Retinol homeostasis in lambs given low and high intakes of vitamin A

Effect of the maternal feeding on the carotenoid and tocopherol content of suckling lamb tissues

The objectives of the present study were to quantify the deposition of carotenoids and tocopherols in the tissues of suckling lamb and to use the levels of those compounds to trace the maternal feeding. Twenty suckling lambs were raised with their dams in vegetative-stage pastures, and 19 suckling lambs were stalled indoors with dams that received hay ad libitum, until the lambs reached 10-12 kg. The lambs' weekly intake of carotenoids and tocopherols was estimated from the milk production of the ewes and the carotenoid and tocopherol content of the milk. Samples of the subcutaneous and perirenal fat, longissimus thoracis muscle, and liver of the suckling lambs were collected at 24 h after slaughter. The pasture-raised lambs had greater intake of lutein than their indoor counterparts throughout the suckling period (p < 0.05), more retinol during the second and third weeks of the suckling period (p < 0.05), and more α-tocopherol during the first three weeks of the suckling period (p < 0.05), being similar thereafter. The pasture-raised lambs, when compared to the lambs raised indoors, had greater lutein content in the muscle and liver (p < 0.001), retinol and α-tocopherol content in all tissues (p < 0.001) and muscle and liver γ-tocopherol content (p < 0.05). The maternal feeding could be accurately predicted from the carotenoid and tocopherol content of whole lamb carcasses and muscle tissue but not from those of ewes' milk, lamb liver tissue or lamb fat deposits.

Simultaneous determination of carotenoids, tocopherols, retinol and cholesterol in ovine lyophilised samples of milk, meat, and liver and in unprocessed/raw samples of fat

An accurate, fast, economic and simple method to determine carotenoids, tocopherols, retinol and cholesterol in lyophilised samples of ovine milk, muscle and liver and raw samples of fat, which are difficult to lyophilise, is sought. Those analytes have been studied in animal tissues to trace forage feeding and unhealthy contents. The sample treatment consisted of mild overnight saponification, liquid-liquid extraction, evaporation with vacuum evaporator and redissolution. The quantification of the different analytes was performed by the use of ultra-high performance liquid chromatography with diode-array detector for carotenoids, retinol and cholesterol and fluorescence detector for tocopherols. The retention times of the analytes were short and the resolution between analytes was very high. The limits of detection and quantification were very low. This method is suitable for all the matrices and analytes and could be adapted to other animal species with minor changes.

Single High-Dose Vitamin A Supplementation to Neonatal Piglets Results in a Transient Dose Response in Extrahepatic Organs and Sustained Increases in Liver Stores

Background: Neonatal vitamin A (VA) supplementation is being evaluated as a public health policy for preventing infant mortality, but inconsistencies in mortality trials demand mechanistic work to determine biological plausibility.Objectives: We investigated the absorption, distribution, and storage of single large oral VA doses administered shortly after birth.Methods: Fifty pregnant sows (Sus scrofas domesticas) were fed a VA-free diet. Male and female newborn piglets (n = 313) were orally administered 0, 25,000, 50,000, or 200,000 IU VA in oil within 12 h of birth when mean ± SD weight was 1.56 ± 0.25 kg. Blood was drawn to determine absorption and storage 0.5-240 h after administration. Metabolic and postnatal dose-timing substudies were performed. Liver, lung, kidney, spleen, and adrenal VA concentrations were determined 7-240 h after administration.Results: Serum retinol and retinyl ester concentrations responded to treatment (P < 0.0001); however, differences between groups disappeared by 96 h. Liver VA concentrations responded to treatment (P < 0.0001), which persisted for 240 h. Liver VA for control piglets at 10 d (mean ± SD: 0.05 ± 0.02 μmol/g) was ≤0.1 μmol/g (deficiency), whereas groups that received VA maintained concentrations >0.1 μmol/g. Extrahepatic tissue VA concentrations displayed treatment effects (P ≤ 0.0077); groups that received treatments had higher VA concentrations than controls at early time points. Lung, kidney, and spleen VA did not differ between groups by 96 h, whereas adrenal glands did not differ by 240 h. Body weight was affected by treatment (P = 0.0002); VA-deficient piglets weighed 23-29% more than all treated groups 240 h after administration.Conclusions: A high dose of VA administered to newborn piglets was well absorbed, appeared in serum primarily as retinyl esters, and was taken up dose-dependently in all tissues studied; however, enhancement did not persist in sera, lungs, kidneys, spleens, or adrenal glands. Short-term impacts of retinoid signaling on weight gain remain to be elucidated, and longer follow-up studies are needed.

Late administration of antenatal vitamin A promotes pulmonary structural maturation and improves ventilation in the lamb model of congenital diaphragmatic hernia

PURPOSE

The lungs in congenital diaphragmatic hernia (CDH) are hypoplastic and immature making respiratory support one of the most challenging aspects of caring for these neonates. Vitamin A is essential for normal lung growth and development. It also promotes alveolarization. The aim of this study is to investigate the effects of antenatal vitamin A on lung growth and alveolarization and ventilation in the lamb model of CDH.

METHODS

This study was approved by the Animal Care Committee of the State University of New York at Buffalo, and conforms to the National Institute of Health guidelines. Diaphragmatic defects were created at 79-81 days gestation. Group 1 lambs (CDH, n = 5) were untreated. In group 2 (CDH + vitamin A, n = 6) and group 3 lambs (control + vitamin A, n = 3) right jugular venous catheters were inserted at 118-120 days and retinyl palmitate (vitamin A) was administered until 135 days. The control group (n = 5) consisted of twin littermates. Lambs were delivered at 136-139 days and ventilated for 2 h according to a set protocol. The left lungs were harvested and fixed for histology.

RESULTS

Lung compliance was significantly higher in CDH + vitamin A (median 0.27, range 0.1-0.48 ml/cmH(2)O/kg) versus CDH lambs (median 0.07, range 0.07-0.18 ml/cmH(2)O/kg), P < 0.05. At 1 h CDH + vitamin A lambs experienced significantly lower PaCO(2) (median 115, range 35-194 mmHg vs. median 192, range 168-234 mmHg) and higher arterial pH (median 7.0, range 6.74-7.35 vs. median 6.73, range 6.5-6.81) than CDH lambs, P < 0.05. The lung weight to body weight ratio of CDH + vitamin A lambs was significantly less than that of CDH lambs (P < 0.05). Histology showed small thick walled air-spaces and no true alveoli in CDH lambs. In contrast, true alveoli and thinning of the inter-alveolar septums were seen in CDH + vitamin A lambs.

CONCLUSION

This is the first study to demonstrate an improvement in lung function and structural maturation when antenatal vitamin A is given in a surgical model of CDH.

Dietary vitamin A modulates the concentrations of RRR-alpha-tocopherol in plasma lipoproteins from calves fed milk replacer

The practice of supplementing milk replacers fed to neonatal calves with high concentrations of vitamin A has raised concerns regarding the effect of excess vitamin A on the bioavailability of vitamin E. A 4 x 2 factorial experiment evaluated the effects of four dietary amounts of vitamin A [0, 1.78 [National Research Council (NRC)(6) requirement, control], 35.6 and 71.2 micromol daily as retinyl acetate] and two forms of vitamin E (RRR-alpha-tocopherol and RRR-alpha-tocopheryl acetate, 155 micromol daily) on plasma RRR-alpha-tocopherol and RRR-gamma-tocopherol and RRR-alpha-tocopherol associated with plasma lipoproteins (Lp) from milk replacer-fed Holstein calves from birth to 28 d of age. The VLDL, LDL, HDL and very high-density lipoprotein (VHDL) fractions were separated by ultracentrifugal flotation, and the amount of vitamin E associated with each fraction was determined by normal-phase HPLC. The amount and distribution of RRR-alpha-tocopherol in Lp fractions were unaffected by the form of dietary vitamin E. Plasma and Lp RRR-alpha-tocopherol concentrations increased with age (P < 0.0001) and were maximal at 28 d of age. Concentrations of RRR-alpha-tocopherol associated with Lp were 25% (P < 0.01) to 39% (P < 0.0001) lower in calves fed 35.6 and 71.2 micromol of vitamin A daily than in control calves at 28 d of age. The RRR-gamma-tocopherol concentrations were unaffected by dietary vitamin A (P >/= 0.05). In conclusion, dietary vitamin A modulated the amount and distribution of RRR-alpha-tocopherol in the circulation of milk replacer-fed neonatal calves. Because of the essential antioxidant role of vitamin E, the health-related consequences associated with the depression of the LP RRR-alpha-tocopherol concentrations in calves fed vitamin A at 35.6 and 71.2 micromol need to be investigated.

Fat-soluble vitamin nutrition for dairy cattle

The need for supplementation of dairy cow diets with fat-soluble vitamins depends on the amount of vitamins naturally present in the diet, the availability of dietary vitamins, and the vitamin utilization rate of the animal. Fresh forage contains ample amounts of the vitamin A precursor beta-carotene as well as vitamin E. Irrespective of the dietary amount, however, the availability of vitamins A, D, and E, as well as beta-carotene, can be adversely influenced by poor fat digestion, as commonly occurs due to enteric disease in young calves. In addition, high-grain diets appear to increase the amount of ruminal vitamin destruction and may thus increase vitamin requirements. The vitamin utilization rate may be increased by inflammation as well as dietary and environmental factors. The factors influencing vitamin availability and utilization rate should be considered when formulating rations. Because the vitamin requirement is variable, blood concentrations of vitamins should be monitored when conditions such as poor fertility, weak calves, and poor immune response are present.

[The vitamin A requirement and the vitamin A status of growing cattle. 2. Studies of fattening cattle]

Three long time individual feeding experiments (greater than 258 days) with 48 beef cattle each (dairy breed and beef breed, 50% each) were carried out in order to measure the influence of various vitamin A supply (0, 2,500, 5,000 and 10,000 IU vitamin A per 100 kg body weight and day) on fattening and slaughtering performance, vitamin A concentration of liver and serum as well as carotene concentration of serum. The bulls consumed corn silage (experiments 1 and 2; 9.4 and 18.3 mg carotene per kg dry matter) or NaOH-treated and pelleted straw (experiment 3; no carotene). The roughages were supplemented with 2 (exp. 1 and 2) and 3 kg (exp. 3) concentrate per day. The vitamin A supply of corn silage diet did not significantly influence the dry matter intake (exp. 1: means: 6.95; 6.91 to 7.05; exp. 2: means: 6.54; 6.53 to 6.54 kg dry matter per animal and day) and the daily weight gain of bulls (exp. 1: means: 1076; 1028 to 1157; exp. 2: means: 1058; 1041 to 1057 g per animal). The bulls consumed 8.87 kg dry matter per day, the daily weight gain amounted to 1030 g per animal and day in experiment 3. The bulls of unsupplemented group reduced feed intake and weight gain after 150 days, an additional vitamin A supply was necessary. At the end of experiments 1 and 2 the liver vitamin A concentration of unsupplemented groups amounted to 38.8 and 65.9 mumol/kg, it increased after vitamin A supply (up to 153.4 mumol/kg). Feeding of pelleted straw effected a liver vitamin A concentration lower than 10 mumol/kg except the group supplemented with 10,000 IU vitamin A per 100 kg body weight and day (35.7 mumol per kg fresh matter of liver). The vitamin A concentration of blood is unsuitable for evaluation of vitamin A status of cattle. The carotene content of feeds and level of vitamin A supply determined the carotene concentration of blood. Recommendations for a suitable vitamin A supply of ration of growing cattle were given depending on body weight and type of diet.

[The vitamin A requirement and the vitamin A status of growing cattle. 1. Studies of calves]

Five experiments with 18 to 36 male calves each of the black and white dairy cattle breed (age: 14-21 days, initial live weight: approximately 45 kg per animal) were carried out in order to investigate the influence of various vitamin A supply (0-80,000 IU per 100 kg LW and day) on dry matter intake and weight gain as well as the vitamin A status of liver and blood plasma over 84 days. The calves consumed a diet free of carotene and vitamin A consisting of milk replacer, concentrate and chopped wheat straw. The calves were fed in three experiments for a longer time in order to observe the further vitamin A depletion. Nine animals consumed an unsupplemented ration, nine other one got 10,000 IU vitamin A per 100 kg LW and day. Biopsies of liver and plasma samples were taken from 4 animals per group every four weeks. The various vitamin A supplementation did not significantly influence the dry matter intake (Mean: 1.67; 1.48 to 1.80 kg DM per animal and day) and the weight gain of calves (Mean: 702, 599 to 770 g per animal and day). First vitamin A deficiency symptoms (reduced feed intake, decreased weight gain, diarrhoea etc.) were observed in animals of unsupplemented group after 100 days of experiments. After 84 days the vitamin A concentration of liver of animals of unsupplemented groups decreased to 1.3-32.2% compared with the begin of experiments (60.6-155.7 mumol/kg fresh matter). Up to 51% of initial concentration were found when 10,000 IU vitamin A per 100 kg LW and day were fed. About 25,000 IU vitamin A per 100 kg LW and day were required in order to keep the initial level of vitamin A concentration of liver. The plasma vitamin A concentration is unsuitable for estimation of vitamin A status of calves. The concentration of vitamin A of liver and plasma amounted to 114 mumol per kg and 0.25 mumol per litre at the begin of experiments. The vitamin A concentration of liver of unsupplemented group decreased to 20 mumol per kg, that of plasma increased to 0.28 mumol per 1 at the end. A strong vitamin A deficiency (liver concentration: less than 10 mumol/kg) may cause a decrease of vitamin A concentration of blood.

[Serum vitamin A determinations and their value in determining vitamin A status]

As demonstrated in the literature on vitamin A metabolism and homeostasis of retinol in serum, the concentration of retinol in serum is regulated very exactly if the liver stores are within the physiological range (20-300 micrograms/g liver). Therefore, the serum level indicates the status of vitamin A storage only if there is an extreme depletion or overconsumption of vitamin A. At marginal depletion, however, there is damage to peripheral tissue before changes in the vitamin A level in serum occur. At the beginning of hypervitaminosis A, changes in the level of vitamin A in serum also occur later. Therefore, the determination of vitamin A in serum gives no information on the adequacy of liver reserves for judging the necessity of a substitution.

Vitamin A absorption and metabolism in the chick: response to high dietary intake and to tocopherol

Absorption of 14C-labelled retinol was determined along the gastrointestinal tract of chicks, using 141Cerium as a non-absorbed reference substance, as influenced by high dietary vitamin A and the addition of tocopherol to the diet. The site of major vitamin A absorption was the proximal small intestine and high intake of vitamin A reduced slightly the percentage over-all absorption. Labelled glucuronides were secreted into the duodenum and were 50-60% reabsorbed in the small intestines. High-vitamin-A intakes enhanced the duodenal flow of retinyl glucuronides. In vitro hepatic retinol esterification and glucuronide production were enhanced in chicks given high dietary vitamin A. Plasma transport and clearance of retinol were enhanced by feeding high levels of vitamin A and further enhanced when tocopherol at high concentrations was present in the diet. Dietary tocopherol had no effect on absorption, increased hepatic vitamin A stores and in vitro retinol esterification, and decreased retinyl glucuronide flows through the duodenum.