Maximizing Fertility of Semen

Turkeys are the only commercial poultry species completely dependent
upon artificial insemination for fertile egg production. Although time-
and labour-intensive, artificial insemination has proven to be a key
strategy for achieving rapid genetic improvements in economically
important traits such as growth rate and feed efficiency. The practice
of artificial insemination also has resulted in more efficient
utilization of the male by increasing the ratio of toms to hens, where
diluted semen from one parent-stock tom can be inseminated into 10 or
more hens. One benefit of artificial insemination that has not been
fully realized by the industry is that it maximizes the fertility
potential of turkey semen.

Turkeys are the only commercial poultry species completely dependent upon artificial insemination for fertile egg production. Although time- and labour-intensive, artificial insemination has proven to be a key strategy for achieving rapid genetic improvements in economically important traits such as growth rate and feed efficiency. The practice of artificial insemination also has resulted in more efficient utilization of the male by increasing the ratio of toms to hens, where diluted semen from one parent-stock tom can be inseminated into 10 or more hens. One benefit of artificial insemination that has not been fully realized by the industry is that it maximizes the fertility potential of turkey semen.

A Little Goes  a Long Way Small improvements during the course of semen collection, handling and insemination will maximize the fertility potential of toms. Advertisement

Semen Evaluation
Experienced semen collectors know to avoid pooling turkey semen that is yellow in colour or has a watery consistency; however, there are other indicators of semen quality that cannot be determined by visual inspection of the semen. For example, the number of live, motile sperm in semen cannot be assessed without scientific instrumentation. One parameter that has been directly correlated with tom fertility is sperm mobility, or the ability of sperm to swim forward through a dense medium.

While a large percentage of sperm within an ejaculate may be motile, not all sperm movements are as equally effective in propelling sperm through the female reproductive tract. For example, sperm swimming in a circular pattern are less likely to reach the sperm storage tubules in the hen’s reproductive tract than sperm moving forward with straight-line velocity. Research has proven that the sperm mobility phenotype of the tom can predict paternity. When semen from seven to 10 toms of differing sperm mobility was pooled and inseminated, the one or two toms with the highest sperm mobility phenotype sired the majority of the poults.1

Selecting sires on the basis of sperm mobility has the potential to alter the way breeder toms are managed. Sorting out males that are not contributing to production could translate into significant savings for turkey breeders. Not only is the sperm mobility phenotype heritable in poultry, the trait also is maintained throughout production.2,3 More recently, we identified physiological differences in sperm from high and low mobility phenotype toms.4 Use of sperm mobility as a selection tool, however, requires growing males to sexual maturity. Ideally, the use of genetic markers to predict sperm mobility phenotype in younger birds would translate into significant savings for the industry.

Semen Handling
Even if breeder operations only use semen from high mobility toms, mishandling semen after collection can affect the outcome of artificial insemination regardless of semen quality. Failure to protect the semen from light, allowing water to come in contact with semen, improper semen dilution and inconsistent holding conditions all can diminish the fertilizing potential of turkey semen. Strict attention to semen holding conditions is especially important when toms are maintained in a stud-farm setting, as semen will be transported long distances to reach hen barns.

Once semen is diluted, the two most important conditions for holding semen are proper aeration and temperature. Because turkey sperm require a source of oxygen to maintain metabolism, semen transport vials should not be completely filled and should be loosely capped. Ideally, using a mechanical agitator and ensuring an adequate surface area for gas exchange will maintain semen viability for up to four hours after collection if the transport temperature is close to refrigeration (4˚C). The lower temperature slows sperm metabolism and prolongs the ‘shelf-life’ of diluted semen.

It has been suggested that maintaining semen at a temperature of 0˚C during transport is beneficial. We have evaluated holding semen at both temperatures and found no significant differences in candled fertility; however, the overall percentage of early-dead embryos was lower for semen held at 0˚C (2.56 per cent) than 4˚C (5.14 per cent).

It is important to document semen-handling procedures, as accurate data logs can help to troubleshoot unexpected drops in fertility. This is true whether toms are maintained on-farm or in a stud-farm setting. It is often mistakenly assumed that semen from on-farm toms requires minimal evaluation and/or record keeping compared to semen from stud farms. Considering the investment in purchasing and maintaining large numbers of toms, semen quality control should not be overlooked. Semen collection and handling logs enable the breeder to pinpoint the semen source in the event of disease outbreak or determine if semen was inadvertently mishandled by holding too long prior to insemination.

Equally important to maintain are insemination report logs documenting the semen delivery time (if applicable), number of hens inseminated per semen pool, and the time taken to use each semen pool. Keeping a record of time from semen collection through actual use of the semen will call attention to the amount of time semen is being held, and provide an effective mechanism for improving semen quality, especially when toms are not located on the same farm as hens.

Artificial Insemination
Sperm storage tubules are a reproductive feature in birds and reptiles that permits a reservoir of sperm to be held and continuously released over time to fertilize a succession of eggs. The behavioural strategy behind the physiology is that most hens will not copulate after the first egg has been laid. For example, wild turkeys lay a clutch of 10 to 14 eggs during a two-week period. Multiple copulations prior to the first ovulation ensure that the sperm storage tubules are filled to capacity and that the last ovulated egg will be fertilized even though the hen has not mated for two weeks. Modern insemination practices in the turkey industry make partial use of this reproductive capacity by conducting two to three inseminations during the ‘pre-lay’ period (for example, seven to 10 days after photostimulation), followed by weekly inseminations during the 26 to 28 weeks of egg production to ensure fertility rates >95 per cent.

Given the capacity of the hens to store semen for two weeks, the full fertilizing potential of semen is not being realized within the turkey industry. A common misconception is that inseminating large numbers of sperm each week will improve fertility when, in fact, good insemination techniques permit lower semen doses without compromising fertility.

Weekly insemination doses as low as 100-150 x 106 sperm/hen from average to high mobility toms, when properly inseminated, will yield 96 to –100 per cent fertility throughout production.4 Most breeder operations inseminate 12-18 hens/ml of semen, which is equivalent to 250-375 x 106 sperm/hen if the starting sperm concentration of the undiluted semen is 9 x 109 sperm/ml (which is the average sperm concentration for turkeys). A further complication occurs if the sperm concentration of the semen pool is not determined, as the actual number of sperm inseminated is unknown and may be either too high or too low. Inseminating higher sperm numbers than needed wastes semen; while inseminating sperm numbers <100 million sperm could compromise fertility, especially if semen is mishandled and/or the insemination technique is poor.

summary
Small improvements during the course of semen collection, handling and insemination will maximize the fertility potential of toms. Quality control and accurate record keeping throughout the process are often overlooked as sources of improvement. The potential exists in today’s breeder operations to more effectively utilize toms through sire selection, lower semen doses and decreased insemination frequency.

This paper was presented at the Midwest Poultry Federation Convention. To contact the author,
e-mail: julie.long@ars.usda.gov
Full references are available at www.canadianpoultry.com .