Deuterium Oxide Dilution Research Articles

Relationship between nutrition, weight change, and fluid compartments in preterm infants during the first week of life

This study was conducted to investigate the redistribution of fluid compartments and to examine the factors contributing to the variability of early weight loss in premature infants. Fourteen preterm infants (mean +/- SD: birth weight, 1473 +/- 342 gm; gestational age, 30.7 +/- 2.4 weeks) were studied at 1 and 7 days of age. Total body water was measured by deuterium oxide dilution, extracellular volume by bromide dilution, and intracellular volume by the difference between total body water and extracellular volume. There were significant changes in body fluid distribution per concurrent weight from birth to age 1 week. Extracellular volume decreased by 11%, and intracellular volume increased by 8.5% with no change in total body water. Infants were then grouped according to postnatal weight loss (group 1 (n = 7) > 10% and group 2 (n = 7) < 5% of birth weight). In group 1 there was a significant loss of both weight (mean +/- SD: 15.6% +/- 3.7%) and extracellular volume (15.9% +/- 9% of birth weight), with no change in intracellular volume. In group 2 there was no significant weight loss (1.4% +/- 1.8%), but a significant loss of extracellular volume (13.0% +/- 5.4% of birth weight) and a significant increase in intracellular volume. Other differences between the groups were a lower energy intake in group 1 than in group 2 (mean +/- SD: 177 +/- 46 vs 269 +/- 45 kilojoules/kg per day; p < 0.005) and a higher physiologic stability index in group 1 (p < 0.05). We conclude that significant postnatal weight loss as a result of the contraction of the extracellular compartment occurs only in less stable infants whose energy intake is inadequate. With adequate energy intake, weight loss is minimal because of the expansion of the intracellular compartment, which may be related to the onset of growth.

The effect of aerobic exercise training on internal body fat in obese women

A group of 11 obese women (from 13% of ideal weight and higher) volunteered to participate in a study designed to reduce weight in a 92-day program of aerobic exercise. Before and after the weight reduction period, body fat indices were measured by deuterium oxide (D2O) dilution and by skinfold anthropometry. Changes in internal body fat and subcutaneous fat were calculated. Mean weight loss was 3.6 +/- 1.2 kg, and internal body fat and subcutaneous fat were 1.8 +/- 1.3 kg (21.2%) and 3.0 +/- 0.9 kg (16.0%), respectively. Highly significant correlation were obtained between changes in internal body fat and total body fat (r = 0.856, p < 0.001). However, changes in internal body fat were not significantly associated with changes in waist to hip ratio (WHR). In the present study, we found that changes in total body fat were significantly related to changes in internal body fat during treatment of obesity with aerobic exercise. However, changes in internal body fat were not valid estimates of changes in body fat distribution in relation to changes in WHR.

Mass and Energy Transfer during Lactation in a Small Phocid, the Harbor Seal (Phoca vitulina)

In true seals (family Phocidae), the large energetic costs of lactation are supported primarily by mobilization of stored fat. We studied the magnitude of fat and energy depletion in lactating harbor seals (n = 17) on Sable Island, and fat and energy storage in their pups, using cross-sectional morphometric and isotopic methods. Initial mass of mothers studied ranged from 87 to 94 kg. Maternal mass declined by 33% over the first 19 d of the 24-d lactation period. Most of this loss (68.8%) was from the sculp (i.e., skin and attached blubber). Estimated maternal body fat, derived from dilution of deuterium oxide, decreased from 24% at parturition to about 7% at 19 d postpartum. Mothers lost 163 kg (78.7%) of their stored fat and 3.1 kg (20.0%) of stored protein, representing 713.8 MJ (169 Mcal) or 60.5% of stored energy. Newborn pups contained 93.0 MJ (22.1 Mcal) of energy, divided similarly between fat (46 4%) and protein (53.6%). Pup body mass increased from 10.6 kg to 25.8 kg. Sculp mass accounted for 62. 7% of mass gained by the pup. Total body fat of pups increased from 11% at birth to 35% at 19 d. Pups deposited 346 8 MJ (82.2 Mcal) or 48. 7% of energy withdrawn by females from body stores. Unlike large phocid species, lactating harbor seals initiate feeding during lactation apparently because energy reserves are insufficient to cover the combined costs of lactation and maternal metabolism.

Recombinant porcine somatotropin for sows during late gestation and throughout lactation.

Two experiments were conducted to evaluate whether administration of recombinant porcine somatotropin (pST) to sows (Hampshire-Yorkshire) enhanced lactational performance. In Exp. 1, sows (n = 84) were fed a corn-soybean meal diet (17.8% CP), or a similar diet with 8% added fat, from d 108 of gestation to d 28 of lactation. Half of the sows fed each diet were injected with 6 mg/d of pST from d 108 of gestation to d 24 of lactation. Diets were fed at 2.27 kg/d from d 108 of gestation until farrowing and then were self-fed during lactation. By d 3 of lactation, litter size was standardized at 8 to 10 pigs per litter. Treating sows with pST resulted in a 10-fold increase (P less than .001) in serum somatotropin at 4 h postinjection. Serum glucose was increased (P less than .01) and serum triglycerides, creatinine, and urea N were decreased (P less than .01) by pST. During the summer, apparent heat stress occurred in pST-treated sows, resulting in 14 deaths. Most (10) of the deaths occurred just before, during, or shortly after farrowing. Fewer (P less than .08) deaths occurred when pST-treated sows were fed the diet with added fat. Sows treated with pST consumed less feed (P less than .10) and lost more backfat (P less than .10) during lactation than controls. Increasing the dietary fat did not prevent these changes. Weaning weights of pigs and milk yield of sows (estimated by deuterium oxide dilution) were not affected by pST treatment. In Exp. 2, sows (n = 42) were injected weekly with 0 or 70 mg of pST on d 3, 10, 17, and 24 of lactation. Litters were standardized by d 3 at 8 to 10 pigs, and sows were fed the same control (low fat) diet as in Exp. 1. Sows treated with pST consumed less feed and lost more weight and backfat during lactation than untreated sows. Litter size, average pig weaning weights, and milk yield were not influenced by pST treatment. These data indicate that a 6-mg daily injection of pST from 6 d prepartum to d 24 of lactation or a 70-mg weekly injection of pST from 3 d postpartum to d 24 of lactation does not increase milk production in lactating sows.

Body composition of rural Beninese women in different seasons assessed by skinfold thickness and bioelectrical-impedance measurements and by a deuterium oxide dilution technique

Body composition of 24 rural Beninese women was assessed in a pre- and a postharvest season by using skinfold-thickness measurements, bioelectrical-impedance analysis (BIA), and deuterium oxide (D2O) dilution. Fat mass assessed by D2O dilution was 12.3 +/- 3.3 kg; by skinfold-thickness measurements, 13.8 +/- 3.3 kg; and by BIA, 14.1 +/- 2.9 kg. Fat mass assessed by D2O was significantly lower (P less than 0.05) than fat mass assessed by the other two methods. Body weight in the postharvest season was 0.8 +/- 1.6 kg higher (P less than 0.05) than during the preharvest season. All three methods demonstrated that there were no significant changes in fat mass but that fat-free mass increased significantly (P less than 0.05) from pre- to postharvest season.

The validity of bioelectrical impedance analysis in estimating total body water in patients with cirrhosis

This study assessed the validity of bioelectrical impedance analysis (BIA) to predict total body water (TBW) in patients with cirrhosis. TBW was estimated by deuterium oxide dilution (D2O) and compared with TBW predicted by BIA in 27 patients with cirrhosis with and without ascites or edema (Group A), in a subgroup of 18 'dry' cirrhotics without clinical signs of fluid overload (Group B) and in 27 healthy controls. Three different BIA regression equations were used. In all three groups of subjects high correlation coefficients were obtained between D2O-TBW and BIA-TBW (r > 0.88). In the cirrhotic Group A, BIA significantly underpredicted D2O-TBW by all 3 equations (2.9-3.8 l) and the regression lines were different from the lines of identity by two equations. Standard errors of estimate were high in Group A (3.04-3.97 l) in comparison with Group B (1.79-2.46 l) and the controls (1.03-1.41 l). In the 'dry' cirrhotics (Group B) and in the controls, TBW was correctly predicted by two of three BIA equations, and regression lines were not significantly different from lines of identity. Correlation coefficients in Group B were higher than in Group A (r = 0.96-0.97 vs. 0.89-0.92) and were comparable with controls (r = 0.98-0.99). We conclude that BIA is not a valid method of estimating TBW in cirrhotic patients with ascites and edema. In cirrhotic patients without clinical signs of fluid overload BIA can be used to predict TBW, although accuracy is slightly lower than in healthy controls.

Ascites dynamics in cirrhosis: Proposal and validation of a methylene blue dilution test

In order to investigate ascites dynamics, we examined a simple compartmental model based on the analysis of the peritoneal clearance rate of methylene blue in 58 patients with cirrhosis and ascites. After abdominal injection of 10–50 mg methylene blue, the ascitic concentration of the dye progressively decreased, following an exponential trend. The dye distribution volume (7.1 + 0.6 l, mean + SE) and its peritoneal clearance (87.6 + 5.0 ml/min) were determined by mathematical analysis. The accuracy of volume determinations was controlled in 5 subjects by total paracenteses. In 6 patients, methylene blue clearances were also compared with free-water peritoneal clearances, estimated by a deuterium oxide dilution technique. The decrease in the ascitic concentrations of both tracers followed a corresponding exponential decay in all patients, and the parameters of ascites dynamics determined by the two techniques (peritoneal volumes and clearance values) showed no statistical difference. We therefore suggest the use of the methylene blue dilution test to estimate free-water transperitoneal dynamics, which may be useful in the evaluation and control of cirrhotic patients with ascites.

Optimum doses of deuterium oxide and sodium bromide for the determination of total body water and extracellular fluid

A practical approach for determining optimum tracer doses is described for measurements of total body water (TBW) and extracellular water (ECW) based on dilution of deuterium oxide and sodium bromide with respective analyses by nuclear magnetic resonance and anion-exchange chromatography. Using these techniques and plasma concentrations corresponding to adult doses up to 1.5 g kg-1 body weight of deuterium oxide and 0.05 g kg-1 of sodium bromide, the variations of analyses of these tracers, at these respective doses, were calculated. TBW determination with an RSD of less than 2% was found to require administration of 0.4 g kg-1 of deuterium oxide. Because basal concentrations of bromide are quantifiable, the accuracy of the extracellular water determination depends upon the magnitude of the increase in plasma bromide concentration; a sodium bromide dose of 0.01 g kg-1 provides a deviation in the determined ECW volume of approximately 1%.

Body composition and sexual maturation in premenarcheal athletes and nonathletes

The purpose of this study was to compare premenarcheal athletes (A) and nonathletes (NA) in terms of body composition and sexual maturation and to discern the relationship between these variables. Percent body fat (%BF) was determined by the three-component system of Siri utilizing body density from hydrostatic weighing and total body water measured by deuterium oxide dilution. Sexual maturation was self-assessed using the system described by Marshall and Tanner. ANOVAs and polynomial regression analysis revealed that both the A (N = 73) and NA (N = 53) showed similar values and linear increases (P less than 0.001) in height (HT), weight (WT), breast (B) and pubic hair (PH) development from 7 to 15 yr but not in %BF (XA = 15.7 +/- 4.6; XNA = 20.5 +/- 6.4 (P less than 0.001]. The NA exhibited a quadratic curve (P less than 0.01) in %BF over age, while the A showed a negative linear relationship (P less than 0.001) with age. Scheffe post hoc tests revealed significant differences (P less than 0.03, A less than NA) at 11 and 12-15 yr. When %BF was compared to maturation, the A were found to have less fat (P less than 0.01) at stages 1 and 4 of PH and at stages 2, 3, and 4 of B. There were no significant differences between A and NA in the age at which B2, 3, or 4 or PH2, 3, or 4 occurred. Both groups exhibited similar and significant correlations between age, HT, WT, B, and PH development but not %BF.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of total body water by bioelectrical impedance analysis in blacks.

Several differences exist between the body composition of blacks and whites. This study was designed to investigate the applicability of bioelectrical impedance analysis (BIA) in blacks, using prediction equations developed in whites. A multiple regression equation developed on 79 white adults, using deuterium oxide dilution space total body water (D2 O-TBW) as the reference method, was prospectively applied to 88 blacks aged 19-50 years. Although the regression line of D2 O-TBW on BIA-TBW was not significantly different from the line of identity (r = 0.98, SEE = 1.71 liters), mean TBW was significantly underestimated by 0.84 liter. Other BIA equations from the literature also underestimated D2 O-TBW in blacks, except for an equation developed on a mixed black and white population. Multiple regression analysis on the data of the black and white subjects combined showed that race, offered as a separate independent variable, improved the correlation with D2 O-TBW slightly but significantly (P < 0.01). It was concluded that BIA may be valuable in the assessment of body composition in blacks as well as in whites. In this study a small underestimation of TBW occurred in blacks, using (BIA) equations from whites. This may be due to racial differences in body composition or to factors unrelated to ethnicity.

Increased protein turnover despite normal energy metabolism and responses to feeding in patients with lung cancer : Melville S, McNurlan MA, Calder AG, Garlick PJ. Rowett Research Institute, Aberdeen AB2 9SB. Cancer Res 1990;50:1125-31

We have examined the responses of energy and protein metabolism to nutrient intake in nine patients with lung carcinoma, of whom none were cachexic and only one had distant metastases, compared with nine control patients for elective aneurysm surgery, who were comparable in terms of age, body mass index, and smoking habits. Whole-body protein turnover and leucine oxidation were assessed by primed continuous infusion of L-[13C]leucine. Indirect calorimetry was used to determine energy expenditure and rates of carbohydrate and fat utilization. Lean body mass (LBM) was estimated from dilution of deuterium oxide. Measurements were made over an 8-h period, including 4 h postabsorptive followed by 4 h of feeding, during which small hourly meals were consumed. In the post-absorptive state, the rate of incorporation of leucine into protein was higher in the cancer group (mean +/- SD, cancer versus control: 102 +/- 21 versus 86 +/- 8 mumol/kg LBM/h, P less than 0.05), as was the release of leucine by protein degradation (126 +/- 19 versus 110 +/- 10 mumol/kg LBM/h, P less than 0.01), but there was no difference in rates of leucine oxidation (27 +/- 6 versus 27 +/- 5 mumol/kg LBM/h) or leucine balance (-25 +/- 7 versus -24 +/- 4 mumol/kg LBM/h). There were no differences between the cancer and control groups with respect to either resting energy expenditure (37.3 +/- 3.5 versus 35.2 +/- 3.8 kcal LBM/day) or the postabsorptive pattern of nutrient utilization (61 +/- 13% fat, 26 +/- 10% carbohydrate, and 13 +/- 2% protein versus 65 +/- 7%, 21 +/- 7%, and 14 +/- 2%, respectively). During feeding, leucine oxidation rose relative to the postabsorptive state, incorporation into protein remained the same, and release by protein degradation fell. Incorporation (106 +/- 20 versus 89 +/- 7 mumol/kg LBM/h, P less than 0.05) and release (59 +/- 12 versus 42 +/- 14 mumol/kg LBM/h, P less than 0.02) remained higher in the cancer group than in controls, but leucine oxidation (43 +/- 15 versus 43 +/- 12 mumol/kg LBM/h) and leucine balance (+48 +/- 10 versus +47 +/- 12 mumol/kg LBM/h) were the same. Energy expenditure during feeding increased to 43.8 +/- 5.1 versus 43.2 +/- 4.2 kcal/kg LBM/day, derived from 32 +/- 11% fat, 52 +/- 9% carbohydrate, and 16 +/- 5% protein in cancer patients and 36 +/- 7%, 48 +/- 8%, and 16 +/- 4%, respectively, in controls.(ABSTRACT TRUNCATED AT 400 WORDS)

Body composition of adult cystic fibrosis patients and control subjects as determined by densitometry, bioelectrical impedance, total-body electrical conductivity, skinfold measurements, and deuterium oxide dilution

This study contrasts body compositions (by six methods) of eight cystic fibrosis (CF) subjects with those of eight control subjects matched for age, height, and sex. CF subjects weighed 84% as much as control subjects. Densitometry and two bioelectrical impedance-analysis methods suggested that reduced CF weights were due to less lean tissue (10.7, 9.5, and 10.4 kg). Total-body electrical conductivity (TOBEC) and skinfold-thickness measurements indicated that CF subjects were leaner than control subjects and had less fat (5.4 and 3.6 kg) and less lean (5.2 and 7 kg) tissue. D2O dilution showed a pattern similar to TOBEC (8.3 kg less lean, 2.7 kg less fat tissue). Densitometry estimates of fat (mass and percent) were not correlated (r less than 0.74, p greater than 0.05) with any other method for CF subjects but were correlated with all other methods for control subjects. CF subjects contained less fat and lean tissue than did control subjects. Densitometry by underwater weighing is unsuitable for assessing body composition of CF patients.

Estimation of minimal weight of adolescent males using multicomponent models

The purpose of this study was to determine whether the estimation of minimal weight (the body weight at which 5% of the weight is fat) of adolescent males could be improved by accounting for differences in hydration state and bone mineral content. Improvement was defined as a larger value for minimal weight and a smaller standard deviation compared to minimal weight estimated from body density. Forty adolescent males (mean age +/- SD, 15.5 +/- 1.4 yr) were measured for height, weight, body density (hydrostatic weighing), total body water (deuterium oxide dilution), and bone mineral content (single photon absorptiometry). Twenty-two adult males (mean age +/- SD, 23.6 +/- 2.2 yr) were measured as a reference group. Percent body fat and minimal weight were calculated from the body density (MWD), body density adjusted for total body water (MWDW), and body density adjusted for body water and bone mineral content (MWDWB). Repeated-measures ANOVA was used to test for differences between the methods and for trends in the data. The results showed a slight but nonsignificant increase in minimal weight for the adolescent group when body water and bone mineral data were added. The means +/- SD for MWD, MWDW, and MWDWB values of the adolescents were 54.6 +/- 9.0 kg, 54.8 +/- 8.6 kg, and 55.4 +/- 8.4 kg, respectively. It was concluded that the multicomponent methods, which accounted for hydration and bone mineral status, did not significantly improve the estimates of minimal weight of adolescent males compared to the single component method, i.e., minimal weight from body density.

Validation of bioelectrical-impedance analysis as a measurement of change in body composition in obesity

The bioelectrical-impedance-analysis (BIA) method accurately measures body composition in weight-stable subjects. This study validates the use of BIA to measure change in body composition. Twelve obese females underwent weight loss at a mean rate of 1.16 kg/wk. Body composition was measured by deuterium oxide dilution (D2O), BIA, and skinfold anthropometry (SFA) at baseline and at 5% decrements in weight. Highly significant correlations were obtained between D2O and BIA (r = 0.971) and between D2O and SFA (r = 0.932). Overall, BIA predicted change in fat-free mass with greater accuracy (to 0.4 kg) and precision (+/- 1.28 kg) than did anthropometry (to 0.8 kg and +/- 2.58 kg, respectively). We conclude that BIA is a useful clinical method for measuring change in body composition.

Relationships between secretory patterns of growth hormone, prolactin and body reserves and milk yield in dairy ewes under different photoperiod and feeding conditions

ABSTRACTDairy ewes (Prealpes breed) were subjected to differential photoperiod treatments: either long (15·5 light (L): 8·5 dark (D) or short (8·5 L: 15·5 D). Treatments started 15 days before lambing and continued until the 5th week of lactation. After lambing the 22 ewes of each photoperiodic treatment were divided in two groups and fed on either a high or low plane (19 v. 10·5 MJ/day and 370 v. 237 g crude protein per day). Milk yield was not affected by photoperiod but significantly modified by feeding levels (1154 v. 789 ml/day). Protein content of the milk was reduced under long days (—4·9 g/1) compared with short days, while no effect was observed for fat content. Body chemical composition changes, estimated by the deuterium oxide (heavy water) dilution technique between weeks 1 and 4, were affected by both treatments, with a significant interaction between photoperiod and diet for body protein changes: under short days lipid and protein changes were closely related while under long days they were independent.Blood samples were taken on day 23 of lactation from six ewes per group, every 30 min from 07.30 to 15.30 h for growth hormone (GH) and prolactin (PRL) measurements. The timing of GH and PRL pulses were different, but there was evidence that secretory patterns of each hormone were synchronized across ewes within the four treatments. Long photoperiod increased plasma PRL baseline rather than pulse amplitude, with no effect of diet. Undernutrition mainly increased GH pulse amplitude rather than baseline concentration, with no significant effects of photoperiod.High spontaneous concentrations of GH were associated with body lipid mobilization (R2 = 0·51) and were also involved in the control of protein changes (R2 = 0·71). These results indicate that GH (and PRL) are involved in nutrient partitioning in the lactating ewe.

Anthropometry in blacks: applicability of generalized skinfold equations and differences in fat patterning between blacks and whites

To test the accuracy of generalized skinfold (SF) equations in blacks and to compare fat patterning in black and white adults, percent body fat (%BF) was assessed in 90 blacks and 89 whites by deuterium oxide dilution (D2O) and by generalized SF equations [Durnin and Womersely (DW), and Jackson and Pollock and Jackson et al (JP)] by using two calipers (Lange and Holtain). In blacks, JP significantly underpredicted (2.95%) and DW overpredicted (1.74%) D2O %BF with the Lange caliper. With the Holtain caliper DW successfully predicted D2O %BF (r = 0.91, SEE = 3.8%). In whites, DW overpredicted D2O %BF more than in blacks (4.94% vs 1.74%). Lower triceps-subscapular and thigh-subscapular skinfold-thickness ratios in black females and lower suprailiac-subscapular ratios in black males and females were found. It was concluded that blacks may have more visceral and upper-body fat deposition.

Evaluation of techniques for estimating milk production by sows 2. Estimating the milk consumption of piglets by the Deuterium oxide dilution and weigh-suckle-weigh methods

Evaluation of techniques for estimating milk production by sows 2. Estimating the milk consumption of piglets by the Deuterium oxide dilution and weigh-suckle-weigh methods

Evaluation of techniques for estimating milk production by sows 1. Deuterium oxide dilution method for estimating milk intake by piglets

Evaluation of techniques for estimating milk production by sows 1. Deuterium oxide dilution method for estimating milk intake by piglets

Relationship of anabolic status and phase and rate of growth to priorities for protein and fat deposition in steers.

The effects of anabolic implants, growth phase (growing vs finishing) and rate of growth on the priorities for protein and fat deposition were determined in yearling cattle. Santa Gertrudis crossbred yearling steers weighing 290 kg were individually fed diets varying in forage and grain content and either not implanted (n = 16) or implanted (90-d intervals) with Ralgro (n = 13) or Synovex-S (n = 12) implants. The cattle were fed toward a similar expected final empty BW (455 kg). Initial and interim empty body composition was measured via deuterium oxide dilution; final composition was determined by carcass specific gravity. During a 100-d growing phase, rates of protein gain were increased (P less than .12) to 118 and 131 g/d from 98 g/d for Ralgro and Synovex vs nonimplanted cattle, respectively. Concurrently, the fraction of protein in empty body growth was increased (P less than .09) from 17.5% for controls to 23.8 and 19.7% for Ralgro- and Synovex-implanted steers, respectively. This change in protein growth occurred concomitant with mobilization of fat and a reduction (P less than .04) in fat gain with Ralgro and Synovex implants. During the 136-d finishing phase, protein accretion was 115 and 132 vs 93 g/d for Ralgro- and Synovex-implanted cattle vs nonimplanted cattle; this represented a 24 and 42% increase (P less than .03) with Ralgro and Synovex, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein reserves in lactating dairy goats

Six primiparous Alpine does were confined to metabolism crates beginning 2 weeks postpartum. Initially, all were fed a 15.8% crude protein diet which met N.R.C. requirements for maintenance and lactation. Thereafter, subjects were fed an isocaloric diet containing 7.2% crude protein to deplete body protein, and then repleted with the higher protein diet. Nitrogen balances were determined by continuous collection of urine, feces and milk. Samples of these products were analyzed for nitrogen by the Kjeldahl method. Deuterium oxide (D 2O) dilution was used to determine body composition. Nitrogen mobilization ranged from 0 to 10.8% of total body nitrogen. Urinary nitrogen output decreased 75% during the first 6 days of depletion and remained stable until repletion. Milk nitrogen decreased an average of only 31% during the depletion period with wide individual variation while fecal nitrogen declined 26%. Milk and fecal nitrogen declined gradually over the whole depletion period. The primary route of nitrogen conservation appeared to be an immediate decrease in urinary nitrogen, followed by a decline in milk production. Milk production capacities of tested does were related to the ability to mobilize protein or use tissue reserves. This has important implications for the study and management of protein nutrition in lactating ruminants.