Behavioural aspects of feeding constraints: do broilers follow their gut feelings?

Effects of finisher diet nutrients density and slaughter age on energy and protein efficiency, productive and economic performance and meat quality of broilers

BACKGROUND

The current broilers have been greatly optimized for weight gain and breast yield, which necessitates the provision of nutrients-dense diets for maximum potential.

OBJECTIVES

The current study aimed to evaluate the effect of finisher diet nutrients density (ND) on energy and protein efficiency, productive and economic performance and breast meat quality of broilers raised until different slaughter age.

METHODS

A total of 600 23-day-old broiler male chicks (Cobb-500) were assigned to 10 treatments with six replicates and 10 birds each. Experimental treatments were included factorial arrangement of five increment (2.5%) levels of finisher diet ND (92.5%, 95%, 97.5%, 100% and 102.5% as strain recommendation) and slaughtered at 38 or 46 days of age. The relative difference in the energy level of experimental diets was used to increase ND levels at the same ratio.

RESULTS

Feed intake (FI) and breast meat quality traits exception water holding capacity (WHC) were not affected by finisher diet ND. In response to increasing finisher diet ND, energy and protein efficiency, productive traits, bio-economic index (BEI) and breast relative weight (BRW) linearly improved. However, residual feed intake and breast meat WHC improved with a quadratic trend. By using broken-line regression analysis, the optimum dietary ND was obtained at 97.5%-102% of strain recommendation. Energy and protein efficiency, feed conversion ratio and BEI deteriorated by prolonging rearing period. The BRW, meat lightness (L*), redness (a*), hue angle (h*) and WHC values for the birds slaughtered at 46 days of age were significantly higher, and cooking loss was lower than those slaughtered at 38 days old.

CONCLUSIONS

Broilers during the finisher period are not able to regulate their FIs with diet ND. The energy and protein efficiency, productive and economic performance were reduced when broilers were fed diluted diet or the rearing period was prolonged.

Assessment of crop usage in ad libitum fed birds and short-term phytase efficiency as affected by acid addition

1. A field assessment was performed to map the extent of crop usage and thus retention time in broiler chickens. In addition, a broiler experiment was carried out to study the short-term effect of acid addition on phytase efficacy in the crop.2. In the field assessment, the crop content of 40 ad libitum fed broiler chickens from four different farms were sampled at 10, 20 and 30 d of age. The dry matter (DM) content varied from zero to 32 g.3. From 11 d of age, 120 individually caged chickens were intermittently fed a high phytate-P diet with either no addition or 500 FYT C. braakii-derived phytase added or both phytase and 1.4 % formic acid added. Excreta were collected for assessment of phosphorus (P) retention. At 20 and 21 d of age, starved birds were fed for 1 h, and thereafter crop and gizzard contents were collected every 20 min until 140 min after start of the feeding. At 60 and 140 min, the contents from the jejunum and ileum were collected.4. All diets reduced the concentration of phytate in the crop, however the combination of acid and phytase resulted in a higher degradation (P<0.05) than the other diets from 20 min after the start of feeding. Simultaneously, the concentration of the smaller inositol phosphate isomers, such as inositol-5-phosphate, increased (P<0.05). Phytase increased (P<0.05) P retention, and the combination of acid and phytase increased jejunal P digestibility (P<0.05) compared to the other diets.5. The results indicated that lower pH in the crop due to acid addition improved phytase efficacy and increased P digestibility in the anterior digestive tract, even with short retention times.

Influence of the energy and digestible lysine contents of the diet on performance and egg quality traits of brown-egg laying hens from 19 to 59 weeks of age

The influence of nutrient density and standardized ileal digestible lys (DLys) content of the diet on egg production and egg quality traits, was studied in brown-egg laying hens from 19 to 59 wk of age. The experimental design was completely randomized with eight treatments arranged as a 2×4 factorial with two AMEn concentrations (2,680 and 2,780 kcal/kg) and four levels of DLys (0.68, 0.72, 0.76, and 0.80%). Each treatment was replicated nine times and the experimental unit was a cage with nine hens. Hen production, egg components (proportion of albumen, yolk, and shell), egg quality traits (Haugh units, egg shell strength, and incidence of broken, dirty, and shell-less eggs) were measured by period (28 d) and cumulatively. Data were analyzed as a completely randomized design with energy concentration, level of DLys, and their interactions as main effects. In addition, the effects of the level of DLys on the variables studied, were partitioned into its linear and quadratic components. No interactions between AMEn and DLys content of the diet were detected for any of the traits studied and therefore, only main effects are presented. An increase in the AMEn concentration of the diet from 2,680 to 2,780 kcal/kg increased energy intake (P < 0.05) and egg weight (P < 0.001) and improved feed conversion ratio (P < 0.05). An Increase in DLys from 0.68 to 0.80% did not affect the number of eggs produced but increased linearly egg weight (P < 0.01) and egg mass production (P < 0.05). Diet did not affect egg quality. In conclusion, an increase in the AMEn content of the diet from 2,680 to 2,780 kcal/kg increased egg weight and improved feed efficiency. Laying hens require no more than 744 mg DLys/d (corresponding to 0.68% DLys) to optimize egg production. However, when the objective is to maximize egg weight, hens should consume at least 843 mg DLys/d (corresponding to 0.76% D Lys).

Effects of dietary energy level on appetite and central adenosine monophosphate-activated protein kinase (AMPK) in broilers

Adenosine monophosphate-activated protein kinase (AMPK) acts as a sensor of cellular energy changes and is involved in the control of food intake. A total of 216 1-d-old broilers were randomly allotted into 3 treatments with 6 replicates per treatment and 12 broilers in each cage. The dietary treatments included 1) high-energy (HE) diet (3,500 kcal/kg), 2) normal-energy (NE) diet (3,200 kcal/kg), and 3) low-energy (LE) diet (2,900 kcal/kg). The present study was conducted to investigate the effects of dietary energy level on appetite and the central AMPK signal pathway. The results showed that a HE diet increased average daily gain (ADG), whereas a LE diet had the opposite effect (P < 0.05, N = 6). The average daily feed intake (ADFI) of the chickens fed the LE diet was significantly higher than that of the control (P < 0.05, N = 6). Overall, the feed conversion rate gradually decreased with increasing dietary energy level (P < 0.05, N = 6). Moreover, the chickens fed the LE and HE diets demonstrated markedly improved urea content compared with the control group (P < 0.0001, N = 8). The triglyceride (TG) content in the LE group was obviously higher than that in the HE group but showed no change compared with the control (P = 0.0678, N = 8). The abdominal fat rate gradually increased with increased dietary energy level (P = 0.0927, N = 8). The HE group showed downregulated gene expression levels of liver kinase B1 (LKB1), neuropeptide Y (NPY), cholecystokinin (CCK), and glucocorticoid receptor (GR) in the hypothalamus compared with the control group (P < 0.05, N = 8). However, LE treatment significantly increased the mRNA level of AMP-activated protein kinase α2 (AMPKα2) compared with other groups (P = 0.0110, N = 8). In conclusion, a HE diet inhibited appetite and central AMPK signaling. In contrast, a LE diet activated central AMPK and appetite. Overall, the central AMPK signal pathway and appetite were modulated in accordance with the energy level in the diet to regulate nutritional status and maintain energy homeostasis in birds.

Guanidinoacetic acid supplementation in broiler chickens fed on corn-soybean diets affects performance in the finisher period and energy metabolites in breast muscle independent of diet nutrient density

(1) Guanidinoacetic acid (GAA) is the single immediate endogenous precursor of creatine (Cr). It was hypothesised that dietary GAA would have different effects on performance and energy metabolites in breast muscle depending on the nutrient density (ND) of corn-soybean-based diets. (2) A total of 540 one-day-old male Ross 308 broilers were allocated to 9 dietary treatments with 6 replicates (10 birds each) in a 3 × 3 factorial arrangement with three levels of ND (low, 2800; medium, 2950 and high, 3100 kcal metabolizable energy (ME)/kg; and with the other nutrients being constant relative to ME) and supplemented with three levels of GAA (0, 0.6 and 1.2 g/kg) in a 42-d feeding trial. (3) In the starter and grower periods, increasing levels of ND improved body weight (BW), average daily gain (ADG), average daily feed intake (ADFI) and feed conversion ratio (FCR), with the exception of ADFI in the starter period. GAA supplementation did not affect performance characteristics. All performance indicators responded markedly to increasing ND in the finisher period, whereas the highest GAA level reduced ADFI compared to the unsupplemented control (156 vs. 162 g/d) and concomitantly FCR (1.81 vs. 1.93). No interactive effects were noted for any performance trait. The high ND diet resulted in more breast meat yield on d42, associated with higher fat content and darker colour compared to the other ND levels. The GAA supplementation did not affect carcass and breast traits. At the end of the experiment, Cr was elevated when feeding GAA at 1.2 g/kg (5455 vs. 4338 mg/kg fresh muscle). (4) To conclude, ND had a substantial effect on performance and carcass traits, whereas any effect of GAA was limited to FCR in the finisher period and independent of diet ND level.

Live performance, carcass composition, and blood metabolite responses to dietary nutrient density in two distinct broiler breeds of male chickens

A study was conducted to evaluate the effects of varying nutrient density with constant ME:CP ratio on growing performance, carcass characteristics, and blood responses in 2 distinct broiler breeds of male chickens (Arbor Acres, a commercial line, and Beijing-You, a Chinese nonimproved line). Experimental diets were formulated with high, medium, or low nutrient densities for 3 growing phases. Starter diets (1 to 21 d) contained 23, 21, and 19% CP with 3,059, 2,793, and 2,527 kcal/kg of ME; grower diets (22 to 35 d) contained 21, 19, and 17% CP with 3,150, 2,850, and 2,550 kcal/kg of ME; and finisher diets (36 to 42 d for Arbor Acres and 36 to 91 d for Beijing-You) had 19, 17, and 15% CP with 3,230, 2,890, and 2,550 kcal/kg of ME. Male hatchlings (216 of each breed) were randomly assigned to 6 replicates of 12 birds in each treatment. Arbor Acres broilers had better (P < 0.001) BW gain, feed conversion ratio (FCR), and carcass yield, but had greater (P < 0.001) abdominal and carcass fat deposition. In both breeds, the higher nutrient density increased (P < 0.05) BW gain, protein efficiency ratio, and energy efficiency ratio while decreasing (P < 0.05) feed intake and FCR. The breed differences were increased for FCR, protein efficiency ratio, and energy efficiency ratio in the starter period and decreased for carcass chemical composition, respectively, by higher nutrient density. These findings indicate that 1) genetic improvement has a significant effect on broiler responses to dietary nutrient density, 2) performance differences between breeds are lessened with diets of low nutrient density, 3) carcass quality differences are less when birds were fed diets of high nutrient density, 4) carcass composition is hardly modified by nutrient density and both breeds exhibit similar metabolite responses to dietary concentrations, and 5) optimal diets are deduced for these breeds for the 3 growing phases.

Influence of dietary nutrient density, feed form, and lighting on growth and meat yield of broiler chickens

The objective of this study was to examine main and interactive effects of nutrient density (ND), feed form (FF; mash, pellet), and lighting program (12L:12D, 20L:4D) on production characteristics and meat yield of broilers raised to 35 d of age. Diets (starter, grower, and finisher) were formulated so that amino acid levels were in proportion to the dietary energy level. Lighting programs were initiated at 4 d of age. Body weight was not affected by ND when diets were fed in a pellet form but decreased in a linear manner with lower ND when fed as a mash. Final BW of birds fed mash were less than those of birds fed pellet diets. Feed to gain ratio decreased with increasing ND but was not affected by FF. Feed intake decreased with increasing ND and was lower for birds fed mash. The effect of ND on feed intake was less when birds were fed mash in contrast to pellet diets (P(ND x F) < 0.0001). Dietary ND had no effect on mortality, but feeding mash decreased mortality (3.8%) compared with feeding pelleted feed (5.6%). Lighting programs affected production characteristics independently of ND and FF. Use of 12L:12D reduced BW, feed to gain ratio, feed intake, and mortality compared with 20L:4D. Similarly, carcass components were not affected by ND when fed in pellet form but decreased with lower ND when fed as a mash. Overall, carcass yields were reduced when broilers were fed mash or provided with 12L:12D. Female birds had higher carcass yields and increased proportional breast meat deposition compared with males.

Short-Term Number of Pecks and Feed Intake Levels: A Link with the Physical Characteristics of Feed in Four-Week-Old Turkeys

Short-term reactions of young turkeys to changes in the physical characteristics of their feed sometimes give rise to problems of adaptation in the field. Specific feeders were designed for this study to automatically count the number of pecks given at feed by 4-wk-old male turkeys during 95-min sessions. The lighting program was intermittent (0140L:0100D). In experiment 1, 4 series of 12 birds were tested 4 times/day from 28 to 31 d of age. Four control turkeys were consistently tested with 1 feed, and 8 experimental turkeys ate 1 of 32 commercial feeds (30 as pellets and 2 as crumbs) with a distinct feed for each test (16 replicates/experimental feed). Feed intake, total number of pecks, and pecking efficiency (mg/peck) were recorded for each test and normalized for each turkey. The effects of series, day, and test were not significant for controls. The number of pecks and pecking efficiency differed among feeds (P < 0.001) but not feed intake. Hierarchical Cluster Analysis for these variables distinguished 3 groups of feed: group 3 (6 crumb and small pellets) resulted in high pecking and low efficiency. However, group 1 (10 feeds) were pecked at less but more efficiently than group 2 (16 feeds) for similar feed intake, although the average sizes of the pellets were similar (6.23 and 6.16 mm, respectively), as were the average bulk density, hardness, resistance to abrasion, and color characteristics of the pellets for both groups. Two feeds of each of these 2 groups were compared in a second experiment for 12 turkeys receiving the 4 feeds successively each day over 4 d in varying order. The turkeys consistently pecked the feeds of group 1 less and less efficiently compared with group 2. The automated measurement of pecking, combined with a more detailed image analysis of feed particles, might enhance the evaluation of the effects of feed technology on the behavior of turkeys and thus become a useful tool for the feed industry.