Daniel G. Satterlee

Poultry is Louisiana’s biggest animal industry. In 2002, poultry exceeded $600 million in total value (gross farm income and value added). The production of broiler (meat-type) chickens accounts for more than 90 percent of this value. Approximately three million broiler breeder eggs are set weekly to support the number of chicks needed to produce the more than 200 million broilers reared annually in our state for human consumption. The poultry industry boasts of being the fifth largest employer in the state. 

The steady growth of Louisiana’s poultry industry mimics that of the nation and world. The U.S. poultry industry is growing at a rate of about 2 percent to 3 percent annually. In 2002, about nine billion broiler chickens were produced in America, and our country’s production of these meat-type chickens constitutes only about a quarter of broiler production worldwide.

Continued growth in the broiler industry is expected because of:

• A predicted doubling of the human population within the next 50 years.
• The likelihood that chicken meat will remain a low-cost source of high-grade animal protein.
• The favorable health image of eating chicken products.
• The expectation that customer adaptability to new poultry products will remain positive.
• The lack of cultural impediments to poultry consumption.

Because the broiler industry is rapidly expanding and because selection for greater body weight in broilers has been at the expense of egg lay, the production of more eggs is becoming increasingly important. For example, to meet global demands at current expansion rates, an extra 15 million broiler breeders will be needed annually to produce 1.5 billion more broilers for human consumption. To address this need, LSU AgCenter researchers have demonstrated the feasibility of increasing egg production in broiler breeder hens using chicken inhibin-based immunopharmaceuticals.

Inhibin is a peptide hormone produced in the ovary that acts as a brake on egg production. When an inhibin antigen is presented to the bird in the context of a foreign protein, the animal’s immune system is fooled into attacking inhibin. Similar to autoimmune diseases (for example, multiple sclerosis), the bird raises antibodies to, and thereby inactivates, endogenous inhibin, which in essence releases the brake on egg production. We have shown that immunoneutralization of inhibin by vaccination increases ovulation rates in quail, chickens (both egg- and meat-type) and turkeys.

Over the past nine years, LSU AgCenter scientists have been working in close cooperation with multiple corporate sponsors to develop safe, inexpensive and effective inhibin vaccines. The scientific development of these patented vaccines (chicken inhibin-based antigens) has led to the recent discovery of a more practical synthetic vaccine. The vaccine is comprised of a Multiple Antigenic Peptide (MAP) with a poly-lysine backbone linked to four peptides comprising the first 26 amino acids of chicken alpha-inhibin. When appropriately administered to breeder hens, it appears to be on track to produce an increase of around 10 percent in hen-day egg production during the industry standard 40 weeks of lay. This means that producers who use the vaccine could experience an increase in egg lay of about two dozen eggs per housed hen. This represents the single largest on-the-spot enhancement of reproductive performance in the history of the poultry industry. Indeed, it has taken the breeders of egg-type chickens about 20 years to achieve a lesser, about 7 percent, increase in egg lay by traditional methods of genetic selection.

Depending on management, the vaccine increases the onset, magnitude and duration of egg lay. Of equal importance, regardless of how the laying curve is affected, inhibin immunoneutralization has shown no untoward effects on eggs produced by vaccinated hens or on the chicks that hatch from these eggs. The intervention does not alter hen body weight and livability; egg size and egg shell thickness; the fertility and hatchability of eggs; or livability of hatchlings to harvest age.

This remarkable story does not end with the hen. Active immunization against inhibin holds significant promise in enhancing the fertilizing capacity of broiler breeder roosters as well. In a preliminary study, this new vaccine was found to accelerate puberty and increase fertility in aged males.

With the continued emphasis on selection for body weight in yield-type broiler breeders, overall egg fertility is declining at an alarming rate (about a half percent annually). This is most likely due to decreased gonadal function and copulation efficiency of large-bodied males. Marked declines in fertility are now commonly seen in flocks with aged males (more than 36 weeks old). This has caused producers to “spike” their old flocks with young males to increase fertility. This practice is expensive because additional flocks of males have to be maintained and risky from a bio-security standpoint because the standard “all-in, all-out” practice used in poultry is violated when young outsider males are introduced into established flocks.

Inhibin immunoneutralization of broiler breeders is a revolutionary approach that holds promise to change the poultry industry forever in a similar manner as bovine somatotropin (BST) changed the dairy industry.

(This article appeared in the fall 2003 issue of Louisiana Agriculture.)