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Objective of the study was the investigation of the intravenous glucose tolerance test in
young dairy bulls as an additional selection criterion in breeding value estimation. Response on glucose challenge in 541 bulls of the breed Deutsche Holstein within a defined period of 200 to 520 days of age on the basis of the intravenous glucose tolerance test is targeted on within this study. The time response course after glucose challenge was the basis for the creation of individual glucose curves.
All parameters glucose basal value; maximum glucose levels, maximum glucose increase; glucose area under the curve and glucose half-life fulfilled the criteria of normal distribution after logarithmic transformation. The fixed effects of each parameter were determined with the software program VCE (Groeneveld et al. 2010).
Subsequently the heritability coefficients of glucose tolerance test parameters were calculated with the program PEST (Groeneveld und Kovac 1990), adjusted by the effects of herd, year and season. Additionally the correlations between the progeny breeding values and the adjusted glucose tolerance test parameters were calculated.
Insulin sensitivity and glucose absorption capacity, as well as basal glucose levels, are, in terms of phenotypic peculiarities with regard to intravenous glucose tolerance test parameters, influenced by feed rations. In order to make intravenous glucose tolerance test comparisons it is necessary to determine and maintain standardized breeding conditions with standardized rations. The relationship between intravenous glucose tolerance test parameters and the offspring breeding values for functional useful life, reproduction and calving ease, is subjected to a high influence of environmental effects on both sides of the algorithm. There are no significant correlations between the progeny breeding values and the results of glucose tolerance tests.
Thus it is not possible to establish a statement on the proportion of the genetically determined metabolic capacity in the health and reproductiveness of progeny on the basis of progeny breeding values. The tested animals were divided in groups of bulls with high, low and medium mean glucose half-life. The progeny breeding values were compared between those groups. Here as well were no significant relations observed.
The least heritabilities were calculated for the parameters glucose basal value (h² = 0,19), maximum glucose level (h² = 0,14) and maximum glucose increase (h² = 0,12). Thus those parameters are not qualified as a additional breeding value information. The heritability of the parameters glucose are under the curve (h² = 0,43) and glucose half-life (h² = 0,4) is significantly higher.
The determined heritabilities indicate a medium genetic influence on the parameters of the intravenous glucose tolerance tests. The glucose half-life is the most meaningful glucose tolerance test parameter about the individual glucose homeostasis capacity.
In contrast to the slightly higher heritable glucose area under the curve there are only minor methodical and mathematical influences on the glucose half-life. Therefore the glucose half-life is the best suited parameter for the characterization of the genetically determined reaction on a glucose stimulus in the glucose tolerance test. So it could be shown that the glucose tolerance test in young bulls is suited as an additional selection criterion in breeding value estimation because of its genetically determination.
To clarify the question about a relation between glucose tolerance and animal welfare further investigations are necessary. By the collection of clinical data in a large daughter count according to a rule a statement could be made on the relation of the glucose elimination rate of the sires to metabolic disruptions of the progeny as well as reproductive and milk performance of the daughters.