Utilization Of Energy For Maintenance Research Articles

Energy and protein requirements of young Holstein calves in tropical condition.

Our objective was to estimate the energy and protein requirements of Holstein young calves up to 87days old. Forty-two Holstein calves aged 4days were used. From these, ten were randomly selected and slaughtered to compose the baseline slaughter (BS) group. The remaining calves were randomly assigned to eight treatments in a 4 × 2 factorial using a completely randomized design. The treatments were 2, 4, 6, and 8kg/day of milk (297g/kg CP; 319g/kg of fat) fed twice daily, and then harvested at 59 or 87days of age. Calves were fed a starter (193g/kg CP; 133g/kg NDF) ad libitum in all treatments. The calves slaughtered at 87days of age had milk replaced by Coast-cross (Cynodoon sp.) hay (125g/kg CP; 728g/kg NDF). The net requirement of energy for maintenance (NEm) was 0.36MJ/kg EBWG, with efficiency of utilization of energy for maintenance (k m) of 59.4%. The equation obtained to estimate the net requirement of energy for gain (NEg; MJ/d) was 4.40 × EBW(0.099), with the efficiency of utilization of energy for gain (k g) equal to 46.5%. The observed requirements of net and metabolizable protein for maintenance (NPm and MPm) were 3.67 and 3.88g/kg BW(0.75), respectively. The efficiency of use of metabolizable protein for maintenance (k pm ) was 94.6%. The predicted requirements were higher than those observed in the literature, and this study demonstrated that the requirements of newborn calves are higher than the recommended.

Metabolizable Amino Acid Requirements of Feedlot Calves

One hundred ninety-two crossbred steers (229 kg) were used to evaluate the influence of metabolizable amino acid intake on growth performance and health during the initial 42-d receiving period. Treatments consisted of four levels of metabolizable lysine (23, 24, 25 and 26 g/kg diet DM). Morbidity averaged 36%, and was not affected (P > 0.20) by treatments. No steers died during the study. Increasing the metabolizable lysine supply increased DMI, ADG, gain efficiency, and dietary NE (linear effect, P < 0.01). Metabolizable amino acid supply of the basal diet was determined using 6 steers (214 kg) with cannulas in the rumen and proximal duodenum. Metabolizable amino acid supply of the diet was in close agreement with expected (R2 = 0.99; P < 0.0001) based on NRC (2000) [12] Level 1 model. The metabolizable amino acid supplies for treatments in Trial 1 were estimated by adding tabular metabolizable amino acid values for the respective supplemental proteins (cottonseed meal and fish meal) to the observed metabolizable amino acid supply of the basal diet. Treatment effects on metabolizable lysine supply explained 99% of the variation (P < 0.01) in ADG, and 91% of the variation in observed versus expected dietary NE. The biological value for the intestinal chyme was determined based on chemical score technique, using bovine tissue as the reference protein. Accordingly, methionine and lysine were closely co-limiting amino acids having ratios of 77% and 79%, respectively. We conclude that current NRC standards reliably predict both requirements and supplies of metabolizable amino acids for feedlot calves. Diet formulations that do not meet the metabolizable amino acid requirements may depress both ADG and the partial efficiency of utilization of metabolizable energy for maintenance and gain.

Efficiency of metabolizable energy utilization for maintenance and gain and evaluation of Small Ruminant Nutrition System model in Santa Ines sheep

This study was carried out to estimate efficiencies of the utilization of metabolizable energy for maintenance (km) and weight gain (kg) and to evaluate the Small Ruminant Nutrition System (SRNS) model in predicting dry matter intake and average daily gain of growing Santa Ines sheep. Twenty-four non-castrated Santa Ines sheep, at 50 days of age and with average body weight of 13.00 ± 0.56 kg, respectively, were used. After a 10-day adaptation period, four animals were slaughtered to be used as reference for estimating initial empty body weight and body composition of the other animals. The remaining animals were distributed in a random block design, with the treatments consisting of diets containing different levels of metabolizable energy (2.08, 2.28, 2.47 and 2.69 Mcal/kg of DM), with five replicates. The metabolizable energy use efficiencies for maintenance and for weight gain were calculated from the relationship between the dietary net energy for maintenance and gain and ME concentration in the diets. Evaluation of the SRNS model was performed by adjustment of simple linear regression model between the predicted (independent variable) and observed (dependent variable) values. The estimated energy use efficiency for maintenance (km) was 0.70; and for gain weight (kg) it showed to be inversely proportional to the increase of metabolizable energy concentration in the diet. The dry matter intake predicted by the SRNS model did not statistically differ from that observed, but the model overestimated the average daily gain by 5.18%. Those results can contribute to the construction of a database, which could be condensed into several others in a predictive model of performance and feed planning for sheep reared in Brazil.

Estimation of the total efficiency of metabolizable energy utilization for maintenance and growth by cattle in tropical conditions

Data of 320 animals were obtained from eight comparative slaughter studies performed under tropical conditions and used to estimate the total efficiency of utilization of the metabolizable energy intake (MEI), which varied from 77 to 419 kcal kg-0.75d-1. The provided data also contained direct measures of the recovered energy (RE), which allowed calculating the heat production (HE) by difference. The RE was regressed on MEI and deviations from linearity were evaluated by using the F-test. The respective estimates of the fasting heat production and the intercept and the slope that composes the relationship between RE and MEI were 73 kcal kg-0.75d-1, 42 kcal kg-0.75d-1 and 0.37. Hence, the total efficiency was estimated by dividing the net energy for maintenance and growth by the metabolizable energy intake. The estimated total efficiency of the ME utilization and analogous estimates based on the beef cattle NRC model were employed in an additional study to evaluate their predictive powers in terms of the mean square deviations for both temperate and tropical conditions. The two approaches presented similar predictive powers but the proposed one had a 22% lower mean squared deviation even with its more simplified structure.

ENERGY EXPENDITURE AND ITS COMPONENTS IN FREE-LIVING ARABIAN BABBLERS (TURDOIDES SQUAMICEPS)

We determined the energy budget of the Arabian babbler (Turdoides squamiceps; Timaliidae), including the efficiency of energy use, using published data on resting metabolic rate (RMR), existence energy (EE), and field metabolic rate (FMR) of this desert passerine. Resting metabolic rate of the babblers was 0.65 kJ g-1 d-1 and EE was 1.10 kJ g-1 d-1. Therefore, RMR was approximately 59% of existence energy, and the efficiency of utilization of metabolizable energy for maintenance was 0.59. The heat increment of feeding (HIF) for maintenance for a diet of insects was 0.41, that is, 41% of the metabolizable energy consumed was used for food utilization. FMRs in summer and winter were similar and averaged 1.65 kJ g-1 d-1,breeding was 2.02 kJ g-1 d-1. The difference between either summer or winter FMR and EE in non-breeding babblers, 0.55 kJ g-1 d-1, was due to activity, mainly foraging, and may have included thermoregulatory costs in free-living birds. Breeding babblers required 0.37 kJ g-1 d-1 more than non-...

Energy cost of ectoparasitism: the fleaXenopsylla ramesison the desert gerbilGerbillus dasyurus

AbstractMetabolizable energy intake and changes in body mass was measured in the desert gerbilGerbillus dasyuruswhen parasitized by the fleaXenopsylla ramesis. We hypothesized that energy requirements for maintenance, or average daily metabolic rate, of parasitized gerbils would be higher than those of non‐parasitized gerbils. We also hypothesized that the efficiency of utilization of energy for maintenance would be the same for parasitized and non‐parasitized gerbils, as this measurement is dependent mainly on dietary quality. Fifty fleas feeding on a gerbil consumed 3.68±1.19 mg blood, in total. This amounted to 34.3±1.8% of body mass of a starving flea and only about 0.17% of the blood volume of the host. The absolute amount of blood consumed byX. ramesisis the lowest reported for fleas in other studies. This suggested that the pressure of parasitism ofX. ramesisonG. dasyurusin terms of blood consumed was relatively low. Both our hypotheses were confirmed. Average daily metabolic rate of the parasitized gerbils (7.75 kJ g−0.54d−1) was 16% higher than that of non‐parasitized gerbils (6.69 kJ g−0.54d−1). In addition, at zero metabolizable energy intake, the parasitized gerbils lost body mass at a faster rate than the non‐parasitized gerbils (4.34vs3.95% body mass d−1). The efficiency of utilization of energy in the parasitized and non‐parasitized gerbils was similar.

Net energy value of timothy and bromegrass silages for beef cattle

Metabolizable energy (ME), net energy for maintenance and net energy for growth of grass silages were evaluated by the comparative slaughter technique using a 2 × 2 × 3 factorial design. Sixty medium frame beef steers (259 ± 29 kg BW) were divided in groups of five and fed during 3 months either Timothy (T) or Bromegrass (B) harvested at stem elongation (S) of the first cut or at boot stage of the aftermath (A). Forages were fed at one of three levels of intake: ad libitum (FF), 80% of FF, or 65% of FF. Silages averaged 26.9% DM, 16.0% CP and 37.7% ADF. Regression of logarithm of heat production (HE) against ME intake were similar for all silages (log HE = 0.00046*ME + 2.4923; r2 = 0.89). From this equation, fasting HE of 311 kJ kg−0.75 d−1, ME for maintenance of 559 kJ kg−0.75 d−1 and efficiency of utilization of energy for maintenance of 56% were determined. Regression of ME intake against retained energy (RE) were similar for all silages. Efficiency of ME utilization for growth was 33% using the regression of ME over RE with a ME requirement for maintenance fixed at 559 kJ kg−0.75 d−1. Net energy for maintenance and growth were similar for all silages, averaging 6.17 and 3.70 MJ kg−1, respectively. The use of a prediction equation based on ADF of forages underestimated ME values of silages by approximately 25%. Moreover, NRC (1984) equations that estimate NE from experimentally estimated ME values tended to overestimate the net energy of our grass silages. Key words: Net energy, grass silages, timothy, bromegrass, beef cattle

Average daily metabolic rate of rodents: habitat and dietary comparisons

1.Average daily metabolic rate (ADMR) is the metabolizable energy intake required by a caged animal to maintain constant body energy content. Linear regression of standardized, phylogenetically independent contrasts was used to describe the allometric relationship between ADMR and body mass in rodents. It was predicted that desert species would have a lower ADMR than non‐desert species and that granivores would have a lower ADMR than those of herbivores and omnivores. The efficiency of utilization of energy for maintenance was also determined in these species. Here, it was predicted that the efficiency in granivores would be higher than in both herbivores and omnivores and in desert species would be higher than in non‐desert species.2.The regression of the phylogenetic contrasts of ADMR on body mass (mb) for 53 independent data points based on 63 species of rodents was highly significant (P&lt; 0·0001) with an allometric slope of 0·53. Independent comparisons of both basal metabolic rate (BMR) and ADMR showed significantly lower rates in desert than in non‐desert species. There was a trend for granivores to have a lower ADMR per g0.53than either omnivores or herbivores, but this trend is not significant in independent comparisons between the categories. Thus, the predictions in regard to desert and non‐desert habitats were confirmed, and there is a non‐significant trend in the predicted direction with respect to diet. Herbivores and omnivores showed no significant difference in either BMR or ADMR.3.In independent comparisons between categories, there was no evidence for trends in the efficiency of utilization of energy for maintenance (BMR:ADMR ratio orkm) with either habitat or diet categories. Thus, these results are not in agreement with our predictions. Taking simple means,kmequals 0·47±0·21, 0·37±0·12 and 0·56±0·11 for granivores, omnivores and herbivores, respectively, and 0·37±0·12 and 0·55±0·16 for desert and non‐desert mammals, respectively.4.It is recommended that conditions for ADMR measurements be standardized, as is common for basal metabolic rate measurements. This would allow more reliable comparisons among species measured in different laboratories and also provide more accurate estimates of efficiency of utilization of energy.

Energy utilization for maintenance and growth in preruminant kid goats and lambs

Energy metaboclism of the Granadina kid goat and the Segureña lamb was analysed by an experiment on different feeding levels and comparative slaughter. The metabolizable energy (ME) intake, total energy retention, energy retained as protein and energy retained as fat were determined in both kinds of animal for their first 2 months of life. ME requirements for maintenance, ME efficiencies for energy retention and ME intake values at which protein retention and fat deposition begin to occur were estimated by the regression method. The estimated ME requirements for maintenance and ME efficiencies for energy retention were: 456 kJ per kg 0.75 per day and 0.55 for kid goats, and 393 kJ per kg 0.75 per day and 0.54 for lambs, respectively. Values of ME intake at which protein retention and fat deposition begin to occur were: 258 and 575 kJ per kg 0.75 per day for kid goats, and 428 and 362 kJ per kg 0.75 per day for lambs, respectively. According to the results obtained, it was deduced that kid goats compared with lambs show a higher ME requirement for maintenance together with a higher partial efficiency of ME utilization for protein retention and a lower partial efficiency of ME utilization for fat deposition.

Energy and protein metabolism of the Chinese pig.

Sixteen Chinese pigs (Meishan breed) from four litter outcome groups with initial weights ranging from 6 to 22 kg BW were used in a 28-d comparative slaughter experiment to determine the utilization of energy for maintenance and growth and the utilization of protein and amino acids (AA) by the Chinese pigs. Pigs were randomly allotted from litter outcome groups to four replicates of four pens each and to four treatments within replicates. A corn-soybean meal basal diet was formulated to provide all the nutrients except energy at twice the recommended levels for 10- to 20-kg pigs. The treatments were the basal diet fed at 3, 4, or 5% of BW. The fourth treatment was the initial slaughter group. As level of feeding increased, ADG increased linearly (P < .01) and gain:feed ratios increased quadratically (P < .06). Increasing the level of feeding had no effect on apparent digestibility coefficients of DM, N, or GE. Fecal N, urinary N, urinary urea N, and N retention increased linearly (P < .01) as feed intake increased. Level of feeding did not affect the DE, ME, or NE concentration in the diet. Metabolizable energy as a percentage of DE averaged 92.7% and was not affected by feeding level. Percentage of ether extract and DM of the empty body increased linearly (P < .01), but percentage of water decreased linearly (P < .01) with the level of feeding. Percentage of CP and ash of the empty body were not affected by the level of feeding (P > .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cimaterol on energy utilization for maintenance and for protein and fat deposition by wether and ewe lambs given chopped lucerne hay or lucerne-barley pellets

ABSTRACTThe effects of sex (wethersv.ewes), diet (chopped lucerne hayv.lucerne-barley pellets) and cimaterol on energy utilization by Suffolk cross lambs were determined by comparative slaughter. Quadratic regression of energy retention (RE) on metabolizable energy intake (MEI) enabled estimation of maintenance energy requirements (Em), efficiencies of gain (ktotal) and maximum rates of gain (REMAX). Regressions using RE in fat and proteinv.MEI yielded analogous parameters for fat and protein deposition (Em fat, kfat, REMAX fatand Emprotcin, kprolein, REMAXprotcinrespectively). Emwas lower in wethers than ewes (455v.510 kJ/kg M0·75per day respectively), but was unaffected by diet or cimaterol. Sex and cimaterol did not affect ktotai. which was higher in lambs given pellets compared with lambs given hay (0·417v.0·224 respectively). Similarly, REMAXwas higher in lambs given pellets than in lambs given hay (326v.114 kJ/kg 0·75 per day respectively). None of the groups differed significantly in the parameters of fat deposition, which averaged 480 kJ/kg 0·75 per day for Emfal, 0·224 for ktat, and 250 kJ/kg M0·75per day for REMAX, fat-Em.proteinwas lower in wethers than in ewes (466v.569 kJ/kg 0·075 per day, respectively), and was further reduced by cimaterol (418 and 507 kJ/kg 0·75 per day for wethers and ewes respectively). Estimates of kprotcin were higher in wethers than in ewes (0·091v.0·064 respectively), and were increased by cimaterol (0·115 and 0·089 for wethers and ewes respectively). Similarly REMAX protein was higher in wethers than in ewes (47v.37 kJ/kg 0·75 per day respectively), and was increased by cimaterol (58 and 48 kJ/kg 0·75 per day for wethers and ewes respectively). The repartitioning action of cimaterol was additive with effects of diet, intake and sex.

Within-herd variation in energy utilization for maintenance and gain in beef cows.

Fourteen mature, nonpregnant, nonlactating Angus cows (498 kg) were individually fed through two consecutive phases (maintenance [M], 80 d and ad libitum [A], 70 to 79 d) to estimate within-herd variation in individual cow ME requirements for maintenance (MEm) and to identify factors contributing to this variation. Body composition was determined at initiation of phase M, at termination of phase M (also initiation of phase A) and at the end of phase A by a two-pool D2O dilution technique. Daily MEm averaged 156.7 kcal/kg BW.75 (SD = 18.4 kcal/kg BW.75) and efficiency of ME use for tissue gain or loss averaged 76% (SD = 30%). Estimates of ME intake to maintain 1 kg of protein or 1 kg of fat were 192.9 (SE = 24.8) or 20.7 (SE = 21.5) kcal. These data indicate that among cows of similar fat masses, those with larger protein masses had higher energy requirements for maintenance. Daily MEm was positively correlated (P less than .16) with liver weight (r = .40) and relative proportions of liver (r = .44; P less than .16) and heart (r = .48; P less than .10) in the empty body. Also, daily MEm was correlated negatively (P less than .05) with weight (r = -.71) and relative proportion of omental and mesenteric fat (r = -.78). Estimates of ME required for deposition of 1 kcal of protein or fat were 5.56 (SE = 1.01) or 1.26 (SE = .09) kcal. Weight of liver and the sum of liver, spleen, kidney and heart weights increased 1.58 (R2 = .47) and 1.95 kg (R2 = .52) per kilogram of daily weight gain during phase A. These results indicate that increased performance caused increased organ mass (liver).

Monensin induced metabolic changes in cattle fed a restricted intake of lucerne hay

O'Kelly (1985) has presented evidence which suggests that at the same feed intake Brahman cross cattle synthesize more microbial lipid than British cattle with a resultant increased efficiency of utilization of metabolizable energy for maintenance. The lipid content of bacteria associated with both liquid and solid fractions of rumen contents is also higher in Brahman than in Hereford cattle (J. C. O'Kelly &amp; W. G. Spiers, unpublished). The reasons for these breed differences are unknown. A step in investigating the problem could be to determine whether microbial lipid content in Hereford cattle can be increased by altering rumen fermentation patterns in association with changes in the microbial population. Ionophores alter rumen fermentation by increasing the production of propionic acid relative to other volatile fatty acids and also inhibit Gram-positive bacteria by facilitating the formation and transport across cell membranes of lipid-soluble complexes with various cations (Bergen &amp; Bates, 1984). However, there are no reports on the effects of ionophores on microbial lipid metabolism in cattle on restricted feed intakes typical of those in tropical areas.

The energy value to sheep of saturated and unsaturated fat fed singly or in combination

ABSTRACTFour diets containing either 0 or 50 g fat per kg were prepared from a basal mix of barley, sugar-beet pulp, soya-bean meal and molasses. The fats used were tallow (saturated), soya-acid oil (unsaturated), or a 45:5 mixture of both fats. The diets were given with chopped dried grass to adult wether sheep in the ratio 4:1 of diet to dried grass. Measurements of heat production of the sheep were made in closed-circuit respiration chambers and from the data the efficiencies of utilization of energy for maintenance (km) and production (kf) were calculated for each diet, together with the metabolizable energy (ME) values for the fats.Values for bothkmandkfwere not significantly different between diets, the means were 0·81 and 0·61 respectively. The ME values (MJ/kg DM) of the fats were for tallow 36·2, for soya-acid oil 36·6 and for the tallow/soya mixture 31·6; these values were not significantly different.No evidence of any synergistic effect caused by the addition of an unsaturated fat to a saturated fat was seen in this experiment.

Utilization of Energy for Maintenance and Gain in Broilers and Leghorns at Two Ages

Regression equations describing die relationship between energy gain and metabolizable energy intake per unit metabolic weight were derived for 8- to 22-day-old and 28- to 42-day-old broilers and 14- to 28-day-old and 28- to 42-day-old Leghorns. The estimated maintenance energy requirements were lower in the 28-to 42-day-old birds than in the younger birds, but the decreases were small. Maintenance energy requirements of Leghorns were 36% less than those of broilers. Age had no effect on the efficiency of energy utilization above maintenance in broilers. However, the efficiency of energy utilization above maintenance in Leghorns was 43% lower in the older birds. This was correlated with a lower percentage fat gain in the older Leghorns. The percentage fat gain in broilers was substantially higher in the older birds, but this was not correlated with changes in energetic efficiency.

Adaptation to Underfeeding in Growing Rats. Effect of Energy Restriction at Two Dietary Protein Levels on Growth, Feed Efficiency, Basal Metabolism and Body Composition

Adaptation to a 50% restriction in energy at two levels of protein intake was studied in growing male and female rats. Growth was proportional to diet intake. The basal metabolic rate (BMR) (VO2/kilogram0.75) was unaltered, whereas the percent fat deposited was reduced in diet-restricted rats at both 10% and 20% levels of protein. The percent of the total energy intake for tissue deposition was reduced in food-restricted groups to such an extent that the amount of energy available over what is required for tissue deposition was the same in all groups. The relationship between energy available for maintenance and that for BMR was low in diet-restricted groups. These observations suggest that growing rats adapt to low energy intake by reducing tissue deposition and by better utilization of energy for maintenance without reducing BMR. By lowering protein level in the diet feed efficiency is reduced in both diet-restricted groups and groups fed ad libitum.

Utilization of energy for maintenance and production in dairy cows given protected tallow during early lactation

SummaryDuring the first 13 weeks of lactation, four groups of seven cows were given hay and a basal concentrate mix containing 0, 1·7, 3·3 or 5·0 kg/day of a protected lipid supplement (320 g long-chain fatty acid/kg D.M.). The proportion of hay to total concentrate was maintained at 25:75 and cows were fed to appetite.The total amount of energy digested corrected for endogenous loss (DEc) was partitioned into crude protein energy (CPEc), fatty-acid energy (FAEc), ‘carbohydrate’ (non-protein non-fatty acid) energy (CEC) and non-fatty-acid energy (NFAEc = CPEc + CEc).Partial efficiency of milk production and live-weight gain was curvilinearly related to FAEc, maximum efficiency occurring at about 30 MJ/day of FAEc.Net energy utilized was significantly related to DE0c for both of the periods considered, Weeks 2–6 and weeks 7–13. In addition, a curvilinear effect of the ratio of fatty acid energy to non-fatty-acid energy was established. At fixed intakes of digestibl energy, net energy utilized was maximal for ratios of FAEc/NFAEc of 0·14 and 0·18 for weeks 2–6 and 7–13 respectively.Milk yield was significantly related to DEc for weeks 1–6 and 7–13; milk energy yield was significantly related to DEc for weeks 7–13. The multiple regression relationships between milk yield or milk energy yield and CPEc, FAEc and CEc gave a negative effect of crude protein, possibly indicating that the proportion of total energy supplied as crude protein (18–26% of DEc) was above the optimum requirement.At fixed intakes of digestible energy, outputs of milk and milk energy were maximal at ratios of FAEc/NFAEc of 0·16 and 0·15 for weeks 1–6 and 7–13 respectively. The inclusion of a curvilinear effect of total energy (DEc2) gave some indication that utilization of energy for milk production for weeks 7–13 diminished at the highest digestible energy intakes whilst energy utilized for live-weight gain increased.

Utilization of Energy for Maintenance and for Fat and Lean Gains by Mice Selected for Rapid Postweaning Growth Rate

The metabolizable energy intake (MEI) required for maintenance and the efficiency of utilization of metabolizable energy available for gain (MEA) were determined for a line of mice (rapid growth) selected for 41 generations for rapid postweaning weight gain and for a contemporarily mated line (control) that had been randomly selected. Feed intake of individually housed rapid growth and control males was restricted above maintenance or was ad libitum from 21 to 42 days of age. Regressions of change in body energy per unity metabolic body size on MEI per unit metablic body size showed that the maintenance requirement for each line of mice was 176 kcal per unit metabolic body size per day and that the rapid growth line was more efficient than the control line in utilizing MEA (50% vs. 23%) to promote an increase in body energy. Although the proportions of MEA used for fat (PF) and lean (PL) gains and the net efficiencies with which those proportions were utilized for fat (NF) and lean (NL) gains were unknown, the products of proportion and efficiency for fat gain (PF X NF or fat energy deposition coefficient) and for lean gain (PL X NL or lean energy deposition coefficient) were determined. The results demonstrate that 41 generations of selection for rapid postweaning weight gain did not change the lean energy deposition coefficient, but did alter the fat energy deposition coefficient. These data suggest that the two lines of mice use different proportions of MEA for fat gain and/or utilize MEA for fat gain at different efficiencies.

Maintenance requirements for energy in cross-bred cattle.

1. Twenty-seven energy and protein balances were done using nine cross-bred (Brown Swiss times Sahiwal) mature bullocks in a series of three balance trials. The bullocks were fed 75, 100 and 125 percent of the metabolizable energy (ME) and digestible crude protein standard values recommended by the (US) National Research Council (1966). Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. 2. Utilization of energy for maintenance and fat production was estimated by computing regression of energy balance v. digestible energy (DE) and ME separately on a metabolic body size (kg body-weight (W)0-75) basis. Maintenance energy requirements and efficiency of utilization of ME for lipogenesis were estimated using multiple regression of ME intake, also. Heat production (and thus energy balance) was corrected for excess nitrogen intake. 3. An attempt was made to measure basal heat production of bullocks so that the net energy requirements for maintenance could be estimated. Extrapolation of the regression line of energy balance v. ME intake below maintenance on a W0-75 basis gave a basal metabolism of 348-09 kJ/W0-75 per d. 4. Energy requirements for maintenance were (kJ/kg W0-75 per d): 539-43 DE, 448-81 ME and 348-09 net energy. The results of multiple regression gave a requirement of 432-15 kJ ME/kg W0-75 per d for maintenance. 5. The efficiency of utilization of ME for maintenance was 81-34 percent while for lipogenesis it was 54-5 percent.

The net energy value of three subtropical forages

Energy and nitrogen balance experiments with three subtropical forages, a legume and two grasses, are reported. Each forage was given to four sheep at several levels of feeding. One of the forages had a low nitrogen content (4% crude protein) and was supplemented with urea and molasses containing 7 g nitrogen and 56 kcal/day. This caused voluntary consumption to increase by 50% and digestibility of all chemical constituents to increase by 6–12 units. Utilization of metabolizable energy for maintenance also improved by approximately 10%. Digestible energy (42–62%) was predicted quite accurately from chemical composition by means of published equations which refer to forages grown in temperate climates. Metabolizable energy was close to 82% of digestible energy, as found with non-tropical forages. Net availability of metabolizable energy for maintenance ranged from a very low 60% to 80%. It was predicted more accurately from percentage metabolizable energy than from digestible crude fibre: the reverse applied to net availability for production (40–50%).