*Dr. William A. Dudley-Cash is a poultry and fish nutritionist and has his own consulting firm in Kamuela, Hawaii. To expedite answers to questions concerning this column, please direct inquiries to Feedstuffs, Bottom Line of Nutrition, 7900 International Dr., Suite 650, Bloomington, Minn. 55425, or email [email protected]
THE opening section of the technical presentations at the Australian Poultry Science Symposium was titled "Early Chick Nutrition."
Genetic selection and improvements in nutrition have reduced the time required to produce a 4 lb. broiler to 60% or less of the time it took 40 years ago. The neonatal period (sometimes defined as the first seven days after hatch) now represents 20% or more of the whole production cycle and is expected to continue to increase as a percentage of the growout period.
The neonatal period is a time when the chick requires special management and nutrition.
Immediately after hatch, under commercial conditions, processing and delivery may delay access to food and water for 24 to as long as 72 hours. In addition, efforts to control metabolic disorders such as leg problems and ascites have led to recommending early feed (or nutrient) restriction during the first two weeks post-hatch. It is important to understand the effect of these management practices on subsequent chick development.
S. Velleman of The Ohio State University presented a paper on how nutrition affects broiler breast meat development, including possible transdifferentiation of myogenic satellite cells to an adipogenic lineage.
First off, Velleman's presentation of a complicated technical topic was given with sufficient clarity that even a nutritionist (like me) could understand it.
Velleman explained the importance of the relationship of neonatal nutrition to muscle development. Adult myoblasts (satellite cells) are myogenic stem cells. The development of skeletal muscle occurs as a result of the proliferation and differentiation of myoblasts that fuse to form multinucleated myotubes.
Muscle growth and development can be divided into two distinct periods: hyperplasia and hypertrophy. Hyperplasia occurs during the embryonic period and is characterized by an increase in muscle fiber number (proliferation).
Post-hatch muscle growth is termed hypertrophy and results in the enlargement of existing muscle fibers (differentiation and nuclear fusion with adjacent muscle fibers). The increased number of nuclei in muscle fibers coincides with increased protein synthesis and muscle fiber size enlargement. Myoblast cells are extremely responsive to the mitogenic effects of their environment, including nutrition. Nutritional deprivation or restriction has a significant effect on the myoblast cells.
Research was conducted to evaluate the effects of an immediate post-hatch feed restriction on breast muscle formation. Fertile eggs were obtained from a commercial broiler breeder company and hatched. The chicks were divided into a full-fed group and an 80% feed restriction group for the first two weeks post-hatch. Samples of the breast muscle were studied using histology to assay structure and RNA analysis of gene expression of MyoD and myogenin. MyoD expression is necessary for proliferation, and myogenin is required for differentiation.
The expression of MyoD and myogenin was affected by feed restriction during the first four days post-hatch. The restricted birds had a significant increase in MyoD expression, which would indicate an increase in myoblast cell proliferation. In contrast, the myogenin expression was reduced by about 50% in the feed-restricted group. These results indicate that the 20% feed restriction may have increased the number of muscle cells but interfered with the ability of the muscle cells to increase in size.
Morphologically, there was a significant difference in the development and structure of the breast muscle between the feed-restricted and unrestricted groups through the 42-day length of the study. In addition, increased fat deposition was observed in the breast muscle of the birds with the 20% feed restriction.
Velleman cited other authors who have found that the first week post-hatch appears to be the most intense period of myoblast cell activity in broilers. Feed depravation during the first two days post-hatch had the greatest effect on growth compared to depravation periods beginning at day 4 or day 6 after hatch.
To investigate the effect of the timing of post-hatch feed restriction on broiler breast muscle development, Velleman reported on experiments that incorporated a 20% feed restriction during the first week post-hatch compared to chicks that were fully fed the first week, followed by a 20% feed restriction in the second week post-hatch.
Limiting the feed restriction to the first week post-hatch resulted in similar changes in MyoD and myogenin expression as observed with the two-week feed restriction. The MyoD levels were increased during the first four days post-hatch, and myogenin levels were significantly decreased. Fat deposition in breast muscle was also increased as a result of the feed restriction during the first week post-hatch.
In contrast, fully feeding the birds for the first week post-hatch and restricting the feed during the second week post-hatch restored the MyoD and myogenin expression to normal levels. Morphologically, fat deposition was decreased in the breast muscle for the week 2 restricted birds.
Velleman also reported the results of cell culture research investigating the influence of levels of methionine/cysteine — above and below an optimal level — on myoblast cell development. Levels of methionine/cysteine either above or below the optimum interfered with the normal proliferation and differentiation of broiler breast muscle myoblast cells.
The Bottom Line
Nutrient deprivation in the first few days after hatch may interfere with normal muscle protein development in broiler chicks. However, if you believe that flavor and juiciness follow the fat, there may be some benefit from early feed restriction. This possibility, however, was not a part of the paper.
O. Halevy, R. Kornasio and Z. Uni of Hebrew University in Israel presented a paper on the nutritional status and muscle development in pre- and post-hatch broilers.
Reprising the comments of the previous speaker, Halevy et al. stated that holding hatchlings without food and water for more than 24 hours has long-lasting negative effects on both broilers and turkeys.
Hatchlings become more susceptible to pathogens and have decreased weight and decreased development of critical tissues and organs such as the intestinal tract and skeletal muscles. In addition, glycogen reserves are utilized during the hatching process and cannot be replenished until the newly hatched chicks have access to food.
Insufficient glycogen forces the embryo to mobilize muscle protein for gluconeogenesis, reducing subsequent growth and development. These changes affect hatchling quality and subsequent performance.
Skeletal muscle growth flows from adult myoblasts (satellite cells) mediated by a number of growth factors. Satellite cell mitotic activity begins as early as embryonic day E15 (day of incubation), peaks on day 2 or 3 post-hatch and decreases significantly by day 8 post-hatch. These developmental days are critical in the chicks' growth.
Halevy et al. reported that recent studies have shown that approaches aimed at enhancing the pool of satellite cells in muscle during pre- and post-hatch periods for broilers have long-term effects on muscle growth and meat production. Among these are monochromatic green-light illumination and thermal manipulations.
For example, incubation at 39.5 degrees C (an increase of 1.7 degrees C from normal conditions) from E16 to E18 for three or six hours daily increased hypertrophy and enhanced absolute muscle growth relative to controls. Moreover, in this study and previous studies, when the incubation temperature was increased by only 0.7 degrees C, or when post-hatch chicks were exposed to mild heat on day 3 post-hatch, insulin-like growth factor-I levels in the muscle tissue were higher in the treated groups. Halevy noted that in all of these studies, the hatchlings had immediate access to feed and water.
In ovo injection. According to Halevy et al., the digestive capacity in broilers begins to develop a few days before hatch, and most of the development occurs in the immediate post-hatch hours when the neonatal chick begins consuming feed.
Since the late-term embryo naturally consumes amniotic fluid, injecting a nutrient solution into the amniotic fluid (in ovo injection) may enhance development. Previous research demonstrated that in ovo injection of a nutrient solution that included carbohydrates and beta-hydroxy-beta-methyl butyrate (HMB), a metabolite of leucine, three to four days before hatch elevates the glycogen stores depleted during the pre-hatch period and increases subsequent bodyweight and absolute muscle growth. Similar results have been obtained in turkeys and ducks.
An experiment was conducted to examine if in ovo injection of nutrients would reduce the effects of the physiological stress and deficiency caused by a 36-hour delay in first access to feed after hatch. There were four treatments: a six-hour or 36-hour delay in feeding post-hatch and with or without in ovo injection at day E18. The in ovo solution contained 10% dextrin and 0.4% calcium-HMB in 0.4% sodium chloride.
As expected, the delay in first feeding to 36 hours post-hatch resulted in irreversible growth reduction. The in ovo injection of chicks subjected to the 36-hour delay in feed and water resulted in increased bodyweight and pectoralis muscle weight on days 14 and 35 compared to the non-injected birds. In ovo injection also had a positive effect on body and muscle weights of chicks fed early at six hours post-hatch.
Biochemical analyses were conducted to elucidate the mechanism(s) underlying the supportive effect of in ovo injection on myogenic differentiation in early- and late-fed chicks. These results were also discussed in the paper.
The Bottom Line
Monochromatic green-light illumination during brooding, thermal manipulations in the incubator and during brooding, as well as in ovo injections have been shown to be effective in stimulating satellite-cell proliferation and differentiation, resulting in enhanced muscle growth. In ovo injection helps to counteract the effect of delayed feeding.
Satellite cell activity
D. Powell, W. Muir and A. Cowieson of the University of Sydney, D. McFarland of South Dakota State University and Velleman presented a paper on the influence of nutritional restriction on satellite cell activity and adipogenic transdifferentiation.
To investigate the role of nutrient restriction on satellite cell proliferation and differentiation, isolated broiler pectoralis major satellite cells were subjected to restricted protein availability. This was accomplished in an in vitro cell culture system by manipulating the levels of methionine/cysteine. Six levels of methionine/cysteine were employed: 60/192, 30/96 (control), 7.5/24, 3/9.6, 1/3.2 and 0/0 mg/L. Satellite cell proliferation and differentiation were evaluated based on DNA concentration.
Both increased and decreased levels of methionine/cysteine caused decreased proliferation compared to the control (30/96 mg/L) methionine/cysteine level. The differentiation rate decreased in a dose-dependent manner.
Two indicators of adipogenic activity (fat cell creation) were employed: analysis for adipogenic marker genes and staining of the satellite cells with the fat-soluble dye Oil-Red-O. Peak Oil-Red-O staining was observed in the highest and lowest methionine/cysteine treatments during proliferation and in the two lowest methionine/cysteine treatments during differentiation.
The Bottom Line
These in vitro results confirmed that nutrient levels have a significant effect on muscle protein growth and the conversion of satellite cells to fat cells.
Optimization of brooding and neonatal conditions is becoming widely recognized as having a major effect on the performance of broilers. A paper on incubation and brooding conditions essential for the optimization of neonatal nutrition was presented by R. Molenaar and T. Gooding of Turi Foods in Australia, D. Lamot and P. Wijtten of Cargil Velddriel in the Netherlands and C. Van der Pol, C. Maatjens and I. Van Roovert-Reijrink of HatchTeck B.V. in the Netherlands.
Temperature is one of the most important environmental conditions to start embryo development, according to Molenaar. The temperature the embryo experiences during incubation is especially important and has a major effect on prenatal and postnatal survival and development.
The embryo temperature differs from the air temperature inside the incubator as well as the temperature displayed on the outside of the incubator. Actual embryo temperature is difficult to measure without killing the developing chick. Egg shell temperature is often used as an indicator of embryo temperature and rarely deviates more than 0.2 degrees C from the actual embryo temperature. Egg shell temperature must be measured at the equator of the egg. A simple infrared ear thermometer is adequate to get a good indication of the egg shell temperature, according to Molenaar.
Studies have shown that an egg shell temperature of 37.8 degrees C during incubation results in the best hatchability, chick quality and post-hatch performance. Relatively small deviations from the optimal egg shell temperature can easily occur yet have a major impact on survival and development. This is thought to be the result of changes in nutrient utilization and physiological processes during incubation.
Although the chick embryo is fully grown at hatch, further development and maturation of the thermoregulatory, gastrointestinal and immune systems is necessary in the brooding period, which is the first seven days after hatch. The importance of the brooding period is highlighted by the fact that chicks are unable to regulate their body temperature post-hatch and are completely dependent on the environmental temperature to maintain their body temperature.
Ideally, the body temperature of the chick should be in the range of 40.0-41.0 degrees C throughout this brooding period in order to achieve the lowest mortality and best development. Molenaar's opinion is that temperature is the most important factor that must be controlled during the brooding period.
Second, Molenaar noted that feed consumption is essential to stimulate intestinal and immunological development in the brooding period. The time between hatch and first feed consumption must be minimized. Early feed consumption is important because intestinal development and growth are much greater with feed than without feed. Furthermore, early feed consumption can improve the immune status of the chick because immunoglobulins from the residual yolk can be utilized for that purpose rather than as an energy source.
With the objective of minimizing the time from hatch to first feed consumption and optimizing brooding conditions, companies are developing specialized brooding systems.
The Patio system (Vencomatic, the Netherlands) and the HatchBrood system (HatchTech) have been specifically developed to optimize the early life conditions of the chick.
In the Patio system, the hatching and growout phase are combined. Eggs are transported at day E18 of incubation from the hatchery to the Patio system houses. The chicks hatch in these specialized broiler houses and can eat and drink immediately. The unit contains different rows and levels to grow the chicks to slaughter age. The Patio system eliminates the conventional hatcher and is a replacement for the conventional broiler house.
The HatchBrood system is a specialized building (or large room) that contains units that provide optimal conditions for the newly hatched chicks. The HatchBrood system is inserted between the conventional hatcher and the conventional broiler farm. The newly hatched chicks are moved from the hatcher to the HatchBrood system as quickly as possible. The system incorporates multiple levels of trays, similar to hatching trays but with flowing water and feed troughs along the sides of the trays. The system maintains the ideal temperature, light and humidity for all of the chicks. After four days, the chicks are moved to the broiler house.
The HatchTech website has a table comparing the reported commercial performance of chicks grown in a conventional production system and chicks grown in the HatchBrood system. The table shows improvements from 1,951 g to 2,156 g in bodyweight, from 1.72 to 1.65 in feed conversion and from 3.31 to 2.46 in percent mortality related to using the HatchBrood system (at 38 days of age).
The Bottom Line
Clearly, there are many ways to skin this cat (chick). If these kinds of performance improvements are achievable, the broiler industry needs to be working diligently on reducing the time to first feed and water and optimizing environmental conditions for the neonatal chick.
The proceedings of the Australian Poultry Science Symposium may be found at http://sydney.edu.au/vetscience/apss/proceed.shtml.