Managing the modern broiler breeder female so that she will produce a large number of high quality hatching eggs is a delicate combination of both art and science. Over the past few decades, broiler breeders have undergone intensive selection for faster growth rate, increased yield and improved feed conversion. Although these traits are measured at the broiler level, they impact the breeder hen in ways we often do not consider. The objective with broiler breeders is to have them consume an “ideal” amount of nutrients within a given time period to produce a bird whose weight, body condition and frame allow the reproductive organs to mature and function at their best. How do we combine art and science to manage the sexual maturation of today’s broiler breeder female?


Photostimulation

One of the most critical time periods in broiler breeder hen management is the time from photostimulation (lighting) to peak production (Robinson, 1995). This period is characterized by relatively fast weight gains, in addition to changes brought about by the development of a functioning, hormone-producing ovary. Lighting the breeder pullet flock is generally considered the cue to initiate puberty, although the response to lighting can be modified by the feeding program.

At photostimulation, light energy passes through the skull of the breeder pullet into the brain and “illuminates” the hypothalamus. The hypothalamus in the brain is much like the main circuit breaker in a house; it controls a variety of body processes including reproduction. The brain acts in concert with the liver, skeletal system, ovary and oviduct to make up the reproductive system in the breeder hen. After the hypothalamus receives a photostimulatory signal (long day length above a certain threshold of intensity), the hypothalamus secretes specific hormones that travel to the anterior pituitary portion of the brain (Robinson, 1999). The anterior pituitary produces hormones known as Luteinizing hormone and Follicle Stimulating hormone that travel to specific tissues in the ovary to stimulate ovarian function.

One of the first responses seen when looking at the ovary of the pullet after lighting, is that the tiny ovarian follicles begin to increase in size. These small follicles produce large quantities of estrogens. Estrogen causes most of the reproductive transformation associated with puberty. Firstly, estrogen increases the production of yolk precursors in the liver of the bird. Visibly, the liver can be seen to enlarge and become paler as it increases in fat content for production of egg yolk lipids. Secondly, the oviduct increases in size, as it must be ready to receive ovulated follicles by the time the ovary has mature follicles ready to ovulate. Thirdly, estrogen results in changes to bone composition, so that calcium can be mobilized daily to facilitate egg shell formation. Finally, estrogen, together with male sex hormones, results in changes to plumage, comb size and sexual receptivity to males (Robinson, 1995).

Traditionally, flocks receive photo stimulation when they are 20-22 weeks of age resulting in onset of egg production at approximately 24-25 weeks of age. This program tends to maximize egg numbers, but may result  in eggs that are smaller than standard early in the laying cycle. It also often results in egg production before hens are capable of producing a quality germ cell. Lighting birds later than 20-22 weeks allows females to become larger and more mature at the onset of production. Unfortunately, lighting birds later will likely also delay egg production until 25-26 weeks. However, this may or may not affect the total number of hatching eggs produced.


Ovulatory Cycle

Yolk is deposited into follicles as they proceed through the hierarchy to become mature. Two requirements must be met for the follicle to ovulate. First, the follicle must send a hormonal signal to the hypothalamus through the release of progesterone that signals that it is mature. Second, the hypothalamus must receive the signal from the mature follicle during a 6 to 8 hour period of the day in which the hypothalamus is responsive to the progesterone signal (Robinson, 1999). Follicular maturation typically takes longer than 24 hours, which means, consequently, that the ovulatory cycle is set back slightly each day as eggs are laid progressively later in each day similar to the sequence shown in Table 1. Hens that have slow rates of follicular maturation (26-28 hours or more) lay short (2-3 day) sequences. On the other hand, hens that lay very long sequences typically have maturation rates of 24 hours, or perhaps less. Sequence length changes throughout the egg production year with the longest sequences seen at the time of peak production at about 30-35 weeks of age. All hens lay one characteristically long sequence of eggs known as the “prime sequence” which in broiler breeders is usually about 20 eggs in length (Robinson, 1999).


Table 1. Times of oviposition for individual hens laying 2- to 7-egg sequences¹.

Sequence Length

Time of Oviposition

	Day 1	Day 2	Day 3	Day 4	Day 5	Day 6	Day 7
2 eggs	09:28 AM	01:30 PM
3 eggs	08:08 AM	11:26 AM	02:40 PM
4 eggs	08:20 AM	09:45 AM	01:45 PM	03:37 PM
5 eggs	07:56 AM	09:03 AM	10:45 AM	01:11 PM	03:05 PM
6 eggs	07:20 AM	07:59 AM	09:04 AM	10:11 AM	12:56 PM	03:40 PM
7 eggs	07:47 AM	08:15 AM	09:20 AM	09:40 AM	11:36 AM	01:09 PM	03:24 PM

¹ Adapted from Robinson, 1999.


Feed Requirements

While feeding programs differ across the country due to differences in integrators, complexes, weather  conditions, seasons and genetic strains of birds, it is important to be continually adjusting the feeding program to provide the nutrients needed for optimum performance. Breeders require these nutrients for body maintenance, growth and egg production.

Body maintenance requirements, which include maintaining body temperature and systems within the bird that allow for digestion, respiration, excretion and immune response, range from 50 to 75% of a hen’s daily needs. As with most animals, body maintenance needs have priority, since the breeder hen must maintain her own body to survive. While the growth needs of hens during the post-peak production period do not contribute greatly to the hen’s daily nutrient requirements, pre-peak growth can be substantial. Nutrient needs for reproduction are a function of the number and size of eggs produced. In general, egg production exerts more influence on nutrient requirements than does egg size. This is part of the reason a service technician always has his/her calculator in hand and adjusts the feed allocation on each visit to the farm. This is an attempt to maximize egg numbers and keep hen body weight on target, since overwieght hens produce fewer eggs than trimmer hens.


Flock Uniformity

Flock uniformity is critical to proper feed allotments. If there is a great deal of variability in body weight, and all birds have equal opportunity to eat, the small birds will over-consume and larger birds will under-consume in relation to their nutrient requirements (Robinson, 1999). Uniformity issues are most critical at the time of photo stimulation and will usually result in poor peak performance as well as significant problems in post peak periods. In non-uniform flocks, birds receive the same feed allotment, but feeds are formulated for birds in lay. Since birds in lay have higher nutrient requirements than non-laying birds, nonlaying birds will over consume relative to their requirements and get fat, which will hinder future performance. Clearly, uniformity is necessary to obtain peak performance in breeder females.


Summary

Properly managing the sexual maturation of the modern broiler breeder female is critical to obtaining a high peak and large overall number of quality hatching eggs. The most critical management period for broiler breeders is from photo stimulation (lighting) to peak production. Management deficiencies during this period are always costly and often cannot be compensated for at a later date. Broiler breeders require nutrients for maintenance, growth and egg production. Maintenance needs are met first and until that happens, growth and egg production are reduced. Adjusting the feed allotment throughout the lay cycle controls bird nutrient intake. Intake must be strictly controlled to prevent hens from becoming overweight resulting in decreased egg production. Flocks must be uniform in weight and body condition in order to properly allocate feed allotments. Uniformity is especially critical at the time of lighting. Flocks that vary excessively in uniformity are nearly impossible to properly manage from a feed allotment standpoint. This will have a negative impact on performance and may lead to a low, flat peak and decreased overall production. Remember that the key to managing the modern broiler breeder female is a combination of 1) correct body weight and uniformity, 2) light stimulation, and 3) feed stimulation. A sound, consistent management program must be in place that will address each of these areas in order to be successful.


References

Robinson, F.E. 1995. Broiler breeder research update: Limiting ovarian development to maximize chick production in broiler breeders. University of Alberta, Edmonton, Alberta, Canada.

Robinson, F.E. 1999. Management for control of ovarian development in broiler breeders. Ross Technical Bulletin. April 1999. Ross Breeders, Inc.