عنوان مقاله [English]
Introduction Increasing feed costs are significant issues in the poultry industry. Therefore, poultry producers often interested to feed low energy and nutrient dense diets to reduce production cost, while low energy and nutrients dense diets may not appear to supply sufficient energy for laying hens. Hens can regulate their feed intake to maintain energy and nutrient intake in accordance with their requirements. In this way, hens will consume more of a low energy and nutrients dense diet than of a high energy and nutrients dense diet, ensuring the calories and nutrient consumed be sufficient. However, some studies have shown that hens especially the modern ones are not precise in adjusting their feed intakes, such as the Hy-Line W-36, since they only have a limited capability to increase their feed intake to ensure adequate energy and nutrients intake. While low energy and nutrient dense diets are less expensive to purchase, they may not ensure optimal egg production if hens are unable to adjust their feed intake. On the other hand, the purchase price of low energy and nutrient dense diets can be substantially lower than high-density diets, if they are effective in maintaining long-term egg production performance, so that can result in increased returns for the producer. Thus, feeding low energy and nutrient dense diets to laying hens may result to improve returns due to a lower cost of diets. However, it has been shown that the increased efficiency of birds fed on high energy and nutrient dense diets can offset the higher cost of feed. The hypothesis of this study was to investigate how Hy-Line W-36 laying hens in post molting period can respond to lower energy and nutrients dense diets, through their increase in feed intake to maintain energy and nutrient consumption to support egg production.
Materials and methods The birds that used for this experiment were molted at the 70wk of age on a non-fasting feeding program according to the molting recommendation by Hy-line W36 laying hens guide. Three hundred twenty 78wk Hy-Line W36 hens were individually weighed and randomly assigned to 80 cages of four birds each. Eight replicate groups of 8 hens each (two adjacent cages) were randomly assigned to each of the 5 treatment diets with location within house as blocking criteria. The pre-experimental period was two weeks for acclimatization, and the experimental period was from 92-103 weeks of age (three 28d periods; 92-95, 96-99, 100-103wk of age). Experimental diets were formulated according to the guidelines in the Hy-Line W-36 Commercial Management Guide (2015) for 104g feed intake according to the average pre-experimental period egg production and feed intake data. Thus the control diet (100% of recommendation) was formulated to contain 2845 kcal/kg AMEn; 14.42% CP; 4.14% calcium; 0.48% available phosphorus; 0.17% sodium; 0.67% digestible lysine; 0.36 digestible methionine; 0.56 digestible methionine + cysteine; and 0.47 digestible threonine. Four other dietary concentrations of energy and nutrients density were formulated to provide 91, 94, 97, and 103% and one diet with the 100% of recommendations stated in the 2015 Hy-Line W36 commercial management guide. Egg production (number and weight) and mortality were recorded daily, whereas feed consumption was measured every 4wks as feed disappearance. Six eggs/replicate (48 eggs/treatment) laid in the last 72 h of each 28d period were collected and transported to Egg Quality Laboratory at the Ferdowsi University for of egg weight, albumen, yolk and shell relative weight, Haugh units, egg shape index, egg special gravity, and shell thickness determination. The feed cost/kg egg production was calculated by feed costs time feed conversion ratio. Data were analyzed by ANOVA using the GLM procedure of SAS 9.1 (2003), with dietary treatment and block as independent variables. Diet effects were evaluated using linear and quadratic orthogonal polynomial contrasts. The linear broken-line (LBL) and quadratic-broken line (QBL) regression models were used to estimate the dietary energy and nutrient density ratios for optimization of egg mass and feed conversion ratio.
Results and discussion Previous research showed that hens would linearly adjust their feed intake in response to diet nutrient density by eating significantly more feed that was low in energy and less feed that was high in energy. These changes in feed intake were not in agreement with the results of the current study showed that egg production, and egg mass were increased and feed conversion ratio (FCR) decreased significantly and linearly, with the increase in dietary energy and nutrients density. There was not any significant difference in the egg production, egg mass and feed conversion ratio in birds fed diet containing three percent (103%) more nutrient density than that of strain recommendation. Whereas, feed intake, egg weight, white yolk and shell relative weight, egg shape index, specific gravity, egg shell thickness as well as Haugh unit were not significantly affected by dietary energy and nutrients density. Significant linear increase due to increase in energy and nutrients density were observed for most measured parameters, including hen-day egg production, egg weight, egg mass, feed efficiency, energy intake, and body weight gain. The hen-day egg production showed that hens fed diets containing 91% of control diet laid fewer eggs than those fed diets with 100 or 103% of nutrients recommendation. The energy and nutrient requirement for optimal egg mass (g/b/d) and FCR during the post molting period (92-103Wk) by LBL model were 94.96 and 97.02%, and by QBL model 95.71 and 95.95% of strain recommended, respectively.
Conclusion In summary, the increase in energy and nutrients density in diet of Hy-Line W-36 laying hens increased egg production, egg weight, egg mass, energy intake as well as decreased body weight losses and feed conversion ratio. The regression analyses of data showed that, laying hens diet formulated at the 95-97% of nutrients recommendation had the optimal egg production and economic performance during the second egg production cycle. Furthermore, hens were unable to adjust their feed intakes since the lowest energy and nutrients density diet deteriorate egg production performance.