عنوان مقاله [English]
Introduction: Many studies have been conducted to determine proper corn particle sizes for mash or pelleted diets in broiler chicken’s nutrition, aiming not only to achieve optimum production goals such as higher weight gain and minimum feed conversion ratio but also to reduce milling energy expenditures. However, pelleted and crumbled feed forms are mainly used in intensive poultry production systems in many countries, and mash feed is primarily common in less intensive production systems. Mash feed is less costly and puts less pressure on birds’ metabolic systems to achieve their optimum biological growth potential, which may result in higher welfare and lower metabolic disorders. Therefore, the purpose of this study was to investigate the effects of different proportions of fine and coarse ground corn (3- and 6-mm sieve opening hole size, respectively) on performance, the relative weight of gastrointestinal organs (%), and intestinal morphology in male broiler chickens.
Materials and methods: A total of 576 1-day-old male Ross 308 broiler chicks were purchased from a commercial hatchery and raised from 1 to 42 days of age. All birds received identical basal diets from 1 to 11 days of age, but different experimental diets from 12 to 42 d. Experimental diets (12 to 42 days of age) consisted of six corn mixtures prepared by combining different proportions (w/w) of corn ground through sieves with either hole sizes of 3 or 6 mm as 100:0; 80:20; 60:40; 40:60; 20:80 and 0:100 percentage, respectively. The particle size characteristics including geometric mean diameter (GMD) and geometric standard deviation (GSD) of ground corn and finished feed samples were determined. Birds’ body weight was recorded at 12, 24, and 42 days of age as a group basis for the calculation of birds’ bodyweight gain (BWG) during the grower (12-24 d) and finisher (25-42d) periods. The birds’ feed intakes (FI) were also measured during the same period to calculate the feed conversion ratio (FCR) after adjustments were made for the body weights of dead birds, which were recorded daily. on the 21st day of the experiment, two birds from each pen were selected and killed via cervical dislocation. The liver, gizzard, small intestine, caecum, and pancreas of the sampled birds were carefully removed from their abdominal cavity, their weights were recorded carefully, and the relative weights of these parts to the live body weights were calculated and expressed as the percentage of birds live weights. Gizzard acidity was measured on the 21st day of the experiment. Parts from the middle of the jejunum and ileum of slaughtered birds (21 d) were excised and flushed gently with saline solution and immediately placed in a 10% formalin solution. Villus height, villus width, and crypt depth were measured in the laboratory.
Results and discussion: Results showed that feeding mash diets with different particle sizes (~775, 835, 910, 1000, 1060, and 1150 µm) had no significant effects on birds’ BWG, FI, and FCR during different growth periods. However, the orthogonal polynomial contrast test showed that the changing of feed particle size from fine (~775 µm) to coarser particles by combining different portions of corn ground with a sieve hole size of 3 mm (~775 µm) and 6 mm (~1150 µm) had linearly deteriorated BWG and FCR from 12 to 24 days of age. The birds’ mortality rate (%) was not influenced by average feed particle size from 12 to 42 days of age. The negative influence of very coarse particle size from 12 to 24 days of age (>1000 µm) in the current experiment is an indicator of birds’ gastrointestinal limits in dealing with coarse particles. The coarse grain particles increase the energy required for the growth and maintenance of the gizzard. The results of the current experiment showed that feed particle size did not significantly affect the relative weights of gastrointestinal sections to body weight at 21 d (P>0.05). However, the relative weight of gizzard to live body weight at 21 d significantly (P<0.001) increased in birds fed diets with higher average particle size (≥775 µm). The results of the orthogonal polynomial contrast test showed that the relative weight of gizzard to live body weight at 21 days of age linearly (P<0.0001) increased by changing the feed particle size from fine to coarser particles. Coarse particles increased the digesta content in the gizzard, which stimulates the development of the gizzard. In addition, the findings of the current experiment indicated that ileum and jejunum morphometry traits such as villus height, crypt depth, villus height to crypt depth, villus tips, and base widths were not influenced by changing the average feed particle size. The pH of gizzard content at 21 days of age was not influenced by the feed particle size.
Conclusions: Feed particle size of 775 to 1150 µm in a corn-based mash diet had no significant effect on performance traits or small intestine morphology traits. However, high coarse diets had the potential to deteriorate BWG and FCR at earlier stages of the growth period.