Influence of Age and Body Weight on Supramammary Lymph Node Morphology and Weight in Holstein Dairy Cows.

This study aimed to investigate the morphological characteristics and weight of supramammary lymph nodes (SMLNs) in Holstein dairy cows and to evaluate the effects of age and body weight (BW) on these parameters. A total of 19 cows (aged 2-9 years) culled due to reproductive failure (including repeated insemination failure, confirmed open status, or abortion) were divided into 3 groups: high-age (H, ≥6 years, n = 6), middle-age (M, 3-5 years, n = 6), and low-age (L, 2 years, n = 7). Results demonstrated that the weight of SMLNs generally increased with age, although lower values were observed in the limited number of cows older than 7 years. The length and width of SMLNs observed here were markedly larger than those reported in previous ultrasonographic studies. The H group had significantly heavier left, right, and bilateral SMLNs compared to the L group (p < 0.01). The M group exhibited significantly higher BW than the L group (p < 0.01). Correlation analysis revealed a significant positive association between BW and right SMLN weight in the L group (r = 0.774, p < 0.05), and a strong bilateral concordance in SMLN weight across all cows (r = 0.859, p < 0.001). These preliminary findings suggest that SMLN morphology and weight are associated with age and BW, although larger prospective studies with complete health and lactation records are needed to confirm these relationships.