Effect of High Buttiauxella Phytase Dose Sustains Performance and Bone Quality of Laying Hens Fed Nutrient Compromised Diets

The inclusion of alternative ingredients such as rice bran, DDGs and sunflower meal in layer diets, to reduce feed cost, can result in higher phytate levels, potentially limiting availability of minerals, protein and energy, all of which are important to maintain egg production, eggshell strength and bone strength (Bello and Korver, 2019). Phytase enzymes are commonly used in the animal feed industry primarily to increase phosphorus (P) availability from plant ingredients. Additionally, phytase enzyme improves availability of non-P nutrients like Ca, amino acids (AA), and energy (AME) by facilitating the breakdown of phytate P and thus negating its antinutritional effects (Dersjant-Li et al., 2015). As phytase enzyme can increase the availability of phosphorus, calcium, sodium, amino acids, and energy content of diets, these nutrients may be decreased in the feed formulations as ‘matrix values’ without adverse effects on the bird’s performance. This will reduce the feed costs while maintaining the same level of performance. Currently, a dose level of 300 FTU/kg feed of phytase enzyme is often used in commercial laying hen diets. Increasing the dose of phytase would reduce feed costs further due to higher matrix values but there have been concerns over whether this can be done without compromising laying hen performance. A trial was conducted to determine the efficacy in laying hens of higher inclusion levels of phytase with corresponding matrix application.

A total of 180 Lohmann LSL Lite hens (20 replicates/treatment, three hens/cage) were distributed into four treatment groups at 24 weeks of age. Distribution was a completely randomized design to achieve uniform bodyweight across the treatments at the beginning of the feeding trial. Diets were corn/soybean meal based and fed as mash, ad libitum. A pullet/grower adaptation diet supplemented with a Buttiauxella phytase (Axtra® PHY, Danisco Animal Nutrition) at 300 FTU/kg was fed from 12-23 weeks of age. During the laying stage, the hens were maintained on two diets formulated based on common commercial practices: phase 1 (24-50 weeks of age) and phase 2 (51-60 weeks of age). The positive control (PC) diet contained 3.8% Ca and 0.42% available P (AvP) during phase 1 and 4.0% Ca and 0.41% AvP during phase 2 (the values included the matrix contribution from the phytase at the given dose which was equivalent to 0.17% Ca, 0.16% AvP, 58 kcal/kg AME and 0.35% crude protein) and was supplemented with a Buttiauxella phytase at 300 FTU/kg. The PC diet was reformulated to generate the negative control (NC) diet in which the AvP and Ca contents were decreased by 0.19%, and 0.2% respectively along with a 63.5 kcal/kg reduction in AME and a 0.65% reduction in CP content, compared to the breeder recommended levels. The NC diet was fed either as such or was supplemented with the phytase at 600 FTU/kg. Egg production and feed intake were measured daily and weekly respectively, and all eggs were collected from each replicate cage to determine egg weight at weekly intervals. Every 4 weeks, 4 eggs were randomly selected from each cage to determine eggshell breaking strength. At 80 weeks of age, 1 bird per cage was euthanized and the tibia were collected for morphometric analysis (diaphysis length and mid shaft diameter) and determination of tibia ash. Data was analysed across age and treatment by analysis of variance. Means were compared using ANOVA and Tukey’s test (JMP, SAS software). Significance was taken as P< 0.05.

Feeding the NC diet with reduced nutrient specifications significantly decreased (P < 0.05) hen-day production (HDP) by 3.4 % points, egg weight by 1.6% and egg mass by 5.2% versus the positive control fed birds. Feeding the NC diet also significantly increased (P < 0.05) feed intake by 1.8% and FCR by 13 points versus the positive control across the trial period of 24- 80 weeks (Table 2). Supplementing the NC diet with the phytase at 600 FTU/kg significantly improved (P< 0.05) all the above-mentioned performance traits to the levels obtained with the PC diet. With the PC diet the feed cost/dozen eggs was $0.43 which decreased to $0.42 when the phytase supplemented NC diet was fed (Table 2). Egg breaking force was significantly (P< 0.05) reduced by 10% when birds were fed the un-supplemented NC diet compared to the PC (Table 3). The addition of Buttiauxella phytase at 600 FTU/kg to NC significantly (P< 0.05) improved egg breaking force by 9.4% back to the level of the PC. Feeding the NC significantly (P< 0.05) decreased tibia length, diameter and ash by 8mm (7%), 0.45 mm (8.3%) and 5.5 % points respectively versus the PC. Supplementing the NC diet with 600 FTU phytase significantly improved tibia length by 7mm (6.6%) compared to the NC, and numerically improved tibia diameter and ash by 0.25 mm (5.1%) and 4.2 % points respectively versus the NC. All tibia parameters were restored to the level of the PC (P> 0.05) with supplementation of the NC with 600 FTU phytase.

As expected, diluting the NC diet by 0.19% AvP, 0.20% Ca, 63.5 ME kcal/kg and 0.65% CP, and only supplementing 300 FTU of phytase, decreased performance of laying hens for parameters including HDP, eggshell quality and tibia ash. Supplementing the NC diet with 600 FTU/kg phytase restored all the above-mentioned performance traits to the level of that obtained with the PC group. This is in agreement with earlier findings (Martinez Rojas et al., 2018) that showed performance of birds fed diets reduced in available P could be maintained with phytase supplementation. Dersjant -Li et al., 2022 also demonstrated using a meta-analysis of 13 digestibility studies that phytase gives consistent improvements in amino acid digestibility. One of the important factors that governs the productive performances of laying hens is the Ca to AvP ratio. Previous studies (Augspurger et al., 2007; Meyer and Parsons, 2011; Kim et al., 2017) have shown that increasing the phytase activity in the diet did not show any beneficial effect on egg production traits in laying hens and the most plausible reason for the productive traits being refractory was the altered Ca to AvP ratio. It is postulated that owing to the antagonistic effects that Ca exerts on availability of dietary P when the Ca to AvP ratio widens it mutes the effects of phytase and this was the case in the earlier reported experiments. In the present study, both AvP levels and dietary Ca levels were decreased according to the phytase matrix in both the PC and the NC groups, helping to maintain the Ca to P ratio. This approach facilitated a more efficient utilization of dietary P. Jing et al., 2021 found that performance of laying hens could be maintained with dietary AvP as low as 0.1% if the diet was fortified with 1000 FTU/kg of a phytase. Increasing the dose of phytase should facilitate more complete breakdown of phytate P thus releasing greater quantities of entrapped nutrients (amino acids, trace minerals and starch), reducing the anti-nutritional effects of phytate P and improving the productivity of the hens fed with the phytase supplemented NC diet. In the current study tibia ash content and the eggshell breaking strength of the birds fed the phytase supplemented NC diet were comparable to those of layers fed the PC diet. Supplementation of 600 FTU/kg phytase to the NC diet significantly improved the mineral matrix of eggshell and tibia which could not be possible unless the utilization of efficiency of Ca and P was increased.

The study demonstrated that it was possible to sustain egg production, FCR and eggshell quality of laying hens with diet containing as low as 0.22% AvP when supplemented with 600 FTU/kg Buttiauxella phytase from 24-80 weeks of age. This approach not only helped in bringing down feed cost significantly but should also be viewed as a potential tool to decrease the usage of inorganic P in poultry diet to bring down P excretion into the environment. Dietary inclusion of Buttiauxella phytase was able to replace up to 0.19% AvP, 0.20% Ca, 63.5 ME kcal/kg and 0.65% CP in laying hen diets, reducing feed cost per dozen eggs, whilst maintaining performance.