Sheila E. Scheideler
Dept. of Animal Science
University of Nebraska
Lincoln, NE
U.S.A.
Introduction
Most commercial egg producers know they should add large particle calcium to their laying hen rations as the hens age to optimize night time calcium availability and eggshell quality. This knowledge stems back to research conducted as early as 1892 (Collier, P.).
Collier wrote a New York Agricultural Experiment Station Bulletin recommending oyster shell as a feed source of calcium for laying hens. Scott et.al., (1971) published a fairly in depth research paper on the effects of substituting 2/3 of the calcium in the diet normally from pulverized limestone with "hen size" oyster shell on shell quality. Scott and his colleagues documented improved eggshell breaking strength, increased serum Calcium and increased gizzard retention of calcium particles in hens fed 2/3 of their dietary calcium from oyster shell. This was one of the first modern studies reported which pointed out the advantages of large particle calcium staying in the gizzard during the dark part of the hen's photoperiod, thus providing calcium during the later hours of egg shell calcification.
The next major research reported on this topic was in the early 1990's. In 1990, Rao and Roland reported that hens consuming large particle limestone (LPL) solubilized and retained a higher percentage of calcium compared to hens consuming small particle limestone (SPL). The authors also introduced the concept of in vitro solubility of limestone and attempted to relate in vitro to in vivo limestone solubilities. They reported that the in vitro solubility rate of calcium source had no influence on the in vivo Ca solubilization in laying hens when SPL sources were compared.
In 1992, the same authors (Rao et al) reported that limestone solubility in laying hens improves if retention time is prolonged in the gizzard. This was accomplished by feeding a minimum particle size of 1.0 mm to the laying hen. Less than 1.0 mm did not sustain retention in the gizzard. Zhang and Coon, 1997, more recently further explored the relationship of calcium source, size and in vitro and in vivo solubility on gizzard limestone retention in the laying hen. They reported an inverse relationship between in vivo and in vitro solubility of limestone in the laying hen. Their data showed that feeding a large particle limestone (>.80 mm) with low in vitro solubility (30-50%) was retained in the gizzard for a longer time, thereby increasing in vivo solubility to a 94% maximum.
This article is focused on calcium sources: limestone, oyster shell and eggshells, particle size (large versus small) and percent large particle calcium in the ration. Solubility will not be addressed. There are a number of calcium carbonate feed sources available to the laying hen industry - limestone (of varying particle sizes from various quarries), oyster shell from a limited number of suppliers and eggshells coming primarily from the egg processing industry. All of these feed sources have various attributes and can find their way into the laying hen ration. Oyster shells and limestone have been calcium sources for the laying hen since producers started feeding hens in large-scale production units.
Recycling eggshells waste into a feed ingredient is a more recent management tool and is quite attractive to laying hen operations breaking millions of eggs each day. With care and expertise, eggshells can become a viable and economical source of calcium in the laying hen ration.
We have conducted three studies at the University of Nebraska over the past ten years on this topic and the Author would like to share the results with the readers from those 3 studies.
Trial One: Eggshell calcium effects on egg quality and calcium digestibility in 1st or 3rd cycle laying hens
The objective of this study was to compare the availability of calcium from dried eggshells from two commercial egg breaking plants to various combinations of fine and large particle Ca sources for laying hens at two ages.
Six diets were fed to either 108-wk-old Babcock B300 hens (3rd cycle) or 25-wk-old Dekalb Delta hens for 8 weeks.
The six diets varied in calcium source as follows: 100% whole eggshell from Plant 1, 100% whole eggshell from Plant 2, 50:50 blend of fine and large limestone, 75% fine limestone and 25% oyster shell, 100% fine limestone, 100% ground eggshell from Plant 1.
The whole eggshell products did not contain much large particle size product (>.8mm). Results of this study showed that all of the calcium source treatments adequately supported egg production and egg weight. However, egg specific gravity was significantly greater for eggs from hens on the diets including large particle size calcium (50:50 limestone diet and 75:25 lime:oyster shell diets) compared to hens on diets with 100% fine limestone or 100 % ground eggshell. This does not necessarily mean that the ground eggshells were not available to the hen. Calcium digestibility data indicated very good availability of calcium to the hen from ground eggshells. It was just the lack of large particle size in these diets which negatively affected egg specific gravity. The whole eggshell products by themselves also did not have adequate large particles for the older Babcock hens to support egg specific gravity, but were adequate for the younger Delta hens.
In summary, calcium from ground eggshells is a highly available calcium source, but it needs to be balanced with a large particle calcium source such as large particle limestone or oyster shell to maintain shell quality in laying hens. Whole eggshells (not ground) can also be used but they are not a clearly defined mixed particle size.
Trial Two: Calcium source (particle size) in 3 strains of laying hens
This study was conducted in 1995 at the University of Nebraska. It was a 42 week long trial looking at 3 dietary calcium sources (100% fine limestone, 75% limestone and 25% oyster shell or 50% limestone and 50% oyster shell and 2 levels dietary calcium intake (Step-down or Step-up) in a 3 x 2 factorial arrangement. Dietary treatments were fed to 3 strains of laying hens: Hyline W-36, Babcock B300 and Dekalb Delta.
Table 2 shows the diet and strain effects on egg production parameters and egg specific gravity.
Calcium source (particle size) only significantly affected egg mass and egg specific gravity. Egg mass was greatest for hens fed the 75:25 limestone:oyster shell combination. Extra oyster shell given at a 50:50 combination was detrimental for egg size, but good for shell quality. Egg specific gravity increased significantly as the proportion of large particle increase from 0 to 25 and 50% from oyster shell. Level of calcium in a step-up versus step-down program had no significant effects on any of the egg production parameters or eggshell quality measurements.
Table 3 shows the effects of diet and strain on egg size and percent undergrades. Percent undergrades decreased significantly when oyster shell was increased to 50% compared to 25 or 0% in the ration. However, this improvement in undergrades was accompanied by an increase in the proportion of medium and large size eggs and a decrease in X-large eggs. Calcium level (step-up or step-down programs) had no effect on egg size or incidence of undergrades.
Trial Three: Optimum blend of fine: large particle size limestone and dietary calcium levels for Hy-Line W-36 and W-98 strains of White Leghorn hens
This is the most recent trial conducted at the University of Nebraska on this topic. The goal of this research was to refine the optimal blend of fine: large particle size limestone for specific layer strains (W-36 and W-98). Table 4 shows the dietary treatment combinations for the 52 week long study. Each of the 3 calcium particle size programs was combined in a factorial arrangement with 2 levels of dietary calcium for a total of 6 dietary treatments (Table 4).
Calcium program (particle size) had little to no effect on feed intake, egg production, egg weight, or egg mass. Calcium source particle size did significantly affect percent shell during the peak egg production period and specific gravity during the peak egg production period and for the overall average of the entire experiment (Table 5). The data indicate that Program three did not adequately support eggshell quality compared to Programs one and two during peak egg production. This is not totally surprising given that Program 3 was the 100% fine limestone treatment from 18 to 40 weeks of age. This data is supported by a non-significant increase in percent undergrades from hens on Program 3. Calcium level also significantly affected percent shell and egg specific gravity showing improvements when increased to level II.
Conclusions
Laying hens need at least 25% of their calcium from a large particle calcium source. Both oyster shell and large particle limestone can meet that need. Hens do not produce strong shells on a 100% fine limestone diet even when they are young. Not enough data exists at this time to justify increasing large particle to more than 50% of the ration as hen's age. Ground eggshells can be a good source of fine particle size calcium for laying hens.
References
Collier, P., 1892. Oyster shells as food for laying hens. New York Agr. Exp. Sta. Bul. 38:1-10.
Rao, K.S. and D.A. Roland, 1990. In Vivo Limestone Solubilization in Commercial Leghorns: Role of Dietary Calcium Level, Limestone Particle Size, In Vitro Limestone Solubility Rate, and the Calcium Status of the Hen. Poultry Sci. 69:2170-2176.
Rao, K.S., D.A. Roland, J.L. Adams, and W. M Durboraw, 1992. Improved Limestone Retention in the Gizzard of Commercial Leghorn Hens. J. Appl. Poultry Res. 1:6-10.
Scheideler, S.E., 1998. Eggshell Calcium Effects on Egg Quality and Ca Digestibility in First or Third Cycle Laying Hens. J. Appl. Poultry Res. 7:69-74.
Scott, M.L., S.J. Hull and P.A. Mullenhoff, 1971. The Calcium Requirements of Laying Hens and Effects of Dietary Oyster Shell Upon Egg Shell Quality. Poultry Sci. 50:1055-1063.
Zhang, B. and C.N. Coon, 1997. The relationship of calcium intake, source, size, solubility in vitro and in vivo, and gizzard limestone retention in laying hens. Poultry Sci. 76:1702-1706.
From Proceedings of the "Midwest Poultry Federation Convention", St. Paul, Minnesota, U.S.A.
