The objectives of the first study were to determine metabolic and endocrine factors affecting suckling aggressiveness in newborn Brown Swiss and Holstein calves and to determine if differences exist in suckling aggressiveness between newborn Brown Swiss and Holstein calves. Fifteen Brown Swiss and fifteen Holstein cows and heifers were placed in a maternity barn approximately 0 to 4 d prior to their estimated delivery date. Upon delivery, blood samples were collected from calves at birth (mean sampling time was 25.00 y 15.77 minutes after umbilical cord rupture), pre-suckling (mean sampling time was 79.00 y 61.79 minutes after umbilical cord rupture), 5 minutes into suckling (mean sampling time was 9.00 y 6.22 minutes after the initiation of suckling) and 10 minutes into suckling (mean sampling time was 15.00 y 7.88 minutes after the initiation of suckling). Samples were later analyzed to determine glucose, non-esterified fatty acids, leptin, and ghrelin concentrations. Calves were fed 2 quarts of maternal colostrum and suckling aggressiveness scores were determined (1 - weakly, 2 - moderately, and 3 - aggressively). Breed differences between suckling aggressiveness scores were not apparent. There were no significant (P > 0.05) relationships between suckling aggressiveness and glucose, leptin, or ghrelin, suggesting that these constituents have no effect on suckling aggressiveness. However, calves that subsequently suckled weakly did have lower NEFA concentrations at birth and immediately prior to suckling (P < 0.05) than those that suckled more aggressively. There also tended (P < 0.10) to be low NEFA concentrations at birth and immediately prior to suckling in Brown Swiss calves that subsequently suckled weakly.

The objectives of the second study were to alter glucose levels by administering oral glucose or administering an injection of insulin and observe suckling aggressiveness in newborn calves. Nineteen Holstein cows and heifers were placed in a maternity barn approximately 0 to 4 d prior to their estimated delivery date. Nine of the nineteen Holsteins were heifers carrying Brown Swiss embryos. Initial blood samples were collected from within 3.25 y 1.52 minutes after umbilical cord rupture. Glucose (25 mg oral) and insulin (1 mL intramuscular injection) treatments were alternated by breed and administered within 5.35 y 2.72 minutes after umbilical cord rupture. A second blood sample was obtained within 57.85 y 3.17 min from the time the treatment was administered. Samples were later analyzed to determine glucose, non-esterified fatty acids, leptin, ghrelin, and glutamate concentrations. Calves were fed 2 quarts of colostrum replacer and suckling aggressiveness scores were given 1 - weakly, 2 - moderately, and 3 - aggressively. Brown Swiss calves suckled weakly (P < 0.05) when compared with Holstein calves. Non-esterified fatty acid, leptin, and ghrelin concentrations did not differ significantly (P > 0.05) between breeds, treatments, or suckling aggressiveness scores either at birth or post-treatment. Glucose concentrations did not differ significantly (P > 0.05) between breed, treatment, or suckling aggressiveness at birth and only differed significantly (P < 0.05) between glucose- and insulin-treated calves post-treatment. Glutamate concentrations were significantly (P < 0.05) different by breeds and treatments and tended (0.05 < P < 0.10) to be different by suckling aggressiveness scores in pre-treated calves. Breed differences were still apparent in post-treatment samples. Prior to treatment, Brown Swiss calves had lower concentrations of glutamate than Holstein calves and calves that subsequently suckled weakly had higher concentrations of glutamate than calves that subsequently suckled more aggressively.