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Effects of supplementing Holstein heifers with dietary melatonin during late gestation on growth and cardiovascular measurements of offspring
The objective was to examine the effects of supplementing dams with dietary melatonin during late gestation on offspring cardiovascular and growth measurements. On d 190 of gestation, heifers (n = 20) were blocked by BW and then randomly assigned to one of two dietary treatments: 1). 20 mg of dietary melatonin per day (MEL) or 2). no melatonin supplementation (CON). Dietary treatments were terminated on d 262 of gestation. At birth, calves were separated from their dams and given 3.8 L of colostrum. Calves were fed 5.7 L of whole milk daily and offered 0.9 kg/d of starter grain. Starter was increased by 0.9 kg/d when orts were 0 kg. Calf (n = 18) measurements of growth, blood pressure and cortisol were collected on wk 0, 1, 2, 3, and 4 of age. Calf hepatic portal blood flow, determined by transabdominal Doppler ultrasonography, and concentrations of insulin-like growth factor 1 were determined on wk 0 and 4 of age. Dependent variables were analyzed using repeated-measures ANOVA of the mixed procedure of SAS with the model statement containing treatment, age, and their respective interaction. Calf BW, abdominal girth, hip height, and wither height increased (P < 0.05) with age. An age by treatment interaction (P < 0.01) was observed for calf heart girth, which was decreased at wk 2 in calves from MEL treated heifers compared to calves from control treated heifers. Pulse pressure (41 ± 2 mmHg), mean arterial pressure (90 ± 2 mmHg), absolute hepatic portal blood flow (3,137 ± 326 mL/min), and blood flow relative to body weight (74 ± 8 mL/[min*kg]) were not different (P > 0.05) between treatments. A main effect of calf age (P < 0.05) was observed for concentrations of insulin-like growth factor 1, which was decreased at wk 4 (9.0 ± 0.4 ng/mL) compared to wk 0 (10.8 ± 0.9 ng/mL). An age by treatment interaction (P < 0.05) was observed for concentrations of cortisol, which was decreased at wk 2 in calves from MEL treated dams (1.2 ± 0.8 ng/mL) compared to calves from CON treated dams (5.8 ± 0.8 ng/mL). Early postnatal growth and hepatic portal blood flow were not different in offspring born to dams supplemented with dietary melatonin. However, the difference in offspring concentrations of cortisol following maternal melatonin supplementation needs further investigation.
Keywords: cortisol, hepatic portal blood flow, melatonin