The effect of dietary copper and zinc on cholesterol metabolism

The effects of different amounts of dietary zinc and copper on cholesterol metabolism in the rat were investigated. The levels of the minerals used were comparable to those likely to occur in a normal mixed North American diet. Although the different levels affected the serum, liver, and femur concentrations of the minerals, they had no effect on the levels of serum and liver, total, esterified or free cholesterol, or on high density lipoprotein cholesterol. It was concluded that dietary copper and zinc, at levels likely to occur in a normal mixed diet, are not significant factors in cholesterol metabolism.     

Effect of dietary phytase and high available phosphorus corn on broiler chicken performance

Two trials were conducted to determine the effects on broiler chicken performance and health of reducing dietary phosphorus levels by treating feed with the enzyme phytase, formulating diets using high available phosphorus (HAP) corn, or when diets were formulated with HAP corn and treated with phytase. Cobb x Cobb male broiler chickens were placed in an experimental design consisting of four dietary treatments with six replicate pens of 50 broilers per pen. The dietary treatments consisted of untreated control feed, phytase-supplemented feed (500 U/kg), diets prepared with HAP corn, and diets prepared with HAP corn and supplemented with phytase. The chickens were maintained on these dietary treatments from 1 to 49 d of age with feed and water made available for ad libitum consumption. When the two trials were combined, there was a significant (P < or = 0.05) increase in body weight in the broilers fed the phytase treated diets at 49 d of age. The serum activity of alkaline phosphatase was significantly decreased in the diets supplemented with phytase, and serum cholesterol was significantly decreased in the diets prepared with HAP corn. These data indicate that total phosphorus can be reduced by at least 11% in diets prepared with HAP corn, or in diets supplemented with phytase, without affecting the performance or health of broiler chickens. When diets are prepared with HAP corn and supplemented with phytase, the dietary addition of total phosphorus can be reduced by at least 25% without affecting broiler chicken performance or health.     

Effect of dietary aminoguanidine on tissue pentosidine and reproductive performance in broiler breeder hens

Factors influencing the age-related decline in production parameters of broiler breeder hens are poorly understood. Elevated blood glucose concentrations measured in broiler breeder hens may contribute to this decline. The nonenzymatic attachment of glucose to proteins generates glycoxidation crosslinks in tissue proteins, which can ultimately impair their function. One such glycoxidation crosslink, pentosidine, has been used as a biomarker for aging studies because of its accumulation on the structural protein collagen. The objectives of these studies were to determine whether pentosidine accumulates with age in hens and whether the crosslinking inhibitor, aminoguanidine (AG), could retard this accumulation. An additional objective was to determine whether AG had any effect on production performance. In the first study, broiler breeder hens (n = 318) were randomly assigned to two groups: control and supplemented (400 ppm AG). Pentosidine was measured in the skin of the birds at 20 and 67 wk of age. Egg production was measured daily. In a second study, broiler breeder hens (n = 60) were reared as previously described. Pentosidine was measured in the skin of the birds at 20 and 68 wk of age. Results showed that pentosidine was present in the skin of the hens, and that concentrations increased with age (P < 0.001). Although pentosidine was reduced (P < 0.001) in AG-supplemented birds, production performance was not affected. In conclusion, AG retarded the rate of accumulation of pentosidine during lay in broiler breeder hens, but the reduction in pentosidine did not significantly affect production performance.     

The relative effect of dietary fats and carbohydrates on lipid metabolism in the albino rat

This study is concerned with the effect of two carbohydrates, cane-sugar and corn starch, at four different levels in the presence of two dietary fats, on the serum and the tissue lipids (cholesterol, phospholipid and fatty acid patterns). Keeping the dietary fats (coconut safflower seed oil) at 20% level, diets containing (a) startch (54%) + cane sugar (0%), (b) starch (44%) + cane sugar 10%), (c) starch (10%) + cane sugar (44%) and (d) only cane sugar (54%) were administered to rats for 8 weeks. The lipid levels were determined at the end of the feeding period. The beneficial effect of the unsaturated fat in lowering the serum cholesterol level is nullified by an excess of cane sugar in the diet. In liver, there is an increase of 40-50% of cholesterol, as the cane sugar level in the diet is raised, irrespective of the type of dietary fat. The fatty acid pattern of the serum and tissue lipids is influenced by dietary fats as well as carbohydrates.     

Effect of dietary protein and environmental temperature on growth performance and water consumption of male broiler chickens

The purpose of this study was to investigate whether smokers outside buildings with work-place smoking bans smoke "harder" than those smoking in social settings. An unobtrusive random observational study of smokers followed by structured interview was used, with 143 smokers taking smoking breaks outside their office buildings and 113 smokers in social settings. The main outcome measurements were number of puffs per cigarette and cigarette smoking duration. The mean number of puffs per cigarette for the office building group was 18.7% greater than that for the social settings group (10.7 +/- 3.2 vs. 8.7 +/- 2.7, t = 5.58, df = 253, p < 0.001); 74.8% of smokers outside offices took more than the mean number of puffs for the group compared to 42.5% of smokers in social settings (chi 2 df 1 = 26.31, p < 0.0001). Mean cigarette smoking duration was 30.4% shorter for the work-place group than the social settings group (3.9 +/- 1.2 minutes vs. 5.6 +/- 2.6 minutes). Of smokers outside offices, 55.2% had a cigarette smoking duration between 3 and 4.59 minutes, while 53.1% of smokers in social settings took > or = 5 minutes to smoke the observed cigarette (chi 2 df 2 = 31.55, p < 0.0001). Smokers who scored at the 75th percentile on the Fagerstrom Tolerance Scale took a mean 9.5 +/- 2.6 puffs per cigarette compared to 9.3 +/- 2.7 puffs by those who scored in the 25th percentile on the scale (t = 0.34, df = 145, p = 0.73). Regardless of degree of nicotine dependency, smokers leaving work-stations to smoke outside buildings smoked their cigarettes nearly 19% "harder" than cigarettes smoked in social settings. The individual and public health benefits of reduced smoking frequency engendered by work-place smoking bans may be lessened by policies which allow smokers to take smoking breaks.     

The effects of low dietary copper intake during pregnancy on physiological fluids and reproductive performance of first-litter gilts

Seven pairs of first littermate gilts were used to study the influence of low copper supply and pregnancy on physiological fluids and reproductive performance of first-litter gilts. They were fed semi-purified diets containing either 2.13 or 12.25 micrograms/kg of Cu from 30 days of gestation through two weeks of lactation. Low-Cu gilts had lower plasma Cu in early- and mid- gestation and farrowed piglets with lower plasma Cu and higher plasma Zn concentrations (p < 0.05). Plasma Fe and Mn concentrations were not affected by Cu supply (p > 0.05). Plasma Cu and Fe levels of newborn piglets were lower than those of their dams (p < 0.05) but this was not true for plasma Zn and Mn (p > 0.05). Low-Cu gilts had lower Cu and higher Zn content in colostrum and also lower Cu in milk than control gilts (p < 0.05). No significant differences were found in Fe and Mn levels in colostrum and milk between the two treatments (p > 0.05). Colostrum was richer in Cu and Zn than milk (p < 0.05) but not in Fe and Mn (p > 0.05). The low-Cu diet did not affect (p > 0.05) weight changes during pregnancy. The duration of parturition was shorter for low-Cu than for control gilts (3.19h vs. 5.71h, p < 0.05). Control gilts farrowed larger litters than low-Cu gilts (9.71 vs. 7.57 piglets, p < 0.05). There were no significant differences in live litter weights at birth, one wk. or two wks. of age (p > 0.05). The results indicated that a low-Cu diet and pregnancy had some effect on plasma, colostrum and milk mineral concentrations, as well as on litter size of gilts. An interaction between Cu and Zn was found.     

The effect of dietary flaxseed supplementation on organic anion and osmolyte content and excretion in rat polycystic kidney disease

Progression of chronic renal failure in the Han:SPRD-cy rat polycystic kidney disease is associated with renal depletion of citric acid cycle metabolites and betaine. Amelioration of this disease by a soy protein diet is associated with retention of citric acid cycle anions, despite increased excretion, and preservation of tissue levels of betaine. As we have recently found that modest dietary supplementation with flaxseed preserves renal function and reduces histologic injury in the Han:SPRD-cy rat, we undertook a high-resolution 1H NMR spectroscopic study of urine and renal tissue extracts from Han:SPRD-cy rats to explore the renal biochemical consequences of a flaxseed diet. There was no significant dietary effect upon organic anion, methylamine, or osmolyte excretion in healthy animals. There was increased citrate excretion in Han:SPRD-cy rats fed flaxseed. Urinary ammonium excretion did not differ, suggesting that the observed increase in citrate excretion was not due to an alkaline effect of diet. Tissue extract studies revealed that disease amelioration was associated with tissue retention of succinate and betaine. Amelioration of Han:SPRD-cy rat polycystic kidney disease by diet is associated with alteration in the handling of citric acid cycle metabolites. Betaine may have a metabolic role in the reduction of chronic renal injury.     

Effects of dietary copper and molybdenum on copper status, cytokine production, and humoral immune response of calves

Twenty-four male Holstein calves were used to determine the effects of dietary Cu and Mo on performance, Cu status, and immune function of calves. Calves were fed a milk replacer that was deficient in Cu for 8 wk and then were randomly assigned after weaning to one of four treatments: 1) control (no supplemental Cu or Mo), 2) 10 mg of Cu (from CuSO4)/kg of dry matter (DM) (Cu diet), 3) 5 mg of Mo (from Na2MoO4)/kg of DM (Mo diet), or 4) 5 mg of Cu (from CuSO4) and 5 mg of Mo (from Na2MoO4)/kg of DM (Cu + Mo diet). The basal diet was a semipurified diet that contained approximately 1.1 mg of Cu and 1.1 mg of Mo/kg of DM. Calves fed the Cu and Mo diets gained weight more efficiently than those fed the control and Cu + Mo diets during the 112-d study. By d 84 of the study, calves fed the Cu diet had higher plasma Cu concentrations and plasma ceruloplasmin activities than did calves fed the other three diets and had higher liver Cu concentrations on d 136. Plasma and liver Cu concentrations did not differ among calves fed the control, Mo, and Cu + Mo diets. At d 112, activity of Cu-Zn superoxide dismutase was lower in calves fed the Mo diet than in calves fed the Cu diet. Serum total antibodies to porcine erythrocytes (primary response) were lower in calves fed the Mo diet than in calves fed the Cu diet at 7, 14, and 21 d postinoculation. Production of tumor necrosis factor and interleukin-1 by isolated peripheral blood monocytes was not significantly affected by treatment. Although no differences were apparent in plasma or liver Cu concentrations among calves fed the control, Mo, and Cu + Mo diets, calves fed the Mo diet had a more severe Cu deficiency based on depressed humoral immune response and superoxide dismutase activity.     

The effect of excessive dietary vitamin A on performance and vitamin E status in swine fed diets varying in dietary vitamin E

A study was conducted to evaluate the effects of high dietary vitamin A on vitamin E status and performance of growing-finishing pigs fed diets supplemented with varying levels of vitamin E. Treatments consisted of corn-soybean meal-based diets supplemented with retinyl acetate to provide 2,000 or 20,000 IU of vitamin A/kg of diet and with DL-alpha-tocopheryl acetate to provide 0, 15, or 150 IU of added vitamin E/kg in a 2 x 3 factorial arrangement. The trial involved 84 crossbred pigs (26 kg initial BW) allotted to pens of two pigs each (one gilt, one barrow). Serum was obtained from all pigs on d 0, 3, 7, 21, 35, 63, and 77 of the 83- or 90-d feeding period. Tissue samples (liver, leg, and neck muscle, backfat, and leaf fat) were collected from one pig (barrow) in each pen at the end of the feeding period. Average daily gain and gain:feed were .93 kg and .30, respectively, without treatment differences (P > .10). Serum alpha-tocopherol increased linearly (P < .01) by d 3 with increasing level of dietary vitamin E supplementation. High dietary vitamin A resulted in a small decrease (P < .01) in serum alpha-tocopherol on d 3, but serum alpha-tocopherol concentration was not affected (P > .10) on other days. Tissue alpha-tocopherol increased linearly (P < .001) as dietary vitamin E increased in all tissues examined. No consistent evidence was found to indicate that a high level of dietary vitamin A interfered with performance or with blood serum or tissue alpha-tocopherol concentrations in growing-finishing swine.     

The effect of replacing dietary beet pulp with wheat treated with sodium hydroxide, ground wheat, or ground corn in lactating cows

This experiment examined the effect of complete diets composed of 60% grass silage and 40% concentrate based mainly on beet pulp, ground wheat, wheat treated with NaOH, or ground corn on milk production and ruminal fermentation of dairy cows. Milk production and fat yield were 19.8, 20.7, 20.1, and 21.2 kg/d and 0.71, 0.76, 0.72, and 0.78 kg/d, respectively (18 cows per treatment). Cows fed the diet based on ground corn had higher milk production and fat yield, but lower milk protein concentration, than did cows fed the diet based on beet pulp. Cows fed the diet based on ground corn also had higher fat yields than did cows fed the diet based on wheat treated with NaOH. Cows fed the diet based on ground wheat had lower ruminal pH than did cows fed the diet based on beet pulp (6.34 vs. 6.59) and higher ruminal NH3 concentrations (6.2 vs. 5.2 mmol/L) than did cows fed the diet based on ground corn. These results showed little difference in milk production based on wheat processing method and little advantage to replacing beet pulp with either wheat type in a high forage diet. However, milk production and fat yield were increased by replacing beet pulp with ground corn.     

The influence of extended posthatch holding time and placement density on broiler performance

Extended posthatch holding (in the hatcher) has been reported to dehydrate chicks, reduce broiler performance, and depress immune response. Nevertheless, some commercial hatcheries are increasing incubation time in an attempt to minimize possible bacterial contamination of incompletely healed navels. The objectives of this study were to determine the effects of posthatch holding on broiler performance and the effects of bird density and additive stress on performance and immune response. Twelve hundred broiler eggs (58 to 70 g) were incubated. Chicks were removed from the hatcher after 528 h of incubation, banded, and weighed. Half of the chicks were returned to the hatcher for an additional 24 h (HELD). Both hatcher treatments were placed at two densities (.07 and .12 m2 per bird). Individual BW were taken at 21 and 43 d of placement and 43 d of age. The HELD chicks weighed significantly less than controls at time of placement. At 21 d postplacement the HELD broilers were significantly heavier than controls, but were similar by 43 d. Total feed conversion was not affected in the HELD treatment, but birds in the .07 m2 per bird density were less efficient in terms of total feed conversion. Chick holding time and density seemed to affect antibody titers at 5 wk. Although holding chicks in the hatcher for 24 h did not clinically dehydrate chicks or affect performance, it decreased immune response. In addition to less efficient growth, birds in the more crowded pens had depressed immune response.     

Effects of zinc, copper, and manganese supplementation of high-concentrate ration on gastrointestinal absorption of copper and manganese in Holstein calves

Sixteen Holstein bull calves were fed a high-concentrate ratio supplemented with zinc, copper, and manganese, alone or in combination, for 10 wk. After 6 days of preliminary feeding of chromic oxide, fecal grab-samples were collected for 6 days. Calves were slaughtered, and samples of the contents of the reticulo-rumen, omasum, abomasum, small intestine, cecum, and large intestine were analyzed for chromic oxide, copper, and manganese. Absorption along the gastrointestinal tract, measured by comparison of one segment with the previous segment, indicated net secretion of copper in the abomasum but net absorption from the rest of the tract. The exception was that net secretion into the reticulo-rumen was associated with low dietary copper. Net secretion of manganese was mainly in the small intestine and cecum in all treatments. A higher proportion of copper apparently was absorbed when this mineral was supplemented in the ration. However, absorption of manganese was decreased slightly when manganese was supplemented in the ration. Reabsorption of manganese in the large intestine was probably greater than that of copper.     

The effects of selenium deficiency, dietary selenium, and vitamin E supplementation on the oxidative status of pig liver

The aim of this work was to determine the effect of selenium (Se) deficiency on the porcine liver oxidative stability and to investigate Se content and oxidative status in porcine liver after dietary supplementation with vitamin E (vit E), sodium selenite, and selenized yeast. Experimental animals were fed a basal corn meal, low in Se and vit E, for a 4-week depletion period before being given the experimental diets containing different levels of Se and/or vit E for 5 months. Dietary treatments were the basal diet with no additions (control); the basal diet supplemented with 25 mg of vit E/kg of feed (group I); basal diet + 0.3 mg selenite-Se/kg (group II); basal diet + 0.3 mg selenized yeast-Se/kg (group III); basal diet + 0.1 mg selenite-Se + 10 mg vit E/kg (group IV); and basal diet + 0.3 mg selenite-Se + 25 mg vit E/kg (group V). The Se content in pig liver samples was 33 to 192% lower in the control group than in all the other groups. Dietary Se from selenized yeast had a more pronounced effect on Se level than dietary sodium selenite. The highest Se content was found in liver samples from the Se + vit E supplemented group (group V). All the dietary supplementation schemes significantly improved the oxidative status of porcine liver compared with the control group samples. The best results were obtained by simultaneous dietary supplementation with Se + vit E (groups IV and V) > group III > group II > group I.     

Effects of copper deficiency and copper deficiency coupled with high dietary iron or molybdenum on phagocytic cell function and response of calves to a respiratory disease challenge

A study was conducted to determine the effects of supplementing a diet marginally deficient in copper (Cu) with iron (Fe), molybdenum (Mo), or Cu on phagocytic cell function and disease resistance of calves. Thirty-one calves were born to heifers fed a corn silage-based diet containing 4.5 mg of Cu/kg. Treatments consisted of 1) control (CON; no supplemental Cu, Fe, or Mo), 2) 600 mg of Fe added/kg (FE), 3) 5 mg of Mo added/kg (MO), or 4) 10 mg of Cu added/kg of DM (CU). Activity of superoxide dismutase was lower (P < .06) in neutrophils from MO vs CON or CU calves at 170 d of age. bactericidal activity of neutrophils from MO calves tended (P = .15) to be lower compared with those from CU calves at 70 d of age. Calves were inoculated intranasally with live infectious bovine rhinotracheitis virus (IBRV) 2 d after weaning, followed by intratracheal administration of Pasteurella hemolytica 5 d later. Iron- and Cu-supplemented calves exhibited higher (P < .01) body temperatures and lower (P < .06) feed intakes following IBRV inoculation compared with CON and MO calves. Copper-supplemented calves had higher levels of plasma tumor necrosis factor (TNF) than MO calves at weaning (P < .05) and tended to have higher plasma TNF (P = .11) than FE and MO calves 5 d after IBRV inoculation. These data indicate that dietary levels of Mo and Cu can affect body temperature and feed intake responses to disease by affecting TNF and perhaps other cytokines.     

Effects of dietary supplementation with fish oil on prostanoid metabolism during acute coronary occlusion with or without reperfusion in diet-induced hypercholesterolemic rabbits

We studied the changes in myocardial and aortic concentrations of prostacyclin and thromboxane A2 during acute coronary occlusion with or without reperfusion in rabbits fed with a cholesterol-enriched diet with or without fish oil supplementation for a short (5 days) or long period (6 weeks). New Zealand white male rabbits were divided into 5 groups: Group I, 15 control rabbits fed with a laboratory standard rabbit chow. In addition to the standard chow, the 4 study groups were treated with cholesterol or fish oil. Group II, 17 rabbits fed with a 1% high cholesterol diet for 5 days. Group III, 16 rabbits fed with a diet containing 1% cholesterol and 10% fish oil for 5 days. Group IV, 17 rabbits fed with the same diet as group II for 6 weeks. Group V, 18 rabbits fed with the same diet as group III for 6 weeks. Each group of rabbits was randomly divided into the coronary occlusion or occlusion-reperfusion mode of experiment. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h. Subsequent reperfusion for 4 h was performed in the occlusion-reperfusion rabbits. The aortic tissue above the aortic valve and the ischemic and normal (nonischemic) areas of the left ventricle were excised for the measurement of 6-keto-PGF1 alpha and thromboxane B2 levels by radioimmunoassay. Both during coronary occlusion and occlusion-reperfusion, rabbits showed higher myocardial concentrations of 6-keto-PGF1 alpha and thromboxane B2 in the ischemic area than in the normal myocardium.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of alpha-tocopherol and beta-carotene supplementation on COPD symptoms

The effects of alpha-tocopherol (50 mg/d) and beta-carotene (20 mg/d) supplementation on symptoms of chronic obstructive pulmonary disease were studied among the 29,133 participants of the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study undertaken to investigate the effects of these two substances in the prevention of lung and other cancers. During the follow-up the supplementations did not affect the recurrence or incidence of chronic cough, phlegm, or dyspnea. The prevalence of chronic bronchitis and dyspnea at baseline was lower among those with high dietary intake of beta-carotene (OR = 0.78 and 0.67, respectively) or vitamin E (OR = 0.87 and 0.77) and high serum beta-carotene (OR = 0.59 and 0.62) and alpha-tocopherol (OR = 0.76 and 0.82). High intake and serum levels of retinol were associated with low prevalence of dyspnea (OR = 0.84 and 0.80, respectively) but not with chronic bronchitis. The results indicate no benefit from supplementation with alpha-tocopherol or beta-carotene on the symptoms of chronic obstructive pulmonary disorders but support the beneficial effect of dietary intake of fruits and vegetables rich in these compounds.     

The effect of one night's sleep deprivation on temperature, mood, and physical performance in subjects with different amounts of habitual physical activity

Eleven healthy males were studied twice. On one occasion (control, C), they slept (night 1) and then underwent a battery of tests at 4 h intervals from 06:00 day 1 to 02:00 day 2; then, after a normal sleep (night 2), they were tested from 10:00 to 22:00 on day 2. On the second occasion (sleep deprivation, SD), the subjects remained awake during night 1. Each battery of tests consisted of measurements of tympanic membrane temperature, profile of mood states (POMS), muscle strength, self-chosen work rate (SCWR), perceived exertion, and heart rate (HR) while exercising on a stationary cycle ergometer. Subjects also kept a diary of their activities during the two days and answered a questionnaire about their habitual physical activity. Results showed a significant negative effect of sleep deprivation on most mood states on day 1, but no effect on the other variables. By day 2, mood had tended to recover, though muscle strength tended to be worse in both control and sleep-deprivation experiments. There was also a more general tendency for negative effects to be present at the end of day 1 (02:00) or at the beginning of day 2 (10:00). There was limited support for the view that subjects who were habitually more active showed less negative effects after sleep deprivation and responded less adversely to the poor sleep achieved on the university premises (night 2). These results stress the considerable interindividual variation in the responses to sleep loss and, therefore, the difficulty associated with giving general advice to individuals about work or training capability after sleep loss.     

Placental copper transport in rats: effects of elevated dietary zinc on fetal copper, iron and metallothionein

We hypothesized that the competition between zinc (Zn) and copper (Cu) during fetal accretion of copper could be discriminated at either the dam-to-placenta or placenta-to-fetus stage. This premise was tested by feeding dams a high Zn diet (1000 mg/kg, HZn) during the second half of gestation. One day before delivery, dams were anesthetized, fetuses removed and both maternal and fetal tissues and plasma obtained and assayed. Other rats were fed a normal Zn concentration diet (32.4 mg/kg, ND) throughout pregnancy. There were significantly lower fetal liver Cu concentrations and greater plasma Fe concentrations, but not plasma Cu concentrations or liver Fe concentrations in the HZn group. Both dam and fetal Zn liver concentrations were greater in the HZn than in the ND group. Plasma Cu levels were lower in the HZn-fed than in the ND-fed dams. Placental tissue from the HZn litters had a greater concentration of Zn and Fe than did the ND group, whereas no effect was noted for Cu concentration. Metallothionein (MT) levels were elevated in dam livers and placenta in the HZn group, but there were no differences in fetal liver MT. The dynamic assessment of placental transport was conducted by injecting 2.5 mg/kg Cu acetate intravenously into dams of both groups. Sequential samplings of dam and fetal blood and placentas were taken from 0 to 60 min. After the Cu bolus, there was a consistently higher plasma Cu concentration in the HZn than in the ND dams, but no alteration in the concentration of Cu in the placenta or fetal plasma. This study indicates that placental Cu uptake is not affected by a high Zn diet in the dam. In addition, the greater Zn concentration in the placenta of HZn than in ND litters results in abnormal fetal Cu, Fe and Zn concentrations, suggesting that an imbalanced maternal mineral consumption is deleterious to normal divalent metal accretion.     

Protein supplementation of ammoniated wheat straw: effect on performance and forage utilization of beef cattle

We studied the effects of supplement CP concentration on performance and forage use of cattle allowed ad libitum access to ammoniated wheat straw. During two consecutive winters, crossbred beef cows in late gestation (n = 87 in 1990-1991, n = 84 in 1991-1992) were used in a randomized complete block design with three pens per treatment. Cows were stratified by weight, body condition score (BCS), age, and breed and randomly assigned within strata to 1) control (C, no supplement), or 2 kg/d of 2) low-protein (LP) supplement (12% CP), 3) moderate-protein (MP) supplement (20.1% CP), or 4) high-protein (HP) supplement (31.7% CP) (DM basis). The feeding period was 84 d in 1990-1991 and 60 d in 1991-1992. Supplementation (C vs LP, MP, or HP) increased (P < .01) cow weight gains (32.7 vs 60.7, 62.8, and 72.4 kg, respectively) and improved (P < .01) BCS. Calf birth weights, weaning weights, and ADG were not affected by treatment (P > or = .20). Average calving date, percentage of cows cycling at the start of the breeding season and percentage pregnant after a 60-d breeding season were also similar (P > .20) among treatments. Sixteen ruminally fistulated steers (482 kg, four steers per treatment) were blocked by weight and assigned to the same four supplements in a 30-d digestion trial. Supplementation increased (P < .01) digestible DMI and forage DMI (P < or = .04) and tended (P = .09) to increase digestible NDF intake but did not alter (P > or = .15) apparent DM or NDF digestibility.(ABSTRACT TRUNCATED AT 250 WORDS)