Effect of dietary protein levels and zinc supplementation on growth performance, digestibility, blood constituents and carcass traits of growing rabbits
Published on: 7/27/2017
Author/s : M.S. Ayyat, Al-Sagheer, A.A., Gihan F. Elsisi, H.A. Gabr and G.A. Abd El-Rahman / Animal Production Department, Faculty of Agriculture, Zagazig University, Egypt.
Summary
This study was conducted to investigate the influence of the dietary protein level (low; LP or high; HP) and diet supplemented with zinc on growth performance, nutrients digestibility, blood biochemistry, and carcass traits of growing rabbits. A total of 28 New Zealand White (NZW) male rabbits with an initial body weight of 734.6±14.69 g were randomly divided into 4 treatment groups for 8 weeks feeding trial. Two dietary levels of crude protein, i.e. 14.76 and 18.53% and two levels of zinc oxide (ZnO) 0 and 100 mg /kg diet were used in 2 × 2 factorial design. The results showed that ZnO supplementation caused a significant (P?0.01) increase in final live body weight (FBW), daily body weight gain (DWG), feed conversion ratio (FCR), digestibility coefficients (DM, OM, CP),and nutritive values (DCP, TDN and DE) without significant effects related to its interaction with protein level. However, ZnO supplementation showed insignificant effects in estimated blood parameters dressing percentage and relative weights of liver, kidney, heart, lung and spleen .On the other hand, the final margin was increased with ZnO supplementation in rabbits fed LP and HP diets by 27.17 and 9.23%, respectively. Conclusively, the results revealed that fortification of low or high protein diet with ZnO at level of 100 mg/kg could significantly enhance the growth performance, and nutrients digestibility of growing rabbit without harmful effect on blood constituents. Furthermore, using ZnO in the growing rabbit diets (LP or HP) was more economical than the non-supplemented diets.
Key words: Rabbits, Zinc oxide, growth performance, digestibility, blood biochemistry.
Introduction
In developing countries, rabbits are an excellent and economical producer animals for protein to satisfy the ever-increasing demand human needs (Nehad et al., 2009). Feed is the major item of cost in the animal production. In particular, protein represents a substantial cost but it is considered the most important component in the ration as the high-protein feed being viewed as superior to a lower protein one(Cunha and Cheeke, 2012).
A protein deficiency, caused by either one or more limiting amino acids or an overall inadequate consumption of protein, will result in decreases in some parameters such as growth rate, N retention, feed consumption and utilization (Church, 1991). Several nutritional solutions have been adopted with low-protein diets to improve nutrient utilization with economic efficiency like supplementation of commercial products of amino acids and enzymes (Alagawany et al., 2014; Alagawany et al., 2016).
Zinc (Zn) is an essential nutrient required for many physiological functions including acid base balance, nutrient metabolism ,polymeric organization of macromolecules like DNA and RNA, protein synthesis, cell division besides immune and antioxidant function (Shay and Mangian, 2000; Lukác and Massányi, 2007; García-Contreras et al., 2011). Additionally, Zn has both structural and catalytic functions in more than 200 metalloenzymes (McCall et al., 2000; Shinde et al., 2006). Thus, the presence of Zn in the proper concentration in the diet of the animals is of immense importance not only for the well-being of the animals but also for optimizing the overall performance of the animals and to enhance their production potential (Shinde et al., 2006).
Traditionally, Zn is supplemented in the animal diets as inorganic salt (Wang et al., 2010). Unfortunately, with the introduction the intensive cropping system, and extensive fertilizer application, the mineral profile of the animal feedstuffs has rapidly deteriorated in many parts of the world. More than half of the soil samples were found deficient in Zn in many with the result that feeds and fodders have been found to be Zn deficient (Shinde et al., 2006). Additionally, a previous study reported that soybean meal and wheat bran were major ingredients of rabbit diets, which were rich in phytate and had an antagonistic effect on available Zn (Baker and Halpin, 1988). However, supplemental Zn could compensate for dietary Zn complexes with phytic acid in feed ingredients. The proposed Zn requirements for rabbits vary from 25 to 60 mg/kg (Mateos et al., 2010). Better weight gain and feed intake were observed in rabbits receiving a diet supplemented with 90 mg/kg Zn (Hossain and Bertechini, 1993). Similarly, a previous work demonstrated that growing rabbits responded positively to 100 mg/kg of supplemental Zn, in terms of a significant improvement in live body weight gain (Nessrin et al., 2012).
However, no recent trials have been conducted in rabbits to study the response to low protein diets supplemented with ZnO. Thus, the present study aimed at evaluating the effect of zinc oxide at low and high protein diet levels in growing rabbits. Emphasis was also placed on productive performance, mortality rate, nutrients digestibility coefficients, carcass characteristics, blood constituents and economical evaluation.
Materials and methods
The experimental work was carried out in the Animal Production Department, Faculty of Agriculture, Zagazig University, Egypt. Twenty eight New Zealand White (NZW) male rabbits with average body weight 734.6 ± 14.69 g were randomly allotted to 4 groups (7 animals in each). Two dietary levels of crude protein, i.e. 14 and 18% and two levels of zinc oxide (0 and 100 mg/kg diet) were used in 2 × 2 factorial design for 8 weeks .The experimental diets were formulated to ensure an adequate supply of all nutrients recommended by (NRC, 1977) for growing rabbits. Ingredients and chemical analysis of the experimental diets were illustrated in Table 1.
Table 1. Formulation and chemical analysis of the basal-diets fed to rabbits
* Each 1.5 kg of minerals and vitamins mixture contains: manganese 80 g, zinc 60 g, iron 30 g, copper 4 g, iodine 0.5 g, selenium 0.1 g and cobalt 0.1 g, vitamin A 12000000 IU, vitamin D3 3000000 IU, vitamin E 10000 mg, vitamin K3 2000 mg, vitamin B1 1000 mg, vitamin B2 5000 mg, vitamin B6 1500 mg, vitamin B12 10 mg, Biotin 75 mg, folic acid 1000 mg, nicotinic 30000 mg and pantothenic acid 10000 mg.
Daily fresh water was available all time. Live body weight of rabbits was recorded weekly in grams; the average daily weight gain (DWG) was individually calculated. Average daily feed intake (DFI) was recorded weekly and feed conversion ratio (g feed /g gain) was calculated. Mortality rate was recorded weekly .At the end of the experimental period, apparent nutrients digestibility were determined for experimental diets. Four animals from each experimental group were housed individually in metabolic cages that allowed feces separation. The feed intake was accurately determined. Feces excreted were collected in labeled polyethylene bags and samples were taken for the chemical analysis. Proximate analysis of the experimental diets and feces samples were carried out according to the (AOAC, 1990).
At the end of the experimental feeding period, blood samples of 4 rabbits were collected at slaughter time to estimate blood parameters. Hemoglobin and hematokrite concentrations as well as red blood cells count were determined. Also, serum total protein, albumin, aspertate amino transferase (AST) and alanine amino transferase (ALT) were analyzed using commercial kits purchased from Diamond Diagnostics Company, Egypt. The globulin values were obtained by subtracting the values of albumin from the corresponding values of total proteins. Also, the internal organs (liver, kidneys, heart and lungs) were removed from the body, and then weighted. Economic evaluation was calculated according to (Ayyat, 1991) as the following equation: Final margin (Profit) = Income from body gain weight - feed cost.
The data were statistically analyzed using two-way ANOVA method according to (SAS, 2002). Duncan’s new Multiple Range procedure was performed to separate means (Duncan, 1955). The following model was applied:
Yijk=µ+Pi+Zj+(PZij)+eijk
Where:
µ=general mean. Pi=dietary crude protein effect, Zj= zinc supplementation effect, PZij= zinc by protein interaction effect and eijk= experimental error.
Results and discussion
Growth Performance and Feed Utilization
Growth performance results of growing NZW rabbits as affected by dietary protein level and ZnO supplementation are presented in Table 2. Results indicated that the low protein (14.76%, LP) caused in a significant (P?0.001) decrease in FBW and DWG from 7 to 15 weeks of age. However, significant (P?0.01) increase in DFI and FCR has been observed in group fed LP compared with high protein (18.53%, HP) group.
ZnO supplemented group was significantly (P?0.01) increased in FBW, DWG and FCR, while the DFI was not affected .Similarly, rabbits supplemented with 170 mg Zn/kg of diet as ZnSO4 showed a significant increase in the body weight gain (El-Rahim et al., 1995). Also, (Ayyat and Marai, 2000) reported that supplementing rabbit diets with 100, 200 or 300 Zn mg/kgsignificantly (P<0.05) increased live weight gains, but had no effect on DFI compared with the control group.
The significant improvement in body weight of rabbits given the additional Zn may be attributed to sufficient Zn level to plays an important role in polymeric organization of macromolecules like DNA and RNA which are responsible for the growth and development of skeleton and synthesis of body protein (García-Contreras et al., 2011). In addition, Zn is one of trace elements essential for biological functions of all living matter and necessary for growth, appetite, skin integrity and mental activity, Zn is an essential trace element required for the action of more than 200 metalloenzymes (Shinde et al., 2006). The obtained results showed no significant effects related to the interaction between protein level and ZnO supplementation (Table 2).
Table 2. Growth performance of New Zealand White rabbits as affected by protein level, dietary zinc supplementation and their interactions
Means in the same column bearing different letters differ significantly (P<0.05).
NS = Not significant, **P<0.01 and *** P<0.001.
Digestibility Coefficient and Nutritive Values
The results of digestibility coefficient and nutritive values as affected by protein level and ZnO supplementation or their interaction are shown in Table 3. Digestibility coefficient values of dry matter (DM), organic matter (OM) and nitrogen free extract (NFE) recorded in rabbit feed LP was significantly (P?0.05) lower than those fed HP diet. No significant differences in crude protein (CP), ether extract (EE) and crude fiber (CF) digestibility were observed between groups fed LP and HP diets. The rabbits fed the LP diet obtained significantly (P?0.01) the lowest values of digestible crude protein (DCP), total digestible nutrients (TDN) and digestible energy (DE).
Rabbits fed diets supplemented with ZnO was significantly (P<0.05) higher than the rabbits fed the control diet in DM, OM, CP digestibility and nutritive values (DCP, TDN and DE, Table 3). These results are in agreements with those reported by Gad Alla (2001) who found that apparent digestibility of DM, OM and EE was significantly (P<0.05) greater due to adding of Zn, but CP, and CF tended to be insignificantly higher than the control group. Hafez et al. (2002) also found that rabbit’s diets supplemented with Zn recorded higher digestibility of nutrients.
A previous research showed that feeding 3000 mg/kg Zn as ZnO to weanling pigs had an enteric effect of producing deeper crypts in the duodenum and a trend for longer villi (Carlson et al., 1998). Thus the enhanced digestibility and nutrient utilization following ZnO supplementation could be directly related to the superior absorptive capacity of the mucous membrane. Also, the improvement of digestion coefficients may be due to Zn supplementation affects protein and carbohydrate metabolism, which found in many highly purified enzymes functioning in protein and carbohydrate digestion (Underwood and Suttle, 1999).
Increasing the digestive ability of rabbit by Zn supplementation may be attributed to increasing the activity of some enzymes related to the digestion of carbohydrates, fats and protein such as amylase, lipase, trypsinogen, chemotrypsinogen and some peptidases, since these enzymes are known to be Zn-dependent enzymes (Banerjee, 1988). No significant differences in EE, CF and NFE digestibility were observed as a result of ZnO supplementation. Also, the results of the interaction effects between protein level and ZnO supplementation (Table 3) showed insignificant effects on digestibility coefficient and nutritive values.
Table 3. Digestibility and nutritive values of the experimental diets as affected by protein level, dietary zinc supplementation and their interactions
Means in the same column bearing different letters differ significantly (P < 0.05).
NS = Not significant, *P<0.05, **P<0.01 and *** P<0.001.
Blood Parameters
As shown in Table 4, the concentrations of total protein, albumin, globulin and ALT were significantly (P<0.05) decreased with rabbits fed LP diets. However, ZnO supplementation showed insignificant effect in estimated blood parameters (Tables 4 and 5). Similarly, an experiment in fattening pigs supplemented with Zn either as inorganic salt (ZnSO4, 84.3 mg/kg of diet) or metallo-organic complex (Zn-Met, 40.9 mg/kg of diet) did not show any significant differences in the total protein and albumin (Rupic et al., 1997). On the contrary, the serum albumin concentration of female Holstein calves was increased when their basal diet was supplemented with 20, 40, or 80 ppm ZnSO4 (Guang Zhou et al., 1995). But this difference could be related to the animal species used.
The results of the interaction effects between protein level and ZnO supplementation showed insignificant differences on estimated blood parameters (Tables 4 and 5).
Table 4. Blood parameters of New Zealand White rabbits as affected by protein level, dietary zinc supplementation and their interactions
Means in the same column bearing different letters differ significantly (P<0.05).
NS=Not significant, *P<0.05 and **P<0.01.
Table 5. Hematological parameters of New Zealand White rabbits as affected by protein level, dietary zinc supplementation and their interactions
Means in the same column not bearing different letters differ significantly.
NS = Not significant.
Carcass Traits
Results representing some carcass characteristics at 15 weeks of age are shown in Table 6. Slaughter weight (SW) affected significantly with protein level (P<0.001) and ZnO supplementation (P<0.05), while carcass weight was significantly affected with protein level (P<0.01) only. In regard to dressing percentage and relative weights (g/kg SW) of liver, kidney, heart, lung and spleen presented no significant differences were observed within all groups as a result of either protein level, ZnO supplementation or their interaction. Correspondingly, Al-Khalifa (2006) reported that supplemental dietary Zn by levels of 50, 100, or 200 ppm had no significant effect on dressing percentage of rabbits. Also, (Ayyat and Marai, 2000) reported that supplementing rabbit diets with 100, 200 or 300 Zn mg kg-1 had no effect on dressing yield of the rabbits compared with the control.
Table 6. Carcass and some internal organ weights of growing New Zealand White rabbits as affected by protein level, dietary zinc supplementation and their interactions
Means in the same column bearing different letters differ significantly (P < 0.05).
NS = Not significant, *P<0.05, **P<0.01 and *** P<0.001.
Economical Evaluation
Table 7 show that the feed cost and income from gain per rabbit were increased with ZnO supplementation within each protein groups. Final margin was increased with ZnO supplementation in rabbits fed LP and HP diets by 27.17 and 9.23%, respectively. The improvement in final margin may be due to the enhancement of weight gain and feed conversion ratio with ZnO supplementation. Hence the economical feed efficiency in this study showed that the using ZnO in the growing rabbit diets (LP or HP) was more economical than the non-supplemented diets.
Table 7. Economical visibility of growing New Zealand White rabbits as affected by protein level, dietary zinc supplementation and their interactions
Conclusion
It could be concluded that the growing rabbit responded positively to 100 mg supplemental ZnO/kg of low (14.76%) or high protein (18.53%) diet, in terms of significant improvement in FBW, DWG, FCR, and SW. Additionally, the former level of ZnO had no negative effect on blood biochemistry so it could be used safely.
Acknowledgment
Special thanks are due to Dr. Adham A. Al-Sagheer, Lecturer of Animal Nutrition, Animal Production Department, Faculty of Agriculture, Zagazig University for his great help in carrying out the present work.
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