Sixteen New Zealand Holstein-Friesians (NZ HF) and 15 overseas HF (OS HF) grazing pasture or fed a total mixed ration (TMR) were subjected to an epinephrine challenge during early lactation. A genotype x diet interaction trend (P=0.10) was observed; when grazing, OS HF displayed the greatest glycerol response, with the reverse occurring on TMR. No genotype or diet differences were observed for the glycerol or non-esterified fatty acid response. Dairy cows of both genotypes fed TMR produced a glucose response 31% greater than both genotypes grazing pasture. These preliminary results suggest that genotype x diet-induced differences in the rate of lipolysis may occur in Holstein-Friesians during early lactation. These differences may be a function of small differences in energy balance. Feeding TMR was associated with a greater glucogenic response to epinephrine, which probably resulted from greater hepatic reserves of glycogen or simply a greater energy demand by the mammary gland.
Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 48-51, 2001
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