Nutritional Modulation of Metabolic–Endocrine Integration and Growth Performance in Tropical Dairy Heifers

This study evaluated short-term haematological, metabolic, endocrine, and growth responses to calcium-protected oil and cornmeal in tropical dairy heifers. We allocated 128 heifers to four dietary treatments (32 heifers per treatment): R1, 60% roughage + 40% concentrate; R2, R1 with 4% Ca-oil; R3, R1 with 4% cornmeal; and R4, R1 with 2% Ca-oil + 2% cornmeal. We assessed blood biomarkers at two monthly sampling points and analysed weekly growth longitudinally. We detected treatment differences in erythrocytes, haemoglobin, MCV, MCH, MCHC, RDW-CV, eosinophils, HDL cholesterol, total protein, and albumin (p < 0.05). We found no statistically detectable treatment effects for most leukocyte indices, energy metabolites, reproductive hormones, growth-related hormones, or cortisol. Body measurements increased over time (p < 0.001), and we detected a treatment × week interaction only for body length (p = 0.014). The combined diet was associated with the highest values for several erythrocyte and protein variables, but the design does not distinguish synergy from additive or dose effects. These results should therefore be interpreted as short-term associations requiring confirmation through fully specified repeated-measures analyses and longer-term functional outcomes.