Technical note: Extrapolation of hepatic glycogen concentration of the whole organ by performing a liver biopsy

Glycogen, a complex polysaccharide, is the form of storage of glucose in mammals that can be released rapidly when needed. Recent studies have mainly reported hepatic glycogen concentration for early-lactating cows, when the energy demand is higher than the energy supply from dry matter intake, driving the cow to use the energy stored as hepatic glycogen. Generally, liver samples are obtained through percutaneous needle biopsies in the right lobe of the liver. Our objective was to analyze the variation of glycogen concentration in the livers of Holstein and Jersey cows among different liver locations representing all lobes, to evaluate whether samples obtained by liver biopsies are representative of the whole organ. Liver from 10 culled lactating cows (5 Holstein and 5 Jersey cows) from 30 to 113 mo of age at slaughter were obtained. Each liver was sampled no more than 3 h after death on the following sites: 3 sites in the right lobe (1 to 3), 2 in the diaphragmatic surface of the left lobe (4 and 5), 3 in the visceral surface of the left lobe (6 to 8), 1 in the quadrate lobe (9), and 1 in the caudate lobe (10). Samples were snap frozen in liquid N₂ and were then analyzed for glucose concentration after conversion of glycogen to glucose using amyloglucosidase (EC 3.2.1.3). Glycogen results are reported as grams of glucose per 100 g of wet weight of liver (i.e., percent of wet weight of liver). Liver weights averaged 5.1 [standard deviation (SD) 1.2, minimum 3.3, maximum 6.2] kg for Holstein and 6.0 (SD 1.8, minimum 4.7, maximum 8.9) kg for Jersey cows. Holstein cows [1.31, standard error of the mean (SEM) 0.05% of wet weight] had greater liver glycogen concentration than did Jersey cows (0.75, SEM 0.05% of wet weight). No significant difference was noted among the 10 liver locations regarding glycogen concentration and averaged, for both breeds, 1.03% of wet weight (SEM 0.10). These results suggest that, in dairy cows, percutaneous needle liver biopsy in the right lobe is an accurate technique to fairly extrapolate glycogen concentration of the whole organ.