The effect of biotin deficiency and dietary protein content on lipogenesis, gluconeogenesis and related enzyme activities in chick liver.

Chicks were given biotin-deficient diets containing either suboptimal (low) or supraoptimal (high) concentrations of protein from 1-d-old until they were used during their fourth week of life. The low-protein diet predisposed chicks to develop fatty liver and kidney syndrome and the high-protein diet to develop classical biotin deficiency signs. Two other groups, as controls, received biotin-supplemented rations. Low dietary protein increased lipogenesis by isolated hepatocytes but had little effect on gluconeogenesis compared to high dietary protein. Low dietary protein decreased activities of hepatic isocitrate dehydrogenase (EC 1.1.1.42), fructose-1,6-bisphosphatase (EC 3.1.3.11) and glucose-6-phosphatase (EC 3.1.3.9; GP) and increased activities of fatty acid synthase (FAS), citrate cleavage enzyme (EC 4.1.3.8; CCE) and malate dehydrogenase (decarboxylating) (EC 1.1.1.39). When biotin deficiency was superimposed, the rate of lipogenesis by isolated hepatocytes (from fed birds) was decreased. Gluconeogenesis from lactate and glycerol was also depressed. Activity of GP was further decreased by biotin deficiency on the low-protein regimen and FAS and CCE were further increased. PK activity was increased by biotin deficiency.

Aspects of metabolism related to the occurrence of skin lesions in biotin-deficient chicks.

1. Chicks were fed on biotin-deficient low- and high-protein diets supplemented with increasing concentrations of biotin. 2. Biotin deficiency decreased hepatic activity of pyruvate carboxylase [EC 6.4.1.1] but activity of acetyl-CoA carboxylase [EC 6.4.1.2] was comparatively unaffected. 3. Increasing dietary protein increased the severity of biotin deficiency as assessed by skin lesions and decreased plasma biotin concentrations. 4. The severity of the skin lesions over all the treatments was most closely related to plasma biotin concentration.

Blood pyruvate carboxylase activity as a criterion of biotin status in young pigs.

A basal diet containing isolated soybean protein was supplemented with 100 and 500 microgram biotin/kg and another basal diet containing hen-egg albumen was supplemented with 1300 microgram biotin/kg. The five diets were fed to groups of young pigs from four to 12 weeks old. Growth depression or skin or foot lesions characteristic of biotin deficiency were not seen but the undersurfaces of the hooves of pigs given the basal albumen diet were unusually soft. Blood pyruvate carboxylase activity showed a maximum response to dietary biotin at six weeks but by 12 weeks there was no response to supplemental levels greater than 100 microgram/kg. Plasma biotin concentration gave a good indication of biotin intake at all ages.

Blood pyruvate carboxylase (EC 6.4.1.1) activity as a criterion of biotin status in chickens and turkeys.

1. Blood pyruvate carboxylase (pyruvate-CO2 ligase (ADP-forming); EC 6.4.1.1; PC) activities in young chickens and turkeys given low-biotin diets supplemented with biotin at graded levels were studied in three experiments. 2. In both species PC activity was related positively to the supplemental biotin level. The relationship was sigmoid and maximum activity was attained with supplemental levels above those required to give maximal growth response. 3. Enzyme activity decreased between 2 and 4 weeks of age but remained almost constant thereafter. 4. Activity in chicks was not affected by alterations in the fat or protein content of the diet. 5. Changing poults from high to low and from low to high supplemental biotin levels resulted in reversals in the levels of enzyme activity. 6. It is concluded that blood PC activity is a promising new criterion for assessing the biotin status of young chickens and turkeys.

The involvement of biotin in preventing the fatty liver and kidney syndrome in chicks.

Three experiments were carried out to investigate the involvement of vitamins in the fatty liver and kidney syndrome. The compounds studied, singly and in combination, were thiamin, riboflavin, nicotinic acid, pyridoxine, pantothenic acid, biotin, folic acid vitamin B12, ascorbic acid, choline and inositol and of these, only biotin prevented the syndrome. The minimum levels of supplemental dietary biotin required to prevent mortality varied from 0-05 to 0-15 mg/kg, depending on the diet. These levels were higher than the amounts required for maximum liveweight.

The involvement of dietary fat and vitamins, stress, litter and starvation on the incidence of the fatty liver and kidney syndrome in chicks.

Dietary and environmental factors involved in the fatty liver and kidney syndrome (FLKS) were studied. Addition of maize oil, tallow or olive oil isoenergetically at the expense of starch to the standard highmortality diet reduced mortality from 19 to 7 per cent. Supplementation of the standard diet with a mixture of vitamins reduced mortality to 1 per cent whereas supplementation with thiamin alone reduced it to 11 per cent. Mortality was 53 per cent higher among females than males. At 25 days of age mortality was 94 per cent higher among birds that had been subjected to repeated stressing. Withdrawal of food on day 36 resulted in a marked increase in mortality.