# Analysis of Behavioral, Growth and Metabolic Indicators in Suckling Calves Under Outdoor Winter Rearing Conditions Using Fuzzy Comprehensive Evaluation

## TL;DR

This study shows that Holstein calves raised outdoors in cold winter conditions can grow well and adapt without health issues, supported by a new method to assess cold stress.

## Contribution

A novel AHP-FCE cold stress evaluation system was developed to quantify cold stress in calves under outdoor winter conditions.

## Key findings

- Outdoor calves experienced mild cold stress but showed better long-term growth than indoor calves.
- Twenty differential metabolites linked to energy metabolism were identified in outdoor calves.
- No adverse health effects were observed in calves raised outdoors during the 60-day trial.

## Abstract

This study explored winter rearing for Holstein calves via a 60-day trial (indoor 5 °C vs. outdoor −5~−28 °C). An AHP-FCE cold stress evaluation system was established, identifying outdoor calves in “mild cold stress”. During the 60-day trial period, outdoor-housed calves exhibited superior long-term growth performance and adaptive behaviors, with no adverse health effects observed, and 20 differential metabolites associated with energy metabolism were identified. The research supports optimized winter outdoor rearing in cold regions.

This study aimed to scientifically assess cold stress in dairy calves and optimize winter rearing protocols. A combined approach of feeding trials, expert surveys, and multidimensional data analysis was used to evaluate the effects of outdoor (−5~−28 °C) and indoor (5 °C) environments on Holstein dairy calves. A 60-day controlled trial was conducted with 20 healthy 5-day-old calves. In parallel, an interdisciplinary panel of 20 experts and 8 farmers established a cold stress evaluation system via the analytic hierarchy process (AHP), with cold stress levels quantified through fuzzy comprehensive evaluation. Environmental (weight = 0.62), physiological (weight = 0.22), and behavioral (weight = 0.16) factors contributed differentially to cold stress assessment, with data showing that outdoor calves were under mild cold stress (maximum membership degree = 0.64). The temperature–humidity index (THI) showed significant correlations with multiple physiological and biochemical parameters. Generalized linear mixed model (GLMM) analysis confirmed that THI variation significantly influenced calf standing time, respiratory rate (RR), malondialdehyde (MDA) content, and total antioxidant capacity (T-AOC). In feeding trials, indoor calves exhibited marginally higher average daily gain and body weight in early stages, whereas outdoor calves demonstrated significantly better growth performance by day 60. The outdoor group displayed increased lying and defecation behaviors, along with reduced locomotor/standing time and respiratory frequency. No significant intergroup differences were observed in serum immune or antioxidant indicators. Metabolomic analysis identified 20 differentially expressed metabolites, indicating an enhancement in the activity of energy metabolism pathways in calves. This study establishes a quantitative methodology for cold stress evaluation, clarifies environment–physiology–behavior interactions, and provides a theoretical basis for winter calf management. The results confirm that outdoor cold exposure did not hinder calf growth without compromising health, offering scientific support for optimizing outdoor rearing strategies in cold regions.