[Circadian variations in the content of plasma constituants in the brood mare].

The study investigates the circadian variations in plasma constituents of heavy brood mares during different physiological states – pregnancy, lactation, and non-pregnant periods. Blood samples were taken throughout the day to evaluate levels of various metabolites. The prandial period (time around feeding) and dietary factors were notably influential on metabolite levels, indicating a relationship between nutrient intake and metabolic activity in these horses.

Study Design and Parameters

• Twenty-one heavy brood mares, in different physiological states – pregnant, lactating, or dry (non-pregnant), were the subjects of this study. They were fed with a diet rich in forage, containing varying levels of energy and nitrogen.
• The researchers conducted circadian blood profile sampling, taking seven samples at different times over a day, starting at 8 a.m., and ending at 8 a.m. the next day. The feeding of the animals was intentionally done at 8:30 a.m.
• The plasma constituents evaluated were glucose, non-esterified fatty acids, beta-hydroxybutyrate, acetate, alanine, and insulin (all energy metabolites), along with urea and total protein (nitrogen metabolites), and calcium, inorganic phosphorus and magnesium (mineral metabolites).

Results of the Study

• The prandial period (between 8 a.m. and 11 a.m.) showed an increase in glucose, insulin, and alanine while non-esterified fatty acids, acetate, and beta-hydroxybutyrate decreased.
• The glucose and insulin peaks were short-lived with the other constituents returning slowly to their pre-feed values. At night, the levels of acetate and beta-hydroxybutyrate were highest.
• Moderate increases in urea was observed during feeding. Protein concentration remained stable.
• Diet and physiological state influenced the levels of metabolites. High concentrate diets led to higher glucose and insulin peaks. Stable circadian variation of non-esterified fatty acids, beta-hydroxybutyrate, and acetate was observed in well-fed, non-pregnant mares. High forage diet led to higher acetate levels.
• Circadian mineral variations were higher during lactation than during pregnancy.

Correlation and Origins of Metabolite Variations

• There were significant correlations in the prandial variations between glucose and insulin, acetate and beta-hydroxybutyrate, beta-hydroxybutyrate and non-esterified fatty acids, and acetate and non-esterified fatty acids.
• Two main factors contributed to these variations: a very rapid digestion of concentrate leading to a glucose and insulin increase, and the volatile fatty acids from the hindgut that led to nocturnal peaks of acetate and beta-hydroxybutyrate.
• The study observed that a lipogenic phase after meal intake alternated with a lipolytic phase, which consistent with a reduction in non-esterified fatty acids, acetate, and beta-hydroxybutyrate post-feeding.