The effect of birth weight on passive immunity transfer in kangal breed lambs

Abstract

Objectives: This study evaluates the influence of birth weight on the passive transfer of immunity (PTI) in Kangal breed lambs, a robust and economically significant Turkish sheep breed. Materials and Methods: A cohort of 38 healthy neonatal lambs was assessed to elucidate the associations between birth weight and key indicators of PTI, including serum Optical Brix percentage, total protein (TP) concentration, and gamma-glutamyl transferase (GGT) enzyme activity. Blood samples were collected 48– 72 hours postpartum and analyzed using cost-efficient and field-applicable methods such as refractometry, automated TP quantification, and enzymatic assays. Results: The findings demonstrated that lambs with birth weights below 4.53 kg exhibited significantly reduced serum Brix percentages (P=0.003), TP concentrations (P=0.002), and GGT activity levels (P=0.028), indicative of compromised colostral immunoglobulin absorption. Receiver operating characteristic (ROC) analysis identified 4.53 kg as the critical threshold for adequate PTI, with the discriminatory performance primarily supported by TP and GGT ROC analyses, while optical Brix refractometry showed supportive but comparatively weaker discriminatory capacity. Birth weight exhibited a moderate to strong positive correlation with TP (R=0.351) and GGT (R=0.471) concentrations, whereas Brix refractometry showed a strong correlation with TP (R=0.880), indicating good diagnostic agreement. These findings highlight the importance of considering breed-specific PTI thresholds, particularly in breeds such as the Kangal, which are characterized by relatively higher mean birth weights. Conclusions: In circumstances where direct measurement of immunoglobulin G (IgG) is not feasible, indirect indicators such as Brix refractometry, total protein (TP), and GGT measurements may serve as practical, field-applicable, and economically accessible approaches for evaluating passive transfer under field conditions. Ensuring timely and adequate colostrum intake in lambs below the identified threshold (<4.53 kg) are imperative for mitigating immunological deficits and enhancing neonatal survival outcomes in Kangal sheep husbandry.