A series of papers has just been published by workers at the Department of Poultry Science, North Carolina State University (G. B. Havenstein, P. R. Ferket, M. A. Qureshi and M.A. Cheema, Poultry Science Vol. 82). The various production parameters between the 1957 Athens-Canadian Random Bred Control (ACRBC) strain and in the 2001 Ross 308 strain of broilers were compared.

The objective of the studies was to attempt to assess the relative contributions of genetics and nutrition to changes in the various production parameters that have occurred between 1957 and 2001. A similar exercise was published in 1994 by the same workers in which the 1957 ACRBC strain was compared to a 1991 Arbor Acre’s strain.

The ACRBC population was established in 1957 by scientists at Agriculture Canada and has been maintained for most of its existence at the Southern Regional Poultry Breeding Laboratory or at the University of Georgia Department of Poultry Science. This old strain of birds is an extremely valuable tool for measuring genetic change over time. An analysis of the data from the ACRBC strain shows that there has been no measurable genetic improvement in the strain since it was established. The modern strain selected for the experiment was the Ross 308.

Table 1: Diets used for the 1957 regime

The trial was conducted for a period of 85 days, with measurements being taken at 21, 42, 56, 70 and 84 days of age. A summary of the results obtained for 21, 42 and 84 days are shown in the table 3. Mortality was approximately twice as much in the modern strain in the current study, as it was in the ACRBC strain, but is still at a modest level at normal market ages.

From these data it was concluded that, genetics, nutrition and management changes over the last 44 years have resulted in a broiler that required one-third the time (32 vs. 101 d) and threefold decrease in the amount of feed consumed (estimated FC of 1.47 vs. 4.42) to produce an 1,815-g broiler.

Assuming that the Arbor Acres strain used previously (1991), and the Ross 308 (2001) were representative of the commercial broilers being grown at the time, the difference in growth between these two strains in relation to the growth of the ACRBC strain led to the conclusion that broiler growth rate has continued to increase at least at the same rate, and possibly faster during the past 10 years than reported earlier. Within and between strain selection is the primary contributor to this change in performance.

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The second part of the study was to provide an assessment of the changes that have taken place in terms of broiler body composition and yield, as well as to estimate that genetics and nutrition have made to these changes.

Practically, we need to compare the 43 day data for the Ross 308 with the 85 day data (marketable age) for the ACRBC birds. Apart from the significant differences in carcass weight it is interesting to note that the dressing percentage is some 6% higher in the modern bird. The modern bird has almost twice the breast meat of the older strain and that at the time of slaughter it contained 4 to 5% less fat in the carcass.

Genetic differences have been shown to influence the disease outcome in chickens. A negative consequence of high growth rate is increased susceptibility to disease, such as Marek’s disease. Commercially, fast growing broilers exhibited higher mortality from commonly encountered infectious or metabolic diseases when compared with slower-growing birds.

Several studies have shown specific dietary effects on immune response. For example, deficiencies in amino acids, calories, or both, in chicken diets compared with basal dietary levels, resulted in a decline in thymic T cells, as well as humoral immune response to sheep red blood cells (SRBC).

The immune response between the strains was compared on the different dietary regimes. The methods used included antibody response against SRBC, in vivo lymphoproliferation against Phytohemagglutinin (PHA-P), and the measurement of inflammatory and phagocytic responses to the macrophages. It was concluded that genetic selection for improved broiler performance has had a negative impact on the adaptive arm of the immune response (antibody production). At the same time, it appears that cell-mediated and inflammatory responsiveness of the immune system has been improved in strains that have been selected for rapid growth rate. Diet and sex effects were inconsistent between strains for all immune function parameters tested.

The data in the current study, in agreement with earlier studies, shows that genetic selection brought about by breeding companies has brought about 85 to 90% of the change that has occurred in broiler growth rate over the past 45 years. Nutrition has provided 10 to 15% of the change. The impact that the improvement in genetic potential has had on the ability of the birds to mount an immune response may well mean that breeding companies will need to bear this in mind in future selection programs.

This article carries some of the information, particularly that which is new or relevant contained in the paper presented at the recent WPSA scientific day by Prof. Khalid Benabdeljelil. The full paper occurs in the proceedings of the 22^nd Scientific Day.

Full Fat Soybean (FFS) is the term used to describe soybeans that have been processed without the extraction of its valuable and high quality oil content. It is a product that has been used since the sixties and has evolved rapidly from an alternative ingredient to a widely accepted feedstuff in the nineties.

The last few years have seen a proliferation of knowledge regarding the effects of processing on the nutritive quality of ingredients such as FFS. Any system or method of heating may improve the nutritional value of soybean and the successful conversion of soybean into FFS. Heat denatures the heat labile anti-nutritional factors present in raw-soybeans. This is particularly true for Trypsin Inhibitor (TI). These would include extrusion (most commonly), autoclaving, toasting, roasting, microwave cooking, micronisation, gama irradiation and expansion (jet sploding). Regardless of method, a controlled, reliable procedure, involving the correct moisture, T°, dwell time and other parameters, is required.

The oil contained in FFS contains lower amounts of peroxides, free fatty acids, trace minerals, sterols, phosphatides, unsaponifiable matter, moisture and volatile matter than the oil of solvent extracted crude soybean oil. In addition the structure of the NSP‘s in soybean is changed by extrusion, allowing increased digestion and absorption in the chick intestine.

Quality control programs are of importance for all processes. Bioassays including feeding trials and performance measurements remain the most sensitive but are time consuming and costly. The objective of any test is to examine whether TI content has been adequately reduced, protein quality has been maintained and as much oil as possible has been released from its cells.

Urease activity is frequently used to assess the extent of TI destruction by heat treatment. Values in the range 0.02 to 0.4 are considered to be acceptable. Urease activity is not a good measurement for evaluating over-processing. The Protein solubility test has been suggested as a method to evaluate over-processing. Low values of solubility indicate that FFS has been over heated. Protein solubility values >85% and <70% indicate product under- or overheating, respectively. Solubility >65% has been shown to impair poultry performance.

FFS is an ingredient with a number of interesting characteristics and advantages. It is used in a wide range of feeds as it combines a high protein level with a high oil level. Its protein digestibility is similar to that of solvent-extracted SBM.

As a granular material, it can be handled at a lower cost than fat in some feed mills. Having the fat within the matrix of the feed particle, that allows high fat levels to be used without consequent loss of pellet quality.

On the other hand, the physical structure of FFS may affect flow ability when the product is ground to a fine structure, creating problems during transport and storage. Pelleting FFS based products can become difficult. Homogeneity of some feed can be affected when FFS is included in the diets.

The nutritional value of FFS is impacted on by the processing method used in its manufacture. The ME value of FFS is directly related to oil availability, highlighting the fact that the extent of physical damage of the beans during processing results in increased oil availability. Most processes such extrusion, combining, pressure, friction and heating (grinding, flaking, rolling etc.) increases physical damage and are associated with high ME values.