Jeannette Klüß

Plasma insulin, glucose and amino acids responses to duodenal infusion of leucine in dairy cows

Carbohydrates are not the only macronutrients triggering insulin release following food intake. Besides other components, leucine (Leu) has been demonstrated to induce insulin secretion in humans and in laboratory rodents. We hypothesized that Leu stimulates the release of insulin in dairy cows, and thus our objective was to test the effects of a single-dose of Leu infused intraduodenally on the concentrations of insulin, glucose and free amino acids (AA) in blood plasma as compared to infusions with either glucose or saline. Six duodenum-fistulated Holstein cows were studied in a replicated 3 × 3 Latin square design with 3 periods of 7 d, in which the treatments were applied at the end of each period. The treatments were duodenal bolus infusions of Leu (DIL; 0.15 g/kg BW), glucose (DIG; at Leu equimolar dosage) or saline (SAL). Blood samples were taken at -15, 0, 10, 20, 30, 40, 50, 60, 75, 90, 120, 180, 210, 240 and 300 min relative to the infusion and the concentrations of insulin, glucose and AA were determined in plasma. In DIG, insulin and glucose concentrations peaked at 30-40 and 40-50 min after the infusion, respectively. Insulin concentrations were greater (P<0.05) from 30-50 min in DIG than DIL and SAL. In DIG, glucose concentrations were greater (P≤0.01) from 30-75 and 40-50 min than in DIL and SAL, respectively. In DIL, Leu concentrations peaked 50-60 min after infusion, reaching 20 and 15-fold greater values than that in DIG and SAL, respectively. The plasma concentrations of total AA minus Leu were affected by treatment (P<0.0001), resulting in lowest mean concentrations of total AA minus Leu in DIL, followed by DIG and SAL. The data suggest that Leu infusion did not elicit an apparent insulin response, but may stimulate the tissue uptake of AA by mechanisms yet to be elucidated.Breeding goals of Holstein dairy cattle in New Zealand (NZL) focus on traits reflecting adaptation to pasture-based systems. Due to high prices for concentrates, and advantages for cattle health and welfare, low input grazing systems become important in regions of North-West Germany. The present study addresses the hypothesis that progeny of NZL-Holstein sires are superior in 30 German grassland farms compared to offspring of Holstein sires being progeny tested in German indoor systems. A research design was implemented to create three different genetic groups (F1 generation) within herds on the basis of a German Holstein cow (GHC) population: Group 1=GHC x NZL sires, group 2=GHC x GH sires, group 3=GHC x GH_pasture sires. GH_pasture sires represent bulls of German origin with high breeding values for the traits being important in NZL. Group comparison focused on the full set of production and functional traits from official recording systems, and in addition on further novel traits reflecting cow health and welfare: Scores for body condition (BCS), locomotion (LOCS), hock lesions (HLS), and total hygiene (THS). Linear and generalized linear mixed models were applied to estimate group differences for a longitudinal data structure (2998 observations). In parity 1, daughters of NZL sires had the highest LSMean for BCS (2.56), and lowest LSMean for LOCS (0.10), HLS (0.25) and THS (3.67), reflecting an enhanced robustness of HF strains from NZL. Within breed genetic analyses simultaneously considering all genetic groups revealed a moderate genetic background with the following heritabilities: BCS (0.25), LOCS (0.12), HLS (0.04), and THS (0.17). Genotype by environment interactions between pasture-based and indoor systems were studied by applying multiple trait models. For all traits, rg were smaller than 0.80, especially indicating GxE interactions for low heritability functional traits.