The effect of animal species on in sacco degradation
of dry matter and protein of feeds in the rumen
K.S. Nandra
a, R.C. Dobos
b, B.A. Orchard
c,*, S.A. Neutze
d,
V.H. Oddy
b, B.R. Cullis
c, A.W. Jones
aaElizabeth Macarthur Agricultural Institute, PMB 8, Camden, NSW 2570, Australia bNSW Agriculture Beef Industry Centre, Armidale, NSW 2350, Australia cWagga Wagga Agricultural Institute, PMB, Wagga Wagga, NSW 2650, Australia
dNovartis Animal Health, Australasia Pty Ltd, 140-150 Bungaree Rd., Pendle Hill, NSW 2145, Australia
Received 17 November 1998; received in revised form 3 August 1999; accepted 11 November 1999
Abstract
A study was undertaken on lucerne (LUC), ryegrass (RG), kikuyu (KIK), soybean meal (SBM), wheat grain (WG) and meat and bone meal (MBM) to determine the effect of animal species (sheep versus cattle) on in sacco degradation of dry matter (DM) and protein. The approach of cubic smoothing splines ®tted as a linear mixed model was used for the analysis of degradability of DM and protein of feeds.
The quickly degradable DM (QDDM), cumulative slowly degradable DM (CSDDM), total degradable DM (TDDM) and rate of degradation of slowly degradable DM of LUC, RG, KIK, SBM and WG in the rumen of sheep and cattle were not different (p> 0.05). The QDDM, CSDDM and TDDM of these forages and concentrates ranged from 22.9 to 57.6, 35.3 to 54.9 and 70.2 to 92.9 (g/100 g).
Estimates of in sacco quickly degradable protein (QDP), cumulative slowly degradable protein (CSDP), total degradable protein (TDP), rate of degradation of slowly degradable protein of LUC, RG, KIK and SBM were similar (p> 0.05) for sheep and cattle. For the WG a vertical shift was found in the species cubic splines ®tted to logit transformed protein degradation data. This resulted in QDP of 52.0 and 43.8 g/100 g, CSDP of 41.6 and 48.0 g/100 g and TDP of 93.6 and 91.6 g/100 g for sheep and cattle, respectively.
In sacco degradation of DM and protein of MBM was irregular for both sheep and cattle, consistent with extreme heterogeneity of the concentrate.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Degradability; In sacco; Protein; Dry matter; Sheep versus cattle 83 (2000) 273±285
*Corresponding author.
E-mail address: orcharb@agric.nsw.gov.au (B.A. Orchard).
1. Introduction
Information about the extent and rate of dry matter (DM) and protein degradation of ruminant feeds in the rumen is crucial to match feed inputs to animal requirements. While there is some information available regarding differences between sheep and cattle in their ability to digest feed, there is little information on the degradation of components of feed dry matter and protein in the rumen. The rumen in sacco technique has been adopted as the standard method for determining DM and protein degradation. Sheep or cattle are used depending on the facilities of the various research establishments. It is important to understand the applicability of results obtained from one species, to the other species.
Playne et al. (1978) speculated that cattle had higher microbial activity and therefore faster DM degradation relative to sheep. Few differences were observed between sheep and cattle by (érskov et al., 1983) when comparing the in sacco degradation of dry matter of feeds after 9 or 24 h incubation. Prigge et al. (1984) have demonstrated that mature ruminant species generally degrade feeds similarly. Huntington and Givens (1997) concluded that mature ruminant species (sheep and cattle) when fed at maintenance, degrade DM of hay, soybean meal and ®sh meal similarly as measured by the in sacco technique.
In a recent European ring test involving 23 laboratories, Madsen and Hvelplund (1994) observed a large variation in in sacco estimates of protein degradability. There was no apparent difference between sheep and cattle in in sacco rumen protein degradability, although a possible species effect could have been masked by other factors in the procedure varying among laboratories.
The present study was designed to determine whether in sacco degradability of DM and protein, of some forages and concentrates differ between sheep and cattle fed the same basal diet to maintain live weight.
2. Materials and methods
2.1. Animals and basal diet
Nine rumen cannulated Merino wethers (3±4 years old, mean live weight 55 kg) and three rumen cannulated heifers (mean live weight 444 kg) were individually housed and were offered 0.9 and 6.0 kg/day, respectively of the same diet, half at 0730 h and half at 1530 h. These quantities of feed were calculated to approximately maintain live weight (Oddy, 1983). The diet consisted of 60% lucerne chaff (5±7 cm chop length) (904 g DM/ kg, 890 g organic matter (OM)/kg DM, 346 g acid detergent ®bre (ADF)/kg DM, 29.8 g N/kg DM, estimated metabolisable energy (ME) concentration of 7.2 MJ/kg DM) and 40% calf pellets consisting mainly of cereal grain and roughage (912 g DM/kg, 910 g OM/kg DM, 102 g ADF/kg DM, 32.3 g N/kg DM, estimated ME concentration of 9.6 MJ/kg DM) (Oddy et al., 1983).
2.2. Sample preparation
Dried forages and concentrates (soybean meal (SBM), meat and bone meal (MBM) and wheat grain (WG)) were ground through a Christie and Norris hammermill (Checley Everitt & Associates, Victoria, Australia) ®tted with 4 and 2.25 mm screens, respectively. A `test' sieving was done on the concentrates by shaking the feeds for 3 h on a 0.45 mm sieve. Where losses were >5% (soybean meal and wheat), the feed was sieved in this manner to remove ®ne particles before incubation in bags.
2.3. In sacco degradability study
The protocol for the measurement of in sacco degradability of feeds was similar to that recommended by the Agricultural and Feed Research Council (AFRC, 1992), the only difference being that cannulated animals were offered feed only twice daily. Approximately 2 g sieved feed was weighed into each dacron bag (80 mm120 mm, 36±38mm pores). Bags were made of polyester single thread woven with welded crossheads (Allied Screen Fabrics, Hornsby, New South Wales, Australia).
Table 1 presents the experimental design for this study of in sacco protein and dry matter degradation in the rumen of sheep and cattle. Samples from the three forages and three concentrates were placed in dacron bags in the rumen of three cattle and nine sheep on four occasions (periods) at weekly intervals commencing 27 March 1995. The total duration of the in sacco study was six weeks, two weeks adaptation period followed by four weeks degradation studies. In any one period, each heifer received three test feeds and each sheep one test feed, with the test feed allocation outlined in Table 1. Some attempt was made to balance the allocation of the feed types to animals between periods, though the particular allocation of feed types to animals and periods is not optimal in the presence of animal or period effects. Six bags per test feed, were inserted in the rumen simultaneously. Bags inserted in the rumen containing forages were withdrawn after 4, 8, 12, 24, 48 and 72 h, while those containing concentrates were withdrawn after 2, 4, 8, 12, 24 and 48 h. Bags were hand-rinsed brie¯y under cold tap water, then washed for 30 min Table 1
Experimental design for the degradability study
Species
Heifer 1 1,2,3 4,5,6 1,2,3 4,5,6
Heifer 2 1,2,3 4,5,6 1,2,3 4,5,6
Heifer 3 1,2,3 4,5,6 1,2,3 4,5,6
Sheep 1 1 4 2 5
aFeed types: 1, lucerne; 2, kikuyu; 3, ryegrass; 4, soybean meal; 5, meat and bone meal; 6, wheat.
on a cold rinse cycle in a washing machine. The value at time zero was obtained by washing the bag and test feed contents without incubation. The bags were then fully dried at 558C in a forced-draught oven. Disappearance of DM was measured as the loss of weight of the bag contents and the material left in the bag at each incubation time was analysed for nitrogen content.
2.4. Chemical analyses
Organic matter of the basal diet was determined after ignition in a muf¯e furnace for 3 h at 6008C and the acid detergent ®bre (ADF) of the basal diet was estimated by re¯ux according to Faichney and White (1983). The nitrogen content (N) of the basal diet, the test feeds and the residue left in the nylon bags after incubation in the rumen of sheep and cattle was determined by the combustion analyser method (Sweeney, 1989) using a LECO FP-428.
Crude protein (CP, g/100 g DM) was calculated as N (g/100 g DM)6.25. The CP content of LUC, RG, KIK, SBM, MBM, WG was 23.00, 23.00, 25.81, 51.69, 51.56 and 12.50, respectively.
2.5. Statistical methods
Five of the six test feeds were considered for statistical analysis. MBM was not included in this analysis because the degradation of MBM was irregular, consistent with extreme heterogeneity (Fig. 1a and b).
Table 2 presents the decomposition of the terms in the analysis of the degradation data. This is consistent with the experiment design being a cross-over design with animals, periods, animalperiods and animalperiodssamples being the strata in the design. `Samples' represent a factor notionally randomized to sampling times within an animal for a particular period.
Modelling of the degradation of DM or protein is via the cubic smoothing spline, which is a smooth (that is, continuous in the ®rst derivative over the domain of de®nition) function comprising piece-wise cubic polynomials between sampling times. The decomposition of the terms in the animalperiodsample strata follows from Verbyla et al. (1999).
Preliminary plots of the residuals of percent dry matter and protein degradation indicated severe variance heterogeneity. This was ameliorated by use of the logit transformation. The signi®cance of all ®xed terms was assessed using Wald tests and the signi®cance of random terms was assessed using residual maximum likelihood ratio tests (Verbyla et al., 1999). All analyses were performed using ASREML (Gilmour et al., 1999).
érskov and McDonald, 1979 de®ne the exponential decay functionf(t)eÿktto be the
fraction of the feed which still remains in the rumen aftert hours given k, the rate of passage from the rumen. Using this rate of passage k, and denoting the percentage degraded at timetbyp(t), the corrected rate of disappearance is given byf(t) dp(t)/dtand the cumulative slowly degradable protein up to timet (CDSP(t) or, CDSP for short) is then obtained using
Fig. 1. (a) Original dry matter degradation data for sheep and cattle. (b) Original protein degradation data for sheep and cattle.
Table 2
Sources of variation in the linear mixed model analysis of degradation data
Term Decomposition Fixed or
animalperiodfeed (group)c4 R
Animalperiodsamples
linear (ta) F *** ***
spline (t) R **
deviations (random (t))d,e R *
specieslinear (t) F
speciesspline (t) R
deviations (speciesrandom (t))d,f R
animallinear (t)c1 R
due to soybean meal within animalperiod R *** *** error
*
p< 0.05, **p< 0.01, ***p< 0.001, respectively.
a`t' represents time of incubation in the rumen. b`
' indicates the ®xed effect was included because of marginality constraints.
c1±4indicate pairs of terms for which a covariance may be included.
dDenotes terms estimating `deviations' which estimate systematic deviation at the particular mean level. eRepresents deviations at the overall mean level.
fRepresent systematic deviations at the species mean level and so forth.
CSDP
Z t
0
f udp u
du du (1)
In this study, the cumulative slowly degradable protein (CSDP) has been calculated using f(t)eÿkt for k0.02/h and with p(u) representing the equation of the
back-transformed logit cubic spline ®tted for either an individual test feed or a particular species by test feed combination. The accuracy of the results of this integration depends on the precision of the S-PLUS (Version 3.4, Release 1) `integrate' function (Statistical Sciences, 1995). The rate of disappearance of slowly degraded protein (SDP) has been calculated using
whereg(t) represents the particular test feed or test feed by species logit spline. The total degradable protein (TDP) in the rumen at a particular ¯ow rate (k0.02) was calculated as the sum of the quickly degraded protein (QDP) (or zero hour protein) and the CSDP. An analysis analogous to that performed for protein degradation was performed for dry matter degradation with comparable calculations for total degradable dry matter (TDDM), quickly degradable dry matter (QDDM) and cumulative slowly degradable dry matter (CSDDM).
3. Results
3.1. Protein degradation
The salient features of the ®nal model were an interaction of feed type with the linear component of the cubic smoothing spline, an interaction between species and feed type, and some evidence of a differential curvature in the cubic smoothing spline between feeds (see Table 2). The ®tted curves from this model are presented in Fig. 2. The feed type by species interaction resulted in a signi®cant (p< 0.01) difference between sheep and cattle for wheat only.
The value of QDP for each test feed is given in Table 3, which also includes the value of QDP for each species by feed curve. The corresponding values for CSDP from (1) and TDP are also presented.
While the values of QDP, CSDP and TDP varied between feeds, there were no differences between sheep and cattle for LUC, RG, KIK and SBM. The difference in the QDP between cattle and sheep for WG (43.8 and 52.0 g/100 g, respectively) may re¯ect a `lag' in protein degradation for cattle but this was not included in the analysis as there was insuf®cient data in the 0±4 h period. The calculated CSDP of WG at a rumen out¯ow rate of 0.02 per hour appears somewhat higher in cattle (48.0 g/100 g) than in sheep (41.6 g/100 g), but the TDP of WG for cattle and sheep are similar (91.8 and 93.6 g/ 100 g, respectively).
The rate of degradation of SDP for the test feed curves and for the feed curves of each species, with fractional rumen out¯ow ratekof 0.02 per hour, is presented in Table 4. The
Fig. 2. Protein degradation curves for sheep and cattle on the logit and percentage scale.
280
K.S.
Nandr
a
et
al.
/
Animal
F
eed
Science
and
T
ech
nology
83
(2000)
Table 3
Quickly degradable protein (QDP), cumulative slowly degradable protein (CSDP) at fractional out¯ow rate of 0.02 per hour and corresponding total degradable protein (TDP) measured as percentage of total protein
Overall feed QDP CSDPa TDP
Kikuyu 23.4 55.3 78.7
aCSDP was calculated assuming the cubic spline to be linear passed the ®nal data point and usingt! 1,
suf®cient for consistency to 0.0001.
Table 4
Rate of degradation (percentage per hour) of slowly degradable protein in the rumen at fractional out¯ow rate of 0.02 per hour
Overall feed Hours
0 2 4 8 12 24 48 72
Kikuyu 2.73 2.97 2.99 2.57 1.85 0.60 0.11 0.02
Lucerne 4.03 3.95 3.51 2.29 1.24 0.18 0.04 0.02
Ryegrass 3.27 3.48 3.40 2.75 1.83 0.44 0.06 0.01
Soybean meal 3.89 4.65 4.87 3.90 2.84 0.43 0.02 ±
Wheat 6.04 5.50 4.32 2.06 0.85 0.09 0.01 ±
Heifers by feed
Kikuyu 2.73 2.98 2.99 2.57 1.85 0.60 0.11 0.02
Lucerne 4.05 3.95 3.50 2.27 1.22 0.18 0.04 0.01
Ryegrass 3.23 3.44 3.38 2.76 1.85 0.44 0.06 0.01
Soybean meal 4.06 4.79 4.93 3.84 2.25 0.04 0.02 ±
Wheat 5.96 5.64 4.60 2.30 0.97 0.10 0.01 ±
Sheep by feed
Kikuyu 2.73 2.97 2.98 2.57 1.85 0.60 0.11 0.02
Lucerne 4.00 3.94 3.52 2.32 1.26 0.19 0.04 0.02
Ryegrass 3.32 3.50 3.41 2.74 1.81 0.43 0.06 0.01
Soybean meal 3.72 4.50 4.78 3.95 2.42 0.46 0.03 ±
Wheat 6.04 5.29 4.02 1.84 0.74 0.07 0.01 ±
maximum degradation rate of protein occurred in the 0±4 h period after bag insertion. No differences are apparent in the rate of degradation of SDP at different times between sheep and cattle for LUC, RG, KIK or SBM. However, for WG the rate of degradation of SDP appears to be somewhat higher in cattle between 2 and 24 h after insertion of the feed bags, as compared to sheep.
3.2. Dry matter degradation
The important features of the ®nal model for DM degradation included a signi®cant (p< 0.001) interaction of feed type with the linear component of the cubic smoothing spline and signi®cantly different (p< 0.001) curvature due to feed type (Table 2).
In the model for DM degradation there was no evidence of species or species by feed differences (p> 0.05). The DM degradation curves for each test feed are given in Fig. 3. While the estimated values of quickly degradable dry matter (QDDM), cumulative slowly degradable dry matter (CSDDM), and total degradable dry matter (TDDM) and rate of degradation of SDDM, varied between test feeds, no difference for these parameters between sheep and cattle for LUC, RG, KIK, SBM and WG was evident. Therefore, Tables 5 and 6 present the overall QDDM, CSDDM, TDDM and rate of degradation of SDDM (withk0.02 per hour) for the test feeds only.
4. Discussion
4.1. Parametric model
The traditional approach to the analysis of degradation curves is to ®t a non-linear model, typically the exponential model (érskov and McDonald, 1979). There has been evidence to suggest that the exponential model may not be entirely appropriate (McDonald, 1981; Dhanoa et al., 1995; Huntington and Givens, 1997; Lopez et al., 1999).
All of the competing models are continuous and smooth, in the sense that they are all functions of the incubation time which exhibit continuity in the ®rst derivative. The biological basis for these models is essentially empirical, with the choice of model determined by statistical rather than entirely biological reasons (Lopez et al., 1999).
The cubic smoothing spline represents a semi-parametric alternative which avoids choosing a parametric model. The estimation of all key biological parameters such as CSDDM and CSDP is straightforward. The additional advantage of the cubic smoothing spline is that other relevant sources of variation such as animal and period effects can be easily incorporated in the cubic smoothing spline's linear mixed model formulation (Verbyla et al., 1999).
Table 5
Quickly degradable dry matter (QDDM), cumulative slowly degradable dry matter (CSDDM) at rumen out¯ow rate of 0.02 per hour and corresponding total degradable dry matter (TDDM) measured as percentage of total DM
Overall feed QDDM CSDDMa TDDM
Kikuyu 22.9 48.7 71.6
Lucerne 32.5 37.7 70.2
Ryegrass 31.0 45.3 76.3
Soybean meal 33.8 54.9 88.7
Wheat 57.6 35.3 92.9
aCSDDM was calculated assuming the cubic spline to be linear passed the ®nal data point and usingt
! 1,
suf®cient for consistency to 0.0001.
Table 6
Rate of degradation (percentage per hour) of slowly degradable dry matter in the rumen at a fractional rumen out¯ow rate of 0.02 per hour
Overall feed Hours
0 2 4 8 12 24 48 72
Kikuyu 1.32 1.41 1.60 2.01 1.91 0.72 0.10 0.04
Lucerne 2.01 2.26 2.74 2.32 1.08 0.17 0.06 0.01
Ryegrass 1.47 1.55 1.77 2.16 1.88 0.55 0.07 0.04
Soybean meal 4.12 4.08 3.59 3.04 2.07 0.34 0.03 ±
Wheat 7.22 5.25 2.91 0.81 0.37 0.12 0.03 ±
4.2. Degradability
Following the ring tests, the Technical Committee on responses to nutrients (AFRC, 1992) made no de®nitive recommendation regarding the species of animal to be used for protein degradability. Therefore, the present study focused on determining species differences for protein degradability of concentrates and forages.
Although feed and feedspecies were signi®cant in the ®nal model for protein degradation in the rumen, the only test feed for which these terms were associated with a signi®cant vertical shift in logit curves was WG. No signi®cant species differences were evident for protein degradation for the forages studied (LUC, RG and KIK). In the case of SBM, signi®cant heterogeneity of variance was detected but was not associated with any species differences in protein degradability.
For the forage and concentrate feeds examined (except MBM), parameters for DM degradation were independent of the species of animal (sheep or cattle). There was no signi®cant species effect and no interaction of species with either feed or period. Therefore, a single curve for each test feed from either sheep or cattle (on the logit scale) may be used to represent the DM degradation in the rumen. The results of the present study are in accordance with the ®ndings of Huntington and Givens (1997) who found no differences between host species on in sacco DM disappearance of hay, SBM and ®sh meal. Uden and van Soest (1984) also found that mature ruminant species degrade the ®bre fraction of feeds similarly.
5. Conclusions
The ®ndings of this planned study have quanti®ed no difference between sheep and cattle in the in sacco degradability of DM for LUC, RG, KIK, SBM and WG. In sacco degradability of protein (QDP, CSDP and TDP) of LUC, RG, KIK and SBM were also found to be similar in cattle and sheep.
For WG, there were species differences in the in sacco degradation characteristics of protein, the nature of which was a vertical shift in the logit scale degradation splines. Future work needs to examine the difference in the in sacco degradability of protein of various grains.
Acknowledgements
The authors wish to acknowledge the assistance of Ms. K. Riley in the animal house and Dr. R. Hegarty for his valuable comments for the preparation of the manuscript.
References
Agricultural and Food Research Council (AFRC), 1992. Nutritive requirements of ruminant animals: Protein. AFRC Technical Committee on Responses to Nutrients. Report No. 9. Nutr. Abstr. and Rev. (Series B) 62, pp. 787±835.
Dhanoa, M.S., France, J., Siddons, R., Buchanan-Smith, J.G., 1995. A non-linear compartmental model to describe forage degradation kinetics during incubation in polyester bags in the rumen. Br. J. Nutr. 73, 3±15. Faichney, G.L., White, G.A., 1983. Methods for the analysis of feeds eaten by ruminants. Commonwealth
Scienti®c and Industrial Research Organisation, Melbourne, Victoria, pp. 4±9.
Gilmour, A.R., Cullis, B.R., Welham, S.J., Thompson, R., 1999. ASREML Reference Manual. N.S.W. Agriculture Biometrics Bulletin No. 3., NSW Agriculture, Orange, Australia, pp. 7±46.
Huntington, J.A., Givens, D.I., 1997. Studies on in situ degradation of feeds in the rumen. 1. Effect of species, bag mobility and incubation sequence on dry matter disappearance. Anim. Feed Sci. Technol. 64, 227±241. Lopez, S., France, J., Dhanoa, M.S., Mould, F., Dijkstra, J., 1999. Comparison of mathematical models to describe disappearance curves obtained using the polyester bag technique for incubating feeds in the rumen. J. Anim. Sci. 77, 1875±1888.
Madsen, J., Hvelplund, T., 1994. Prediction of in situ protein degradability in the rumen. Results of a European ringtest. Livest. Prod. Sci. 39, 201±212.
McDonald, I.M., 1981. A revised model for the estimation of protein degradability in the rumen. J. Agric. Sci. Cambr. 96, 251±252.
Oddy, V.H., 1983. Feed requirements of sheep and cattle during drought using a Metabolizable Energy system. AG Bulletin 3. Department of Agriculture NSW, Australia, pp. 12±13.
Oddy, V.H., Robards, G.E., Low, S.G., 1983. Prediction of in vivo dry matter digestibility from the ®bre and nitrogen content of a feed. In: Robards, G.E., Packham, R.G. (Eds.), Feed Information and Animal Production. Commonwealth Agricultural Bureau: Slough, United Kingdom, pp. 395±398.
érskov, E.R., McDonald, I., 1979. The estimation of protein degradability in the rumen from incubation measurements weighted according to rate of passage. J. Agric. Sci. Cambr. 92, 449±503.
érskov, E.R., Hughes-Jones, M., Elimam, M.E., 1983. Studies on degradation and out¯ow rate of protein supplements in the rumen of sheep and cattle. Livest. Prod. Sci. 10, 17±24.
Playne, M.J., Khumnalthong, W., Echevarria, M.G., 1978. Factors affecting the digestion of oesophageal ®stula samples and hay samples in nylon bags in the rumen of cattle. J. Agric. Sci. 90, 193±204.
Prigge, E.C., Baker, M.J., Varga, G.A., 1984. Comparative digestion rumen fermentation and kinetics of forage diets by steers and wethers. J. Anim. Sci. 59, 237±245.
Statistical Sciences, 1995. S-Plus Guide to Statistical and Mathematical Analysis version 3.3. Seattle: StatSci, a division of MathSoft Inc., 24±18 to 24±19.
Sweeney, R.A., 1989. Generic combustion method for determination of crude protein in feeds: collaborative study. J.A.O.A.C. 72, 770±774.
Uden, P., van Soest, P.J., 1984. Investigations of the in situ bag technique and a comparison of the fermentation in heifers, sheep, ponies and rabbits. J. Anim. Sci. 58, 213±221.
Verbyla, A.P., Cullis, B.R., Kenward, M.G., Welham, S.J., 1999. The analysis of designed experiments and longitudinal data by using smoothing splines. Applied Statistics 48, 269±311.
