A trial was conducted to assess the requirement of digestible threonine concentration in the diets of WL layers. Pullets (390) were fed (25-44 weeks) with 13 test diets (6+6+1)containing protein at two levels i.e. 13.46 at 0.65% lysine and 15.56 at 0.60% lysine each with six graded concentrations of threonine (60, 63, 66, 69, 72,75) and a control with 17 % protein , 0.70 % lysine and 66% of threonine. Each diet was fed adlibitum to five replicates of six birds. Hen day egg production (HDEP) did not varied with threonine concentration in diet in low crude protein group (LCP), where as a significant increase in HDEP was noticed in medium crude protein (MCP) group. Feed intake (FI) was significantly decreased with increase in threonine in LCP group, but no variation was observed in FI in MCP group. Other production parameters like egg weight, egg mass, feed efficiency (g/g), mortality and body weight gain were not influenced (p>0.05) by the concentration of threonine in diet. Returns over the feed cost were highest at 63% threonine concentration at both the protein levels. It can be concluded that WL layers require approximately 63% of lysine as threonine in diet for optimum production.
Ideal protein concept is currently being used to determine the ideal amino acid profile in diets of poultry (Pastor et al., 2013). Formulation of diets based on crude protein (CP) concept leads to a situation that lack or excess of certain amino acids. As a result the performance of the birds will get affected. Instead of providing CP as such, supplementation of essential amino acids to layer diet will fulfil the needs without affecting the performance. Low protein diets prepared with corn soy, threonine is the third limiting amino acid in low protein diets prepared with cornsoy for commercial poultry and the level of threonine in diet compromises the performance of the layers (Schmidt et al., 2010). Threonine is important for formation of protein and maintenance of protein turnover. Threonine functions as a nutrient immunomodulator in maintaining the intestinal barrier function (Azzam et al., 2011). Threonine participates in synthesis of protein and several important metabolic products viz. glycine, acetyl Co-A, pyruvate (Kidd and Kerr, 1996) and uric acid (Martinez et al., 1999). Further, threonine aids in formation of collagen, elastin, and antibodies (Sa et al., 2007). Threonine @470mg/d is required for layers as per NRC, 1994. Whereas, (Gheisar et al., 2011) inferred that low protein diets with threonine supplementation had no negative effect on production in layers. But the exact requirement of digestible threonine for layers in corn soy ration at lower protein levels was not clear. Hence, a study was conducted to assess the threonine requirement for the layers at peak production as a ratio to lysine at various protein levels.
Materials and Methods
A total of 390 white leghorn layers (BV-300) at 24 weeks with body weight ranges form 1285-1315g were randomly distributed and housed in colony cages (3 birds/cage). Two adjacent cages with a common feeder were considered as one replicate. Birds were allotted into 13 treatment groups of 5 replicates each with 6 hens per replicate. The laying hens were offered experimental diets from 25-44 weeks of age. Hens were given free access to water and experimental diets. The protocol of the current study was approved by the Animal Ethics committee of the institute.
A total of 13 diets were prepared. A diet with 0.70 per cent digestible lysine (17.0% CP) and 66% of lysine as threonine was kept as control (Table 1). Two basal diets were prepared one with lysine at 0.65 per cent and 13.46 per cent CP second basal diet was with 0.60 per cent lysine at 15.56 per cent CP. To these basal diets crystalline threonine was supplemented at six graded concentrations (60, 63, 66, 69, 72 and 75% of lysine as threonine). Energy levels in all 13 diets were maintained at 2700 kcal / kg. The ratio between digestible methionine +cystine (M+C), tryptophan (Trp), arginine (Arg), isoleucine (Ile) and valine (Val) to digestible lysine (Lys) were 86, 19, 114, 72 and 80 per cent respectively and were maintained constant in all the diets. Diets 1-6 were prepared by adding crystalline L-threonine at 0,1.2, 2.4, 3.6, 4.8 and 6.0 per cent respectively, while diets 7-12 were prepared by adding crystalline L-threionine at 0, 0.9, 1.8, 3.6, 5.4 and 7.2 per cent respectively.
Table 1: Ingredient composition (%) of dietary treatments fed to layers (25-44weeks)
|Ingredient(in Kg)||Basal Diet-I||Basal Diet -II||Control|
|d. Thr (%)||60||60||66|
|d. Lysine (%)||0.65||0.60||0.70|
|Soy bean meal||70||27||108|
|Deoiled rice bran||126||192||150|
|Pearl Millet (Bajra)||190||120||98|
|Ground nut cake||41||103||95|
|Cotton seed meal||15||50||40|
|Crude Protein (%) $||13.46||15.56||17.05|
*Provided (/Kg diet): Vit. A 50MIU, Vit. D3 14miu, Vit. E 20g, Vit. K3 8g, Vit. B1 3.2g, B2 32g, B6 3.6g, B12 0.024g, Niacin 28g, Calcium pantothenate 16g, Folic acid 5.6g. Trace minerals (in each kg): Manganese 70g, Zinc 70g, Iron 50g, Cobalt 0.6g, Iodine 0.6g, Copper 10g, Selenium 0.06g. Saccharomyces and Lactobacillus species, Acidifier; # Calculated; $ Analyzed
The body weight (BW) of three birds per replicate was recorded at the beginning and at the end of each period (28 days). Feed intake and feed efficiency (g/g) were measured weekly and pooled for the period. Egg production and mortality were recorded daily. Egg weight was calculated as mean weight of eggs collected in the last three consecutive days of each period. Egg mass (egg production × average egg weight) was calculated period wise. During the last 3 consecutive days in each period 2 eggs /replicate and a total of 130 eggs/day were collected and analyzed for egg quality traits.
Data was statistically analysed by one-way ANOVA using SPSS for windows (SPSS Inc. 2002). The significant differences (p< 0.05) seen in between means was determined by Duncans multiple comparison test (Duncan, 1955). The effect of various concentration of d. threonine were determined by using orthogonal polynomials for linear, quadratic, and cubic effects. Quadratic regression and equation were also determined.
Results and Discussion
Hen Day Egg Production (%)
Egg production (EP) was not influenced by the concentration of threonine in LCP group, whereas increase in production with increase in threonine concentration was observed in MCP group (Table 2). The mean egg production was higher at 74(R2 =0.008) and 75% (R2 =0.253) threonine in LCP and MCP groups (Table 6&7). Threonine concentration in LCP group had no influence on HDEP might be due to the increased intake of threonine in LCP group when compared to MCP group (Table 4). Availability of lysine and other amino acids (essential) are more in LCP group than MCP group may be the reason for lower production at medium protein group than LCP (Table 4).
Table 2: Effect of various concentrations of d. Threonine on production parameters in WLH layers (25-44 weeks)
|Groups||d. Lysine / CP (%)||d. thr. (lysine)||HDEP||FI/B (g)||EW(g)||EM(g)||FE(g/g)||Mortality (%)||BWG (g)|
This results indicating the need of amino acids is equal or less than the lowest level tested in this work (60% of lysine as threonine) at LCP group. These are coincides with results of (Figueiredo et al., 2012), who reported no effect on egg production by incorporation of various levels of lysine (0.675, 0.743,0.811 and 0.879%) in combination with various concentrations of threonine (0.542, 0.596 and 0.650%) in diets of Hy-Line W36 laying hens at 42-58 weeks of age. The increase in egg production in MCP group may be due to lesser the intake of threonine (Table 4) and low supplemental levels might not be sufficient to meet the production potential.
Feed Intake (g)
Significantly lower feed intake/bird (FI/B) was observed at 72 % (R2 =0.056) threonine concentration in LCP group, but no variations in FI in MCP group (R2 =0.163). Higher the feed intake in LCP group might be for meeting the egg production potential at low threonine concentrations birds. Similar observations were noticed (Rocha et al., 2013) by incorporation of various digestible threonine to lysine ratios (65, 70, 75, 80, 85 and 90%) at 14.2% CP in layers of 24 to 40 weeks age. Similarly, (Azzam et al., 2011; Faria et al., 2002 and Martinez- Amezcua et al., 1999) also reported the same.
Table 3: Economics in WL layers fed with various concentrations of d.threonine at two levels of d. lysine
|Groups||d.Lysine/ CP (%)||d.Thr./ d.lys.||Cost of feed (Rs./Kg)||Cumulative feed cost/ entire experiment/bird (₹.)||Returns through sale of eggs (₹.)||Returns over feed cost (₹.)||Gain over control ₹.)|
Table 4: Various levels of lysine and threonine in diet and their intake by WL layers (25-44weeks of age)
|CP (%)||Lysine (%)||Lysine level in diet (mg)||Lysine intake (mg/b/d)||Threonine (%) in diet||Threonine level in diet (mg)||Threonine intake (mg/b/d)|
Table 5: Egg quality parameters of eggs collected from WL layers (25-44weeks) fed with various concentrations of threonine in diet
|Lysine/CP||Threonine (%)||Shape index||Haugh unit||Yolk Index||Shell Thickness(mm)||Yolk colour|
Table 6: Quadratic equation summary of threonine (%) requirements of WL layers (25-44wks) at LCP (13.46%)
|Parameters||Quadratic equation||R2||Requirement of Threonine (%)|
|Egg production (%)||Y= 88.772+1.073X-0.088X2||0.008||74|
|Feed intake/bird(g)||Y= 120.384-4.716X+0.569X2||0.056||74|
|Egg weight (g)||Y= 55.89-1.071X+0.120X2||0.041||60|
|Egg mass(g/period)||Y= 1417.8-17.259X+2.446X2||0.044||60|
|Feed efficiency (g/g)||Y= 3.028-0.087X+0.010X2||0.01||74|
|Mortality (%)||Y= 0.524+0.263X-0.013X2||0.041||60|
|Body weight gain(g)||Y= 1379.054+15.946X-2.773X2||0.023||74|
Table 7: Quadratic equation summary of threonine (%) requirements of WL layers (25-44wks) at MCP (15.56%)
|Parameters||Quadratic equation||R2||Requirement of Threonine (%)|
|Egg production (%)||Y= 86.641-0.603X+0.195X2||0.253||75|
|Feed intake/bird(g)||Y= 112.189-2.640X+0.426X2||0.163||75|
|Egg weight (g)||Y= 54.751+0.060X-0.028X2||0.002||75|
|Egg mass(g/period)||Y= 1339.91-16.393X+3.585X2||0.084||60|
|Feed efficiency(g/g)||Y= 3.021-0.024X+0.002X2||0.046||75|
|Mortality (%)||Y= 0.724-0.573X+0.103X2||0.119||75|
|Body weight gain(g)||Y=1448.03-2.366X-1.444X2||0.131||60|
Feed Efficiency (FE)
Feed efficiency was not influenced by the concentration of threonine in diet irrespective to the level of protein and lysine in diet of WL layers from 25-44 weeks of age. Feed efficiency was calculated in this study on g/g basis. Even though increase in production with increase in threonine concentration in MCP group, but the HDEP values were lower than the HDEP in LCP group. Feed intake/b is higher in LCP group than MCP group. Higher feed intake and higher egg production in LCP group and low HDEP and low feed intake in MCP are the reasons for no effect of threonine on feed efficiency.
Egg weight (EW), egg mass (EM), mortality and body weight gain (BWG) were not influenced by the concentration of threonine. Similarly (Biazzi et al., 2014) reported that no effect on egg weight, egg mass, feed efficiency, mortality and body weight gain by incorporation of 4.6, 4.8, 5.2, 5.5 and 5.8 g/kg of digestible threonine in Sahver brown pullets at 75-90 weeks of age. These are in line with (Azzam et al., 2014 and Figueiredo et al., 2012). This indicating that the need for this amino acid is at or below the first level used in this work i.e. 60% of lysine as threonine or 457.08 and 392.76 mg/b/d in LCP and MCP groups respectively. Nunes et al., 2015, inferred that no significant effect of digestible threonine levels (0.460, 0.490, 0.520, 0.550 and 0.580%) on feed intake, egg production, egg weight, feed conversion ratio and egg mass in shaver brown layers at 50-66 weeks of age.
Higher the return over the feed cost through sale of eggs was observed at 63% threonine concentration in diet of layers at both the protein groups (Table 3).
Egg Quality Parameters
Except Haugh unit score other quality parameters were not influenced by the concentration of threonine in diet. Haugh unit score was not influenced by the concentration of threonine in LCP group whereas, decrease the HU with increasing the concentration of threonine, in diet was observed in MCP group. Haugh unit score indicates the quality of albumin. Higher the value indicates the best quality of albumin. Major portion of albumin is made up of proteins. There was no significant variation in HU scores in LCP group indicating that the diet /nutrients are optimum for maintaining egg quality. Whereas, decrease in HU score in MCP might be due to lower the availability of essential amino acids in MCP group. (Shim et al., 2013) reported that higher the mean Haugh unit values in low protein diets (21.62, 19.05, 16.32, and16.05% are high protein diets, 2% less than is medium and 4% less than these are low protein diets) of Bovans (18-74weeks). Whereas, Gunawardana et al., 2008, observed no effect on HU by various protein levels in layer diets.
Feed efficiency and economics will influence the profits in the poultry industry. Hence, basing on these two factors it can be concluded that the lowest concentrations supplemented i.e. 63% of lysine as threonine is sufficient enough to maximize the profits at both the protein levels (13.46% CP with 0.65% lysine and 15.56% CP with 0.60% lysine) in diet of WL layers at 25-44 weeks of age. The availability of threonine /bird/day is 454.92 and 412.90mg in 13.46 and 15.56% CP supplementation groups respectively.
The authors are thankful to Sri Venkteswara Veterinary University for financial assistance.