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Energy intake, heat production and energy and nitrogen balances of sheep and goats fed wheat straw as a sole diet
Livestock Science 125 (2009) 88–91
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Livestock Science j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / l i v s c i
Short communication
Energy intake, heat production and energy and nitrogen balances of sheep and goats fed wheat straw as a sole diet S. El-Meccawi a, M. Kam b, A. Brosh c, A.A. Degen b,⁎ a
Research and Development of Negev Bedouin, PO Box 999, Hura 85730, Israel Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel c Beef Cattle Section, Agricultural Research Organization, Newe Yaar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel b
a r t i c l e
i n f o
Article history: Received 11 November 2008 Received in revised form 15 January 2009 Accepted 23 February 2009 Keywords: Desert adapted sheep and goats Low-quality wheat straw Dry matter intake and digestibility Heat production Energy balance Nitrogen balance
a b s t r a c t Large areas of the Negev desert are used for rain-fed winter cereal production. Consequently, cereal straw is an important dietary component of sheep and goats raised by the Bedouin in the Negev Desert under both grazing and pen-fed conditions. Often, it is the sole feed offered, although it is relatively low in crude protein content and metabolizable energy yield. We determined metabolizable energy intake and heat production in desert adapted fat-tailed Awassi sheep (n = 8; 49.5 ± 6.6 kg) and mixed breed goats (n = 8; 42.6 ± 11.7 kg) when offered only wheat straw ad libitum, and calculated their energy and nitrogen balances. We hypothesized that there is a difference between sheep and goats in the ability to use wheat straw and predicted that goats would be better able to use wheat straw as an energy and nitrogen source than would sheep. Dry matter intakes of the wheat straw by sheep and goats were similar, 43.4 and 42.6 g kg− 0.75 d− 1, respectively, as were apparent dry matter digestibilities, 44.1% and 43.6%, respectively. Metabolizable energy intakes in sheep and goats were also similar, 308.9 and 302.9 kJ kg − 0.75 d− 1, respectively, as were their heat productions, 502.3 and 501.0 kJ kg − 0.75 d− 1, respectively. Sheep and goats were in negative energy balance, and both lost similar amounts of body reserves, 193.6 and 198.1 kJ kg − 0.75 d− 1, respectively. Also, both were in negative nitrogen balances; however, the goats were in a lesser deficit (P b 0.05) than the sheep, 0.161 and 0.196 g kg − 0.75 d− 1, respectively. Therefore, our predictions were partially confirmed in that the goats were better able to use the nitrogen but not the energy when consuming low-quality wheat straw. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Large areas of the semi-arid to arid Negev Desert are used for dry-land (rain-fed) winter cereal production, mainly for wheat but also for barley. After harvesting the grain, sheep and goats often graze the remaining stubble, generally from June to September. In addition, the straw is baled and used as fodder. Consequently, wheat stubble and wheat straw are important components in the diet of sheep and goats under ⁎ Corresponding author. Desert Animal Adaptations and Husbandry, Ben-Gurion University, Beer Sheva 84105, Israel. Tel./fax: +972 8 6460515. E-mail address: [email protected] (A.A. Degen). 1871-1413/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2009.02.018
both grazing and penned conditions in the Negev Desert (Landau et al., 2000; Landau et al., 2006). Sheep and goats raised by Bedouin pastoralists in the Negev Desert are generally low producing in terms of milk and offspring output but are well adapted to the climatic conditions and often subsist only on low-quality forage (Degen, 2007). In this study, we determined metabolizable energy intake and heat production in local fat-tailed Awassi sheep and mixed breed goats when offered only wheat straw ad libitum and calculated their energy and nitrogen balances. These local small ruminants are well adapted to desert conditions and are commonly fed low-quality roughages such as wheat straw. In previous studies, it was reported that
S. El-Meccawi et al. / Livestock Science 125 (2009) 88–91 Table 1 Chemical composition of wheat straw offered to sheep and goats as a sole diet. Component Gross energy (kJ g− 1 dry matter) Dry matter (g kg− 1 fresh matter) Crude protein (g kg− 1 dry matter) Ash (g kg− 1 dry matter) NDF (g kg− 1 dry matter) ADF (g kg− 1 dry matter) ADL (g kg− 1 dry matter)
17.8 945 49.3 47 804 495 73
NDF = neutral detergent fiber; ADF = acid detergent fiber; ADL = lignin.
goats had a greater voluntary feed intake, higher apparent dry matter digestibility and higher amount of N recycled to the rumen than sheep when consuming low-quality forage (Wahed and Owen, 1986; Domingue et al., 1991). Furthermore, energy requirements were reduced substantially in small, desert adapted Sinai goats when they were offered only low-quality wheat straw (Brosh et al., 1986). We hypothesized that there is a difference between sheep and goats to use wheat straw and predicted that in this study goats would be better able to use straw as an energy and nitrogen source than would sheep. 2. Materials and methods 2.1. Animals and maintenance Eight fat-tailed Awassi sheep (49.5 ± 6.6 kg) and eight local goats of mixed breed (42.6 ± 11.7 kg), all males and oneyear of age, were selected randomly from a flock raised by Bedouin in the Negev Desert. The animals were maintained individually in metabolic cages and offered wheat straw and water ad libitum. Five days were allowed to adjust to the conditions followed by 10-days of measurements of daily food intake and faeces and urine output. A sample from the diet was taken daily and oven dried at 50 °C to constant mass for analyses. Faeces and orts were pooled every five days so that two samples per animal were obtained. 2.2. Composition and metabolizable energy yield of wheat straw Dry matter composition of the wheat straw, faeces and orts was determined by drying in an oven at 60°C until constant mass. Samples were analyzed for nitrogen (N) content by the Kjeldahl method and for ash by burning at 550°C (AOAC 1984). Crude protein was calculated as 6.25 × N. Neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) were determined as described by Van Soest, Robertson and Lewis (1991), applying a Fiertec System M6 (Tecator, Haganas, Sweden). Gross energy (GE) yields of feed, orts and faecal samples were measured by bomb calorimetry (Gallenkamp, model CBB-370, Loughborough, UK) using benzoic acid as a standard (26,453 J/g, BCS-CRM No. 190n, Bureau of Analyzed Samples Ltd, Bristol, UK). Metabolizable energy intake was determined as described by Degen and Kam (1991) in which it was assumed that metabolizable energy = 0.82 digestible energy (DE).
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2.3. Heat production Rates of oxygen (O2) consumption were measured two times in each sheep and goat; once in the morning and once in the afternoon. An open circuit mask system (Landau et al., 2006) was used in which the flow through the system, regulated by a calibrated flow meter, was 30 l/minute. The concentration of O2 in exhaled air was measured by using an oxygen analyzer based on the paramagnetic principle (Servomex 1400, Crowborough, Sussex, UK). For each measurement day, the N2 recovery of the system was assessed gravimetrically by bleeding 40 g N2 into the mask (McLean and Tobin, 1990). It was found to be in the in the range between 100% and 102%. Measurements were converted to daily energy expenditure using 20.47 kJ per litre of O2 consumed (Nicol and Young, 1990). 2.4. Statistical analysis A t-test was used to compare responses by the sheep and goats and a level of P b 0.05 was chosen as the minimum for significance. Data are presented as means ± SD. 3. Results Gross energy yield of the wheat straw per g dry matter was 17.8 kJ, and the wheat straw contained 49.3 g crude protein (7.9 g N), 804 g NDF, 495 g ADF, 73 g ADL and 47 g ash per kg dry matter (Table 1). Dry matter intake of the wheat straw by goats and sheep were similar, 42.6 g kg− 0.75 d− 1and 43.4 g kg− 0.75 d− 1, respectively, as were dry matter digestibilities, 43.6% and 44.1%, respectively. Metabolizable energy intakes in goats and sheep were also similar, 302.9 and 308.9 kJ kg − 0.75 d− 1, respectively as were O2 consumption 24.54 and 24.47 l kg − 0.75 d− 1, respectively. Consequently, heat productions were similar for the two small ruminants and averaged 501.0 kJ kg − 0.75 d− 1 for goats and 502.3 kJ kg − 0.75 d− 1 for sheep. Goats and sheep were in negative energy balance, and both lost similar amounts of body reserves, 198.1 and 193.6 kJ kg − 0.75 d− 1, respectively (Table 2). Also, both were in negative nitrogen balance, but the sheep were in a greater deficit (P b 0.05) than the goats, 0.196 and 0.161 g kg − 0.75 d− 1, respectively (Table 3).
Table 2 Energy budgets in sheep (n = 8) and goats (n = 8) receiving wheat straw as a sole diet for 10 days. Measurement a
Sheep
Goats
Body mass (kg) DMI (kg d− 1) (g kg− 0.75 d− 1) Apparent DMD (% DMI) MEI (MJ d− 1) MEI (kJ kg− 0.75 d− 1) O2 uptake (l kg− 0.75 d− 1) HP (kJ kg− 0.75 d− 1) ER (g kg− 0.75 d− 1)
49.5 ± 6.6 0.81 ± 0.11 43.4 ± 3.41 44.1 ± 5.2 5.76 ± 0.17 308.7 ± 9.6 24.54 ± 0.98 502.3 ± 20.0 −193.6 ± 15.1
42.6 ± 11.7 0.71 ± 0.11 42.6 ± 3.5 43.6 ± 4.2 5.05 ± 0.29 302.9 ± 20.06 24.47 ± 0.80 501.0 ± 16.3 −198.1 ± 5.8
DMI = dry matter intake; DMD = dry matter digestibility; MEI = metabolizable energy intake; HP = heat production; ER = energy retention. a No measurement was significantly different between sheep and goats.
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4. Discussion Tolkamp and Brouwer (1993) compared sheep and goat digestibilities in 342 data sets and found that “the overall feed digestibility was significantly higher in goats compared with sheep but the difference was very small (+0.8 units). The difference was not affected by species-average digestibility or crude fibre content but was increased at low crude protein content in the diet.” These authors then concluded that “the slightly higher overall feed digestibility in goats compared with sheep is of no practical significance with the possible exception of diets very low in crude protein content.” Furthermore, Wilson (1977) reported that digestibility of high quality forage is similar between goats and sheep, but that goats are better able to digest poor quality forage. Other studies found that the intake of low-quality roughage was higher in goats than in sheep, in part due to their larger rumen pool (Domingue et al., 1991). Consequently, the characteristics of the low-quality wheat straw, high fibres and low protein contents, led us to predict a higher dry matter intake and higher apparent dry matter digestibility by the goats than the sheep. However, these predictions were not supported in this study as dry matter intakes and apparent dry matter digestibilities were similar between the sheep and goats. It should be pointed out that the fat-tailed Awassi are well adapted to Negev Desert conditions and can survive on very low-quality forage. These sheep were able to digest the high fibrous wheat straw as well as the goats and consume a similar amount of dry matter. Total heat production was similar between the sheep and goats when consuming the wheat straw, and was higher in each species than the metabolizable energy intake. Therefore, both small ruminants were using their energy reserves and part of the heat production also included that released by the mobilization of body energy. Furthermore, there was no difference in the rate of use of energy between the sheep and the goats. Very few ruminants can maintain energy balance on solely a wheat straw diet; neither the sheep nor goats in this study were able to do so. Dorper sheep, a breed well adapted to desert conditions, lost 381 g body mass per day when fed solely a wheat straw diet (Degen and Kam 1991). However, Bedouin goats were able to maintain body mass on only wheat straw when watered infrequently (Brosh et al., 1986). They were able to do so by lowering their heat production drastically. In contrast, the sheep and goats in this study did not lower their heat productions and maintained Table 3 Nitrogen (N) budgets in sheep (n = 8) and goats (n = 8) receiving wheat straw as a sole diet for 10 days. Measurement
Sheep
Goats
N intake (g d− 1) Faecal output (kg d− 1) Urine output (kg d− 1) Faecal N (g kg− 1 DM) Urine N (g kg− 1) Faecal N output (g d− 1) Apparent N digestibility (%) Urine N output (g d− 1) N balance (g d− 1) (g kg− 0.75 d− 1)
6.40 ± 6.6 0.45 ± 0.08 1.37 ± 0.88 11.4 ± 0.70 3.60 ± 0.06 5.13 ± 0.66 19.8 ± 5.2 4.93 ± 0.17 − 3.66 ± 0.04 − 0.196 ± 0.04
5.61 ± 11.7 0.40 ± 0.05 1.25 ± 0.33 12.3 ± 0.60 2.71 ± 0.08 a 4.92 ± 0.66 12.3 ± 4.2 3.37 ± 0.29 a − 2.68 ± 0.06 a − 0.161 ± 0.03 a
a
Means between sheep and goats are different (P b 0.05).
relatively high rates, even when compared to sheep and goats on high quality lucerne hay (El-Meccawi et al., 2008). Both sheep and goats were in a negative nitrogen balance; however the rate of loss was greater in the sheep than in the goats (0.196 vs 0.161 g kg− 0.75 d− 1). This difference was mainly due to the lower urine N losses in the goats than in sheep (2.71 vs 3.60 g d− 1, respectively), as losses via faeces were similar in the two species (4.92 vs 5.13 g d− 1, respectively). Therefore, our prediction that the goats would be able to use N more efficiently than the sheep was supported. Goats are able to recycle N to the rumen to a greater extent than sheep and in this way conserve more nitrogen. The conservation of nitrogen on a low protein wheat diet was particularly evident in the desert adapted Bedouin goat (Silanikove et al., 1980; Silanikove 1984; Brosh et al., 1987). In contrast, desert adapted Dorper sheep weighing 40 kg showed a N deficit of about 0.329 g kg− 0.75 d− 1 (Degen and Kam 1991), which was greater than the deficit of the sheep and goats in this study. 4.1. Straw as fodder for sheep and goats The wheat straw is low in crude protein, high in fibres and low in apparent digestibilities and both the sheep and goats were unable to satisfy their energy and N needs, although the goats were able to utilize the N better than the sheep. Therefore, improvements should and can be made in the use of cereal straws as a fodder for small ruminants. Of prime importance is a supplementary protein source, which can increase the intake and digestibility of the cereal straws. Both non-protein (usually urea) and true protein sources can be used with sheep and goats, although responses to the true protein sources are greater (Ben Salem and Smith, 2008). Supplementary legumes can be of particular value in providing crude protein to the small ruminants when low-quality roughages are offered (Goodchild and McMeniman, 1994). Ebong (1995) supplemented tef (Eragrostis tef) straw with leguminous tree species, even though these trees contained high tannin contents, to improve dry matter intakes in sheep. Alicata et al. (2002) suggested feeding sheep a mixture of Atriplex halimus with wheat straw, as A. halimus has a high crude protein content, but also a high salt content which limits its intake. This mixture led to an increase in the total digestible organic matter intake of the diet. Both leguminous trees (El-Meccawi et al., 2008) and halophytes (Benjamin et al., 1995) are readily available in the Negev Desert and can be used as relatively cheap, crude protein sources in conjunction with straw. Acknowledgements We thank Abdullah Abou-Rachbah for technical help and Roger Benjamin for useful advice. We also thank Musa Abu-Kaf for his help and use of his animals and an anonymous referee for helpful suggestions. The study was funded by a grant from the Ministry of Science, Culture and Sport, State of Israel. References Alicata, M.L., Amato, G., Bonanno, A., Leto, G., 2002. In vivo digestibility and nutritive value of Atriplex halimus alone and mixed with wheat straw. J. Agric. Sci. 139, 139–142. AOAC, 1984. Official methods of analysis, 14th edition. Association of Official Analytical Chemists, Arlington, VA.
S. El-Meccawi et al. / Livestock Science 125 (2009) 88–91 Benjamin, R.W., Lavie, Y., Forti, M., Barkai, D., Yonatan, R., Hefetz, Y., 1995. Annual regrowth and edible biomass of two species of Atriplex and of Cassia sturtii after browsing. J. Arid Environ. 29, 63–84. Ben Salem, H., Smith, T., 2008. Feeding strategies to increase small ruminant production in dry environments. Small Rumin. Res. 77, 174–194. Brosh, A., Shkolnik, A., Choshniak, I., 1986. Metabolic effects of infrequent drinking and low-quality feed on Bedouin goats. Ecology 67, 1086–1090. Brosh, A., Shkolnik, A., Choshniak, I., 1987. Effect of infrequent drinking on the nitrogen metabolism of Bedouin goats maintained on different diets. J. Agric. Sci. 109, 165–169. Degen, A.A., 2007. Sheep and goat milk for pastoral societies. Small Rumin. Res. 68, 7–19. Degen, A.A., Kam, M., 1991. Energy intake, nitrogen balance and water influx of Dorper sheep when consuming different diets. J. Arid Environ. 21, 363–369. Domingue, M.F., Dellow, D.W., Barry, T.N., 1991. Voluntary intake and rumen digestion of a low-quality roughage by goats and sheep. J. Agric. Sci. 117, 111–120. Ebong, C., 1995. Acacia nilotica, Acacia seyal and Sesbania sesban as supplements to tef (Eragrostis tef) straw fed to sheep and goats. Small Rumin. Res. 18, 233–238. El-Meccawi, S., Kam, M., Brosh, A., Degen, A.A., 2008. Heat production and energy balance of sheep and goats fed sole diets of Acacia saligna and Medicago sativa. Small Rumin. Res. 75, 199–203. Goodchild, A.V., McMeniman, N.P., 1994. Intake and digestibility of low quality roughages when supplemented with leguminous browse. J. Agric. Sci. 122, 151–160. Landau, S., Barkai, D., Dvash, L., Brosh, A., 2006. Energy expenditure in Awassi sheep grazing wheat stubble in the northern Negev Desert of Israel. Livest. Sci. 105, 265–271.
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Landau, S., Perevolotsky, A., Bonfil, D., Barkau, D., Silanikove, N., 2000. Utilization of low quality resources by small ruminants in Mediterranean agro-pastoral systems: the case of browse and aftermath cereal stubble. Livest. Prod. Sci. 64, 39–49. McLean, J.A., Tobin, G., 1990. Animal and Human Calorimetry. Cambridge University Press, Cambridge, UK. Nicol, A., Young, B.A., 1990. Short-term thermal and metabolic responses of sheep to ruminal cooling: effects of level of cooling and physiological state. Can. J. Anim. Sci. 70, 833–842. Silanikove, N., 1984. Renal excretion of urea in response to changes in nitrogen intake in desert (black Bedouin) and non-desert (Swiss Saanen) goats. Comp. Biochem. Physiol. 79A, 651–654. Silanikove, N., Tagari, H., Shkolnik, A., 1980. Gross energy digestion and urea recycling in the desert black Bedouin goat. Comp. Biochem. Physiol. 67A, 215–218. Tolkamp, B.J., Brouwer, B.O., 1993. Statistical review of digestion in goats compared with other ruminants. Small Rumin. Res. 11, 107–123. Wahed, R.A., Owen, E., 1986. Comparison of sheep and goats under stallfeeding conditions: roughage intake and selection. Anim. Prod. 42, 89–95. Van Soest, P.J., Robertson, J.B., Lewis, B.A., 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74, 3583–3592. Wilson, A.D., 1977. The digestibility and voluntary intake of the leaves of trees and shrubs by sheep and goats. Aust. J. Agric. Res. 28, 501–508.
Contents lists available at ScienceDirect
Livestock Science j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / l i v s c i
Short communication
Energy intake, heat production and energy and nitrogen balances of sheep and goats fed wheat straw as a sole diet S. El-Meccawi a, M. Kam b, A. Brosh c, A.A. Degen b,⁎ a
Research and Development of Negev Bedouin, PO Box 999, Hura 85730, Israel Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel c Beef Cattle Section, Agricultural Research Organization, Newe Yaar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel b
a r t i c l e
i n f o
Article history: Received 11 November 2008 Received in revised form 15 January 2009 Accepted 23 February 2009 Keywords: Desert adapted sheep and goats Low-quality wheat straw Dry matter intake and digestibility Heat production Energy balance Nitrogen balance
a b s t r a c t Large areas of the Negev desert are used for rain-fed winter cereal production. Consequently, cereal straw is an important dietary component of sheep and goats raised by the Bedouin in the Negev Desert under both grazing and pen-fed conditions. Often, it is the sole feed offered, although it is relatively low in crude protein content and metabolizable energy yield. We determined metabolizable energy intake and heat production in desert adapted fat-tailed Awassi sheep (n = 8; 49.5 ± 6.6 kg) and mixed breed goats (n = 8; 42.6 ± 11.7 kg) when offered only wheat straw ad libitum, and calculated their energy and nitrogen balances. We hypothesized that there is a difference between sheep and goats in the ability to use wheat straw and predicted that goats would be better able to use wheat straw as an energy and nitrogen source than would sheep. Dry matter intakes of the wheat straw by sheep and goats were similar, 43.4 and 42.6 g kg− 0.75 d− 1, respectively, as were apparent dry matter digestibilities, 44.1% and 43.6%, respectively. Metabolizable energy intakes in sheep and goats were also similar, 308.9 and 302.9 kJ kg − 0.75 d− 1, respectively, as were their heat productions, 502.3 and 501.0 kJ kg − 0.75 d− 1, respectively. Sheep and goats were in negative energy balance, and both lost similar amounts of body reserves, 193.6 and 198.1 kJ kg − 0.75 d− 1, respectively. Also, both were in negative nitrogen balances; however, the goats were in a lesser deficit (P b 0.05) than the sheep, 0.161 and 0.196 g kg − 0.75 d− 1, respectively. Therefore, our predictions were partially confirmed in that the goats were better able to use the nitrogen but not the energy when consuming low-quality wheat straw. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Large areas of the semi-arid to arid Negev Desert are used for dry-land (rain-fed) winter cereal production, mainly for wheat but also for barley. After harvesting the grain, sheep and goats often graze the remaining stubble, generally from June to September. In addition, the straw is baled and used as fodder. Consequently, wheat stubble and wheat straw are important components in the diet of sheep and goats under ⁎ Corresponding author. Desert Animal Adaptations and Husbandry, Ben-Gurion University, Beer Sheva 84105, Israel. Tel./fax: +972 8 6460515. E-mail address: [email protected] (A.A. Degen). 1871-1413/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.livsci.2009.02.018
both grazing and penned conditions in the Negev Desert (Landau et al., 2000; Landau et al., 2006). Sheep and goats raised by Bedouin pastoralists in the Negev Desert are generally low producing in terms of milk and offspring output but are well adapted to the climatic conditions and often subsist only on low-quality forage (Degen, 2007). In this study, we determined metabolizable energy intake and heat production in local fat-tailed Awassi sheep and mixed breed goats when offered only wheat straw ad libitum and calculated their energy and nitrogen balances. These local small ruminants are well adapted to desert conditions and are commonly fed low-quality roughages such as wheat straw. In previous studies, it was reported that
S. El-Meccawi et al. / Livestock Science 125 (2009) 88–91 Table 1 Chemical composition of wheat straw offered to sheep and goats as a sole diet. Component Gross energy (kJ g− 1 dry matter) Dry matter (g kg− 1 fresh matter) Crude protein (g kg− 1 dry matter) Ash (g kg− 1 dry matter) NDF (g kg− 1 dry matter) ADF (g kg− 1 dry matter) ADL (g kg− 1 dry matter)
17.8 945 49.3 47 804 495 73
NDF = neutral detergent fiber; ADF = acid detergent fiber; ADL = lignin.
goats had a greater voluntary feed intake, higher apparent dry matter digestibility and higher amount of N recycled to the rumen than sheep when consuming low-quality forage (Wahed and Owen, 1986; Domingue et al., 1991). Furthermore, energy requirements were reduced substantially in small, desert adapted Sinai goats when they were offered only low-quality wheat straw (Brosh et al., 1986). We hypothesized that there is a difference between sheep and goats to use wheat straw and predicted that in this study goats would be better able to use straw as an energy and nitrogen source than would sheep. 2. Materials and methods 2.1. Animals and maintenance Eight fat-tailed Awassi sheep (49.5 ± 6.6 kg) and eight local goats of mixed breed (42.6 ± 11.7 kg), all males and oneyear of age, were selected randomly from a flock raised by Bedouin in the Negev Desert. The animals were maintained individually in metabolic cages and offered wheat straw and water ad libitum. Five days were allowed to adjust to the conditions followed by 10-days of measurements of daily food intake and faeces and urine output. A sample from the diet was taken daily and oven dried at 50 °C to constant mass for analyses. Faeces and orts were pooled every five days so that two samples per animal were obtained. 2.2. Composition and metabolizable energy yield of wheat straw Dry matter composition of the wheat straw, faeces and orts was determined by drying in an oven at 60°C until constant mass. Samples were analyzed for nitrogen (N) content by the Kjeldahl method and for ash by burning at 550°C (AOAC 1984). Crude protein was calculated as 6.25 × N. Neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) were determined as described by Van Soest, Robertson and Lewis (1991), applying a Fiertec System M6 (Tecator, Haganas, Sweden). Gross energy (GE) yields of feed, orts and faecal samples were measured by bomb calorimetry (Gallenkamp, model CBB-370, Loughborough, UK) using benzoic acid as a standard (26,453 J/g, BCS-CRM No. 190n, Bureau of Analyzed Samples Ltd, Bristol, UK). Metabolizable energy intake was determined as described by Degen and Kam (1991) in which it was assumed that metabolizable energy = 0.82 digestible energy (DE).
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2.3. Heat production Rates of oxygen (O2) consumption were measured two times in each sheep and goat; once in the morning and once in the afternoon. An open circuit mask system (Landau et al., 2006) was used in which the flow through the system, regulated by a calibrated flow meter, was 30 l/minute. The concentration of O2 in exhaled air was measured by using an oxygen analyzer based on the paramagnetic principle (Servomex 1400, Crowborough, Sussex, UK). For each measurement day, the N2 recovery of the system was assessed gravimetrically by bleeding 40 g N2 into the mask (McLean and Tobin, 1990). It was found to be in the in the range between 100% and 102%. Measurements were converted to daily energy expenditure using 20.47 kJ per litre of O2 consumed (Nicol and Young, 1990). 2.4. Statistical analysis A t-test was used to compare responses by the sheep and goats and a level of P b 0.05 was chosen as the minimum for significance. Data are presented as means ± SD. 3. Results Gross energy yield of the wheat straw per g dry matter was 17.8 kJ, and the wheat straw contained 49.3 g crude protein (7.9 g N), 804 g NDF, 495 g ADF, 73 g ADL and 47 g ash per kg dry matter (Table 1). Dry matter intake of the wheat straw by goats and sheep were similar, 42.6 g kg− 0.75 d− 1and 43.4 g kg− 0.75 d− 1, respectively, as were dry matter digestibilities, 43.6% and 44.1%, respectively. Metabolizable energy intakes in goats and sheep were also similar, 302.9 and 308.9 kJ kg − 0.75 d− 1, respectively as were O2 consumption 24.54 and 24.47 l kg − 0.75 d− 1, respectively. Consequently, heat productions were similar for the two small ruminants and averaged 501.0 kJ kg − 0.75 d− 1 for goats and 502.3 kJ kg − 0.75 d− 1 for sheep. Goats and sheep were in negative energy balance, and both lost similar amounts of body reserves, 198.1 and 193.6 kJ kg − 0.75 d− 1, respectively (Table 2). Also, both were in negative nitrogen balance, but the sheep were in a greater deficit (P b 0.05) than the goats, 0.196 and 0.161 g kg − 0.75 d− 1, respectively (Table 3).
Table 2 Energy budgets in sheep (n = 8) and goats (n = 8) receiving wheat straw as a sole diet for 10 days. Measurement a
Sheep
Goats
Body mass (kg) DMI (kg d− 1) (g kg− 0.75 d− 1) Apparent DMD (% DMI) MEI (MJ d− 1) MEI (kJ kg− 0.75 d− 1) O2 uptake (l kg− 0.75 d− 1) HP (kJ kg− 0.75 d− 1) ER (g kg− 0.75 d− 1)
49.5 ± 6.6 0.81 ± 0.11 43.4 ± 3.41 44.1 ± 5.2 5.76 ± 0.17 308.7 ± 9.6 24.54 ± 0.98 502.3 ± 20.0 −193.6 ± 15.1
42.6 ± 11.7 0.71 ± 0.11 42.6 ± 3.5 43.6 ± 4.2 5.05 ± 0.29 302.9 ± 20.06 24.47 ± 0.80 501.0 ± 16.3 −198.1 ± 5.8
DMI = dry matter intake; DMD = dry matter digestibility; MEI = metabolizable energy intake; HP = heat production; ER = energy retention. a No measurement was significantly different between sheep and goats.
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4. Discussion Tolkamp and Brouwer (1993) compared sheep and goat digestibilities in 342 data sets and found that “the overall feed digestibility was significantly higher in goats compared with sheep but the difference was very small (+0.8 units). The difference was not affected by species-average digestibility or crude fibre content but was increased at low crude protein content in the diet.” These authors then concluded that “the slightly higher overall feed digestibility in goats compared with sheep is of no practical significance with the possible exception of diets very low in crude protein content.” Furthermore, Wilson (1977) reported that digestibility of high quality forage is similar between goats and sheep, but that goats are better able to digest poor quality forage. Other studies found that the intake of low-quality roughage was higher in goats than in sheep, in part due to their larger rumen pool (Domingue et al., 1991). Consequently, the characteristics of the low-quality wheat straw, high fibres and low protein contents, led us to predict a higher dry matter intake and higher apparent dry matter digestibility by the goats than the sheep. However, these predictions were not supported in this study as dry matter intakes and apparent dry matter digestibilities were similar between the sheep and goats. It should be pointed out that the fat-tailed Awassi are well adapted to Negev Desert conditions and can survive on very low-quality forage. These sheep were able to digest the high fibrous wheat straw as well as the goats and consume a similar amount of dry matter. Total heat production was similar between the sheep and goats when consuming the wheat straw, and was higher in each species than the metabolizable energy intake. Therefore, both small ruminants were using their energy reserves and part of the heat production also included that released by the mobilization of body energy. Furthermore, there was no difference in the rate of use of energy between the sheep and the goats. Very few ruminants can maintain energy balance on solely a wheat straw diet; neither the sheep nor goats in this study were able to do so. Dorper sheep, a breed well adapted to desert conditions, lost 381 g body mass per day when fed solely a wheat straw diet (Degen and Kam 1991). However, Bedouin goats were able to maintain body mass on only wheat straw when watered infrequently (Brosh et al., 1986). They were able to do so by lowering their heat production drastically. In contrast, the sheep and goats in this study did not lower their heat productions and maintained Table 3 Nitrogen (N) budgets in sheep (n = 8) and goats (n = 8) receiving wheat straw as a sole diet for 10 days. Measurement
Sheep
Goats
N intake (g d− 1) Faecal output (kg d− 1) Urine output (kg d− 1) Faecal N (g kg− 1 DM) Urine N (g kg− 1) Faecal N output (g d− 1) Apparent N digestibility (%) Urine N output (g d− 1) N balance (g d− 1) (g kg− 0.75 d− 1)
6.40 ± 6.6 0.45 ± 0.08 1.37 ± 0.88 11.4 ± 0.70 3.60 ± 0.06 5.13 ± 0.66 19.8 ± 5.2 4.93 ± 0.17 − 3.66 ± 0.04 − 0.196 ± 0.04
5.61 ± 11.7 0.40 ± 0.05 1.25 ± 0.33 12.3 ± 0.60 2.71 ± 0.08 a 4.92 ± 0.66 12.3 ± 4.2 3.37 ± 0.29 a − 2.68 ± 0.06 a − 0.161 ± 0.03 a
a
Means between sheep and goats are different (P b 0.05).
relatively high rates, even when compared to sheep and goats on high quality lucerne hay (El-Meccawi et al., 2008). Both sheep and goats were in a negative nitrogen balance; however the rate of loss was greater in the sheep than in the goats (0.196 vs 0.161 g kg− 0.75 d− 1). This difference was mainly due to the lower urine N losses in the goats than in sheep (2.71 vs 3.60 g d− 1, respectively), as losses via faeces were similar in the two species (4.92 vs 5.13 g d− 1, respectively). Therefore, our prediction that the goats would be able to use N more efficiently than the sheep was supported. Goats are able to recycle N to the rumen to a greater extent than sheep and in this way conserve more nitrogen. The conservation of nitrogen on a low protein wheat diet was particularly evident in the desert adapted Bedouin goat (Silanikove et al., 1980; Silanikove 1984; Brosh et al., 1987). In contrast, desert adapted Dorper sheep weighing 40 kg showed a N deficit of about 0.329 g kg− 0.75 d− 1 (Degen and Kam 1991), which was greater than the deficit of the sheep and goats in this study. 4.1. Straw as fodder for sheep and goats The wheat straw is low in crude protein, high in fibres and low in apparent digestibilities and both the sheep and goats were unable to satisfy their energy and N needs, although the goats were able to utilize the N better than the sheep. Therefore, improvements should and can be made in the use of cereal straws as a fodder for small ruminants. Of prime importance is a supplementary protein source, which can increase the intake and digestibility of the cereal straws. Both non-protein (usually urea) and true protein sources can be used with sheep and goats, although responses to the true protein sources are greater (Ben Salem and Smith, 2008). Supplementary legumes can be of particular value in providing crude protein to the small ruminants when low-quality roughages are offered (Goodchild and McMeniman, 1994). Ebong (1995) supplemented tef (Eragrostis tef) straw with leguminous tree species, even though these trees contained high tannin contents, to improve dry matter intakes in sheep. Alicata et al. (2002) suggested feeding sheep a mixture of Atriplex halimus with wheat straw, as A. halimus has a high crude protein content, but also a high salt content which limits its intake. This mixture led to an increase in the total digestible organic matter intake of the diet. Both leguminous trees (El-Meccawi et al., 2008) and halophytes (Benjamin et al., 1995) are readily available in the Negev Desert and can be used as relatively cheap, crude protein sources in conjunction with straw. Acknowledgements We thank Abdullah Abou-Rachbah for technical help and Roger Benjamin for useful advice. We also thank Musa Abu-Kaf for his help and use of his animals and an anonymous referee for helpful suggestions. The study was funded by a grant from the Ministry of Science, Culture and Sport, State of Israel. References Alicata, M.L., Amato, G., Bonanno, A., Leto, G., 2002. In vivo digestibility and nutritive value of Atriplex halimus alone and mixed with wheat straw. J. Agric. Sci. 139, 139–142. AOAC, 1984. Official methods of analysis, 14th edition. Association of Official Analytical Chemists, Arlington, VA.
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