Correlation between physical measurements and dietary
energy values of wheat for poultry and pigs
J. Wiseman
*Division of Agriculture and Horticulture, School of Biological Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leics, LE12 5RD, UK
Received 5 October 1999; received in revised form 5 January 2000; accepted 7 February 2000
Abstract
A number of wheat samples were obtained for evaluation: for young poultry, 50 wheats (10 varieties each grown at ®ve sites) with bushel weights/thousand grain weights ranging from 69.5 to 80.0 kg/hl and 34.6 to 59.3 g, respectively; for pigs (8 different varieties each grown at 2 sites) with bushel weights/thousand grain weights ranging from 71.0 to 81.5 kg/hl and 40.9 to 56.7 g, respectively. Apparent metabolisable energy (AME) and coef®cient of metabolisability of gross energy (CAME) were determined with young broilers; Digestible energy (DE) and coef®cient of total tract apparent digestibility (CTTAD) of gross energy were determined with growing ®nishing pigs. Wheat was added at a rate of 750 and 900 g/kg diet for poultry and pigs, respectively, in a series of metabolism trials. AME values ranged from 8.49 to 12.45 MJ/kg DM and CAME from 0.491 to 0.702. DE values ranged from 14.55 to 16.07 MJ/kg DM and CTTAD from 0.848 to 0.890. There were signi®cant differences between variety and site (together with interaction terms) in both, the physical and biological measurements, but not in a structured fashion. There were no signi®cant relationships between the two physical measurements and any dietary energy value (either in terms of concentration or coef®cient), con®rming previous work. The two lowest bushel weight wheats had among the highest AME values for poultry, con®rming that evaluation of the variability in nutritional value of wheat for poultry should only proceed against a background of detailed knowledge of genotype. Comparisons on the basis of variety name alone appear inappropriate as individual varieties do not seem to respond in a uniform fashion.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Poultry; Pigs; Wheat; Dietary energy; Bushel weight; Thousand grain weight
*Tel.:44-0-115 9516054; fax:44-0-115-9516060.
E-mail address: julian.wiseman@nottingham.ac.uk (J. Wiseman)
1. Introduction
Wheat is a major raw material for inclusion into diets for non-ruminants; it is conventionally used at a rate of 300 g/kg in diets for growing/®nishing pigs and its rate of inclusion may approach 600 g/kg in diets for broilers in those countries where the crop is available and its cost appropriate.
Although wheat is frequently ascribed a uniform dietary energy value, evidence has been accumulating for some years that, at least for poultry, this is probably not the case (e.g. Mollah et al., 1983; Rogel et al., 1987; Wiseman and Inborr, 1990). There has been a considerable amount of work designed to investigate the reasons for this variation in nutritional values and attention has been focussed on the non-starch polysaccharide (NSP) content and structure (e.g. Choct and Annison, 1990; Annison, 1991; Choct et al., 1996; Austin et al., 1999).
Analyses of the NSP content and structure are, however, relatively complex and there has been renewed interest in the relationship between more simple tests and subsequent nutritional value of wheat. The advantage of these latter tests is their speed as well as their simplicity which renders them easily performed on a routine basis by both, the growers and feed compounders alike. There have been limited studies on the correlation between physical tests (e.g. bushel weight and thousand grain weight) and nutritional value although Sibbald and Price (1976) were unable to demonstrate signi®cant relationships between these and metabolisable energy (ME) values in broilers; however, this study was undertaken with adult birds and it is known that the younger broiler is more sensitive to variations in dietary inputs.
The current programme was designed to examine the relationship between simple physical tests and nutritional value of wheat for young broilers. Selection of wheat samples was in a structured fashion, with named cultivars being grown at different locations to investigate environmental interactions, thus removing some of the variability in previous data from wheats of unknown cultivars and locations of growth.
In contrast to poultry, dietary energy values of wheat for pigs are not variable to any extent (see, e.g. Wiseman et al., 1979). Fuller et al. (1989) concluded that there was no evidence that differences in wheat variety and husbandry (fertiliser, seed rate, fungicide, growth regulator) signi®cantly in¯uenced the digestibility of starch or gross energy. Nevertheless, bushel weight and thousand grain weight are sometimes considered accurate indicators of nutritional value of wheat for pigs. A second objective of the current programme was to examine this possibility with speci®c varieties grown at two known locations.
2. Method and materials
2.1. Poultry metabolism trial
Ten wheat samples were obtained from each of the ®ve growth sites. Physical measurements are presented in Tables 1 and 2, respectively, for bushel weight and thousand grain weight. The range in data was considered suf®cient for subsequent
nutritional evaluation. A preliminary trial with wheats had revealed that, when samples were incorporated into diets at a rate of inclusion of 900 g/kg, low apparent metabolisable energy (AME) values were recorded, suggesting that the young chick was unable to digest wheat (although no further studies were undertaken in attempts to explain why). A subsequent rate of inclusion of 750 g/kg was investigated which gave a range of AME, allowing conclusions on the relative value of individual samples to be drawn and the rate was adopted. Rates <750 g/kg would have increased the probability that no differences
Table 1
Mean 74.3 72.9 76.2 72.6 77.4 74.6
S.E. p
Variety 1.47 0.001
Site 1.01 <0.001
Table 2
Thousand grain weight (g) Ð poultry trial
Variety Site Mean
Mean 47.7 46.6 42.0 43.2 52.6 46.4
S.E. p
Variety 3.04 0.430
between wheat samples would have been detected. However, it was not the objective of the current study to investigate optimum rates of inclusion for evaluation.
Wheat samples were ground in a hammer mill (3-mm screen) and incorporated into an experimental diet (Table 3). Each diet was fed to six replicates of a cage containing two broiler cocks, of initial age 10 days, housed in an environment-controlled metabolism room maintained under conditions suitable for the chick. A subsequent 3-day adaptation and 3-day total collection period, during which birds were fed ad libitum, was undertaken with food consumed and excreta voided recorded. Following drying, excreta were ground through a hammer mill ®tted with a 3-mm screen and stored to await analysis for dry matter, nitrogen and gross energy. No further chemical measurements were undertaken as the programme was designed speci®cally to examine relationships between physical measurements and digestibility. Biological data were statistically analysed as a variety*site factorial design.
2.2. Pig metabolism trial
As larger quantities are required for evaluation with pigs, only eight wheat samples were obtained each from two growth sites (both cultivars and sites were different from those in the poultry trial). As with poultry, the range in both, bushel weight and thousand grain weight (Table 4) was thought wide enough to proceed with nutritional evaluation. Samples were ground through a hammer mill ®tted with a 3-mm screen. Each sample was incorporated into a diet (Table 3) at a rate of 900 g/kg. The 16 experimental diets were evaluated with 16 gilts (commercial white genotype) of25 kg initial weight. Each gilt evaluated four diets over four time periods in a Latin Square design. Each time period was based on a 10-day acclimatisation period on experimental diets followed by a 5-day
Table 3
aDesigned to meet the macro and micro-nutrient (vitamin and mineral) requirements of the young broiler when included at this rate.
bDesigned to meet the micro-nutrient (vitamin and mineral) requirements of the growing ®nishing pig when included at this rate.
collection period during which animals were housed in metabolism crates. Pigs were fed twice daily on semi-liquid diets (water:feed as 2:1, v:w). Feed allowances were 0.9 of estimated ad libitum intake, with the quantities offered being determined at the start of each time period. Total 5-day faecal collection was delineated with the use of the inert dye indigo carmine added to the evening meals on days 1 and 6. Urine collection was on a timed basis (between a ®xed time on the mornings of days 2 and 7). A representative sub-sample of both quantitative faecal and urinary outputs was taken and stored atÿ208C prior to analysis. Full details are found in Wiseman et al. (1990).
All wheat, diet, faecal (pig)/excreta (poultry) samples were analysed for dry matter, gross energy and nitrogen (pig trial), from which the digestible energy (DE) and AME for diets were calculated. Nitrogen digestibility was also determined for diets fed to pigs. Assumed values for the other dietary ingredients were then employed to estimate the DE and AME values for individual wheat samples.
3. Results and discussion
3.1. Physical measurements
Bushel weight and thousand grain weight, both determined from the samples as received, are presented in Tables 1 and 2, respectively, for wheats evaluated with poultry, and Table 4 for pigs. Bushel weights for those wheats evaluated with poultry ranged from 69.5 kg/hl (wheat A, Site 4) to 80.0 (wheat H, Site 5). Analysis of variance revealed a highly signi®cant difference between both, variety (p0.001) and site (p<0.001); as only one value was available for each sample, the interaction terms could not be analysed. The range in bushel weights for wheats evaluated with pigs was 71.0 (wheat A at both sites,
Table 4
Bushel weight (kg/hl) and thousand grain weight (g) for wheats evaluated with pigs
Variety Bushel weight (kg/hl) Thousand grain weight (g)
Site Mean Site Mean
Mean 76.9 77.0 77.0 46.3 46.4 46.4
S.E. p S.E. p
Variety 1.35 0.002 1.68 0.001
1 and 2) to 81.5 (wheat F at both sites, 1 and 2). These data compare favourably with those from France reported by Metayer et al. (1993), who observed a range from 73.4 to 81.3 for 70 wheat samples. However, the range reported by Sibbald and Price (1976) was from 63.8 to 87.0 (n35, with an exceptionally low value of only 38.7 associated with extreme climatic conditions prior to harvest). The range presented by Zijlstra et al. (1999) was from 45.4 to 77.6; whilst frost pre-harvest was sometimes associated with lower values, this was not always the case.
Thousand grain weights in the current study ranged from 34.6 to 59.3 g for samples evaluated with poultry (p0.430 and <0.001, respectively, for the effect of variety and site) and from 40.9±56.7 g for wheat evaluated with pigs (p0.001 and 0.966, respectively, for variety and site). Data from Metayer et al. (1993) were 26.9±43.8 g and from 24.7±53.1 g (again excluding an exceptional low value of 15.8 which was from the same sample recording the very low bushel weight) from Sibbald and Price (1976). The range for 27 wheats reported by March and Biely (1973) was 27.9±51.6 g.
Data from the current trial were, therefore, considered to represent a suf®ciently wide range to establish whether or not there was a correlation with subsequent dietary energy values. However, the correlation between bushel weight and thousand grain weight was variable, which illustrates that there need not be a direct relationship between the two measurements; indeed, there were examples of samples (e.g. D Ð Table 1) with low bushel weight that had high, 1000, grain weight (Table 2).
3.2. Biological data
Data from the poultry metabolism trial are presented in Table 5 for AME and in Table 6 for coef®cient of energy metabolisability; the latter term is preferable in comparisons as it
Table 5
Poultry Ð apparent metabolisable energy (AME, MJ/kg DM)
Variety Site Mean
1 2 3 4 5
A 12.04 11.75 12.35 10.74 11.21 11.62
B 11.40 10.90 11.89 11.33 10.51 11.21
C 11.84 11.20 12.11 11.05 12.45 11.73
D 11.88 12.25 9.92 11.97 9.96 11.20
E 12.33 10.59 11.65 10.63 11.29 11.30
F 10.49 10.77 12.00 11.00 11.61 11.18
G 10.61 12.27 8.49 12.31 8.82 10.50
H 11.54 11.49 10.88 11.85 12.18 11.59
I 11.43 11.34 11.27 11.21 12.43 11.54
J 11.20 11.38 11.47 10.81 11.24 11.22
Mean 11.48 11.40 11.20 11.29 11.17 11.31
S.E. p
Variety 0.398 0.129
Site 0.281 0.794
Variety*site 0.889 0.001
removes any variation in AME that might be attributable to differences in gross energy. AME ranged from 8.49 to 12.45 MJ/kg DM, thus con®rming many previous trials that dietary energy values of wheat fed to young poultry are variable (e.g. March and Biely, 1973, with a range of 2.54 MJ/kg; Mollah et al., 1983, range 4.9 MJ/kg; Rogel et al.,
Table 6
Poultry Ð coef®cient of apparent metabolisability of energy (CAME)
Variety CAME
Site Mean
1 2 3 4 5
A 0.672 0.661 0.673 0.591 0.620 0.643
B 0.644 0.606 0.647 0.637 0.590 0.625
C 0.671 0.626 0.679 0.612 0.694 0.656
D 0.674 0.668 0.555 0.670 0.569 0.627
E 0.702 0.600 0.649 0.597 0.635 0.637
F 0.599 0.598 0.661 0.606 0.646 0.622
G 0.596 0.679 0.491 0.684 0.489 0.588
H 0.657 0.638 0.618 0.658 0.685 0.651
I 0.634 0.628 0.642 0.632 0.675 0.642
J 0.642 0.637 0.652 0.605 0.625 0.632
Mean 0.649 0.634 0.627 0.629 0.623 0.632
S.E. p
Variety 0.022 0.510
Site 0.016 0.151
Variety*site 0.050 0.011
Table 7
Pigs Ð digestible energy (DE, MJ/kg DM) and coef®cient of total tract apparent digestibility (CTTAD Ð E) of gross energy
Variety DE CCTAD - E
Site Mean Site Mean
1 2 1 2
A 14.66 15.17 14.92 0.848 0.862 0.855
B 14.96 15.85 15.40 0.857 0.880 0.868
C 15.72 15.43 15.58 0.890 0.872 0.881
D 16.07 15.42 15.72 0.885 0.882 0.883
E 15.79 15.19 15.49 0.878 0.866 0.872
F 15.20 15.48 15.34 0.870 0.880 0.875
G 15.45 14.55 15.00 0.856 0.873 0.864
H 15.66 15.08 15.37 0.887 0.868 0.878
Mean 15.43 15.27 15.35 0.871 0.873 0.872
S.E. p S.E. p
Variety 0.187 0.001 0.0106 0.774
Site 0.093 0.102 0.0053 0.165
1987, range 4.46 MJ/kg). However, there were no signi®cant differences attributable to variety or to site in the current study, although a signi®cant variety*site interaction (p0.001) was observed.
Table 7 presents data from the pig metabolism trial. The range of DE values was from 14.55 to 16.07 MJ/kg DM; there was a signi®cant difference between varieties (p0.001), although there was no signi®cant effect of either variety or site (or the interaction between the two) in terms of coef®cient of total tract apparent digestibility (CTTAD) of gross energy. Differences between samples for content of digestible nitrogen (Table 8) were attributable substantially to variation in total nitrogen content as CTTAD of nitrogen was not in¯uenced by variety, although a sitevariety interaction was detected (p<0.001). The lack of major differences between wheat samples in terms of DE value for growing pigs con®rms previous observations (Wiseman et al., 1979; Fuller et al., 1989) that wheat for pigs is a comparatively uniform raw material.
Table 8
Pigs Ð total nitrogen (g/kg DM), digestible nitrogen (Dig N, g/kg DM) and coef®cient of total tract apparent digestibility (CTTAD Ð N)
A 18.3 19.1 18.7 0.846 0.853 0.850
B 19.3 17.3 18.3 0.859 0.854 0.857
C 18.3 19.0 18.5 0.870 0.871 0.870
D 21.6 19.2 20.4 0.871 0.878 0.875
E 18.2 15.2 16.7 0.834 0.830 0.832
F 16.7 16.8 16.7 0.855 0.851 0.853
G 19.6 19.1 19.3 0.864 0.857 0.860
H 20.1 21.1 20.6 0.855 0.863 0.859
Mean 19.0 18.3 18.7 0.857 0.857 0.857
S.E. p S.E. p
Variety 0.13 <0.001 0.0061 <0.001
Site 0.07 <0.001 0.0030 0.878
Variety*Site 0.19 <0.001 0.0086 0.791
The main objective of the current programme was to relate basic physical measurements to nutritional values of wheat samples. Initially, the two physical measurements were related; there was no correlation between the two for those wheats evaluated with poultry although a signi®cant (p<0.05, r20.447) relationship was observed for those wheats evaluated with pigs. As the two trials were not based on the same cultivars or locations, it was not thought appropriate to combine them for this comparison. The data of Sibbald and Price (1976) allowed a comparison between bushel weight and thousand grain weight to be calculated; the r2 values derived (0.398 and 0.324, respectively, with, and without, the very low individual sample) con®rm that there is no relationship between the two variables. It is, moreover, probable that individual wheat cultivars have speci®c grain ®lling properties (D. Stokes, University of Nottingham, personal communication), thus rendering comparison between cultivars on the basis of physical measurements invalid.
There were no signi®cant correlations established between the two physical measurements and biological data. Similarly, recalculation of the data of Sibbald and Price (1976), bearing in mind that AME values were determined with adult birds, established that the relationship between the same two physical terms and either AME or metabolisability of gross energy was not signi®cant with the anomalously low value being removed from the calculations. The correlation coef®cient between grain weight and ME reported by March and Biely (1973) was onlyÿ0.004.
The general conclusions from the current trial are that there does not appear to be any relationship between two commonly derived physical measurements and dietary energy value of wheat for young poultry and pigs. In the case of the latter species, although there were differences between wheat samples in physical measurements, the lack of appreciable variability in nutritional value would not have allowed any meaningful correlations to be established. For young poultry, however, there were differences in both physical and biological measurements. Nevertheless, the two could not be linked (Fig. 1). In fact, the two wheat samples (wheat G at Site 3, wheat G at Site 5) with the lowest AME (8.49 and 8.82 MJ/kg DM, respectively) were among the highest bushel weights (77.0 and 78.0 kg/hl, respectively).
The current programme (named wheats grown at speci®c sites) and previous studies (wheats from many locations Ð March and Biely, 1973; Sibbald and Price, 1976) indicate that bushel weight or thousand grain weight are not associated with nutritional values of wheat for poultry or pigs. It remains to be established whether bushel weights below 69.5 (the lowest in the current poultry study) are associated in a structured fashion (as opposed to one with an extremely low value as evaluated by Sibbald and Price, 1976) with poorer nutritional value. Whilst the data of Zijlstra et al. (1999) appear to indicate that bushel weights below65 kg/hl are associated with poorer DE values of wheat for pigs, it should be noted that a sample with a high bushel weight (73.6 kg/hl) had one of the lowest DE values (15.87 MJ/kg DM); furthermore, a sample with an extremely low bushel weight (45.4 kg/hl) had a DE value (15.45 MJ/kg DM) very similar to samples with bushel weights of 57.8 and 63.8 kg/hl (DE of 15.48 and 15.51 MJ/kg DM).
The current trial, in establishing that poor AME values may be associated with high bushel weights, appears to con®rm that evaluation of the variability in nutritional value of wheat for poultry should only proceed against a background of detailed knowledge of genotype (as concluded by Short et al., 1999). Comparisons on the basis of variety name alone appear inappropriate as individual varieties do not seem to respond in a uniform fashion. Variability in DE values of wheat for pigs is still not considered suf®ciently great to warrant detailed investigation.
Acknowledgements
The support of the United Kingdom Home-Grown Cereals Authority and the technical staff at the University of Nottingham is gratefully acknowledged.
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