Net Protein Requirement For Maintenance Research Articles

A new protein requirement system for dairy cows

Accurate prediction of protein requirements for maintenance and lactation is needed to develop more profitable diets and reduce N loss and its environmental impact. A new factorial approach for accounting for net protein requirement for maintenance (NPM) and metabolizable protein (MP) efficiency for lactation (EMPL) was developed from a meta-analysis of 223 N balance trials. We defined NPM as the sum of the endogenous protein fecal and urinary excretion and estimated it from the intercept of a nonlinear equation between N intake and combined total N fecal and urinary excretion. Our model had a strong goodness-of-fit to estimate NPM (6.32 ± 0.15 g protein/kg metabolic body weight; n = 807 treatment means; r = 0.91). We calculated the EMPL as a proportion of the N intake, minus N excreted in feces and urine, that was secreted in milk. A fixed-EMPL value of 0.705 ± 0.020 was proposed. In a second independent data set, nonammonia-nonmicrobial-N and microbial-N ruminal outflows were measured, and the adequacy of the MP prediction (51 studies; n = 192 means treatments) was assessed. Our system based on the fixed-EMPL model predicted the MP requirement for lactation and maintenance with higher accuracy than several North American and European dairy cattle nutrition models, including the INRA (2018) and NASEM (2021). Only the NRC (2001), CNCPS 6.5, and Feed into Milk (2004) models had similar accuracy to predict MP requirement. Our system may contribute to improve the prediction for MP requirements of maintenance and lactation. However, most refined predictive models of intestinal digestibility for rumen undegradable protein and microbial protein are still needed to reduce the evaluation biases in our model and external models for predicting the MP requirements of dairy cows.

Energy and Protein Requirements for the Maintenance of Growing Male Sika Deer (Cervus nippon).

The objective of this study is to study the effects of dietary intake levels on energy metabolism, carbon (C), and nitrogen (N) balance and to determine the maintenance requirements of energy and protein for male sika deer during their growing period. A total of 16 1-year-old male sika deer with similar body weight (BW) (63.25 ± 2.42 kg) were selected, with four animals per feed intake level. The feeding levels of the four groups for deer were 40, 60, 80, and 100% of the recommended amount, respectively. The nutrient digestibility and methane production were measured through digestion trials and respiratory trials. A 4 × 4 Latin Square design was performed in a respirometry trial. The results show that the apparent digestibility of C and N gradually increased as the level of feed intake decreased. Furthermore, with a decrease in feed intake level, the metabolic energy intake (MEI), heat production (HP), and retained energy (RE) of male sika deer significantly decreased (P < 0.01). The requirements of metabolic energy for maintenance (MEm) and net energy for maintenance (NEm) of growing deer are 251.17 and 223.62 kJ kg−1BW0.75d−1, respectively, as estimated according to the logarithmic regression equations between HP and MEI. The net N requirement for maintenance (NNm) and net protein requirement for maintenance (NPm) of growing male sika deer based on the linear relationship between retained nitrogen (RN) and daily nitrogen intake (NI) were 251.8 mg kg−1BW0.75d−1 and 1.57 g kg−1BW0.75d−1, respectively. The NEm and NPm values obtained from this experiment fill the gap in net energy and protein requirements and serve as basic data for establishing the nutritional standards forsika deer breeding in China.

Metabolizable Protein: 2. Requirements for Maintenance in Growing Saanen Goats.

This study aimed to estimate the protein requirements for the maintenance of growing Saanen goats of different sexes from 5 to 45 kg of body weight (BW) using two methods and applying a meta-analysis. For this purpose, two datasets were used. One dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the comparative slaughter technique. This dataset was composed of 185 individual records (80 intact males, 62 castrated males, and 43 females) from six studies. The other dataset was used to evaluate the effects of sex on the protein requirements for maintenance using the N balance method. This dataset was composed of 136 individual records (59 intact males, 43 castrated males, and 34 females) from six studies. All studies applied an experimental design that provided different levels of N intake and different levels of N retention, allowing the development of regression equations to predict the net protein requirement for maintenance (NPM) and the metabolizable protein (MP) requirements for maintenance (MPM) in Saanen goats. The efficiency of MP use for maintenance (kPM) was computed as NPM/MPM. The efficiency of MP use for gain (kPG) was calculated using the equation of daily protein retained against daily MP intake above maintenance. A meta-analysis was applied using the MIXED procedure of SAS, in which sex was considered a fixed effect, and blocks nested in the studies and goat sex were considered as random effects. The NPM did not differ between sexes, irrespective of the approach used. The daily NPM estimated was 1.23 g/kg0.75 BW when using the comparative slaughter technique, while it was 3.18 g/kg0.75 BW when using the N balance technique for growing Saanen goats. The MPM estimated was 3.8 g/kg0.75 BW, the kPM was 0.33, and the kPG was 0.52. We observed that the NPM when using the comparative slaughter technique in growing Saanen goats is lower than that recommended by the current small ruminant feeding systems; on the other hand, the MPM was similar to previous reports by the feeding systems. Sex did not affect the protein requirements for maintenance and the efficiencies of use of metabolizable protein.

Estimation of the net energy and protein requirements for maintenance of male arctic foxes (Alopex lagopus) during the growth period1,2.

The maintenance requirements of net energy and net protein were assumed to represent the most accurate and important values totally for the animal's utilization. The objective of this experiment was to determine the net energy and net protein requirements for maintenance of growing arctic foxes. The experiments was evaluated using regression models estimated from data collected by means of indirect calorimetry, nitrogen balance trials, and digestion and metabolism experiments. Thirty-six growing arctic foxes (3 487 ± 261.7 g) at the age of 85 days were randomly assigned to four groups with 9 animals in each group. Arctic foxes were fed a complete formula diet at four intake levels (100%, or 80%, 60%, and 40% of feed requirements) from 24 July 2017 to 23 September 2017. Arctic foxes in each treatment were kept individually in respiration chambers after 1-d adaptation at day 2 for a 3-d balance trial and then at day 5 followed by a 3-d fasting period. The metabolizable energy intake (MEI), heat production in the fed state (HP), and retained energy (RE) of arctic foxes significantly decreased (P < 0.01) as the feed intake level decreased. Fasting heat production (FHP) of arctic foxes was not influenced by feed intake level (P > 0.05). The metabolizable energy maintenance requirement (MEm) and net energy maintenance requirement (NEm) estimated from the linear relationship between RE and MEI were 230 and 217 kJ/kg of body weight BW0.75/d, respectively. The MEm and NEm estimated by logarithmic regression of HP on MEI were 225 and 209 kJ/kg BW0.75/d, respectively. The net N maintenance requirement (NNm) and net protein maintenance requirement (NPm) estimated from the linear relationship between retained nitrogen (RN) and daily nitrogen intake (NI) were 179.6 mg/kg BW0.75/d and 1.123 g/kg BW0.75/d, respectively. It is concluded that NEm and NPm values obtained fill the net energy and protein requirements shortage, and provide the basic data for establishing the standard of nutrition demand of breeding arctic foxes in China.

Energy and protein requirements during the growing phase of indigenous goats

The objective of this study was to investigate both energy and protein requirements for the maintenance and growth of indigenous goats, based on data from two separate studies. Goats were weaned at 79 ± 4.4 days of age, with milk and solid diet intake recorded daily. To determine energy maintenance requirements, 32 kids of 4.90 ± 0.302 kg initial body weight (BW) were used. Ten kids were slaughtered at 5.40 ± 0.484 kg BW to estimate initial body composition, with the remaining kids randomly assigned to one of two DM intake levels: ad libitum and restricted-fed (1.2-times maintenance level). Heat production (HP) was calculated as the difference between ingested metabolizable energy (MEI) and retained energy. Net energy requirement for maintenance (NEm) was estimated as the ?0 parameter of the relationship between HP and MEI [HP = ?0 × exp (?1 × MEI)]. Metabolizable energy required for maintenance (MEm) was calculated iteratively, as HP = MEI. Efficiency of energy utilization for maintenance (km) was calculated as NEm/MEm. The intercept of the linear regression of retained CP on CP intake was used to calculate net protein requirements for maintenance (NPm). Net energy and protein requirement for gain (NEg and NPg, respectively) were obtained using 26 kids fed ad libitum and randomly slaughtered at 5.40 ± 0.484 kg BW (n = 10), 15.8 ± 0.655 kg BW (n = 10), and 26.3 ± 1.27 kg BW (n = 6). The first derivative of the allometric equation (used to calculate energy and protein contents in empty body weight (EBW)) with respect to EBW yielded estimates of NEg and NPg. A Monte Carlo-based method was employed to simulate variation in MEm, NEg, and NPg. This study indicated that the net energy required for maintenance is 310.1 ± 36.7 kJ kg-0.75 EBW, with MEm estimated at 499.1 ± 52.1 kJ kg-0.75 EBW and km equal to 0.62. This study indicated that 1.246 g CP kg-0.75 EBW is required by indigenous kids weighing from 5 to 25 kg BW to meet their NPm. In addition, indigenous goats require between 186.6 ± 2.97 and 214.3 ± 12.9 g CP, and between 5.39 ± 1.49 and 9.74 ± 2.57 MJ to gain one kilogram of EBW. This study may contribute to future adjustments in feeding system energy and protein recommendations for indigenous kids.

Energy and protein requirements for maintenance of Hu sheep during pregnancy

This study aimed to determine the effect of stage and level of feed intake on energy metabolism, carbon-nitrogen (C-N) balance, and methane emission to determine energy and protein requirements for maintenance of maternal body including pregnancy tissues during pregnancy using the method of C-N balance. Twenty-one ewes carrying twin fetuses were randomly divided into three groups of seven ewes each in the digestion and respirometry trial at d 40, 100, and 130 of gestation, respectively. Three groups were fed a mixed diet either for ad libitum intake, 70 or 50% of the ad libitum intake during pregnancy. The results showed that the apparent digestibility of C and N were increased as feeding levels decreased at each stage of gestation. The daily net energy requirements for maintenance (NEm) were 295.80, 310.09, and 323.59 kJ kg−1 BW0.75 (metabolic body weight) with a partial efficiency of metabolisable energy utilization for maintenance of 0.664, 0.644, and 0.620 at d 40, 100, and 130 of gestation, respectively. The daily net protein requirements for maintenance were 1.99, 2.35, and 2.99 g kg−1 BW0.75 at d 40, 100, and 130 of gestation, respectively. These results for the nutritional requirements of the net energy and protein may help to formulate more balanced diets for Hu sheep during pregnancy.

Energy and protein requirements for maintenance of Southern Yellow cattle fed a corn silage or straw-based diet

Abstract The objective of this study was to estimate the net energy and net protein requirements for maintenance (NEm and NPm) of Southern Yellow cattle in China. A database involving 175 cattle with body weight (BW) ranging from 211 to 454 kg was obtained from a series of calorimetry experiments. The diets offered to cattle consisted of proportionately corn-soybean meal concentrate and roughage containing corn silage, rice straw and wheat straw. Linear regression equations of the logarithm of heat production (HP) and retained energy (RE) against metabolizable energy intake (MEI) were developed to predict the maintenance requirements for metabolizable energy (MEm) and NEm. The combined data indicated that the MEm and NEm were 522 and 348 MJ/kg0.75 of BW d−1, respectively. In addition, the partial efficiency of use of ME for maintenance was 0.66, and the partial efficiency for growth was 0.51. Similarly, there was also a linear relationship between retained nitrogen (RN) and nitrogen intake (NI). The pooled data provided a NPm of 2.63 g/kg0.75 of BW d−1 and a metabolizable protein requirement for maintenance (MPm) of 3.93 g/kg0.75 of BW d−1 for Southern Yellow cattle. In conclusion, our estimate of NEm was extremely similar to the value of the AFRC nutritional system, whereas it was slightly greater than that recommended by the NRC nutritional system. Additionally, the MPm value obtained in the current study was in agreement with the NRC recommendation.

Energy and protein requirements for maintenance of dairy goats during pregnancy and their efficiencies of use.

It has been suggested that maintenance requirements are similar among animals of different physiological stages; however, important physiological changes occur in the maternal body during pregnancy. Therefore, the aim of this study was to determine the energy and protein requirements for the maintenance of pregnant dairy goats and to estimate their efficiency of energy and protein utilization for maintenance and pregnancy. We used 66 multiparous pregnant goats having 49.0 ± 1.59 kg initial BW (around the third or fourth parturition) arranged in a randomized block design with a 3 × 3 factorial scheme including slaughter at different days of pregnancy (DOP; 80, 110, and 140 d) and feed restriction (0, 20, and 40% feed restriction). The comparative slaughter technique was used to estimate energy and protein maintenance requirements. Goats slaughtered at 140 DOP were subjected to digestibility trials at around 80, 110, and 140 DOP to estimate diet metabolizability and N balance (NBAL). Metabolizability decreased with feed restriction and was 63.3 ± 2.16, 55.7 ± 2.35, and 58.2 ± 2.30% at 0, 20, and 40% of feed restriction, respectively ( < 0.01). There was no effect of DOP on NE or the requirements of ME for maintenance (ME), which were 197 and 315 kJ/kg empty body weight (EBW), respectively, and the efficiency of ME utilization for maintenance (k) was 0.63. Similarly, DOP did not affect thedaily net protein requirements for maintenance (NP) estimated using the comparative slaughter technique (1.38 ± 0.512 g/kg EBW; = 0.003) or the NP estimated using NBAL (2.49 ± 0.594 g/kg EBW; < 0.01). The MP requirement for maintenance (MP) estimated using the comparative slaughter technique was not affected by DOP and was 3.22 g MP/kg EBW ( < 0.01). The efficiency of MP utilization for maintenance (k) was 0.43. The efficiency of ME utilization for pregnancy (k) increased with the progress of pregnancy and was 0.058, 0.10, and 0.19 at 80, 110, and 140 DOP, respectively. Similarly, the efficiency of MP utilization for pregnancy (k) increased with DOP and was 0.12, 0.21, and 0.43 at 80, 110, and 140 DOP, respectively. There was no evidence that pregnancy affected NE, ME, NP, and MP or k and k, which were also unaffected by DOP. However, k and k increased with pregnancy progress as a response to the physiological changes that pregnant females are subjected to.

Energy and protein requirements of weaned male and female Saanen goats.

The objective of this research was to estimate the energy and protein requirements for maintenance and growth in male (castrated and intact) and female Saanen goat kids between 15 and 30kg BW. To determine the net energy requirements for maintenance (NEm ) and the net protein requirements for maintenance (NPm ), 75 goats (25 castrated and 26 intact males and 24 females) were used. Twenty-one goats (seven castrated and eight intact males and six females) were randomly assigned for slaughter to estimate the initial empty body composition. The 54 remaining animals (18 castrated and 18 intact males and 18 females) were randomly assigned in a split-plot design using a 3×3 factorial arrangement with three sexes and three levels of intake (adlibitum and restricted feed to 75% or 50% of the adlibitum intake). Within each sex, six blocks (three goats per block) were formed and one goat was randomly assigned to each level of intake. The 75% and the 50% of adlibitum rationing were determined daily, based on the DMI of the animal fed adlibitum on the previous day. All animals within block were slaughtered when the animal fed adlibitum reached 30kg BW. The net energy requirements for gain (NEg ) and the net protein requirements for gain (NPg ) were obtained using 58 animals (20 castrated and 20 intact males and 18 females). The animals were fed adlibitum and slaughtered at targeted BW (15, 23 or 30kg). Sex did not affect NEg and NPm (277.8kJ/kg0.75 BWday and 2.98gCP/kg0.75 BWday respectively), as well as NPg (180.9±6.48 g/kgEBW gain) in Saanen goat kids. However, castrated males and females had similar NEg (varied from 12.6±0.424 to 17.9±1.38MJ/kg EBW gain), greater than intact males (varied from 9.74±0.420 to 10.7±0.984MJ/kg EBW gain), as the BW increased from 15 to 30kg.

Protein and energy requirements of castrated male Saanen goats

A comparative slaughter trial was conducted to determine the energy and protein requirements for growth of castrated male Saanen goats weighing from 20 to 35kg body weight (BW). Regarding maintenance requirements, 36 castrated male Saanen goats with an initial BW of 20.7±0.5kg, and aged 3.3±0.6 months, were used. Nine animals were randomly chosen and slaughtered at the beginning of the experimental phase (BW of 21.0±0.4kg), representing the baseline (BL) group. The 27 remaining castrated male goats were pair-fed into nine groups (blocks) of three animals each, fed either ad libitum or restricted to 30 or 60% of ad libitum intake. A group was slaughtered when the animal fed ad libitum reached 35kg BW. Regarding requirements for gain, 27 castrated male Saanen goats were fed ad libitum and nine were slaughtered at 21.0±0.4kg BW, nine at 27.7±0.5kg BW and nine at 35.1±0.3kg BW. The BL and ad libitum-fed animals used to determine maintenance requirements were also used to estimate gain requirements. The net energy (NE) requirement for maintenance was 261.5kJ/kg0.75 BW. The metabolizable energy (ME) requirement for maintenance was 404.2kJ/kg0.75 BW; therefore, the partial efficiency of use of ME for NE was 0.65. The minimal endogenous N losses were 262±48.4mgN/kg0.75 empty BW (EBW), corresponding to a net protein requirement for maintenance of 1.39±0.257g/kg0.75 BW. The net energy for gain increased by approximately 40% (from 12 to 17MJ/kg EBW gain) and the net protein for gain slightly decreased by 3% (from 166 to 160g/kg EBW gain) as the BW increased from 20 to 35kg. Our study contributes to the improvement of goat nutrition because it provides estimates of the protein and energy requirements of castrated male Saanen goats.

Body composition and net energy and protein requirements of Morada Nova lambs

A comparative slaughter trial was conducted with 48 Morada Nova lambs to assess the net energy and protein requirements for growth and maintenance. The animals were non-castrated and 2 months of age, with initial body weights averaging 12.05±1.81kg (BW). Eight animals were slaughtered at the beginning of the trial as a reference group, in order to estimate initial empty body weight (EBW) and body composition. The remaining animals were assigned to a randomized block design with eight replications per block and five diets with increasing metabolizable energy contents (0.96, 1.28, 1.72, 2.18 and 2.62Mcal/kg of dray matter (DM)). The heat production (HP) logarithm was regressed against metabolizable energy intake (MEI) and the net energy requirements for maintenance (kcal/kgEBW0.75/day) were estimated by extrapolation, when MEI was set at zero. The daily N excretion was estimated by extrapolating regression equations of N intake (g/kgBW0.75/day) as a function of retention (g/kgBW0.75/day) for zero intake. Regression equations for the logarithm of body fat, body energy and protein were fitted on the EBW logarithm. The derivatives of these equations allowed the estimation of the fat content of the empty body weight gain (EBWG) and the net energy requirement for EBWG. The net energy requirement for maintenance (NEm) obtained was 52.36±1.34kcal/kgEBW0.75/day. The energy and fat contents of the EBW of the animals increased from 1.64Mcal/kg and 79.38g/kg, to 2.11Mcal/kg and 123.73g/kg of EBW, respectively, as the BW increased from 15 to 30kg. The net energy requirements for EBWG increased from 2.15 to 2.78Mcal/kg EBWG for body weights of 15 and 30kg. Daily nitrogen excretion was 293.17±0.07mg/kgBW0.75/day and the net protein requirement for maintenance (NPm) was 1.83g/kgBW0.75/day. Protein content of the EBW of the animals increased from 161.67 to 175.28g/kg of EBW when the BW of the animals increased from 15 to 30kg. The amount of protein deposited during the gain increased from 177.84 to 192.93g/kg of EBWG with the increase in body weight of the animals from 15 to 30kg. The net energy and protein requirements for maintenance and gain in Morada Nova lambs is lower than values commonly recommended by the main evaluation systems for feed and nutritional requirements for lambs.

Estimation of endogenous contribution and urinary excretion of purine derivatives from the total digestible nutrient intake in Nellore heifers

The objectives of this experiment were to estimate the endogenous excretion of purine derivatives (PD), the intake and digestibility of nutrients, the urinary excretion of PD from the intake of total digestible nutrients (TDN) and digestible organic matter (DOM) in Nellore heifers. Eight heifers, 267±17 kg body weight (BW), were assigned to two 4 × 4 latin squares. The planned treatments were four dry matter intake (DMI) levels: 10, 14, 18 and 22 g/kg BW. The diet contained 70% corn silage and 30% concentrate. The endogenous losses were obtained by regression between excretion of PD (mmol/BW0.75) and DMI (g/BW0.75). When PD excretion (mmol/d) was related to the intake of DOM and TDN (kg/d), the following equations were obtained: ŶPD= 32.98 + 21.94*DOM and ŶPD= 32.47 + 20.40*TDN, respectively. The excretion of PD (mmol/d) was a function of DMI (kg/d): ŶPD = 0.605 + 0.014 x (r² = 0.46), and 0.60 mmol/BW0.75 was the endogenous fraction of PD. The endogenous losses of PD and nitrogen compounds obtained when the animals were fasted for 5 d, with free access to water, were 0.332 mmol/BW0.75 and 0.384 gN/BW0.75, respectively. The net protein requirement for maintenance was estimated at 2.4 g/BW0.75. Creatinine excretion is not affected by feed restriction.

Composição corporal e exigências líquidas proteicas de ovinos Santa Inês em crescimento

Avaliou-se o efeito de diferentes níveis de energia metabolizável na dieta sobre a composição corporal e as exigências de proteína líquida de 24 ovinos Santa Inês em crescimento, não-castrados, com idade e peso corporal médio de 50 dias e 13,00 ± 0,56 kg. Após um período de adaptação de 10 dias, quatro animais foram abatidos para serem utilizados como referência para as estimativas do peso do corpo vazio (PCVZ) e da composição corporal inicial dos demais. Os animais remanescentes foram distribuídos em um delineamento em blocos casualizados com rações contendo diferentes níveis de energia metabolizável (2,08; 2,28; 2,47 e 2,69 Mcal/kg MS) e proteína bruta (12,74; 14,36; 15,97 e 17,65% PB na MS) com cinco repetições. A excreção diária de N foi estimada extrapolando-se a equação de regressão de consumo de N (g/kg PC0,75/dia) em função da retenção de N (g/kg PC0,75/dia) para o consumo zero. A derivada da equação de regressão do logaritmo do conteúdo de proteína em função do logaritmo do PCVZ dos animais permitiu a estimativa da exigência proteica líquida para ganho de peso de corpo vazio (GPCVZ). A excreção diária de N foi estimada em 277 ± 0.05 mg/kg PC0,75/dia e a exigência de proteína líquida para mantença em 1,73 g/kg PC0,75/dia. O conteúdo de proteína no PCVZ dos animais diminui de 157,83 para 144,33 g/kg PCVZ quando o peso corporal aumentou de 15 para 30 kg, respectivamente. A quantidade de proteína depositada no ganho diminuiu de 137,47 para 125,71 g/kg GPCVZ com o aumento do peso corporal de 15 para 30 kg, respectivamente. A excreção fecal de nitrogênio e exigência líquida de proteína para mantença de ovinos Santa Inês em crescimento foi inferior ao preconizado pelos principais sistemas de avaliação de alimentos e exigências nutricionais para pequenos ruminantes.

Protein requirements of Texel crossbred lambs

A comparative slaughter trial was conducted to determine the protein requirements for maintenance and growth of feedlot Texel crossbred lambs. Thirty 11/16 Texel × 5/16 Ile de France crossbred noncastrated male lambs weaned at 42 days of age (16.2 ± 2.1 kg of shrunk body weight; SBW) were used. Five lambs were chosen randomly and slaughtered after 10 days of experimental management and diet adaptation (baseline group). Fifteen lambs were fed ad libitum and slaughtered at 25, 30 or 35 kg of SBW. The remaining 10 lambs were then assigned randomly to two levels of dry matter intake, either 70 or 55% of the ad libitum intake, and were slaughtered concomitantly with lambs slaughtered at 35 kg of SBW but given free choice access to feed. Total body N content and retention were determined. Additionally, six Texel × Ile de France crossbred lambs (30.4 ± 2.6 kg of SBW) housed in individual metabolic cages were used in a replicated 3 × 3 Latin square digestibility trial to evaluate diet digestibility and microbial protein synthesis at the different levels of feed intake. The endogenous N loss was 243 ± 29 mg/kg 0.75 of SBW, corresponding to a net protein requirement for maintenance of 1.52 ± 0.18 g/kg 0.75 of SBW. The metabolizable protein (MP) requirement for maintenance was 2.31 g/kg 0.75 of SBW, and the efficiency of MP use for maintenance was 0.66. Fleece-free body protein content decreased from 163 to 155 g/kg of empty body weight (EBW) as EBW increased from 13 to 28 kg. However, when protein in fleece was considered the whole-body protein content remained nearly constant. Net protein requirements for body weight gain and wool growth of lambs at 15 and 35 kg of SBW, and an average daily gain of 250 g, were 28.7 and 27.3 g/day and 3.8 and 5.8 g/day, respectively. Estimated efficiencies of MP use for body weight gain ( k pg) and wool growth ( k pw) were, respectively, 0.71 and 0.46. Growth pattern of the wool has a high influence on protein requirements of lambs. Texel crossbred growing lambs used in our study showed protein requirements for growth lower than those reported by the most nutritional systems.

Determination of the Amino Acid Requirements and Optimum Dietary Amino Acid Pattern for Growing Chinese Taihe Silky Fowls in Early Stage

A mathematical model has been constructed to estimate the amino acid requirements for growing Taihe silky fowls in early stage. A requirement was taken as the sum of the needs for maintenance, for gain in carcass weight without feathers, and for the feathers. The maintenance requirement was considered to be the sum of the needs for replacing skin and intestinal losses and for the obligatory creatinine excretion in the urine. A comparative slaughter trial and nitrogen balance trials with growing and adult Taihe silky fowls, respectively, were conducted to estimate the parameters in the model. The amino acid requirements were then calculated with the constructed models. The results showed as following: the replacement needs for skin nitrogen loss was determined at 213.41 mg/d for adult male fowls (body weight 1.60 kg); creatinine excretion in these birds was 4.04 mg/d. when fed an nitrogen-free diets, the adult male fowls with body weight 1.60 kg excreted a total of 246.10 mg/d endogenous nitrogen. The net protein requirement for maintenance was estimated at 11.24 mg/wg 0.75 /d. Per gram of body weight gain contained 27.18 mg carcass nitrogen for growing birds in early stage, but feathers nitrogen in per gram of body weight gain increased with age. The amino acid requirements for growing Taihe silky fowls were slightly higher than for starting and growing pullets, but lower than that of broiler chicks. The amino acid requirements patterns changed with weeks of age. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 12 : 1782-1788)

Factors for Computing Requirements of Protein for Maintenance of Cattle

Factors for daily losses of endogenous urinary nitrogen, skin nitrogen, and metabolic fecal nitrogen were derived from published data. Endogenous urinary nitrogen from 82 experiments with cattle ranging from 28 to 625kg normal body weight averaged .44g per kg.5. Mean daily skin nitrogen losses from 61 experiments were .035g per kg.6 body weight. From healthy calves fed whole milk, practically all fecal nitrogen is metabolic. Under such conditions metabolic fecal nitrogen averages .2% of dry-matter intake. Metabolic fecal nitrogen for ruminating cattle was estimated from 70 natural and semi-synthetic low protein diets by subtracting from fecal nitrogen 10% of feed nitrogen. Mean metabolic fecal nitrogen was 10.9g per kg fecal dry matter or 4.7g per kg dry-matter intake. The sum of factorial nitrogen losses multiplied by 6.25 is the net protein requirement for maintenance. Crude protein of feed is obtained by dividing the net protein for maintenance by the product of percentage of feed protein absorbed and percentage of absorbed protein utilized. Net protein efficiency varies from .7 for milk-fed calves to .45 for mature ruminant diets. Protein for maintenance can be calculated from body weight, type of diet, dry-matter intake, and dry-matter digestibility.