calves are asymmetrical with evidence of "brain sparing", and highlights the impact of prenatal factors on calf size at birth. Further research is needed to determine the long-term effects of being born SGA on growth, reproductive performance, and productivity. [ABSTRACT FROM AUTHOR]