Associations of insulin resistance with calving difficulty and birth weight of offspring in late pregnant beef cows

Insulin resistance increases during late pregnancy in cows due to foetal and placental development; however, its relationship with dystocia remains unclear. This study aimed to elucidate the association between insulin-resistance-related markers during late pregnancy and both calf birth weight and the incidence of dystocia in beef cows. Blood samples were collected from 45 pregnant Japanese Black cows between 229 and 285 days of gestation, and calving status was recorded. Calf birth weights and serum concentrations of glucose, insulin, non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), pregnancy-associated glycoproteins, and oestrone sulphate were measured. Indices of insulin resistance-HOMA-IR (HR), revised quantitative insulin sensitivity check index (RQUICKI; RQ), revised quantitative insulin sensitivity check Index-β-hydroxybutyrate (RQUICKIBHB; RQBHB), and the glucose-to-insulin ratio (G:I) were calculated. The area under the curve (AUC) for each marker and its correlation with birth weight were analysed. Results were compared between cows with eutocia (n = 29) and dystocia (n = 16). The dystocia group showed a significantly lower AUC for insulin during the first half of late pregnancy, but higher AUCs for RQ and G:I (both P < 0.05). Additionally, NEFA AUC was significantly higher in the dystocia group in the second half of late pregnancy (P < 0.05). These findings suggest that lower insulin levels and higher RQ and G:I in the first half, along with elevated NEFA levels in the second half of late pregnancy, may serve as potential biomarkers for assessing the risk of dystocia in pregnant beef cows.