![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
*
Nutreco Poultry Research Centre, Casarrubios del Monte, Toledo, Spain; the
Animal Production Systems Group and the
**
Animal Nutrition Group, Wageningen University, Wageningen, The Netherlands
3To whom correspondence should be addressed. E-mail: ruud.eits{at}nutreco.com.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
KEY WORDS: • growth • nutrition • fat-free body composition • model • broiler chickens
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
–3
). This implies that the relationships between water and protein, and between ash and protein, are both considered to be independent of nutritional factors.
The relationships between water and protein, and ash and protein, in growing animals, have been described for several species, e.g., fattening pigs (3
,4
), layer pullets (5
) and turkeys (6
). However, the relationships were usually determined with animals growing according to their potential growth curve under the conditions of ad libitum consumption of balanced diets. It is unclear whether at restricted nutrient intakes the relationships between water or ash and protein are similar to conditions of ad libitum consumption. Results for pigs (7
) suggest that the relationship between water and protein is independent of feed intake level (FI-level)4
and of the dietary protein to energy ratio (PE-ratio). Several studies have reported different results concerning the relationship between ash and protein (8
,9
). In some cases, the relationship between ash and protein seems to be independent of the nutritional regimen. A low PE-ratio, however, increased the ash to protein ratio in several pig studies (10
,11
). In the latter studies, the development of skeletal muscles might have been limited more by a low PE-ratio than the development of the skeleton. In that case, an effect of PE-ratio on the ash to protein ratio would be expected, particularly in the carcass, more than in the organs. Information on possible nutritional effects on the relationships among water, ash and protein in body components is not clear. It has implications for growth simulation models, as mentioned before, and for other variables, such as meat quality (12
).
The objectives of this study were to investigate the allometric relationships of water and ash with protein in growing broiler chickens and to analyze whether these relationships are affected by nutritional factors. The second question was answered by testing whether water and ash contents at a certain protein weight varied among dietary treatments. The hypothesis was that the amounts of water and ash at a certain protein weight, both in carcass and organs, are independent of both FI-level and PE-ratio. An alternate hypothesis was that the amount of ash at a certain protein weight would be increased by a low PE-ratio, but only in the carcass and not in the organs.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
Detailed descriptions of the design of the experiments and of the dissection procedures have been presented elsewhere (13
). They are summarized here. Two experiments of similar design were performed with in total 126 individual floor pen housed male broiler chickens (Ross 208; Ross Breeders, New Bridge, Midlothian, UK) in two body weight ranges: from 10-d-old (
200 g) until 800 g (expt. 1) and from 800 g until 1600 g (expt. 2). Day-old chicks for both experiments were hatched on the same day and were housed in the same room. Each broiler chicken was assigned to either three (expt. 1) or four (expt. 2) blocks of 18 pens, according to a randomized block design. Each block consisted of one replicate for each of the 18 treatments. At d 10, seven additional birds were killed and dissected as a reference for the body composition at the start of the experiment.
Both experiments consisted of 18 dietary treatments: two levels of feed intake combined with nine ratios of ideal protein to energy. Feed intake levels were 1.7 and 2.1 times the maintenance requirement for energy; energy was defined on a protein-free basis (13
). Protein-free metabolizable energy was calculated from apparently digestible crude fat (38.83 kJ/g) and apparently digestible carbohydrates (17.32 kJ/g) (14
). The metabolizable energy requirement for maintenance was estimated as 450 kJ/kg metabolic body weight (kg0.75) (15
). Birds were fed twice per day. Protein-free energy intakes at the low and high feed intake levels corresponded with, respectively, 70% and 83% of the mean protein-free energy intake of birds in the same experiments eating ad libitum (13
; results not presented here).
Ideal protein to energy ratios were 0.80, 0.91, 1.03, 1.08, 1.14, 1.20, 1.26, 1.37 and 1.48 (expt. 1) and 0.76, 0.87, 0.98, 1.03, 1.09, 1.14, 1.19, 1.30 and 1.41 (expt. 2) g apparently digestible lysine per MJ protein-free energy. The middle of the nine ratios was assumed to be optimal for protein deposition, at least in birds with ad libitum intake. Starting from ideal protein (16
), all essential amino acids were supplied at levels of at least 115% of their requirements, relative to lysine. Therefore, the first-limiting amino acid for protein deposition was most likely always lysine. Broilers of expt. 2 had free access to the diet with 1.09 g digestible lysine per MJ protein-free energy during the pretreatment period (10 d old until 800 g body weight). Each of the experimental feeds was made by mixing two basal feeds (an energy and protein feed; 3-mm pellet; Table 1
) in different ratios. An official Dutch committee on animal care and ethics approved the experimental protocol.
|
Birds were killed with an injection of 0.2 mL T61 (contains per liter: 250 g embutramide, 50 g mebezonium iodide and 5 g tetracaine hydrochloride). They were not bled and were stored at 2°C for a maximum of 7 d. At dissection, birds were defeathered and the metabolic and digestive organs were removed from the body. The gastrointestinal tract was stripped of its contents. The, so-called, organ fraction consisted of esophagus, trachea, proventriculus, gizzard, intestines, heart, liver, bile bladder, kidneys, lungs, spleen and the Bursa of Fabricius. The remaining body, including abdominal fat pad, was defined as the carcass fraction. In expt. 2, three (of four) birds per treatment group were dissected. The fourth was a spare one in case of mortality. Carcass and organ fractions of each chick as well as the experimental diets were analyzed in duplicate for dry matter, lipid, ash and nitrogen content, as described by Eits et al. (13
). Protein content was calculated as 6.25 times nitrogen content. Protein weight in the carcass was calculated by multiplying protein content in the carcass by the carcass weight. Protein weight in organs and weights of ash and water were calculated similarly.
Curve fitting and statistical analysis.
The procedures for analyzing the relationship between water and protein weight will be described below. For ash and protein, the same procedures were adopted.
The relationships between water and protein weight in the different body parts (carcass, organs and carcass + organs) of growing broiler chickens were described. The data used were from broilers of 200, 800 (expt. 1) and 1600 (expt. 2) g body weight. The data were not ideal for the purpose because they were not equally distributed over the domain described. Curve fitting was performed using the allometric model of Huxley (17
), which describes the log-log linear relationship of two body components [ln(W) = ln(
) + ß x ln(P)], in which: ln = natural logarithm, W = water weight (kg), = scale parameter, ß = allometric slope and P = protein weight (kg).
The effect of the dietary treatments on the amount of water at a certain protein weight was tested. This was tested separately for 800 g (expt. 1) and 1600 g body weight (expt. 2). Water weights as measured were recalculated to the mean protein weight at 800 g and at 1600 g (corrected water weights). Recalculation to a mean protein weight was necessary because birds were killed at a similar body weight and not at a similar protein weight. The details of the calculation are in the Appendix section. The effect of dietary treatments (FI-level and PE-ratio) on the corrected water weights in the different body parts was analyzed according to the following model:
 | (1) |
, where Wcorr = corrected water weight, 
= mean corrected water weight at P/E = 1.12, FIi = fixed effect of FI-level i, ß1 = effect of P/E-ratio, ß2i = interaction between P/E-ratio and FI-level i, (P/E)j = PE-ratio of bird j, 1.12 = mean P/E-ratio (g digestible lysine per MJ protein-free energy), 
ij = error, i = 1, 2 and j = 1...27.
All statistical analyses were performed with linear (GLM) (18
) regression procedures. Significance was assigned at P < 0.05; tendencies were assigned at 0.05 < P < 0.10.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
Allometric relationships.
Relationships for water or ash weight with protein weight in the carcasses and organs are presented in Figure 1
. For each line in the graph, there are data of the three weight groups, corresponding with (from the left to the right side of the graph) the initial slaughter group, the chickens of 800 g body weight, and the chickens of 1600 g body weight. On the log-log scale, both of the relationships between water or ash and protein were essentially linear (Fig. 1)
. Linearity on log-log scales is a necessary feature of an allometric relationship.
|
. Based on the goodness-of-fit criteria, the allometric relationship gave accurate descriptions of water or ash weight related to the total range of protein weights (Table 2)
.
|
). This means that, with increasing protein weights, the amount of water per unit of protein decreased continuously. In the carcass fraction, the allometric slope (0.939) was also below unity. In the organ fraction, however, the allometric slope (1.018) was greater than unity. For ash in the carcass + organs, the allometric slope was very close to unity and not different from it (P > 0.10). This implied that for this range of protein weights, the ash to protein ratio in the body did not change systematically with protein weights. This seemed to be a consequence of an increasing ash weight per unit protein in the organs (b = 1.075) combined with a generally decreasing (P > 0.10) ash weight per unit protein in carcass (b = 0.969) as protein weight increased (Table 2)
. Nutritional influences.
Effects of FI-level and the dietary PE-ratio on water and ash weights at a given protein weight are given in Table 3
. For all treatments, carcass weight accounted for 86% of the weight of the carcass + organs fraction. Effects in the carcass + organs fraction, thus, mainly reflected effects found in the carcass fraction (Table 3)
.
|
7% lower than at the highest PE-ratio (419 g; Table 3
). In expt. 2, this difference was only 1% (P > 0.1).
Ash weight at a given protein weight tended to be affected by the FI-level, but only in the carcass (P < 0.10); at the low FI-level, ash weight at a given protein weight in carcass was 6% higher than at the high FI-level in both experiments (Table 3)
. Ash weight at a given protein weight was also affected by PE-ratio (P < 0.05; Table 3
). In the carcass, a lower PE-ratio tended to increase ash weight compared with a higher one; across the range the difference was 13% in expt. 1 and 28% in expt. 2. In the organs, a low PE-ratio increased the ash weight by 6%, but only in expt. 1 (P < 0.10). This latter effect was the only effect of the dietary treatments in the organs.
There were significant interactions between FI-level and PE-ratio on ash weights in expt. 2 (Table 3)
in both carcasses and organs (P < 0.05). In carcasses, the difference in ash weight between the low and high FI-levels was much larger at the lowest PE-ratio (44.9 vs. 37.0 g, respectively) than at the highest PE-ratio (29.7 vs. 30.8 g, respectively). The background of the interaction in organs was that at the low FI-level, ash weight increased (P < 0.01) with increasing PE-ratio, whereas at the high FI-level, ash weight generally decreased (P > 0.10) with increasing PE-ratio.
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
Although all chickens were slaughtered at a fixed body weight, protein weights differed systematically among dietary treatments. These differences in protein weight mainly reflected differences in fat weights. To prevent that these differences in protein weight would interfere with the analysis for possible nutritional effects on the water to protein ratio or the ash to protein ratio, water and ash weights were recalculated to a common (the mean) protein weight. This recalculation was based on the relationships between water and protein, and ash and protein, within treatments. In this way, bias in the subsequent analyses for differences between treatments was prevented.
Water weights.
The relationship between water and protein in the body of animals, at least at maturity, seems independent of genotype (19
,20
). Literature evidence is lacking regarding the dependency of the relationship between water and protein on nutritional strategy. Kyriazakis and Emmans (9
) assumed that, under conditions that limit the growth of an animal, the water to protein ratio in a given component is not changed compared with that seen in normal growth. In other words, in the case of limited growth, deposition rates of water and protein are assumed to decrease in line with their inherent allometric relationship. For nutritional limitations of growth, this assumption was supported by the study of De Greef et al. (7
) of growing pigs, in which water weight at a certain protein weight seemed not to be affected by differences in FI-level or PE-ratio.
In our study, the FI-level and PE-ratio did also not affect water weight at a certain protein weight, except in the carcass at 800 g body weight. The reduction in water weight in the carcass at 800 g body weight due to a low PE-ratio suggests that the assumption of Kyriazakis and Emmans (9
), mentioned above, may not be generally valid across genotypes or degrees of maturity of the animal. The anatomical background of the reduction in water weight in carcass could be a disproportional reduction in the growth of different tissues in the carcass, with different water to protein ratios; for example, a greater reduction in the growth of muscle protein compared with collagen protein (21
). Data of Gerrits et al. (22
) on the amino acid composition of preruminant calves also suggested that the growth of muscle protein would be more inhibited by a low PE-ratio than would that of collagen protein. This proposed explanation, however, does not clarify why in older broilers, of 1600 g body weight, the effect of the PE-ratio on carcass water weight was not present.
Ash weights.
Both in carcass and organs, a low FI-level and a low PE-ratio reduced the rate of protein deposition by reducing the intake of lysine, the first limiting nutrient (13
). In the carcass, the rate of protein deposition was reduced more than the rate of ash deposition, resulting in an increased ash weight at a given protein weight. In organs, however, a low FI-level and a low PE-ratio caused, in most cases, a proportional reduction in rates of protein and ash deposition, resulting in similar ash weights at the mean protein weight. A possible explanation for this difference between carcass and organs is that in the carcass, protein and ash are physically less related than in the organs. In the carcass fraction, ash is mainly in skeletal tissues and protein relatively more in nonskeletal tissues, whereas in the organ fraction, ash and protein are distributed more equally among the different tissues. Therefore, considerable effects in carcass on ash weight at a given protein weight most likely reflect changes in the muscle to bone ratio. In apparent contrast with this idea on differences between carcass and organs, the PE-ratio tended (P < 0.10) to affect ash weight at a given protein weight in organs also (at 800 g body weight; Table 3
). It seems unlikely that the relationship between ash and protein in a given organ is affected by nutrition. The effect on ash weight at a given protein weight in the organ fraction likely reflects a disproportional reduction of the growth of different organs with different ash to protein ratios. For example, with decreasing PE-ratio, the proportion of kidneys in the organ fraction was significantly reduced in this study (data not shown).
Opposing views exist regarding the nutritional effects on the relationship between ash and protein in the body of the animal. A low PE-ratio increased ash to protein ratio in piglets (10
,11
) and preruminant calves (23
), whereas a low FI-level induced similar effects in growing broiler breeders (24
,25
). In contrast, the studies of Wilson (26
,27
) with domestic fowl, of Elsley et al. (8
) with pigs and lambs and of Kwakkel (28
) with layer pullets, suggest that the relation between ash and protein, or skeleton and lean body, is independent of nutrition.
Discrepancies in results of these studies are probably related to differences among studies in animal characteristics, nutritional treatments and data analysis. For example, differences in genotype, length of the experimental period and age at the beginning of this period may explain the difference in results with the pigs. Zimmerman and Khajarern (10
) and Kyriazakis et al. (11
) used relatively modern pig breeds, whereas Elsley et al. (8
) used data of pigs from before 1940. Muscle to bone ratio, or fat-free body composition, of well-fleshed modern breeds might respond more dramatically to dietary PE-ratio than might that with more traditional breeds. Besides, in the first two pig studies, pigs were grown from 5 kg to 12 or 23 kg body weight, whereas in the latter study, pigs were grown from 5 to 83 kg body weight. With a relatively long experimental period, effects at a young age might be partly compensated for at an older age. Whether an effect of FI-level or PE-ratio is found on ash weight at a certain protein weight may depend on which nutrient is limiting the growth. For example, if lysine intake is limiting protein deposition, as in our study, a low FI-level and a low PE-ratio both reduce the intake of the limiting nutrient, and may therefore cause similar effects on body composition. In contrast, when energy is the limiting nutrient for protein deposition, the PE-ratio has less effect on the intake of the limiting nutrient than FI-level, and, therefore, effects of PE-ratio and FI-level on body composition may differ. Finally, the data analysis of Kwakkel (28
) differed from most other studies mentioned. Kwakkel (28
) analyzed the development of body components during the experimental period, while most other studies analyzed body composition only at the end of the experimental period. With the latter approach, it becomes more critical when exactly the experiment is finished, compared with the approach of Kwakkel (28
).
Kwakkel (28
) suggested that discrepancies between his results and those of Yu et al. (24
), regarding ash/protein (in)dependence, can be explained by whether feathers are included in the carcass fraction. Our results, however, with defeathered carcasses also showed an effect of nutrition on ash weight at the mean protein weight. Thus, they do not support the suggestion of Kwakkel (28
).
We suggest that in studies of the relationship between nutrition and fat-free body composition, effects of genotype (e.g., fleshiness of the animal) and nutrient composition (e.g., the limiting nutrient) should be considered explicitly.
Growth simulation models.
The assumption in several growth models that water and ash deposition are determined solely by protein deposition (1
–3
) is not supported by this study. Particularly with diets high or low in PE-ratio, considerable differences were found in the weights of water and ash at a given protein weight compared with diets with a more average nutrient composition. Simulating growth of chemical body components based on protein deposition only does not consider these effects. For simulation of body weight gain based on protein deposition only, the effects on water weight are numerically of greater importance than the effects on ash weight. The effect (6%) on water weight at 800 g body weight denotes an effect on body weight of 3–4%. For ash weight, even the large effect (27%) of the PE-ratio on ash weight in carcass + organs at a body weight of 1600 g signifies an effect of <0.6% on body weight, and <1.2% on body weight gain between 800 and 1600 g. Thus, simulation of body weight gain or chemical body composition solely based on protein deposition might be accurate in case of animals with ad libitum consumption of balanced diets but can induce systematic errors in the simulations in case of low FI-levels or extreme PE-ratios. Because the values of other variables in models such as maintenance, heat loss, ad libitum food intake and physical body composition are often related to body weight, simulation errors in body weight may have a great impact on the accuracy of predictions by such models (29
).
The allometric relationships between water or ash and protein differed between carcasses and organs. The relationship between water and protein was, in most cases, not affected by nutrition, whereas the relationship between ash and protein was strongly affected, particularly by the PE-ratio. The extreme PE-ratios caused differences in ash weight at a given protein weight in the carcass by up to 28%. Results suggest that the muscle to bone ratio in carcass is dependent on nutrition. We conclude that, at least for modern meat-type animals, nutritional strategy can have significant effects on fat-free body composition at a certain fat-free body weight, at least in the short term. The nutritional effects on fat-free body composition could be incorporated into models of the chemical body composition of growing animals.
|
APPENDIX 1 |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
 | (i) |
, where Wcorr = corrected water weight, W = measured individual water weight, c = correction factor, P = measured individual protein weight and 
= mean experimental protein weight. The values used for and c (four values each: for carcasses and organs in expts. 1 and 2) are presented below. Values for were 18.1 and 31.1 g in organs and 110.6 and 225.2 g in carcasses, in expts. 1 and 2, respectively. Values for parameter c, which is the regression coefficient between W and P at 800 (expt. 1) or 1600 g body weight (expt. 2), could not be estimated over the different dietary treatments, because values of P were systematically different for the dietary treatments. Therefore, values for parameter c in equation (2
) were estimated based on the relation between W and P within dietary treatments, using the following regression equation:
 | (ii) |
, where c = correction factor, Wij = water weight of animal j at dietary treatment i, 
i = mean water weight at dietary treatment i, Pij = protein weight of animal j at dietary treatment i and i = mean protein weight at dietary treatment i, i = 1.18 and j = 1,2,3. For the correction of water weights, estimated values for c were 3.84 and 2.91 in organs and 1.21 and 1.21 in carcasses, in expts. 1 and 2, respectively. For the correction of ash weights, estimated values for c were 0.061 and 0.060 in organs and 0.116 and -0.141 in carcasses, in expts. 1 and 2, respectively. Corrected water weights (Wcorr) in carcass + organs were calculated for the individual animal as the sum of Wcorr in carcasses and Wcorr in organs. For the correction of ash weight, the same procedures were adopted as for the correction of water weight.
|
ACKNOWLEDGMENTS |
|---|
|
FOOTNOTES |
|---|
2 Supported in part by a grant from the Dutch Ministry of Economic Affairs.
4 Abbreviations used: FI-level, feed intake level; PE-ratio, dietary protein to energy ratio.
Manuscript received 26 December 2001. Initial review completed 4 February 2002. Revision accepted 20 March 2002.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAPPENDIX 1LITERATURE CITED |
|---|
1. Emmans, G. C. (1981) A model of the growth and feed intake of ad libitum fed animals, particularly poultry. Computers in Animal Production 1981:103-110 British Society of Animal Production Occasional Publication No. 5.
2. Black, J. L., Campbell, R. G., Williams, I. H., James, K. J. & Davies, G. T. (1986) Simulation of energy and amino acid utilisation in the pig. Res. Dev. Agric. 3:121-145.
3. Moughan, P. J., Smith, W. C. & Pearson, G. (1987) Description and validation of a model simulating growth in the pig (20–90 kg live weight). N. Z. J. Agric. Res. 30:481-489.
4. Kotarbinska, M. (1969) Badania Nad Przemiana Energii u Rosnacych Swin 1969 Institure of Zootechnology Krakow, Wydawn. .
5. Kwakkel, R. P., Verstegen, M.W.A. & Ducro, B. J. (1997) Diphasic allometric growth of body components in white leghorn pullets fed ad libitum and restricted diets. Poultry Sci 76:1020-1028.
6. Emmans, G. C. (1989) The growth of turkeys. Recent Advances in Turkey Science 1989:135-166 Butterworths Poultry Science Symposium No. 21.
7. De Greef, K. H., Verstegen, M.W.A. & Kemp, B. (1992) Validation of a porcine growth model with emphasis on the composition of the body. Livest. Prod. Sci. 32:163-180.
8. Elsley, F.W.H., McDonald, I. & Fowler, V. R. (1964) The effect of plane of nutrition on the carcasses of pigs and lambs when variations in fat content are excluded. Anim. Prod. 6:141-154.
9. Kyriazakis, I. & Emmans, G. C. (1992) The growth of mammals following a period of nutritional limitation. J. Theor. Biol. 156:485-498.[Medline]
10. Zimmerman, D. R. & Khajarern, S. (1973) Starter protein nutrition and compensatory responses in swine. J. Anim. Sc. 36:189-194.
11. Kyriazakis, I., Stamataris, C., Emmans, G. C. & Whittemore, C. T. (1991) The effects of food protein content on the performance of pigs previously given foods with low or moderate protein contents. Anim. Prod. 52:165-173.
12. Berri, C. (2000) Variability of sensory and processing qualities of poultry meat. World Poultry Sci. J. 56:209-224.
13. Eits, R. M., Kwakkel, R. P., Verstegen, M.W.A., Stoutjesdijk, P. & De Greef, K. H. (2001) Protein and lipid deposition rates in male broiler chickens: separate responses to amino acids and protein-free energy. Poultry Sci 81:472-480.
14. Centraal Veevoederbureau (2000) Veevoedertabel [Dutch Feeding Tables] 2000 Centraal Veevoederbureau Lelystad, The Netherlands. .
15. Zoons, J., Buyse, J. & Decuypere, E. (1991) Mathematical models in broiler raising. World Poultry Sci. J. 47:243-255.
16. Baker, D. H., Parsons, C. M., Fernandez, S., Aoyagi, S. & Han, Y. (1993) Digestible amino acid requirements of broiler chicks based upon ideal protein considerations. Proc. Ark. Nutr. Conf. 1993:22-32 Fayetteville .
17. Huxley, J. S. (1932) Problems of Relative Growth 1932 Methuen & Co London, UK. .
18. SPSS (1997) SPSS Base 7.5 for Windows User’s Guide 1997 SPSS, Inc. Chicago, IL. .
19. Emmans, G. C. (1988) Genetic components of potential and actual growth. Animal Breeding Opportunities 1988:153-181 British Society of Animal Production. .
20. Wang, Z. M., Deurenberg, P., Wang, W., Pietrobelli, A., Baumgartner, R. N. & Heymsfield, S. B. (1999) Hydration of fat-free body mass: review and critique of a classic body-composition constant. Am. J. Clin. Nutr. 69:833-841.
21. Ashgar, A., Morita, J-I., Samejima, K. & Yasui, T. (1986) Variations of proteins in myofibrils and connective tissue of chicken red and white skeletal muscles influenced by undernutrition. Agric. Biochem. Chem. 50:1941-1949.
22. Gerrits, W.J.J., Schrama, J. W. & Tamminga, S. (1998) The marginal efficiency of utilization of all ileal digestible indispensable amino acids for protein gain is lower than 30% in preruminant calves between 80 and 240 kg live weight. J. Nutr. 128:1774-1785.
23. Gerrits, W.J.J., Dijkstra, J. & France, J. (1997) Description of a model integrating protein and energy metabolism in preruminant calves. J. Nutr. 127:1229-1242.
24. Yu, M. W., Robinson, F. E. & Robblee, A. R. (1992) Effect of feed allowance during rearing and breeding on female broiler breeders: growth and carcass characteristics. Poultry Sci 71:1739-1749.[Medline]
25. Katanbaf, M. N., Dunnington, E. A. & Siegel, P. B. (1989) Restricted feeding in early and late-feathering chickens: organ size and carcass composition. Poultry Sci 68:359-368.
26. Wilson, P. N. (1954) Growth analysis of the domestic fowl: effect of plane of nutrition on carcass composition. J. Agric. Sci. 44:67-85.
27. Wilson, P. N. (1954b) Growth analysis of the domestic fowl: effect of plane of nutrition on carcass composition of cockerels and egg yields of pullets. J. Agric. Sci. 45:110-124.
28. Kwakkel, R. P. (1994) Multiphasic Growth in the Layer Pullet: Effects of Nutrient Restrictions during Rearing. PhD thesis 1994 Wageningen University Wageningen, The Netherlands. .
29. Emmans, G. C. & Kyriazakis, I. (1995) A general method for predicting the weight of water in the empty bodies of pigs. Anim. Sci. 61:103-108.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
