The effect of giving Maillard reaction products (MRP) on zinc metabolism was investigated in the rat. In Expt 1, MRP were prepared by incubating casein with either glucose or lactose under controlled reaction conditions, and were quantified as either ‘early’ or ‘advanced’ after estimation of lysine loss and lysine destruction respectively. In Expt 2, the effect of the purified early MRP fructose–lysine (FL) on Zn metabolism was studied. The experimental diets containing 20 mg Zn/kg were given to weanling rats for 21 d. Zn balance was assessed over 9–14 d (Expt 1), or 1–14 d (Expt 2). Femur, liver, kidney and serum Zn concentrations were determined at 21 d. The major effect of the MRP in the casein-sugar mixtures was on urinary Zn excretion. The casein-glucose MRP induced up to a 6-fold increase in the quantity of Zn excreted in the urine. The magnitude of the hyperzincuria increased with the extent of the Maillard reaction. Similar dietary levels of casein-lactose MRP increased urinary Zn loss 2-fold. Free FL had no effect on urinary Zn. Faecal Zn, Zn retention, liver, femur and serum Zn were generally not influenced by giving MRP from casein-sugar mixtures or by giving free FL, although kidney Zn was decreased in rats fed on FL. It was concluded that although urinary Zn excretion can be increased by the presence of MRP in the diet, this is only a minor excretory pathway and would have little influence on overall Zn nutrition in individuals fed on a diet adequate in Zn.

Sixteen pigs were given a purified diet of maize flour and casein from 5 to 25 d of age with or without a biotin supplement (100 μg/kg). From 26 to 94 d of age, eight of the pigs were changed to a wheat and casein diet with or without the biotin supplement and eight continued on the maize flour and casein diet. The weight gain and feed conversion ratio of the pigs were not affected by the dietary biotin supplement or the carbohydrate source. The pigs given the unsupplemented maize flour diet developed foot lesions, scaly skins and showed a reduction in carcass length. The excretion of biotin in the faeces was similar for the pigs given the biotin-supplemented and unsupplemented diets. The excretion of biotin in the faeces of pigs given the wheat diet was ten times as great as that of the pigs given the maize flour diet. The excretion of biotin in urine was 6 μg/d in the pigs given the unsupplemented maize flour diet and 67 μg/d in the pigs given the biotin-supplemented diet between 91 and 94 d of age. The biotin contents of the liver, heart, kidney, adrenals and plasma were increased by biotin supplementation of the maize flour diet. The 16:1/16:0 and 18:1/18:0 fatty acids ratios in the liver were decreased by biotin supplementation of the maize flour diet.

Twenty pigs weaned at 5 d were given pelleted diets based on maize flour and casein and supplemented with 0,50,100,150 or 200 μg biotin/kg diet. The performance of the pigs was not influenced by the biotin content of the diets. Typical biotin deficiency symptoms (foot lesions and skin pustules) were observed in pigs given the unsupplemented diet and the diet supplemented with 50 μg biotin/kg diet. Tissue biotin concentration plateaued when 100 μg biotin/kg was added to the diet. Faecal biotin excretion was independent of dietary biotin intake, but increased with age. Urine biotin excretion at 102 d was significantly lower for the unsupplemented pigs than for the pigs given various levels of dietary biotin supplements. A dietary requirement of biotin for young pigs between 50 and 100 μg/kg diet is suggested from the results of the present experiment.

Eight pigs were given a semi-purified diet based on maize flour and casein containing 10 μg biotin/kg. The diet was given ad lib. with or without a supplement of 70 μg biotin/kg diet from 5 to 94 d of age. The flow of biotin in the stomach was similar to the biotin intake (13.5 and 112 μg/d) for the unsupplemented and biotin-supplemented pigs respectively. The flow of biotin through the small intestine decreased for the biotin-supplemented pigs from 39 μg/d in the first quarter of the small intestine to 7.9 μg/d in the last quarter. The flows of biotin in the caecum, large intestine and colon were similar for both the unsupplemented and biotin-supplemented pigs, with values of 17–54 μg/d, indicating the synthesis of biotin in the hind-gut.

Six pigs (initial weight 30 kg) were fitted with T-shaped cannulas in the ileum, 0.3 m from the ileocaecal junction. Each pig was given each of seven diets for a 10 d period. The diets contained wheat (var. Banks and Egret), barley, sorghum, meat meal, soya-bean meal or casein as test feedstuffs. The apparent digestibilities of biotin to the ileum of the pigs were 0.06, -0.03, -1.23, 0.18, 0.82, 0.12 and 0.95 for the diets containing wheat (var. Banks), wheat (var. Egret), sorghum, barley, meat meal, soya-bean meal and casein respectively. The same diets were given to 168 chickens. Digesta were collected from the terminal ileum after 7 d. The apparent digestibilities of biotin to the ileum of the chickens were 0.11, −0.10, −0.73, 0.05, 0.69, 0.28 and 0.75 for the diets containing wheat (var. Banks), wheat (var. Egret), sorghum, barley, meat meal, soya-bean meal and casein respectively.

Six pigs were given a biotin-deficient diet (10 μg biotin/kg) for 14 weeks. The pigs were given the same diet for a further 42 d with one of three biotin treatments: no supplement, 400 μg biotin/d given orally, 400 μg biotin/d infused into the caecum. The concentrations of biotin in the liver, kidney and heart, at the conclusion of 42 d were greater in the pigs given the oral biotin supplement than in the unsupplemented pigs. The values for the pigs given the caecal infusion of biotin were intermediate. The excretion of biotin in faeces was increased from 35 to 101 μg/d by the caecal biotin infusion, and the urinary excretion was increased from 35 to 83 μg/d. The oral dose of biotin increased urinary biotin excretion from 35 to 345 μg/d, but there was no change in faecal biotin excretion. Two pigs were fitted with ileal cannulas and catheters in the vena cava. The pigs were given a dose of [14C] biotin either into the caecum, when the ileum was occluded by a bladder catheter, or orally. [14C] biotin was measured in the urine and plasma and showed that post-ileal biotin absorption was 8 % as efficient as the absorption of biotin after oral dosing.