Creating the ideal hatching egg

The modern breeder female is a genetic compromise between two very different selection criteria. This parent must have the genetics for rapid and efficient growth, and yet exhibit a high rate of egg production to supply the next generation of broiler chicks.

Reproductive problems arising from decades of genetic selection for meat production traits have impaired the reproductive ability of both broiler parents (Siegel and Dunnington, 1985). Managing the ovary of the broiler breeder is the core of effective broiler breeder management.

Understanding the ovarian function of the chicken and its interaction with nutritional status, age, and strain is essential to getting this done effectively. Specific feed ingredients, bird age, and flock management decisions can directly affect semen quality, the oviduct environment, and the egg environment.


Sexual maturation

Estrogen is a key hormone in the reproductive process. It is responsible for many of the visible changes during the transformation of a pullet into a hen. As plasma levels of estrogens increase, externally visible features include reddening and enlargement of the comb and wattles, a prenuptial feather molt (feather drop) and a widening of the pubic bones to permit egg passage.

Internally, estrogen stimulates liver production of egg yolk lipids with a significant change in the color and size of the liver. Finally, the oviduct enlarges and becomes a secretory organ for deposition of albumen. The hormone messages being relayed between the ovary and the hypothalamic and pituitary control centers are altered by feed intake. Besides affecting follicle formation and reproductive control, feeding level can alter the viability of the embryo through changes to the egg and to the early maturation process.

Following mating, the hen will store sperm in the highly specialized microenvironments of the sperm storage tubules. The survival of the sperm to the point of insemination depends on a combination of sperm quality and the ability of the hen to provide a safe environment.


Nutritional impact on fertility

The fertility of a broiler breeder flock typically peaks between 30 and 35 weeks of age and declines thereafter. The male has a declining sperm number with age, and egg fertility and hatchability also decrease – partly due to large egg size in combination with reduced shell quality. Rapid declines in flock fertility are often due to insufficient bodyweight control.

Flock fertility is often inversely correlated with growth rate. Hocking et al. (2002) reported that feed-restricted and overfed hens have similar fertility when provided a similar semen source, but overfed hens have a reduced hatchability due to an increase in late embryonic death.

Duration of fertility (measured by monitoring fertility in consecutive eggs) is also reduced under conditions of overfeeding (Goerzen et al., 1996). Underfeeding hens, while being potentially detrimental to rate of lay, does not appear to hurt fertility or hatchability (Fattori et al., 1991).


Egg composition

Chickens lay their eggs in sequences, which are periods of consecutive egg laying days.

Overfed hens typically have shorter laying sequences (Robinson et al., 1991a), which will result in more ‘first of sequence’ eggs. These eggs contain a follicle that was held back from ovulation over the pause day(s) and is more likely to undergo embryonic death (Robinson et al., 1991b). Short sequence length may also be due to erratic oviposition (laying eggs at odd times of the day), which increases the likelihood of inadequate shell formation and can further reduce hatchability.

As hens age, egg size increases while shell quality goes down. Rate of egg production has a big influence on egg size and composition. High producing hens sometimes have both smaller eggs and poorer shell quality because they are not able to keep up with the magnitude of the demands of their rate of egg production.

A hen that is not laying as well will not have as many large yellow follicles on the ovary. These larger follicles result in a greater egg size. The correlation of egg size with chick size is about 0.89. Whereas big chicks tend to make big broilers, ultimately feed intake is the most important factor affecting broiler weight (Pinchasov, 1991). Increased dietary energy content can increase the percentage of yolk in the egg, thereby providing more energy and protein to the offspring (Spratt and Leeson, 1987).

In colder climates, low barn temperatures can influence egg size by diverting nutrients towards maintaining body temperature. High temperatures do not decrease feed intake in broiler breeders to the extent they do in layers, but can affect shell quality. Panting reduces bicarbonate retention, which can reduce the ability of the hen to deposit shell.


Link between egg quality and hatchability

Some factors affecting embryo survival, such as hen age, are out of our control. However, factors such as hen body condition, egg size and hatchery environment can be influenced through management decisions. Egg storage in older flocks, for example, can cause a more rapid deterioration in albumen quality, which may contribute to the reductions we see in hatchability with age (Lapao et al., 1999). Storage times of seven days have also been reported to reduce broiler weights between 21 and 42 days of age (Tona et al., 2004).

Hatchability is characteristically lower prior to peak production. These young flocks lay eggs with high viscosity albumen and benefit from storage for a few days prior to incubation to thin the albumen (Lapao et al., 1999). Albumen pH rises with storage and hen age. Normally pre-incubation storage leads to reduced hatchability through morphological changes in the blastoderm and embryo malformations (Mather and Laughlin, 1979).

The albumen gradually liquefies with storage, which may facilitate movement of nutrients from the albumen to the blastoderm. In eggs from older hens, storage can cause too much albumen degradation, which can allow the blastoderm to move too close to the shell and cause mortality through dehydration (Brake et al., 1993). These negative effects on albumen quality already begin to appear one day after lay (Lapao et al., 1999).

Despite links to reduced hatchability, the storage of eggs is part of the commercial incubation process. Stabilizing the albumen or slowing the rate of deterioration during storage would alleviate hatchability problems caused by extended storage periods. Several Brazilian studies examined the effects of an organic form of selenium (Se) (Sel-Plex®, Alltech Inc.) on albumen quality and consistency and noted an improvement in albumen height with organic selenium (see Rutz et al., 2005). Payne et al. (2005) reported the opposite effect, demonstrating that other factors may also influence the results obtained.

Whereas Monsalve et al. (2004) did not report a difference in vitelline membrane strength due to either an inorganic or organic selenium source, they did report a positive effect of increased selenium concentration on membrane strength.

The selenium content of the egg is greater with the use of organic compared to inorganic forms of selenium (Payne et al., 2005). There may be a protective effect of selenium on the cellular membranes of the magnum under certain conditions.

Rutz and co-workers (2005) theorized that the indirect mode of action of organic selenium might be through enhanced function of the selenium-dependent GSH-Px antioxidant system. If the secretory cells and tubular glands of the magnum are able to function more effectively, more protein will be secreted into the lumen of the magnum, resulting in a more viscous egg white (Butts and Cunningham, 1972). However, this relationship may require more examination to determine the reason for observed inconsistencies.


Antioxidant status and embryo viability

During embryo development, oxidative metabolism increases substantially over the incubation period and especially in the last few days before hatch. This normal respiration related to embryo growth results in the production of free radicals, which can cause tissue damage through lipid peroxidation, with polyunsaturated fatty acids being especially vulnerable (Surai, 1999).

The primary defense mechanisms of the embryo are a group of three enzymes (superoxide dismutase, glutathione peroxidase, and catalase), which convert free radicals produced by cellular respiration into less harmful alcohols (Ursiny et al., 1997). A second level of defense is the natural antioxidants – vitamin E, carotenoids, ascorbic acid, and glutathione protect the developing chick (Surai, 1999). The protective effects of antioxidants are especially apparent during the highly oxidative state of late incubation and the first few days after hatch.

Ensuring a good supply of antioxidant dietary ingredients, such as vitamin E, vitamin C, organic selenium and menhaden oil appears to have protective effects on the embryo, enhancing its survival. By increasing one antioxidant, others can also be affected. For example, supplementing organic selenium to breeder diets has been shown to increase levels of other antioxidants (vitamin A, E and carotenoids) in the egg (Surai and Sparks, 2001).


Maintaining male fertility: response to vitamin E and Sel-Plex® organic selenium

The need for defense from oxidative damage is also clear in the male, where antioxidant enzymes play a key role in maintaining the sperm cells. Sperm cells contain large amounts of polyunsaturated fatty acids, which allow them to maintain flexibility relating to motility (Surai, 2002). However, this means that they are also a target for lipid peroxidation.

We tested the individual and combined effects of vitamin E and selenium in broiler breeder males to see if the age-related decline in reproductive efficiency could be slowed. Individuallycaged males were fed the following diets between 45 and 65 weeks of age: Control: 10 IU/ kg of vitamin E and 0.1 mg/kg Se (as sodium selenite); Vitamin E: vitamin E increased to 100 IU/kg; Sel-Plex®: selenium increased to 0.3 mg/kg by adding 0.2 mg/kg Sel-Plex® Se; Vitamin E + Sel-Plex®: enriched levels of both ingredients. Feed allocation was based on the mean BW of the entire group.

There was a dietary treatment effect on growth efficiency. Control males lost 53 g in body weight during the experimental period while the vitamin E, Sel-Plex® and the combination treatment gained 23, 107, and 155 g between 45 and 65 weeks of age, respectively (Table 1).

While all feeding treatments increased semen concentration to some degree, vitamin E alone provided the largest improvement relative to the control. Testis weight at 65 weeks of age was also the greatest in the treatment combinations including vitamin E (Table 1). These were caged males provided the same feed allocation.

Differences in body weight over the course of the study may be a reflection of differences in nutrient utilization efficiency due to enhanced absorptive capacity at the level of the gut. Vitamin E in particular may afford some protection of gonad weight as birds age, although its impact on other measures of reproductive quality still needs to be assessed.


Table 1. The effect of additional vitamin E and/or Sel-Plex® organic selenium between 45 and 65 weeks of age on body weight gain and 65 week testis weight in male broiler breeders.





Effect of selenium source on broiler breeder hens

This experiment was designed to provide information on the role of dietary selenium form on female fertility. It was built on previous work, which suggested that the use of an organic selenium source (Sel-Plex®) could lead to improved egg production, shell quality, sperm viability, and embryo survival. The objective was to characterize specific effects of dietary selenium source on fertility and embryo viability aspects in an individually caged commercial broiler breeder stock (Ross 508).

From photostimulation (22 weeks of age), pullets were fed a selenium-free laying ration (NEG), a standard (STD) ration containing sodium selenite (0.3 mg/kg), or a selenium yeast ration (0.3 mg/kg of Sel-Plex® Se). Basal dietary selenium was 0.16 mg/ kg. The BW of the entire flock was used to determine feed allocation each week.

Individual production traits were recorded, including total and unsettable (double-yolks or shell defects) egg production, fertility, and hatchability.

The rate of lay was similar until later in lay (49-58 weeks of age) when the Sel-Plex® hens were laying at 68% compared to 61% (STD) and 60% (NEG) in the other treatments (Table 2).

A similar trend has been noted in turkey stocks, where birds with 0.2 mg Se/ kg from an organic source had a superior rate of lay starting approximately half-way through the lay cycle (Renema, unpublished data). Total and settable egg production values were statistically similar (Table 2). While overall unsettable egg production rates were also similar, during the late lay period (49-58 wk), the Sel-Plex® hens produced significantly fewer unsettable eggs (0.9%, 1.7% and 3.3% for Sel-Plex®, STD and NEG hens, respectively).


Table 2. The effect of dietary selenium inclusion and source on egg production traits of broiler breeders.


^a,bMeans within a column with no common superscript differ (P<0.05).



By the end of the trial, 100% of the Sel-Plex® hens were still in active production compared to only 87% (NEG) and 90% (STD) of the other hens. Reproduction in the broiler breeder can be a fragile state and is often the first thing to go when there is stress, or nutrients are perceived to be insufficient. The fact that all Sel-Plex® birds were still in production may relate to an improved efficiency of nutrient uptake. During the late production period, these birds were producing more eggs than hens of the other treatments (Table 2) with no effect on body weight relative to that of hens on the other treatments.

Fertility, hatchability, and hatch-of-fertile demonstrated the beneficial nature of dietary selenium, but did not differentiate between selenium sources (Table 3). Selenium in the diet was also important when comparing early embryonic mortality (1-14 days of incubation), when 5.33% of NEG embryos died compared to a mean of 3.62% in the other treatments.

A beneficial effect of organic selenium was expected for the late incubation and hatch period, as this is the time of the greatest oxidative load for the embryo, and when the protected antioxidant effects of the Sel-Plex® may be most apparent. Variability among birds was high at this time, however, and late embryonic mortality, dead-in-shells, and hatchery culls totaled 3.66%, 3.85%, and 3.14% of eggs set for the NEG, STD, and Sel-Plex® treatments, respectively (Table 3).

However, after starting from the same point at peak production, late embryonic mortality stayed almost constant in NEG and STD hens as they aged, while it actually decreased in Sel-Plex® hens. As feed allocations were reduced with age, the micronutrients would have been in shorter supply. Protective effects of the more easily absorbed organic selenium may have become more apparent at this time.


Table 3. The effect of dietary selenium inclusion and source on fertility, hatchability, embryo mortality and chick production traits of broiler breeder females.


^a,bMeans within a column with no common superscript differ (P<0.05)
¹Includes embryo mortality to hatch, dead-in-shell, and hatchery culls.



Ultimately what determines the success of a broiler breeder management program is chick production. Chick production was calculated to be 131.3 (NEG), 139.1 (STD) and 145.3 (Sel-Plex®) chicks/hen-housed by 58 weeks of age – a range of 14.1 chicks/ hen (Table 3).

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