A fresh egg has thick albumen (egg-white), whereas an egg with watery albumen is considered to be an older egg. However, it is not always the age that determines the quality of the albumen. Many factors are involved. It is now questioned if in hot summers the quality of drinking water has a role to play in the quality of the albumen.
By Michael A. Grashorn and Saskia Simonovic, Department of Poultry Science, University of Hohenheim, Stuttgart, Germany (firstname.lastname@example.org)
Freshness is the most important quality criteria for table eggs and can be visibly noted by the size of the air chamber or by the height of the thick albumen in the broken egg. It is well known that ageing of the egg during storage increases egg chamber size and decreases height of thick albumen. Thick albumen is the result of the linkage between egg white proteins ovomucin and lysozyme, which is most stable at pH 7.5. During egg storage, water and carbondioxid are released from the egg by the pores resulting in an increase in pH. Ovomucin and lysozyme then dissolve and the egg albumen turns to liquid.
Besides ageing of the egg, it is knownthat genetic background and the healthstatus of the hen as well as climatic conditions in the house, bird feed composition and drinking water qualitymay influencethe quality of thick albumen. Especially during summer months, eggs on the farm are often observed with liquid albumen, even though they are only a few days old. As temperature increases and feed intake may remain stable, it is questioned whether the quality of drinking water may be responsible for the observed changes in albumen consistency. Therefore, an experiment (see Box) was conducted to investigate the effects of different pH levels in drinking water and supplementation of diets with or without organic acids on albumen quality.
Treatments were as follows:
• ET- = temperature continuous 22°C
• ET+ = 14 hours 22°C and 10 hours 30°C• W- = drinking water pH = 6.5
• W+ = drinking water pH = 9.5
• D- = with organic acid in water
• D+ = no organic acid
In the trial, water intake as well as egg production were recorded daily. Feed intake was recorded once a week, and faeces of hens and eggs were collected once a week for further analyses. In the faeces, dry matter content and pH were determined. In eggs, egg weight, albumen height, pH and dry matter content of albumen were recorded. Haugh units were calculated on the basis of egg weight and albumen height. All data was subject to an analysis of variance considering factors, including temperature, diet and drinking water and their interactions. Changing of climatic chambers was considered as a co-variate in the statistical model.
Water intake of hens increased under high environmental temperatures and high pH-level of drinking water (W+) distinctly (Figure 1). In contrary, supplementation of diets with organic acids did not affect water intake. Mean water intake amounted to 250 ml per hen per day with a difference of 30 ml/d between W- and W+ and 50 ml/d between ET- and ET+, respectively.
Feed intake was higher for the diet without supplementation of organic acid and in hens offered drinking water with low pH (W-). In contrary to general knowledge, feed intake was higher under higher temperatures. Furthermore, a significant interaction was observed between environmental temperature and diet. Under normal temperature (ET-) hens ate more feed with organic acid (D+) and under high temperature (ET+) hens ate more feed without organic acid (D-).
Drinking water with low pH resulted in a lower pH in faeces and drinking water with high pH resulted in a higher pH (Figure 2).
Supplementation of the diet with organic acid did not change pH in faeces, but pH of faeces was higher under high environmental temperature. Dry matter content of faeces was higher for drinking water with low pH, for feed with supplementation of organic acid and for moderate environmental temperature (Figure 3).
Egg quality was also influenced by treatments. Feeding a diet with organic acid increased egg weight, and albumen height was higher for treatments drinking water with low pH, feed with organic acid and high environmental temperature (Figure 4). Drinking water with high pH, feed without organic acid and moderate temperature resulted in higher albumen pH (Figure 5). Dry matter content of albumen was lower for drinking water with high pH and feed without organic acid. Also, dry matter of albumen was higher under high environment altemperatures. This is in agreement with the higher water intake in these groups.
No negative effect of temperature
The experiment confirmed expectations that albumen quality is affected by ion concentration in drinking water and feed. High concentration of H+ ions (low pH, acidic) resulted in lower pH, higher height and higher dry matter content of albumen. In contrast, lower concentration of H+ ions (high pH,basic/alkaline) impaired albumen quality.
Furthermore, drinking water with high pH negatively affected consistency of faeces, which was visible by a lower dry matter content. In contrary to the effects of concentration of H+ ions in drinking water, supplementation of a diet with organic acids did not affect albumen or faeces quality distinctly.
A surprising observation in the present investigation was the missing negative effect of high environmental temperature on albumen quality. Increased water intake under high environmental temperature did not impair albumen quality, although it did result in a higher dry matter content of faeces. Obviously, 30°C ambient temperature is not sufficient to provoke heat stress with its negative effects.
Water has a minimal effect
In conclusion, observed effects of treatment factors (pH drinking water, organic acid in diet, environmental temperature) on albumen quality were not extended enough to explain liquefaction of albumen during the summer months. Obviously, changes in the concentration of H+ ions in drinking water and feed, which strongly affect the acid base equilibrium in the hen’s organism, are not compensated by excretion via the egg. The water balance in the hen is mainly corrected by excretion via the faeces. This is not surprising as during incubation the albumen of the egg has the function of an antimicrobial barrier for the protection of the developing embryo.
Changes in the pH of the albumen result in decreased activity of albumen enzymes (like lysozyme) and by this the protective capacity is reduced. The visible effect of this change is the liquefaction of albumen.
For the general assessment of the results, one important point has to be considered. In this experiment only concentration of H+ ions was modified by adding either sodium hydroxide or hydrochloric acid. Therefore, the total concentration of ions was not markedly changed. In literature it is documented that severe changes of the electrolyte equilibrium in the drinking water may have distinct effects on the hen’s metabolism. So, the general conclusion is that further research on the potential reasons for the observed liquefaction of the albumen during the summer is necessary.
In the study, 32 LSL laying hens aged 24 weeks were used. The hens were kept in single cages in two climatic chambers at the University of Hohenheim, Stuttgart, Germany. One chamber was run with a continuous temperature of 22°C (ET-), whereas, in the other chamber a temperature programme of 14 hrs 22°C and 10 hrs 30°C (ET+) was applied. Hens were provided ad libitum a standard layer diet with (D+) or without (D-) supplementation of 1% calcium propionate (Luprosil®). Drinking water was adjusted to either pH 6.5 (W-) or pH 9.5 (W+) according to the German drinking water directive by using hydrochloric acid (HCl) and/or sodium hydroxide (NaOH), respectively. Drinking water solutions were freshly prepared every day. Treatments were distributed over chambers in a systematic way resulting in a 3-factorial approach: (2 climatic conditions) x (2 diets) x (2 drinking water) = 8 treatments x 4 hens = 32 hens, in total. Temperature conditions of chambers were exchanged after 2 weeks. The whole experimental period lasted 4 weeks. Lighting was 16 hrs of light and 8 hrs darkness per day.