The impact of feeding growing-finishing pigs with daily tailored diets using precision feeding techniques on animal performance, nutrient utilization, and body and carcass composition.

The impact of moving from conventional to precision feeding systems in growing-finishing pig operations on animal performance, nutrient utilization, and body and carcass composition was studied. Fifteen animals per treatment for a total of 60 pigs of 41.2 (SE = 0.5) kg of BW were used in a performance trial (84 d) with 4 treatments: a 3-phase (3P) feeding program obtained by blending fixed proportions of feeds A (high nutrient density) and B (low nutrient density); a 3-phase commercial (COM) feeding program; and 2 daily-phase feeding programs in which the blended proportions of feeds A and B were adjusted daily to meet the estimated nutritional requirements of the group (multiphase-group feeding, MPG) or of each pig individually (multiphase-individual feeding, MPI). Daily feed intake was recorded each day and pigs were weighed weekly during the trial. Body composition was assessed at the beginning of the trial and every 28 d by dual-energy X-ray densitometry. Nitrogen and phosphorus excretion was estimated as the difference between retention and intake. Organ, carcass, and primal cut measurements were taken after slaughter. The COM feeding program reduced (P < 0.05) ADFI and improved G:F rate in relation to other treatments. The MPG and MPI programs showed values for ADFI, ADG, G:F, final BW, and nitrogen and phosphorus retention that were similar to those obtained for the 3P feeding program. However, compared with the 3P treatment, the MPI feeding program reduced the standardized ileal digestible lysine intake by 27%, the estimated nitrogen excretion by 22%, and the estimated phosphorus excretion by 27% (P < 0.05). Organs, carcass, and primal cut weights did not differ among treatments. Feeding growing-finishing pigs with daily tailored diets using precision feeding techniques is an effective approach to reduce nutrient excretion without compromising pig performance or carcass composition.

Apparent total tract digestibility of dietary calcium and phosphorus and their efficiency in bone mineral retention are affected by body mineral status in growing pigs.

Improving dietary P utilization without modifying pig performance is crucial for production sustainability. A feeding program comprising three 28-d phases (20 to 40, 40 to 70, and 70 to 100 kg) was used to feed 72 pigs with an initial BW of 20 kg. The ability of the pigs to modify the digestive and metabolic utilization of P when fed either a control (CON) diet or a low-P (LOW) diet providing 40% less digestible P with a constant Ca:digestible P was studied using different sequences of dietary P and Ca restriction (i.e., depletion [LOW]) and recovery (i.e., repletion [CON]), namely CON-CON-CON, CON-CON-LOW, CON-LOW-LOW, LOW-CON-CON, LOW-LOW-CON, and LOW-LOW-LOW. Bone mineral content (BMC) was measured in the lumbar region (L2-L4) by dual-energy X-ray absorptiometry at the beginning and end of each feeding phase. Total feces and urine were collected during phases 2 and 3. At the end of phase 1, BMC was lower in the LOW pigs than in the C pigs (29%; P < 0.001). During phase 2, the BMC gain was greater in the LOW-CON pigs than in the CON-CON pigs (16%; P < 0.001). During phase 3, the LOW-LOW-CON pigs absorbed 26% more Ca (P < 0.001) and retained 56% more BMC (P < 0.001) than the CON-CON-CON pigs did. Digestive and metabolic adaptations allowed the LOW-LOW-CON and LOW-CON-CON pigs to reach BMC similar to that of the CON-CON-CON pigs. These metabolic adaptations are promising, but practical applications of these results requires a better understanding of the underlying mechanisms to fine-tune the degree of depletion, pig age, and the duration of P and Ca depletion and repletion periods.

Meta-analytical study of productive and nutritional interactions of mycotoxins in growing pigs.

A meta-analysis was carried out in order to study the association of mycotoxins with performance and organ weights in growing pigs. A total of 85 articles published between 1968 and 2010 were used, totaling 1012 treatments and 13 196 animals. The meta-analysis followed three sequential analyses: graphical, correlation and variance-covariance. The presence of mycotoxins in diets was seen to reduce the feed intake by 18% and the weight gain in 21% compared with the control group. Deoxynivalenol and aflatoxins were the mycotoxins with the greatest impact on the feed intake and growth of pigs, reducing by 26% and 16% in the feed intake and by 26% and 22% in the weight gain. The mycotoxin concentration in diets and the animal age at challenge were the variables that more improved the coefficient of determination in equations for estimating the effect of mycotoxins on weight gain. The mycotoxin effect on growth proved to be greater in younger animals. In addition, the residual analysis showed that the greater part of the variation in weight gain was explained by the variation in feed intake (87%). The protein and methionine levels in diets could influence the feed intake and the weight gain in challenged animals. The weight gain in challenged pigs showed a positive correlation with the methionine level in diets (0.68). The mycotoxin effect on growth was greater in males compared with the effect on females. The reduction in weight gain was of 15% in the female group and 19% in the male group. Mycotoxin presence in pig diets has interfered in the relative weight of the liver, the kidneys and the heart. Mycotoxins have an influence on performance and organ weight in pigs. However, the magnitude of the effects varies with the type and concentration of mycotoxin, sex and the animal age, as well as nutritional factors.

Meta-analysis of the relationship of mycotoxins with biochemical and hematological parameters in broilers.

A meta-analysis was carried out to study the association of mycotoxins with hematological and biochemical profiles in broilers. Ninety-eight articles published between 1980 and 2009 were used in the database, totaling 37,371 broilers. The information was selected from the Materials and Methods and Results sections in the selected articles and then tabulated in a database. Meta-analysis followed 3 sequential analyses: graphic, correlation, and variance-covariance. Mycotoxins reduced (P < 0.05) the hematocrit (-5%), hemoglobin (-15%), leukocytes (-25%), heterophils (-2%), lymphocytes (-2%), uric acid (-31%), creatine kinase (-27%), creatinine (-23%), triglycerides (-39%), albumin (-17%), globulin (-1%), total cholesterol (-14%), calcium (-5%), and inorganic phosphorus (-12%). Mycotoxins also altered (P < 0.05) the concentrations of alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase. A quadratic effect was observed on the relationship between the concentration of aflatoxin in diets and the serum concentration of alkaline phosphatase, γ-glutamyl transferase, alanine aminotransferase, and aspartate aminotransferase. The total protein concentration in blood was 18% lower (P < 0.05) in broilers challenged by aflatoxins compared with that of the unchallenged ones. The inclusion of antimycotoxin additives in diets with aflatoxins altered (P < 0.05) some variables (uric acid, creatinine, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, and γ-glutamyl transferase) in relation to the group that received diets with the mycotoxin and without the additive. The meta-analysis performed in this study allowed us to address and quantify systematically the relationship of mycotoxins with alterations in hematologic and biochemical profiles in broilers.

Development of sustainable precision farming systems for swine: estimating real-time individual amino acid requirements in growing-finishing pigs.

The objective of this study was to develop and evaluate a mathematical model used to estimate the daily amino acid requirements of individual growing-finishing pigs. The model includes empirical and mechanistic model components. The empirical component estimates daily feed intake (DFI), BW, and daily gain (DG) based on individual pig information collected in real time. Based on DFI, BW, and DG estimates, the mechanistic component uses classic factorial equations to estimate the optimal concentration of amino acids that must be offered to each pig to meet its requirements. The model was evaluated with data from a study that investigated the effect of feeding pigs with a 3-phase or daily multiphase system. The DFI and BW values measured in this study were compared with those estimated by the empirical component of the model. The coherence of the values estimated by the mechanistic component was evaluated by analyzing if it followed a normal pattern of requirements. Lastly, the proposed model was evaluated by comparing its estimates with those generated by the existing growth model (InraPorc). The precision of the proposed model and InraPorc in estimating DFI and BW was evaluated through the mean absolute error. The empirical component results indicated that the DFI and BW trajectories of individual pigs fed ad libitum could be predicted 1 d (DFI) or 7 d (BW) ahead with the average mean absolute error of 12.45 and 1.85%, respectively. The average mean absolute error obtained with the InraPorc for the average individual of the population was 14.72% for DFI and 5.38% for BW. Major differences were observed when estimates from InraPorc were compared with individual observations. The proposed model, however, was effective in tracking the change in DFI and BW for each individual pig. The mechanistic model component estimated the optimal standardized ileal digestible Lys to NE ratio with reasonable between animal (average CV = 7%) and overtime (average CV = 14%) variation. Thus, the amino acid requirements estimated by model are animal- and time-dependent and follow, in real time, the individual DFI and BW growth patterns. The proposed model can follow the average feed intake and feed weight trajectory of each individual pig in real time with good accuracy. Based on these trajectories and using classical factorial equations, the model makes it possible to estimate dynamically the AA requirements of each animal, taking into account the intake and growth changes of the animal.

Meta-analytical study of productive and nutritional interactions of mycotoxins in broilers.

A meta-analysis was carried out to study the association of mycotoxins with performance, productive indices, and organ weights in broilers. Ninety-eight papers published between 1980 and 2009 were used, totaling 1,401 diets and 37,371 animals. Meta-analysis followed 3 sequential analyses: graphical, correlation, and variance-covariance. The mycotoxin presence in diets reduced (P < 0.05) feed intake by 12% and weight gain by 14% compared with control group. Ochratoxins and aflatoxins were the mycotoxins with the greatest effect on feed intake and bird growth, reducing (P < 0.05) feed ingestion by 17 and 11%, respectively, and weight gain by 20 and 11%, respectively. The mycotoxin concentration in diets and the animal age at challenge were the variables that more improved the coefficient of determination for equations to estimate mycotoxin effect on weight gain. The mycotoxin effect on growth proved to be greater in young poultry. The residual analysis revealed that 65% of the variation in weight gain was explained by feed intake. The variation in weight gain of challenged broilers in relation to nonchallenged broilers was also influenced by ingestion of nutrients such as protein and methionine. Mortality was 8.8 and 2.8 times greater (P < 0.05) in groups that received diets with deoxynivalenol and aflatoxins, respectively. Mycotoxins also increased (P < 0.05) the relative weight of liver by 15%, of kidneys by 11%, of lungs by 9%, and of gizzard by 3%. Mycotoxins influenced broiler performance, productive indices, and organ weights. However, the magnitude of the effects varied with type and concentration of mycotoxin, animal age, and nutritional factors.

Alimentação de porcas lactantes com dietas contendo silagem de grãos úmidos de milho e ácido fumárico / Lactating sows fed diets with high moisture corn silage and fumaric acid

Estudou-se o efeito de dietas elaboradas com silagem de grãos úmidos de milho e ácido fumárico sobre os desempenhos de porcas lactantes e suas leitegadas. Foram utilizadas 20 porcas de genética comercial em um delineamento de blocos ao acaso com quatro tratamentos - dieta basal (DB), elaborada a cada 24h; DB + 0,3 por cento de ácido fumárico - (AF); DB + 0,6 por cento AF; e DB + 0,9 por cento de AF, e cinco repetições. As dietas contendo ácido fumárico foram elaboradas a cada 48 horas. O consumo médio diário da dieta das porcas lactantes foi de 7,42kg de matéria natural e não houve diferença (P>0,05) entre os tratamentos. A adição de 0,9 por cento de ácido fumárico às dietas reduziu (P<0,01) em 6 por cento o pH do leite em relação à dieta-basal. A média de ganho diário e a média de peso dos leitões não diferiram (P>0,05) entre os tratamentos. A adição de ácido fumárico às dietas não alterou os desempenhos de porcas lactantes e de suas leitegadas. A adição de ácido fumárico às dietas de lactação elaboradas com silagem de grãos úmidos de milho reduziu o pH do leite e aumentou a frequência de fezes normais dos leitões lactentes.

The effect of lactation diets containing high moisture corn silage and fumaric acid was evaluated on the performance of lactating sows and their piglets. Twenty sows of commercial genetic lines were used in a randomized complete block experimental design with four treatments (basal diet - BD, elaborated each 24h; BD + 0.3 percent fumaric acid - FA; BD + 0.6 percent FA; and BD + 0.9 percent FA) and five replicates. Diets with fumaric acid were elaborated each 48 hours. The average daily feed intake of lactating sows was 7.42kg of natural matter and it was not affected (P>0.05) by treatments. The 0.9 percent fumaric acid addition in diets reduced in 6 percent (P<0.01) the pH of milk compared to basal diet. The average daily weight gain and average weaning live weight of piglets were not influenced (P>0.05) by treatments. The addition of fumaric acid in diets did not alter the performance of lactating sows and piglets. The addition of fumaric acid in lactation diets elaborated with high moisture corn silage increased the normal feces frequency in sucking piglets.

Systematic comparison of the empirical and factorial methods used to estimate the nutrient requirements of growing pigs.

Empirical and factorial methods are currently used to estimate nutrient requirements for domestic animals. The purpose of this study was to estimate the nutrient requirements of a given pig population using the empirical and factorial methods; to establish the relationship between the requirements estimated with these two methods; and to study the limitations of the methods when used to determine the level of a nutrient needed to optimize individual and population responses of growing pigs. A systematic analysis was carried out on optimal lysine-to-net-energy (Lys : NE) ratios estimated by the empirical and factorial methods using a modified InraPorc® growth model. Sixty-eight pigs were individually simulated based on detailed experimental data. In the empirical method, population responses were estimated by feeding pigs with 11 diets of different Lys : NE ratios. Average daily gain and feed conversion ratio were the chosen performance criteria. These variables were combined with economic information to estimate the economic responses. In the factorial method, the Lys : NE ratio for each animal was estimated by model inversion. Optimal Lys : NE ratios estimated for growing pigs (25 to 105 kg) differed between the empirical and the factorial method. When the average pig is taken to represent a population, the factorial method does not permit estimation of the Lys : NE ratio that maximizes the response of heterogeneous populations in a given time or weight interval. Although optimal population responses are obtained by the empirical method, the estimated requirements are fixed and cannot be used for other growth periods or populations. This study demonstrates that the two methods commonly used to estimate nutrient requirements provide different nutrient recommendations and have important limitations that should be considered when the goal is to optimize the response of individuals or pig populations.

Alimentação de leitoas pré-púberes com dietas contendo zearalenona / Feeding of pre-pubertal gilts with diets containing zearalenone

O desempenho, o peso de alguns órgãos e a morfologia vulvar de leitoas pré-púberes, alimentadas por 28 dias com dietas contendo zearalenona, foram avaliados. O delineamento experimental utilizado foi inteiramente ao acaso, com dois tratamentos, dieta controle (DC) e dieta controle + 2mg kg-1 de zearalenona (DZ), e seis repetições cada. Não houve diferença (P>0,05) entre os tratamentos para consumo médio diário de ração (1,24 x 1,19kg), ganho médio diário de peso (0,68 x 0,71kg), conversão alimentar (1,86 x 1,71) e peso vivo (PV); (30,9 x 30,4kg). A zearalenona não alterou (P>0,05) os pesos absoluto e relativo do coração (137 x 141g e 0,45 x 0,45 por cento PV), fígado (699 x 699g e 2,31 x 2,26 por centoPV), rins (47 x 49g e 0,15 x 0,16 por centoPV) e baço (166 x 171g e 0,55 x 0,55 por centoPV). Houve aumento (P<0,05) no comprimento (17 x 27cm) e no peso (23 x 157g e 0,07 x 0,51 por centoPV) do trato reprodutivo das leitoas do grupo DZ. O volume vulvar ao final do período foi 820 por cento maior (P<0,05) nos animais alimentados com zearalenona (941 x 8658mm³/kgPV0,6). Os resultados indicam que em suínos a zearalenona e seus metabólitos possuem atividade estrogênica, mas não interferem no desempenho dos animais.

The performance, the weights of some organs, and the vulvae morphology in pre-pubertal gilts fed diets containing zearalenone were evaluated during 28 days. The experimental design was completely randomized with two treatments (control diet, ZD - control diet + 2mg kg-1 of zearalenone) and six replications of each were done. No differences (P>0.05) between treatments for daily feed intake (1.24 x 1.19kg), average daily gain (0.68 x 0.71kg), feed conversion ratio (1.86 x 1.71), and live weight (30.9 x 30.4kg) were observed. Zearalenone did not change (P>0.05) the absolute and relative weights of heart (137 x 141g and 0.45 x 0.45 percentBW), liver (699 x 699g and 2.31 x 2.26 percentBW), kidneys (47 x 49g and 0.15 x 0.16 percentBW), and spleen (166 x 171g and 0.55 x 0.55 percent BW). However, zearalenone increased (P<0.05) the length (17 x 27cm) and weight (23 x 157g and 0.07 x 0.51 percentBW) of the reproductive tract. The final vulvae volume was 820 percent larger (P<0.05) in gilts fed diets containing zearalenone than those fed control diet (941 x 8658mm³/kgBW0.6). Results suggested that zearalenone and its metabolites have an estrogenic activity in pigs without changing the animal performance.

Utilização do triticale e de enzimas em dietas para suínos: digestibilidade e metabolismo / Utilization of triticale and of enzymes in pig diets: digestibility and metabolism

Avaliou-se o efeito da inclusão de níveis de triticale sobre o valor nutritivo de dietas para suínos com ou sem enzimas. Foram utilizados 24 suínos machos, castrados, com peso inicial de 59kg, alojados em gaiolas metabólicas. O delineamento foi de blocos ao acaso em arranjo fatorial 3 x 2 (níveis de triticale, 0, 30 e 60 por cento, com ou sem enzimas), com quatro repetições cada. A inclusão de triticale na dieta em até 60 por cento e a adição de enzimas não influenciou (P>0,05) a digestibilidade da matéria seca, fósforo, energia bruta, metabolização da energia, energia digestível e metabolizável e o balanço do N. Os valores médios de energia digestível e metabolizável foram de 3.537 e 3.435kcal. Houve interação triticale x enzimas na proteína digestível aparente (PDa) (P<0,01). Na dieta com 60 por cento de triticale sem adição de enzimas a PDa foi 6 por cento inferior à controle. Na dieta com 30 e 60 por cento de triticale com enzimas, a PDa foi similar à controle e 5 por cento superior à dieta com 60 por cento de triticale sem enzimas. A inclusão de 60 por cento de triticale em dietas para suínos reduz a PDa. A adição de enzimas melhora a PDa em dietas com 30 e 60 por cento de triticale.

The effect of triticale levels with or without enzyme supplementation on nutritive value of pig's diet was evaluated using twenty four barrows weighting 59kg, housed in metabolic crates. A complete randomized experimental block design in a 3 x 2 factorial arrangement (triticale levels -0, 30 e 60 percent with or without enzymes) with four replicates each was utilized. No effects of triticale levels and enzymes supplementation (P>0.05) were observed on dry matter digestibility, phosphorus, crude energy, metabolization of energy, digestible and metabolizable energy and nitrogen balance. The average values of digestible and metabolizable energy were 3,537 e 3,435kcal. An interaction triticale x enzymes effect on apparent digestible protein (DPa) (P<0.01) was observed. Apparent digestible protein for 60 percent triticale diets without enzymes supplementation was 6 percent lower than control diet while DPa of 30 and 60 percent triticale diets with enzymes supplementation were similar to DPa of the control diet and 5 percent higher than 60 percent triticale diets without enzyme supplementation. The inclusion of 60 percent triticale in pig diets reduces the DPa. Enzymes supplementation improves the DPa for diets containing 30 and 60 percent of triticale.

Substituição de milho por sorgo baixo tanino em dietas para suínos: digestibilidade e metabolismo / Replacement of corn by low tannin sorghum in pig diets: digestibility and metabolism

Um experimento foi realizado para avaliar os efeitos digestivos e metabólicos da substituição de milho por sorgo em dietas para suínos. Foram utilizados 12 suínos machos castrados, meio-irmãos paternos, com peso vivo médio inicial de 40,8kg, mantidos em gaiolas metabólicas. O delineamento experimental foi inteiramente casualizado com três tratamentos (T1 = dieta controle; T2 = substituição de 50 por cento do milho por sorgo e T3 = substituição de 100 por cento) e quatro repetições. As digestibilidades da proteína e da energia brutas foram 5 e 4 por cento superiores (P<0,05), respectivamente, nos suínos alimentados com a dieta que tinha 50 por cento de substituição, comparadas àquela com substituição total do milho por sorgo. A substituição total do milho por sorgo reduziu (P<0,05) as digestibilidades, em relação à dieta-controle, em 3 por cento para MS, 8 por cento para PB e 5 por cento para EB. O N fecal foi 25 por cento maior (P<0,05), o N absorvido 10 por cento menor (P<0,05) e a excreção fecal de energia 15 por cento maior (P<0,05) para a dieta com substituição total, em relação à dieta-controle. A excreção fecal de N e energia e a absorção de N são influenciadas negativamente pela substituição total de milho por sorgo nas dietas. A substituição em até 50 por cento do milho por sorgo em dietas para suínos não influi na digestibilidade das dietas e no metabolismo dos animais.

An experiment was carried out to evaluate metabolic and digestive effects replacement of corn by sorghum in pig diets. Twelve half brothers barrows weighing 40.8kg and housed in metabolic cages in a completely randomized design with three treatments (T1 = control diet; T2 = replacement of 50 percent corn by sorghum and T3 = replacement of 100 percent) with four replicates. Crude protein and gross energy the digestibilities were 5 percent and 4 percent higher (P<0.05), respectively, for pigs fed 50 percent of corn replacement diet, in comparison with the diet where corn was totally replaced by sorghum. Total replacement of corn by sorghum diets decreased (P<0.05) the digestibilities, in comparison to control diet, in 3 percent for DM, 8 percent for CP and 5 percent for GE. Fecal N was 25 percent higher (P<0.05), absorbed N was 10 percent lower (P<0.05), and the fecal excretion energy was 15 percent higher (P<0.05) for total substitution diet in comparison to control diet. Fecal excretion and absorption of nitrogen are negatively influenced by total replacement of corn by sorghum in the diets. Replacements of up to 50 percent of corn by sorghum in pig diets do not affect the digestibility diet and metabolism of animals.

Effects of feed restriction and subsequent refeeding on energy utilization in growing pigs.

An experiment was carried out to evaluate the metabolic utilization of energy in crossbred barrows during feed restriction and subsequent refeeding. Ten pigs, initially weighing 52 kg, were used in 5 blocks of 2 littermates each. A 7-d adaptation period (P1) was used in which pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). This adaptation period was followed by a 7-d period (P2), in which 1 pig of each block continued to receive feed at the same level of feeding, whereas for its littermate a 40% reduction in feed intake was imposed (i.e., 1.55 MJ of ME.kg of BW(-0.60).d(-1)). During the subsequent 7-d period (P3), both pigs were offered feed at 2.60 MJ of ME.kg of BW(-0.60).d(-1). After P3, pigs were fasted for 1 d. Heat production (HP) was measured for all pigs during the last 3 d of P1 and on all days for P2 and P3. Heat production was measured using an open-circuit respiration chamber. Energy and N balances were determined for P1, P2, and P3. The HP was partitioned into HP due to physical activity, the short-term thermic effect of feeding, and resting HP. Feed restriction during P2 decreased (P < 0.01) total HP, resting HP, short-term thermic effect of feeding, and retained energy, whereas HP due to physical activity was not affected by feed restriction (P = 0.50). Likewise, fecal and urinary N loss, protein gain, lipid gain, and ADG were reduced during feed restriction (P < 0.01). There were no differences in components of HP and metabolic utilization of energy between the 2 groups during P1 and P3. Nevertheless, urinary N loss was decreased (P < 0.05) and ADG increased (P < 0.01) during P3 for pigs that were restricted in P2. Compensatory growth after a period of feed restriction does not seem to be related to a change in the metabolic utilization of energy for gain but more likely is due to gain in water and gut contents.

Modeling homeorhetic and homeostatic controls of pig growth.

A dynamic mechanistic model of homeorhetic and homeostatic controls of pig growth was developed. The homeorhetic principles were based on changes in time of fractional rates of anabolism and catabolism of tissues. A minimum number of homeostatic principles integrated current data on plasma kinetics and the partitioning of nutrients between anabolism and catabolism of body tissues, and endogenous losses with integument and into the gut. The major features of the model are two levels of organization (tissue and plasma) and three body tissues (carcass proteins, visceral proteins, and body lipids). The protein tissues and plasma amino acids were subdivided into lysine, methionine and cystine, threonine, tryptophan, other essential AA, and nonessential AA compartments. Plasma glucose and fatty acids were also considered. Adenosine triphosphate and adenosine diphosphate were used to represent energy transformations, although these energy transformations were not included in the homeostatic control of pig growth. The mass variations within each of the 23 basic compartments were described with a specific deterministic, dynamic differential equation. The simulated metabolic rates of the protein and lipid tissues were similar to published data. The principal outputs from the model (protein and lipid gain, body weight, chemical body constituents, plasma parameters) showed that the proposed homeorhetic and homeostatic controls provide a mechanistic approach to modeling growth.