The aim of the study was to establish the relationship between parametres included in the glucose tolerance test (GTT) of heifers aged 9-10 months and their subsequent milk yield and composition in lactation I. Used were 42 Holstein-Friesian heifers selected from the herd with a mean individual yield of 9600 kg milk/year with 4.32% fat and 3.44% protein. Over 24 hrs preceding the GTT the animals were offered only water and small amount of hay. After that time a “0” blood sample was withdrawn from each heifer and animals were infused intravenously with 40% water solution of glucose (the volume applied was equivalent to 1g glucose/kg W0.75). Then nine blood samples were withdrawn at 6 min intervals, and glucose and insulin contents of serum were determined.After calving, the heifers were maintained under uniform conditions and fed according to TMR system (INRA feeding standards) till the end of lactation I. Simple correlation coefficients were calculated between the area under the glucose and under insulin concentration curves (AGLUCC and AINSCC), ratio AGLUCC/AINSCC (GLIN combined index), maximum glucose concentration (GLUMAX) and maximum insulin concentration (INSMAX). Moreover, coefficients of regression were calculated of the GTT individual indicators on milk production traits and respective regression equations were derived. The GLIN index appeared to be the most suitable GTT parametre to predict future milk traits in dairy heifers. It can be anticipated that GTT may be employed in practical breeding work as an additional criterion of preliminary selection of heifers assigned for dairy herd replacement.
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