Relationship between Holstein Friesian genetic contribution, milk yield, and disease incidence in F1 and F2 crossbred cattle

Crossbreeding with Holstein Friesian (HF) cattle has become a widely adopted strategy for improving dairy productivity in Bangladesh. However, limited information is available regarding the optimum level of HF genetic contribution that maximizes milk production while maintaining disease resilience in crossbred cattle under smallholder farming conditions. This study evaluated the relationship between HF blood percentage, lactation milk yield, and the incidence of common livestock diseases in F1 and F2 crossbred cattle. It was hypothesized that increasing HF genetic contribution would improve milk yield without significantly affecting the occurrence of major diseases. Data were collected from 1,694 crossbred cattle (847 F1 and 847 F2) maintained by marginal farmers across 27 districts of Bangladesh from May, 2022 to October, 2024. Animals were classified according to HF sire blood percentage. Lactation milk yield and the occurrence of Foot-and-Mouth Disease, Hemorrhagic Septicemia, mastitis, reproductive tract disorders, and dystocia were evaluated. One-way ANOVA, Kruskal–Wallis H test, and Pearson's Chi-square test were used to determine the effects of HF blood percentage on productive performance and disease incidence. HF blood percentage had a highly significant effect on lactation milk yield in both F1 and F2 generations (P < 0.001). Crossbred cattle with 93.75% HF blood consistently achieved the highest milk yield in both generations, whereas milk production generally declined with increasing local genetic inheritance. Breed upgradation speed also influenced productive performance, with fast and very fast upgradation producing higher mean lactation yields than normal and moderate upgradation. In contrast, no significant association was observed between HF blood percentage and the incidence of the investigated diseases (P = 0.614), indicating that disease occurrence was largely independent of genetic composition. HF genetic contribution improves milk production, whereas disease susceptibility is influenced primarily by non-genetic factors. Strategic crossbreeding and proper management are essential for sustainable dairy production. The findings support sustainable dairy breeding programmes that combine genetic improvement with effective management to enhance milk production while maintaining the adaptability of crossbred cattle.