Alternative Feeding Regimen of Calcium Source and Phosphorus Level for Better Eggshell Quality in Commercial Layers

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1 2003 Poultry Science Association, Inc. Alternative Feeding Regimen of Calcium Source and Phosphorus Level for Better Eggshell Quality in Commercial Layers H. A. Ahmad 1 and R. J. Balander 2 Center for Computational Epidemiology, Bioinformatics and Risk Analysis, 107 Williams-Bowie Hall, CVMNAH, Tuskegee University, Tuskegee, Alabama Primary Audience: Poultry Nutritionists, Extension Personnel, Commercial Producers, Researchers SUMMARY Eggshell quality, due to its economical impact on commercial egg production, has always been a matter of great concern. Numerous studies have been conducted to address separately various parameters influencing shell quality including calcium, vitamin D 3 levels, and blood chemistry. There has been little research conducted to deal with these issues collectively. In this project, eggshell quality, egg production, and egg weight were evaluated as affected by a combination of different calcium sources, phosphorus levels, and time of feeding. Results suggest that there is a potential to improve eggshell quality with reduced economic losses by changing the feeding patterns of commercial layers using alternative calcium sources and phosphorus levels in the morning and evening feedings. Key words: eggshell quality, alternative feeding, calcium source, phosphorus level 2003 J. Appl. Poult. Res. 12: DESCRIPTION OF PROBLEM Poor eggshell quality accounts for major economic losses to commercial egg producers. Roland [1] surveyed U.S. producers representing 81 million commercial layers and determined that total eggs cracked or lost prior to reaching their final destination ranged from 13 to 20%, with a dollar value between $1.32 to $2.00/bird per year for an estimated total industry loss of $477.9 million per year. There are numerous factors involved in eggshell formation and its subsequent quality. The macro factors include, but are not limited to, the source and level of calcium in the diet, phosphorus level in the diet, and temporal intake of these minerals. The source and particle size of calcium used in laying hen diets are two factors that have received considerable attention in recent years [2, 3]. Oyster shell and limestone are the 2 principal sources of calcium used in laying hen rations. There have been contradictory reports indicating the beneficial effects of oyster shell over limestone and vice versa. The partial replacement of limestone with oyster shell in the diet has reportedly im- 1 To whom correspondence should be addressed: ahmadh@tuskegee.edu. 2 Animal Science Department 1250D Anthony Hall, Michigan State University, East Lansing, MI

2 510 proved different aspects of eggshell quality [4, 5, 6, 7, 8]. Phosphorus plays a significant role in eggshell formation. Eggshells contain very little phosphorus (calcium:phosphorus in eggshell is approximately 100:1), but this element interacts with calcium during bone formation. Calcium is stored in the skeleton almost entirely as calcium phosphate; therefore, synthesis of medullary bone requires dietary phosphorus. This phosphorus is however, involved in an essentially futile process, because if the calcium is used for shell formation, the phosphorus must be excreted. Nutritional interest in phosphorus has been stimulated by several observations that dietary excess of this element has a detrimental effect on shell quality [9, 10, 11, 12]. It is not clear whether this phosphorus excess, by accumulating in the blood, interferes with mobilization of skeletal reserves of calcium phosphate during shell formation or whether there is a direct antagonistic effect of blood phosphorus on the shell-forming process. Whatever the mechanism, there is no doubt that dietary treatments which lead to an increase in plasma phosphate, cause a decline in egg specific gravity. Miles and Harms [13] showed a clear negative linear correlation between specific gravity and plasma phosphate over a range of treatments. The NRC recognized this fact and lowered its recommended daily intake of nonphytate phosphorus to 250 mg/h per day for normal production and health [14]. Several other reports also indicate that the minimum total phosphorus requirement of the laying hen is below 0.50% in the diet [8, 15, 16]. Mongin and Sauveur [17] observed that higher calcium consumption takes place early in the morning and late in the afternoon, primarily on days concurrent with ovulation and oviposition. Other investigators [5, 18] have reported that hens become deficient in calcium during the early morning hours and that the timing of calcium intake is important to the ability of a hen to calcify eggshells. The importance of timing of calcium intake is believed to be due to the inability of the hen to maintain adequate calcium reserves in the small intestine during shell formation [19]. It has also been reported that the period of greatest calcium JAPR: Research Report deficiency in the digestive tract of the laying hen is between midnight and 0400 h. It must be kept in mind that during the early morning hours, eggshell calcification usually occurs at a very rapid rate. During this phase of a hen s daily egg laying cycle, calcium and phosphorus are being mobilized from bone, and the phosphorus level in the blood begins to rise. Van de Velde et al. [20] reported peak plasma organic phosphorus concentration 15 h after ovulation, which might be attributable to medullary bone resorption during shell formation. It is speculated that this rise in blood phosphorus level interferes with calcification of eggshell on the one hand, and taxes the hen s body through excess excretion on the other. The aim of the present study was to consider these three topics: calcium source, phosphorus level and the effect of changing the phosphorus level and calcium source in the evening feed of layers, and the effects of these components and timing on eggshell quality. To our knowledge no single study has considered all of these factors combined. We believe reduced dietary phosphorus in the evening feed (normal phosphorus in the morning feed) with oyster shell replacing a portion of the limestone as the calcium source will improve the eggshell quality of laying hens under commercial conditions. MATERIALS AND METHODS Fourteen hundred forty Hy-line W-36 pullets were randomly divided into 3 treatment groups of 480 (8 replicates of 60 birds per treatment group). These birds were housed in a stair-step, 4-tier cage system. There were 8 rows (4 per side) in each cage system with 12 cages in each row, and each cage housed 5 birds for a total of 60 birds per row. Treatment 1 was a commercial layer ration (Table 1, ration 1) provided as morning and evening feed with limestone as the calcium source and served as the control. Treatment 2 was the commercial ration (control) provided in the morning; the evening feed contained a normal calcium level with limestone as the calcium source but a lower phosphorus level than control feed (Table 1, ration 2). Treatment 3 feed contained normal calcium and phosphorus in the morning but low phosphorus in the evening feed (same level as treatment 2 evening feed). The calcium

3 AHMAD AND BALANDER: FEEDING PATTERN AND EGGSHELL QUALITY 511 TABLE 1. Ingredient composition of experimental rations Ingredient Ration 1 A Ration 2 B Ration 3 C Corn Soybean meal, 44% CP Dried alfalfa meal Fat Vitamin mineral premix DL-Methionine Salt Limestone Oystershell Dicalcium phosphate Total Calculated analysis ME (kcal/kg) 2,666 2,676 2,676 Crude protein (%) Crude fiber (%) Calcium (%) Total phosphorus (%) Available phosphorus (%) Proximate analysis D (%) Moisture Crude protein Crude fat Acid-detergent fiber Calcium Phosphorus A Ration 1. Commercial ration with normal calcium and phosphorus levels, provided morning and evening, with limestone as the calcium source; served as the control. B Ration 2. Commercial ration (control) in the morning, and the evening feed contained a normal calcium level with limestone as the calcium source but a lower phosphorus level than the control feed. C Ration 3. Commercial ration (control) in the morning, and the evening feed contained a normal calcium level (50% limestone and 50% oyster shell) but low phosphorus (same level as treatment 2 evening feed). D Proximate analysis conducted in duplicate at the Michigan Department of Agriculture state lab. source for treatment 3 was 50% limestone and 50% oyster shell (Table 1, ration 3). The morning feed was fed from 0800 to 1600 h, and the evening feed was fed from 1600 to 0800 h. Excess feed was removed before the next feed was offered. The experimental feed formulation and chemical and proximate analyses of the feeds are given in Table 1. All treatments were initiated at about 28 wk of age when the birds had achieved peak egg production. The birds in all 3 treatment groups were fed a commercial layer ration from 18 to 28 wk. The experimental diets were fed for 36 wk (28 to 64 wk of age). Feed and water were provided ad libitum throughout the egg production cycle. Incandescent light was provided 16 h per day from 0800 h to midnight. Lights were turned off by time clock between midnight and 0800 h. Egg Production Eggs were collected every morning at 1100 h. Egg production along with mortality in each replicate was recorded every day. Hen-day egg production was calculated by dividing the number of eggs produced by the number of live birds in each replicate. Average weeks of henday egg production were determined for the entire 36-wk experiment (Table 2). Egg Specific Gravity Egg specific gravity was conducted using 30 eggs randomly collected from each replicate on a weekly basis. These eggs were immersed in a series of salt solution (0.005-increments between and 1.090) to determine specific gravity. For statistical analysis, the data thus obtained were recorded as the percentage of eggs above [21] (Table 2).

4 512 JAPR: Research Report TABLE 2. Effects of dietary treatments on production performance of laying hens Egg specific gravity Treatment Egg Egg Shell and age production weight thickness % > slopes Treatment 1 A wk 70.6% a 62.2 g a mm b 81.1% a wk 59.9% b mm a 75.0% a wk 57.7% b mm a 67.9% b Treatment 1 average 62.7% y,z mm 74.7% y Treatment 2 B wk 69.3% a mm b 79.5% a wk 59.3% b mm a 70.8% b wk 57.7% b mm a 66.8% b Treatment 2 average 62.1% y mm 72.4% y Treatment 3 C wk 71.8% a mm b 88.4% a wk 58.3% b mm a 78.8% a wk 58.5% b 68.7 g b mm a 72.5% b Treatment 3 average 62.9% z mm 79.9% z a,b Means of the response variables for age groups with different superscripts within each column are significantly different (P < 0.05). y,z Means of the response variables (egg production, egg weight, shell thickness, and egg specific gravity) for the three dietary treatments (highlighted) with different superscripts within each column are significantly different (P < 0.05). A Treatment 1. Commercial ration with normal calcium and phosphorus levels, provided morning and evening, with limestone as the calcium source; served as the control. B Treatment 2. Commercial ration (control) in the morning, and the evening feed contained a normal calcium level with limestone as the calcium source but a lower phosphorus level than control feed. C Treatment 3. Commercial ration (control) in the morning while the evening feed contained normal calcium level (50% limestone and 50% oyster shell) but low phosphorus (same level as treatment 2 evening feed). Eggshell Thickness Eggshell thickness was measured on 30 eggs randomly collected from each replicate on a monthly basis. A micrometer was used to measure the thickness of a shell chip from the equator of the egg. These observations were averaged to determine eggshell thickness for each replicate. Egg Weight Egg weights were measured only twice throughout the experiment once at the beginning and again near the end of the experiment. Thirty eggs were randomly collected from each replicate for 240 eggs per treatment or 720 eggs in total. Statistical Analysis The complete hen day-egg production data were analyzed by split block design, using the analysis of variance with treatment and age as the main factors. The percentage of eggs greater than was subjected to linear regression analysis to determine the correlation between specific gravity and age (week of production). The slopes (unit change in specific gravity per unit change in age) obtained for each treatment between these 2 parameters were further subjected to analysis of variance. The average eggshell thickness data was analyzed, using a split block design by analysis of variance with treatment and age as the main factors. The egg weights were averaged across each replicate, and data were used for analysis of variance with treatments and age as the main factors. RESULTS AND DISCUSSION Egg Production Average 36-wk hen-day egg productions for the 3 dietary treatments were 62.7, 62.1, and 62.9% for treatments 1, 2, and 3 respectively. There was a significant difference between treatment means (P < 0.05) and age groups (P < 0.01) (Table 2). Egg production in treatment 3 (reduced phosphorus with 50% limestone and 50% oyster

5 AHMAD AND BALANDER: FEEDING PATTERN AND EGGSHELL QUALITY 513 shell as the calcium source) was significantly higher (P < 0.05) than in treatment 2 (reduced phosphorus with limestone as calcium source) but not in treatment 1. There was no difference between treatments 1 and 2. Reduction of phosphorus alone (treatment 2 vs. treatment 1) did not improve egg production, but replacement of limestone with oyster shell (treatment 3 vs. treatment 2) improved egg production. The improved egg production with oyster shell is in agreement with Hamilton et al. [22] who found increased egg production with oyster shell supplementation. These findings, however, do not agree with other investigations [23, 24] that did not find any difference in egg production with different calcium sources including 4.5% oyster shell meal or limestone replacement with oyster shell, respectively. Lack of response in egg production due to reduced available phosphorus in hen diets agreed with other published reports [25, 26, 27]. Average hen-day egg productions at 12 weekly intervals (28 to 40 wk, 41 to 52 wk, and 53 to 64 wk of production) were significantly different and are given in Table 2. Specific Gravity The percentages of eggs equal to or above egg specific gravity were 74.7, 72.4, and 79.9 for treatments 1, 2, and 3, respectively (P < 0.05). The linear regression slopes were 0.628, 0.607, and for treatments 1, 2, and 3, respectively. There was a significant difference among the treatment means (P < 0.05) but not in the slopes (Table 2). Treatment 3 (control diet in the morning and reduced phosphorus in the evening with 50% limestone and 50% oyster shell as the calcium source) eggs had higher specific gravities than those from treatment 1 (control diet, morning and evening) (P < 0.05). Treatment 3 was also higher than treatment 2 (control diet in the morning and reduced phosphorus with all limestone as calcium source in the evening) (P < 0.05). Treatment 1 and 2, however, were not different from each other. The improvement in specific gravity of treatment 3 appeared to be a function of the calcium source (oyster shell) rather than reduced phosphorus, was evidenced by the lack of any difference between treatments 1 and 2, in which reduced phosphorus was the only difference between the 2 treatments. These results are in agreement with previous reports [4, 5, 6] that partial replacement of limestone with oyster shell in the diet improves different aspects of shell quality including egg specific gravity. Results are further substantiated by a report [8] that did not find any significant difference in eggshell quality when available phosphorus was reduced from 0.4 to 0.2% with constant 3.5% calcium in laying hen diets. Eggshell Thickness The treatment means for eggshell thickness was 0.388, 0.384, and mm for treatments 1, 2, and 3, respectively. There was no significant difference in eggshell thickness among the 3 dietary treatments. The main effect of age had a significant effect on eggshell thickness (P < 0.05) (Table 2). Egg Weight The treatment means for egg weight were 65.4, 65.7, and 65.3 g for treatment 1, 2, and 3, respectively. Egg weights were 62.2 and 68.7 g for 28 and 64 wk respectively. Treatments were not significantly different from each other; however, the egg weights were significantly higher (P < 0.05) at the end of the experiment (64 wk) compared with the beginning (28 wk). Calcium source and reduced phosphorus levels did not affect egg weights. Only the increase in age of the birds increased egg weight. Lack of difference in egg weights by different calcium sources is in agreement with Cheng and Coon [24], who concluded through a series of experiments that switching from limestone to oyster shell, in short-term laying trials, showed no significant differences in eggshell quality or layer performance including egg weight. The increase in egg weight with the age of the hen is well documented. These results are also in agreement with those of Keshavarz [26] who found no significant difference in egg weight when hens were fed reducing phosphorus levels from 0.46 to 0.24% with 3.5 to 5.5% calcium.

6 514 JAPR: Research Report CONCLUSIONS AND APPLICATIONS 1. Partial (50%) replacement of limestone with oyster shell as the calcium source in the evening feed of laying hens was helpful in improving the eggshell quality as measured by specific gravity but not eggshell thickness. 2. Oyster shell was also helpful in increasing hen-day egg production. There was no difference in egg weight among the 3 treatments at a given time. Egg weights increased as hens aged. 3. Reduction of available phosphorus from 0.45 to 0.32% did not result in improved eggshell quality (egg specific gravity or shell thickness) or production performance (egg production or egg weight). 4. We concluded that eggshell quality can be improved by partial (50%) replacement of limestone with oyster shell. REFERENCES AND NOTES 1. Roland, D. A., Sr Eggshell problems: Estimates of incidence and economic impact. Poult. Sci. 67: Roland, D. A., Sr Eggshell quality. 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