Nutritional evaluation and utilization of quality protein maize (QPM) in animal feed - Guang-Hai Qi^*, Qi-Yu Diao^*, Yan Tu^*, Shu-Geng Wu^* and Shi-Huang Zhang^**

Guang-Hai Qi^*, Qi-Yu Diao^*, Yan Tu^*, Shu-Geng Wu^* and Shi-Huang Zhang^**
*Feed Research Institute and
^**Institute of Crop Breeding and Cultivation,
Chinese Academy of Agricultural Sciences, Beijing, P. R. China

INTRODUCTION

Maize is well accepted as the king of feed ingredients. It is a primary source of energy supplement and can contribute up to 30 percent protein, 60 percent energy and 90 percent starch in an animal’s diet (Dado,1999). About 70-80 percent of maize production is used as a feed ingredient in the world. Although normal maize (NM) contains between eight and nine percent protein, the quantity of two essential amino acids, lysine and tryptophan, is below nutritional requirements for monogastric animals. Therefore, utilization of quality protein maize (QPM) can correct this deficiency and may be advantageous in the diets of livestock, and monogastric animals in particular.

Improving the protein quality of cereal grains has been a major concern of scientists in the last two decades. Mutant germ plasma with high levels of lysine has been identified in maize (Mertz et al., 1964), but inherent agronomic defects of this germ plasm, particularly its low yield and high susceptibility to disease and insects, discourage many breeders from further investigation. Through several cycles of recurrent selection, the maize breeders in the International Maize and Wheat Improvement Center (CIMMYT) have combined the high-lysine potential of the opaque-2 gene with a sufficient number of modifier genes to change the original soft opaque-2 endosperm into a hard vitreous type (Vasal et al., 1980). QPM populations that have superior lysine content and yield and agronomic characteristics similar to those of normal corn are now available (Ortega et al., 1986). QPM has smaller, more dense, harder kernels than food grade maize. Over the last 10 years in China, scientists at the Institute of Crop Breeding and Cultivation, Chinese Academy of Agricultural Sciences (CAAS) have developed a group of QPM cultivars. Among them, Zhong Dan 9409 (ZD9409) is one of the best, with an 80 percent increase in lysine and tryptophan and 8-15 percent increase in grain production. However, for a number of reasons, the planting area of QPM in China is still less than 70 000 ha (Zhang, Shi-Huang, personal communication). The major obstacle to more widespread planting of QPM is information on nutrition and the utilization of QPM in animal diets. A series of experiments to overcome this problem has therefore been conducted using broilers, laying hens and pigs at the Chinese Academy of Agricultural Sciences.

NUTRITIONAL EVALUATION OF QPM

Chemical analysis

Chemical analysis. Researchers have compared the chemical composition of QPM with NM (Ortega et al., 1986; Sproule et al., 1988; Osei et al., 1999). The percentage lysine content of QPM varies between 0.33 and 0.54 with an average of 0.38. This is 46 percent higher than NM and QPM also contains 66 percent more tryptophan (0.08 percent) (Table 1).

Two maize samples each of NM and QPM, were recently analyzed for their composition and amino acid contents (Zhai, 2002) (Table 2). The approximate composition of QPM was similar to that of NM, although QPM tended to have higher levels of crude protein, ether extract and crude fibre (data not shown). The amino acid profiles show that of the five critical amino acids, QPM had higher levels of arginine (+18 percent), cystine, tryptophan and lysine (+30 percent) than NM, while the level of methionine in QPM was 5 percent less than in NM. In addition, the ratio of leucine to isoleucine was lower in QPM than in NM (2.97:1 vs 3.36:1).

ENERGY AVAILABILITY

The energy content of QPM and its availability in terms of different animals and in comparison with NM were determined using chicken and pigs (Tables 3 and 4). There were no significant differences in gross energy (GE), apparent metabolizable energy (AME) (poultry) and apparent digestible energy (ADE) (pigs) between QPM and NM (P>0.10). Although NM has a higher GE content than QPM, its AME for poultry and ADE for pigs are lower than those of QPM. It indicates that the energy available from QPM is little higher than that from NM (P>0.10).

TABLE 1
Comparison of the nutritional composition of quality protein maize (QPM) and normal maize (NM) (dry basis)

TABLE 2
Amino acid content of quality protein maize (QPM) and normal maize (NM) (dry basis)

Source: Zhai, 2002

TABLE 3
Energy content of quality protein maize (QPM) and normal maize (NM) (dry basis), MJ/kg)*

Source: Zhai, 2002; Gao, 2002;
*Means within a row with different letters differ significantly (P<0.10).

Availability of protein and amino acids

A force-feeding assay was employed to determine apparent and true digestibility of amino acids in QPM and NM (Zhai, 2002). The apparent and true amino acid digestibility of the two types of maize is shown in Table 4. It shows there is no significant difference in apparent and true digestibility of amino acids between the two types of maize with the exception of cystine digestibility for poultry.

In contrast to the poultry study, when QPM was fed to pigs it had a higher apparent and true ileal amino acid digestibility of most amino acids than NM. QPM not only had a higher content of lysine but it was also digested better by the pigs. The reason for these differences is possibly due to the improvement of protein quality by a higher level of albumins/globulins. The lower digestibility of methionine with QPM should be notified if it is used in animal feed because methionine is one of the most limiting amino acids in animal feeds.

QPM Utilization in Animal feed

NM contributes up to a third or more of the crude protein content of chicken diets. On the other hand, maize is low in protein in addition to its general deficiency in essential amino acids, particularly lysine and tryptophan. Thus, feeding NM necessitates the use of expensive protein ingredients, including fishmeal and soybean meal. Nutritional evaluation of QPM in various locations has proved the superiority of QPM over NM in the feeding of various animals.

A series of animal trials using broilers, laying hens and pigs are summarized as follows (Bai, 2002; Gao, 2002; Zhai, 2002).

Pig Trial

Gao (2002) conducted a pig trial at the Chinese Academy. It included five dietary treatments. Treatment 1 was a NM-soybean meal (SBM) based diet. Treatment 2 was the same as Treatment 1, except NM was totally replaced by QPM in the same dietary proportion. Treatment 3 was an NM-SBM based diet with lysine content adjusted to that in Treatment 2. In Treatment 4, some of the SBM was replaced by cottonseed meal with lysine content being adjusted to that in Treatment 1. Treatment 5 was was similar to Treatment 2 but had less SBM and its lysine content was adjusted to the same level as that in Treatment 1. Two stage diets relating to pig growth stages of 20-50 kg and 50-80 kg, were made for each treatment (Table 6).

TABLE 4
Apparent and true amino acid digestibility of quality protein maize (QPM) and normal maize (NM) for poultry

Source: Zhai, 2002;
* Means within a row with different letters differ significantly (P<0.10).

TABLE 5
Apparent and true ileal amino acid digestibility of quality protein maize (QPM) and normal corn (NC) maize (NM) for pigs

Source: Gao, 2002; * Means within a row with different letters differ significantly (P<0.10).

TABLE 6
Dietary treatments used at different growth stages in the pig trial

Source: Gao, 2002.

The growth performance of the pigs used in the experiments is shown in Table 7. In the grower phase (20-50kg), replacement of NM by an equal ratio of QPM in the pig diet significantly improved the average daily gain (ADG) and feed conversion ratio (FCR) (P<0.10) (Table 7). In the finisher phase (50-80kg), replacement of NM by an equal ratio of QPM in the pig diet remarkably increased ADG. This indicates that QPM has a superior quality to NM. The reason for the weight gain and FCR improvement is possibly due an increase in the lysine content and higher digestibility of critical essential amino acids. Similar results were obtained by Sullivan (1989) in grower pigs and Burgoon (1992) in finisher pigs.

When the lysine content in the NM based diet (Treatment 2) was similar to that in the QPM based diet (Treatment 3), ADG and FCR greatly improved in comparison with the NM based diet. However, there was no significant difference in performance between Treatment 2 and Treatment 3. It suggests that it is the higher lysine content in QPM that is the main contributor to the feeding benefits of QPM. Sullivan (1989) and Brugoon (1992) obtained similar results. Table 7 also shows that for pigs, some soybean meal in the QPM based diet could be replaced by cottonseed meal without compromising their performance (Treatments 4 and 5). This is of great significance since cottonseed meal is much cheaper than soybean meal in China.

TABLE 7
Growth performance of pigs fed different maize based diets*

Source: Gao, 2002;
* Means within a row with different letters differ significantly (P<0.10). ** F = feed per day, kg, G = growth per day, kg

There was no significant difference in carcass dressing percentage as a result of the diets (Table 8). For carcass length, there was no significant difference between Treatments 1, 2, 3 and 5, but Treatment 4 resulted in more lean meat than Treatment 3. Dietary treatment had no significant effect on back-fat thickness. This disagrees with Jin et al (1998) who suggest that using QPM rather than NM in the diet could decrease back-fat thickness. The reason for this disagreement remains unknown. It is interesting to note (Table 8) that the loingissimus dorsi area was significantly increased when NM was completely replaced by QPM. In summary, QPM has no significant effect on the carcass characteristics of pigs.

TABLE 8
Carcass characteristics of pigs fed different maize based diets*

Source: Gao, 2002; *Means within a row with different letters differ significantly (P<0.10).

Laying Hen Trial

Zhai (2002) conducted a laying hen trial. The dietary treatments and their major nutritional contents are shown in Table 9. Simply replacing NM by QPM significantly enhanced egg production (P < 0.10). The QPM based diet increased feed intake of the birds remarkably (P < 0.10). It implies that QPM may contain an appetizer regardless of its lysine content. Using QPM in a laying hen diet could enhance yolk pigmentation. However, dietary treatment has no noticeable effects on egg weight, FCR, soft and broken egg percentage or Haugh unit (P>0.10) (Table 10).

TABLE 9
Dietary treatments and their major nutritional contents

Source: Zhai, 2002

TABLE 10
Effect of dietary treatments on the performance of laying hens*

Source: Zhai, 2002; * Means within a row with different letters differ significantly (P<0.10).

In addition, Osei et al (1999) carried out an evaluation of QPM for layer pullets. The trial was conducted in two phases:

1. Growing phase (from 8 to 18 weeks) and
2. Laying phase (from 19 to 51 weeks).

The results of the grower phase suggested that when QPM was added to pullet diets, protein levels could be reduced to 14 percent without any adverse effects on their performance. In comparison, when NM is used, performance is lowered. The addition of QPM to layer diets had significant effects on the age at first egg (P < 0.01), at the age when 50 percent egg production was achieved (P < 0.05), and on the daily production of housed hens (P < 0.001). It indicates that QPM can be used in layer chicken diets to cut down on the use of fish meal and results in considerable financial benefits without sacrificing performance.

Broiler Trial

Bai (2002) conducted a laboratory broiler trial using Avian day-old broiler chicks. Dietary treatment is shown in Table 11.

TABLE 11
Dietary treatments used in ofthe broiler trial conducted by Bai (2002)

Source: Bai, 2002

The effect of dietary treatment on performance of broilers is shown in Table 12. Dietary replacement of NM by QPM significantly increased weight gain during days 21-42, 42-49 and 1-49. Meanwhile, feed efficiency was greatly improved (P< 0.10).

There was no significant difference between Treatments 1 and 3 relating to carcass percentage, abdominal fat percentage, percentage of eviscerated yield and percentage of eviscerated yield with giblets. At a given digestible lysine content, using QPM tended to increase weight gain but there was no statistical evidence to support this (P>0.10). Therefore, using QPM to replace NM in the broiler diet may have economic benefits due to improved weight gain and FCR and decreasing of dietary lysine supplementation.

TABLE 12
Effect of dietary treatment on the performance of broilers*

Source: Bai, 2002;
* Means within a row with different letters differ significantly (P<0.10).

CONCLUSIONS AND IMPLICATIONS

QPM is superior to NM in its amino acids balance and nutrient composition, and could improve the performance of various animals. It is more economical to use diets incorporating QPM as it can lead to progressive reductions in the use of fishmeal and synthetic lysine additives.

Acknowledgements

Jun Gao, Shao-Wei Zhai, and Xue-Feng Bai are acknowledged for their skillful participation in the laboratory studies. Thanks are also extended to Ji-Xin Guan and Xin-Hai Li for their help during this study.

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