Effect of specific weight on the metabolizable energy content of four cultivars of wheat grain in ewes

Animal Feed Science and Technology 105 (2003) 215–224

Short communication

Effect of specific weight on the metabolizable energy content of four cultivars of wheat grain in ewes J.M. Wilkinson a , Helen M. Miller a,∗ , K.J. McCracken b , Anne Knox c , J. McNab c , S.P. Rose d a

School of Biology, University of Leeds, West Yorkshire LS2 9JT, UK The Queen’s University, NewforgeLane, Belfast, County Antrim BT9 5PX, UK c The Roslin Institute, Roslin, Midlothian EH26 9PS, UK Harper Adams University College, Edgmond, Newport, Shropshire TF10 8NB, UK b

d

Received 12 February 2002; received in revised form 15 January 2003; accepted 15 January 2003

Abstract To determine the effect of specific weight on the metabolizable energy value of wheat grain for ruminants, 16 samples of winter wheat grain, comprising four cultivars (Riband, Buster, Consort and Haven) each at four specific weights ranging from 60 to 78 kg/hl were fed in a pelleted concentrate (wheat = 0.7 of total fresh weight) to housed mature sheep at the maintenance level of feeding. The concentrate comprised 0.6 of total daily dry matter (DM) intake, and chopped winter wheat straw comprised 0.4 of total daily DM intake. There was no effect of specific weight on apparent digestibility of whole-diet DM or on whole-diet estimated metabolizable energy (ME) concentration. There were no interactions between specific weight and cultivar in terms of apparent digestibility of whole-diet DM. Apparent digestibility of DM was lower (P < 0.05) for Buster and Consort than for Riband and Haven. Estimated concentration of ME was lower (P < 0.05) for Buster than for Riband and Haven. There is energetic flexibility in the use of winter wheat of different specific weights in diets for ruminants, since there is no relationship between specific weight and metabolizable energy content. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Wheat grain; Specific weight; Apparent digestibility; Ruminants; Sheep

Abbreviations: DM, dry matter; CP, crude protein; hl, hectolitre; DE, digestible energy; LW, live weight; MADF, modified acid detergent fibre; ME, metabolizable energy; NDF, neutral detergent fibre; NS, not significant; S.E.D., standard error of differences between means ∗ Corresponding author. E-mail addresses: [email protected] (H.M. Miller), [email protected] (J.M. Wilkinson). 0377-8401/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0377-8401(03)00047-6

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1. Introduction Recent research into factors affecting the nutritional value of cereal grains for ruminants has focused on digestion of starch in the rumen (Reynolds et al., 1997; Phillippeau et al., 1999), and on effects of species of cereal on digestion of fibre (Martin et al., 1999). However, relatively little work has been carried out with wheat grain on effects of physical factors such as specific weight, which might influence energetic value indirectly due to the negative correlation between specific weight of the grain and its concentration of fibre (Sibbald and Price, 1976; Hickling, 1994). Specific weight is one of several assessments of quality used by buyers of grain in determining the price paid to the producer since it is presumed to be an indicator of energetic value. Thus the guideline minimum specific weight for wheat to be sold into central government support buying in the European Union is 73 kg/hl (UK Intervention Board, 2000). An additional justification for the use of specific weight as a trading standard is that grain of lower specific weight may be more expensive to transport and store than material of relatively higher specific weight. In a review of literature on relationships between specific weight of wheat grain and its energetic value for farm livestock, Miller and Wilkinson (1998) stated that, although specific weight gives an indication of starch and fibre concentrations, variation in morphology of the grain can also affect specific weight and reduce its accuracy as a predictor of chemical composition. They concluded that specific weight was a poor indicator of energy value. Grimson et al. (1987) found no effect of specific weight of barley grain on rate of growth of beef cattle. Bhatty et al. (1974) observed that specific weight was negatively related to the concentration of digestible energy (DE), determined in mice, in 17 cultivars of Canadian wheat. The relationship was much stronger for cultivars with hard endosperms (r = −0.71, P < 0.05) than for those with soft endosperms (r = −0.17, NS). Moss et al. (1999) found no relationship between the specific weight of 84 samples of wheat grain and the calculated metabolizable energy (ME) concentration for ruminants, and observed that specific weight was strongly influenced by cultivar. It is apparent that several studies of the relationship between the specific weight of grain and its energy value to livestock were compromised by sample selection on the basis of specific weight without regard to cultivar (Miller and Wilkinson, 1998). There has been no research to determine effects of specific weight on digestibility and metabolizable energy value to ruminants. Accordingly, this experiment was conducted over as wide a range of specific weights as possible with different cultivars of wheat grown in the United Kingdom. The experiment was part of a larger programme, which also involved digestion and feeding trials with pigs and poultry (Miller et al., 2001). 2. Materials and methods 2.1. Feeds Sixteen samples of winter wheat of four cultivars (i.e. Riband, Buster, Consort, Haven), each of four different specific weights, were obtained from different locations in the United

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Kingdom following the 1998 (10 samples) and 1999 harvests (6 samples). The cultivars Riband and Consort were characterised as having a “soft” grain endosperm texture, whilst Buster and Haven were characterised as having a “hard” endosperm texture (NIAB, 1995). A constraint in the collection of the samples was that the moisture concentration should not exceed 150 g/kg fresh weight, since it was recognised that specific weight was affected by moisture (Hook, 1984; Moss et al., 1999). Sub-samples were assayed for confirmation of cultivar and for cultivar purity at the laboratory of the National Institute of Agricultural Botany (Cambridge, England) by acid polyacrylamide gel eletrophoresis (ISTA, 1996). The physical and chemical characteristics of the 16 samples are in Table 1 as main effects of cultivar and specific weight. Pour and tap density were determined on ground grain by the method of CIPAC (1995). The concentrations of DM, starch, crude protein (CP), neutral detergent fibre (NDF) and modified acid detergent fibre (MADF) were determined using methods in MAFF (1986). NDF, expressed with residual ash, was determined with the addition of alpha amylase and sodium sulphite. Acid ether extract (oil) was determined by the method of Alderman (1985). Hagberg Falling Number, the standard measure of alpha amylase activity in cereal grains, was determined using the method of Hagberg (1960). The samples of wheat grain were transported to an experimental feed mill at the Roslin Institute, Edinburgh, where they were hammer-milled through a 3 mm screen and extruded as concentrate pellets. The formulation of the concentrate was: wheat (686.5 g/kg fresh weight), molassed sugar beet pulp (175 g/kg fresh weight), extracted soyabean meal (100 g/kg fresh weight), minerals (34 g/kg fresh weight), titanium dioxide (3.0 g/kg fresh weight), amino acids (1.6 g/kg fresh weight). Titanium dioxide (TiO2 ) was added as a marker for estimation of digestibility. There were small differences between the 16 feeds in the concentration of CP (range 128–147 g/kg fresh weight). With the exception of Consort, the lower concentrations of CP in the concentrates were generally associated with the samples at specific weight 4 (Table 1). 2.2. Animals Fourteen mature Blue-faced Leicester × Swaledale ewes were selected from the University of Leeds flock on the basis of their live weight (LW). The ewes had been sheared 35 days previously. Each ewe was examined visually to ensure that it was not lame or lacking in teeth and dosed with an anthelmintic drench (Panacur, Hoechst Roussel Vet Ltd., Milton Keynes, UK). Two ewes were housed in an adjacent room as potential replacements during the course of the experiment. These replacements were given a diet of 700 g per day of high-temperature dried grass pellets and bedded on winter wheat straw. The LW of each sheep was determined at weekly intervals throughout the experiment. The 12 ewes were installed in individual pens (average size 4.5 m2 ) comprising steel gates mounted on rubber mats. The pens were bedded with “Drybed” (Fosse Ltd., Whetstone Magna, Lutterworth Road, Whetstone, England), an inert high-absorbency material manufactured from re-processed newspaper. The bedding was added to each pen daily to ensure that each pen remained relatively dry throughout the experiment. The material was unpalatable to the animals and was not observed to be eaten. Wet material

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Specific weighta

Cultivar

Specific weight (kg/hl) Thousand grain weight (g) Pour density (kg/hl) Tap density (kg/hl) Hagberg Falling Number Dry matter (g/kg fresh weight) Starch (g/kg DM) Crude protein (g/kg DM) Neutral detergent fibre (g/kg DM) Modified acid detergent fibre (g/kg DM) Acid ether extract (g/kg DM)

S.E.D.

Buster

Consort

Haven

Riband

1

2

3

4

71.8 cd 39.1 59.2 69.0 262 897 b 619 114 126 c 30.1 24.1 ab

73.6 b 37.4 60.3 72.1 234 905 a 644 105 174 ab 32.4 30.5 a

68.1 f 39.5 57.0 66.7 187 897 b 608 120 141 bc 29.8 22.5 b

70.5 de 35.3 57.8 67.8 292 883 d 605 121 208 a 31.4 28.1 ab

64.7 g 31.8 b 54.0 b 63.5 b 229 896 bc 588 119 171 33.1 a 27.5

69.1 def 37.2 ab 54.1 b 64.6 b 258 893 bc 623 114 162 33.0 a 27.0

72.6 bc 38.9 ab 61.5 a 71.1 ab 255 892 c 632 116 169 30.7 a 25.4

77.6 a 43.4 a 64.7 a 76.3 a 234 897 b 632 111 147 27.0 b 25.2

Means with different letters on the same row are different (P < 0.05). a 1: lowest, 4: highest specific weight.

0.660 3.02 2.26 2.62 39.6 1.44 19.1 5.75 14.7 1.90 2.34

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Table 1 Physical and chemical characteristics of the wheat samples

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was removed daily. Each pen was equipped with three containers, one to hold the pelleted concentrate, one to hold winter wheat straw chopped to 60 mm average particle length by a mechanical straw chopper, and one for water which was offered ad libitum and replenished twice daily. The ewes remained in the same pens throughout the experiment. 2.3. Experimental design and procedures The design of the experiment was a balanced incomplete Latin Square with four periods and three replications of each individual diet. The ewes were allowed a period of 11 days pre-experimental acclimatisation period, during which time their diet was gradually changed from one of pelleted dried grass to one of pelleted concentrate and chopped straw. The dried grass was reduced and concentrate was increased daily in increments of 100 g/head per day, up to a maximum of 700 g/head per day. Chopped straw was offered ad libitum during the acclimatisation period, and the amount eaten increased steadily during this period from about 150 g/head per day to about 400 g/head per day. Each experimental period was of 14 days, with two sub-periods. The first, of 9 days, was an adjustment period to the new wheat diet. The second sub-period was of 5 days, during which faeces samples were taken daily per rectum from each animal at 09.30 h, frozen immediately after collection and bulked for subsequent analysis. Data for the intake of concentrate and straw for the second sub-period of each period were used to calculate apparent digestibility and the estimated metabolizable energy concentration of each diet. Each diet was given to the ewes once daily at 09.00 h. The daily quantity of pelleted concentrate offered to the sheep was 700 g fresh weight/head per day, based on an estimated requirement of 7.75 MJ ME per day for the maintenance of mature, non-pregnant sheep weighing 70 kg LW (AFRC, 1993). Chopped wheat straw was also offered ad libitum. Samples of each concentrate feed were taken daily, and bulked for each 5-day sub-period during which the faeces samples were being taken, for subsequent analysis. One sample of straw was collected during each experimental period for analysis. Samples of feeds and faeces were analysed for dry matter (DM) by oven drying at 100 ◦ C for 24 h, for TiO2 (Leone, 1973) and for gross energy by adiabatic bomb calorimetry (Gallenkamp Autobomb Automatic Adiabatic Bomb Calorimeter Model CBA350-K). 2.4. Statistical analyses Intake of concentrate DM, straw DM, digestibility of whole-diet DM and whole-diet ME value were analysed using a linear mixed model (Genstat 5 Release 3.1, Lawes Agricultural Trust, 1993) using restricted estimate maximum likelihood to allow for the unbalanced nature of the design. The blocking factors, sheep and period with the interaction, were considered as random effects and the treatment factors, cultivar and ranked specific weight and the interaction, as fixed effects. The physical and chemical characteristics of the diets were analysed as a two-factor design using the interaction as the error term.

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3. Results 3.1. Characteristics of the wheat samples The attempt to obtain a matrix of samples of wheat from four cultivars at four different specific weights was only partially successful. Although a sample of wheat was obtained at each specific weight rank, the mean specific weights differed between cultivars (P < 0.001) in that the mean for Haven was lower, and that of Consort higher, than the other three cultivars, with Buster and Riband intermediate (Table 1). The differences in specific weight between ranks (mean 4.3 kg/hl) were all significant (P < 0.001, Table 1). There were differences between both specific weight rank (P < 0.05) and cultivar (P < 0.001) in DM concentration, though the magnitude of the differences between the means was small and there was no consistent trend in DM with change in specific weight rank (Table 1). Pour density, tap density and thousand grain weight increased with increasing specific weight rank (P < 0.001, 0.001 and 0.05, respectively). There were no differences between specific weight rank in Hagberg Falling Number, starch, CP, NDF or acid ether extract. There was a trend (P = 0.073) for starch to be lower in the samples of lowest specific weight (588 g/kg DM at specific weight 1 compared to 632 g/kg DM at specific weights 3 and 4). The concentration of MADF decreased with increasing specific weight rank (P < 0.05). There were no differences among cultivars in pour density, tap density, thousand grain weight, Hagberg Falling Number, starch or CP, although there was a trend (P = 0.082) for the Consort samples to have a lower CP concentration than the other cultivars. There was a significant effect of cultivar on the concentration of NDF (P < 0.01), with Riband having the highest, Buster the lowest, and the other two cultivars having intermediate concentrations. However, the numerical differences between cultivar in concentrations of MADF were not significant (i.e. P > 0.05), suggesting that the differences in NDF reflected differences between cultivars in hemicellulose. Haven had the lowest concentration of acid ether extract, whilst Consort had the highest (P < 0.05), with Buster and Riband intermediate. 3.2. Intake and digestibility The mean LW of the sheep at the start of the experiment was 66.7 kg (S.D. 3.71 kg) and the mean LW at the end of the experiment, 53 days later, was 68.4 kg (S.D. 3.73 kg). Intakes of concentrate and straw DM are in Table 2. There were no effects of specific weight or of cultivar on intake of either concentrate DM or straw DM. The mean intake of concentrate DM was 0.59 of total DM and the mean proportion of wheat grain was 0.40 of total DM. Treatment means for whole-diet apparent digestibility of DM are in Table 2. There were no differences in digestibility due to specific weight, but there was a main effect (P < 0.05) of cultivar. Apparent digestibility was lower for Buster and Consort than for Riband and Haven (P < 0.05). The interaction term for specific weight × cultivar was not significant. The concentration of ME in the whole-diet was estimated using the equation (Eq. (1), Ministry of Agriculture, Fisheries and Food (MAFF, 1975)): ME (MJ/kg DM) = 0.81 DE (MJ kg/DM). Treatment means for estimated ME in the whole-diet DM are in Table 2, and there was no effect of specific weight. The mean estimated ME concentration of Haven was

Specific weighta

Cultivar

Intake of concentrate DM (g per day) Intake of straw DM (g per day) Apparent digestibility of whole-diet DM (g/kg) Estimated concentration of metabolizable energy in whole-diet DM (MJ/kg DM)

S.E.D.

Buster

Consort

Haven

Riband

1

2

3

4

586.8 432.2 725 b 10.36 c

605.7 422.8 723 b 10.73 bc

612.9 404.3 772 a 11.46 a

621.3 444.3 781 a 11.17 ab

618.6 419.6 752 10.81

603.4 444.7 743 10.82

608.7 417.6 758 11.14

596.2 421.7 748 10.96

Means with different letters on the same row are different (P < 0.05). a 1: lowest, 4: highest specific weight.

18.40 22.99 17.68 0.231

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Table 2 Effects of specific weight and cultivar on apparent digestibility of DM and estimated metabolizable energy value in sheep

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higher (P < 0.05) than that of Buster and Consort, and that of Riband was higher than that of Buster (P < 0.05). 4. Discussion The objective of the experiment was to determine the effect of the specific weight of wheat grain on its apparent digestibility and energy value in ruminants at the maintenance level of feeding. However, it was recognized at the outset that starch in processed wheat grain would be digested rapidly in the rumen. Thus Martin et al. (1999) recorded a decrease of two pH units in ruminal pH over a 5 h period following the first feeding in steers fed wheat (0.75 of total dietary DM) at 0.95 of intake ad libitum in two daily feedings (09.00 and 16.00 h). This rapid fermentation might affect the microbial population of the rumen adversely. Accordingly, the ewes in the present experiment were introduced gradually to the wheat-based concentrates over an 11-day period, and were also offered chopped straw ad libitum in an attempt to maintain normal rumen function. To reduce the risk of sub-clinical ruminal acidosis, it is recommended to restrict the proportion of starch in ruminant diets to less than 0.25 of the total diet DM (Chamberlain and Wilkinson, 1996). This is equivalent to about 0.4 as wheat grain if it is the only source of starch in the total diet, similar to the proportion of wheat in the total diet in the present experiment. In the experiment of Martin et al. (1999), apparent digestibility of NDF was relatively low, at 494 and 572 g/kg for the rumen and whole tract, respectively, whilst values for apparent digestibility of DM were 488 and 755 g/kg for the rumen and whole tract, respectively. These low values for digestion in the rumen were associated with reduced microbial polysaccharidase and glycosidase activities, possibly a reflection of acidification of the rumen contents. If a similar situation existed in the present study, then the wheat samples of lower specific weight, which had relatively higher concentrations of NDF (Table 1), might have been expected to show relatively lower apparent digestibilities of DM. However, despite a relatively wide range in specific weight, from 60 to 78 kg/hl, there was no effect of specific weight on apparent digestibility of DM (Table 2), which averaged 750 g/kg in agreement with Martin et al. (1999). Possibly the relatively higher proportion of straw in the total diet (0.4 of total DM) than in the experiment of Martin et al. (1999) ameliorated the adverse effect of the rapid digestion of starch on fibre digestibility. The estimated concentrations of ME (Table 2) generally reflected values for apparent digestibility of DM, and were in reasonable agreement with published values. Taking mean literature values of 13.7, 12.5, 13.3 and 6.0 MJ ME/kg DM for wheat grain, molassed sugar beet pulp, soyabean meal and wheat straw, respectively (MAFF, 1992), the calculated ME concentration of the whole-diet was 10.1 MJ/kg DM, compared to the overall mean value of 10.9 MJ/kg DM. This slightly higher value may have reflected incomplete recovery of TiO2 , which would result in under-estimation of total faecal output and over-estimation of digestibility and ME concentration. Titanium dioxide, however, is considered to be a relatively reliable technique for use in digestibility studies with ruminants, since its recovery is very high and it is not specifically associated with either the solid or the liquid phases of the digesta (Mayes and Dove, 2000).

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The main effect of specific weight rank on estimated concentration of ME was not significant, nor were there any differences in estimated ME concentration among the four different specific weights within each cultivar. Moss et al. (1999) also found no relationship between ME and specific weight in 31 samples of wheat grown in the United Kingdom. The mean estimated ME concentration of Haven was higher than that of Buster and Consort (Table 2). This contrasts to Wiseman and McNab (1995), who found that the concentration of ME for Haven in young poultry was markedly lower than that of 21 other wheat cultivars, which may have reflected a relatively high extract viscosity in vitro for this cultivar, as Miller et al. (2001) found. Further, there was no evidence to link concentration of ME with endosperm hardness, since both Haven (highest) and Buster (lowest) had hard endosperm textures (NIAB, 1995). The differences between cultivars in estimated concentration of ME may have reflected small differences in proportion of concentrate in the total diet DM, since both proportion of concentrate and ME were lowest for Buster, and highest for Haven, with the other two cultivars intermediate.

5. Conclusions There was no effect of grain specific weight on apparent digestibility and ME value of the whole-diet (60:40 concentrate:straw) when given to mature ewes at a maintenance level of feeding. Apparent digestibility of whole-diet DM and estimated concentration of ME were lower (P < 0.05) for the cultivar Buster than for the cultivars Riband and Haven. There appears to be energetic flexibility over a wide range of specific weights, with regard to use of wheat grain in concentrate diets for ruminants, as there is no relationship between specific weight and metabolizable energy content.

Acknowledgements The authors wish to thank the farmers and grain merchants who helped with the procurement of the wheat samples. We also thank Dr. N.J. Kendall and Ms. K. Hemmings for help in the design and execution of the experiment. We acknowledge the assistance of Mr. D. Jackson (University of Leeds), Ms. C.R. Collins (Natural Resource Management Ltd.), and Mr. J. White (National Institute of Agricultural Botany) in the analyses of the wheat samples. Drs. A. Roberts (Biomathematics and Statistics Scotland), S. Maw (University of Leeds) and H.M.R. Greathead (University of Leeds) helped with the statistical analysis of the results. The work was funded by the United Kingdom Home-Grown Cereals Authority, whose support is gratefully acknowledged.

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