Small for Gestational Age Calves: Part II—Reduced Fertility, Productive Performance, and Survival in Holstein Friesian Heifers Born Small for Their Gestational Age.

Simple Summary: Recently: more attention has been given to low-birth-weight calves, often without considering gestation length. Similar to human medicine, calves classified as small for gestational age (SGA) weigh below the 10th percentile at birth. The present study aimed to investigate the long-term effects on fertility, productive performance, and overall survival in Holstein Friesian (HF) heifers born SGA. We found that while SGA calves showed initial catch-up growth at six months of age, they were still significantly lighter at twelve months. SGA heifers required significantly more inseminations to conceive compared to their average (AGA) and large (LGA) counterparts. Additionally, more SGA heifers were culled during their first lactation and had lower survival rates to the second calving. SGA heifers also had a higher risk of leaving the herd prematurely. Although overall lifespan and total milk yield were similar among all groups, SGA heifers produced less milk per productive day. This study reveals that HF calves born SGA face significant long-term health and productivity challenges, emphasizing the need for further research on the economic impact of rearing SGA heifers. Recently: more attention has been given to low-birth-weight calves, often without considering gestation length. Calves can be classified as small for gestational age (SGA) when their birth weight is below the 10th percentile, similar to the definition in human medicine. While SGA babies face various health risks, it remains unclear if SGA calves face similar long-term health consequences. This study aimed to investigate the long-term effects on fertility, productive performance, and overall survival in Holstein Friesian (HF) heifers born SGA. Chi-squared analysis assessed culling and survival rates, and linear mixed-effect models evaluated the impact of gestational age group (small, average, or large for gestational age, respectively, SGA, AGA, and LGA) on growth, fertility, milk yield, and lifespan. SGA calves showed catch-up growth at six months but weighed significantly less at twelve months (p = 0.003). Age at first insemination and calving did not differ significantly, although SGA heifers required more inseminations (2.3 ± 1.50) compared to AGA and LGA heifers (1.7 ± 0.98 and 1.5 ± 0.89, respectively, p = 0.006). SGA calves tended to be culled more during the first lactation than AGA calves (25.0% vs. 11.9%, p = 0.078) and showed lower survival to second calving (p = 0.019) compared to AGA and LGA heifers. The Kaplan–Meier analysis indicated a tendency for gestational age to affect overall survival (p = 0.1), with SGA heifers having a higher risk of leaving the herd prematurely (p = 0.035, hazard ratio = 1.53). Milk yield per productive day was significantly lower in SGA heifers (21.2 ± 8.73 kg) compared to AGA and LGA heifers (26.9 ± 5.01 kg and 26.3 ± 3.38 kg, respectively, p = 0.006). This study reveals that HF calves born SGA suffer long-term consequences, although further research is needed to understand the economic impact of rearing SGA heifers. [ABSTRACT FROM AUTHOR]