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Effects of live weight, maturity and genotype of sheep fed a hay-based diet, on intake, digestion and live weight gain
Livestock Production Science 63 (2000) 291–296 www.elsevier.com / locate / livprodsci
Effects of live weight, maturity and genotype of sheep fed a hay-based diet, on intake, digestion and live weight gain a a, b a A.L.G. Lourenc¸o , A.A. Dias-da-Silva *, A.J.M. Fonseca , J.T. Azevedo a
´ Universidade de Tras-os-Montes e Alto Douro, Department of Animal Production, Apartado 202, 5001 Vila Real Codex, Portugal b ˜ , Rua do Monte, Crasto, ˆ ´ ´ de Vairao Instituto de Ciencias Biomedicas de Abel Salazar, Universidade do Porto, Campus Agrario 4450 Vila do Conde, Portugal Received 21 December 1998; received in revised form 3 June 1999; accepted 14 June 1999
Abstract The effects of initial live weight (LW; 18 and 30 kg), maturity (40 and 65% mature LW) and genotype on dry matter intake (DMI), LW gain (LWG), organic matter digestibility (OMD), rumen outflow rate of solid phase and urinary allantoin-N excretion were examined in 14 and 21 female lambs from the local breed Churra da Terra Quente (CH) and Ile-de-France (IF), respectively. LW at 40 and 65% maturity was 18 and 30 kg and 30 and 49 kg for CH and IF lambs, respectively. Lambs were individually fed coarsely ground meadow hay (4 cm) ad libitum supplemented with a protein concentrate over a period of 12 weeks. DMI (g kg 21 LW 0.75 ) and rumen outflow rate were higher and OMD lower (P , 0.01) in CH than in IF lambs, irrespective of LW or degree of maturity. Daily allantoin-N excretion (mg kg 21 LW) was higher in CH than in IF lambs (P , 0.10) at the same degree of maturity. LWG was unaffected by LW or maturity and was higher in IF than in CH lambs (P , 0.001; 92.3 vs. 47.1 g day 21 ). Regression analysis of LWG on digestible organic matter intake suggests that energy requirements for maintenance of CH lambs are higher than for IF lambs. It is suggested that differences between breeds in digestive ability and outflow rate should be confirmed at the same level of intake. Experiments should also be designed to measure energy retention and more closely estimate energy requirements for maintenance of the two breeds. 2000 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Feed intake; Digestibility; Live weight; Maturity; Genotype
1. Introduction Fibrous feeds moderately lignified are an important feed resource for ruminant animals. For an efficient utilisation of fibrous resources an anaerobic microbial fermentation is required and ruminants *Corresponding author. Tel.: 1351-59-320-409; fax: 1351-59320-629. E-mail address: [email protected] (A.A. Dias-da-Silva)
have developed different strategies to achieve this objective. It is well known that small ruminant species, if allowed, tend to select a more digestible diet or eat more, while large ruminants have a greater ability to utilise poor diets by prolonging feed retention in the forestomach (Van Soest, 1994). Differences between sheep breeds in their ability to both ingest and digest low quality roughage have also been reported. Weyreter and Engelhardt (1984) found that Heidschnucken sheep, a German autoch-
0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00134-7
292
A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
thonous sheep breed, were better able to adapt to a fibrous diet than Merino sheep by increasing the volume of the reticulorumen and prolonging the retention time of fluid and particles, while Blackhead sheep were not able to make such an adaptation. Givens and Moss (1994) reported that Cheviot sheep had greater digestive efficiency than Suffolk3Mule sheep, and Ranilla et al. (1997) found that Spanish Churra showed a higher rate of in situ roughage fermentation than Merino. Churra da Terra Quente (CH) is the most important sheep breed in the northeast region of Portugal. This breed is well adapted to poor quality Mediterranean pastures and to periods of feed scarcity. However, there is no information about its ingestive and digestive ability. Therefore, a study was designed to compare voluntary intake and digestibility of CH sheep with that of a European improved sheep breed (Ile-de-France, IF), as influenced by live weight or degree of maturity. A preliminary account of part of the work reported here ˜ et al., 1998). has already been given (Guimaraes
2. Materials and methods
2.1. Animals, design and management Two groups of CH and three groups of IF lambs were used in this experiment. The initial live weight (LW) and degree of maturity of the lambs are shown in Table 1. All the animals were kept indoors with 18 h light per day in individual pens with slatted floors and free access to water. The barn was well ventilated. The experiment was performed between February and May, 1996. The lambs were fed grass hay ad libitum supplemented with a protein concentrate (75:25 on dry matter basis; Table 2). Before being offered, the hay
Table 2 Chemical composition of the feeds used in the experiment (g kg 21 DM; mean6standard deviation)a Feed
Ash
Crude protein
Neutral-detergent fibre
Hay Concentrate b
69.665.0 96.466.2
63.963.2 313.0616.8
703.2619.2 187.467.6
a
Each value is the mean of 10 observations. 66% soyabean meal130% ground maize14% of a mineral– vitamin mixture. b
was coarsely ground through a 4 cm screen. The concentrate allowance was adjusted weekly according to the total dry matter (DM) intake observed in the previous week. The supplement was offered once a day (08.00 h) and was readily eaten in totality. The hay was offered ad libitum with fresh feed being introduced in the morning after the supplement and in the afternoon at 16.00 h. The troughs were cleaned out each morning and refusals collected and weighed. They represented 15–20% of the hay offered. Voluntary intake and LW gain (LWG) were measured over a period of 12 weeks after an initial period of 2 weeks during which the animals were adapted to the diet. Lambs were weighed at the beginning of the experimental period and subsequently every 2 weeks. Samples of hay and supplement were taken twice each week for DM determination. Refusals were sampled once each week for the same purpose. The dried material was bulked for later chemical analysis. In the 6th, 7th, 8th and 9th weeks of the experimental period one or two lambs from each group were selected at random and moved to metabolic cages to measure the digestibility of the diet by total collection of faeces over 7 days. In total, six animals per group were used for this purpose. Samples of hay, supplement, refusals and faeces were taken
Table 1 Initial live weight (LW; kg), degree of maturity and number of lambs used in the experiment
Initial LW (mean6SD) Degree of maturity (%) Number of lambs Abbreviation
Churra da Terra Quente
Ile de France
18.761.1 40 7 CH 18 / 40
19.561.6 25 7 IF 18 / 25
30.861.4 65 7 CH 30 / 65
30.462.1 40 7 IF 30 / 40
45.563.5 65 7 IF 49 / 65
A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
daily and dried in a forced-air drying oven at 658C for 24 h and bulked over the period. Total collection of urine was also made. About 100 ml of 1 M H 2 SO 4 was added to the urine containers to give a final pH value below 3. The daily urine excreted was made up to 4 l with water, filtered through nylon cloth and sampled (100 ml). Daily samples were stored at 2208C until analysed. Rumen digesta outflow rate of solid phase was also measured in three lambs per group. Chromium (Cr) mordanted hay fibre, prepared as described by ´ et al. (1980), was used as marker. The animals Uden were given a dose of 15–20 g of Cr-mordanted fibre mixed with the concentrate supplement at 08.00 h. Total faeces were collected at 12, 15, 19, 24, 27, 30, 33, 36, 39, 43, 48, 51, 54, 57, 60, 63, 67, 72, 76, 80, 84, 88, 91, 96, 100, 104, 108, 112, 115, 121, 126 and 132 h after the concentrate distribution. Rate constants were calculated as the slope of the straight line obtained by plotting the natural logarithm of the Cr concentration against time for the descending part of the excretion curve (Grovum and Williams, 1973).
293
Urinary allantoin-N was measured by the manual method described by Chen and Gomes (1992). Faecal Cr concentration was determined by atomic absorption spectrophotometry.
2.3. Statistical analyses Data were subjected to standard analyses of variance procedures (Steel and Torrie, 1980) using the statistical package Systat (Wilkinson et al., 1992). When differences were significant treatment means were compared by contrasts (Steel and Torrie, 1980). Daily LWG of each animal was calculated by linear regression of LW on time (12 weeks).
3. Results The chemical analysis of hay refusals (ash, CP and NDF; not shown) did not show any significant difference between groups. Therefore, it can be assumed that selective intake of hay, if any, did not differ between groups. The observed proportion of concentrate in the total intake fell within the range 24.5–25.4 which is very close to the objective.
2.2. Chemical analysis Ground samples (1 mm) of hay, concentrate, refusals and faeces were analysed for ash and Kjeldahl nitrogen (AOAC, 1990). Crude protein (CP) was calculated as Kjeldahl nitrogen36.25. Neutral-detergent fibre (NDF) was determined as described by Robertson and Van Soest (1981).
3.1. Feed intake and live weight gain Data on dry matter intake (DMI) and LWG are presented in Table 3. DMI per kg of metabolic live weight (LW 0.75 ) of the whole diet and hay were
Table 3 Effects of breed, initial live weight (LW) and maturity on dry matter intake and live weight gain Treatment CH 18 / 40 Number of animals
7
SEM CH 30 / 65
IF 18 / 25
IF 30 / 40
7
7
7
F
IF 49 / 65 7
Contrast Breed
LW
Maturity
7
Total dry matter intake g day 21 g kg 21 LW 0.75 g kg 21 LW
698 69.9 32.5
1002 72.1 30.0
731 66.7 30.2
881 61.9 25.5
1143 60.7 22.8
53.8 2.45 0.859
*** * ***
ns ** ***
*** ns ***
*** ns **
Hay dry matter intake g day 21 g kg 21 LW 0.75 g kg 21 LW
524 52.5 24.4
747 53.7 22.4
553 50.4 22.8
665 46.7 19.3
861 45.7 17.2
40.5 1.85 0.650
*** * ***
ns ** ***
*** ns ***
*** ns **
57.0
37.3
97.5
93.3
86.2
11.6
**
***
ns
ns
LW gain (g day 21 )
ns, non-significant; *P , 0.05; **P , 0.01; ***P , 0.001.
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A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
Table 4 Effects of breed, initial live weight (LW) and maturity on total organic matter digestibility (OMD), digestible organic matter intake (DOMI), urinary allantoin-N excretion and rumen fibre outflow rate Treatment
Number of animals Total OMD (kg kg 21 ) Total DOMI (g kg 21 LW 0.75 ) Urinary allantoin-N excretion mg day 21 mg kg 21 LW mg kg 21 DOMI Number of animals Fibre outflow rate (h 21 )
SEM
CH 18 / 40
CH 30 / 65
6 0.565 36.6
5 0.577 38.6
290.5 12.9 842.1 3 0.036
503.0 14.8 970.9
IF 18 / 25 6 0.607 37.3 377.3 14.0 842.1
3 0.042
3 0.022
IF 30 / 40 6 0.601 34.3 430.1 12.0 867.1 3 0.024
F
IF 49 / 65 6 0.599 33.4 523.3 10.1 833.5 3 0.017
6 0.010 1.40 40.4 1.01 73.8 3 0.003
Effects Breed
LW
Maturity
* ns
** ns
ns ns
ns ns
** * ns
ns ns ns
** ns ns
** ns ns
***
***
ns
ns
ns, non-significant; *P , 0.05; **P , 0.01; ***P , 0.001.
significantly higher in CH than in IF lambs (P , 0.01), but were not affected by LW or maturity. When expressed per kg LW, the difference between breeds was still higher (P , 0.001) and the effects of LW or maturity were also highly significant. LWG was significantly higher for the IF breed (P , 0.001) and was unaffected by LW or maturity.
3.2. Digestibility, urinary allantoin-N excretion and rumen fibre outflow rate CH sheep showed lower organic matter digestibility (OMD) values (P , 0.01) and higher fibre outflow rates (P , 0.001) than IF sheep (Table 4). Neither LW nor maturity affected these parameters. The absolute amount of urinary allantoin-N excretion (mg day 21 ) was unaffected by breed but was significantly higher (P , 0.01) in heavier or more mature animals, as expected. No difference was observed due to breed, LW or maturity (P . 0.05) when excretion was expressed per kg LW. However, breed effect on this parameter and on digestible organic matter intake (DOMI) reached significance at P , 0.10. None of the factors affected excretion per kg of DOMI.
4. Discussion The particle size of the hay used in the present study was deliberately chosen to force the animals to eat the same diet and this was successfully achieved.
Under these conditions, it was observed that the DM intake per kg LW or kg LW 0.75 of the native CH breed was clearly higher than in the improved IF breed, particularly when comparisons were made at the same degree of maturity. Among ruminant species, data reviewed by Van Soest (1994) indicate that species having lower body weight at maturity exhibit higher DM intake per unit of weight, which is in agreement with the present data. However, no comparisons between sheep breeds were found in the literature. The decrease in DM intake per kg LW, as LW increased, was expected, since energy requirements for maintenance also decrease per unit of LW, as LW increases (AFRC, 1993). Data on DM intake are consistent with data on rumen fibre outflow rate. Regardless of LW or maturity, which did not affect this parameter, CH lambs showed outflow rates 70 to 85% higher than IF lambs. This is contrary to the findings of Weyreter and Engelhardt (1984), who reported that Heidschnucken sheep, a German autochthonous breed, fed ad libitum on heather or straw, were able to enlarge rumen capacity and prolong retention time of feed particles in the rumen, while Blackhead sheep showed much less of such an adaptation under the same conditions, the response of Merino sheep being intermediate. However, data on LW of animals used were not provided in that report. The large difference in outflow rates between the breeds observed in the present study suggests that the CH breed has an inherently higher rate of passage of feed particles than the IF breed. Assuming that gastroin-
A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
testinal capacity limits the intake and utilisation of forage diets and given the fact that, within a species, smaller animals require more feed per unit of LW for maintenance than larger adult animals (Van Soest, 1994) as was observed in this study, a higher rate of passage of feed particles can be seen as an adaptation mechanism by smaller animals to cope with their higher requirement for feed. The lack of an effect of LW on digestive ability indicates that all lambs were full ruminants at the time the experiment started. Givens and Moss (1994) did not find significant effects of age and LW on digestibility of dried grass, or any interaction between either of these variables and digestibility, although the range of weights of the animals they used was much more limited than in the present study. The lower digestive ability of CH lambs observed in this study is consistent with the higher intake and outflow rate values measured in this breed. Regression of OMD on intake did not reach significance and so breed comparisons at the same level of
295
feeding could not be made. Given the high cell-wall content of the diet used (57.4% NDF) our data suggest that the CH breed does not rely on enhanced ability for fibre digestion as an adaptation mechanism to its natural environment. Differences in digestive ability between sheep breeds were also observed by Givens and Moss (1994), who found that OMD of dried grass was higher in Cheviot than in Suffolk3Mule wethers. As expected, microbial protein supply to the small intestine as assessed by urinary allantoin-N excretion (Chen et al., 1992) was higher in heavier or more mature animals since these animals exhibited higher DMI. The data of this study suggest that the efficiency of microbial protein supply, expressed as mg allantoin-N excreted per kg DOMI, is similar in the two breeds. The tendency for a higher excretion per kg LW observed in CH lambs (P , 0.1) is in agreement with the tendency for a higher DOMI also observed in these animals (P , 0.1). Since DOMI was higher and LWG was almost half in CH than in IF lambs, particularly in those
Fig. 1. Daily live weight gain (LWG; y) versus digestible organic matter intake (DOMI; x) of all lambs used in the experiment.
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A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
having the same degree of initial maturity, the question of a different partition of dietary energy in the two breeds arises. Setting all the individual data of LWG against DOMI (Fig. 1) indicates that estimates of energy requirements for maintenance of the two breeds are different (P , 0.001), the estimate for the CH breed being considerably higher than for the IF breed. However, the variation is large, particularly among CH lambs, and therefore this hypothesis should be examined closely in further studies. It is suggested that differences in digestive ability and outflow rate between these breeds should be confirmed by offering a similar diet at the same level of intake. It is also suggested that ingestive behaviour should be studied, allowing breeds to exhibit their own selective ability when fed roughages ad libitum in the long form. Finally, experiments should be designed to measure energy retention and more closely estimate energy requirements for maintenance of the two breeds.
Acknowledgements A.L.G. Lourenc¸o gratefully acknowledges the ˆ ´ da Ciencia receipt of a scholarship from Ministerio e Tecnologia of Portugal (Grant PRAXIS XXI / BM / 2114 / 94).
References Agricultural and Food Research Council (AFRC), 1993. Energy and Protein Requirements of Ruminants. An Advisory Manual prepared by the AFRC Technical Committee on Responses to Nutrients. CAB International, Wallingford, UK, 159 pp. Association of Official Analytical Chemists (AOAC), 1990.
Official Methods of Analysis, Vol. 1, 14th ed. AOAC, Washington, DC, 684 pp. Chen, X.B., Gomes, M.J., 1992. Estimation of microbial protein supply to sheep and cattle based on urinary excretion of purine derivatives — an overview of the technical details. Occasional Publication. Rowett Research Institute, Bucksburn, Aberdeen, UK, 20 pp. Chen, X.B., Chen, Y.K., Franklin, M.F., Orskov, E.R., Shand, W.J., 1992. The effect of feed intake and body weight on purine derivate excretion and microbial protein supply in sheep. J. Anim. Sci. 70, 1534–1542. Givens, D.I., Moss, A.R., 1994. Effect of breed, age and bodyweight of sheep on the measurement of apparent digestibility of dried grass. Anim. Feed Sci. Technol. 46, 155–162. Grovum, W.L., Williams, V.J., 1973. Rate of passage of digesta in sheep. Differential rates of passage of water and dry matter from the reticulo-rumen, abomasum and caecum and proximal colon. Br. J. Nutr. 30, 231–240. ˜ Guimaraes, A., Dias-da-Silva, A.A., Fonseca, A., Azevedo, J., 1998. Effects of live weight, maturity and genotype of sheep on intake and digestibility of a hay-based diet. In: Book of Abstracts No. 4, EAAP — 49th Annual Meeting, Warsaw, 24–27 August 1998, p. 240. ´ C., Giraldez, ´ ´ Ranilla, M.J., Carro, M., Valdes, F., Lopez, S., 1997. A comparative study of ruminal activity in Churra and Merino sheep offered alfalfa hay. Anim. Sci. 65, 121–128. Robertson, J.B., Van Soest, P.J., 1981. The detergent system of analysis and its application to human foods. In: James, W.P.T., Theander, O. (Eds.), The Analysis of Dietary Fibre in Food. Marcell Dekker, New York, pp. 123–158. Steel, R.G.D., Torrie, J.H., 1980. Principles and Procedures of Statistics. A Biometrical Approach, 2nd ed. McGraw-Hill, New York, 663 pp. ´ P., Colucci, P.E., Van Soest, P.J., 1980. Investigation of Uden, chromium, cerium and cobalt as markers in digesta. Rate of passage studies. J. Sci. Food Agric. 31, 625–632. Van Soest, P.J., 1994. Nutritional Ecology of the Ruminant, 2nd ed., Comstock. Cornell University Press, Ithaca, NY, 476 pp. Weyreter, H., Engelhardt, W.v., 1984. Adaptation of Heidschnucken, Merino and Blackhead sheep to a fibrous roughage diet of poor quality. Can. J. Anim. Sci. 64 (Suppl.), 152–153. Wilkinson, L., Hill, M., Welna, J.P., Birkenbeuel, G.K., 1992. Systat for Windows: Statistics, version 5 ed. Systat Inc., Evanston, IL, 750 pp.
Effects of live weight, maturity and genotype of sheep fed a hay-based diet, on intake, digestion and live weight gain a a, b a A.L.G. Lourenc¸o , A.A. Dias-da-Silva *, A.J.M. Fonseca , J.T. Azevedo a
´ Universidade de Tras-os-Montes e Alto Douro, Department of Animal Production, Apartado 202, 5001 Vila Real Codex, Portugal b ˜ , Rua do Monte, Crasto, ˆ ´ ´ de Vairao Instituto de Ciencias Biomedicas de Abel Salazar, Universidade do Porto, Campus Agrario 4450 Vila do Conde, Portugal Received 21 December 1998; received in revised form 3 June 1999; accepted 14 June 1999
Abstract The effects of initial live weight (LW; 18 and 30 kg), maturity (40 and 65% mature LW) and genotype on dry matter intake (DMI), LW gain (LWG), organic matter digestibility (OMD), rumen outflow rate of solid phase and urinary allantoin-N excretion were examined in 14 and 21 female lambs from the local breed Churra da Terra Quente (CH) and Ile-de-France (IF), respectively. LW at 40 and 65% maturity was 18 and 30 kg and 30 and 49 kg for CH and IF lambs, respectively. Lambs were individually fed coarsely ground meadow hay (4 cm) ad libitum supplemented with a protein concentrate over a period of 12 weeks. DMI (g kg 21 LW 0.75 ) and rumen outflow rate were higher and OMD lower (P , 0.01) in CH than in IF lambs, irrespective of LW or degree of maturity. Daily allantoin-N excretion (mg kg 21 LW) was higher in CH than in IF lambs (P , 0.10) at the same degree of maturity. LWG was unaffected by LW or maturity and was higher in IF than in CH lambs (P , 0.001; 92.3 vs. 47.1 g day 21 ). Regression analysis of LWG on digestible organic matter intake suggests that energy requirements for maintenance of CH lambs are higher than for IF lambs. It is suggested that differences between breeds in digestive ability and outflow rate should be confirmed at the same level of intake. Experiments should also be designed to measure energy retention and more closely estimate energy requirements for maintenance of the two breeds. 2000 Elsevier Science B.V. All rights reserved. Keywords: Sheep; Feed intake; Digestibility; Live weight; Maturity; Genotype
1. Introduction Fibrous feeds moderately lignified are an important feed resource for ruminant animals. For an efficient utilisation of fibrous resources an anaerobic microbial fermentation is required and ruminants *Corresponding author. Tel.: 1351-59-320-409; fax: 1351-59320-629. E-mail address: [email protected] (A.A. Dias-da-Silva)
have developed different strategies to achieve this objective. It is well known that small ruminant species, if allowed, tend to select a more digestible diet or eat more, while large ruminants have a greater ability to utilise poor diets by prolonging feed retention in the forestomach (Van Soest, 1994). Differences between sheep breeds in their ability to both ingest and digest low quality roughage have also been reported. Weyreter and Engelhardt (1984) found that Heidschnucken sheep, a German autoch-
0301-6226 / 00 / $ – see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 99 )00134-7
292
A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
thonous sheep breed, were better able to adapt to a fibrous diet than Merino sheep by increasing the volume of the reticulorumen and prolonging the retention time of fluid and particles, while Blackhead sheep were not able to make such an adaptation. Givens and Moss (1994) reported that Cheviot sheep had greater digestive efficiency than Suffolk3Mule sheep, and Ranilla et al. (1997) found that Spanish Churra showed a higher rate of in situ roughage fermentation than Merino. Churra da Terra Quente (CH) is the most important sheep breed in the northeast region of Portugal. This breed is well adapted to poor quality Mediterranean pastures and to periods of feed scarcity. However, there is no information about its ingestive and digestive ability. Therefore, a study was designed to compare voluntary intake and digestibility of CH sheep with that of a European improved sheep breed (Ile-de-France, IF), as influenced by live weight or degree of maturity. A preliminary account of part of the work reported here ˜ et al., 1998). has already been given (Guimaraes
2. Materials and methods
2.1. Animals, design and management Two groups of CH and three groups of IF lambs were used in this experiment. The initial live weight (LW) and degree of maturity of the lambs are shown in Table 1. All the animals were kept indoors with 18 h light per day in individual pens with slatted floors and free access to water. The barn was well ventilated. The experiment was performed between February and May, 1996. The lambs were fed grass hay ad libitum supplemented with a protein concentrate (75:25 on dry matter basis; Table 2). Before being offered, the hay
Table 2 Chemical composition of the feeds used in the experiment (g kg 21 DM; mean6standard deviation)a Feed
Ash
Crude protein
Neutral-detergent fibre
Hay Concentrate b
69.665.0 96.466.2
63.963.2 313.0616.8
703.2619.2 187.467.6
a
Each value is the mean of 10 observations. 66% soyabean meal130% ground maize14% of a mineral– vitamin mixture. b
was coarsely ground through a 4 cm screen. The concentrate allowance was adjusted weekly according to the total dry matter (DM) intake observed in the previous week. The supplement was offered once a day (08.00 h) and was readily eaten in totality. The hay was offered ad libitum with fresh feed being introduced in the morning after the supplement and in the afternoon at 16.00 h. The troughs were cleaned out each morning and refusals collected and weighed. They represented 15–20% of the hay offered. Voluntary intake and LW gain (LWG) were measured over a period of 12 weeks after an initial period of 2 weeks during which the animals were adapted to the diet. Lambs were weighed at the beginning of the experimental period and subsequently every 2 weeks. Samples of hay and supplement were taken twice each week for DM determination. Refusals were sampled once each week for the same purpose. The dried material was bulked for later chemical analysis. In the 6th, 7th, 8th and 9th weeks of the experimental period one or two lambs from each group were selected at random and moved to metabolic cages to measure the digestibility of the diet by total collection of faeces over 7 days. In total, six animals per group were used for this purpose. Samples of hay, supplement, refusals and faeces were taken
Table 1 Initial live weight (LW; kg), degree of maturity and number of lambs used in the experiment
Initial LW (mean6SD) Degree of maturity (%) Number of lambs Abbreviation
Churra da Terra Quente
Ile de France
18.761.1 40 7 CH 18 / 40
19.561.6 25 7 IF 18 / 25
30.861.4 65 7 CH 30 / 65
30.462.1 40 7 IF 30 / 40
45.563.5 65 7 IF 49 / 65
A.L.G. Lourenc¸o et al. / Livestock Production Science 63 (2000) 291 – 296
daily and dried in a forced-air drying oven at 658C for 24 h and bulked over the period. Total collection of urine was also made. About 100 ml of 1 M H 2 SO 4 was added to the urine containers to give a final pH value below 3. The daily urine excreted was made up to 4 l with water, filtered through nylon cloth and sampled (100 ml). Daily samples were stored at 2208C until analysed. Rumen digesta outflow rate of solid phase was also measured in three lambs per group. Chromium (Cr) mordanted hay fibre, prepared as described by ´ et al. (1980), was used as marker. The animals Uden were given a dose of 15–20 g of Cr-mordanted fibre mixed with the concentrate supplement at 08.00 h. Total faeces were collected at 12, 15, 19, 24, 27, 30, 33, 36, 39, 43, 48, 51, 54, 57, 60, 63, 67, 72, 76, 80, 84, 88, 91, 96, 100, 104, 108, 112, 115, 121, 126 and 132 h after the concentrate distribution. Rate constants were calculated as the slope of the straight line obtained by plotting the natural logarithm of the Cr concentration against time for the descending part of the excretion curve (Grovum and Williams, 1973).
293
Urinary allantoin-N was measured by the manual method described by Chen and Gomes (1992). Faecal Cr concentration was determined by atomic absorption spectrophotometry.
2.3. Statistical analyses Data were subjected to standard analyses of variance procedures (Steel and Torrie, 1980) using the statistical package Systat (Wilkinson et al., 1992). When differences were significant treatment means were compared by contrasts (Steel and Torrie, 1980). Daily LWG of each animal was calculated by linear regression of LW on time (12 weeks).
3. Results The chemical analysis of hay refusals (ash, CP and NDF; not shown) did not show any significant difference between groups. Therefore, it can be assumed that selective intake of hay, if any, did not differ between groups. The observed proportion of concentrate in the total intake fell within the range 24.5–25.4 which is very close to the objective.
2.2. Chemical analysis Ground samples (1 mm) of hay, concentrate, refusals and faeces were analysed for ash and Kjeldahl nitrogen (AOAC, 1990). Crude protein (CP) was calculated as Kjeldahl nitrogen36.25. Neutral-detergent fibre (NDF) was determined as described by Robertson and Van Soest (1981).
3.1. Feed intake and live weight gain Data on dry matter intake (DMI) and LWG are presented in Table 3. DMI per kg of metabolic live weight (LW 0.75 ) of the whole diet and hay were
Table 3 Effects of breed, initial live weight (LW) and maturity on dry matter intake and live weight gain Treatment CH 18 / 40 Number of animals
7
SEM CH 30 / 65
IF 18 / 25
IF 30 / 40
7
7
7
F
IF 49 / 65 7
Contrast Breed
LW
Maturity
7
Total dry matter intake g day 21 g kg 21 LW 0.75 g kg 21 LW
698 69.9 32.5
1002 72.1 30.0
731 66.7 30.2
881 61.9 25.5
1143 60.7 22.8
53.8 2.45 0.859
*** * ***
ns ** ***
*** ns ***
*** ns **
Hay dry matter intake g day 21 g kg 21 LW 0.75 g kg 21 LW
524 52.5 24.4
747 53.7 22.4
553 50.4 22.8
665 46.7 19.3
861 45.7 17.2
40.5 1.85 0.650
*** * ***
ns ** ***
*** ns ***
*** ns **
57.0
37.3
97.5
93.3
86.2
11.6
**
***
ns
ns
LW gain (g day 21 )
ns, non-significant; *P , 0.05; **P , 0.01; ***P , 0.001.
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Table 4 Effects of breed, initial live weight (LW) and maturity on total organic matter digestibility (OMD), digestible organic matter intake (DOMI), urinary allantoin-N excretion and rumen fibre outflow rate Treatment
Number of animals Total OMD (kg kg 21 ) Total DOMI (g kg 21 LW 0.75 ) Urinary allantoin-N excretion mg day 21 mg kg 21 LW mg kg 21 DOMI Number of animals Fibre outflow rate (h 21 )
SEM
CH 18 / 40
CH 30 / 65
6 0.565 36.6
5 0.577 38.6
290.5 12.9 842.1 3 0.036
503.0 14.8 970.9
IF 18 / 25 6 0.607 37.3 377.3 14.0 842.1
3 0.042
3 0.022
IF 30 / 40 6 0.601 34.3 430.1 12.0 867.1 3 0.024
F
IF 49 / 65 6 0.599 33.4 523.3 10.1 833.5 3 0.017
6 0.010 1.40 40.4 1.01 73.8 3 0.003
Effects Breed
LW
Maturity
* ns
** ns
ns ns
ns ns
** * ns
ns ns ns
** ns ns
** ns ns
***
***
ns
ns
ns, non-significant; *P , 0.05; **P , 0.01; ***P , 0.001.
significantly higher in CH than in IF lambs (P , 0.01), but were not affected by LW or maturity. When expressed per kg LW, the difference between breeds was still higher (P , 0.001) and the effects of LW or maturity were also highly significant. LWG was significantly higher for the IF breed (P , 0.001) and was unaffected by LW or maturity.
3.2. Digestibility, urinary allantoin-N excretion and rumen fibre outflow rate CH sheep showed lower organic matter digestibility (OMD) values (P , 0.01) and higher fibre outflow rates (P , 0.001) than IF sheep (Table 4). Neither LW nor maturity affected these parameters. The absolute amount of urinary allantoin-N excretion (mg day 21 ) was unaffected by breed but was significantly higher (P , 0.01) in heavier or more mature animals, as expected. No difference was observed due to breed, LW or maturity (P . 0.05) when excretion was expressed per kg LW. However, breed effect on this parameter and on digestible organic matter intake (DOMI) reached significance at P , 0.10. None of the factors affected excretion per kg of DOMI.
4. Discussion The particle size of the hay used in the present study was deliberately chosen to force the animals to eat the same diet and this was successfully achieved.
Under these conditions, it was observed that the DM intake per kg LW or kg LW 0.75 of the native CH breed was clearly higher than in the improved IF breed, particularly when comparisons were made at the same degree of maturity. Among ruminant species, data reviewed by Van Soest (1994) indicate that species having lower body weight at maturity exhibit higher DM intake per unit of weight, which is in agreement with the present data. However, no comparisons between sheep breeds were found in the literature. The decrease in DM intake per kg LW, as LW increased, was expected, since energy requirements for maintenance also decrease per unit of LW, as LW increases (AFRC, 1993). Data on DM intake are consistent with data on rumen fibre outflow rate. Regardless of LW or maturity, which did not affect this parameter, CH lambs showed outflow rates 70 to 85% higher than IF lambs. This is contrary to the findings of Weyreter and Engelhardt (1984), who reported that Heidschnucken sheep, a German autochthonous breed, fed ad libitum on heather or straw, were able to enlarge rumen capacity and prolong retention time of feed particles in the rumen, while Blackhead sheep showed much less of such an adaptation under the same conditions, the response of Merino sheep being intermediate. However, data on LW of animals used were not provided in that report. The large difference in outflow rates between the breeds observed in the present study suggests that the CH breed has an inherently higher rate of passage of feed particles than the IF breed. Assuming that gastroin-
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testinal capacity limits the intake and utilisation of forage diets and given the fact that, within a species, smaller animals require more feed per unit of LW for maintenance than larger adult animals (Van Soest, 1994) as was observed in this study, a higher rate of passage of feed particles can be seen as an adaptation mechanism by smaller animals to cope with their higher requirement for feed. The lack of an effect of LW on digestive ability indicates that all lambs were full ruminants at the time the experiment started. Givens and Moss (1994) did not find significant effects of age and LW on digestibility of dried grass, or any interaction between either of these variables and digestibility, although the range of weights of the animals they used was much more limited than in the present study. The lower digestive ability of CH lambs observed in this study is consistent with the higher intake and outflow rate values measured in this breed. Regression of OMD on intake did not reach significance and so breed comparisons at the same level of
295
feeding could not be made. Given the high cell-wall content of the diet used (57.4% NDF) our data suggest that the CH breed does not rely on enhanced ability for fibre digestion as an adaptation mechanism to its natural environment. Differences in digestive ability between sheep breeds were also observed by Givens and Moss (1994), who found that OMD of dried grass was higher in Cheviot than in Suffolk3Mule wethers. As expected, microbial protein supply to the small intestine as assessed by urinary allantoin-N excretion (Chen et al., 1992) was higher in heavier or more mature animals since these animals exhibited higher DMI. The data of this study suggest that the efficiency of microbial protein supply, expressed as mg allantoin-N excreted per kg DOMI, is similar in the two breeds. The tendency for a higher excretion per kg LW observed in CH lambs (P , 0.1) is in agreement with the tendency for a higher DOMI also observed in these animals (P , 0.1). Since DOMI was higher and LWG was almost half in CH than in IF lambs, particularly in those
Fig. 1. Daily live weight gain (LWG; y) versus digestible organic matter intake (DOMI; x) of all lambs used in the experiment.
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having the same degree of initial maturity, the question of a different partition of dietary energy in the two breeds arises. Setting all the individual data of LWG against DOMI (Fig. 1) indicates that estimates of energy requirements for maintenance of the two breeds are different (P , 0.001), the estimate for the CH breed being considerably higher than for the IF breed. However, the variation is large, particularly among CH lambs, and therefore this hypothesis should be examined closely in further studies. It is suggested that differences in digestive ability and outflow rate between these breeds should be confirmed by offering a similar diet at the same level of intake. It is also suggested that ingestive behaviour should be studied, allowing breeds to exhibit their own selective ability when fed roughages ad libitum in the long form. Finally, experiments should be designed to measure energy retention and more closely estimate energy requirements for maintenance of the two breeds.
Acknowledgements A.L.G. Lourenc¸o gratefully acknowledges the ˆ ´ da Ciencia receipt of a scholarship from Ministerio e Tecnologia of Portugal (Grant PRAXIS XXI / BM / 2114 / 94).
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