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<p>This study aimed to evaluate whether hormone and metabolite concentrations in blood vary according to time of day (a.m. vs. p.m.), milking and concentrate intake (before vs. after), and to describe the feeding behavior of dairy cows in pasture-based systems. Blood samples were collected from 14 pregnant lactating Holstein cows over three consecutive days at four time points: (1) and 3) morning and afternoon, respectively, 30 to 60&#xa0;min after leaving pasture and before milking, (2) and 4) morning and afternoon, respectively, 30 to 60&#xa0;min after concentrate intake and after milking. Plasma concentrations of progesterone (P4), cortisol, β-hydroxybutyrate (BHB), cholesterol, glucose, triiodothyronine (T3) and tetraiodothyronine (T4) varied significantly throughout the day (<i>p</i> &lt; 0.02). P4 and cortisol were highest after grazing and lowest after milking (<i>p</i> &lt; 0.0001). T3 concentrations were higher after afternoon milking (<i>p</i> = 0.0111), while T4 was lowest before morning milking (<i>p</i> = 0.0170). BHB peaked after afternoon milking (<i>p</i> &lt; 0.0001), cholesterol was highest after the morning concentrate (<i>p</i> = 0.0071) and glucose was lowest before afternoon milking (<i>p</i> = 0.0024). Cows spent more time grazing during the day than at night (31.37 vs. 15.55&#xa0;min/hour; <i>p</i> = 0.029), while rumination time did not change (<i>p</i> = 0.166). These findings provide new insights into daily variations of hormones and metabolites in pasture-based systems, which showed a behavioral profile characterized by spending most of the daytime grazing. Under these conditions, the study described for the first time how certain hormones, such as P4 and cortisol, are modified according to milking. These findings enhance our understanding of metabolic and endocrine responses in grazing dairy cows.</p>

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Diurnal changes in blood metabolite and hormone concentrations according to milking and feeding times in Holstein cows in pasture-based systems

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • M. C. Prieto,
  • J. P. Damián,
  • A. Félix,
  • A. Meikle,
  • V. de Brun

摘要

This study aimed to evaluate whether hormone and metabolite concentrations in blood vary according to time of day (a.m. vs. p.m.), milking and concentrate intake (before vs. after), and to describe the feeding behavior of dairy cows in pasture-based systems. Blood samples were collected from 14 pregnant lactating Holstein cows over three consecutive days at four time points: (1) and 3) morning and afternoon, respectively, 30 to 60 min after leaving pasture and before milking, (2) and 4) morning and afternoon, respectively, 30 to 60 min after concentrate intake and after milking. Plasma concentrations of progesterone (P4), cortisol, β-hydroxybutyrate (BHB), cholesterol, glucose, triiodothyronine (T3) and tetraiodothyronine (T4) varied significantly throughout the day (p < 0.02). P4 and cortisol were highest after grazing and lowest after milking (p < 0.0001). T3 concentrations were higher after afternoon milking (p = 0.0111), while T4 was lowest before morning milking (p = 0.0170). BHB peaked after afternoon milking (p < 0.0001), cholesterol was highest after the morning concentrate (p = 0.0071) and glucose was lowest before afternoon milking (p = 0.0024). Cows spent more time grazing during the day than at night (31.37 vs. 15.55 min/hour; p = 0.029), while rumination time did not change (p = 0.166). These findings provide new insights into daily variations of hormones and metabolites in pasture-based systems, which showed a behavioral profile characterized by spending most of the daytime grazing. Under these conditions, the study described for the first time how certain hormones, such as P4 and cortisol, are modified according to milking. These findings enhance our understanding of metabolic and endocrine responses in grazing dairy cows.