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Associative effects on total tract digestibility in horses fed
different ratios of grass hay and whole oats
*
C. Palmgren Karlsson , J.E. Lindberg, M. Rundgren
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management, P.O. Box 7024, S-750 07 Uppsala,
Sweden
Received 5 March 1999; received in revised form 18 October 1999; accepted 27 October 1999
Abstract
The present experiment was performed according to a 434 Latin square design with diets composed of (on dry matter (DM) basis) the following ratios of grass hay to whole oats: 100:0 (O0), 80:20 (O20), 60:40 (O40) and 40:60 (O60). Four mature Standardbred geldings weighing 493 (S.D. 34) kg were used. The digestibility of DM, organic matter and energy (dE) increased in a curvilinear pattern with the increasing inclusion levels of oats. It is suggested that this was a reflection of the significantly lowered digestibility of nutrients and particularly of fibrous components for the O60 diet as compared with the other three rations, thus resulting in negative associative effects between grass hay and oats. On the basis of the present data, and excluding the results of the O60 diet, the digestibility of dE of oats was estimated to be 75%. As an expression of the associative effect at the O60 level, the dE of the total diet was estimated to be 58%, as compared with 63% when estimated on the oats value of 75% and the O0 diet, resulting in a depression of dE of the total diet by 8%, mainly affecting the utilization of fibrous components. Urinary energy losses decreased with increasing level of oats. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Horses; Hay; Oats; Digestibility; Associative effects; Fibre; Nutrients
1. Introduction Martin-Rosset et al. (1984), the digestibility of horse rations is equivalent to the weighted sum of the In computing rations for horses it is assumed that nutrients supplied as forages and the associated the nutritive value of a diet corresponds to the sum amounts of concentrates. This assumption is sup-of the individual feedstuffs included. According to ported by other studies (Hintz et al., 1971a,b; Martin-Rosset and Dulphy, 1987; Vermorel et al., 1991), in which no associative effects were observed between dietary components and diet digestibility. *Corresponding author. Tel.: 146-18-672-094; fax: 1
46-18-However, it should be noted that the systematic 672-995.
effect of diet composition on the digestibility of
E-mail address: [email protected] (C.
Palmgren Karlsson) fibrous components was not evaluated by these
authors, with the exception of Hintz et al. (1971a,b). 2. Materials and methods
In contrast, Thompson et al. (1984) found
associa-tive effects for several nutrients, implying that the 2.1. Experimental design and animals digestibility of the total ration was not equivalent to
the weighted sum of the individual components, in Four hay-based rations with increasing proportions agreement with Kienzle et al. (1999). The literature of oats were fed according to a 434 Latin square cited deals only superficially with the effect of diet design. Four Standardbred geldings (4–11 years old) composition on the digestibility of individual fibrous with an average body weight (BW) of 493 (S.D. 34) components in mixed rations fed to horses. kg were used. The horses were weighed before and
There are several factors (i.e. diet composition, after each collection period.
level of feed intake, feeding routines) that could Each experimental period comprised 14 days, 9 influence ileal digestibility of nutrients in diets for days of adaptation to the new diet followed by a horses, and thus indirectly also influence hindgut 4-day period of quantitative and separate collection fermentation (Meyer et al., 1982; Schwabenbauer et of faeces and urine. The change in rations between al., 1982; Radicke et al., 1991). When comparing experimental periods was made gradually in the first feeding with 4 g versus 2 g starch / kg body weight 3 to 4 days of the adaptation period. The collection (BW), Meyer and Landes (1994) observed that the period was divided into two sub-periods of 2 days postprandial pH of the jejunal chyme decreased each with 1 day of rest in between, to reduce the substantially. As demonstrated by Kienzle (1994) discomfort for the horses.
high levels of starch (oats and barley) in the small During the adaptation period and the day of rest intestine decreased starch digestibility, a result of the the horses were kept in individual pens and had intestinal pH dropping below the optimal pH of access to a common grass free paddock 5 to 7 h per intestinal a-amylase. day. During the 4 days of faeces and urine collection The caecum and colon are the predominant sites of the horses were kept in metabolism stalls equipped fibre digestion in the horse. The microbial digestion with rubber mats. The horses were not given any in the hindgut depends on the nature of the ration additional exercise.
(Kern et al., 1974; Tisserand et al., 1980; Meyer et
al., 1995). The proportion of lignified products in 2.2. Diets and feeding plant cell walls generally influences the development
of the cellulolytic activity and biomass in the large The horses were fed rations consisting of grass intestine (Tisserand, 1989). In addition, the propor- hay, harvested in a late state of maturity, and whole tion of roughage to concentrate in the ration in- (unprocessed) oats. The chemical composition of the creases VFA production (Schwabenbauer et al., feedstuffs is shown in Table 1. Dietary treatments 1982) and the excretion of H2 and CH4 in the consisted of, on dry matter (DM) basis, the follow-exhalation (Nyari, 1992). The concentrate composi- ing ratios between hay and oats (O): 100:0 (O0), tion with different ileal starch digestibility might also 80:20 (O20), 60:40 (O40) and 40:60 (O60). The aim influence the hindgut microbial activity (Radicke et was to provide the horses with the same daily al., 1991). Furthermore, by increasing feed intake amount of DM and gross energy (GE) on a BW basis Meyer et al. (1982) demonstrated an increase in the in all treatment groups (Table 2). The daily feed caecal VFA concentration, as well as a marked intake varied depending on BW and was for ration
decrease in pH. O0: 7.4–8.9 kg hay; ration O20: 5.9–7.1 kg hay and
Table 1 2.3. Collection of samples Chemical composition (g per kg DM) and gross energy content
(MJ / kg DM) of hay and oats
Feed samples were collected at every feeding Hay Oats occasion, and after each collection period, they were
Organic matter 952 966 pooled, mixed, sampled and kept at 2208C. Faeces Crude protein 65 130 were collected several times during the day directly
Crude fat 8 40 on the rubber mats and stored at 1108C. At the end
a
Starch 1 418
b of each collection day the faeces were mixed,
Sugars 96 12
sampled and frozen (2208C). Urine was collected
Total fibre 782 365
Neutral detergent fibre 617 268 with a plastic funnel attached to the horse with a Acid detergent fibre 354 128 girth, and connected with a tube to a can containing
Crude fibre 311 106 1 l 10% sulphuric acid to keep pH below 3. Each
Lignin 75 47
collection day the urine was weighed, made up to
Gross energy 18.5 19.3
constant volume with water, sampled and frozen
a requirements for energy and protein, according to the
Swedish standards (LBS, 1989; metabolizable Feed and faeces analyses were performed on oven
0.75
energy (ME) MJ / day50.553BW and 5.5 g dried (658C, 24 h) samples after milling through a digestible crude protein (CP) / MJ ME). The horses 1-mm screen. DM, ash and crude fibre (CF) were were fed twice a day at 08:30 and 16:30 h with the determined according to the official methods given daily feed allowances evenly distributed. Hay was by Jennische and Larsson (1990). CP was based on given 15 min before the oats. Water and salt blocks total nitrogen (N) content (also including urine were offered ad libitum. A commercial mineral analysis) determined according to Kjeldahl (Nordisk
´
mixture (50 g / day; 14.6% Ca, 6.6% P and 7.0% Mg) Metodikkommitte, 1976) and multiplied by 6.25. was given once a day in the adaptation periods until Crude fat (EE) was analysed according to the EEC-2 days before each collection period. method B (Larsson, 1989). Starch and sugars were
Table 2
Daily dietary intake of nutrients (g / kg BW) and gross energy (kJ / kg BW)
Ratios (hay:oats)
O0 (100:0) O20 (80:20) O40 (60:40) O60 (40:60) S.E.M.
a b b b
Dry matter 15.5 15.3 15.3 15.2 0.04
Organic matter 14.7 14.6 14.6 14.6 0.04
d c b a
Crude protein 1.0 1.2 1.4 1.6 0.01
d c b a
Total fibre 12.1 10.7 9.4 8.2 0.07
a b c d
Neutral detergent fibre 9.5 8.4 7.3 6.3 0.05
a b c d
Acid detergent fibre 5.5 4.7 4.0 3.4 0.03
a b c d
Crude fibre 4.8 4.2 3.5 2.9 0.02
a b c d
Lignin 1.2 1.1 1.0 0.9 0.01
b b ab a
Gross energy 287 287 288 290 0.7
a – d
Least square mean values within rows with differing superscript letters differed significantly: P,0.05.
e
Sum of starch and maltodextrins.
f
analysed according to Larsson and Bengtsson 3. Results
(1983). Neutral detergent fibre (NDF) was analysed
according to Robertson and Van Soest (1977) with a 3.1. Intake of nutrients modified procedure (Pettersson and Lindberg, 1997),
acid detergent fibre (ADF) and lignin according to Daily nutrient intake was expressed as g / kg BW Goering and Van Soest (1970). Total fibre (TF) was (Table 2). In comparison with the other three rations, computed by subtraction of the analysed contents of diet O0 resulted in a slightly higher (P,0.05) intake sugars, starch, CP, EE and ash from the DM content. of DM / kg BW, and diet O60 a slightly higher Gross energy (GE) was determined using an iso- (P,0.05) intake of GE / kg BW than the others. With thermal calorimeter (dds CP 500 calorimeter, North- increasing proportion of oats in the rations, the cliff, South Africa). intake of CP and starch increased (P,0.05), while the intake of CF, TF, NDF, ADF, lignin and sugar decreased (P,0.05), in agreement with that ex-2.5. Calculations
pected. For calculating, by difference, the nutrient and
3.2. Total ration nutrient digestibility energy digestibilities in oats in the present study and
in the concentrate part used in the literature referred
Due to unrealistic digestibility values for two of to in Table 5, the following equation was used:
the horses in the first period (diet O40 and O60),
d nutrientoats5(d nutrienttotal these data were excluded from the calculations.
2(a /T3d nutrienthay)) /(b /T ) However, this did not change any major trends in the results in the present experiment.
where d is digestibility, a is content (%) in the diet The inclusion of oats (O20, O40, O60) resulted in of the nutrient from hay, b is content (%) in the diet a higher (P,0.05) digestibility of DM, organic of the nutrient from oats and T is the total content matter (OM) and gross energy (dE) of these rations (%) in the diet of the nutrient. in comparison with hay alone (O0). However, di-gestibility did not differ significantly between oat 2.6. Statistical analysis substituted rations. The digestibility of CP in the rations was improved (P,0.05) linearly as the Analyses of variance were performed according to proportion of oats increased, but for the digestibility a Latin-square design (Patterson and Lucas, 1962) of EE the effect levelled off at the higher levels of using the GLM procedure (SAS, 1990). The model oats inclusion (O40, O60) (Table 3).
used was: Digestibility of the fibre fraction decreased at the
highest (O60) level of oat inclusion. For diet O60,
Yijkl5m 1 a 1 b 1 g 1i j k eijkl
the digestibility coefficients of the fibrous compo-when Yijkl is the ijklth observation, m is the general nents (NDF, ADF, and CF) were lower (P,0.05) mean,aiis the fixed effect of the ith diet (i51, 2, 3, than for the other rations (Table 3). By testing the 4),bjis the fixed effect of the jth period ( j51, 2, 3, curvilinearity for NDF, ADF and CF as quadratic
2
4),gk is the random effect of the kth animal (k51, functions of the inclusion level of oats, the R -values
2
2, 3, 4) and eijkl is the residual variation. increased (R 50.26, 0.33 and 0.37, respectively), Effects of interactions between period and animal compared with the corresponding linear models
2
were tested and found non-significant (P.0.05). (R 50.16, 0.21 and 0.23, respectively). Differences between dietary treatments were tested
with least squares (LS) means (SAS, 1990). Results 3.3. Calculated nutrient digestibilities of oats are presented as LS means with their standard errors.
digestibili-Table 3
Total ration nutrient digestibility coefficients (%)
Ratios (hay:oats)
O0 (100:0) O20 (80:20) O40 (60:40) O60 (40:60) S.E.M.
n 4 4 3 3
b a a a
Dry matter 48 55 58 58 1.3
b a a a
Organic matter 49 56 59 60 1.3
c b ab a
Crude protein 54 65 72 76 2.0
c b a a
Ether extract 236 15 42 51 6.6
a a a b
Total fibre 44 46 43 36 1.9
a a a b
Neutral detergent fibre 37 39 35 26 2.3
a a a b
Acid detergent fibre 29 32 24 12 3.2
a a a b
Least square mean values within rows with differing superscript letters differed significantly: P,0.05.
ty of the nutrient in oats is either 0% or 100%, Rosset and Dulphy (1987) ( y551.710.32x). The respectively (Fig. 1). The measured digestibilities of higher regression coefficient of these authors is ADF and CF of the rations were lower than when explained by differences in the composition of the assuming that the oat fibre digestibility was zero. concentrate mixture fed, i.e. maize–barley versus Thus, when calculating by difference, on the basis of oats in our experiment. However, the curvilinearity the pure hay diet, the digestibility coefficients of of the diet digestibility of nutrients and energy with NDF, ADF and CF of oats for the levels of 20, 40 increasing level of oats inclusion (Fig. 1) indicates and 60% inclusion in each ration, the following negative associative effects between the two dietary values have been computed; NDF: 58, 40 and 13%; components. This associative effect was most appar-ADF: 62, 26 and ,0% and CF: 88, 26 and ,0%, ent at the highest level of oats inclusion (O60) with
respectively. the digestibility of fibrous components declining
For the estimation of dE of oats, a straight line from O0 to O60 (Fig. 1). Similarly, by increasing the extrapolation of the data was used, where the O60 inclusion of oats Thompson et al. (1984) observed a results were excluded, since this level contributed to significant, more linear and almost constant, negative
curvilinearity. associative effect on the digestibility of the fibrous
components (Fig. 2a). The results of Hintz et al. 3.4. Urinary excretion of nitrogen and energy (1971b) also seem to indicate curvilinearity for the digestibility of NDF (Fig. 2b), where a significant The urinary excretion of N increased, as expected, increase is levelled off by a drop in the digestibility with increasing level of oats inclusion (Table 4). For (from 91 to 62% calculated by difference) at the the four treatment groups on average 64% of the highest level of cereal inclusion. This effect had not digested N was retained. The urinary energy per g N been commented on by the authors. In a subsequent was significantly higher for diet O0 and decreased investigation (Hintz et al., 1971a) a significantly with increasing oats inclusion. linear increase in the digestibility of the fibrous components with increasing level of cereal inclusion (shelled maize) was reported (Fig. 2c). Difference
4. Discussion calculations on the data from Hintz et al. (1971a) show a nearly complete digestibility of NDF and This investigation demonstrates an enhanced di- ADF of the cereal part of the diet.
gestibility of OM ( y) of the rations with increasing The tendency towards an improved digestibility of the percentage of oats (x) fed ( y550.710.21x, the fibrous fraction, noticeable in the present
Fig. 1. The apparent digestibility coefficients (♦) of (a) organic matter, (b) energy, (c) crude protein, (d) neutral detergent fibre, (e) acid detergent fibre and (f) crude fibre found in the present study, compared with values predicted assuming that the digestibility of the nutrients in oats is 0% (s) or 100% (d).
Table 4
Urinary excretion of nitrogen, nitrogen retained, urinary energy loss and urinary energy percentage of digestible energy
Ratios (hay:oats)
O0 (100:0) O20 (80:20) O40 (60:40) O60 (40:60)
b b b a
Least square mean values within rows with differing superscript letters differed significantly: P,0.05.
responds more positively to oats compared with 100% (Fig. 2a–f). In these figures the percentage of maize. However, as demonstrated by Kienzle (1994) nutrients and energy, respectively, derived from the the maximum amount of starch provided at a feeding concentrate, have been used as independent vari-occasion should not exceed 2–2.5 g / kg BW to avoid ables. An overview of the background of the studies digestive upsets. Although the amount of starch per referred to is given in Table 5.
feeding occasion did not exceed (1.9 g) this recom- The feeding routines of horses may also be of mendation in the present study, a depression in importance to explain differences between
experi-digestibility occurred. ments and maybe the occurrence of associative
Fig. 2. The apparent digestibility coefficients (♦) of (a) acid detergent fibre (Thompson et al., 1984), (b) neutral detergent fibre — trial 1 (Hintz et al., 1971b), (c) neutral detergent fibre — trial 2 (Hintz et al., 1971a), (d) acid detergent fibre (Pereira et al., 1989), (e) crude fibre — hay: maintenance (Martin-Rosset and Dulphy, 1987) and (f) crude fibre — hay: 1.43maintenance (Martin-Rosset and Dulphy, 1987), compared with values predicted assuming that the digestibility of the nutrients in oats is 0% (s) or 100% (d).
be the result of a changed supply of the cereal part in the small intestine compared with oats (Meyer et over time when providing pellets, but also by using al., 1993).
Table 5
Information on the feeding background in the different studies referred to in the text
b
Roughage Composition of Concentrate of Feeding References
a
concentrate , % total rations, %
L F CM
Oat forage hay Milo (95%) 0, 20, 40, 60 M 2 Total Pereira et al., 1989 SBM (5%)
Long grass hay Maize (59.5%) 0, 30, 60 M 2 Total Martin-Rosset and Dulphy, 1987
Barley (30%) 1.43M
Nut meal (8%) ad lib
(pelleted)
Maize silage Maize (48%) 0, 30, 60, 90 M 2 Total Martin-Rosset and Dulphy, 1987
Barley (25.2%) 1.43M
Alfalfa hay Oats (crimped) 0, 20, 40, 60, 80 ? – Total Thompson et al., 1984 (long stem)
a
Minerals and vitamins up to 100%; SBM, soybean meal.
b
L, level; F, frequency; CM, method of collection; M, maintenance; AIA, acid insoluble ash.
extrapolation has been chosen, excluding the data of by the fact that the faeces samples were dried at the O60 diet. A value for the dE of 75% was 658C, which also resulted in an overestimation of N obtained, which agrees fairly well with the dE of deposition. The estimates of total tract CP digestibili-73% and 71% given by NRC (1989) and INRA ty are also of limited value since they are greatly (1984), respectively. The difference between our affected by the extent of hindgut fermentation and value and those of NRC (1989) and INRA (1984) the microbial mass produced (Sauer et al., 1980; could be related to differences in the CF contents Low and Zebrowska, 1989; Meyer, 1992).
USDA Agricultural Research Service, p. 20, Handbook number which is also reflected in the decline in percent of
379. urinary energy of the DE (Nehring, 1972; Blaxter,
Hintz, H.F., Argenzio, R.A., Schryver, H.F., 1971a. Digestion
1989). coefficients, blood glucose levels and molar percentage of
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