Management to Minimize Reduction in Fertility and Hatchability Late in Lay

In all avian species, as well as in other animals in the animal kingdom, increasing age has an adverse effect on reproductive success. The age related decrease in reproduction in the commercial fowl is due, in part, to a decline in egg production, fertility and hatch of fertile. This decline in egg production begins to occur once hens reach their peak in egg production. However, the precise factors that influence and cause the age related decline in reproduction are poorly understood.

The decrease in fertility and hatchability with increasing hen age may be due to a decline in the ability of older hens to retain sperm in special sperm host glands in their oviduct. Research has shown that the number of sperm residing in the sperm storage glands of virgin old and young chicken hens was equivalent. However, the release of the sperm from the sperm host glands in old hens was twice that observed in young hens. The exact cause of the release of larger numbers of stored sperm cells by older hens is unknown.

However, in older hens which have experienced a decrease in fertility, artificially insemination with an increased number of sperm or by reducing the time frame between inseminations can reduced the drop in fertility. From a practical standpoint, this means that older hens require inseminations at a greater frequency than when they were young. Perhaps this supports the belief that the older hens are somehow less able than younger hens to internally store sperm for long periods.

A study was conducted to determine the effects of age of both the male and the female broiler breeder on sperm penetration, and thus fertility, using artificial insemination in caged birds. In this study, young hens had significantly higher sperm penetration values [holes in the outer membrane of the yolk caused by sperm cell attachment ] (7.27), and fertility (73.7%) as compared to old hens (4.79, and 54.9%, respectively). When comparing the males based on age, interestingly enough, old males had slightly higher sperm penetration and fertility values (7.24 and 70.6%) as compared to young males (4.82 and 58.0%), respectively. As expected, egg production from the old hens was significantly lower over the four-week period than the young hens (37.3 vs. 79.2%, respectively).

Male role in infertility. It has been well documented that as males age the decline in fertility is associated with a reduction in the number of spermatozoa in the ejaculate and the volume of semen produced. However, when artificially inseminating hens with 50 million total sperm from either young or old males, there was not a decline in fertility or sperm penetration with increased age of the male. These results were not expected, but indicate that the physiological capabilities of sperm to penetrate and fertilize the ovum remains largely intact in older males. Results from this study show that if the physical abilities and libido of older males is preserved, their ability to fertilize hens will not be reduced as they age. The challenge, then, lies in preserving the older males desire and physical abilities to successfully complete matings. In the hen, physical impairments or the lack of response to male aggression may contribute to the decrease in fertility; while male competition, physical injuries and decreased libido are contributing factors in the male.

Many producers try to overcome the negative effects of the older males by spiking flocks with young males beginning at ~40 weeks of age or when the male to female ratio gets too low. According to the literature, these young males should have higher concentrations of sperm and ejaculates of greater volume, however this may not always be the case. More often than not, the benefits of spiking are not due to increased mating by the newly added younger males. The primary initial reproductive benefits come from an increase in activity and aggression of the older, established males as they are challenged by new males. This idea is supported by the concept of intra-spiking in which a number of males are switched from either one end of the house to the other, or same age males moved from adjoining houses on the same farm. The young males used to spike flocks should be well fleshed and physically fit in order to establish themselves in the house and avoid the social castration that occurs to males unable to compete with the established males in a flock.

Hen role in infertility. As expected, in the previously mentioned study there was a considerable effect of hen age on egg production. Also, as expected, there was a corresponding drop in fertility in older hens as compared to the younger hens. Although the effects of age on fertility and egg production are well understood, prior to this study it was not known whether sperm had the same opportunities to fertilize ova from older hens as compared to the younger hens. Results from this study indicate that, when artificially inseminated with similar numbers of sperm, average sperm penetration was decreased in the older hens as compared to the young hens (4.8 vs. 7.3 holes) regardless of the age of the males used for sperm collection and insemination. However, the method of evaluating sperm penetration used in this study evaluated both sperm transport and storage within the hen and the capabilities of sperm to bind and penetrate. Thus, it was impossible to determine if the decrease in fertility was due to a reduction in the sperm transport and storage capacity of the hen or if sperm were less able to bind and penetrate. Nevertheless, the data indicate an obvious reduction in the ability of older hens to maintain optimum fertility when managed similarly to younger hens.

A few possible explanations exist as to why this drop in fertility occurs in older hens. These possibilities are: 1) sperm are released from the sperm storage glands in older hens more readily or in larger numbers than in young hens, 2) older hens are typically heavier and fatter which likely reduces the size of the sperm storage tubules thus older hens would not store as many sperm as younger hens, 3) sperm stored in older hens do not retain their viability as long as when stored in young hens, or 4) older hens produce less receptor sites on the ovum for which the sperm are able to bind and penetrate prior to fertilization.

The first scenario involving a more rapid release of sperm from the storage tubules does not seem as likely as a sole player in the reduction in fertility. This is due to the fact that if viable sperm were released from the sperm storage tubules in larger numbers in the older hens, this should be reflected in a subsequent increase in the measured sperm penetration values while not necessarily indicated by increases in fertility. From the previous study, following a single insemination older hens actually had a more drastic drop off in sperm numbers available to fertilize the ovum than younger hens.

The second scenario would help to explain why older, heavier hens can attain similar fertility levels if they are inseminated more frequently. If the reduction in fertility was solely due to less sperm available for fertilization then simply increasing sperm numbers in older hens would provide adequate fertility as data in our study showed. This would mean that commercial flocks in peak production with males which deposit excess sperm into the hens with each mating are likely to see a less drastic drop in fertility as the birds age. However, flocks in which the males do not produce and deposit excess sperm, will undoubtedly experience fertility problems much earlier in their life.

The third suggestion that sperm that is stored in older hens do not retain their viability as long is also possible. The more rapid decline in sperm penetration and fertility in older hens following a single insemination could occur due to sperm cells that are less capable of fertilizing the egg. There may be enough physiological changes in the hen to change the environment in the reproductive tract where sperm are stored in the host glands. If there are enough changes in the sperm storage environment of the hen's oviduct, a smaller percentage of the stored sperm would remain viable and capable of fertilizing the egg.

Lastly, there is likely a decrease in the number of sperm receptors on the surface of the ovum in older hens. When values for sperm penetration of the outer membrane of the ovum were determined for both old and young hens in vitro (outside the body of the hen), there was less sperm penetration in ovum from older hens. This method removes factors such as sperm release from storage sites, quantity of sperm stored, and duration of viable sperm storage as well as sperm transport in the oviduct and the success rate of actual insemination.

From this study then, what is the effect of age on the ability of older hens to produce fertile eggs? While it is commonly believed that most flock fertility problems are male related, from this study it is evident that the reduced fertility in older flocks is due in part to physical and physiological changes in the hen. However, given the fact that each male is responsible for anywhere from seven to ten hens, and through proper flock management fertility is often maintained, male management is still often to blame for poor fertility.

Recently, records from broiler breeder flocks raised in the last several years were sorted and analyzed. These records were then separated out to include all flocks where a male body weight, or a hen body weight was recorded. Each record included flock information for a specific week of production, therefore, the total number of records does not indicate a total number of flocks. The records which included either a hen or male body weights were then sorted by age and records were pulled to compare all flocks at 30, 35, 40, 45, 50, 55, and 60 weeks of age. Flock production was then compared with the average body weight of the breeders.

Effects of male body weight. For the records which included a male body weight, each group from 35 to 55 weeks of age showed an increase in production parameters as there was a corresponding decrease in male body weight as shown in Figures 1 and 2. Obviously, there is a happy medium in obtaining proper male body weight. Too light a male will also cause serious problems reproductively. However, the data from this large sample of commercial broiler breeder flocks, clearly suggest that flocks with overweight males do not perform as well as those flocks where male body weight has been kept in control. As previously mentioned, although most older males are physiologically capable of producing high levels of fertility, they tend to lose the physical necessities to effectively mate breeder hens as often as necessary. The reduction in the physical necessities to mate may be caused by soreness in the legs and feet which restrict the mobility and balance necessary to successfully complete matings, or they simply lose the desire to mate hens frequently. Also, as was discussed previously, older hens require more frequent matings in order to maintain fertility, and overweight males often do not provide this.

 

Although this concept is well understood by most broiler breeder managers, too often they are more concerned with having under weight or under fed males as opposed to a thicker, robust and slightly heavy male. Also, it is well understood that breeder males should not lose weight at anytime in their life cycle, so keeping them gaining a small amount, but not too much weight is difficult. Indeed, while severely under weight males will actually shut down their reproductive system, over weight males often do not experience physical problems which reduce fertility until late in the production cycle of the flock. While many producers feel that a slightly heavy male may be more active and capable of attaining fertility early, from this data set flocks with the lowest male body weight at 35, 40 and 45 weeks of age also had better reproductive performance. So, from this data, the benefits of strict control of male body weight are seen throughout the production life of the flock. Strict control of weight gain and over all body and fitness can only be achieved through monitoring the body weight from a sufficient number of males often and correctly throughout the breeder house.

Effects of hen body weight. Other than egg production and shell quality, reproductive performance of a flock is determined by fertility, and when problems exist the male is generally blamed. Indeed, considering that each male is 'responsible for' eight to ten hens, it would appear that male problems can rapidly affect a large number of hens. However, this concept is probably over rated with hens contributing a greater responsibility to fertility than previously believed. Using the same data set discussed previously, flocks with hen weights recorded at 50 and 55 weeks of age were sorted by reproductive success and it was found that hen body weight was also a significant factor in overall flock hatchability as seen in Figures 3 and 4.

Again, there is a happy medium as to maintaining breeders too light, but the data set indicates that when older hens are too heavy, reproductive performance suffers as well as egg production. The possible explanations of this are several. One, relates to the storage of sperm cells in the sperm storage glands. As it was postulated, when hens become overweight, the excess mass in the abdominal region may cause the holding capacity of the sperm storage tubules to be reduced. If these hens, which are already less capable of producing fertilized eggs, have a reduced ability to store viable sperm cells long term, and cannot internally store as many total sperm cells, fertility problems due to age would be compounded. Additionally, excess body weight, whether a function of a larger frame size or body mass, may decrease the success rate of male mating activity. In either case, the data makes it apparent that heavier hens do not reproduce as well as lighter hens as they age.

 

In conclusion, it is well understood that age does negatively affect reproduction and fertility in broiler breeders. While the fertilizing and penetration abilities of sperm from older males appears to be relatively unaffected by age, the hen undergoes some physiological changes as they age that affect their ability to be fertilized. However, in addition to management practices such as spiking, and maintaining appropriate active male:female ratios, body weight is clearly a major factor to maintain broiler breeder physical ability and desire to produce fertile eggs. While frame size and actual fleshing of the bird are equally important to actual body weight, these data clearly indicates a strong correlation between weight control in breeders and achieving a high fertility level throughout the life a broiler breeder flock.