Effect of pre-starter diet ingredients and moisture content on performance, yolk sac utilization and small intestine morphology in broiler chickens

Abstract

A 5 × 2 factorial experiment was conducted to investigate the impact of different iso-energetic and iso-nitrogenous pre-starter diets varying in nutritive ingredients and moisture content on growth parameters, yolk sac utilization and intestine morphology of broiler chickens. A total number of 600-day-old Ross 308 male broiler chicks were randomly assigned to 10 experimental treatments, each replicated 4 times, with 15 birds per replicate for 42 days. Dietary treatments included a control diet supplemented by each of the four combination of casein and dextrose (CD), casein and starch (CS), gluten and dextrose (GD) or gluten and starch (GS) prepared in either dry or semi-moist form by adding 0.3 L water/kg diet (SmControl, SmCD, SmCS, SmGD and SmGS) and fed from day 1 to day 7. Diet composition and moisture content interacted for feed intake (FI), weight gain (WG) and feed conversion ratio (FCR) over the first week and entire period of the study. Feeding birds with semi-moist diets caused an increase (P < 0.001) in final WG (days 1–42) in the birds fed control, GD and GS accompanied with an improved in FCR except for the control. Moisturising the diets increased the length of chickens at day 3 (P < 0.05) and day 5 (P < 0.01) and decreased carcass (P < 0.05) fat when assessed independent of diet composition. On day 7, diets and moisture content interacted for the jejunal crypt depth where birds fed SmGD and SmGS showing the lowest figures compared with control group of birds. To conclude, inclusion of GD and GS in semi-moist form in pre-starter diets would result in increased FI, improved gut development and feed efficiency and a carryover effects on productive traits can be observed at later stages of growth.

Keywords:

• pre-starter diet
• diet moisture
• broiler performance
• gut development
• yolk sac utilization

1. Introduction

The modern breeds of broiler chickens have been selected for fast growth and at present, broilers reach slaughter weight at a physiologically younger age. Consequently, the embryonic developmental period as well as the first week after hatching represents a larger proportion (45%) of the whole life span (Bigot et al. 2003). It is well documented that body weight (BW) enhances threefold to fourfold during the first week of age and considerable changes in gut, muscle weight and morphology are observed (Jin et al. 1998). The first week after hatch is an extremely important time for all young poultry. During the past 40 years, the market age of broiler chickens has been reduced by approximately 1 day each year. Nowadays, the first 7 days represent approximately 17% of the growing period in time and 5–10% in weight as a percentage of final BW (Lilburn 1998; Havenstein et al. 2003). In newly hatched chicks, the remaining yolk (yolk sac) – which comprises approximately 14% of the chick's BW at the time of hatching – provides the so-called internal feed for survival in the first days of life. Yolk sac contents are absorbed and utilized for growth of the small intestine and to supply energy (Noy & Sklan 1998) and nutrient reserves for several days (Uni et al. 2003) until the introduction of external feed intake (FI; Sklan, 2001). Consequently, one of the major changes occurring immediately after hatch is a shift in the source of available nutrients for the neonatal chick; the hatchling has to make the transition from metabolic dependence on endogenous lipid-rich yolk to utilization of exogenous carbohydrate and protein-rich feed (Noy & Sklan 1995). Newly hatched chicks have an immature digestive system and the digestive tract has to undergo major morphological and physiological changes in the first week of age to allow proper digestion and utilization of ingested nutrients (Willemsen et al. 2010). As young chicks are less efficient in utilising nutrients from complex nutritive components, they could possibly benefit from diets containing easily digested ingredients. Current broiler feeding programmes provide a starter feed from chick placement to 10 days of age. However, the chicks' requirements change quickly during their early days of life, and this should be taken into account when composing starter diets (Swennen et al. 2009). Therefore, the composition of pre-starter diet can influence the subsequent growth and development of broiler chickens; consequently suitable feed composition and optimal feed formulations, specifically for the first-day post-hatch, may be of great importance for broiler chickens to manifest their genetic potential growth rate. The use of an appropriate pre-starter diet consisting of simple sources of protein and energy supplements would meet the specific needs of the newly hatched chicks more efficiently.

The impact of pre-starter diet composition, more specifically highly digestible protein and energy supplements in pre-starter diet for broiler chickens, is less investigated. Thus, this study was carried out to investigate the effects of pre-starter diet supplementation with highly digestible protein (casein and gluten) and energy (starch and dextrose) sources, and diet moisture, on productive traits, gastrointestinal morphology and carcass characteristics of broiler chickens.

2. Materials and methods

2.1. Experimental design and diets

A total number of 600 newly hatched (Ross 308) male broiler chicks were obtained from a commercial hatchery. Chicks were assigned to each of the 10 experimental diets, so that each group had approximately similar initial weight (41 ± 0.6 g) and weight distribution. Dietary treatments were randomly allocated to four pens of 15 chicks in a 5 × 2 factorial arrangement comprising five diets [control diet, diets supplemented by casein and dextrose (CD), casein and starch (CS), gluten and dextrose (GD) or gluten and starch (GS)] and two levels of diet moisture (no added water and 0.3 L water added/kg diet). A mould inhibitor was incorporated into the semi-moist diets (SmControl, SmCD, SmCS, SmGD and SmGS) at the time of formulation. The diets were formulated to have similar metabolisable energy content, essential amino acids, calcium and available phosphorus, to meet nutrient requirements provided by Ross Manual (2009; Table 1). The 10 experimental diets were fed from 1 to 7 days of age; afterwards a same commercial diet (Table 2) was fed to all treatment groups until day 42. Birds were raised for six weeks in floor pens (length 120 cm × width 120 cm × height 80 cm) with one hanging tube feeder and one suspended drinker in floor pens with wood shavings as bedding material. The lighting programme consisted of a period of 23 h light and 1 h darkness, and the ambient temperature was gradually decreased from 33°C at first week to 25°C on day 21 and was then kept constant. All the experimental procedures were assessed and approved by the Institutional Animal Care and Ethics Committee from the Islamic Azad University, Khorasgan Branch, and all national and institutional guidelines were followed.

Table 1. Composition and nutrient specifications of the experimental diets fed from day 1 to day 7 of the trial.

Diet ingredients (%)	Control	Casein dextrose	Casein starch	Gluten dextrose	Gluten starch
Corn	57.90	57.39	56.81	52.92	53.27
SBM	32.28	25.47	25.75	30.59	30.54
Fish meal	4.50	–	–	–	–
Corn starch	–	–	4.00	–	4.00
Dextrose	–	4.00	–	4.00	–
Corn gluten	–	–	–	6.00	6.00
Casein	–	6.00	6.00	–	–
Canola oil	2.05	2.32	2.64	1.81	1.28
Limestone	0.89	1.28	1.28	1.28	1.28
Dicalcium phosphate	1.09	2.01	2.01	1.93	1.93
Sodium chloride	0.20	0.20	0.20	0.20	0.20
Sodium bicarbonate	0.21	0.21	0.21	0.21	0.21
Vitamin premix^a	0.25	0.25	0.25	0.25	0.25
Mineral premix^b	0.25	0.25	0.25	0.25	0.25
Choline Cl 70%	0.05	0.10	0.08	0.10	0.10
L-lysine	0.02	0.04	0.04	0.12	0.12
DL-methionine	0.23	0.21	0.21	0.20	0.20
L-threonine	0.04	0.23	0.23	0.06	0.06
Total	100	100	100	100	100
Calculated composition
Crude protein (%)	22	22	22	22	22
AMEn kcal/kg	3020	3020	3020	3020	3020
Ca (%)	1.00	1.00	1.00	1.00	1.00
Avail phosphorus (%)	0.48	0.48	0.48	0.48	0.48
Digestible Met + Cys (%)	0.83	0.81	0.83	0.83	0.83
Digestible methionine (%)	0.46	0.43	0.45	0.44	0.45
Digestible lysine (%)	1.10	1.08	1.09	1.10	1.10
Digestible threonine (%)	0.73	0.74	0.74	0.73	0.73
Digestible arginine (%)	1.18	1.12	1.12	1.16	1.16

^a Vitamin premix per kg of diet: vitamin A (retinol), 2.7 mg; vitamin D3 (Cholecalciferol), 0.05 mg; vitamin E (tocopheryl acetate), 18 mg; vitamin k₃, 2 mg; thiamine 1.8 mg; riboflavin, 6.6 mg; pantothenic acid, 10 mg; pyridoxine, 3 mg; cyanocobalamin, 0.015 mg; niacin, 30 mg; biotin, 0.1 mg; folic acid, 1 mg; choline chloride, 250 mg; antioxidant, 100 mg.

^b Mineral premix per kg of diet: Fe (FeSO₄.7H₂O, 20.09% Fe), 50 mg; Mn (MnSO₄.H₂O, 32.49% Mn), 100 mg; Zn (ZnO, 80.35% Zn), 100 mg; Cu (CuSO₄.5H₂O), 10 mg; I (KI, 58% I), 1 mg; Se (NaSeO₃, 45.56% Se), 0.2 mg.

Table 2. Composition and nutrient specifications of the basal diets fed from day 7 to day 42 of the experiment.

Diet composition (%)	Starter (7–14 days)	Grower (14–28 days)	Finisher (28–42 days)
Corn	54.5	56.4	57.2
Soybean meal	39.1	37.3	35.5
Soybean oil	1.52	2.45	3.76
Dicalcium phosphate	1.84	1.62	1.52
Calcium carbonate	1.31	0.88	0.83
Sodium bicarbonate	0.34	0.26	0.25
DL-Methionine	0.29	0.22	0.12
L-lysine	0.21	0.03	–
L-threonine	0.18	0.08	0.05
Vitamin Premix^a	0.25	0.25	0.25
Mineral Premix^b	0.25	0.25	0.25
Sodium chloride	0.21	0.26	0.27
Total	100	100	100
Calculated Composition
AMEn (kcal/kg)	2850	2950	3050
Crude protein (%)	21.2	20.6	20.0
Ca (%)	0.99	0.84	0.81
Available phosphorous (%)	0.48	0.42	0.40
Digestible Met + Cys (%)	0.91	0.72	0.69
Digestible lysine (%)	1.0	0.97	0.94
Digestible threonine (%)	0.78	0.67	0.61
Digestible arginine (%)	1.11	1.00	0.96
Linoleic acid (%)	1.91	2.42	2.81

^a Vitamin premix per kg of diet: vitamin A (retinol), 2.7 mg; vitamin D3 (Cholecalciferol), 0.05 mg; vitamin E (tocopheryl acetate), 18 mg; vitamin k₃, 2 mg; thiamine 1.8 mg; riboflavin, 6.6 mg; pantothenic acid, 10 mg; pyridoxine, 3 mg; cyanocobalamin, 0.015 mg; niacin, 30 mg; biotin, 0.1 mg; folic acid, 1 mg; choline chloride, 250 mg; antioxidant, 100 mg.

^b Mineral premix per kg of diet: Fe (FeSO₄.7H₂O, 20.09% Fe), 50 mg; Mn (MnSO₄.H₂O, 32.49% Mn), 100 mg; Zn (ZnO, 80.35% Zn), 100 mg; Cu (CuSO₄.5H₂O), 10 mg; I (KI, 58% I), 1 mg; Se (NaSeO₃, 45.56% Se), 0.2 mg.

2.2. Data collection and sampling

After arrival, chicks were weighed and chick length was determined by stretching the chicken along a ruler, measuring length from top of the beak to the tip of the middle toe, excluding the nail (Hill 2001; Molenaar et al. 2008). Chick weight was 41 ± 0.6 g and chick length was 18.4 ± 0.04 cm and not different among treatment groups. Consequently, BW was determined at 7, 21 and 42 days of age. Feed consumption was recorded at the same periods and food conversion ratio [FI/weight gain (WG)] was calculated, accordingly. At 3, 5 and 7 days of age chicks' length (as described above) was determined for all chicks, then two birds from each replicate were killed and yolk residual weight percentage was recorded. At days 21 and 42 of the experiment, 12 birds were randomly selected from each treatment, had feed removed for 6 h (water was allowed) and then weighed and slaughtered. After dressing abdominal fat, small intestine, bursa and spleen were collected, weighed and calculated as a percentage of live BW.

At days 7 and 21 of the experiment, three randomly chosen birds from each replicate were killed to collect small intestine. The small intestines of chicks were removed and segments of duodenum (from the pylorus to the distal point of entry of the bile ducts) and jejunum (from entry of the bile ducts to Meckel's diverticulum) were taken and gently flushed twice with physiological saline solution to remove the intestinal content. For morphological analysis, approximately 5 cm of the middle portion of the duodenum, jejunum and ileum was excised and fixed in 10% formalin. Six cross sections of 70% ethanol preserved segments for each sample were then prepared for staining with hematoxylin and eosin using standard paraffin embedding procedures (Uni et al. 1995). Villus height (VH) and crypt depth were measured using a light microscope (Olympus CX31, Tokyo, Japan). Villus length was measured from the top of the villus to the top of the lamina propria, whereas villus:crypt ratio (VCR) was determined as the ratio of VH to crypt depth.

2.3. Statistical analysis

Data were analyzed in a 5 × 2 factorial arrangement of dietary treatments using analysis of variance and General Linear Model (GLM) procedure of SAS (SAS/STAT Version 9.2, SAS Institute Inc., Cary, NC) to determine the main effects of dietary supplements, added water to the diets, and their interaction. If a significant effect was detected, differences between treatments were separated using Duncan's multiple range test. Differences between mean values were considered significant at P ≤ 0.05.

3. Results

3.1. Performance parameters

As shown in Table 3, interaction of diet composition and moisture was found significant for the feed consumption of the birds during the first week (P < 0.05) and across the 42-day study (P < 0.01). Providing semi-moist diets in the first 7 days of age increased FI only in birds fed SmGS and SmGD diets. When assessed for 42 days, birds in CD and CS diets exhibited the lowest FI, regardless of diet moisture content; and the highest FI was recorded for SmControl and SmGS diets (P < 0.01). Similar to FI, diet and moisture interacted for body weight gain (BWG) during the first week (P < 0.001) and entire study (P < 0.05). Considering first 7 days, the BWG of the birds fed CD and CS was lower than control birds regardless of the moisture treatment. Moisture added to the diets only increased (P < 0.001) the WG of the birds (1–42 days) fed control or gluten-supplemented diets. Assessing the feed conversion ratio (FCR), interaction of diet and moisture addition was also significant (P < 0.05) across the study. Birds (7-day-old) fed the control, GS and GD diets exhibited (P < 0.05) lower FCR when compared to birds on CS and CD diets. Considering the entire experimental period (1–42 days), birds provided diets containing CS in semi-moist form had a lower FCR than those fed control diets. Added moisture improved feed efficiency over 1- to 42-day period.

Table 3. Effect of experimental diets on broiler performance over 1- to 7-day and 1- to 42-day periods.

		FI (g/bird/day)		WG (g/bird/day)		FCR (g/g)
Treatments	Moisture	1–7 days	1–42 days	1–7 days	1–42 days	1–7 days	1–42 days
Control	−	25.6^b	103.8^b	23.1^ab	59.7^bc	1.11^c	1.74^cb
CD	−	24.8^b	98.1^bc	18.9^c	53.5^c	1.31^a	1.84^ab
CS	−	24.2^b	95.6^c	18.9^c	50.2^c	1.28^a	1.91^a
GD	−	26.2^b	108.7^a	22.4^bc	62.7^ab	1.17^c	1.73^cb
GS	−	24.8^b	102.0^b	21.5^bc	59.2^bc	1.15^c	1.72^cb
SmControl	+	28.2^ab	111.1^a	23.1^ab	64.5^a	1.22^b	1.72^cb
SmCD	+	25.3^b	97.3^cb	19.7^c	56.9^cb	1.28^a	1.72^cb
SmCS	+	24.1^b	96.8^c	19.1^c	61.6^ab	1.26^ab	1.57^d
SmGD	+	29.6^a	102.3^b	24.9^a	62.8^ab	1.19^bc	1.63^cd
SmGS	+	30.1^a	107.2^ab	25.7^a	63.3^ab	1.17^c	1.69^cd
	SEM	2.21	3.68	1.84	1.67	0.032	0.012
Main effect
Dry diet		25.12^b	101.64	20.96	57.03^b	1.20	1.78^a
Semi-moist diet		27.46^a	102.98	22.25	61.8^a	1.22	1.66^b
P value
Diet composition		0.004	0.001	0.001	0.001	0.001	0.192
Diet moisture		0.002	0.181	0.45	0.001	0.004	0.001
Composition × moisture		0.045	0.007	0.001	0.04	0.042	0.002

Note: Values within a column with no common superscript letters differ significantly (LSD test at P ≤ 0.05).

Control diet: CD, casein + dextrose; CS, casein + starch; GD, gluten + dextrose; GS, gluten + starch; SmControl, semi-moist control; SmCD, semi-moist casein + dextrose; SmCS, semi-moist casein + starch; SmGD, semi-moist gluten + dextrose; SmGS, semi-moist gluten + starch; SEM, standard error of means.

3.2. Yolk sac utilization, chick length and carcass characteristics

There was no effect of experimental factors on yolk residual at days 3, 5 and 7 (Table 4). However, 7-day-old chicks fed semi-moist diets tended (P = 0.08) to have lower residual yolk than birds fed normal diets. Moisturising the diets increased the length of chickens at day 3 (P < 0.05) and day 5 (P < 0.01) when assessed independent of diet composition. At day 7, diet type and moisture interacted (P < 0.01) where length of the birds was only affected when moist diets were provided. Feeding CD- and CS-supplemented diets resulted in the lowest (P < 0.001) chicken length among all other dietary treatments.

Table 4. Effect of experimental diets on yolk residual and chick's length at days 3, 5 and 7.

		Yolk residual (g/100g live weight)			Chick length (cm)
Treatments	Moisture	Day 3	Day 5	Day 7	Day 3	Day 5	Day 7
Control	−	0.64	0.48	0.15	21.4^ab	24.0	25.5^a
CD	−	0.73	0.45	0.12	21.7^ab	23.8	24.0^b
CS	−	1.02	0.36	0.18	21.7^ab	22.8	24.9^b
GD	−	0.42	0.31	0.12	21.9^ab	23.8	25.3^ab
GS	−	0.71	0.17	0.06	20.9^b	23.4	25.0^ab
SmControl	+	0.56	0.17	0.07	22.0^a	24.1	25.2^ab
SmCD	+	0.71	0.27	0.09	21.8^ab	24.3	25.1^ab
SmCS	+	0.65	0.48	0.08	21.7^ab	23.7	24.8^b
SmGD	+	0.97	0.25	0.09	21.9^ab	24.5	25.6^a
SmGS	+	0.69	0.12	0.08	22.2^a	24.0	26.3^a
	SEM	0.58	0.32	0.012	0.21	0.32	0.22
Main effect
Dry diet		0.17	0.354	0.15^a	21.5^b	23.5^b	24.9^b
Semi-moist diet		0.16	0.261	0.07^b	21.9^a	24.1^a	25.4^a
P value
Diet composition		0.62	0.22	0.42	0.84	0.08	0.001
Diet moisture		0.90	0.22	0.08	0.02	0.01	0.002
Composition × moisture		0.06	0.44	0.63	0.09	0.80	0.002

Note: Values within a column with no common superscript letters differ significantly (LSD test at P ≤ 0.05).

Control diet: CD, casein + dextrose; CS, casein + starch; GD, gluten + dextrose; GS, gluten + starch; SmControl, semi-moist control; SmCD, semi-moist casein + dextrose; SmCS, semi-moist casein + starch; SmGD, semi-moist gluten + dextrose; SmGS, semi-moist gluten + starch; SEM, standard error of means.

The data for carcass characteristics at days 21 and 24 are presented in Table 5. Carcass yield was not influenced by dietary treatments. Interaction of diet and moisture content was significant for the fat content (P < 0.01) at day 42. Birds fed control, CD, CS and GD diets with added moisture had a lower fat (P < 0.05) compared with the control group fed diet with no added moisture. No interaction was detected for the relative weights of small intestine, bursa and spleen. However, semi-moist diets led to a significant increase (P < 0.01) of small intestine weight regardless of diet composition. Diet composition or moisture had no impact on bursa and spleen relative weights.

Table 5. Effect of experimental diets on carcass characteristics¹ of broiler chicks at days 21 and 42.

		Carcass yield		Fat		Intestine		Bursa		Spleen
Treatments	Moisture	Day 21	Day 42	Day 21	Day 42	Day 21	Day 42	Day 21	Day 42	Day 21	Day 42
Control	−	60.8	72.9	1.13	1.48^a	6.74	3.94	0.26	0.06	0.08	0.11
CD	−	62.3	71.1	1.16	1.47^a	8.56	3.57	0.26	0.09	0.09	0.12
CS	−	61.7	71.2	1.25	1.41^ab	7.38	4.51	0.23	0.08	0.08	0.08
GD	−	62.0	70.9	1.12	1.38^ab	6.37	3.58	0.23	0.12	0.07	0.10
GS	−	60.6	73.3	1.21	1.42^ab	6.19	4.21	0.23	0.08	0.10	0.09
SmControl	+	62.5	71.8	1.13	1.14^b	7.36	3.98	0.21	0.10	0.07	0.10
SmCD	+	60.8	71.7	1.09	1.19^b	7.48	4.56	0.22	0.10	0.08	0.11
SmCS	+	62.2	70.9	1.01	1.24^b	7.68	5.03	0.22	0.10	0.09	0.11
SmGD	+	60.6	72.6	1.14	1.21^b	6.42	4.08	0.24	0.09	0.08	0.10
SmGS	+	61.4	72.0	1.04	1.32^b	6.74	4.73	0.26	0.09	0.09	0.09
	SEM	0.87	1.46	0.09	0.12	1.48	1.32	0.03	0.06	0.02	0.02
Main effect
Dry diet		61.4	71.8	1.17	1.43^a	6.91	3.96^b	0.23	0.09	0.085	0.102
Semi-moist diet		61.5	71.8	1.08	1.22^b	7.02	4.47^a	0.23	0.10	0.084	0.101
P value
Diet composition		0.17	0.24	0.27	0.71	0.001	0.006	0.81	0.72	0.15	0.76
Diet moisture		0.73	0.91	0.18	0.005	0.67	0.004	0.77	0.49	0.76	0.96
Composition × moisture		0.21	0.65	0.42	0.002	0.06	0.52	0.59	0.38	0.84	0.90

Note: Values within a column with no common superscript letters differ significantly (LSD test at P ≤ 0.05).

Control diet: CD, casein + dextrose; CS, casein + starch; GD, gluten + dextrose; GS, gluten + starch; SmControl, semi-moist control; SmCD, semi-moist casein + dextrose; SmCS, semi-moist casein + starch; SmGD, semi-moist gluten + dextrose; SmGS, semi-moist gluten + starch; SEM, standard error of means.

¹ g/100g live body weight.

3.3. Small intestine morphology

Results of intestinal morphometric analysis at days 7 and 21 are summarized in Table 6. At day 7, experimental factors interacted for the VH (P < 0.01), crypt depth (CrD; P < 0.05) and VH to CrD (VCR; P < 0.01) in duodenum of the birds. The VH was the highest in duodenum of the bird fed SmGD and the lowest was found in bird raised on CD. At the same time, exposing birds to semi-moist diets decreased (P < 0.05) the duodenal crypt depth only in the birds received SmGS. Chicks also had higher VCR (P < 0.001) in the duodenum (day 7) exclusively caused by feeding SmGS. No effect was found on the VH in jejunum of 7-day-old chickens. However, there was interaction between diets and moisture for the jejunal CrD where birds grown on SmGD and SmGS showed the lowest figures compared with control group of birds. Independent to diet composition, an increase (P < 0.05) in jejunal VCR was noticed as a result of moisture addition to the diets. At three weeks of age, there was an interaction (P < 0.05) between diet and moisture for all the parameters, measured in duodenum excluding CrD that was not affected. At the same time, the highest VH was observed in duodenum of broilers fed SmControl and SmGS. Along with an interaction, feeding SmGS led to a significant increase in the duodenal VCR at day 21. In the jejunum of 21-day-old chicks, CrD was the only affected measurement with a significant (P < 0.01) interaction between experimental factors where the deepest crypt was detected in birds fed CS while the lowest was for SmGD.

Table 6. Effect of experimental diets on morphological parameters (µ) of duodenum and jejunum of broiler chickens at days 7 and 21.

		Day 7						Day 21
		Duodenum			Jejunum			Duodenum			Jejunum
Treatments	Moisture	VH	CD	VCR	VH	CD	VCR	VH	CD	VCR	VH	CD	VCR
Control	−	1221^b	165^bc	7.4^ab	750	132^ab	5.7	1643^b	228	7.2^b	1158	161^ab	7.2
CrD	−	1049^c	204^a	5.6^b	661	144^a	4.6	1621^b	222	7.3^b	1020	167^ab	6.1
CS	−	1202^bc	197^a	6.1^b	675	141^a	4.8	1711^ab	255	6.7^b	1116	192^a	5.8
GD	−	1133^bc	180^ab	6.3^b	726	127^ab	5.7	1669^b	206	8.1^ab	1069	160^ab	6.7
GS	−	1280^ab	175^ab	7.3^ab	826	148^a	5.9	1710^ab	204	8.4^ab	1078	166^ab	6.5
SmControl	+	1321^ab	174^ab	7.6^ab	767	139^ab	5.5	1812^a	232	7.8^ab	1151	151^bc	7.6
SmCD	+	1254^b	184^a	6.8^b	779	128^ab	6.1	1651^b	226	7.3^b	1016	164^ab	6.2
SmCS	+	1178^b	184^a	6.4^b	646	113^b	5.7	1763^ab	235	7.5^b	1140	187^a	6.1
SmGD	+	1385^a	146^bc	9.5^a	697	109^b	6.4	1737^ab	209	8.3^ab	1175	141^c	8.6
SmGS	+	1290^ab	124^c	10.4^a	774	101^b	7.7	1841^a	200	9.2^a	1180	151^cb	7.8
	SEM	63	13	1.87	94	11.8	1.65	71	18	1.14	87	8.56	1.73
Main effect
Dry diet		1196^b	184^a	6.5^b	737	138^a	5.3^b	1671^b	223	7.5^b	1088	169	6.46
Semi-moist diet		1285^a	162^b	8.1^a	732	118^b	6.2^a	1760^a	220	8.1^a	1139	159	7.26
P value
Diet composition		0.003	0.096	0.004	0.27	0.031	0.080	0.421	0.64	0.241	0.67	0.003	0.15
Diet moisture		0.012	0.016	0.001	0.56	0.025	0.036	0.045	0.48	0.057	0.28	0.62	0.28
Composition × moisture		0.006	0.023	0.008	0.35	0.006	0.152	0.005	0.06	0.038	0.47	0.007	0.76

Note: Values within a column with no common superscript letters differ significantly (LSD test at P ≤ 0.05).

Control diet: CD, casein + dextrose; CS, casein + starch; GD, gluten + dextrose; GS, gluten + starch; SmControl, semi-moist control; SmCD, semi-moist casein + dextrose; SmCS, semi-moist casein + starch; SmGD, semi-moist gluten + dextrose; SmGS, semi-moist gluten + starch; VH, villus height; CrD, crypt depth; VCR, villus height to crypt depth ratio; SEM, standard error of means.

4. Discussion

4.1. Performance parameters

The composition and moisture content of the pre-starter diets had marked influence on FI and WG. Chicks fed the semi-moist pre-starter diets had a higher FI in pre-starter period which was most pronounced for chicks on SmGS diet. This trend was also observed at later stages of the experiment so that chicks on SmControl and SmGS diets consumed more feed over the entire experimental period (1–42 days). A possible explanation for improvement in FI with semi-moist feeding may relate to the faster rate that the diet would become soluble in the gut, thereby facilitating faster digestion, gut clearance and ultimately higher FI (Scott 2002). It has been reported that although the wet-fed broilers grow faster as a result of higher intake during the early age, their ability to utilize feed is reduced as compared to the dry-fed birds (Yalda & Forbes 1995). However, current findings showed that despite the higher FI of chicks on semi-moist diets feed efficiency was not impaired indicating a sustainable improved intestinal development and increased nutrient utilization reflected at better performance indices carried over to the grower and finisher phases of the experiment. Adding water may have a positive effect on solubilisation of dietary components. Given the very rapid transit of feed particularly in broilers, this early solubilisation gives more time for absorption to take place and thereby wetting feed increases a more rapid penetration of digestive juices (Yasar & Forbes 2001), rendering the feed more digestible. This allows the actual digestibility of the feed to approach more closely to the potential digestibility that would be achieved if the feed retention time remained longer in the gastrointestinal tract (Yasar & Forbes 2000). Supplementation of CS or CD of the diets in either moist or semi-moist form resulted in a significant reduction of body WG and deteriorated FCR in pre-starter period. Birds could not fully catch up for this growth retardation at the end and exhibited lower BW and feed efficiency at 42 days compared to the other treatments. The poor performance of CD and CS chicks was not completely expected. Casein as a protein supplement might have formed some complex composition in the diets which were not readily available for chicks. The lower availability of nutrients from CD and CS for the first-week post-hatch may also be ascribed to the underdevelopment of digestive enzyme activity and gastrointestinal function (Nitsan et al. 1991; Noy & Sklan 1997), so that casein was not utilized optimally, yielded no stimulation of intestinal processes and consequently limited available protein of the diets. Dietary protein content has been shown to have a larger impact on growth, energy and protein metabolism and on intermediary metabolites compared to the carbohydrates and fat fraction in iso-energetically formulated diets (Swennen et al. 2007). On the other hand, the improved BWG and FCR of chicks on semi-moist GS and GD diets reflect better availability of nutrients from these diets, as young chicks are more susceptible to nutrients' quality due to their immature GIT and their high nutrients requirement specifically protein for the development of specific tissues post-hatch (Sklan 2001).

4.2. Yolk sac utilization, chick length and carcass characteristics

The residual yolk after hatch provides 30% of the nutrients required for growth and maintenance (O'Sullivan et al. 1991). Yolk sac utilization was not influenced by dietary treatments on days 3 and 5 of the experiment. However, at 7 days of age, the highest utilization of the yolk (lowest yolk sac residue) was seen in chicks fed semi-moist diets. It has been reported that the consumption of feed increases gastrointestinal activity and bird metabolism, which may explain the more rapid secretion of yolk sac contents through the vitelline duct into the intestines of fed chicks (Feher & Gyuru 1971). Murakami et al. (1992) stated that the residual yolk has an essential role in replenishing the nutritional deficiencies of the diet. However, the experimental diets fed in the current study were formulated to provide equal amounts of major nutrients (Metabolizable energy [ME], crude protein and amino acids), thus the higher absorption rate of the yolk sac in semi-moist diets may be explained by the higher feed consumption which should have increased GIT activity and associated metabolism, leading to higher absorption of yolk sac into the intestine. The possible impact of diet moisture content on yolk sac utilization has not been previously reported but findings of Dibner and Knight (2003) indicate that fasting, early feeding and early diet type did not change the rate of yolk sac utilization implying that fasted birds do not show accelerated use of their residual yolk in a way to compensate for a lack of feed. In line with current results, Noy and Sklan (2001) showed increased utilization of yolk sac in fed chicks with higher intake than fasted chicks.

Chicken length is an effective, fast, repeatable and non-destructive method to evaluate chick development. Chick length is positively related to yolk-free body mass at hatch and is an indicator of subsequent field performance (Molenaar et al. 2008). No marked effect of diet composition was observed on chick length at days 3 and 5 post-hatch. A higher chick length was recorded for birds on semi-moist diets compared to the other treatments at days 3, 5 and 7. It has been reported that for the first two weeks, chick length in the hatchery was a good predictor of broiler performance based on BW (Joseph et al. 2006). Interestingly, Brink and Rhee (2007) also reported higher chick length for chicks fed on a semi-moist diet immediately post-hatch compared to those on a dry diet. These results are in line with the findings of Van den Brand et al. (2010) who recorded higher chick length and BW over the first-day post-hatch for chicks fed a pre-starter diet supplemented with dextrose or albumen.

Diet composition had no effect on the relative weight of abdominal fat pad and small intestine at day 21, but at day 42 lower percentage of abdominal fat and higher intestine weight were observed for birds fed semi-moist diets. Early and proper FI post-hatch not only boosts growth, but it also increases the relative growth of internal organs such as the small intestine. A proper early development of the foregut segments, that plays an important role in the digestion process, may contribute to an optimal feed digestion and utilization at later ages. Generally, the influence of pre-starter diet moisture (wet versus dry feeding) on carcass parameters in the present study was much greater than that of pre-starter diet composition. These findings are consistent with those of Brink and Rhee (2007) who showed that chicks with access to a semi-moist diet for 48 h post-hatch showed significantly longer intestines compared with both the non-fed chicks and the chicks fed dry feed.

4.3. Small intestine morphology

It is well documented that the digestive capacity begins to develop a few days before hatch; however, most of the development occurs post-hatch when the neonatal chick begins consuming feed (Ferket & Uni 2009). During the post-hatch period the small intestine develops at a faster rate than the body mass (Sklan 2001). Hence providing a complete diet with highly available energy and protein content may lead to better development of the GIT in chicks. VH and crypt depth increased as the birds aged; however, each structure behaved differently in each segment as a function of age. The higher VH and lower crypt depth and subsequently higher VH:CD ratio recorded at the duodenal segment at days 7 and 21 of age for birds on SmGD and SmGS imply better morphological development of small intestine in this treatment, which could account for superior productive performance of birds in these treatments. Yasar and Forbes (1999) stated that the beneficial effects of wet feeding may be attributed to a decreased viscosity of gut contents; so there may be a better development of the layer of the villus in the digestive segments and a reduced crypt cell proliferation rate in the crypts to result in an increased absorptive area in the digestive tract. The deeper crypt indicates fast tissue turnover and a high demand for new tissue which would suggest a high potential for cell proliferation (Iji et al. 2001). The considerable decrease in VH and increased crypt depth observed in chicks on casein-supplemented diets particularly in dried form possibly have decreased absorption of nutrients which could, at least to some extent, explain partly poor observed BWG over the first week and across the 42-day study. Lack of access to feed for 48-h post-hatch has been reported to decrease duodenum VH and increase duodenum CD and subsequently decrease VH:CD ratio on day 7 (Tabeidian et al. 2010). In agreement to these findings, previous studies have also shown that diet composition at first-week post-hatch can influence morphological development of the small intestine (Noy & Sklan 1998; Tabeidian et al. 2010).

5. Conclusion

According to the current results, it could be concluded that pre-starter diet with proper ingredients and moisture content can positively affect chick development, optimize feed consumption and utilization and consequently improve productive traits. A carry over effects of pre-starter diet for FI, body WG and feed efficiency can be observed at later stages of growth.

Acknowledgement

The financial assistance for the current study provided by Islamic Azad University, Khorasgan Branch is gratefully acknowledged.