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Archives of Animal Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gaan20
Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits ab
b
a
Ahmed A.A. Abdel-Wareth , Saskia Kehraus , Abdalla H.H. Ali , a
Zeinhom S.H. Ismail & Karl-Heinz Südekum
b
a
Department of Animal and Poultry Production, Faculty of Agriculture, South Valley University, Qena, Egypt b
Institute of Animal Science, University of Bonn, Bonn, Germany Published online: 14 Jan 2015.
Click for updates To cite this article: Ahmed A.A. Abdel-Wareth, Saskia Kehraus, Abdalla H.H. Ali, Zeinhom S.H. Ismail & Karl-Heinz Südekum (2015) Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits, Archives of Animal Nutrition, 69:1, 69-78, DOI: 10.1080/1745039X.2014.1002672 To link to this article: http://dx.doi.org/10.1080/1745039X.2014.1002672
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Downloaded by [University of Montana] at 15:12 06 April 2015
Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Archives of Animal Nutrition, 2015 Vol. 69, No. 1, 69–78, http://dx.doi.org/10.1080/1745039X.2014.1002672
Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits Ahmed A.A. Abdel-Waretha,b, Saskia Kehrausb, Abdalla H.H. Alia, Zeinhom S.H. Ismaila and Karl-Heinz Südekumb* a
Downloaded by [University of Montana] at 15:12 06 April 2015
Department of Animal and Poultry Production, Faculty of Agriculture, South Valley University, Qena, Egypt; bInstitute of Animal Science, University of Bonn, Bonn, Germany (Received 3 October 2014; accepted 18 December 2014) The aim of the study was to evaluate the effect of a temporary quantitative feed restriction on growth performance, nutrient digestibility and carcass criteria of rabbits. A total of 80 weaned male Californian rabbits (30 d of age) were randomly assigned to four treatments of 20 rabbits each. The Control group was fed ad libitum during the whole experimental period (days 30–72 of age). For the three restricted fed groups the feed intake was reduced by 15%, 30% and 45% compared to the Control group, respectively. The feed restriction was applied after weaning and lasted for 21 d. Thereafter, at 51 d of age, in all treatments the feed supply returned to ad libitum intake till 72 d of age (AL period). The feed restriction decreased the body weight gain of rabbits (during the restriction period and the whole experimental period, p < 0.001) and improved feed conversion ratio during all tested periods (p < 0.001). In the AL period, the daily body weight gain of all groups was similar. After the AL period, the digestibility of all measured nutrients was significantly higher for animals fed restrictively. Furthermore, feed restrictions significantly decreased the proportion of perirenal and scapular fat and increased relative weight and length of the gastrointestinal tract. Therefore, it can be concluded that the applied feed restriction improved feed conversion, nutrient digestibility and reduced fat at the slaughter age of Californian rabbits, but the reduced body weight gain could not be compensated by a subsequent ad libitum feeding for 3 weeks. Keywords: carcass quality; digestibility; feed restriction; performance; rabbit feeding
1. Introduction Worldwide, consumption of rabbit meat continues to rise in both developed and developing countries. World rabbit meat production increased to 1.83 million tonnes in 2012 (FAOSTAT 2013) and currently the leading producer of rabbit meat is China with 735 · 103 t/year. Rabbit meat production is rising in Egypt and has reached 56 · 103 t/year, while in Germany it amounted to about 38 · 103 t/year. Rabbit meat is characterised by low fat content, less saturated fatty acids and low cholesterol contents (Hernández 2008). These nutritional qualities are of great value for the meat industry and consumers. Recently, rabbit production in Egypt has developed rapidly, most notably using Californian rabbits, to meet an increased demand for fresh meat for human consumption as well as a source of extra income. Generally, rabbits for meat production reach 50–55% of their adult weight within 9–10 weeks of age (Eiben et al. 2001). A possible nutritional strategy to reduce feed costs and mortality is a quantitative feed restriction, which leads to slower growth but meat quality and feed *Corresponding author. Email: [email protected] © 2015 Taylor & Francis
Downloaded by [University of Montana] at 15:12 06 April 2015
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conversion ratio are improved, particularly when the rabbits are fed again ad libitum, as compensatory growth occurs (Gidenne et al. 2012). Moreover, this feed restriction strategy can be used for different periods (from 1 to 3 weeks after weaning) or at different levels of restriction (as percentage of ad libitum intake) (Di Meo et al. 2007). During feed restriction, an improved feed conversion ratio (Dalle Zotte et al. 2005) and improved gut integrity (Di Meo et al. 2007; Gidenne et al. 2012) may be achieved. However, rabbit performance and carcass traits are the main variables commonly used to evaluate the production process when assessing alternative feeding strategies. The effects of feed restriction strategies have been studied with regard to digestive health and mortality as well as morbidity of growing commercial French breeding rabbits (Gidenne et al. 2009, 2012), on growth of Dutch rabbits (Akpobasa 2013) and on reproductive performance of New Zealand White rabbit does (Eiben et al. 2001). The results were variable and depended on the specific breeding situation, rabbit breed or strain. No information is available about the optimum feed restriction level relative to growth performance, nutrient digestibility and carcass traits during the first growing period of Californian rabbits. Thus, the objective of this study was to examine the effects of quantitative linear restrictions of feed intake on growth performance, nutrient digestibility, carcass characteristics and on percentage of internal organs of growing male Californian rabbits.
2. Materials and methods 2.1. Experimental animals, design and management The present study was conducted at the rabbit Research Farm of the Animal and Poultry Production Department, Faculty of Agriculture of the South Valley University, Egypt. A completely randomised design was used for investigating an intensive reduction of feed intake. A total of 80 weaned male Californian rabbits (weaned at 30 d of age) were randomly assigned to four treatments of 20 rabbits each (n = 20). The rabbits of the Control group were fed ad libitum from 30 to 72 d of age. The other three groups were fed restrictively, where the feed intake was reduced by 15%, 30% and 45% relative to the Control group (represents 100%) (Groups R15, R30 and R45, respectively). The feed restriction was applied after weaning and lasted for 21 d. When the rabbits of Groups R15, R30 and R45 reached 51 d of age, also their feed supply returned to ad libitum intake till 72 d of age (AL period). Rabbits were reared individually in cages of galvanised wire net (width × length × height: 40 cm × 50 cm × 30 cm), equipped with an automatic drinker and a manual feeder. Ambient temperature was maintained at 22°C with a 12-h light/dark cycle. Fresh tap water was available for ad libitum intake via stainless steel nipples located inside each cage. During the total experimental period of 42 d, rabbits were housed under the same managerial, hygienic and environmental conditions. Throughout the trial, the rabbits were handled according to the principles for the care of experimental animals (Lebas et al. 1984), and the experiment was approved by the Committee of Ethics of the Animal and Poultry Production Department of the South Valley University, Egypt. During the whole experiment, the rabbits were subjected to regular inspections for health and body condition. The assessments of body condition were carried out by touching the ribs, pelvis and spine of the rabbits. Ingredients, chemical composition and the energy value of the experimental diets are presented in Table 1. During the whole experiment, animals of all treatments received the same diet that was formulated to meet the standard nutritional requirements for growing
Archives of Animal Nutrition Table 1.
Ingredients and chemical composition of the experimental diet of growing male rabbits.
Ingredients
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71
Maize grain Wheat bran Soybean meal (44% CP) Wheat straw Lucerne hay Rice bran Linseed straw Sunflower meal Lime stone Sodium chloride Vitamins and minerals premix§ DL-Methionine
Contents [%] 32.0 20.0 18.0 12.0 5.0 5.0 2.8 2.5 2.0 0.3 0.3 0.1
Chemical composition (analysed) Dry matter[%] Ash [%] Crude protein [%] aNDFom† [%] ADFom‡ [%] Ether extract [%] Sugar [%] Starch [%] Gross energy [MJ/kg] Calcium [%] Phosphorus [%] Lysine [%] Methionine [%]
Contents 91.4 9.8 17.0 30.6 16.7 2.9 4.0 30.5 18.2 1.3 0.86 0.60 0.41
Notes: §Vitamin and mineral premix provided per kg of diet: vitamin A, 10.000 IU; vitamin D3, 900 IU; vitamin E, 50 mg; vitamin K, 2 mg; vitamin B1, 2 mg; folic acid, 5 mg; pantothenic acid, 20 mg; vitamin B6, 2 mg; choline, 1.2 g; vitamin B12, 10 µg; niacin, 50 mg; biotin, 0.2 mg; Cu, 0.1 mg; Fe, 75 mg; Mn, 8.5 mg; Zn, 70 mg; † aNDFom, Neutral detergent fibre amylase treated, exclusive residual ash; ‡ADFom, Acid detergent fibre, exclusive residual ash.
meat-type rabbits (Lebas 2004). The mean gross energy and crude protein concentrations were 18.2 MJ/kg and 170 g/kg, respectively. Individual feed intake was recorded daily at 8:00 h. Each rabbit was weighed weekly at the same day at 07:00 h. Feed conversion ratio was calculated by dividing daily feed consumption by average daily body weight gain. Mortality was recorded as it occurred and any signs of diarrhoea were documented daily.
2.2. Digestibility trial At the end of the experiment, a digestibility period was introduced that lasted 4 d. Within each treatment, 10 rabbits (n = 10) were randomly selected and individually housed in metabolic cages that allowed separation of faeces and urine. Every day at the same time, the animals were fed the pelleted experimental diet and had always free access to clean drinking water. Feed residues and faeces were collected every day and weighed to the nearest 1 g using an analytical scale. During the digestibility trial, caecotrophy was not prevented because the feeding habit should be as normal as possible. Moreover, coprophagy may improve nutrient economy (Hörnicke 1981), which may partly alleviate negative effects of reduced feed intake. Faeces were stored frozen, and after thawing samples were dried and ground. The samples prepared in this way were analysed for chemical composition and energy value to calculate digestibility coefficients of nutrients and energy. The digestibility coefficient (DC) of nutrients was calculated according to the following equation: DC ½% ¼ ½ðt f Þ=t 100; where t is the nutrient intake during the collection period [g] and f is the amount of nutrient excreted in faeces [g].
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Downloaded by [University of Montana] at 15:12 06 April 2015
2.3. Chemical analysis Chemical analysis of the samples was done at the Institute of Animal Science, University of Bonn, Germany. The diet and the partially dried faecal samples (at 60°C for 48 h) were ground to pass through a 1-mm screen using a centrifugal mill (KG type ZM1, Retsch, Haan, Germany) and analysed according to the methods of VDLUFA (2012, method numbers in parentheses). Dry matter was determined by oven-drying at 100°C for 24 h (method 3.1). Total nitrogen (N) was estimated by combustion assay (Rapid N cube, Elementar Analysensysteme, Hanau, Germany) (method 4.1.2) and crude protein was expressed as N · 6.25. The contents of neutral detergent fibre (assayed with a heat stable amylase and without sodium sulphite, aNDFom; method 6.5.1) and acid detergent fibre (ADFom; method 6.5.2), using Ankom2000 Fiber Analyzer (ANKOM Technology, Macedon, NY, USA) were both expressed exclusive of residual ash. The content of ether extract was assayed with Soxhlet method (method 5.1.1) after HCl digestion. The gross energy contents of the diet and energy content of faeces were measured using an adiabatic bomb calorimeter (model C 200; IKA, Heitersheim, Germany). Additionally, contents of ash (method 8.1) sugar (method 7.1.2) and starch (method 7.2.1) were quantified in the diet. Calcium was measured using atomic absorption spectrometry and phosphorus was analysed using a colorimetric method (method 10.6.1). Lysine and methionine (after oxidation) were analysed in the diet using an amino acid analyser after hydrolysis (method 4.11.1).
2.4. Carcass measurements Ten representative rabbits from each treatment were selected to obtain similar final body weight (slaughter weight) and slaughtered on termination of the experimental period at 72 d of age. The slaughtering and carcass dissection procedures followed the World Rabbit Science Association (WRSA) recommendations described by Blasco and Ouhayoun (1996). The slaughtered rabbits were bled and then the skin, genitals, head, urinary bladder, gastrointestinal tract and the distal part of legs were removed. Head and full gastrointestinal tract were weighted and expressed as percentage of slaughter weight. Also the length of full gastrointestinal tract was measured. Carcasses with liver, heart, spleen, lungs, kidneys, as well as perirenal and scapular fat were weighed and calculated as per cent of hot carcass. Carcass yield was calculated as per the following: Carcass yield ½% ¼ ðHot carcass weight ½g=Body weight ½gÞ 100: Intermediate part (loin) and hind part of carcass were weighed and expressed as percentage of hot carcass weight. The ratio of the internal organs to the hot carcass weight was calculated as required.
2.5. Statistical analysis The statistical analysis was performed using a completely randomised design and the general linear model (GLM) procedure of SAS 9.2 (SAS Institute 2009). The model included the level of feed restriction only. Orthogonal polynomial contrasts were used to determine the linear and quadratic effects of the increasing restriction of feed intake in the trial. Significance was declared at p ≤ 0.05, p-values less than 0.001 are expressed as ‘< 0.001’ rather than the actual value.
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3. Results 3.1. Feed intake and growth performance During both experimental periods (days 30–51 and 51–72 d of age), the general health status of the rabbits was good. No signs of diarrhoea, idle behaviour and deaths were observed across treatment groups, indicating that rabbit health status and body condition were not compromised by experimental treatments. Rabbit pelvis and ribs easily palpated and felt sharp and the rump area was flat. Data presented in Table 2 show significant differences in feed intake, body weight, body weight gain and feed conversion ratio amongst the various treatments. The feed restriction (during 30–51 d of age) resulted in a linear decrease in daily feed intake (p < 0.001) and therefore a linear effect was observed on body weight and a linear decrease in daily body weight gain (p < 0.001) with feed restriction. The feed conversion ratio was improved and showed a linear response (p < 0.001) with increasing feed restriction. Compared to the ad libitum-fed Control group, the feed conversion ratio of Groups R15, R30 and R45 was improved by 9%, 14% and 24%, respectively. In the AL period (following the restriction period, days 51–72 of age), rabbits of Groups R15, R30 and R45 had a similar daily body weight gain as the Control group, but their body weights at 72 d of age were still lower than for rabbits of the Control group (p < 0.001, Table 2). During the AL period, the previous feed restriction of Groups R15, R30 and R45 resulted in a reduced feed intake (p < 0.001) and linear improvement in feed conversion ratio (p = 0.044). For the whole experimental period of 6 weeks (30–72 d of age), the general health status of the rabbits was also good. There was no mortality observed in the four treatments. For this whole period, the temporary feed restriction caused comparable responses to the performance of rabbits as the restriction period, as a reduced body weight and body weight gain and an improved feed conversion ratio. Table 2. Effects of a temporary feed restriction (days 30 to 51) on the productive performance of growing male rabbits. Restrictively fed groups Control group (fed ad libitum)
R15 (15%)* R30 (30%) R45 (45%)
Body weight [g] 518 528 Day§ 30 Day 51 1330 1300 Day 72 2123 2076 Daily body weight gain [g] Days 30–51 38.7 36.7 Days 51–72 37.7 37.0 Days 30–72 38.2 36.9 Daily feed intake [g] Days 30–51 97.7 83.8 Days 51–72 135 133 Days 30–72 116 109 Feed conversion ratio [g feed/g gain] Days 30–51 2.54 2.30 Days 51–72 3.67 3.62 Days 30–72 3.05 2.96
523 1191 1980
523 1104 1924
SEM# 10 15 22
p-Value† 0.847
Archives of Animal Nutrition Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gaan20
Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits ab
b
a
Ahmed A.A. Abdel-Wareth , Saskia Kehraus , Abdalla H.H. Ali , a
Zeinhom S.H. Ismail & Karl-Heinz Südekum
b
a
Department of Animal and Poultry Production, Faculty of Agriculture, South Valley University, Qena, Egypt b
Institute of Animal Science, University of Bonn, Bonn, Germany Published online: 14 Jan 2015.
Click for updates To cite this article: Ahmed A.A. Abdel-Wareth, Saskia Kehraus, Abdalla H.H. Ali, Zeinhom S.H. Ismail & Karl-Heinz Südekum (2015) Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits, Archives of Animal Nutrition, 69:1, 69-78, DOI: 10.1080/1745039X.2014.1002672 To link to this article: http://dx.doi.org/10.1080/1745039X.2014.1002672
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &
Downloaded by [University of Montana] at 15:12 06 April 2015
Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions
Archives of Animal Nutrition, 2015 Vol. 69, No. 1, 69–78, http://dx.doi.org/10.1080/1745039X.2014.1002672
Effects of temporary intensive feed restriction on performance, nutrient digestibility and carcass criteria of growing male Californian rabbits Ahmed A.A. Abdel-Waretha,b, Saskia Kehrausb, Abdalla H.H. Alia, Zeinhom S.H. Ismaila and Karl-Heinz Südekumb* a
Downloaded by [University of Montana] at 15:12 06 April 2015
Department of Animal and Poultry Production, Faculty of Agriculture, South Valley University, Qena, Egypt; bInstitute of Animal Science, University of Bonn, Bonn, Germany (Received 3 October 2014; accepted 18 December 2014) The aim of the study was to evaluate the effect of a temporary quantitative feed restriction on growth performance, nutrient digestibility and carcass criteria of rabbits. A total of 80 weaned male Californian rabbits (30 d of age) were randomly assigned to four treatments of 20 rabbits each. The Control group was fed ad libitum during the whole experimental period (days 30–72 of age). For the three restricted fed groups the feed intake was reduced by 15%, 30% and 45% compared to the Control group, respectively. The feed restriction was applied after weaning and lasted for 21 d. Thereafter, at 51 d of age, in all treatments the feed supply returned to ad libitum intake till 72 d of age (AL period). The feed restriction decreased the body weight gain of rabbits (during the restriction period and the whole experimental period, p < 0.001) and improved feed conversion ratio during all tested periods (p < 0.001). In the AL period, the daily body weight gain of all groups was similar. After the AL period, the digestibility of all measured nutrients was significantly higher for animals fed restrictively. Furthermore, feed restrictions significantly decreased the proportion of perirenal and scapular fat and increased relative weight and length of the gastrointestinal tract. Therefore, it can be concluded that the applied feed restriction improved feed conversion, nutrient digestibility and reduced fat at the slaughter age of Californian rabbits, but the reduced body weight gain could not be compensated by a subsequent ad libitum feeding for 3 weeks. Keywords: carcass quality; digestibility; feed restriction; performance; rabbit feeding
1. Introduction Worldwide, consumption of rabbit meat continues to rise in both developed and developing countries. World rabbit meat production increased to 1.83 million tonnes in 2012 (FAOSTAT 2013) and currently the leading producer of rabbit meat is China with 735 · 103 t/year. Rabbit meat production is rising in Egypt and has reached 56 · 103 t/year, while in Germany it amounted to about 38 · 103 t/year. Rabbit meat is characterised by low fat content, less saturated fatty acids and low cholesterol contents (Hernández 2008). These nutritional qualities are of great value for the meat industry and consumers. Recently, rabbit production in Egypt has developed rapidly, most notably using Californian rabbits, to meet an increased demand for fresh meat for human consumption as well as a source of extra income. Generally, rabbits for meat production reach 50–55% of their adult weight within 9–10 weeks of age (Eiben et al. 2001). A possible nutritional strategy to reduce feed costs and mortality is a quantitative feed restriction, which leads to slower growth but meat quality and feed *Corresponding author. Email: [email protected] © 2015 Taylor & Francis
Downloaded by [University of Montana] at 15:12 06 April 2015
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A.A.A. Abdel-Wareth et al.
conversion ratio are improved, particularly when the rabbits are fed again ad libitum, as compensatory growth occurs (Gidenne et al. 2012). Moreover, this feed restriction strategy can be used for different periods (from 1 to 3 weeks after weaning) or at different levels of restriction (as percentage of ad libitum intake) (Di Meo et al. 2007). During feed restriction, an improved feed conversion ratio (Dalle Zotte et al. 2005) and improved gut integrity (Di Meo et al. 2007; Gidenne et al. 2012) may be achieved. However, rabbit performance and carcass traits are the main variables commonly used to evaluate the production process when assessing alternative feeding strategies. The effects of feed restriction strategies have been studied with regard to digestive health and mortality as well as morbidity of growing commercial French breeding rabbits (Gidenne et al. 2009, 2012), on growth of Dutch rabbits (Akpobasa 2013) and on reproductive performance of New Zealand White rabbit does (Eiben et al. 2001). The results were variable and depended on the specific breeding situation, rabbit breed or strain. No information is available about the optimum feed restriction level relative to growth performance, nutrient digestibility and carcass traits during the first growing period of Californian rabbits. Thus, the objective of this study was to examine the effects of quantitative linear restrictions of feed intake on growth performance, nutrient digestibility, carcass characteristics and on percentage of internal organs of growing male Californian rabbits.
2. Materials and methods 2.1. Experimental animals, design and management The present study was conducted at the rabbit Research Farm of the Animal and Poultry Production Department, Faculty of Agriculture of the South Valley University, Egypt. A completely randomised design was used for investigating an intensive reduction of feed intake. A total of 80 weaned male Californian rabbits (weaned at 30 d of age) were randomly assigned to four treatments of 20 rabbits each (n = 20). The rabbits of the Control group were fed ad libitum from 30 to 72 d of age. The other three groups were fed restrictively, where the feed intake was reduced by 15%, 30% and 45% relative to the Control group (represents 100%) (Groups R15, R30 and R45, respectively). The feed restriction was applied after weaning and lasted for 21 d. When the rabbits of Groups R15, R30 and R45 reached 51 d of age, also their feed supply returned to ad libitum intake till 72 d of age (AL period). Rabbits were reared individually in cages of galvanised wire net (width × length × height: 40 cm × 50 cm × 30 cm), equipped with an automatic drinker and a manual feeder. Ambient temperature was maintained at 22°C with a 12-h light/dark cycle. Fresh tap water was available for ad libitum intake via stainless steel nipples located inside each cage. During the total experimental period of 42 d, rabbits were housed under the same managerial, hygienic and environmental conditions. Throughout the trial, the rabbits were handled according to the principles for the care of experimental animals (Lebas et al. 1984), and the experiment was approved by the Committee of Ethics of the Animal and Poultry Production Department of the South Valley University, Egypt. During the whole experiment, the rabbits were subjected to regular inspections for health and body condition. The assessments of body condition were carried out by touching the ribs, pelvis and spine of the rabbits. Ingredients, chemical composition and the energy value of the experimental diets are presented in Table 1. During the whole experiment, animals of all treatments received the same diet that was formulated to meet the standard nutritional requirements for growing
Archives of Animal Nutrition Table 1.
Ingredients and chemical composition of the experimental diet of growing male rabbits.
Ingredients
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71
Maize grain Wheat bran Soybean meal (44% CP) Wheat straw Lucerne hay Rice bran Linseed straw Sunflower meal Lime stone Sodium chloride Vitamins and minerals premix§ DL-Methionine
Contents [%] 32.0 20.0 18.0 12.0 5.0 5.0 2.8 2.5 2.0 0.3 0.3 0.1
Chemical composition (analysed) Dry matter[%] Ash [%] Crude protein [%] aNDFom† [%] ADFom‡ [%] Ether extract [%] Sugar [%] Starch [%] Gross energy [MJ/kg] Calcium [%] Phosphorus [%] Lysine [%] Methionine [%]
Contents 91.4 9.8 17.0 30.6 16.7 2.9 4.0 30.5 18.2 1.3 0.86 0.60 0.41
Notes: §Vitamin and mineral premix provided per kg of diet: vitamin A, 10.000 IU; vitamin D3, 900 IU; vitamin E, 50 mg; vitamin K, 2 mg; vitamin B1, 2 mg; folic acid, 5 mg; pantothenic acid, 20 mg; vitamin B6, 2 mg; choline, 1.2 g; vitamin B12, 10 µg; niacin, 50 mg; biotin, 0.2 mg; Cu, 0.1 mg; Fe, 75 mg; Mn, 8.5 mg; Zn, 70 mg; † aNDFom, Neutral detergent fibre amylase treated, exclusive residual ash; ‡ADFom, Acid detergent fibre, exclusive residual ash.
meat-type rabbits (Lebas 2004). The mean gross energy and crude protein concentrations were 18.2 MJ/kg and 170 g/kg, respectively. Individual feed intake was recorded daily at 8:00 h. Each rabbit was weighed weekly at the same day at 07:00 h. Feed conversion ratio was calculated by dividing daily feed consumption by average daily body weight gain. Mortality was recorded as it occurred and any signs of diarrhoea were documented daily.
2.2. Digestibility trial At the end of the experiment, a digestibility period was introduced that lasted 4 d. Within each treatment, 10 rabbits (n = 10) were randomly selected and individually housed in metabolic cages that allowed separation of faeces and urine. Every day at the same time, the animals were fed the pelleted experimental diet and had always free access to clean drinking water. Feed residues and faeces were collected every day and weighed to the nearest 1 g using an analytical scale. During the digestibility trial, caecotrophy was not prevented because the feeding habit should be as normal as possible. Moreover, coprophagy may improve nutrient economy (Hörnicke 1981), which may partly alleviate negative effects of reduced feed intake. Faeces were stored frozen, and after thawing samples were dried and ground. The samples prepared in this way were analysed for chemical composition and energy value to calculate digestibility coefficients of nutrients and energy. The digestibility coefficient (DC) of nutrients was calculated according to the following equation: DC ½% ¼ ½ðt f Þ=t 100; where t is the nutrient intake during the collection period [g] and f is the amount of nutrient excreted in faeces [g].
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2.3. Chemical analysis Chemical analysis of the samples was done at the Institute of Animal Science, University of Bonn, Germany. The diet and the partially dried faecal samples (at 60°C for 48 h) were ground to pass through a 1-mm screen using a centrifugal mill (KG type ZM1, Retsch, Haan, Germany) and analysed according to the methods of VDLUFA (2012, method numbers in parentheses). Dry matter was determined by oven-drying at 100°C for 24 h (method 3.1). Total nitrogen (N) was estimated by combustion assay (Rapid N cube, Elementar Analysensysteme, Hanau, Germany) (method 4.1.2) and crude protein was expressed as N · 6.25. The contents of neutral detergent fibre (assayed with a heat stable amylase and without sodium sulphite, aNDFom; method 6.5.1) and acid detergent fibre (ADFom; method 6.5.2), using Ankom2000 Fiber Analyzer (ANKOM Technology, Macedon, NY, USA) were both expressed exclusive of residual ash. The content of ether extract was assayed with Soxhlet method (method 5.1.1) after HCl digestion. The gross energy contents of the diet and energy content of faeces were measured using an adiabatic bomb calorimeter (model C 200; IKA, Heitersheim, Germany). Additionally, contents of ash (method 8.1) sugar (method 7.1.2) and starch (method 7.2.1) were quantified in the diet. Calcium was measured using atomic absorption spectrometry and phosphorus was analysed using a colorimetric method (method 10.6.1). Lysine and methionine (after oxidation) were analysed in the diet using an amino acid analyser after hydrolysis (method 4.11.1).
2.4. Carcass measurements Ten representative rabbits from each treatment were selected to obtain similar final body weight (slaughter weight) and slaughtered on termination of the experimental period at 72 d of age. The slaughtering and carcass dissection procedures followed the World Rabbit Science Association (WRSA) recommendations described by Blasco and Ouhayoun (1996). The slaughtered rabbits were bled and then the skin, genitals, head, urinary bladder, gastrointestinal tract and the distal part of legs were removed. Head and full gastrointestinal tract were weighted and expressed as percentage of slaughter weight. Also the length of full gastrointestinal tract was measured. Carcasses with liver, heart, spleen, lungs, kidneys, as well as perirenal and scapular fat were weighed and calculated as per cent of hot carcass. Carcass yield was calculated as per the following: Carcass yield ½% ¼ ðHot carcass weight ½g=Body weight ½gÞ 100: Intermediate part (loin) and hind part of carcass were weighed and expressed as percentage of hot carcass weight. The ratio of the internal organs to the hot carcass weight was calculated as required.
2.5. Statistical analysis The statistical analysis was performed using a completely randomised design and the general linear model (GLM) procedure of SAS 9.2 (SAS Institute 2009). The model included the level of feed restriction only. Orthogonal polynomial contrasts were used to determine the linear and quadratic effects of the increasing restriction of feed intake in the trial. Significance was declared at p ≤ 0.05, p-values less than 0.001 are expressed as ‘< 0.001’ rather than the actual value.
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3. Results 3.1. Feed intake and growth performance During both experimental periods (days 30–51 and 51–72 d of age), the general health status of the rabbits was good. No signs of diarrhoea, idle behaviour and deaths were observed across treatment groups, indicating that rabbit health status and body condition were not compromised by experimental treatments. Rabbit pelvis and ribs easily palpated and felt sharp and the rump area was flat. Data presented in Table 2 show significant differences in feed intake, body weight, body weight gain and feed conversion ratio amongst the various treatments. The feed restriction (during 30–51 d of age) resulted in a linear decrease in daily feed intake (p < 0.001) and therefore a linear effect was observed on body weight and a linear decrease in daily body weight gain (p < 0.001) with feed restriction. The feed conversion ratio was improved and showed a linear response (p < 0.001) with increasing feed restriction. Compared to the ad libitum-fed Control group, the feed conversion ratio of Groups R15, R30 and R45 was improved by 9%, 14% and 24%, respectively. In the AL period (following the restriction period, days 51–72 of age), rabbits of Groups R15, R30 and R45 had a similar daily body weight gain as the Control group, but their body weights at 72 d of age were still lower than for rabbits of the Control group (p < 0.001, Table 2). During the AL period, the previous feed restriction of Groups R15, R30 and R45 resulted in a reduced feed intake (p < 0.001) and linear improvement in feed conversion ratio (p = 0.044). For the whole experimental period of 6 weeks (30–72 d of age), the general health status of the rabbits was also good. There was no mortality observed in the four treatments. For this whole period, the temporary feed restriction caused comparable responses to the performance of rabbits as the restriction period, as a reduced body weight and body weight gain and an improved feed conversion ratio. Table 2. Effects of a temporary feed restriction (days 30 to 51) on the productive performance of growing male rabbits. Restrictively fed groups Control group (fed ad libitum)
R15 (15%)* R30 (30%) R45 (45%)
Body weight [g] 518 528 Day§ 30 Day 51 1330 1300 Day 72 2123 2076 Daily body weight gain [g] Days 30–51 38.7 36.7 Days 51–72 37.7 37.0 Days 30–72 38.2 36.9 Daily feed intake [g] Days 30–51 97.7 83.8 Days 51–72 135 133 Days 30–72 116 109 Feed conversion ratio [g feed/g gain] Days 30–51 2.54 2.30 Days 51–72 3.67 3.62 Days 30–72 3.05 2.96
523 1191 1980
523 1104 1924
SEM# 10 15 22
p-Value† 0.847
