Utilization Of Metabolizable Energy For Maintenance Research Articles

Energy requirement for primiparous Holstein × Gyr crossbred dairy cows

Our objective was to estimate the requirements of metabolizable energy (ME) and NEM of lactating and dry cows, the efficiency of ME utilization for milk production (kl) and tissue gain (kg), and the use of body energy mobilization for milk production (kt) throughout the lactation of primiparous crossbred Holstein × Gyr cows, using open-circuit respiration chambers. Twenty-nine primiparous Holstein × Gyr crossbred cows with an initial BW averaging 563 ± 40.1 kg and 2.5 ± 0.09 yr old were used throughout lactation and dry periods. The cows were kept nonpregnant throughout the study to eliminate possible confounding factors. Apparent digestibility assays, followed by calorimeter measurements, were performed 6 times throughout the lactation period. In the dry-off period, the cows were also evaluated but fed with restricted intake (DMI = 1.1% BW/d) to achieve heat production close to maintenance. After 21 d of diet adaptation, an apparent digestibility assay followed by calorimeter measurements was performed. Parameter estimates for lactation period were obtained by mixed models including lactation stage as repeated measures. For restricted feeding at dry-off and fasting period assays, the requirements were estimated by exponential regression. For whole lactation, the values of the ME requirement for maintenance (MEM) and NEM were 0.588 and 0.395 MJ/BW0.75, respectively. The efficiencies of kl, kg, and kt were 0.672, 0.771, and 0.814, respectively. However, MEM and NEM were higher in early and mid lactation than late, whereas kl was higher in early than other lactation stages. Dry and nonpregnant cows had MEM of 0.434 MJ/BW0.75 and NEM of 0.351 MJ/BW0.75 for maintenance level, and MEM of 0.396 MJ/BW0.75 and NEM of 0.345 MJ/BW0.75 for fasting metabolism level, and efficiency of ME utilization for maintenance was 0.80. Our findings confirmed that F1 crossbred Holstein × Gyr dairy cows have differences in energy requirement and efficiency throughout the lactation stages, suggesting the use of different values in each stage. The estimated values of energy requirement for maintenance and efficiencies for primiparous lactating crossbred Holstein × Gyr were similar to those reported in the literature in specific studies and requirements systems.

Oscillating and static dietary crude protein supply: II. Energy and protein requirements of young Nellore bulls.

:The objective of this study was to evaluate whole body chemical composition and energy and protein nutrient requirements for maintenance and gain of Nellore bulls. Fifty young bulls, with an average age of 7 ± 1 mo and initial body weight (BW) of 260.0 ± 8.1 kg, were used in this experiment. Four bulls were used as baseline reference animals and were slaughtered at the beginning of the experiment. Four bulls were fed at maintenance (12 g dry matter [DM]/kg of BW), whereas 42 bulls were divided into six groups (n = 7/group) and were randomly assigned to the following dietary treatments 105 (low [LO]), 125 (medium [MD]), or 145 (high [HI]) g crude protein (CP)/kg DM, LO to HI (LH), LO to MD (LM), or MD to HI (MH) oscillating CP at a 48-h interval for 140 d. At the end of the experiment, bulls were slaughtered and samples of the whole body were collected. All samples were lyophilized, ground, and composed as percentage of component of empty body weight (EBW) from each bull. A power model was used to estimate carcass, non-carcass components, and gastrointestinal content of the shrunk body weight (SBW), and CP and water present in the empty body, whereas an exponential model was used to estimate adipose tissue and ether extract (EE) present in the EBW. Nonlinear regression equations were developed to predict heat production from metabolizable energy (ME) intake and retained energy (RE). The net energy requirements for maintenance and ME for maintenance were 77 and 122.75 kcal/EBW0.75/d, respectively. The efficiency of ME utilization for maintenance was 62.7%. The equation obtained for net energy for gain (NEg) was: NEg (Mcal/EBW0.75/d) = 0.0535 × EBW0.75 × EBG0.7131, where EBG is the empty body gain, and the efficiency was 24.25%. Net protein requirement for growth (NPg) was: NPg (g/d) = 227.372 × EBG – 19.479 × RE. There was a linear increase for carcass, CP, and water present in the EBW as the animal grew. The EE deposition exponentially increased as EBW increased.

Energy requirements of hair sheep in the tropical regions of Latin America. Review

Los ovinos de pelo juegan un papel importante en la producción animal en las regiones tropicales; sin embargo, sus requerimientos nutricionales no se han determinado en la misma medida que los de las razas de lana. Debido a las condiciones ambientales de las regiones tropicales (clima, calidad y disponibilidad de alimentos), es razonable la hipótesis de que los requerimientos de energía metabolizable (EM) y la eficiencia de utilización de la EM pueden ser diferentes entre los ovinos de razas de pelo y de lana. La información disponible en ovinos de pelo muestra una gran discrepancia en cuanto a las necesidades de energía. Con base en datos de la literatura disponible para hembras ovinas, el requerimiento de EM para mantenimiento (EMm) fue de 419±129 kJ/kg PC0.75 (media ± desviación estándar) y para machos fue 388±123 kJ/kg BW0.75. El requerimiento de energía neta para la ganancia de peso (ENg) varió de 8.75 a 14.06 kJ/g (11.63±1.86 kJ/g). Las eficiencias de utilización de la EM para el mantenimiento (km) y la ganancia de peso (kg) fueron de 0.66±0.023 y 0.42±0.044, respectivamente. Esta revisión también indicó que la información es escasa para ovejas adultas en diferentes etapas fisiológicas (mantenimiento, lactancia y gestación).Se requiere más trabajo de investigación con relación a la estimación de las necesidades de energía de los ovinos de pelo, con el fin de hacer ajustes a los modelos existentes de alimentación, con el objetivo de predecir la respuesta de los animales con la condición que prevalece en los trópicos (tipo de animal, medio ambiente y alimentos disponibles).

Energy partitioning and methane emission by sheep fed sorghum silages at different maturation stages

Energy partitioning and methane production by sheep fed silages of three commercially available sorghum hybrids (BRS 610, BR 700 and BRS 655) harvested at three maturation stages (milk, soft dough and floury) were evaluated in open circuit respiration chambers. A complete randomized design was used in a 3 × 3 (hybrids × maturity stages) factorial arrangement, and the means were compared by the Student-Newman-Keuls (SNK) test (P<0.05). The intake of dry matter, digestible dry matter, gross energy, digestible energy and metabolizable energy were not affected by maturation stage, but were influenced by hybrid. The net energy intake was influenced by maturity and sorghum genetics. The fecal output represented the main source of energy loss, as percentage of gross energy intake (48% to 52%), followed by heat increment (10% to 19%), methane emissions (4% to 6%) and urine (1% to 2%). There were no differences (P>0.10) among the treatments for the apparent digestibility of gross energy and metabolizability (qm). An interaction (P<0.05) between sorghum hybrid and maturation stages was observed for the efficiency of metabolizable energy utilization for maintenance (km), which ranged between 0.53 and 0.78. No differences (P>0.10) among treatments occurred in the daily methane production. There is substantial genetic diversity within sorghum species, determining different nutritional values. Sorghum genetics and maturity at harvest should not be an opportunity to reduce the contribution of agriculture to methane emissions.

Energy requirements for maintenance and growth of Dorper crossbred ram lambs

This study aimed to determine the energy requirements of Dorper crossbred sheep that have been used for meat production in China. Thirty-five 1/2 Dorper×1/2 thin-tailed Han crossbred noncastrated ram lambs [34.1±0.6kg body weight (BW)] were used in a comparative slaughter trial. Seven ram lambs were randomly selected as the baseline group and slaughtered at 35kg BW. The remaining 28 lambs were randomly divided into four groups of seven lambs each. Three of the four groups were fed a mixed diet either for ad libitum intake, 60% or 45% of the ad libitum intake. The three groups were slaughtered when the ram lambs that were fed ad libitum reached 50kg BW. The ram lambs from the fourth group were also fed ad libitum as an intermediate group and slaughtered at 43kg BW. Total body energy, nitrogen, fat, ash, and moisture content were measured. In a digestibility trial, another 15 ram lambs (41.3±0.8kg BW) were housed in metabolism cages to estimate the metabolizable energy (ME) value of the diet at the three levels of feed intake. The daily net energy (NE) requirement for maintenance was 263kJ/kg0.75 of BW or 278kJ/kg0.75 of shrunk BW (SBW), with a partial efficiency of ME utilization for maintenance of 0.69. The NE requirement for growth ranged from 1.12 to 5.31MJ/d for daily gains of 100–400g BW, or from 1.29 to 6.18MJ/d for daily gains of 100–400g SBW. The partial efficiency of ME utilization for growth was 0.46. The energy requirements of Dorper×thin-tailed Han crossbred ram lambs were lower than those recommended by the British or American nutritional systems.

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.

Effect of Protein Sources with Different Rumen Degradability in a Diet on the Efficiency of Utilization of Metabolizable Energy by Calves

Abstract. To evaluate the effect of dietary protein of diverse rumen degradability on the efficiency of metabolizable energy (ME) utilization by calves at the growth and maintenance levels of feeding. A total of 54 energy balance trials were conducted using 18 Holstein castrated male calves given four diets containing soybean meal (SBM), cottonseed meal (CSM), heated soybean meal (HSBM) and corn gluten meal (CGM) as a main source of protein. The trials were carried out at the ages of 13 weeks for the growth (G) level of feeding and 15 weeks for maintenance (M) followed by the 24-h measurement of fasting (F) heat production after 3-day fasting. The dg values were 0.657, 0.543, 0.463 and 0.413 for SBM, CSM, HSBM and CGM, respectively. The regression analyses of energy retention (ER, kJ/W0.75) on the intake of ME (IME, kJ/W0.75) above the maintenance level revealed no significant differences among diets and gave a following pooled equation: ER = 0.56(±0.04)IME – 311, r = 0.897 (P<0.01). The below M level resulted in the following two distinct equations for the diet with a higher dg of protein source and that of a lower dg: ER = 0.77(±0.02)IME – 403, r = 0.994 (P<0.01) for SBM + CSM. ER = 0.60(±0.03)IME – 350, r = 0.982 (P<0.01) for HSBM + CGM. We concluded that ME utilization for maintenance may be influenced by the protein sources of different dg, but not for growth.

The Influence of Different Fiber and Starch Types on Nutrient Balance and Energy Metabolism in Growing Pigs

A repeated 4×4 Latin square design was conducted with eight ileal cannulated castrates to examine the effect of source of starch and fiber on nutrient balance and energy metabolism. Pigs were fed on one of the four experimental diets: Control diet (C) mainly based on cooked rice; and diets P, S and W with the inclusion of either raw potato starch, sugar beet pulp or wheat bran supplementation, respectively. With the exception of an increased (p 0.05) in the ratio of metabolizable energy (ME)/digestible energy, the utilization of ME for fat deposition and for protein deposition, energy loss as hydrogen and urinary energy were found between diets. The efficiency of utilization of ME for maintenance was lower (p 0.05) by addition of potato starch. In comparison with diets C and P, a lowered ileal or fecal digestibility of energy with diets S and W was observed (p 0.05). An increased (p<0.05) proportion of NSP excreted in feces was seen by the supplementation of wheat bran. Higher NSP intake caused an increased daily amount of NSP in the ileum, but the ileal NSP proportion as a percentage of NSP intake was unaffected by diets. Feeding potato starch resulted in increased daily amount of starch measured in the ileum and the proportion of ileal starch as a percentage of starch intake, while no significant influence on fecal starch was found. Higher (p<0.05) daily amount of fecal starch and the proportion of fecal starch as a percentage of starch intake were found with fiber sources supplementation compared with diets C and P. By increasing the dietary NSP content the fecal amount of starch increased (p<0.01). (Asian-Aust. J. Anim. Sci. 2004. Vol 17, No. 2 : 263-270)

A dynamic model of metabolizable energy utilization in growing and mature cattle. I. Metabolizable energy utilization for maintenance and support metabolism

Models to predict heat production attributable to maintenance and support metabolism in growing and mature cattle were developed on the basis of three concepts. The first concept is that animals fed fixed amounts of the same diet achieve weight equilibrium over an extended feeding period, and that the ME consumed at weight equilibrium is the maintenance requirement. The second concept is that a part of the heat production resulting from ME consumed above the maintenance requirement is associated with an elevation of vital functions (support metabolism), and this heat production can be modeled as a function of the level of feeding. The third concept is that previous levels of nutrition affect current estimates of heat production, and that this impact can be modeled as a delayed response in heat production associated with support metabolism. Experimental data on feed consumption showed that maintenance requirements varied in simple proportion to BW, not only for different breeds of mature cattle at BW equilibrium, but also for calves and growing steers held at BW stasis. Experimental data in which different breeds of cattle achieved weight equilibrium when fed fixed amounts of a specific diet were used to estimate breed parameters associated with maintenance for 21 breeds of cattle and 15 biological types of crossbred cattle. Level of feeding was estimated as a multiple of the maintenance intake and used to model heat production associated with support metabolism. Other experimental data on growing cattle were used to estimate breed parameters for predicting heat production associated with support metabolism for 21 breeds of cattle and 15 biological types of crossbred cattle. A distributed lag function was used to model the delayed response in heat production associated with support metabolism with changes in plane of nutrition. The models were tested by simulating experimental data for three breeds of weaned steers finished on high-energy diets. Results for the total heat production associated with maintenance and support metabolism expressed on a unit BW basis showed a similar response with stage of maturity when compared with other experimental data.

Eficiência de utilização da energia metabolizável para ganho de peso e exigências de energia metabolizável, nutrientes digestíveis totais e proteína metabolizável de bezerros da raça holandesa

Este trabalho visou avaliar os efeitos de diferentes níveis de volumoso nas dietas, sobre a eficiência de utilização de energia metabolizável (EM) para mantença e ganho de peso e as exigências de EM, nutrientes digestíveis totais (NDT) e proteína metabolizável (PM). Quarenta e quatro bezerros Holandeses, puros por cruzamento, não-castrados, com idade média de 60 dias e peso vivo inicial de 78 kg foram usados. Oito animais foram abatidos ao início do experimento, como referência. Os 36 animais restantes foram distribuídos nos tratamentos, em delineamento inteiramente casualizado, em quatro grupos de nove animais, de acordo com o nível de volumoso nas dietas: 10, 25, 40, e 55%, na base da MS, usando-se feno de capim coast-cross (Cynodon dactylon), fubá de milho e farelo de soja, os quais constituíram dietas com aproximadamente 16% de PB. Cinco animais de cada tratamento foram abatidos quando atingiram 190 ± 10 kg e quatro, quando atingiram 300 ± 10 kg. As concentrações de energia líquida das dietas e as eficiências de utilização da EM para mantença e ganho de peso foram calculadas. As eficiências de utilização de EM para ganho de peso foram estimadas, por meio de análise de regressão, entre a energia líquida para ganho (ELg), em função da EM das dietas. As exigências médias diárias de EM, nutrientes digestíveis totais (NDT) e proteína metabolizável (PM) foram estimadas. As exigências de EM para ganho de 1 kg de peso corporal vazio aumentaram, à medida que se elevou o PCVZ dos animais. As eficiências de utilização da energia metabolizável para ganho de peso em: 0,45; 0,40; 0,40 e 0,39, respectivamente, para as concentrações de 2,98; 2,76; 2,64 e 2,53 Mcal/kg de MS, obtidas para os níveis de 10; 25; 40 e 55% de volumoso nas dietas foram estimadas. As exigências médias totais de EM e de NDT para animais de 100, 200 e 300 kg de peso vivo foram de 10,06; 14,45 e 18,12 Mcal/dia e 2,79; 4,00 e 5,02 kg/dia, respectivamente. A eficiência de utilização da EM para ganho foi maior para dietas com menor nível de volumoso.

Adaptation of whole animal energy metabolism to undernutrition in ewes: influence of time and posture

AbstractThe effects of undernutrition and of the duration of undernutrition on changes in whole animal energy metabolism and on spontaneous physical activity were studied in adult, non-lactating, non-pregnant ewes. Animals were first given food at 338 kj metabolizable energy (ME) per day per kg live weight 0·75 (LW0·75), (M). Intake was then reduced by half (0·5M) during 7 weeks. Diet apparent digestibility decreased slightly with undernutrition. Rate of LW loss remained constant throughout the whole 0·5M period. Heat production (HP) declined by proportionately 0·18 within the 1st week at 0·5M and by another 0·05 in the following weeks. These latter changes were directly related to LW loss, since HP scaled to metabolic LW remained unchanged over the whole 0·5M period. Time spent standing decreased with undernutrition from proportionately 0·42 at M to 0·33 at 0·5M as a result of a reduction in the average duration of individual standing periods at all hours of the day except in a few hours preceeding feeding times. Energy cost of standing could not be dissociated from the energy cost of eating; these overall costs were not clearly modified by undernutrition but varied with time post prandially. Standing cost alone was estimated at 10 J/min per kg LW. Efficiency of ME utilization for maintenance (km) was calculated at 0·71, and ME requirements for maintenance (MEm) at 338 kj/day per kg LW0'75. No adaptation was noted with the duration of undernutrition. Accounting for the behavioural adaptation tended to increase km to 0·74 but MEm remained unchanged, suggesting that the behavioural changes observed with undernutrition were not sufficient to significantly modify whole animal energy metabolism.

Feeding and growth of glass eels, Anguilla anguilla L.: the effect of feeding stimulants on feed intake, energy metabolism and growth

Abstract. Two experiments were conducted in which glass eels, Anguilla anguilla L., were fed with six different diets. Two natural diets, cod roe and minced bovine spleen, and four artificial diets, an unflavoured trout fry crumble and three trout fry crumble diets with added feeding stimulants, were used. The feeding stimulants tested were cod roe extract, spleen extract and a mixture of synthetic L-amino acids. In the first experiment the glass eels were fed at a restricted feeding level and in the second experiment at an ad libitum feeding level. The intake of metabolizable energy (ME) was determined as the sum of retained energy and heat production. Metabolizability of the diets decreased with increasing feeding level and was 75-95% for cod roe, 35-50% for spleen and 40-60% for the artificial diets. Since utilization of ME for maintenance and growth was not affected by feeding level and diet, differences in growth rates could be explained by differences in ME intake. Group ME intake in turn was determined by the fraction of the fish which were actually eating. The uniform feeding response of the glass eels fed the natural diets resulted in the highest ad libitum ME intake (80-90 kJ/kg0.8/day) and growth rate (4-4-4-9g/kg0.8/day). Addition of feeding stimulants significantly increased the ad libitum ME intake of the artificial diets from 45 kJ/kg0.8/day to 50-60 kJ/kg0.8/day, which resulted in an increase in growth rate from 1·3 g/kg0.8/day to 24 g/kg0.8/day.

Energy balance studies with growing Granadina goats during fasting and maintenance

Six growing female goats of the Granadina breed, aged 6 months, with weights ranging from 13.1 to 21.9 kg were used. Digestibility, nitrogen and energy balance measurements were made during two consecutive experiments with a diet of pelleted luzerne ( Medicago sativa) hay, barley and sunflower cake, which was given at about maintenance level. Gas exchange was measured by open-circuit calorimetry. Fasting heat production (FHP) was also determined. By regression analysis of body energy retention (RE) on metabolizable energy (ME) intake, FHP and efficiency of utilization of ME for maintenance ( k m) were found to be 320 kJ/kg BW 0.75/d and 0.760, respectively. Energy requirement for maintenance (ME m) was 421 kJ/kg BW 0.75/d. It also was concluded that extrapolation of FHP values from sheep can lead to underestimation of energy requirements for maintenance of goats.

Protein and energy requirements for maintenance of indigenous Granadina goats

Sixteen adult castrated male goats of the Granadina breed, with initial live weights ranging from 26.0 to 33.3 kg were used in two experiments to determine their protein and energy requirements for maintenance. Digestibility, nitrogen and energy balance measurements were made during the experiments. Two diets, which were based on pelleted lucerne (Medicago sativa) hay alone or on this forage and barley, were individually given at about maintenance level once daily. Gas exchange was measured using open-circuit respiration chambers. Fasting heat production was also determined. By regression analysis endogenous urinary N and maintenance requirements for N were estimated to be 119 mg/kg body-weight (W)0.75 per d and 409 mg total N/kg W0.75 per d respectively. Fasting heat production was 324 kJ/kg W0.75. The energy requirement for maintenance was calculated by regression of energy balance on metabolizable energy (ME) intake and a value of 443 kJ/kg W0.75 per d was found. The overall efficiency of utilization of ME for maintenance was 0.73.

The effect of dietary inclusion of starch, sucrose and xylose on the utilization of dietary energy in sheep

A calorimetric experiment of 4 × 4 Latin square design was undertaken to study the effect of sugar-beet pulp (SBP), maize starch, sucrose and xylose on energy metabolism in sheep. The four diets comprised a diet (A) of dried grass, soya-bean meal and SBP (450, 50 and 500 g kg −1 on dry matter (DM) basis) and corresponding diets in which 400 g kg −1 of SBP was replaced by maize starch (B), sucrose (C) or xylose (D); all diets were offered at a level of 600 g DM day −1. After the Latin square was completed, energy value of the basal diet of dried grass and soya-bean meal (900 and 100 g kg −1 DM; 600 g day −1) was determined in the same four sheep. Treatment differences in organic matter, gross energy, nitrogen (N) and neutral detergent fibre (NDF) digestibility were non-significant. Differences in N retention were not significant. Digestible energy (DE) contents (MJ kg −1 DM) were 13.27, 13.22, 13.21 and 13.21 MJ kg −1 for diets A, B, C and D, respectively. Energy loss in methane was higher ( P < 0.05) for Diet A than for other diets. Metabolizable energy (ME) contents for the diets A-D were 11.25, 11.22, 11.32 and 11.40 MJ kg −1 DM, respectively. Metabolizability ( q) of the diets averaged 0.642 and was not significantly affected by the diet given. There was a trend for heat production to be higher in sheep given the sucrose-containing diet (C) than in those given other diets (6.34 versus 6.04 MJ day −1) and as a result, energy retention was lower (0.38 versus 0.64 MJ day −1), but the difference did not reach statistical difference. Efficiencies of utilization of ME for maintenance and fattening ( k mf ) averaged 0.67 and were in good agreement with those predicted from equations of the Agricultural Research Council (1980) excepting the lower k mf (0.63) for Diet C. The mean ME content of SBP calculated by difference was 13.05 MJ kg −1 DM and the corresponding values for mixtures of SBP + starch, SBP + sucrose and SBP + xylose (600 and 400 g kg −1 DM) were 12.98, 13.16 and 13.36 MJ kg −1 DM, respectively.

The efficiency of energy utilization in growing cattle consuming fresh perennial ryegrass (Lolium perenne cv. Melle) or white clover (Trifolium repens cv. Blanca).

1. Twenty Friesian steers (225 kg live weight) were fed on mid- (M) (June-July) and late- (L) (August-September) season crops of either fresh perennial ryegrass (Lolium perenne cv. Melle) (G) or white clover (Trifolium repens cv. Blanca) (C). Each of the forage diets was offered at three restricted planes of nutrition above maintenance to compare the effect of forage species on the efficiency of energy utilization. All diets were harvested daily from swards of regrowth forage of intended equivalent digestibility. 2. Faecal and urine excretions were measured for 7 and 5 d respectively, followed by two consecutive 24 h measurements of methane, carbon dioxide and oxygen exchange in open-circuit respiration chambers. 3. The apparent digestibility of the energy in perennial ryegrass (0.759) was marginally higher (P less than 0.01) than that in white clover (0.748); the mid- and late-season forages were of similar (P greater than 0.05) digestibilities. Metabolizable energy (ME): digestible energy (DE) in diet G (0.837) was significantly (P less than 0.001) different from that in diet C (0.812). The partition of energy losses when expressed as MJ/GJ gross energy intake (GEI) indicated that energy lost as methane was not significantly different (P greater than 0.05) either between forages (G 62.8, C 63.4) or between seasons (M 63.2, L 63.1). Energy excretion in urine was higher for cattle fed on diet C (77.5) compared with diet G (60.5) (P less than 0.001). Heat production was similar (P greater than 0.05) between forages (G 480, C 478), but lower (P less than 0.01) for L (471) compared with M(486). Energy retention (by difference) was lower (P less than 0.001) for diet C (132) than G (156) and for M (138) than L (149) (P less than 0.05). 4. Parallel-line analysis of unscaled ME intake (MEI) in relation to retained energy (RE; MJ/d) indicated that the efficiency of utilization (kt) was similar (P greater than 0.05) between perennial ryegrass (0.42) and white clover (0.46). Linear extrapolation of the values to zero energy retention indicated that maintenance requirements of ME (Em; MJ/d) were 23.3 for diet G and 28.8 for diet C. The extrapolated Em when expressed in relation to a measured fasting heat production (FHP) of 22.8 (MJ/d) resulted in a derived efficiency of utilization of ME for maintenance (km) of 0.97 (G) and 0.79 (C), suggesting an underestimate of Em for diet G.(ABSTRACT TRUNCATED AT 400 WORDS)

Undernutrition in sheep. The effect of supplementation with protein on protein accretion.

In a comparative-slaughter experiment, individually rationed wether lambs initially of 42 kg were given 235, 362 or 456 kJ metabolizable energy (ME)/kg live weight (LW)0.75 per d as sodium hydroxide-treated barley straw with urea (six lambs per treatment), or NaOH-treated barley straw with urea plus 125 g/d white-fish meal to give 307 or 488 kJ ME/kg LW0.75 per d (seven lambs per treatment) for 92 d. All unsupplemented lambs lost both fat and body protein. The changes in fat were -3.53, -2.75 and -1.40 (SE 0.59) kg (initial value 8.6 kg), and the changes in body protein were -0.47, -0.09 and -0.14 (SE 0.13) kg (initial value 4.9 kg) for the three unsupplemented groups respectively. When supplemented with fish meal, fat was again lost as -1.53 and -0.93 (SE 0.55) kg, but wool-free body protein was increased, and gains were 0.48 and 0.89 (SE 0.12) kg for the two supplemented groups respectively. All animals lost wool-free body energy, total changes being -150, -111, -59 and -49 and -16 MJ respectively. When corrected to an equal ME intake the supplemented lambs, when compared with the unsupplemented lambs, gained (instead of losing) body protein (P less than 0.001) and lost less fat (P less than 0.05). Wool growth did not respond to supplemental protein, but was related to ME intake with an increase of 0.78 g wool fibre for each additional MJ ME. The maintenance requirements of the unsupplemented and supplemented groups respectively were estimated by regression analysis to be 554 and 496 kJ ME/kg LW0.75 per d. The apparent utilization of ME below energy equilibrium (km) was 0.31 (SE 0.08) for the unsupplemented animals, and 0.12 (SE 0.10) for the supplemented animals, well below a km of 0.70 which current UK standards (Agricultural Research Council, 1980) would predict. Most of these differences could be reconciled if basal metabolism was assumed not to be constant. It is concluded that lambs in negative energy balance can continue lean body growth at the expense of body fat, provided sufficient dietary protein is available. It is also concluded that since the animals at the lowest ME intakes required less ME than predicted by current feeding standards, the effect was that it would have been difficult to distinguish between the apparent utilization of ME for maintenance (km) and for fattening (kf).

The nutritive value of silages. Energy metabolism in sheep receiving diets of grass silage or grass silage and barley.

1. Two calorimetric experiments were conducted to study the utilization of energy in sheep given diets of grass silage or grass silage and barley. Three silages were investigated. One was made from first-harvest grass in the spring (S) and the others from regrowth cut either early or late in the autumn (E and L respectively). All were of perennial ryegress (Lolium perenne) and preserved with formic acid. Each silage was given at two levels of feeding, the lower providing approximately a maintenance energy intake. The S and L silages were also given supplemented with barley. 2. The digestibilities of organic matter, cellulose and energy in the silages were high. Measured at maintenance, digestible energy (DE) contents (MJ/kg dry matter (DM))were 11.83, 14.67 and 12.90 for S, E and L respectively. The DE contents of the S and E silages were depressed at the higher level of feeding but the effect was offset by changes in the energy losses as methane and urine. Metabolizable energy (ME) contents (MJ/kg DM) for the three silages, S, E and L were respectively 9.88, 12.54 and 10.73 at the low level of feeding and 9.91, 11.99 and 11.08 at the high level of feeding. The mean ME content of barley calculated by difference was 13.76 MJ/kg DM. 3. The mean efficiencies of utilization of ME for maintenance (km) for the S, E and L silages were 0.69, 0.71 and 0.68 respectively. Corresponding values for fattening (kf) were 0.21, 0.57 and 0.59. Excepting the kf for the S silage which was low, observed efficiencies were in broad agreement with those predicted by the equations of the Agricultural Research Council (1965). Similar agreement was obtained with all diets consisting of silage and barley.

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.