Introduction

Zinc is an essential trace element for animals, being a component of more than 300 metallo-enzymes affecting growth, health and reproduction of the animals. The concentration of Zinc in livestock feeds and fodders is critically deficient in the state of Andhra Pradesh (Nagalakshmi et al., 2009) and most parts of country (Alloway, 2008). Therefore to avoid Zn deficiency, supplementation of Zn beyond the requirement is common practice at field level. However over supplementation of one mineral may interfere with the absorption and availability of other minerals like copper (Spears, 1996). To overcome this problem, the concept of organic minerals was developed, in which minerals are chelated with organic source and relatively high bioavailable compared to inorganic minerals (Spears, 1996). Even though this concept was well established, it has not reached to the farmer level completely because cost of organic minerals has to be considered for economic livestock production. One of the viable approaches to economize the cost is replacing a portion of inorganic mineral supplement with organic source. Hence, the present study was carried out to study the effect of organic zinc (Zinc proteinate-Zn Prot) in combination with inorganic zinc (Zinc sulphate – ZnSO₄) on performance and nutrient digestibility in buffalo heifers.

Materials and Methods

Eighteen Murrah buffalo heifers (24 to 30 months age) with average body weights of 261.1±11.6 kg were randomly divided in to three groups of six animals in each in completely randomized design and fed the experimental diets. All the experimental animals were housed in a well-ventilated animal house with the provision for individual feeding and watering. All the buffalo heifers were vaccinated and dewormed as per schedule. The concentrate mixture, prepared from the locally available feed ingredients (Table 1, 2 & 3) and para grass was offered to meet the nutrient requirements of buffalo heifers (ICAR, 1998).

Table 1: Ingredient composition (%) of basal diet

¹Trace mineral premix provided (mg/kg diet): Iron, 41; manganese, 21; copper, 10; cobalt, 0.1; Iodine, 0.27; selenium, 0.3. Vitamin A, D and E were provided to supply 2927 IU; 1097 IU and 39 IU per kg diet, respectively

Three experimental diets were formulated by replacing 100% (80 ppm) inorganic (ZnSO₄) Zn supplementation in the concentrate mixture, with organic Zn @ 25 or 50%. The experimental diets include 80 ppm Zn supplied from 100% ZnSO₄ (100I-0O), 75% Zn from ZnSO₄ and 25% from ZnProt (75I-25O), and 50% from ZnSO₄ and 50 % as ZnProt (50I-50O). Experiment was carried for a period of 90 days, at the end of the experiment 7 days digestibility trail was carried out to study the nutrient digestibilities. Throughout the experimental duration feed intake was calculated every fortnightly interval according to body weight changes. All experimental animals were weighed at fortnight intervals. Representative samples of feed and faeces were collected and analyzed for proximate principles (AOAC, 1997) and fibre fractions (Vansoest et al., 1991).

The data was subjected to statistical analysis by one way ANOVA as per the procedures of Snedecor and Cochran (1980). The differences between the means were tested for significance by using Duncan’s multiple range (Duncan, 1955) test.

Results and Discussion

The chemical composition of ingredients used in concentrate mixture and concentrate mixture were presented in Table 2 and Table 3 respectively.

Table 2: Chemical composition (% DMB) of feed ingredients used in experimental diets

CP: Crude protein; CF: Crude fibre; EE: Ether extract; TA: Total ash

Table 3: Chemical composition (% DMB) of the concentrate mixture fed to buffalo heifers

I: Inorganic Zn source, O: Organic Zn source

The fortnightly body weights, total gain and ADG during the feeding trial was comparable (P>0.05) among the three groups (Table 4). No effect on body weights or ADG with supplementation of organic Zn replacing inorganic Zn was reported by many workers. In Holstein calves, supplementing 20, or 500 ppm either as ZnSO₄, ZnMet, or ZnProt and their combination (50 % of 20 ppm Zn from ZnSO₄ and remaining from the ZnProt) had no effect on weight gain (Wright and Spears, 2004). Arrayet et al. (2002) reported that supplementing 60 ppm Zn as ZnSO_4, ZnMet, or ZnLys did not shown any significant affect on ADG in calves. Similarly, Zn supplementation at 35 ppm Zn through ZnSO₄ or ZnProp in crossbred cattle (Mandal et al., 2007), 200 ppm Zn as ZnSO₄ orZnMet in heifers (Huerta et al., 2002), 30 ppm Zn from ZnSO₄, Zn-AAC or Zn-psc in beef steers (Malcolm-Callis et al., 2000), 15, 30 or 45 ppm Zn from either ZnSO₄ or ZnProt to BD in Nellore lambs (Nagalakshmi and Himabindhu, 2013) had no effect on body weights or daily weight gains. In contrast to present study Jia et al. (2009) observed beneficial effect (P<0.01) of organic Zn (Zn methionine) supplementation in Cashmere goats compared to ZnSO₄.

Table 4: Effect of organic zinc supplementation on fortnightly body weight changes (kg) in buffalo heifer

I: Inorganic, O: Organic, ADG: Average daily gain, SEM: Standard error mean

In the present study, the fortnightly daily DMI, average DMI expressed as percent body weight in buffalo heifers was comparable among 100% inorganic, 25% and 50% organic Zn supplemental groups (Table 4). The results of this study validated with findings of Wright and Spears (2004) who observed comparable DMI in Holstein calves supplemented with 20 mg of Zn/kg of DM as ZnSO₄ or ZnProt or 50% of each. Similarly, Nagalakshmi and Himabindu (2013) observed no effect on DM and nutrient intake by lambs fed BD (basal diet) supplemented with 15, 30 or 45 ppm Zn from either ZnSO₄ or ZnProt. Similar observations were made by Mandal et al., 2008, in crossbred calves with replacement of 35 ppm Zn supplemented from ZnSO₄ with ZnProt. Nunnery et al. (2007) reported that replacing 75 ppm supplemental Zn from ZnSO₄ with organic source (ZnMet, or ZnProt) had no effect on feed intake corroborating with present findings. The feed conversion efficiency and efficiency of nutrient (CP) utilization did not differ among organic Zn groups (75I-25O and 50I-50O) compared to inorganic Zn (100I-0O) supplemental group heifers (Table 4). Similar findings were reported in lambs with 100% replacement of organic (ZnProt) source to inorganic (ZnSO₄) Zn at levels of 15, 30 or 45 ppm of ZnSO₄ (Nagalakshmi and Himabindu, 2013).

The intake and digestibilities of DM, OM, CP, EE, CF, NDF, ADF, hemicellulose and cellulose were comparable the dietary treatments (Table 5).

Table 5: Effect of organic zinc supplementation on nutrient digestibility in buffalo heifers

I: Inorganic, O: Organic, SEM: Standard error mean

Conclusion

These results are in agreement with the finding of Mandal et al., 2008, who observed that, replacement of 100% inorganic (35 ppm Zn as ZnSO₄) with organic (35 ppm Zn as ZnProp) Zn in crossbred bulls did not affect the intake and digestibilities of DM, CP, EE, NDF, ADF. Similarly, supplementation of organic Zn (ZnProt) at 100 % replacement to inorganic Zn(ZnSO₄) source at levels of 15, 30 or 45 ppm had no effect on digestibility of nutrients and fibre fractions in Nellore ram lambs (Nagalaksmi and Himabindu, 2013). Whereas, Garg et al. (2008) observed comparable digestibilities of DM, OM, CP, EE, NDF and hemicellulose were comparable, while digestibility of cellulose and ADF was improved significantly (P<0.05) in lambs with 100% replacement of 20 mg Zn/kg DM as ZnSO₄ with ZnMet in lambs. Similarly, Jia et al., 2009 supplemented 20 ppm of Zn as ZnSO₄ and when replaced with 100% organic Zn source (ZnMet) in cashmere goats observed no influence on digestibility of DM, CP, EE and NDF. While, ADF digestibility improved with supplementation of Zn as ZnMet in cashmere goats. Based on results it was concluded that growth performance and nutrient digestibility were comparable in heifers fed diets supplemented with 80ppm Zn from 100% ZnSO₄ or as combination of ZnSO₄ and ZnProt in ratio of 75:25 and 50:50.

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