Effect of sodium bicarbonate supplementation and
variation in the proportion of barley and sugar beet pulp
on growth performance and rumen, blood and carcass
characteristics of young entire male lambs
P. Mandebvu
1, H. Galbraith
*Department of Agriculture, University of Aberdeen, 581 King Street, Aberdeen, AB9 1UD, UK
Received 29 September 1998; received in revised form 3 March 1999; accepted 28 July 1999
Abstract
Forty-eight SuffolkMule entire male lambs (22.3 kg average live weight, two months old) were used to study the effects of addition of sodium bicarbonate and increasing quantities of molassed sugar beet pulp (MSBP) to diets based on barley grain (780 g kgÿ1fresh weight and
approximately iso-energetic and iso-nitrogenous). Measurements were made of dry matter (DM) intake, growth, some ruminal and blood plasma metabolites and hormone profiles and body composition. The animals were allocated by randomised block design on the basis of live weight to one of six dietary treatments and an initial slaughter control group (n7 and mean live weight22.3 kg per treatment). Animals in the initial slaughter control group were slaughtered on
Day 1 of the study in which barley was supplemented with sodium bicarbonate (15 g kgÿ1fresh
weight) (Experiment A) or replaced with increasing quantities of MSBP in a separate experiment (B) to provide diets containing 75, 50, 25 and 0% of the maximum quantity of barley (Experiment B). The diets had similar in vitro dry matter digestibility and contained similar estimated values for metabolisable energy concentration.
In Experiment A, the inclusion of sodium bicarbonate had no significant effect on live weight gain, DM intake, feed utilisation efficiency, ammonia concentration and the molar proportion of ruminal volatile fatty acids, rumen fluid, carcass and soft tissue characteristics and composition.
In Experiment B, increases in level of barley in the diet had no effect on ruminal pH, but linearly increased the molar proportion of propionate in rumen fluid (p< 0.01), hot- and cold-carcass weights (p< 0.01), empty body weight (p< 0.01), perirenal and retroperitoneal fat (p< 0.05) and gain of crude protein in cold carcass (p< 0.01). Evidence was also obtained for decreases in
Animal Feed Science and Technology 82 (1999) 37±49
*Corresponding author. Tel.:44-1224-274232; fax:44-1224-273731 E-mail address: [email protected] (H. Galbraith)
1Present address: W.H. Miner Agricultural Research Institute, P.O. Box 100, Chazy, NY 12921, USA. 0377-8401/99/$ ± see front matter#1999 Elsevier Science B.V. All rights reserved.
concentrations of ruminal ammonia and plasma area associated with increasing concentrations of dietary MSBP. Certain significant quadratic effects on plasma insulin concentration, which were not associated with indices of carcass and digesta-free body growth, were also recorded. It is concluded that the diet based on MSBP alone was not utilised as effectively for growth and body weight gain as MSBP-based diets also containing barley grain. The results suggest that any limitations in growth performance by entire male lambs fed a diet containing high levels of MSBP may be effectively abolished by the replacement with barley at a substitution rate of 25% or greater.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Entire male lambs; Sugar beet pulp; Barley grain; Growth; Carcass
1. Introduction
Carbohydrate concentrate feeds are important components of the diet of ruminant farm animals. Of these, rations based on cereal grain, such as barley, have assumed an important place in systems designed to promote rapid growth of sheep and cattle. (Macdonald et al., 1996).
However, disadvantages of the use of high-starch cereals include (1) the lowering of ruminal pH which can cause reduction of the digestion of cellulose-based dietary components and (2) the production of soft fat thought to occur as a consequence of production of ruminal propionate in excess of the gluconeogenic capacity of the liver, and its utilisation for the production and deposition of odd-numbered and methyl-branched long chain fatty acids (e.g. érskov and Ryle, 1990; Berthelot et al., 1998).
One means of reducing the use of cereals in ruminant rations involves their replacement by high-energy non-cereal by-products such as molassed sugar beet pulp (MSBP). Previous studies (e.g. Rouzbehan et al., 1994) evaluated the response of castrate male lambs aged 7±8 months to loose-mix diets containing MSBP and rolled barley in the ratios of 0.8 : 0.2 and 0.5 : 0.5. Significantly lower dry matter (DM) intakes by sheep on the high MSBP ration were ascribed to its physical form, being composed of pelleted unground shreds which had a slow passage rate from the rumen. Rouzbehan et al. (1996b) also described the response of sheep to MSBP given separately or ensiled together with grass to form big bale silage in which the water absorptive properties of MSBP were investigated.
The optimisation of dry matter intake by animals is essential for efficient growth and conversion into live weight gain. A major aim of the study reported here was, therefore, to provide diets in a more uniform physical form. This was achieved by grinding MSBP followed by pelleting in different proportions with other dietary ingredients.
An additional study was conducted to provide comparative information on the use of diets based on barley alone and to determine the efficiency of the use of sodium bicarbonate supplementation, including its potential buffering effect and alleviation of ruminal acidosis. (Reynolds et al., 1992; Zinn and Borques, 1992). Measurements of ruminal pH, and concentrations of end-products of digestion including the major volatile fatty acids and ammonia, blood metabolites and plasma insulin were also made to contribute to an explanation for recorded responses to the different diets in growth and gross carcass characteristics.
The studies were conducted using young entire male lambs which, when appropriately fed, grow quickly and can attain early slaughter weight needed to meet the requirements of the seasonally-determined early finished lamb market.
2. Materials and methods
2.1. Diets
Experiment A: pelleted diets were formulated which contained (g kgÿ1
DM) for diets 100% Ba1 (no supplementation) and 100% Bas (sodium bicarbonate supplemented), respectively, whole barley grain 780 and 770; sodium bicarbonate 0.0 and 15; soyabean meal 99 and 97; white fish meal 47 and 46; molasses 58 and 57; urea 7.0 and 7.9; and a mineral/vitamin supplement, 1.0. In addition, the animals in group 100% Bal were offered a `salt lick' containing sodium chloride to compensate for inadequate provision of dietary sodium, concentrations of which were adequate for the other groups (Macdonald et al., 1996).Experiment B: essentially similar rations were prepared as for Experiment A, except that barley was replaced by MSBP to give ratios in the diets as follows (barley: MSBP); 0.520 : 0.174 (75% Ba) 0.35 : 0.35 (50% Ba); 0.176 : 0.528 (25% Ba); 0 : 0.704 (0% Ba). Values for chemical and nutrient composition of the diets were determined by conventional techniques (Rouzbehan et al., 1994, 1996a, b) and are given in Table 1. Estimates for metabolisable energy were derived from published values (Macdonald et al., 1996).
2.2. Animals, feeding, sampling and slaughter procedure
Forty-two Suffolk-cross entire male lambs (22.3 kg average live weight, aged two months and obtained from a single source) were ranked and blocked by weight, and randomly assigned to one of the six treatment groups and an initial slaughter (IS) group.
Table 1
Chemical and nutrient composition of diets fed to lambsa
Experiment A Experiment B
Modified acid detergent fibre (g kgÿ1DM) 69 63 79 103 121 140 Estimated metabolisable energy (MJ kgÿ1DM) 127 127 126 126 125 125 In vitro DM disappearance 0.87 0.88 0.89 0.90 0.89 0.89
aAnimals were fed pelleted diets containing barley (780 g kgÿ1 fresh weight) at 100% without sodium bicarbonate (100% Bal), 100% with sodium bicarbonate (100% Bas), and 75 (75% Ba), 50 (50% Ba), 25 (25% Ba) and 0% (0% Ba), following progressive substitution of barley by molassed sugar beet pulp. Where tested, *p< 0.05; **p< 0.01; ***p< 0.001.
The lambs were individually penned and offered a diet based on 80% barley and 20% molassed SBP in a 14-day adjustment period. The lambs were fed once daily at 0900 h and had free access to water. The lambs in the IS group were slaughtered on Day 1 of the study as described by Sulieman et al. (1986). Two groups of the lambs were allocated to Experiment A and were fed to appetite with feed continuously available to avoid acidotic digestive upsets throughout the study from Day 1 to Day 56. The remaining groups were assigned to Experiment B and were fed to appetite from Day 1 to Day 17 of the trial and then to support a live weight gain of 0.360 kg dayÿ1
from Day 17 to Day 37, and 0.4 kg dayÿ1from Day 38 to Day 56 (AFRC, 1993). This feeding system was designed to provide high and uniform levels of intake in the absence of differential intakes associated with negative effects of SBP observed in our earlier studies (Rouzbehan et al., 1994).
Unconsumed food was removed and fresh diet supplied at approximately 0800 h each day. Blood samples were collected from lambs in Experiment B by jugular venepuncture on Days 38 and 47 of the trial at 0900, 1030, 1200, 1330 and 1500 h and plasma was prepared and stored as described by Galbraith (1980) and MacVinish and Galbraith (1988). Rumen fluid was collected by stomach tube on Day 43, commencing at 0800 h (prior to the supply of fresh feed), and Day 51 (1200 h) of the trial from lambs in Experiment B and on Day 51 (1200 h) from lambs in Experiment A. Rumen pH (Experiment B only) and concentrations of ammonia and volatile fatty acids (VFA) were determined as described by Rouzbehan et al. (1994).
At the end of the study, all lambs were shorn, and slaughtered as described by Sulieman et al., 1986. Weights of hot carcass and certain non-carcass soft tissues were recorded and the carcasses chilled overnight. The cold-dressed carcass was then weighed and measurements recorded for M. longissimus dorsi. The carcasses were minced and representative samples (160 g) from each lamb were then freeze-dried for three days. The samples were then ground finely in liquid nitrogen and subjected to analysis. (MAFF, 1986; Sulieman et al., 1986). Plasma testosterone was determined as described previously (Galbraith, 1980).
2.3. Statistical analyses
Data analysed for Experiment A were subjected to one-way analysis of variance and the significance of the difference between treatment means determined by F-test (Snedecor and Cochrane, 1982). Because of the differences in experimental protocol, the data for Experiment B were subjected separately to one-way analysis of variance utilising a polynomial design which tested for linear and quadratic relationships in addition to deviations from these among treatment means.
3. Results
3.1. Composition of the diets
The overall mean values for nutrient composition of representative samples of selected diets are given in Table 1. The values for individual components are essentially as
expected with the major differences in modified acid detergent fibre being produced by increasing substitution of barley by MSBP. Values for in vitro dry matter disappearance after 48 h in the conventional Dacron bag system were of a closely similar order for all diets.
3.2. Growth performance, and weights of body and carcass components
In Experiment A, there were no significant effects due to dietary supplementation with sodium bicarbonate in any of the growth, carcass or non-carcass parameters recorded. (Table 2). Similarly, substitution of barley by MSBP in the diet did not produce any significant effect on live weight gain (LWG) or food conversion ratio but produced a significant linear negative response in weights of digesta-free (empty) body weight, hot and cold carcass, and perirenal and retroperitoneal fat. A comparison of individual means indicated significant differences between treatments 0% Ba and 75% Ba, and 50% Ba only, for LWG and digesta-free weight. There were no treatment effects on the cross-sectional area or fat depth ofM. logissimus dorsi.
3.3. Carcass composition and gains in chemical components
None of the treatments in Experiment A or Experiment B resulted in significant effects on the major carcass components of dry matter and proportion in the dry matter of ash, crude protein or fat. (Table 3). However, analysis of gains in comparison with the IS control group indicated significant negative linear effects for weights of carcass crude protein with decreasing proportions of barley in the diet. Analysis of differences between means in Experiment B indicated a significantly reduced mean value for group 0% Ba compared with all other groups, individual differences between which did not attain significance. Fat gain was not affected by diet.
The unexpectedly low values for ash composition and gain in group 50% Ba gave rise to the significant effects for deviation from linear or quadratic relationships.
3.4. Ruminal concentrations of ammonia and volatile fatty acids
There were marked trends towards greater molar proportions of acetate and reduced propionate and reduction in the ratio of propionate to acetate associated with sodium bicarbonate supplementation in this Experiment A, although statistical significance was not attained (p> 0.05) (Table 4).
While values for ruminal pH for lambs in Experiment A were not available, it was apparent in Experiment B that the pre-feeding (before provision of fresh feed) values for pH were greater (consistently above 7.0) than these recorded post-feeding on Day 51 which were consistently below 6.5. There were significant negative linear and quadratic effects for ammonia on Day 51 and significant negative linear effects for propionate, and in the ratio of propionate: acetate on Day 43. These responses were also associated with significant differences between treatments 75, 50 and 25% Ba and treatment 0% Ba. Similarly, there was a significant positive linear relationship for butyrate with increasing proportions of MSBP in the diet.
Table 2
Daily liveweight gain (LWG), dry matter intake (DMI), food conversion efficiency (FCE) and body and carcass characteristics.
Experiment Aa,b Experiment Ba Statistical analysis
100% Ba1 100% BaS SED 75% Ba 50% Ba 25% Ba 0% Ba SED LIN QUAD DEV
LWG (kg dayÿ1) 0.373 0.386 0.159 0.438 0.436 0.434 0.427 0.144 NS NS NS
DMI (kg dayÿ1) 1.09 1.11 0.22 1.31 1.32 1.33 1.34 0.14 NS NS NS
FCE (LWG) 0.36 0.36 0.04 0.33 0.32 0.31 0.30 0.02 NS NS NS
Weight:
Hot carcass (kg) 20.6 20.2 0.8 22.7 22.6 22.2 21.1 0.6 ** NS NS
Cold carcass (kg) 19.8 19.4 0.8 21.9 21.7 21.4 20.4 0.5 ** NS NS
Digesta-free body (kg) 35.7 35.8 1.5 40.0 39.6 39.4 37.9 0.7 ** NS NS
Perirenal and retroperitoneal fat, (kg) 0.16 0.18 0.03 0.23 0.21 0.18 0.19 0.02 * NS NS
Mesenteric fat (kg) 0.25 0.26 0.04 0.31 0.27 0.26 0.22 0.04 NS NS NS
M. longissimus dorsiarea (cm)2 16.8 16.1 1.2 18.4 21.2 19.6 19.3 1.2 NS NS NS
aTreatments as for Table 1.
bThere were no treatment differences for Experiment A.
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Table 3
Carcass composition and gains in chemical components compared with initial slaughter (IS) controls
IS control Experiment Aa,b Experiment Ba Statistical analysis 100%Ba1 100%BaS SED 75% Ba 50% Ba 25% Ba 0%Ba SED LIN QUAD DEV
Carcass composition:
Dry matter (DM) (g kgÿ1fresh weight) 36.5 39.5 40.3 9.1 41.0 40.6 39.3 42.3 12.3 NS NS NS
Ash (g kgÿ1DM) 4.9 5.0 4.4 5.7 4.7 3.4 4.7 4.3 2.1 NS NS NS
Crude protein (g kgÿ1DM) 19.1 17.5 17.4 3.9 17.3 16.9 17.6 17.2 3.5 NS NS NS
Fat (g kgÿ1DM) 12.0 17.9 19.3 11.1 18.7 19.7 17.9 18.9 12.4 NS NS NS
Cold carcass gain from IS control(kg)
Ash ± 0.48 0.34 0.13 0.50 0.34 0.57 0.40 0.08 NS NS *
Crude protein ± 1.44 1.34 0.19 1.77 1.71 1.72 1.44 0.09 ** NS NS
Fat ± 2.26 2.45 0.29 2.80 3.04 2.55 2.53 0.27 NS NS NS
aTreatments as in Table 1.
bThere were no treatment differences for Experiment A.
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Table 4
pH, ammonia concentrations (mM) and molar proportions of volatile fatty acids (VFA) in rumen fluid sampled from lambs on Day 43 1 h before, and on Day 51 3 h after, feeding
Day Experiment Aa,b Experiment Ba Statistical analysis
100% Ba1 100% BaS SED 75% Ba 50% Ba 25% Ba 0% Ba SED LIN QUAD DEV
pH 43 ± ± ± 7.1 7.1 7.2 7.1 0.1 NS NS NS
51 ± ± ± 6.0 6.1 6.4 6.2 0.2 NS NS NS
Ammonia 43 ± ± ± 3.7 3.4 2.0 3.0 1.3 NS NS NS
51 6.8 7.1 0.6 4.5 3.5 1.9 2.6 0.54 ** * ±
Acetate (A) 43 ± ± ± 65.3 68.3 66.0 68.6 1.6 NS NS NS
51 51.7 61.6 4.7 67.7 64.0 65.6 64.8 2.85 NS NS NS
Propionate (P) 43 ± ± ± 25.3 25.4 24.2 19.3 1.4 ** * NS
51 36.1 26.2 6.5 20.1 22.4 20.1 20.3 3.38 NS NS NS
A:P 43 ± ± ± 0.39 0.37 0.37 0.28 0.03 ** NS NS
51 0.73 0.47 0.2 0.31 0.36 0.31 0.32 0.06 NS NS NS
n-Butyrate 43 ± ± ± 5.6 5.3 7.3 9.4 1.2 ** NS NS
51 9.5 10.0 2.6 ± ± ± ± ± ± ± ±
n-Valerate 43 ± ± ± 2.11 1.02 1.00 2.04 0.55 NS * NS
51 2.69 2.30 0.49 ± ± ± ± ± ± ± ±
Iso-butyrate 43 ± ± ± 0.91 0.17 1.16 0.92 0.36 NS NS *
51 0.08 0.05 0.01 ± ± ± ± ± ± ±
Iso-valerate 43 ± ± ± 0.77 0.01 0.48 0.04 0.31 NS NS *
51 0.01 0.01 0.01 ± ± ± ± ± ± ± ±
aTreatments as in Table 1.
bThere were no differences between treatment means in Experiment A.
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3.5. Plasma urea and glucose concentrations
A consistently positive linear relationship with dietary barley concentration was recorded for all five samples collected on Day 47 and analysed for plasma urea (Table 5). There was evidence also of a significant quadratic effect which was associated with elevated concentrations in group 50% Ba at 1200 h which appeared consistently, although not significantly, at other sampling times. This group also had more elevated concentrations of plasma glucose and lower values for insulin at 0900 and 1030 h than group 75% Ba. There were also significant quadratic effects for insulin concentration for all sampling times which were associated with the lowest concentration of the hormone occurring on diets 50% Ba and 25% Ba.
Although not shown here, concentrations of plasma testosterone (mg/l) peaked at 2.8
(75% Ba) 1.75 (50% Ba) and 1.8 (0% Ba), indicating that the lambs were exhibiting post-pubertal concentrations at the time of sampling.
4. Discussion
The differences in growth performance of the lambs in the two experiments were essentially as predicted from their intake of feed (AFRC, 1993) and reflect the lower intake and apparent capacity of animals offered diets based on barley alone. In
Table 5
Plasma urea and glucose concentrations (sampled on d 47) and insulin (sampled on days 38) in lambs in Experiment B
Sampling time, h
Experiment Ba Statistical analysis
75% Ba 50% Ba 25% Ba 0% Ba SED LIN QUAD DEV Urea (mg lÿ1) 0900 61.5 65.7 50.8 43.5 4.4 ** NS NS
1030 60.8 66.7 52.7 47.6 4.9 ** NS NS
1200 48.1 54.3 42.0 38.4 3.1 ** * *
1330 43.1 46.8 37.3 32.9 2.7 ** * *
1500 38.5 42.7 33.7 30.2 3.4 ** NS NS
Glucose (mg lÿ1) 0900 91.3 101.0 93.3 102.0 5.0 NS NS NS
1030 98.1 95.7 91.8 95.9 5.0 NS NS NS
1200 86.3 91.1 89.4 90.5 3.9 NS NS NS
1330 82.9 90.0 89.9 83.6 3.4 NS * NS
1500 79.7 85.9 90.7 58.6 3.7 NS * NS
Insulin (mulÿ1) 0900 41.1 27.0 32.9 42.0 2.19 NS ** **
1030 72.0 53.3 36.7 73.2 1.30 ** ** **
1200 67.8 63.3 45.8 74.1 1.71 NS ** **
1330 50.1 44.3 26.6 60.5 4.11 NS ** **
1500 52.8 31.3 34.3 48.2 8.93 NS ** NS
aTreatments as given in Table 1.
Experiment A, the inclusion of sodium bicarbonate in the diet had no significant effect on any of the growth, or carcass compositional measurements made. There was some evidence of increases in ruminal acetate, and reductions in the propionate: acetate ratio in rumen fluid collected 3 h after feeding. These results, although not attaining statistical significance, which partially reflects the high values for experimental or other error, in the data show consistency with the observations of Reynolds et al. (1992). These workers used a higher dose of 120 g kgÿ1
DM in the diet of beef steers.
The results for Experiment A, therefore, do not suggest a benefit from supplement-ation of the barley diet with sodium bicarbonate. However, future studies could usefully investigate the effectiveness of increased concentrations of the buffer in similar diets.
The result from Experiment B indicated that replacement of barley by MSBP had no effect on food intake, growth rate or feed conversion efficiency. However, weights for digesta-free body and hot and cold carcass were reduced linearly with increasing provision of MSBP in the diet. The largest effect tended to occur between animals on diets 25% Ba and 0% Ba. In the previous study by Rouzbehan et al. (1994), and under conditions of feeding to appetite, sheep given loose-mix diets containing barley and MSBP in the ratio of 0.8 : 0.2 grew more quickly then animals given diets in the ratio of 0.5 : 0.5, in this case, partly as a consequence of greater dry matter intake.
The results from the present study in animals given pelleted diets and exhibiting similar intakes of dry matter and estimated dietary metabolisable energy suggest that the utilisation of the diet for weights of gain in empty body, carcass and carcass crude protein were greater on diets containing barley, although the lowest level of inclusion at 25% may be adequate to approach optimisation of the response where the required food intake is at or below the maximum capacity for SBP containing diets. The present results for empty body weight and carcass gain may be associated with the proportionately smaller concentration of ruminal propionate and greater concentration of acetate and butyrate with largest effects occurring on the SBP-only diet. These results are consistent with the previous observations of Galbraith et al. (1988) who demonstrated elevated concentra-tions of ruminal propionate and reduced acetate on diets based on barley compared with sugar beet pulp. Evidence of increased ruminal acetate and reduced propionate has also been obtained following supplementation of grass silage with MSBP in diets of sheep (Rouzbehan et al., 1996b).
Previous authors have considered the biochemical consequences for the utilisation of propionate and acetate which have glucogenic and ketogenic properties, respectively, by animals. Interpretation of the literature is complicated by the different methodologies used. However, in reviewing literature involving intragastric infusion, érskov and Ryle (1990) showed that mixtures of VFA containing 10% or less of the energy in the form of propionate were utilised as efficiently as mixtures containing up to 100%. These authors considered that there was little difference in the efficiency of utilisation for `fattening' of different mixtures of VFA. They also considered that adequately-fed growing animals, such as the sheep in the present study, given supra-maintenance rations providing molar proportions of propionate : acetate : butyrate of approximately 70 : 20 : 10 in the absence of barley were unlikely to be deficient in glucose precursors.
These conclusions appear to be at variance with those of Emmans et al. (1989), who suggested that the relative inefficiency of utilisation of molassed or unmolassed sugar beet feed compared with barley may relate to the greater heat production for protein accretion using substrates derived from the absorption of end-products of digestion of MSBP. The significant reduction in carcass crude protein gain in the animals on the 0% Ba diet, in the present study, is consistent with the suggestion of such a lower efficiency of utilisation.
It is apparent that further work is required to clarify the effect of variations in the supply of VFA on the efficiency of deposition of tissues of different compositions within the body of ruminant animals.
It is also apparent that the lower energy losses associated with reduced ruminal methane and increased propionate could also be expected to contribute to a greater overall efficiency of utilisation of dietary energy for body weight gain on the cereal-containing diets.
Alterations of barley concentration had little effect on the pH of rumen fluid, suggesting the absence of acidosis, which may be due, at least partially, to feed being continuously available throughout the day for all treatments at the high levels of intake provided. As expected, pH values were greater in samples taken 3 h, compared with 23 h, after provision of fresh feed. However, the unexpectedly high values of 7.1 to 7.2 should be considered with caution, perhaps indicating contamination with saliva.
Diets containing decreasing amounts of barley and increased MSBP also achieved lower concentrations of ruminal ammonia. This is a result similar to that observed previously by Rouzbehan et al. (1994) and may be due either to a slower release of ammonia from the diet or more rapid uptake by micro-organisms in the presence of a rapidly fermentable source of molasses carbohydrate.
Plasma urea concentrations which were typical for our studies in growing sheep (e.g. Galbraith et al., 1997) exhibited similarly lower means with increasing MSBP in the diet. This result may be partially due to the observed reductions in provision of ruminal ammonia for subsequent hepatic conversion to urea. The concentrations of ammonia in the diet, in rumen fluid and concentrations of urea in blood would not appear to be related to subsequent deposition of crude protein in the carcass. This result suggests that dietary nitrogenous supply was not a limiting factor for growth in any of the diets since concentrations of the urea waste product were greatest on diets providing for greater empty body and carcass weight gain.
Values for plasma glucose were typical for high-energy diets. Significant quadratic effects were observed for this metabolite at 4.5 and 6 h after food provision with the greatest concentrations occurring on the diets containing 50 or 25% barley. The reasons for this, although consistent at both sampling times, are not clear but may be associated with lower insulin concentrations. For insulin, plasma concentrations increased consistently after feeding and showed a consistent quadratic effect characterised by lowest concentrations in the 50 or 25% Ba group in all five samples taken throughout the day. There was no evidence for reduced concentrations of insulin on the 0% Ba diet.
It may be concluded from this that the reduction in empty body and carcass characteristics associated with complete replacement of barley by MSBP were not associated with reduced concentration of plasma insulin.
5. Conclusions
The results for Experiment A suggest that sodium bicarbonate supplementation at the concentrations used did not alter significantly the growth, carcass, ruminal or blood characteristics compared with responses obtained with unsupplemented barley grain-based diets.
The results for Experiment B suggest that barley grain was utilised more effectively than MSBP for gain in digesta-free body weight, carcass weight, and carcass crude protein, that is to say effects which were associated with greater concentrations of ruminal propionate and plasma urea concentrations.
Despite significant quadratic effects on plasma insulin concentrations, these were not associated with the responses obtained in carcass and digesta-free growth. The results also suggest that SBP may be incorporated along with barley at an inclusion rate of 25% to essentially maintain the superior performances of diets based on greater concentrations of the cereal grain.
Acknowledgements
The authors thank Mr T.W. Begg, Mr J. Struthers, Mr N. Lokke and Mr B. Buchan for the care of experimental animals; Mrs D. Clark, Mr I. Mckay, Mrs M. Fraser, Mr D. Watt and Mr T. Atkinson for analysis of rumen and blood characteristics; Dr J. K. Thompson, Dr D. Scott and Dr M. Franklin for advice on experimental design and statistical analysis and Miss S. McGregor for typing the manuscript.
References
AFRC, 1993. Energy and protein requirements of ruminants. CAB International, Wallingford, UK.
Berthelot, V., Bas, P., Schmidely, P., Duvaux-Ponter, C., Sauvant, D., 1998. Effect of dietary propionate on fatty acid composition of lamb adipose tissues. Proceedings of the 8th Meeting on Nutrition of Sheep and Goats INAPG-Grignon, France, p. 75 (Abstract).
Emmans, G.C., Cropper, M., Dingwall, W.S., Brown, H., Oldham, J.D., Harland, J.I.H., 1989. Efficiencies of the use of the metabolizable energy from foods based on barley or sugar beet feed in immature sheep. Anim. Prod. 48, p. 634 (Abstract).
Galbraith, H., 1980. Growth, hormonal, hormonal and metabolic response of post-pubertal entire male cattle to trenbolone acetate and hexoestrol. Anim. Prod. 35, 269±276.
Galbraith, H., McCulloch, T., Scaife, J.R., Keeling, B.J., 1988. Effect of barley, sugar beet pulp and protein level in the diet on growth, body composition and blood metabolites and insulin concentration of entire male lambs. Anim. Prod. 46, p. 514 (Abstract)
Galbraith, H., Singh, S.B., Scaife, J.R., 1997. Response of castrated male sheep to oestrogenic and androgenic compounds implemented alone or in combination. Anim. Sci. 64, 261±269.
MacVinish, L.J., Galbraith, H., 1988. A note on the concentrations of steroidal residues in tissues of mature female sheep implanted with trenbolone acetate. Anim. Prod. 56, 227±280.
Macdonald, P., Edwards, R.A., Greenhalgh, J.F.D.G., Morgan, C.A., 1996. Animal Nutrition. Longman Scientific and Technical, Harlow, UK.
Reynolds, W.K., Hunt, C.W., Moen, T., Loesche, J.A., 1992. Comparison of corn and barley with and without ruminal buffer in supplements fed in wheat-based diets to beef steers. Anim. Sci. 71, 1326±1334. Rouzbehan, Y., Galbraith, H., Rooke, J.A., Perrott, J.G., 1994. A note on the effects of dietary inclusion of a
yeast culture on growth and ruminal metabolism of lambs given diets containing unground pelleted molassed dried sugar-beet pulp and barley in various proportions. Anim. Prod. 59, 147±150.
Rouzbehan, Y., Galbraith, H., Topps, J.H., Rooke, J., 1996a. Response of growing steers to diets containing big bale silage and supplements of molassed sugar beet pulp with and without white fish meal. Anim. Feed. Sci. Technol. 62, 151±162.
Rouzbehan, Y., Galbraith, H., Topps, J.H., Rooke, J., 1996b. The response of sheep to big bale grass silage ensiled with, or supplemented separately with, molassed sugar beet feed. Anim. Feed. Sci. Technol. 59, 279± 284.
Snedecor, G.W., Cochrane, W.G., 1982. Statistical Methods, sixth ed. Iowa State University Press, Ames, IA. Sulieman, A.S., Galbraith, H., Topps, J.H., 1986. Growth Performance and body composition of early weaned wether lambs treated with trenbolone acetate combined with oestradiol-17 B. Anim. Prod. 43, 109±114. Zinn, R.A., Borques, J.R., 1992. Influence of sodium bicarbonate and monensin on utilisation of a
fat-supplemented, high energy growing finishing diets by feedlot steers. Anim. Sci. 71, 18±25.
