Ostertagia ostertagi infection in the calf: effects of a trickle challenge on the hormonal control of digestive and metabolic function

Metabolic effects of a trickle challenge with the equivalent of 10,000 infective Ostertagia ostertagi larvae per day were investigated in 12 calves allocated to infected, pair-fed control or ad libitum-fed control groups. Changes in hormone levels reflecting abomasal, pituitary and pancreatic function were monitored using radioimmunoassay techniques previously validated for use in cattle. A range of metabolic profile parameters and blood metabolites was also measured. Feed intake of the infected calves began to decline as blood gastrin and pepsinogen levels reached a peak. The depression in appetite recorded in this group was responsible for significant increases in plasma urea and non-esterified fatty acid levels and associated with an increase in growth hormone/insulin ratio. No significant difference in glucagon levels was recorded between groups. A decline in blood albumin values was also shown in the infected group and associated with a drop in nitrogen digestibility. A significant depression in circulating calcium levels was related to either the hypoalbuminaemia or impaired mineral absorption in the intestine. A decrease in plasma cholesterol values in the infected group was associated with changes in digestive function.