- Email: [email protected]
Using markers to estimate apparent dry matter digestibility, faecal output and dry matter intake in dairy ewes fed Italian ryegrass hay or alfalfa hay
Small Ruminant Research 33 (1999) 145±152
Using markers to estimate apparent dry matter digestibility, faecal output and dry matter intake in dairy ewes fed Italian ryegrass hay or alfalfa hay A. Ferret*, J. Plaixats, G. Caja, J. Gasa, P. Prio Departament de Patologia i de Produccio Animals, Universitat AutoÁnoma Barcelona, 08193 Bellaterra, Spain Accepted 26 January 1999
Abstract Thirty six individual digestibility balances with eight diets were conducted. Experimental diets were (1) high-quality Italian ryegrass (Lolium multi¯orum) hay (160 g CP/kg DM) (RG1), (2) the former hay (RG1) plus 0.6 kg/day of concentrate, (3) medium-quality Italian ryegrass (134 g CP/kg DM) hay (RG2), (4) the former hay (RG2) plus 0.6 kg/day of concentrate, (5) low-quality Italian ryegrass (81 g CP/kg DM) hay (RG3), (6) the former hay (RG3) plus 0.6 kg/day of concentrate, (7) medium-quality (181 g CP/kg DM) alfalfa (Medicago sativa) hay fed alone and (8) the former alfalfa hay supplemented with 0.6 kg/day of concentrate. Indigestible acid detergent ®bre (IADF), acid detergent lignin (ADL), indigestible acid detergent lignin (IADL) and rumen-undegraded dry matter (RUDM), as internal markers, and chromic oxide (Cr2O3) as an external marker were used to estimate digestibility and faecal output of DM, respectively. By combining RUDM and Cr2O3 to predict forage intake, the following best equations were obtained for ryegrass (1) y 233.87 0.832x (n 10; r 0.94; p < 0.001; residual SD 73.7) and alfalfa (2) y 423.84 0.771x (n 10; r 0.98; p < 0.001; residual SD 119.1), y and x being measured and estimated DM intake, respectively. In conclusion, it was possible to estimate individually the dry matter intake by dairy ewes kept in groups with minimal disturbances in their social and competitive feeding behaviour. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Apparent digestibility; Faecal output; Intake; Dairy sheep; Markers
1. Introduction The majority of studies to measure voluntary food intake use methods in which animals are subjected to some degree of stress, speci®cally when kept in *Corresponding author. Present address: Facultat de VeterinaÁria (Edifici V), U.A.B., 08193 Bellaterra, Spain. Tel.: +93-581-2815; fax: +93-581-2006; e-mail: [email protected]
individual pens. The negative effects on performance caused by stress make these methods unsuitable, for instance, when dairy ewes are used. In recent years electronic recognition has become available and it is now possible to record the amount of food eaten by each animal though kept in groups. The question is whether this new methodology actually considers the competitive social behaviour that normally occurs when animals are fed.
0921-4488/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 0 1 5 - 2
146
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
as internal markers, to estimate voluntary DM intake by dairy ewes fed Italian ryegrass or alfalfa hays.
Common methods of measuring intake have been based on the simple precept that if the amount of DM excreted and the digestibility of the food DM are known, then the intake can be calculated from the quotient between faecal output and the coef®cient of undigestibility (Greenhalgh, 1982). Faecal output is often estimated using an external marker, frequently chromic oxide. After several days to allow equilibrium to be reached, faeces are collected from the animal by grab sampling from the rectum. From the concentration of the marker in the faeces and the dose of marker, total faecal production can be calculated (Forbes, 1995). In addition, the digestibility of dry matter can be estimated from the ratio of the concentration of an indigestible plant component in the feed to that of the component in the faeces (Le Du and Penning, 1982). Estimates of DM intake should be similar to measured intake by means of the simultaneous use of an internal marker to estimate DM digestibility and an external marker to estimate faecal output (Cochran et al., 1986). Nevertheless, Judkins et al. (1990) af®rmed that caution should be exercised in using markers if the method has not been veri®ed with similar feeds. The aim of this experiment was to test the feasibility of the joint use of chromic oxide, as an external marker, and several indigestible plant components,
2. Materials and methods 2.1. Animals and diets A total of 36 individual digestibility balances with eight diets were conducted using dry Manchega mature ewes (average body weight 63.2 1.5 kg). Ewes were housed in metabolism pens (0.6 m 1.3 m) with free access to water and a vitamin and mineral block. Experimental diets (Table 1) were based on chopped hays (average particle length 2.5 cm) as follows: (1) high-quality Italian ryegrass (Lolium multi¯orum) hay (RG1); (2) the former hay (RG1) plus 0.6 kg/day of concentrate (C1); (3) medium-quality Italian ryegrass hay (RG2); (4) the former hay (RG2) plus 0.6 kg/day of concentrate (C2); (5) low-quality Italian ryegrass hay (RG3); (6) the former hay (RG3) plus 0.6 kg/day of concentrate (C2); (7) medium-quality alfalfa (Medicago sativa) hay and (8) the former alfalfa hay plus 0.6 kg/day of concentrate (C2). Supplements were fed twice daily in equal portions. Animals were allowed ad libitum access to hays.
Table 1 Chemical composition and digestibility of hays and concentrates used Item
DM, g/kg Ash, g/kg DM CP, g/kg DM NDF, g/kg DM ADF, g/kg DM ADL, g/kg DM In vivo apparent DM digestibility, g/kg DM Rumen undegraded DM (RUDM), g/kg DM IADL, g/kg RUDM IADF, g/kg RUDM a
Italian ryegrass (RG) hay
Alfalfa hay
RG1
RG2
RG3
814 120 160 512 259 29 695 81 16 38
847 114 134 606 342 68 576 264 57 156
831 96 81 605 369 53 558 222 34 112
844 107 181 433 352 90 567 265 56 171
Concentrate (C) C1a
C2b
875 93 175 317 162 40 NDc 107 14 48
878 113 187 320 84 18 ND 47 10 27
Barley (94.5%), soybean meal (4%) and vitamin (75 000 UI/kg of vitamin A, 20 000 UI/kg of vitamin D3, 200 UI/kg of vitamin E, 60 mg/kg of vitamin B2, 0.5 mg/kg of vitamin B12 and 270 mg/kg of niacin) and mineral (14.0% Ca, 7% P, 9% Na, 0.52% Mg, 0.18% Fe, 0.5% K, 4 ppm Co, 1125 ppm Zn, 19 ppm I and 5 ppm Se) supplement (1.5%). b Cracked barley (66.5%), sunflower meal (29.7%), limestone (2.1%), calcium phosphate (0.7%), sodium chloride (0.6%) and vitamin (1000 000 UI/kg of vitamin A, 3000 000 UI/kg of vitamin D3, 5000 UI/kg of vitamin E) and mineral (2500 mg Cu, 10 000 mg Mn, 10 000 mg Zn, 100 mg I, 20 mg Co, 80 mg Se, 135 500 mg Ca, 152 500 mg P and 593 00 mg Mg) supplement (0.4%). c ND: not determined.
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
2.2. Digestion trials Voluntary DM intake, apparent DM digestibility and faecal output were measured by digestion trials. Each digestion trial consisted of 14 days for diet adaptation, followed by 7 days for pen adaptation and 7 days for intake recording and total faecal collection. Feed was provided at 09:00 hours and ad libitum access forages were ®xed at 115% of the previous day's consumption. Feed, orts and faeces were weighed and sampled daily during the digestibility trial. Samples were dried in a forced air oven at 658C for 48 h, ground in a hammer mill (1 mm screen) and stored at room temperature until analysis. Duplicate feed samples were analyzed for DM, ash and CP using Association of Of®cial Analytical Chemists, 1990 methods, and for NDF, ADF and ADL according to Goering and Van Soest (1970). Duplicate orts and faecal samples were analyzed for DM by the same procedure. 2.3. Markers To predict voluntary DM intake, four internal markers and one external marker were used to estimate digestibility and faecal output of DM, respectively. The separation of internal markers was accomplished
147
semiautomatic washing machine and dried at 1038C for 48 h. Faecal output was estimated by giving each ewe an oral dose of 1 g of Cr2O3 in two gelatin capsules of 0.5 g at 09:00 and 17:00 hours for a period of 9 days at the end of the digestibility trials. Faecal samples were taken from the rectum during the last 2 days of the period of marker administration at 09:00 and 17:00 hours. This sampling was decided after testing the procedure with six ewes in which fecal samples were taken four times per day, every 6 h. It was found that with 6 days the equilibrium was obtained and with two samples per day the information recorded was suf®cient. Chromic oxide determination in faeces and capsules was according to the method of Le Du and Penning (1982). 2.4. Calculations, validation and statistical analysis The recovery rates of the markers were calculated dividing the total weight of marker excreted in faeces (g) by the total weight of marker given (g). Forage intake fed ad libitum to sheep receiving a constant amount of concentrate (0.6 kg/day) was estimated using both markers from the following equation, assuming the same recovery rate for both forage and concentrate:
Cr intake markerfaeces ÿ CONC intake markerCONC Crfaeces markerforage Crfaeces by: (1) ADF extraction followed by 3 h digestion with 72% H2SO4 (Goering and Van Soest, 1970; ADL); (2) 7 days in situ incubation followed by acid detergent ®bre extraction (IADF); (3) 7 days in situ incubation followed by acid detergent lignin extraction (IADL) and (4) rumen undegradable DM after 7 days in situ incubation (RUDM). To determine the concentration of markers in feed and faeces, six replicate samples (3 g) were incubated in the rumen of a nonlactating dairy cow ®tted with a ruminal canula and fed at maintenance level with a forage-concentrate ratio of 80 : 20 on a dry matter basis. The forages used were ryegrass hay and alfalfa hay at the same proportion. Incubation was performed in nylon bags (125 mm 100 mm; 50 mm pore size), which were removed after 168 h of incubation, washed for 15 min in a
where Cr intake chromium intake (g), [marker]faeces internal marker concentration in faeces (g/g), CONC intake concentrate intake (g), [marker]CONC internal marker concentration in concentrate (g/g), [Cr]faeces chromium concentration in faeces (g/g), and [marker]forage internal marker concentration in hay (g/g). The amount of concentrate chosen (0.6 kg/day) re¯ected the fact that we are interested in forage intake prediction in ewes in late pregnancy, and this is the quantity of concentrate normally administered in commercial situations. To validate the equations obtained in the digestion trials, voluntary DM intake was measured in ®ve different weeks with 48 pregnant Manchega mature ewes (average body weight 69 kg), 24 fed Italian
148
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
ryegrass hay (RG3; Table 1) and 24 fed alfalfa hay (Table 1), both supplemented with 0.6 kg/day of concentrate (C2, Table 1). Ewes were kept in groups of six animals and housed in a pen approximately 3 m 2 m. The feedbunk was 2 m long and was adequate for all six ewes to feed at the same time. Fresh water was always freely available. Dry matter intake was also estimated using the markers chosen after testing them in the digestion trials. The concentration of RUDM in food and faeces was determined as described previously. Two oral doses of 0.5 g Cr2O3 in gelatin capsules at 09:00 and 17:00 hours were given to ewes for a period of 9 days. Faecal samples were also taken from the rectum twice a day the last 2 days of the each period of marker administration and chromium determination was according to the method of Le Du and Penning (1982). For more details see Ferret et al. (1998). Recovery rates different (p < 0.05) from 100% were determined by means of t-test (Steel and Torrie, 1980). Known and estimated intakes were compared using linear regression analysis (Statistical Analysis Systems Institute, 1989). The comparison between the pairs of intake means (measured and estimated) obtained in the validation trial was also made by means of t-test.
3. Results 3.1. Recovery rates Recovery rates of internal and external markers are shown in Table 2. In ryegrass diets, average recovery rates were 103.8, 88.5, 92.1, 98.4 and 99.3%, for ADL, IADL, IADF, RUDM and Cr2O3, respectively. In alfalfa diets, average recovery rates were 92.7, 87.9, 88.2, 93.1 and 104.8%, for ADL, IADL, IADF, RUDM and Cr2O3, respectively. Among the internal markers ADL and RUDM performed best, with recovery rates not different from 100% in ryegrass diets, unlike IADL and IADF which showed recovery rates different from 100% in three and two of the six diets, respectively. With alfalfa diets RUDM was the only marker to yield a recovery rate not different from 100%, in the case of animals fed only with alfalfa hay. No differences between markers were detected in the recovery rates obtained with animals fed alfalfa with 0.6 kg of concentrate. Moreover, the average recovery rate of RUDM was the numerically closest to 100%, in both diets (98.4 and 93.1%, in ryegrass and alfalfa hay, respectively). Chromic oxide recovery averaged 96.6% of marker consumed in ryegrass diets and 104.8% in alfalfa
Table 2 Marker recoveries (% SE) for different diets Diets
ADL
RG1 Fed alone With 0.6 kg of concentrate
101.4 6.2 (6)a 114.5 8.7 (8)
87.4 10.0 (4)* 83.1 0.9 (4)*
RG2 Fed alone With 0.6 kg of concentrate
110.2 1.1 (2) 101.3 3.8 (3)
68.8 4.7 (2) 86.0 15.2 (3)
74.1 2.4 (2) 101.0 5.0 (3)
94.6 4.3 (2) 99.7 4.4 (3)
RG3 Fed alone With 0.6 kg of concentrate
99.4 4.5 (3) 95.9 3.2 (4)
105.9 0.4 (3)* 99.8 4.4 (4)
105.6 0.3 (3) 100.3 4.6 (4)
98.3 1.0 (3) 98.6 3.4 (4)
102.9 0.8 (3) 92.1 3.6 (2)
Alfalfa Fed alone With 0.6 kg of concentrate
88.5 1.2 (5)* 96.8 1.0 (5)*
91.9 6.0 (5)* 83.9 0.7 (5)*
100.5 2.5 (5) 85.6 1.7 (5)*
101.7 3.4 (5) 107.9 2.5 (5)*
a
IADL
In brackets number of ewes employed in the digestion trial. ND: not determined. * Marker recoveries different from 100% (p < 0.05). b
IADF 88.1 4.2 (6) * 83.5 2.2 (8)*
93.7 2.0 (5)* 82.7 1.7 (5)*
RUDM
Cr2O3
104.8 4.7 (6) 94.5 4.0 (8)
103.2 0.7 (2) 98.8 4.2 (4) NDb ND
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Fig. 1. Estimated faecal output (g DM) versus total faecal collection (g DM) with all experimental data n 21).
diets. Recovery rate was different from 100% (p < 0.05) for the alfalfa diet with 0.6 kg/day of concentrate. 3.2. Faecal output, apparent digestibility and forage intake prediction Fig. 1 shows total faecal collection (y; g DM/day) plotted against estimated faecal output (x; g DM/day) for all experimental data (n 21). The equation (Table 3) did not differ from the line of equality. Estimated faecal output explained 94.2% of the variation of total faecal collection. The equation allowed us to estimate faecal output with a CV of 7.1%. The best predictions of apparent dry matter digestibility were obtained with RUDM for ryegrass hay and with ADL for alfalfa hay (Table 3). These equations
149
explained 82.8 and 90.3% of the variation of DM digestibility and allowed us to obtain this estimate with a CVof 4.7 and 1.8%, for ryegrass and alfalfa hay, respectively. To predict forage DM intake, with ewes consuming 0.6 kg of concentrate, the best equations (Table 3) were obtained using the RUDM, as an internal marker, and chromic oxide, as an external marker, together in both kinds of diets. In this case, y was measured intake and x was estimated intake. These equations explained 88.4 and 96.0% of the variation in forage DM intake and allowed us to obtain this estimate with a CV of 6.4 and 8.0% for ryegrass and alfalfa hay, respectively. When these equations were validated (Table 4) we observed an overestimation of 0.4% (69.9 versus 70.0 g DM/kg BW0.75, for average measured and estimated intake, respectively) in ewes fed alfalfa hay, and an overestimation of 4.6% (56.3 versus 58.9 g DM/kg BW0.75, for average measured and estimated intake, respectively) in ewes fed Italian ryegrass hay. Whilst with ryegrass diets there was an overestimation in all the 5 weeks recorded, in the case of alfalfa diet, the overestimation occurred in 3 of the 5 weeks studied and with an underestimation in the other two. In no case, did the comparison between measured and estimated intake reveal signi®cant differences (p > 0.05). 4. Discussion The results showed an effect of the hay type on the recovery rates in some markers. The in¯uence of diet in marker recovery has been described by several
Table 3 Linear regression between parameters measured in vivo and parameters (x) estimated by markers Parameters measured (y)
Marker
Equation
n
r
Significance
Total faecal collection
Cr2O3
41.08 0.934 x
21
0.97
***
Apparent DM digestibility: Ryegrass hay Alfalfa hay
RUDM ADL
0.132 0.803 x 0.277 0.568 x
26 10
0.91 0.95
***
Forage DM intake: Ryegrass hay Alfalfa hay
RUDM/Cr2O3 RUDM/Cr2O3
233.87 0.832 x 423.84 0.771 x
10 10
0.94 0.98
***
***
p < 0.001.
***
***
RSD 42.7 0.030 0.011 73.7 119.1
150
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Table 4 Forage dry matter intake (Mean SE) (g DM/kg BW0.75) measured with animals kept in groups or estimated individually using markers Mean DM intake (g DM/kg BW0.75)
Weeks of measure
Mean value
wk 1
wk 2
wk 3
wk 4
wk 5
Italian ryegrass hay DM intake measured (n 4) DM intake estimated (n 24)
54.5 2.2 55.6 2.3
56.1 2.1 59.1 2.7
58.9 1.3 61.2 1.9
57.9 1.6 58.1 2.5
54.3 2.0 60.3 3.6
56.3 0.9 58.9 1.0
Alfalfa hay DM intake measured (n 4) DM intake estimated (n 24)
65.1 1.3 62.7 1.8
69.5 2.8 65.3 2.6
73.4 1.2 76.8 3.3
72.0 2.9 73.6 3.0
69.4 3.1 71.7 3.4
69.9 1.4 70.0 2.6
authors. Lippke et al. (1986), testing the usefulness of INDF in a study involving 24 forages, concluded that mean ®bre recoveries for subtropical forages ranged from 83 to 111%, although the recovery for immature ryegrass averaged 130%. Judkins et al. (1990) indicated that ADL estimated apparent DM digestibility more accurately with fescue hay than with alfalfa hay and suggested that caution should be exercised in using markers when the method has not been veri®ed with similar feeds. Positive and incomplete recoveries of ADL have also described by several authors (Muntifering, 1982; Cochran et al., 1988). The probable reasons noted by Muntifering (1982) for incomplete lignin recovery were summarized by Fahey and Jung (1983): the true digestion of lignin, which has not been demonstrated in ruminants (Fahey and Jung, 1983); the apparent digestion obtained by formation of soluble-carbohydrate complexes, that pass from the rumen as polymers not recovered in the ®brous residues of faeces (Fahey et al., 1979); the partial distribution of the faecal lignin fraction by reagents used in the analytical methods; and physical and/or chemical differences between feed and faeces in the nature of materials empirically de®ned as lignin by each procedure. Moreover, Van Soest (1994) considered that the most insidious factor affecting recovery is lignin distribution relative to particle size because lignin in feed and faeces tends to be associated with matter of different particle size. While some authors suggest not using lignin as an internal marker (Cochran et al., 1988; Tamminga et al., 1989), or specify that its use should be limited to feeds having more than about 5% lignin in the DM (Van Soest, 1994), others consider that it is possible to use it in certain diets (Krysl et al., 1988; Judkins et al.,
1990). In agreement with the latter results, in our experiment ADL was the best internal marker to predict alfalfa apparent DM digestibility. Several authors have proposed, as an internal marker, the use of the residue of feeds incubated in sacco or in vitro with ruminal liquor for a period long enough to reach their maximum potential degradation (Wilkins, 1969; Cochran et al., 1986; Judkins et al., 1990; Fondevila et al., 1995). In our case, the RUDM provided the best estimate of the apparent DM digestibility for diets based on ryegrass hay. Judkins et al. (1990), working with the residue after 48 or 72 h of ruminal degradation in nylon bags, concluded that these markers provided accurate estimates of digestibility in two of the six diets tested. Fondevila et al. (1995) working with barley straw concluded that the use of rumen undegraded fractions as ratio indicators must be approached with caution because they do not seem to provide accurate estimates across all diets and feeding conditions. We decided to reject IADF and IADL as a result of their negative and variable recoveries. The analytical variations in the extraction of ®bre fractions in the samples after ruminal degradation could be the origin of the variation of the results. Incomplete recoveries of the markers based on ADF or ADL extraction of the residues after 7 days of ruminal degradation agree with the results obtained by others (Lippke et al., 1986; Judkins et al., 1990). Lippke et al. (1986) assumed that variations in sample particle size could explain the bias in ®bre recovery. Indigestible ®bre fractions tend to underestimate digestion of different forages (Judkins et al., 1990; Sunvold and Cochran, 1991). However, some workers have demonstrated the utility of indigestible ®bre residues as an internal marker in
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
certain diets (Krysl et al., 1988; Tamminga et al., 1989; Dove and Coombe, 1992). Faecal recovery rates near to 100% have been observed by several workers (Muntifering, 1982; Melix et al., 1987). The use of Cr2O3 as an external marker to predict faecal output gave good results as also reported by Le Du and Penning (1982) and Furnival et al. (1990). Our experiment showed that by using together RUDM, as an internal marker, and Cr2O3, as an external marker, to predict forage DM intake, the equations obtained presented a low CV (6.4 and 8.0% for ryegrass and alfalfa, respectively), indicating that the predicted values could be considered an accurate estimate of measured intake. The validation allowed us to obtain, in both diets, estimates very close to measured DM intakes. Even though the standard errors of the estimates were higher than standard errors of the measured DM intakes (Table 4), the use of these markers allowed Ferret et al. (1998) to obtain accurate intake estimates by correcting errors in the diagnosis of pregnancy, thereby decreasing the variation in the values of DM intake. In fact, the use of markers to individualize the intake enabled the authors to con®rm the effect of forage type on DM intake by ewes during late pregnancy and moreover revealed the effect of litter size that was not detected when the voluntary DM intake was recorded with ewes housed in groups. 5. Conclusions The joint use of chromic oxide, as an external marker, and the rumen undegraded dry matter, as an internal marker, allowed us to obtain an estimate of forage dry matter intake in dairy ewes fed Italian ryegrass hay or alfalfa hay and supplemented with 0.6 kg/day of concentrate. It is therefore possible to estimate individually the voluntary dry matter intake by dairy ewes kept in groups without altering their social and competitive feeding behaviour, as long as the markers have been tested previously with similar feeds. Acknowledgements Financial support from the European Commission, Directorate General VI (Project CAMAR 8001-CT
151
91-0113) and the ComisioÂn Interministerial de Ciencia y TecnologõÂa of Spain (Project AGF93-0526) is acknowledged. References Association of Official Analytical Chemists, 1990. Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Arlington, VA. Cochran, R.C., Adams, D.C., Wallace, J.L., Galyean, M.L., 1986. Predicting digestibility of different diets with internal markers: evaluation of four potential markers. J. Anim. Sci. 63, 1476± 1483. Cochran, R.C., Vanzant, E.S., DelCurto, T., 1988. Evaluation of internal markers isolated by alkaline hydrogen peroxide incubation and acid detergent lignin extraction. J. Anim. Sci. 66, 3245±3251. Dove, H., Coombe, J.B., 1992. A comparison of methods for estimating supplement intake and diet digestibility in sheep. Proc. Aust. Soc. Anim. Prod. 19, 239±241. Fahey, G.C., Jung, H.G., 1983. Lignin as a marker in digestion studies: a review. J. Anim. Sci. 57, 220±225. Fahey, G.C., McLaren, G.A., Williams, J.E., 1979. Lignin digestibility by lambs fed both low quality and high quality roughages. J. Anim. Sci. 48, 941±946. Ferret, A., Gasa, J., Caja, G., PrioÂ, P., 1998. Voluntary dry matter intake and digesta kinetics of twin or single-bearing Manchega ewes fed Italian ryegrass hay or alfalfa hay in late pregnancy. Anim. Sci. 67, 559±566. Fondevila, M., Castrillo, C., Gasa, J., Guada, J.A., 1995. Rumenundegradable dry matter and neutral detergent fibre as ratio indicators of digestibility in sheep given cereal straw-based diets. J. Agric. Sci. (Camb.) 125, 145±151. Forbes, J.M., 1995. Voluntary Food Intake and Diet Selection in Farm Animals. CAB International, Wallingford, Oxon, 532 pp. Furnival, E.P., Corbett, J.L., Inskip, M.W., 1990. Evaluation of controlled release devices for administration of chromium sesquioxide using fistulated grazing sheep. 1. Variation in marker concentration in faeces. Aust. J. Agric. Res. 41, 969± 975. Goering, H.K., Van Soest, P.J., 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications). Agric. Handbook No. 379. ARS, USDA, Washington, DC. Greenhalgh, J.F.D., 1982. An introduction to herbage intake measurements. In: Leaver, J.D. (Ed.), Herbage Intake Handbook. British Grassland Institute, Hurley, Maidenhead, Berkshire, pp. 1±10. Judkins, M.B., Krysl, L.J., Barton, R.K., 1990. Estimating diet digestibility: a comparison of 11 techniques across six different diets fed to rams. J. Anim. Sci. 68, 1405±1415. Krysl, L.J., Galyean, M.L., Estell, R.E., Sowell, B.F., 1988. Estimating digestibility and faecal output in lambs using internal and external markers. J. Agric. Sci. (Camb.) 111, 19± 25.
152
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Le Du, Y.L.P., Penning, P.D., 1982. Animal based techniques for estimating herbage intake. In: Leaver, J.D. (Ed.), Herbage Intake Handbook. British Grassland Institute, Hurley, Maidenhead, Berkshire, pp. 37±75. Lippke, H., Ellis, W.C., Jacobs, B.F., 1986. Recovery of indigestible fiber from feces of sheep and cattle on forage diets. J. Dairy Sci. 69, 403±412. Melix, C., Peyraud, J.L., Verite, R., 1987. Utilisation de l"oxyde de chrome chez les vaches laitieÁres pour la preÂvision des quantiteÂs de feÁces eÂmises. 1. Etude des variations du taux de reÂcupeÂration et ses conseÂquences sur l'estimation de la digestibilite et des quantiteÂs ingeÂreÂes de rations d'herbe et d'ensilage de maõÈs. Reprod. Nutr. DeÂvelop. 27(1B), 215±216. Muntifering, R.B., 1982. Evaluation of various lignin assays for determining ruminal digestion of roughages by lambs. J. Anim. Sci. 55, 432±438. Statistical Analysis Systems Institute. 1989. SAS/STAT user's guide: statistics, version 6. SAS Institute Inc., Cary, NC.
Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics: A Biometrical Approach, 2nd ed. McGraw-Hill, New York. Sunvold, G.D., Cochran, R.C., 1991. Technical note: Evaluation of acid detergent lignin, alkaline peroxide lignin, acid insoluble ash, and indigestible acid detergent fiber as internal markers for prediction of alfalfa, bromegrass, and prairie hay digestibility by beef steers. J. Anim. Sci. 69, 4951± 4955. Tamminga, S., Robinson, P.H., Mejis, S., Boer, H., 1989. Feed components as internal markers in digestion studies with dairy cows. Anim. Feed Sci. Technol. 27, 49±57. Van Soest, P.J., 1994. Lignin. In: Nutritional Ecology of the Ruminant, 2nd ed. Cornell University Press, Ithaca, New York, pp. 177±195. Wilkins, R.J., 1969. The potential digestibility of cellulose in forages and faeces. J. Agric. Sci. (Camb.) 73, 57±64.
Using markers to estimate apparent dry matter digestibility, faecal output and dry matter intake in dairy ewes fed Italian ryegrass hay or alfalfa hay A. Ferret*, J. Plaixats, G. Caja, J. Gasa, P. Prio Departament de Patologia i de Produccio Animals, Universitat AutoÁnoma Barcelona, 08193 Bellaterra, Spain Accepted 26 January 1999
Abstract Thirty six individual digestibility balances with eight diets were conducted. Experimental diets were (1) high-quality Italian ryegrass (Lolium multi¯orum) hay (160 g CP/kg DM) (RG1), (2) the former hay (RG1) plus 0.6 kg/day of concentrate, (3) medium-quality Italian ryegrass (134 g CP/kg DM) hay (RG2), (4) the former hay (RG2) plus 0.6 kg/day of concentrate, (5) low-quality Italian ryegrass (81 g CP/kg DM) hay (RG3), (6) the former hay (RG3) plus 0.6 kg/day of concentrate, (7) medium-quality (181 g CP/kg DM) alfalfa (Medicago sativa) hay fed alone and (8) the former alfalfa hay supplemented with 0.6 kg/day of concentrate. Indigestible acid detergent ®bre (IADF), acid detergent lignin (ADL), indigestible acid detergent lignin (IADL) and rumen-undegraded dry matter (RUDM), as internal markers, and chromic oxide (Cr2O3) as an external marker were used to estimate digestibility and faecal output of DM, respectively. By combining RUDM and Cr2O3 to predict forage intake, the following best equations were obtained for ryegrass (1) y 233.87 0.832x (n 10; r 0.94; p < 0.001; residual SD 73.7) and alfalfa (2) y 423.84 0.771x (n 10; r 0.98; p < 0.001; residual SD 119.1), y and x being measured and estimated DM intake, respectively. In conclusion, it was possible to estimate individually the dry matter intake by dairy ewes kept in groups with minimal disturbances in their social and competitive feeding behaviour. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Apparent digestibility; Faecal output; Intake; Dairy sheep; Markers
1. Introduction The majority of studies to measure voluntary food intake use methods in which animals are subjected to some degree of stress, speci®cally when kept in *Corresponding author. Present address: Facultat de VeterinaÁria (Edifici V), U.A.B., 08193 Bellaterra, Spain. Tel.: +93-581-2815; fax: +93-581-2006; e-mail: [email protected]
individual pens. The negative effects on performance caused by stress make these methods unsuitable, for instance, when dairy ewes are used. In recent years electronic recognition has become available and it is now possible to record the amount of food eaten by each animal though kept in groups. The question is whether this new methodology actually considers the competitive social behaviour that normally occurs when animals are fed.
0921-4488/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 4 8 8 ( 9 9 ) 0 0 0 1 5 - 2
146
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
as internal markers, to estimate voluntary DM intake by dairy ewes fed Italian ryegrass or alfalfa hays.
Common methods of measuring intake have been based on the simple precept that if the amount of DM excreted and the digestibility of the food DM are known, then the intake can be calculated from the quotient between faecal output and the coef®cient of undigestibility (Greenhalgh, 1982). Faecal output is often estimated using an external marker, frequently chromic oxide. After several days to allow equilibrium to be reached, faeces are collected from the animal by grab sampling from the rectum. From the concentration of the marker in the faeces and the dose of marker, total faecal production can be calculated (Forbes, 1995). In addition, the digestibility of dry matter can be estimated from the ratio of the concentration of an indigestible plant component in the feed to that of the component in the faeces (Le Du and Penning, 1982). Estimates of DM intake should be similar to measured intake by means of the simultaneous use of an internal marker to estimate DM digestibility and an external marker to estimate faecal output (Cochran et al., 1986). Nevertheless, Judkins et al. (1990) af®rmed that caution should be exercised in using markers if the method has not been veri®ed with similar feeds. The aim of this experiment was to test the feasibility of the joint use of chromic oxide, as an external marker, and several indigestible plant components,
2. Materials and methods 2.1. Animals and diets A total of 36 individual digestibility balances with eight diets were conducted using dry Manchega mature ewes (average body weight 63.2 1.5 kg). Ewes were housed in metabolism pens (0.6 m 1.3 m) with free access to water and a vitamin and mineral block. Experimental diets (Table 1) were based on chopped hays (average particle length 2.5 cm) as follows: (1) high-quality Italian ryegrass (Lolium multi¯orum) hay (RG1); (2) the former hay (RG1) plus 0.6 kg/day of concentrate (C1); (3) medium-quality Italian ryegrass hay (RG2); (4) the former hay (RG2) plus 0.6 kg/day of concentrate (C2); (5) low-quality Italian ryegrass hay (RG3); (6) the former hay (RG3) plus 0.6 kg/day of concentrate (C2); (7) medium-quality alfalfa (Medicago sativa) hay and (8) the former alfalfa hay plus 0.6 kg/day of concentrate (C2). Supplements were fed twice daily in equal portions. Animals were allowed ad libitum access to hays.
Table 1 Chemical composition and digestibility of hays and concentrates used Item
DM, g/kg Ash, g/kg DM CP, g/kg DM NDF, g/kg DM ADF, g/kg DM ADL, g/kg DM In vivo apparent DM digestibility, g/kg DM Rumen undegraded DM (RUDM), g/kg DM IADL, g/kg RUDM IADF, g/kg RUDM a
Italian ryegrass (RG) hay
Alfalfa hay
RG1
RG2
RG3
814 120 160 512 259 29 695 81 16 38
847 114 134 606 342 68 576 264 57 156
831 96 81 605 369 53 558 222 34 112
844 107 181 433 352 90 567 265 56 171
Concentrate (C) C1a
C2b
875 93 175 317 162 40 NDc 107 14 48
878 113 187 320 84 18 ND 47 10 27
Barley (94.5%), soybean meal (4%) and vitamin (75 000 UI/kg of vitamin A, 20 000 UI/kg of vitamin D3, 200 UI/kg of vitamin E, 60 mg/kg of vitamin B2, 0.5 mg/kg of vitamin B12 and 270 mg/kg of niacin) and mineral (14.0% Ca, 7% P, 9% Na, 0.52% Mg, 0.18% Fe, 0.5% K, 4 ppm Co, 1125 ppm Zn, 19 ppm I and 5 ppm Se) supplement (1.5%). b Cracked barley (66.5%), sunflower meal (29.7%), limestone (2.1%), calcium phosphate (0.7%), sodium chloride (0.6%) and vitamin (1000 000 UI/kg of vitamin A, 3000 000 UI/kg of vitamin D3, 5000 UI/kg of vitamin E) and mineral (2500 mg Cu, 10 000 mg Mn, 10 000 mg Zn, 100 mg I, 20 mg Co, 80 mg Se, 135 500 mg Ca, 152 500 mg P and 593 00 mg Mg) supplement (0.4%). c ND: not determined.
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
2.2. Digestion trials Voluntary DM intake, apparent DM digestibility and faecal output were measured by digestion trials. Each digestion trial consisted of 14 days for diet adaptation, followed by 7 days for pen adaptation and 7 days for intake recording and total faecal collection. Feed was provided at 09:00 hours and ad libitum access forages were ®xed at 115% of the previous day's consumption. Feed, orts and faeces were weighed and sampled daily during the digestibility trial. Samples were dried in a forced air oven at 658C for 48 h, ground in a hammer mill (1 mm screen) and stored at room temperature until analysis. Duplicate feed samples were analyzed for DM, ash and CP using Association of Of®cial Analytical Chemists, 1990 methods, and for NDF, ADF and ADL according to Goering and Van Soest (1970). Duplicate orts and faecal samples were analyzed for DM by the same procedure. 2.3. Markers To predict voluntary DM intake, four internal markers and one external marker were used to estimate digestibility and faecal output of DM, respectively. The separation of internal markers was accomplished
147
semiautomatic washing machine and dried at 1038C for 48 h. Faecal output was estimated by giving each ewe an oral dose of 1 g of Cr2O3 in two gelatin capsules of 0.5 g at 09:00 and 17:00 hours for a period of 9 days at the end of the digestibility trials. Faecal samples were taken from the rectum during the last 2 days of the period of marker administration at 09:00 and 17:00 hours. This sampling was decided after testing the procedure with six ewes in which fecal samples were taken four times per day, every 6 h. It was found that with 6 days the equilibrium was obtained and with two samples per day the information recorded was suf®cient. Chromic oxide determination in faeces and capsules was according to the method of Le Du and Penning (1982). 2.4. Calculations, validation and statistical analysis The recovery rates of the markers were calculated dividing the total weight of marker excreted in faeces (g) by the total weight of marker given (g). Forage intake fed ad libitum to sheep receiving a constant amount of concentrate (0.6 kg/day) was estimated using both markers from the following equation, assuming the same recovery rate for both forage and concentrate:
Cr intake markerfaeces ÿ CONC intake markerCONC Crfaeces markerforage Crfaeces by: (1) ADF extraction followed by 3 h digestion with 72% H2SO4 (Goering and Van Soest, 1970; ADL); (2) 7 days in situ incubation followed by acid detergent ®bre extraction (IADF); (3) 7 days in situ incubation followed by acid detergent lignin extraction (IADL) and (4) rumen undegradable DM after 7 days in situ incubation (RUDM). To determine the concentration of markers in feed and faeces, six replicate samples (3 g) were incubated in the rumen of a nonlactating dairy cow ®tted with a ruminal canula and fed at maintenance level with a forage-concentrate ratio of 80 : 20 on a dry matter basis. The forages used were ryegrass hay and alfalfa hay at the same proportion. Incubation was performed in nylon bags (125 mm 100 mm; 50 mm pore size), which were removed after 168 h of incubation, washed for 15 min in a
where Cr intake chromium intake (g), [marker]faeces internal marker concentration in faeces (g/g), CONC intake concentrate intake (g), [marker]CONC internal marker concentration in concentrate (g/g), [Cr]faeces chromium concentration in faeces (g/g), and [marker]forage internal marker concentration in hay (g/g). The amount of concentrate chosen (0.6 kg/day) re¯ected the fact that we are interested in forage intake prediction in ewes in late pregnancy, and this is the quantity of concentrate normally administered in commercial situations. To validate the equations obtained in the digestion trials, voluntary DM intake was measured in ®ve different weeks with 48 pregnant Manchega mature ewes (average body weight 69 kg), 24 fed Italian
148
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
ryegrass hay (RG3; Table 1) and 24 fed alfalfa hay (Table 1), both supplemented with 0.6 kg/day of concentrate (C2, Table 1). Ewes were kept in groups of six animals and housed in a pen approximately 3 m 2 m. The feedbunk was 2 m long and was adequate for all six ewes to feed at the same time. Fresh water was always freely available. Dry matter intake was also estimated using the markers chosen after testing them in the digestion trials. The concentration of RUDM in food and faeces was determined as described previously. Two oral doses of 0.5 g Cr2O3 in gelatin capsules at 09:00 and 17:00 hours were given to ewes for a period of 9 days. Faecal samples were also taken from the rectum twice a day the last 2 days of the each period of marker administration and chromium determination was according to the method of Le Du and Penning (1982). For more details see Ferret et al. (1998). Recovery rates different (p < 0.05) from 100% were determined by means of t-test (Steel and Torrie, 1980). Known and estimated intakes were compared using linear regression analysis (Statistical Analysis Systems Institute, 1989). The comparison between the pairs of intake means (measured and estimated) obtained in the validation trial was also made by means of t-test.
3. Results 3.1. Recovery rates Recovery rates of internal and external markers are shown in Table 2. In ryegrass diets, average recovery rates were 103.8, 88.5, 92.1, 98.4 and 99.3%, for ADL, IADL, IADF, RUDM and Cr2O3, respectively. In alfalfa diets, average recovery rates were 92.7, 87.9, 88.2, 93.1 and 104.8%, for ADL, IADL, IADF, RUDM and Cr2O3, respectively. Among the internal markers ADL and RUDM performed best, with recovery rates not different from 100% in ryegrass diets, unlike IADL and IADF which showed recovery rates different from 100% in three and two of the six diets, respectively. With alfalfa diets RUDM was the only marker to yield a recovery rate not different from 100%, in the case of animals fed only with alfalfa hay. No differences between markers were detected in the recovery rates obtained with animals fed alfalfa with 0.6 kg of concentrate. Moreover, the average recovery rate of RUDM was the numerically closest to 100%, in both diets (98.4 and 93.1%, in ryegrass and alfalfa hay, respectively). Chromic oxide recovery averaged 96.6% of marker consumed in ryegrass diets and 104.8% in alfalfa
Table 2 Marker recoveries (% SE) for different diets Diets
ADL
RG1 Fed alone With 0.6 kg of concentrate
101.4 6.2 (6)a 114.5 8.7 (8)
87.4 10.0 (4)* 83.1 0.9 (4)*
RG2 Fed alone With 0.6 kg of concentrate
110.2 1.1 (2) 101.3 3.8 (3)
68.8 4.7 (2) 86.0 15.2 (3)
74.1 2.4 (2) 101.0 5.0 (3)
94.6 4.3 (2) 99.7 4.4 (3)
RG3 Fed alone With 0.6 kg of concentrate
99.4 4.5 (3) 95.9 3.2 (4)
105.9 0.4 (3)* 99.8 4.4 (4)
105.6 0.3 (3) 100.3 4.6 (4)
98.3 1.0 (3) 98.6 3.4 (4)
102.9 0.8 (3) 92.1 3.6 (2)
Alfalfa Fed alone With 0.6 kg of concentrate
88.5 1.2 (5)* 96.8 1.0 (5)*
91.9 6.0 (5)* 83.9 0.7 (5)*
100.5 2.5 (5) 85.6 1.7 (5)*
101.7 3.4 (5) 107.9 2.5 (5)*
a
IADL
In brackets number of ewes employed in the digestion trial. ND: not determined. * Marker recoveries different from 100% (p < 0.05). b
IADF 88.1 4.2 (6) * 83.5 2.2 (8)*
93.7 2.0 (5)* 82.7 1.7 (5)*
RUDM
Cr2O3
104.8 4.7 (6) 94.5 4.0 (8)
103.2 0.7 (2) 98.8 4.2 (4) NDb ND
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Fig. 1. Estimated faecal output (g DM) versus total faecal collection (g DM) with all experimental data n 21).
diets. Recovery rate was different from 100% (p < 0.05) for the alfalfa diet with 0.6 kg/day of concentrate. 3.2. Faecal output, apparent digestibility and forage intake prediction Fig. 1 shows total faecal collection (y; g DM/day) plotted against estimated faecal output (x; g DM/day) for all experimental data (n 21). The equation (Table 3) did not differ from the line of equality. Estimated faecal output explained 94.2% of the variation of total faecal collection. The equation allowed us to estimate faecal output with a CV of 7.1%. The best predictions of apparent dry matter digestibility were obtained with RUDM for ryegrass hay and with ADL for alfalfa hay (Table 3). These equations
149
explained 82.8 and 90.3% of the variation of DM digestibility and allowed us to obtain this estimate with a CVof 4.7 and 1.8%, for ryegrass and alfalfa hay, respectively. To predict forage DM intake, with ewes consuming 0.6 kg of concentrate, the best equations (Table 3) were obtained using the RUDM, as an internal marker, and chromic oxide, as an external marker, together in both kinds of diets. In this case, y was measured intake and x was estimated intake. These equations explained 88.4 and 96.0% of the variation in forage DM intake and allowed us to obtain this estimate with a CV of 6.4 and 8.0% for ryegrass and alfalfa hay, respectively. When these equations were validated (Table 4) we observed an overestimation of 0.4% (69.9 versus 70.0 g DM/kg BW0.75, for average measured and estimated intake, respectively) in ewes fed alfalfa hay, and an overestimation of 4.6% (56.3 versus 58.9 g DM/kg BW0.75, for average measured and estimated intake, respectively) in ewes fed Italian ryegrass hay. Whilst with ryegrass diets there was an overestimation in all the 5 weeks recorded, in the case of alfalfa diet, the overestimation occurred in 3 of the 5 weeks studied and with an underestimation in the other two. In no case, did the comparison between measured and estimated intake reveal signi®cant differences (p > 0.05). 4. Discussion The results showed an effect of the hay type on the recovery rates in some markers. The in¯uence of diet in marker recovery has been described by several
Table 3 Linear regression between parameters measured in vivo and parameters (x) estimated by markers Parameters measured (y)
Marker
Equation
n
r
Significance
Total faecal collection
Cr2O3
41.08 0.934 x
21
0.97
***
Apparent DM digestibility: Ryegrass hay Alfalfa hay
RUDM ADL
0.132 0.803 x 0.277 0.568 x
26 10
0.91 0.95
***
Forage DM intake: Ryegrass hay Alfalfa hay
RUDM/Cr2O3 RUDM/Cr2O3
233.87 0.832 x 423.84 0.771 x
10 10
0.94 0.98
***
***
p < 0.001.
***
***
RSD 42.7 0.030 0.011 73.7 119.1
150
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Table 4 Forage dry matter intake (Mean SE) (g DM/kg BW0.75) measured with animals kept in groups or estimated individually using markers Mean DM intake (g DM/kg BW0.75)
Weeks of measure
Mean value
wk 1
wk 2
wk 3
wk 4
wk 5
Italian ryegrass hay DM intake measured (n 4) DM intake estimated (n 24)
54.5 2.2 55.6 2.3
56.1 2.1 59.1 2.7
58.9 1.3 61.2 1.9
57.9 1.6 58.1 2.5
54.3 2.0 60.3 3.6
56.3 0.9 58.9 1.0
Alfalfa hay DM intake measured (n 4) DM intake estimated (n 24)
65.1 1.3 62.7 1.8
69.5 2.8 65.3 2.6
73.4 1.2 76.8 3.3
72.0 2.9 73.6 3.0
69.4 3.1 71.7 3.4
69.9 1.4 70.0 2.6
authors. Lippke et al. (1986), testing the usefulness of INDF in a study involving 24 forages, concluded that mean ®bre recoveries for subtropical forages ranged from 83 to 111%, although the recovery for immature ryegrass averaged 130%. Judkins et al. (1990) indicated that ADL estimated apparent DM digestibility more accurately with fescue hay than with alfalfa hay and suggested that caution should be exercised in using markers when the method has not been veri®ed with similar feeds. Positive and incomplete recoveries of ADL have also described by several authors (Muntifering, 1982; Cochran et al., 1988). The probable reasons noted by Muntifering (1982) for incomplete lignin recovery were summarized by Fahey and Jung (1983): the true digestion of lignin, which has not been demonstrated in ruminants (Fahey and Jung, 1983); the apparent digestion obtained by formation of soluble-carbohydrate complexes, that pass from the rumen as polymers not recovered in the ®brous residues of faeces (Fahey et al., 1979); the partial distribution of the faecal lignin fraction by reagents used in the analytical methods; and physical and/or chemical differences between feed and faeces in the nature of materials empirically de®ned as lignin by each procedure. Moreover, Van Soest (1994) considered that the most insidious factor affecting recovery is lignin distribution relative to particle size because lignin in feed and faeces tends to be associated with matter of different particle size. While some authors suggest not using lignin as an internal marker (Cochran et al., 1988; Tamminga et al., 1989), or specify that its use should be limited to feeds having more than about 5% lignin in the DM (Van Soest, 1994), others consider that it is possible to use it in certain diets (Krysl et al., 1988; Judkins et al.,
1990). In agreement with the latter results, in our experiment ADL was the best internal marker to predict alfalfa apparent DM digestibility. Several authors have proposed, as an internal marker, the use of the residue of feeds incubated in sacco or in vitro with ruminal liquor for a period long enough to reach their maximum potential degradation (Wilkins, 1969; Cochran et al., 1986; Judkins et al., 1990; Fondevila et al., 1995). In our case, the RUDM provided the best estimate of the apparent DM digestibility for diets based on ryegrass hay. Judkins et al. (1990), working with the residue after 48 or 72 h of ruminal degradation in nylon bags, concluded that these markers provided accurate estimates of digestibility in two of the six diets tested. Fondevila et al. (1995) working with barley straw concluded that the use of rumen undegraded fractions as ratio indicators must be approached with caution because they do not seem to provide accurate estimates across all diets and feeding conditions. We decided to reject IADF and IADL as a result of their negative and variable recoveries. The analytical variations in the extraction of ®bre fractions in the samples after ruminal degradation could be the origin of the variation of the results. Incomplete recoveries of the markers based on ADF or ADL extraction of the residues after 7 days of ruminal degradation agree with the results obtained by others (Lippke et al., 1986; Judkins et al., 1990). Lippke et al. (1986) assumed that variations in sample particle size could explain the bias in ®bre recovery. Indigestible ®bre fractions tend to underestimate digestion of different forages (Judkins et al., 1990; Sunvold and Cochran, 1991). However, some workers have demonstrated the utility of indigestible ®bre residues as an internal marker in
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
certain diets (Krysl et al., 1988; Tamminga et al., 1989; Dove and Coombe, 1992). Faecal recovery rates near to 100% have been observed by several workers (Muntifering, 1982; Melix et al., 1987). The use of Cr2O3 as an external marker to predict faecal output gave good results as also reported by Le Du and Penning (1982) and Furnival et al. (1990). Our experiment showed that by using together RUDM, as an internal marker, and Cr2O3, as an external marker, to predict forage DM intake, the equations obtained presented a low CV (6.4 and 8.0% for ryegrass and alfalfa, respectively), indicating that the predicted values could be considered an accurate estimate of measured intake. The validation allowed us to obtain, in both diets, estimates very close to measured DM intakes. Even though the standard errors of the estimates were higher than standard errors of the measured DM intakes (Table 4), the use of these markers allowed Ferret et al. (1998) to obtain accurate intake estimates by correcting errors in the diagnosis of pregnancy, thereby decreasing the variation in the values of DM intake. In fact, the use of markers to individualize the intake enabled the authors to con®rm the effect of forage type on DM intake by ewes during late pregnancy and moreover revealed the effect of litter size that was not detected when the voluntary DM intake was recorded with ewes housed in groups. 5. Conclusions The joint use of chromic oxide, as an external marker, and the rumen undegraded dry matter, as an internal marker, allowed us to obtain an estimate of forage dry matter intake in dairy ewes fed Italian ryegrass hay or alfalfa hay and supplemented with 0.6 kg/day of concentrate. It is therefore possible to estimate individually the voluntary dry matter intake by dairy ewes kept in groups without altering their social and competitive feeding behaviour, as long as the markers have been tested previously with similar feeds. Acknowledgements Financial support from the European Commission, Directorate General VI (Project CAMAR 8001-CT
151
91-0113) and the ComisioÂn Interministerial de Ciencia y TecnologõÂa of Spain (Project AGF93-0526) is acknowledged. References Association of Official Analytical Chemists, 1990. Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Arlington, VA. Cochran, R.C., Adams, D.C., Wallace, J.L., Galyean, M.L., 1986. Predicting digestibility of different diets with internal markers: evaluation of four potential markers. J. Anim. Sci. 63, 1476± 1483. Cochran, R.C., Vanzant, E.S., DelCurto, T., 1988. Evaluation of internal markers isolated by alkaline hydrogen peroxide incubation and acid detergent lignin extraction. J. Anim. Sci. 66, 3245±3251. Dove, H., Coombe, J.B., 1992. A comparison of methods for estimating supplement intake and diet digestibility in sheep. Proc. Aust. Soc. Anim. Prod. 19, 239±241. Fahey, G.C., Jung, H.G., 1983. Lignin as a marker in digestion studies: a review. J. Anim. Sci. 57, 220±225. Fahey, G.C., McLaren, G.A., Williams, J.E., 1979. Lignin digestibility by lambs fed both low quality and high quality roughages. J. Anim. Sci. 48, 941±946. Ferret, A., Gasa, J., Caja, G., PrioÂ, P., 1998. Voluntary dry matter intake and digesta kinetics of twin or single-bearing Manchega ewes fed Italian ryegrass hay or alfalfa hay in late pregnancy. Anim. Sci. 67, 559±566. Fondevila, M., Castrillo, C., Gasa, J., Guada, J.A., 1995. Rumenundegradable dry matter and neutral detergent fibre as ratio indicators of digestibility in sheep given cereal straw-based diets. J. Agric. Sci. (Camb.) 125, 145±151. Forbes, J.M., 1995. Voluntary Food Intake and Diet Selection in Farm Animals. CAB International, Wallingford, Oxon, 532 pp. Furnival, E.P., Corbett, J.L., Inskip, M.W., 1990. Evaluation of controlled release devices for administration of chromium sesquioxide using fistulated grazing sheep. 1. Variation in marker concentration in faeces. Aust. J. Agric. Res. 41, 969± 975. Goering, H.K., Van Soest, P.J., 1970. Forage fiber analyses (apparatus, reagents, procedures, and some applications). Agric. Handbook No. 379. ARS, USDA, Washington, DC. Greenhalgh, J.F.D., 1982. An introduction to herbage intake measurements. In: Leaver, J.D. (Ed.), Herbage Intake Handbook. British Grassland Institute, Hurley, Maidenhead, Berkshire, pp. 1±10. Judkins, M.B., Krysl, L.J., Barton, R.K., 1990. Estimating diet digestibility: a comparison of 11 techniques across six different diets fed to rams. J. Anim. Sci. 68, 1405±1415. Krysl, L.J., Galyean, M.L., Estell, R.E., Sowell, B.F., 1988. Estimating digestibility and faecal output in lambs using internal and external markers. J. Agric. Sci. (Camb.) 111, 19± 25.
152
A. Ferret et al. / Small Ruminant Research 33 (1999) 145±152
Le Du, Y.L.P., Penning, P.D., 1982. Animal based techniques for estimating herbage intake. In: Leaver, J.D. (Ed.), Herbage Intake Handbook. British Grassland Institute, Hurley, Maidenhead, Berkshire, pp. 37±75. Lippke, H., Ellis, W.C., Jacobs, B.F., 1986. Recovery of indigestible fiber from feces of sheep and cattle on forage diets. J. Dairy Sci. 69, 403±412. Melix, C., Peyraud, J.L., Verite, R., 1987. Utilisation de l"oxyde de chrome chez les vaches laitieÁres pour la preÂvision des quantiteÂs de feÁces eÂmises. 1. Etude des variations du taux de reÂcupeÂration et ses conseÂquences sur l'estimation de la digestibilite et des quantiteÂs ingeÂreÂes de rations d'herbe et d'ensilage de maõÈs. Reprod. Nutr. DeÂvelop. 27(1B), 215±216. Muntifering, R.B., 1982. Evaluation of various lignin assays for determining ruminal digestion of roughages by lambs. J. Anim. Sci. 55, 432±438. Statistical Analysis Systems Institute. 1989. SAS/STAT user's guide: statistics, version 6. SAS Institute Inc., Cary, NC.
Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics: A Biometrical Approach, 2nd ed. McGraw-Hill, New York. Sunvold, G.D., Cochran, R.C., 1991. Technical note: Evaluation of acid detergent lignin, alkaline peroxide lignin, acid insoluble ash, and indigestible acid detergent fiber as internal markers for prediction of alfalfa, bromegrass, and prairie hay digestibility by beef steers. J. Anim. Sci. 69, 4951± 4955. Tamminga, S., Robinson, P.H., Mejis, S., Boer, H., 1989. Feed components as internal markers in digestion studies with dairy cows. Anim. Feed Sci. Technol. 27, 49±57. Van Soest, P.J., 1994. Lignin. In: Nutritional Ecology of the Ruminant, 2nd ed. Cornell University Press, Ithaca, New York, pp. 177±195. Wilkins, R.J., 1969. The potential digestibility of cellulose in forages and faeces. J. Agric. Sci. (Camb.) 73, 57±64.