Postprandial blood hormone and metabolite concentrations influenced by feeding frequency and feeding level in veal calves

This study hypothesized that increased feeding frequency (FF) decreases problems with glucose homeostasis seen at high feeding levels (FL) in heavy veal calves. Effects of FF and FL on hormone and metabolite concentrations were studied in 15 heavy veal calves fed once (FF1; at 12:00), twice (FF2; at 12:00 and 24:00) or four times daily (FF4; at 06:00, 12:00, 18:00 and 24:00). In period 1, all calves were fed at a low FL (FL(low); 1.5 x metabolizable energy requirements for maintenance, ME(m)). In period 2, FF2 and FF4 calves were fed at high FL (FL(high); 2.5 x ME(m)), whereas FF1 calves were still fed at FL(low). Blood was sampled every 30 min from 12:00 to 18:00 and postprandial integrated plasma hormone and metabolite concentrations (AUC(12-18 h)) were calculated. Glucose AUC(12-18 h) increased with increasing FL, but decreased with increasing FF, urea AUC(12-18 h) increased with increasing FL, whereas non-esterified fatty acid AUC(12-18 h) were unaffected by FL and FF. Insulin AUC(12-18 h) decreased with increasing FF and decreasing FL. Glucagon AUC(12-18 h) increased with increasing FL and FF. Growth hormone AUC(12-18 h) decreased, whereas insulin-like growth factor-1 and leptin AUC(12-18 h) increased with increasing FL. Mean thyroxine and 3,5,3'-triiodothyronine concentrations were modified by FF and FL. There were no FF x FL interactions, except for plasma glucose. In conclusion, postprandial hormone and metabolite responses were differentially affected by FF and (or) FL. Glucose and insulin concentrations were maximally increased at high FL and low FF. Hyperglycemia, glucosuria and excessive insulinemia were prevented by increasing FF and decreasing FL.     

Low-dietary protein intake induces problems with glucose homeostasis and results in hepatic steatosis in heavy milk-fed calves

We studied effects of protein intake at two protein-free energy intake levels on plasma glucose and insulin concentrations, urinary glucose excretion and on liver and intestinal fat content in milk-fed veal calves. Two experiments were performed at body weights (BW) of 80-160 kg (mean 120 kg; Exp. 1) and 160-240 kg (mean 200 kg; Exp. 2). In each experiment, 36 calves were allocated to one of six protein intake levels, at each of two energy intake levels. Digestible protein intakes ranged between 0.90 and 2.72 g nitrogen (N)/(kg BW(0.75) x d) in Exp. 1 and between 0.54 and 2.22 g N/(kg BW(0.75)x d) in Exp. 2. The two energy intake levels were kept constant on a protein-free basis and were 663 and 851 kJ/(kg BW(0.75) x d) in Exp. 1 and 564 and 752 kJ/(kg BW(0.75)x d) in Exp. 2. Blood samples were taken between 5 and 6h post-feeding at 14-d intervals until calves reached target BW, and liver fat mass was determined at slaughter. Urinary glucose excretion was quantified at 120 and 200 kg BW in Exps. 1 and 2, respectively. Increased protein-free energy intake increased plasma glucose concentrations and urinary glucose losses in 200 kg calves, but not in 120 kg calves. Increasing protein intake decreased plasma glucose, urinary glucose and plasma insulin in both experiments. Liver fat content decreased with increasing protein intake. In conclusion, long-term low-dietary protein intake increased hyperglycemia, hyperinsulinemia, glucosuria and hepatic steatosis in heavy milk-fed calves, likely associated with increased insulin resistance.     

Mammary arteriovenous differences of glucose, insulin, prolactin and IGF-I in lactating sows under different protein intake levels

Mammary uptake of nutrients is dependent on their availability in the circulation but the role of hormones in that process is not known. Arteriovenous differences (AVD) of glucose and key hormones across the mammary glands were therefore determined in sows fed varying levels of protein. Sixteen lactating sows (four/dietary treatment) were fed a 7.8, 13.0, 18.2 or 23.5% crude protein (CP) isocaloric diet throughout lactation and their litters were standardized to 11 pigs within 48 h of birth. The anterior main mammary vein and a carotid artery were cannulated on day 4+/-1 of lactation and blood samples were collected every 30 min over 6h on days 10, 14, 18 and 22 of lactation to measure glucose, insulin, IGF-I, and prolactin (PRL) concentrations. Amino acid data from these sows were previously published and used here to determine residual correlations. Dietary treatments had no effect on any of the insulin or PRL variables measured (P>0.1) and, on day 18 only, IGF-I AVD was greater (P=0.05) for sows on the 23.5% compared to the 18.2% diet. On days 18 and 22, sows fed the 13% CP diet had greater arterial, venous and AVD glucose concentrations than sows fed other diets (P<0.05). Total arterial amino acid concentrations were correlated to arterial insulin (P<0.001) and PRL (P<0.05) concentrations, but not to those of IGF-I (P>0.1). Mammary AVD for total (P<0.001) and essential amino acids (P<0.05) were correlated to arterial concentrations of insulin, but not to those of IGF-I (P>0.1) or PRL (P>0.1). Mammary AVD of both total (P<0.01) and essential (P<0.05) amino acids were also correlated to mammary PRL AVD. In conclusion, dietary protein level did not affect mammary AVD and circulating lactogenic hormone concentrations. Yet, amino acid utilization by the sow mammary gland seems to be regulated via both circulating insulin concentrations and PRL binding to and uptake by porcine mammary cells.