# Associations Between Milk Composition, Blood Metabolomics, and Systemic Physiological Indices in High- vs. Low-Yielding Guanzhong Dairy Goats During Early Lactation

## TL;DR

High-yielding Guanzhong dairy goats produce more milk by efficiently using nutrients and maintaining better health, as shown through blood and milk analysis.

## Contribution

Identifies metabolic and physiological strategies in high-yielding goats that enhance milk production while maintaining health.

## Key findings

- High-yielding goats have lower blood glucose and protein but higher antioxidants and immune markers.
- Serum metabolomics reveal enhanced fatty acid oxidation and amino acid allocation in high-yielding goats.
- Milk yield is negatively correlated with total protein and creatinine, but positively with certain antioxidants.

## Abstract

This study quantified milk yield divergence in Guanzhong dairy goats managed under identical early-lactation conditions. High-yielding animals produced more milk despite a slightly lower lactose percentage, resulting in greater daily lactose output. Their serum contained less total protein and glucose but higher concentrations of specific antioxidants and immune markers. Metabolomic screening further identified blood metabolites tightly linked to efficient energy utilization and milk synthesis. These findings unveil a physiological strategy whereby HY goats prioritize nutrient allocation to the mammary gland while sustaining superior health, offering metabolic benchmarks for genetic selection and precision feeding that simultaneously increase production and animal welfare.

This study aimed to elucidate the intrinsic regulatory mechanisms by comparing milk quality, blood metabolomics, and physiological indices between high-yielding (BH, n = 15, high milk yield, daily milk yield with 4.08 ± 0.17 kg) and low-yielding (BL, n = 15, low milk yield, daily milk yield with 2.54 ± 0.26 kg) Guanzhong dairy goats during early lactation. The results showed that the lactose content in the BH group was significantly lower than that in the BL group (p < 0.05), but the total daily lactose yield was 60 g higher. No significant differences were observed in milk fat or milk protein (p > 0.05). Among blood biochemical indices, total protein (TP), glucose (GLU), and alkaline phosphatase (ALP) were significantly lower in the BH group (p < 0.05), while β-hydroxybutyrate (BHBA) was significantly higher (p < 0.05). Milk yield exhibited a highly significant negative correlation with TP and creatinine (CRE). Regarding immune and antioxidant indices, catalase (CAT), glutathione peroxidase (GSH-Px), IgM, and IL-2 were significantly elevated in the BH group (p < 0.05), while IL-6 was significantly reduced (p < 0.05). CAT and IL-2 showed positive correlations with milk yield. Using a subset of animals for in-depth profiling (n = 6 per group)Serum metabolomics identified 184 differential metabolites (114 upregulated, 70 downregulated). In the BH group, betaine, acylcarnitines, and L-valine exhibited significant negative correlations with milk yield, implicating pathways related to fatty acid -oxidation, methyl donor regulation, and amino acid metabolism. These findings indicate that high-yielding dairy goats achieve efficient lactation through enhanced fatty acid β-oxidation, optimized methyl donor regulation for milk fat synthesis, and prioritized allocation of amino acids towards the mammary gland.