Factors Influencing the Blood-sugar Level of Dairy Cattle

The sugar of the blood of dairy animals has been the subject of considerable investigation in its relation to milk secretion and disease. It is the precursor of the lactose of milk. Meigs (11)^ has presented a thorough review of the literature on this little-known phase of metabolism. There is good evidence to show that milk sugar is derived from the glucose of the blood, though the process by which the transformation takes place in the mammary gland remains obscure. In recent years the behavior of the blood sugar has been studied in dairy cattle under certain abnormal conditions. Several investigators have presented figuies on the normal concentration of this constituent. Hayden and ShoU (5) after 75 tests with 44 cows concluded that the average concentration of sugar in the blood of dairy cows is 51.75 milligrams per 100 cubic centimeters. Moussu and Moussu (9), working with only 10 cows of different breeds, gave a range of 0.061 to 0.08 per cent, while Hayden and Fish (^), as a result of 68 analyses, gave an average figm*e of 46.52 milligrams per 100 cubic centimeters with a range of 30 to 70 milhgrams. In a later and more extensive piece of work, Hayden (S) reported the low average of 41.15 milligrams of sugar per 100 cubic centimeters of blood for 253 samples taken from 23 cows over a period of 11 months. Scheicher (1^), in studying the ratio of blood sugar to lactose in dairy cattle, observed that the sugar concentration of the blood ranged between 0.055 and 0.10 per cent and averaged 0.0744 per cent, while Anderson and his associates (Í) in a recent investigation gave a range of 43.2 to 142.0 milligrams for animals of aU ages and an average of 51.2 milligrams for animals in the older group. It is evident from these results that the blood-sugar level of dairy animals, while tending toward a mean value somewhere near 50 milligrams per 100 cubic centimeters of blood, is subject to wide variations. The causes of these variations have not been discussed to any extent in articles reporting investigations in this field. Undoubtedly, however, they are due, in part, to the fact that the rate at which sugar enters the blood and the rate at which it leaves the blood vary under different conditions. The actual amount of sugar in the blood at any time depends on the relative intensity of these two opposing sets of conditions. Figuratively speaking, there are three streams of sugar supplying the blood. One enters from the intestines, another arises from the hydrolysis of gly cogen, and a third from the synthesis of sugar from