|Livestock Research for Rural Development 27 (10) 2015||Guide for preparation of papers||LRRD Newsletter||
Citation of this paper
Indigenous chickens (IC) depend on nutrients scavenged for growth and egg production but scavenging alone does not provide sufficient nutrients for both maintenance and high production. Feeding interventions to improve productivity have been applied uniformly without considering the different growth phases though IC exhibit points of low and high rates of growth along their growth curves. This study was designed to provide a scientific basis for feeding strategies that exploit the morphological adaptations induced by the requirements for improved growth rates. The objective was to determine the effect of targeted phase supplementary feeding on gut morphological characteristics at different growth phases. Feeding trials were conducted for a period of 21 weeks with supplementation at three growth phases (5-8weeks (TRT2), 9-14weeks (TRT3) and 15-21weeks (TRT4)) while leaving the chickens to scavenge for the rest of the growing period. The control group (TRT1) was left to scavenge for the entire study period. Three chickens in each phase were randomly selected for examination of histology of digestive system. The weight of the gizzard, length of the small intestines, and number of the villi per cm2 in the three sections of the small intestines were measured.
Treatment significantly affected the intestinal morphology in the duodenum section only but it had no significant effect on the jejunum and ileum. The villi population was highest in the duodenum section suggesting that this was the most active section in nutrient absorption. The control group (TRT1) in both IC ecotypes had the highest gizzard weights (11.13 and 10.71g/Kg live weight for Kakamega (KK) and Bondo (BN) respectively). The same group recorded the highest mean intestinal length in both ecotypes (104.36 and 113.95 cm/ Kg live weight for KK and BN respectively).
Keywords: adaptation, nutrients, villi
Indigenous chickens (IC) are the dominant variety of chicken raised in developing countries like Kenya especially in rural areas (Chemjor 1998). Out of 21 countries in Africa reported, IC comprised more than 70% of the total chicken population in 18 of them. Despite the introduction of exotic chickens in the 1920s, IC still make up more than 74% of all the chickens raised in Kenya (Cheburet 2010). Kenya has an estimated poultry population of over 31 million birds (FAO 2012). Out of these, over 25 million are local or indigenous chickens, which are kept by 90% of rural communities (King’ori et al 2010) under free range conditions.
Digestive organs such as intestines and gizzard play a major role in improving IC productivity. The intestines are the most important site of nutrient absorption (Yamauchi and Thongwittaya 2009). They serve as an integrating segment for mixing and modification of both urinary and intestinal inputs. Much of the transport activity in the lower intestines is regulated by the hormone aldosterone which varies inversely with the dietary salt content. Low salt diets increases cell numbers, microvillus density, length and the proportion of mitochondria-rich cells (Laverty et al 2006). The functions of the intestinal epithelial cells may change or adapt in the response to a wide number of demands or challenges. These include evolutionary forces, genetic selection either natural or artificial, response to altered physiological status, environmental challenges or constraints upon nutrient availability and dietary composition (Mitchell and Moreto 2006).
Chicken small intestines go through morphological, cellular and molecular changes towards the end of incubation. The weight of the intestines, as a proportion to the embryonic weight, increases from approximately 1% at 17 days of incubation to 3.5% at hatch. After hatching, the growth rate of the intestines relative to body weight is reported to be greatest at 5-7 days of age of chicks (Uni 2006). Although the digestive capacity begins to develop a few days before hatch, most of the development occurs post-hatch when the chick begins to consume feed. During the post-hatch period, the weight of the small intestines increases at a faster rate than body mass. In addition, the intestinal crypts, which begin to form at hatch are clearly defined several days post-hatch (Sklan 2001), increasing in both number and size. Villi increase both in size and volume giving them a greater absorptive surface per unit of intestine. The rapid morphological development differs in the duodenum, jejunum and ileum. Duodenum villi growth is almost complete by day 7 while jejunum and ileum go beyond 14 days.
Studies have shown that feeding immediately after hatch accelerates the functional development of the small intestines, while delayed access to external feed hinders the development of the small intestine’s mucosal layer (Sklan 2001). Furthermore, birds denied access to feed within the first 24 to 48 hours exhibited decreased villus length, decreased crypt length and decreased enterocytic migration rate. The difference in growth rates between the ecotypes subjected to the same conditions suggested that the growth rate is related to genetic increases in feed intake and utilization. It may also be assumed that such increased feed intake and efficient feed utilization have also altered intestinal functions, which could influence intestinal morphology (Koh-en and Yutaka 1991). Therefore, possible morphological differences in the small intestines are of considerable interest. Currently, there is no information available on the comparative anatomical appearance of the intestinal surface of the different ecotypes of chicken in Kenya.
Gross and comparative anatomical measurements of each intestinal segment found that birds with heavier body weights had greater intestinal area as broilers had larger and more villi per unit area than the White leghorn in all intestinal segments (Koh-en and Yutaka 1991). The broilers had more developed, larger villi, wider microvilli at the apices of villi and more active extrusions of epithelial cells on the tip of the villi surface than the White leghorn. Such morphological distinctions suggest a greater absorptive area leading to the higher growth rate in broilers. These characteristics are thought to be induced by genetic selection for rapid growth rate in broilers leading to increased feed intake and utilization. However, this research has not been done on indigenous chickens and therefore the findings of this study will be useful in explaining the difference in growth rates between ecotypes in Kenya, and will help in selection towards high growth rates.
The research was carried out at a poultry research unit of the Indigenous Chicken Improvement Program (InCIP), at Egerton University, Njoro Sub County, Nakuru County, Kenya. Njoro sub County lies on the longitude 35.9° East of Greenwich Meridian and Latitude -0.33° south of the equator. It is about 25 km west of Nakuru town. The altitude is between 1800 and 2423 meters above sea level (ASL) with a mean annual temperature of between 17 - 22° C and mean annual rainfall of 700 to 1200 mm range.
Flocks of IC were from a collection of eggs of two ecotypes of IC from Kakamega (KK) and Bondo (BN) which were chosen because there have been minimum exotic genetic dilution in these regions. One hundred and twenty eggs were collected from each area, and each of the area represents an ecotype sample.
The eggs were numbered for tracking identification then artificially incubated. At hatching, each chick was weighed and wing tagged with an identification number. Brooding was from hatching to 5 weeks. All chicks were vaccinated against Marek’s disease at 1 day old, Gumboro disease at 18, 24 and 30 days old, Fowl Typhoid at 5 and 18 days old, Newcastle disease at 24 days, 6 weeks, 13 weeks and 15 weeks old and Infectious Bronchitis at 6, 13 and 15 weeks old as per veterinarian’s recommendations. Any other incidence of disease condition was treated promptly by resident veterinarian. Age-weight data were recorded weekly for each bird until 21 weeks of age. Disinfection of brooding and rearing pens was done one week before introduction of the birds. Wood shavings were used as litter material at about 5 cm initial thickness.
Brooding of chicks was done in deep litter brooders fitted with infra-red electric bulbs. At the beginning of the 6th week, chicks were retransferred to deep litter rearing pens (1m x 3m), within the same house. Each pen was provided with two feeders with a capacity of up to 10 kg of feed and two-5 liters water drinkers. The pens were designed to allow the chickens to move out and scavenge freely during the day time and get back to the pens in the evening. The chickens were allowed to scavenge together for uniformity of scavenging feed resources then move back to their respective pens in the evening. There was group feeding where feed was given ad libitum in each pen. Feed was offered at 8.00 hours where the chickens were allowed free access up to 10.00 hours and then released to scavenge. Feeding was done in the morning only as per the practice with most farmers.
Five weeks old chicks subjected to treatments in a 2 x 3 x 4 factorial arrangement with each of the two ecotypes under three growth phases assigned four treatments. This was meant to capture the effect of treatment on the two ecotypes and the three growth stages.
The birds were offered a chick starter diet ad libitum from 0 to 5 weeks of age. Clean water was provided ad libitum daily. After 5 weeks of brooding, each ecotype was divided into four groups of twenty chicks. The first group, which was the control, was left to scavenge with no supplementation up to 21 weeks. The second group was supplemented from week 5 to 8 with a diet formulated to provide 160g CP/ kg and 12.56 MJ/kg ME then left to scavenge without supplementation up to week 21. The third group was left to scavenge without supplementation up to week 8 then supplemented with a diet containing 160g CP/kg and 10.89 MJ/kg ME up to 14 weeks then left to scavenge without supplementation up to week 21. The fourth group was left to scavenge without supplementation up to week 14 then supplemented up to week 21 with a diet containing 160g CP/kg and 10.05 MJ/kg ME. The variation in energy was as per the energy requirements at every growth stage (King’oriet al 2007).
Three chickens at every growth phase were randomly selected and killed by decapitation under a light anesthesia. The digestive system was excised for histology. The intestinal segment from the gizzard to pancreatic and bile duct was labelled duodenum, from the duct to Meckel’s diverticulum was jejunum, and from the diverticulum to the ileo-caecal-colonic junction was the ileum (Yamauchi et al 2006). The tissue samples, 4 cm segments, was taken from the middle part of each intestinal segment and placed in a 10% buffered formalin solution which was then dehydrated by increasing ethanol concentration (70, 80, 95, and 100%), cleared by two changes of xylene, and embedded in paraffin.
From each chicken, 6 transverse sections (5 µm), i.e. two from each section, were cut by rotary microtome, mounted on glass slides, stained with haematoxylin-eosin and examined with a light microscope. Villus number per cm² was determined for the three intestinal sections and were expressed as a percentage of the body weight. The means of these values were used for analysis of variance. The length of the intestines from the pylorus to the ileo-ceacal junction was compared between the phases and ecotypes. The gizzard weights were measuredand recorded as g/kg of the body live weight.
The PROC GLM of SAS (1998) was used for analysis of variance of gizzard weights, intestinal lengths and villi numberin each treatment.
Table 1 shows the results of the gizzard weights and intestinal lengths of chickens sampled for histology in the four treatments. Intestinal length (IL) and gizzard weights (GW) were expressed as g/kg of live weight. This was meant to cater for the differences in live weights (LW) between the different chicken sampled for histology.
In both ecotypes, treatment significantly (P<0.05) affected the intestinal length (Table 1). The control group (TRT1) had the highest mean intestinal length with TRT2 having the lowest.
The control group (TRT1) had the highest mean gizzard weight 11.13g and 10.71g for KK and BN respectively. This was followed by TRT4 with 10.52g and 10.50g for KK and BN respectively with TRT2 having the least in both ecotypes.
|Table 1. Intestinal lengths and gizzard weights for Bondo and Kakamega ecotypes under the four treatments|
|Ecotype||Treatment||Intestinal length(cm)||Gizzard weight(g)|
|abcMeans on a column with one or more letter superscripts in common are not significantly different (P<0.05)|
Results presented in Table 2 show that treatment significantly affected the villi population in the duodenum section in the two IC ecotypes. TRT3 showed the highest mean number of villi in the duodenum section as compared to other treatments. Villi population was lower in the control group (TRT1) and TRT4 in both ecotypes.
|Table 2. Villi population in the three sections of the small intestines of Bondo and Kakamega ecotypes|
|abcMeans within the same column with one or two similar subscripts are not significantly different (P< 0.05)|
Chickens under control treatment (TRT1) adapted to scavenging. The scavenging feed resources were mainly grass, grains and insects which require grinding in the gizzard. This led to increased gizzard weights, due to the nature of the scavenging feed resources available. The gizzard became more muscular than in TRT2 where the chickens were exposed to supplementation at an earlier stage of growth. This muscularity is as a result of the gizzard being active in grinding grains and fibrous feed resources from scavenging (Mateos et al 2012).
TRT2 was supplemented in the first growth phase with commercial feed which was easily digestible and did not require grinding by the gizzard and therefore the digestive organs did not have to adapt for food restriction. This was the reason why TRT2 recorded the least gizzard weights and intestinal lengths in both IC ecotypes.
In both IC ecotypes, treatment significantly (P<0.05) affected the intestinal length (Table 1). The control group (TRT1) had the highest mean intestinal length. This was lower than in other treatments with TRT2 having the lowest. This, as in the case of the gizzard, was due to adaptation to scavenging where the small intestines elongated to increase absorption of the scarce nutrients in the scavenging feed resources in the control group (TRT1) unlike in TRT2 where the chicken were supplemented at an earlier age.
Silva and Kalubowila (2012) indicated that early feed restriction strategies increased the growth rate and feed efficiency with reduced carcass fats. The study showed that early growth retardation resulting from feed restriction in broiler chicks induced an accelerated growth rate (compensatory growth), when feed was given ad libitum after a 14-day period of restriction. However, some studies have shown that though in general growth was compensated, final body weight of the restricted birds could be lower (Silva and Kalubowila 2012) compared to ad libitum fed counterparts. This is because the birds are not able to regain their full growth potential after re-feeding. Increased weights of liver (Mateos et al 2012), gizzard and intestinal length due to restricted feeding have been reported. This increase in size is due to the organs adapting to efficiently utilize the limited supply of nutrients. The report further suggested that supply organs such as the digestive tract compared to whole body respond more quickly to ad libitum feeding regime after a period of feed restriction.
In this study there was a trend of decreased live weight gain during scavenging period. At the same time, there was a trend of increasing digestive organ weight especially the gizzard. These observations suggest that even at the later stage of growth when nutrients are limited; priority is given for the growth of supply organs such as intestines and gizzard than to whole body. Mateos et al (2012) reported that length of the small intestines, in relation to live weight, increased when chickenswere left to scavenge. This is consistent with the findings of this study where the control group under scavenging had the highest gizzard weights and intestinal lengths in relation to the body weights.
Poultry adapt quickly to changes in dietary fiber content by modifying the intestinal length and weight of digestive organs as well as the rate of passage through the different segments of the gastrointestinal tract. Increasing the dietary fiber content in poultry resulted in increased length of the small intestines, decreased proventriculus weight and increased gizzard weight which is an indication of improved functioning of the gastrointestinal tract (Mateos et al 2012). This could be the reason why both the group under TRT3 and TRT1 showed increased organ weight due to their long period of scavenging at an early growth stage.
The results suggest that the villi responded better to supplementation in the second growth phase (9 -14 weeks). The results also suggest that the villi population increased due to supplementation and reduced due to scavenging. This was contrary to the intestinal length and gizzard weight that seem to increase (Table 1) as a result of adaptation to restricted feed supply in the scavenging group. The reduced number of villi could be due to feed restriction during the scavenging phase and therefore only a fewer number of villi were needed in absorption, unlike during supplementation where a larger number of villi were needed. However, as presented in Table 2, treatment did not significantly affect the morphology of the jejunum and the ileum. This suggests that the two sections do not have as much significance as duodenum in nutrient absorption. This concurs with an earlier study by Yamauchi and Thongwittaya 2009 who reported that the ileum and the jejunum did not show morphological change after fasting and concluded that that the two sections are not actively involved in nutrient digestion and absorption.
The small intestine is the most important site of nutrient absorption. It has been suggested that increased villus numbers result in increased surface area leading to greater absorption of available nutrients (Yamauchi et al 2002). High population of long villi was reported in chickens that showed an increased body weight gain (Yamauchi and Thongwittaya 2009).
Reports of gross anatomical changes of the gut due to the type of diet in broilers fed a no-fiber diet have been published by Yamauchiet al 2002. The small intestine, especially the intestinal villi, plays significant roles in the final phase of nutrient digestion and assimilation. In starved-re-fed trials, the values of villus numbers were low after starving but clearly increased when the animals were re-fed (Yamauchiet al 2002). These results seem to suggest that the morphological changes of the intestinal villi are dependent on the presence of digested nutrients in the small intestinal lumen.
The morphology of the gastrointestinal tract may change or adapt in the response to altered physiological status, environmental challenges or constraints upon nutrient availability and dietary composition. It may also be assumed that increased or decreased feed intake can alter intestinal functions, which could influence intestinal morphology thus possible morphological differences in the small intestines are of considerable interest. The observations from this study suggest that even at the later stage of growth when nutrients are limited; priority is given for the growth of supply organs such as intestines and gizzard than to whole body. Increasing the dietary fiber content in poultry results in increased length of the small intestines and increased gizzard weight which is an indication of improved functioning of the gastrointestinal tract. The study also suggests that villi population is dependent on nutrientavailability in the small intestines.This is more evident in the duodenum section of the small intestines, which is the main site of nutrient absorption.
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Received 1 April 2015; Accepted 11 August 2015; Published 1 October 2015
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