Use of nutrients by broiler chicks post hatch

On the first day of life, the digestion and absorption of amino acids and carbohydrates by broiler chicks is very low and mainly confined to glucose uptake. On the day of hatch the absorption of glucose and amino acids can vary from 43 to 53%, however, as the bird grows, absorption increases, and on day four glucose and amino acids absorption reach over 80% (Noy and Sklan, Reference NOY and SKLAN1999; Reference NOY and SKLAN2001). According to Noy and Sklan (Reference NOY and SKLAN1999) the best use of proteins and carbohydrates occurs when appropriate conditions are reached, including enzymatic activity and sufficient sodium for glucose and amino acids cotransporters in the gut lining. Sklan (Reference SKLAN2003) attributed low intestinal absorption of carbohydrates on the day of hatch to the presence of fatty acids from the yolk sac. As the yolk sac nutrients are hydrophobic, these inhibit the absorption of hydrophilic compounds.

Conversely, the digestion and absorption of fatty acids are highest during the first few days of life, with absorption rate at the day of hatch being over 85% which stays constant during the first four days of life (Noy and Sklan, Reference NOY and SKLAN1999; Sklan, Reference SKLAN2003). This high absorption rate of lipids has been attributed to the mechanisms for digestion and absorption of lipids being already present and primed pre-hatch, as the lipids of yolk sac are digested by the embryo during development. Adaptations for lipid absorption are less significant during post-hatch period.

In ovo feeding

In ovo feeding is possible through the perforation of egg shell and inoculation of nutrients into the amniotic or the allantoic fluid, using a syringe and needle. The late term embryo obtains nutrients via the allantoic fluid (Gonzales et al., Reference GONZALES, OLIVEIRA, CRUZ, LEANDRO, STRINGHINI and BRITO2003; Leitão et al., Reference LEITÃO, LENDRO and PEDROSO2005), and delivery of extra nutrients to this area may be used to compensate for any energy deficiencies during hatch. In ovo feeding has the objective of promoting the early development of the digestive tract, in which interaction between nutrients and the immature intestine induces the development of absorptive epithelium and the enzymatic activity, mainly for digesting carbohydrates.

In ovo feeding of carbohydrates

In ovo supplementation with carbohydrates helps the development of late term embryos, providing the more energy needed during this phase. As a result of carbohydrate supplementation, higher body weight and pectoral muscle weight have been observed at hatch. The appropriate level of glucose available in ovo reduces the use of muscle protein to produces energy via gluconeogenesis. Carbohydrate supplementation during the late term embryonic phase may be increased from 6 to 12 mg of glycogen per gram of liver tissue (Uni et al., Reference UNI, FERKET, TAKO and KEDAR2005; Foye et al., Reference FOYE, UNI and FERKET2006) to supply the extra energy required.

Studies by Uni et al. (Reference UNI, FERKET, TAKO and KEDAR2005) evaluated the effect of injecting carbohydrates associated with β-hydroxy β-methylbutyrate (leucine metabolite) in Cobb and Ross fertile eggs at 17.5 days of incubation. The injection of these nutrients increased body weight in newborn chicks from 5-6% compared with the control group, and increased the relative weight of pectoral muscle (P≤0.05). These apparently advantages remained evident until 25 days of age. The authors concluded that in ovo feeding with carbohydrates increased the energy status of late term embryos and improved the initial performance of broiler chicks.

According to Foye et al. (Reference FOYE, UNI and FERKET2006) the use of carbohydrates in ovo provided a higher body weight at hatch (57 g) in poults when compared with control group (53 g; P≤0.05). The group that received carbohydrates had a higher glycemic index at seven days of age, as compared with control group. Similar results were found by other authors. Zhai et al. (Reference ZHAI, ROWE and PEEBLES2011), studied in ovo injections with different volumes of a carbohydrates solution at 18.5 days of incubation, and verified that chick body weight and the ratio of body weight to egg weight on the day of hatch were positively related to volume used (P≤0.05), although hatchability was negatively affected by increasing the volume of solution injected. In agreement with these results, Salmanzadeh (Reference SALMANZADEH2012) observed higher body weight at hatch and better FCR, feed intake and weight gain at 42 days old for birds that received glucose in ovo in increasing concentrations at seven days of incubation, as compared with a group injected with deionized water and the control group not injected (P≤0.05). However, hatchability decreased from 86% (control group not injected) to 67.5% (0.5ml glucose 15% injection).

Conversely, Leitão et al. (Reference LEITÃO, LEANDRO, CAFÉ, STRINGHINI, PEDROSO and CHAVES2008) reported low hatchability for eggs injected with glucose at 16 days of incubation. The injection of a 50% aqueous solution of glucose increased the time required to the break of inner shell membrane and the egg shell at hatch. On the other hand, when glucose was injected with saline solution there was no effect on these parameters. The same authors verified that the use of 0.6ml of glucose in ovo increased embryo death during post inoculation and decreased hatchability, as compared with the control group not injected (hatchability decreased from 82% to 65%; P≤0.05). At 10 days old there was no difference between the treatments for body weight, gain weight, feed intake and FCR. However the harm caused by using 0.6 ml volumes must be taken into account for this trial design. With this volume of inoculum, a decrease in hatching from 82% in the normal control to 78% in the water inoculated group and 72.5% for those eggs injected with 0.2 ml glucose 50% solution +0.4 ml of water and 65% in eggs inoculated with 0.6 ml of glucose 50% solution, indicated negative effects both by volume and concentration of glucose.

Kornasio et al. (Reference KORNASIO, HALEVY, KEDAR and UNI2011) suggested that late feeding of broiler chicks (36 hours after hatch) retarded the bird's growth which was not compensated for in the growth period to 35 days of age. This slow growth was characterised by a decrease in body weight, which was 15% lower in chicks fed late as compared to chicks fed in ovo. The authors concluded that in ovo feeding with a solution of dextrin and β-hydroxy β-methylbutirate at 18 days of incubation could reduce this negative effect of late feeding on body weight.

According to Smirnov et al. (Reference SMIRNOV, TAKO, FERKET and UNI2006) in addition to the beneficial effect of in ovo feeding on broiler performance, it can have positive effects on the development of the intestinal epithelium. The injection of carbohydrates in ovo at 17.5 days of incubation had a trophic effect on jejunum, increasing villus surface area by 27% on day of hatch which was maintained at 21% increased surface area at three days of age. The intake of carbohydrates increased insulin blood levels, which had an anabolic effect on intestinal epithelium cell proliferation. In ovo feeding with carbohydrates showed positive effects on globet cell ratio and mucin, which increased by 50% 36 hours after supplementation compared with the control group. However, this effect disappeared at hatch and was not applicable to later growth. The negative effects of embryo inoculation could be mostly due to the volume injected. In routine laboratory work, 0.1 ml and up to 0.2 ml volumes have been used in 8-11 day-old embryos, in order to avoid procedure error and unspecific embryonic death (Swayne et al., Reference SWAYNE, SENNE and BEARD1998). Similarly, the inoculum of in ovo vaccines is normally 0.1 ml/egg (Reddy et al., Reference REDDY, SHARMA, AHMAD, REDDY, MCMILLEN, COOK, WILD and SCHWARTZ1996) which is much less than some proposed supplements.

In ovo feeding of amino acids and protein

The amino acid balance remains stable throughout the development of embryo and the amino acids ratio to lysine in egg compounds and embryo are similar during the incubation period. However, during embryonic development, crude protein and fat concentrations decrease in the egg components and increase in the embryo, due to nutrient transfer. The amino acid concentration on the 19th day of incubation is higher in the egg than in the embryo, indicating that the egg amino acid pool is larger than needed for embryo development until hatch (Ohta et al., Reference OHTA, TSUSHIMA, KOIDE, KIDD and ISHIBASHI1999). These latter researchers evaluated the injection of 0.5 ml of an amino acid solution (similar to standard egg amounts) into fertile eggs at days zero and seven of incubation through the air-chamber and into the yolk sac. The hatchability of eggs submitted to in ovo injection of amino acids at day zero was 13%, while in control group hatchability was 87%. No beneficial effect of in ovo injection with amino acids was observed irrespective of incubation day (0 or 7) or inoculation route, on broiler chick body weight at the day of hatch.

Similar results were obtained by Kadam et al. (Reference KADAM, BHANJA, MANDAL, THAKUR, VASAN, BHATTACHARYYA and TYAGI2008), who studied the effect of different amounts of threonine supplementation in the 14^th day of incubation. No beneficial effect was observed on chick body weight at hatch when compared to control group. However, no differences were observed for hatchability between treatments, possibly because the in ovo injections were performed at a less sensitive embryonic age. Higher body weight was seen from 21 to 28 days old on broiler chickens that received threonine supplementation in ovo (P≤0.05), although feed intake and FCR were not affected by treatments. No difference was observed for lymphoid organs weight (bursa, spleen and thymus) or for enzymatic activity of pepsin in the proventriculus or for amylase and trypsin activity in the jejunum and pancreas.

According to Vieira et al. (Reference VIEIRA, FARIA FILHO, TORRES, BORGES, ROSA and FURLAN2006), the supply of 150 µl of glutamine 1% solution in ovo on the 11^th day of incubation did not result in improvements in morphometry of the duodenal mucosa.

The absence of positive results for injected amino acids may be due to the fact that the ideal ratio among amino acids has a major impact on embryonic metabolism. The constant stimulus of each amino acid in embryonic intestinal lumen may be more effective than a single supplementation.

In ovo L-carnitine feeding

The chicken embryo undergoes rapid development and has a low capacity to synthesise L-carnitine, which is a quaternary ammonium compound derived from lysine and methionine and involved in fatty acid transport, and supplementation during incubation could be of benefit for embryonic development. However, in ovo injection of L-carnitine in concentrations varying from 0.05 to 10 μM in the 17 and 18^th days of incubation was not shown to be beneficial for hatchability, yolk sac weight or chick body weight at hatch (Zhai et al., Reference ZHAI, NEUMAN, LATOUR and HESTER2008).

Keralapurath et al. (Reference KERALAPURATH, CORZO, PULIKANTI, ZHAI and PEEBLES2010a; Reference KERALAPURATH, KEIRST, CORZO, BENNETT, PULIKANT and PEEBLES2010b) concluded that the injection of different levels of L-carnitine in fertile eggs at the 18^th day of incubation, did not affect the hatching time or hatchability of broiler chicks, as compared to non-injected control groups, those given a dry or diluent injection. The injection of L-carnitine up to a concentration of 8.0mg/100 μl of diluent in ovo was therefore deemed to be not toxic for the embryos. The inoculated L-carnitine did not show any beneficial effects on the ratio of yolk sac weight to yolk sac compounds. In addition, L-carnitine did not cause positive effects on incubation yield or on broiler performance up to 46 days of age or on slaughter yield at the age of 47 days.

Other substances for in ovo feeding

In ovo inoculation of linoleic acid, glucose and glutamine in increasing quantities at the 16^th day of incubation had negative effects on hatchability and broiler performance up to 10 days of age (Pedroso et al., Reference PEDROSO, CHAVES, LOPES, LEANDRO, CAFÉ and STRINGHINI2006). In a study with in ovo feeding at the 18^th day of incubation, Dos Santos et al. (Reference DOS SANTOS, CORZO, KIDD, MCDANIEL, TORRES FILHO and ARAÚJO2010) injected six different solutions in ovo, either maltose 50% solution; a multivitamin solution; zinc and glycine (0.5%); glutamine (10%); a mixed solution of maltose, vitamins, zinc, glycine and glutamine; or saline solution. No positive effects were seen for any treatments on body weight at hatch, hatchability and mortality at days 18 and 21 of incubation. However, a positive effect was observed for chick body weight at placement in embryos that received either maltose or vitamin supplementation, and these chicks had higher body weight compared to those that received glutamine. However, at the age of seven days after hatching, no persistent positive effect was detected, and there was no effect on feed intake, FCR or carcass yield.

Leandro et al. (Reference LEANDRO, OLIVEIRA, CAFÉ, GONZALES, STRINGHINI, CARVALHO and ANDRADE2010) evaluated in ovo inoculation of prebiotics and organic acids on initial performance of broiler chicks, but observed no effect on performance. The use of prebiotics resulted in a decrease in body weight gain and feed intake up to 10 days of age, and no positive effect were observed on the biometrics of the digestive organs, when compared to control group.