Nutrient concentrations of crop and gizzard contents of indigenous scavenging chickens under rural conditions of Bangladesh

M M Rashid*^,***, M N Islam**, B C Roy***, K Jakobsen* and C Lauridsen*

^*Department of Animal Nutrition and Physiology, Danish Institute of Agricultural Sciences,
Research Centre Foulum , 8830 Tjele, Denmark
charlotte.lauridsen@agrsci.dk
^**Bangladesh Livestock Research Institute, Savar, Dhaka, Bangladesh,
^***Department of Livestock Services, Krishi Khamar Sharak, Farmgate, Dhaka, Bangladesh.

Abstract

The physical and chemical compositions of the crop contents and chemical composition of gizzard contents of two types of scavenging chicken were assessed in this study. A total of 100 indigenous scavenging chickens (layers and growers), collected from rural farmers in Rangpur, a northern district of Bangladesh, were slaughtered, their crops and gizzards dissected, and the crop contents were physically analysed. Sun dried crop and gizzard contents were then subjected to chemical analyses. Twenty-five growers and twenty-five layers were slaughtered in each of two seasons i.e. non-harvesting and harvesting season.

Cereal grains, kitchen wastes and green forages were the main crop contents, and the composition varied with season and the type of bird. The average weight of oven-dried crop contents was 20.1±4.9 g for layers and 13.5±2.5 g for growers. The average dry matter (DM) percentage of crop contents was 47.8±7.5. The overall mean chemical compositions (% of DM) of the crop contents were:10.5±2.2 crude protein (CP), 2.1±1.5 ether extract (EE), 6.4±3.5 crude fibre (CF), 12.5±7.8 crude ash, 68.7±8.6 nitrogen-free-extract (NFE), 0.96±0.67 calcium (Ca) and 0.38±0.18 phosphorus (P), and the calculated metabolisable energy (ME) was 2747±419 kcal /kg. The CP of gizzard contents was 7.3±1.9 % of DM.

DM, EE and CF contents varied significantly (P<0.01) with season, but contents of CP, crude ash, NFE, Ca, P and ME were not influenced by season. CP, Ca and P contents were significantly higher (P<0.01) in layers than in growers, conversely, growers showed higher DM contents of the crop (P<0.05) than layers, but other nutrients did not differ among type of birds. The amino acid profiles in crop contents were below the NRC (1994) recommended levels for production and growth of chickens. The nutrient concentrations of feeds scavenged by indigenous chickens were less than the recommended nutritional levels (NRC 1994), which varied with season and type of bird.

Key words: Crop contents, gizzard contents, nutrient concentrations, scavenging chickens and season

Introduction

The poultry production systems of Bangladesh depend mainly on locally scavenging chickens that are reared in villages. The chickens are of indigenous types and are kept in small flocks. They constitute more than 70% of the country's chicken population (Huque and Paul 2001). The major feed sources for village chickens are earthworms, insects, seeds, green leaves and other plant materials found in household yards. The nutrients available to locally scavenging chickens are generally deficient; not only does their availability vary with the seasons of the year and the localities, as reported in studies carried out in some developing countries such as Sri Lanka (Gunaratne et al 1993), Ethiopia (Dessie 1996), Bangladesh (Huque 1999), and Tanzania (Mwalusanya et al 2002), but the scavenged nutrients also vary to some extent by the foraging habit which may differ with the type of bird (genotype and physiological status) as observed for instance by Mwalusanya et al (2002).

If the capacity of the scavenging feed resource base (SFRB) and the seasonal variations are known, more efficient strategies for production of scavenging village chickens can be developed. In this context, feed supplementation should be considered according to the probable nutrient requirements of the birds and what the birds get from the scavenging sources. Therefore, accurate estimation of the quantity of available feed and nutrient intake by the scavenging village chickens are important prerequisites for improving feeding systems and management, in terms of effective feed supplementation (Ajuyah 1999).

In Bangladesh, the protein and fibre content of the scavenging feed at different locations were found to be too low and too high, respectively, in the light of required nutrients for high egg production (Huque 1999). However, the study evaluated the nutrient contents of mixed ingesta of crop and gizzard, which may not reflect the true nutrient content of scavenged feed. Thus, the present study was undertaken to assess the physical and chemical composition of the crop and gizzard contents of scavenging indigenous chickens separately, in order to estimate the nutritional value of the scavenged feed during two different seasons.

Materials and methods

Study area and seasons

The chicken population studied was comprised of indigenous scavenging flocks at four adjacent villages in Rangpur, northern Bangladesh. It is a shallowly flooded area of the river flood plains, which rises less than 10 meters above sea level. In this part of the country, the rainfall observed is a minimum. Total rainfall was 2365 mm in 1998, and temperature ranged from minimum 7-13^oC to maximum 24-31^oC during the months of November to February (BBS 1999). Chickens, ducks, cattle and goats are common livestock kept. The chickens in the study area were left free to scavenge during daytime and confined in the evening following the procedure usually being practiced.

There are two seasons of the year - harvesting and non-harvesting - on the basis of crop harvesting. Harvest of the main crop, rice, is normally done twice a year, mainly during December and January, and relatively less during May and June. In this study, mid-September to mid-November and mid-November to mid-January were considered as being the non-harvesting and the harvesting season, respectively.

During the non-harvesting season, the field is full of green paddy plants with standing water. Rainfall is occasional with short duration. Grasses like para, durba (Cynodon dectylon), kalmi (Ipomoea aquatica) etc., weeds and herbs are available due to the presence of moisture in soil and air. The chickens are often given supplementation of rice bran, broken rice, poor quality paddy, bran of pulses or household wastes (leftover cooked rice and other dining and kitchen wastes) by the owners because of the unavailability of crops in the field.

During the harvesting season, the main crop paddy becomes ubiquitous, and is threshed after harvesting in the farmer's house. Hence the fields, houses and surroundings become rich sources of paddy and its by-products. Often hens have almost unrestricted access to eat paddy, while being dried on the roads and concrete surfaces. Because of the favourable climate, many vegetables like cabbages, cauliflower, tomatoes, carrots, potatoes, spinach etc. can be grown. Generally, the farmers supplement no grain, but kitchen wastes. Among the grasses, durba (Cynodon dactylon) is available.

Sampling and preparation of samples

Sampling was done twice, the first time during the non-harvesting season (mid-September to mid-November 2002) and the second during harvesting season (mid-November 2002 to mid-January 2003). A total of 100 indigenous hens and growers, an equal number of each, were randomly purchased from different parts of the locality for collection of crop and gizzard contents. The hens had gone through at least one laying cycle (being > 26 weeks of age), while growers were of mixed sex, 3 to 5 months of age. Twenty-five hens and twenty-five growers were slaughtered at each sampling time. During the non-harvesting season, the mean live weight of the 25 layers and 25 growers were 1084 ± 179 g and 646 ± 102 g, respectively. During the harvesting season, the mean live weight of the 25 layers and 25 growers were 1107 ± 189 g and 626 ± 104 g, respectively.

The birds were collected directly from the households in the evening between 5.00 p.m. and 7.00 p.m., when the birds were at the end of the day's scavenging. They were slaughtered on the spot by cutting at the cervical region. Each bird was eviscerated, the crop opened, and the feed items found in the crop of each individual bird were identified visually, and physically separated into different categories and weighed categorically. The gizzards were also opened, and the contents were collected. All samples were kept in the freezer (-20⁰C) until preparation. After taking out the contents of crop and gizzard from the freezer, they were dried under sunlight, and weighed. The dried crop contents were ground. Dried gizzard contents were also ground after the grits had been removed from the samples.

Categorization and quantification of crop contents

Food items found in the crops were separated into four categories, namely grains, kitchen wastes, green forages and 'others' with the help of forceps, and weighed. In this study, whole paddy rice, broken rice, maize and seeds of grass were considered as "grains"; cooked rice, cooked pulses, vegetable trimming and stump, scale and stomach of fish, rice bran, egg shell etc. were considered as "kitchen wastes"; grasses, plant materials, vegetable leaves and herbs were considered as "green forages", and "others" included insects, ants, earthworms, flies, paper products, polythene, pieces of brick, buttons, feathers, hairs, glass and unidentified ingredients.

Chemical analysis

The individually ground crop contents were analysed for the proximate components of dry matter (DM), crude protein (CP), ether extract (EE), crude fibre (CF) and ash, according to AOAC (1990) procedures. Calcium (Ca) and total phosphorus (P) were determined by atomic absorption and spectophotometry, respectively (FAO 1980). Due to little sample availability, gizzard contents were only analysed for crude protein. For analysis of amino acids, samples (1 g) of crop contents were pooled according to the type of bird in each season, giving in total four samples. Amino acid profiles were determined by HPLC, according to AOAC (1990).

True metabolisable energy (TME) of the crop contents was determined by using the formula of Wiseman (1987): TME (kcal/kg DM) = 3951 + 54.4 EE - 88.7 CF - 40.8 ash. Metabolisable energy (ME) was then determined on the basis of TME by assuming that TME was 8% higher than the ME, since TME is noted to be 5-10% higher than ME (Wiseman 1987). Moreover, samples of common feed supplements were obtained from farmers and pooled within ingredient source, and subjected to the analysis of proximate components, Ca and P.

Statistical analysis

Descriptive analysis was performed using mean and standard deviation for each outcome variable. The data were analysed by a General Linear Model (GLM) procedure of SAS (1999), based on the following statistical model:

Y_ijk= m + S_i + T_j + (ST)_ij + E_ijk

where Y_ijk is an observation for a given variable; m is the general mean common to all observations; S_i is the effect due to ith season (I=1,2); T_j is the effect due to jth type of bird (j=1,2); (ST)_ij stands for interaction effects between the ith season and jth bird type; E_ijk represents random effects peculiar to each observation. A 5% significant level was used.

Results

Physical composition of crop contents

The main components of the crop contents were categorised visually into cereal grains, kitchen wastes, green forages and others as described above. These categories of crop contents varied considerably between the individual birds. The season and type of bird had significant influence on quantity of some of the components (Table 1). The occurrence of cereal grains was significantly higher during the harvesting season than in non-harvesting season, whereas kitchen wastes formed higher proportion of the contents of the crops of birds from the non-harvesting season than those from the harvesting season. The proportion of grains in layers' crop contents was lower compared to that in growers' crop contents. However, whole paddy was a major grain in the crops of chickens during harvesting season, while rice, broken rice and seldom maize was observed in the chicken crops in the non-harvesting season. The mean weight of oven-dried crop contents was influenced by season and type of bird.

Chemical composition of available feed supplements

The chemical composition of some common feed supplements obtained from farmers in the area studied is shown in Table 2.

Chemical composition of crop and gizzard contents

The chemical composition of crop contents varied with season and type of bird (Table 3). The mean DM of crop contents was 47.8%, and the overall mean nutrient compositions (% of DM) of the crop contents were 10.5, 2.08, 6.42, 12.5, 68.7, 0.96 and 0.38, for CP, EE, CF, ash, NFE, Ca and P, respectively, and a calculated metabolisable energy content at 2747 kcal (11.49 MJ)/kg DM. During the harvesting season, the DM, EE and CF content were significantly higher than those in the non-harvesting season, but other nutrients did not differ between the two seasons. The CP, Ca and P contents were significantly higher in layers' crop contents compared to growers' crop contents, while DM content was significantly lower in layers than in growers. Significant interactions between season and type of bird were observed with regard to the DM, EE, ash and P content (Table 3), and Table 4 therefore presents the nutrients of the crop contents, which showed interaction effect between season and type of bird.

Table 5 illustrates the absolute weight of nutrient components in the DM of the chicken crops. During the harvesting season, the quantity of all nutrients was higher compared to the non-harvesting season, except for ash, Ca and P. The quantity of all nutrients from layer crops was significantly higher than those from grower crops. Interactions between season and type of bird appeared in CP, ash, Ca and P.

Pooled layers' crop contents and pooled growers' crop contents were analysed for amino acid profiles in each season, and the results are shown in Table 6. The contents of all analysed amino acids were higher during harvesting season compared to the non-harvesting season. Except for serine, the layers' crop contents seemed to have higher amino acid concentration compared to the growers' crop contents.

The gizzard CP was 7.04 % and 7.19 % for layers and growers, respectively during non-harvesting season. In harvesting season, gizzard contents of layers and growers contained 8.18 % and 6.73 % CP, respectively. The CP percentage in gizzard contents was influenced by a significant interaction between season and type of bird (P = 0.034).

Discussion

From visual observation of chickens' crop contents, it was evident that scavenged feed was dependent on the availability of feed from surrounding environment and household refuse. Previous studies (Gunaratne et al 1993; Dessie 1996) reported that planting or harvesting time influenced crop contents of scavenging birds. The mean weight of dried crop contents (20.5 and 14.5 g of layers and growers, respectively) was quite similar to the weight of crop contents reported by Mwalusanya et al (2002). The higher occurrence of grains in the chicken crops and higher weight of dry crop contents during harvesting season might be due to the large consumption of whole paddy rice harvested in this season. Mwalusanya et al (2002) reported similar results as the availability of grains was higher in long rainy season (in which harvesting most likely takes place) than short rainy season, while the reverse was true for the kitchen wastes. A greater amount of grain consumed by growers than layers might be ascribed to the higher attention to growers paid by the farmers regarding feed supplementation during the non-harvesting season.

The higher DM in chickens' crop contents during harvesting season than in non-harvesting season was presumably due to the higher proportion of cereal grains in chicken crops during harvesting time. The main reason for higher DM in growers' crop contents compared to layers' crop contents is attributed to the greater proportion of grains in growers' crop contents. The mean weight of dried crop contents was higher during the harvesting season compared to non-harvesting season; consequently, the quantity of all nutrients during harvesting season became higher.

EE and CF of crop samples were significantly higher, and CP was numerically higher, during the harvesting season than in the non-harvesting season, which might be ascribed to the higher consumption of paddy (rich in EE, CF, and CP) during harvesting season.

The significantly greater amount of CP, Ca and P in the layer crops may be explained by the fact that layers seemed to follow selective feeding, which depends upon nutritional requirements of a particular age group of birds and their production stage. Laying hens have higher requirement of CP and Ca than growers to maintain egg production (Payne 1990, and NRC 1994). Thus, hens are more likely to pick up Ca and protein-rich feedstuffs compared to growers to support egg production (Leeson and Summers 1997). Numerically increased green forages intake may also have contributed to the greater Ca, as well as P, content in layer crops, since green forages are known to have higher Ca and P content than the cereal grains (Ali 1995).

Our observations regarding the content of CF, ash, Ca, and P in grower crops were in accordance with the crop concentrations reported by Mwalusanya et al (2002). In addition, in Bangladesh, Huque (1999) reported similar findings with regard to ash (12.6 %) and P (0.40 %) as in our studies. The calculated energy of layers' crop contents was similar to the 2844 kcal/kg DM, reported by Dessie (1996).

The CP in gizzard contents was approximately 30% less than the CP in crop contents, which might be due to the digestion process of CP in the proventriculus on the way from the crop to the gizzard (Smith 2001).

It is known from other studies that birds filled their crops in four-hour cycles of eating, although some of the feeds may completely bypass the crop depending on the type of feed (Feltwell and Fox 1978). The village chicken is a continuous nibbler and stops feeding only when the crop and gizzard are filled to capacity. Nibbling resumes once ingested feed starts moving from these organs and occur quite often during a day (Ajuyah 1999). Based on these points, it can be assumed that birds fill their crops fully three times a day. Therefore, on the basis of our results, layers might manage to obtain 6.8 g CP and 166 kcal ME per day per head from the scavenging feed resources. This would be in agreement with the findings of Farrell (2000) who estimated that the daily requirement of CP and energy for a scavenging indigenous hen laying at a rate of 20% was 6.0 g and 165 kcal, respectively. Sonaiya et al (2002) reported from a study performed in Nigeria that daily CP and energy consumption per cock (weighing 1.03 kg) were 3.8 g and 119 kcal, respectively, which seem to be lower than the assumption of our findings (6.8 g CP and 166 kcal ME daily).

Slightly higher concentrations of amino acids in crop contents during harvesting season compared to non-harvesting season could be attributed to the slightly higher CP in crop contents in this season, and the amino acids in layers' crop contents logically showed higher content than in growers' crop contents. But none of the amino acids of crop contents could attain the level of layers' diet or growers' diet as recommended by NRC (1994), except for methionine and tryptophan.

From the present results it can be assumed that the SFRB was deficient in CP, Ca, and P when taking the recommended level of chicken diets by Payne (1990) and NRC (1994) into consideration. The energy of crop contents was lower than NRC (1994) recommended level for both layers and growers (2900 kcal and 2850 kcal, respectively), but slightly lower than the level recommended (2643 kcal and 2595 kcal, respectively) by Payne (1990). Harvesting season expectedly increased the amount of nutrients in crop contents compared to non-harvesting season. This may indicate that the nutritional status of scavenging local chickens under village management condition was lower during the non-harvesting season than the harvesting season. Thus, formulation of nutrient supplementation for scavenging chickens may even be more critical during certain seasons of the year, where SFRB is limited.

With the findings of the study, it might be concluded that the concentration of the nutrients (except CF) available to the indigenous scavenging chickens under rural environment was below the requirements of growers and layers for optimum performance. Thus, supplementary feeding is required to express the performance potentiality of hens in the rural areas of northern Bangladesh. Further studies need to be carried out to determine the quantity of SFRB available per chicken per unit of land in a particular location, which could be a starting point in determining the amount of feed and nutrient composition in order to optimise the performance of birds reared under conditions with limited feed resources.

Acknowledgement

The study was supported by Danish International Development agency (DANIDA) through the Network for Smallholder Poultry Development as part of a MSc grant for the first author.

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