Blood plasma 3-methylhistidine, in comparison with other blood variables, has been measured in high-yielding dairy cows with relation to energy and protein supply. Circulating 3-methylhistidine markedly increased to 1 wk after calving, then continuously decreased to 5 wk postpartum to lower than during the last 2 wk of pregnancy. In experiments 36 d after calving, circulating 3-methylhistidine did not change during 24 h despite marked variations of food intake. Peak 3-methylhistidine immediately after parturition coincided with relatively low insulin, thyroxine, triiodothyronine, glucose, protein, and urea with elevated concentrations of nonesterified fatty acids and with greatest estimated energy and protein deficiencies. However, during the ensuing period to 12 wk of lactation, circulating 3-methylhistidine was not closely related to these measures nor to creatinine, beta-hydroxybutyrate, and milk production, but relationships to milk protein yield were close. The postparturient increase of 3-methylhistidine may have been a consequence of enhanced breakdown of skeletal muscle and uterine smooth muscle or another pool with a transiently enhanced turnover rate. Variations of plasma 3-methylhistidine were associated only in part with estimated negative energy and protein balances and corresponding endocrine and metabolic adaptations.

Summary To study metabolic and endocrine adaptation of dairy cows to energy deficiency, blood metabolites and hormones were measured 37 ± 3 days after parturition during 24 h (group LE) and compared to levels in cows receiving high amounts of starch (group HE) or crystalline fat (group CF). Energy balances were −40.1, −19.0 and +1.1 MJ net energy for lactation/day, and milk yield was 30.4, 31.0 and 29.3 kg/day in groups LE, HE and CF, respectively. Animals of group LE were characterized by the lowest mean levels of glucose, triglycerides, cholesterol, albumin, insulin, thyroxine, 3,5,3′‐triiodothyronine and norepinephrine, by highest levels of non‐esterified fatty acids, acetoacetate, β‐hydroxybutyrate and growth hormone, by considerable changes of glucose levels during the 24‐h period, a marked rise of NEFA during the night, but only a small rise of insulin in response to concentrate feeding. Group CF had the highest mean glucose, triglyceride, cholesterol, phospholipid and urea concentrations and the lowest growth hormone levels. Concentrations of non‐esterified fatty acids and urea were higher in group CF than in group HE. Lactate, protein, 3‐methylhistidine, glucagon, cortisol and epinephrine were not significantly affected by energy or fat intake. Metabolic and endocrine changes in group LE were typical for adaptation to energy deficiency. Feeding high amounts of starch, or crystalline fat led to elevated glucose levels, reduced fat mobilisation, and lowered ketogenesis. Zusammenfassung 24‐Stunden‐Muster der Blutkonzentration von Hormonen und Metaboliten bei Hochleistungskühen: Fütterungseffekte bedingt durch Verabreichung niedriger und hoher Mengen an Stärke und durch kristallines Fett Bei Kühen wurde die Anpassung von Stoffwechsel und endokrinen Systemen an ungenügende Energieversorgung 37 ± 3 Tage nach dem Abkalben untersucht durch Messung während 24 Stunden der Blutkonzentration verschiedener Metaboliten und Hormone (Gruppe LE) und die Veränderungen zum gleichen Zeitpunkt verglichen mit denjenigen von Kühen, welche relativ große Kraftfuttermengen (Gruppe HE) oder kristallines Fett erhielten (Gruppe CF). Die Energiebilanzen der Gruppen LE, HE und CF betrugen −40,1, −19,0 bzw. +1,1 MJ Nettoenergie für Laktation/Tag und die fettkorrigierten Milchleistungen 30,4, 31,0 bzw. 29,3 kg/Tag. Die Tiere der Gruppe LE waren charakterisiert durch die tiefsten Glucose‐, Triglycerid‐, Cholesterin‐, Albumin‐, Insulin‐, Thyroxin‐, 3,5,3′‐Triiodthyronin‐ und Noradrenalinkonzentrationen, die höchsten Konzentrationen nichtveresterter Fettsäuren (NEFA), von Acetoacetat, β‐Hydroxybutyrat und Wachstumshormon (GH), durch besonders starke Schwankungen der Glucosekonzentration im Verlaufe der 24‐Stunden‐Periode, einen massiven Anstieg der NEFA während der Nacht, aber einen nur geringen Anstieg der Insulinkonzentration nach Verabreichung von Kraftfutter. Bei der Gruppe CF wurden die höchsten Glucose‐, Triglycerid‐, Cholesterin‐, Phospholipid‐ und Harnstoffkonzentrationen und die tiefsten GH‐Konzentrationen gemessen. Bei der Gruppe ...

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