Effect of Hatching Time on Yolk Sac Percentage and Broiler Live Performance

This study investigated the effects of broiler chick hatching time on the percentage of the yolk sac and subsequent broiler live performance. Broiler hatching eggs were obtained from a commercial flock at 55 wk of age and were stored for 2 d at 18°C and 75% relative humidity (RH) prior to incubation. Chicks were identified as hatching Early (471-477 h), Middle (480-486 h), and Late (494-510 h). All chicks were removed from the trays at 510 h of incubation. Body weight (BW) and yolk weight (YW) were determined at emergence from the shell (initial hatch time) and at placement on feed. Chicks were permanently identified by hatch time with neck tags, feather sexed, weighed, and introduced to feed and water in litter floor pens. Broiler BW and feed consumption (FC) were then determined 7, 21, and 35 d of age. Mortality was recorded daily. Although the percentage of the yolk was similar at hatch time, it was less in Early compared to Middle and Late chicks at placement (p≤0.05). Broiler chick BW was greater at placement in Late chicks compared to Early and Middle chicks (p≤0.05) but this advantage disappeared by 7 d because Late chicks consumed less feed to 7 d (p≤0.05). Early hatched broilers exhibited greater BW than Late with Middle broilers intermediate at 35 d (p≤0.05). There were no significant differences in feed consumption and feed conversion ratio (FCR) at 35 d of age. Additionally, late hatch chicks exhibited greater mortality. Overall, live performance of Late hatching chicks, judged by mortality and BW at 35 d, was reduced compared to Early hatching chicks.


INTRODUCTION
There has always been a natural biological variation in the time that commercial broiler chicks emerged from their egg shells (hatch time) even under optimum conditions of artificial incubation.Thus, early hatching chicks have generally remained in the hatcher longer while awaiting removal of later hatching chicks from the machine (pull time) (Elibol et al., 2011;Powell et al., 2016).It has been reported that performance after placement was negatively associated with the time that chicks remained in the hatcher after hatching (Decuypere et al., 2001;Halevy et al., 2003) or that delayed access to feed depressed growth after access to feed (Careghi et al., 2005), and increased mortality (Hamdy et al., 1991).El Sabry et al. (2013) reported that early hatching chicks were not able to compensate for their post hatch BW loss and weighed less at 35 d of age.However, feed conversion ratio was little affected in these studies.Corless & Sell (1999) reported reduced BW associated with extended post-hatch holding, but these findings were not consistent with the data presented by Casteel et al. (1994), who weighed each group of birds 43 d following placement on feed and water and reported no differences.Work with respect to Elibol O, Brake J

Effect of Hatching Time on Yolk Sac Percentage and Broiler Live Performance
hatch time and post-hatch holding has often differed in that chicks were placed as much or more than 24 h apart, but weighed on the same day subsequently in some experiments (Pinchasov et al., 1993;Vieira & Moran, 1999) or on the basis of days on feed in other studies (Almeida et al., 2006;Lamot et al., 2014;Dişa et al., 2015).Furthermore, holding chicks in the hatcher for 24 h has been reported to not clinically dehydrate chicks or affect live performance (Casteel et al., 1994;Joseph & Moran, 2005;Almeida et al., 2006;Lamot et al., 2014).In fact, the percentage BW gain during the first 7 d was 76.6%, 76.2%, and 74.1% for early, middle, and late hatching groups, respectively, so that the differences in initial hatching BW disappeared and all groups exhibited a similar BW, feed intake, and mortality at 41 d of age (Almeida et al., 2006).In yet another study, early, middle, and late hatched chicks had approximately 26, 19, and 13 h of no feed and water access after hatching, respectively, but early hatch chicks consumed more feed and had numerically greater BW gain to 18 d of age (Lamot et al., 2014).Obviously, early hatching chicks have frequently exhibited a different developmental and growth pattern than did middle or late hatching chicks (Lamot et al., 2014;Brake et al., 2015), which may simply be related to differences in initial appetite.This may be related to having differences in residual yolk sac that may approximate 10% of total BW (Sklan et al., 2000;Wolanski et al., 2006).Residual yolk has been demonstrated to be important to the complex metabolic processes involved in early chick development (Noy & Sklan, 1998a;Noy et al., 2001;Halevy et al., 2003;Tona et al., 2003;Careghi et al., 2005) but required feed consumption to facilitate rapid absorption (Chamblee et al., 1992;Henderson et al., 2008), which has seemed to be greater in early hatching chicks.The objective of the present research was to determine the effects of hatch time on the percentage of the yolk sac at placement and subsequent broiler live performance.

Hatching Eggs and Incubation
The experimental procedures and animal care employed in this experiment were approved by the University of Ankara Institutional Animal Care and Use Committee (Ankara, Turkey).Broiler hatching eggs were obtained from a commercial flock of Ross 308 at 55 wk of age.Hatching eggs were stored for 2 d at 18°C and 75% RH before incubation.A total of 2070 (69.0±4.9 g) eggs were set for incubation in three laboratory incubators (Cimuka Co., Turkey).A singlestage incubation program was used with a gradually decreasing machine set point temperature from 38.1°C at E1 of incubation to 37.5°C at E18. Hatchers had a dry bulb temperature of 37.2°C at E18 that was gradually decreased to 36.4°C at E21. Relative humidity was 53±2% from E1 to E18.The eggs were turned once every hour until E18 of incubation in all cases.
The hatching process was divided into three time periods with 471-477 h termed as Early, 480-486 h termed Middle, and 494-510 h termed Late.Chicks that hatched outside of these time periods were not used in the experiment.
All chicks that had completed the hatching process were removed from the hatching baskets (pulled) at 510 h.Chicks were deemed to be hatched when they exhibited healed navels and dryness about the head and neck.Early and Middle chicks were individually identified with neck tags and placed back inside their original hatcher tray where they awaited the final pull at 510 h.Average holding periods in the hatcher after emergence from the shell for Early, Middle and Late hatched chicks were 36, 27, and 8 h, respectively.The BW of chicks was initially determined at emergence from shell to calculate relative BW loss during the holding period.

Percentage of Yolk Sac at Placement
Ten randomly selected chicks from each hatch time were weighed and killed by cervical dislocation and residual yolk sac weight determined at time of emergence from the shell (initial hatch) and at time of placement into pens before introduction to feed and water.

Broiler Grow-Out Management
The chick processing time from final pull to placement was 8h during which the chicks were held at 24±1°C.During this period, chicks were feather sexed, counted, permanently identified with neck tags and weighed individually before being placed in a floor pen house on new wood shavings.The brooding facilities were preheated for 24 h before chick placement to achieve a stable and uniform litter temperature.At chick placement litter temperature was 33°C, which was gradually decreased to 20°C by 21 d of age and remained at that level until slaughter at 35 d of age.The chicks received continuous light (24L:0D) at a light intensity at pen level of 25 lux.Starter (3,000 kcal ME/ Elibol O, Brake J

Effect of Hatching Time on Yolk Sac Percentage and Broiler Live Performance
kg and 23.5% CP) and grower (3,200 kcal ME/kg and 22.0% CP) diets were fed for 0 to 10 and 11 to 28 d, respectively.The finisher (3,300 kcal ME/kg and 20.0 % CP) diet was fed 29 to 35 d.The feeds were in mash form.Chicks were provided ad libitum access to feed and water, and diets were formulated to meet or exceed NRC (1994) recommendations throughout the grow-out period.

Broiler Live Performance Measurements
From each hatch time chicks were assigned to 9 pens (1 x 1 m) with 9 male plus 9 female chicks each for a total of 486 chicks.Individual BW was recorded at 7, 21, and 35 d of age.Feed consumption was calculated by the difference in feed offered and feed remaining on a pen basis at these times.Mortality was recorded twice a day.

Statistical Analyses
Data on yolk sac, feed consumption, and feed conversion ratio were analyzed using the GLM procedure of SAS (version 9.1, SAS Institute, 2004) according to the following model: Y ij = µ + HT i + e ij , where µ was the overall mean, HT i was the hatching time (Early, Middle, Late), and e ij was the residual error term.Data concerning chick BW were analyzed according to the following model: Y ijk = µ + HT i + sex j + (HT x sex) ij + e ijk , where sex j was the sex of the chick, (HT x sex) ij was the interaction between hatching time and sex, and e ijk was the residual error term.When the means of the GLM were statistically different, means were compared using least squares or with DUNCAN for multiple comparisons.The mortality percentage was analyzed using the chi-square test via Minitab Version 14 (Minitab Inc., United Kingdom).Statements of statistical difference were based upon p≤0.05.

Yolk Sac Percentage
The effect of hatch time on yolk percentage at the time of emergence from the shell (hatch time) and at placement on feed is shown in Table 1.Yolk sac percentage at emergence was not significantly different among the group's hatch time.However, Early chicks possessed less yolk percentage at placement (p≤0.05).Early chicks had less yolk sac weight compared to Late chicks in a manner similar to previous studies (Van de Ven et al., 2013;Özlü et al., 2015;Powell et al., 2016).However, El Sabry et al. (2013) and Lamot et al. (2014) found no effect of hatch time on yolk sac weight.A smaller yolk sac percentage would suggest greater transfer of nutrients, immune bodies, and metabolic information to the hatchling as well as greater appetite as discussed below.The absorption of nutrients from the yolk sac has been reported to be essential to promote subsequent growth (Murakami et al., 1992;Bigot et al., 2001) and early hatching chicks may have had an advantageous developmental and growth pattern (Lamot et al., 2014) due to earlier absorption of the yolk that has typically represented approximately 10% of total BW at initial hatching (Sklan et al., 2000;Wolanski et al., 2006).Early utilization of the yolk could have produced a metabolically more mature chick that was ready to consume feed and concurrently utilize the remaining residual yolk sac materials (Chamblee et al., 1992;Noy & Sklan, 1998b;Halevy et al., 2003;Tona et al., 2003;Yang et al., 2008;Careghi et al., 2005;Bhanja et al., 2009;Shinde et al., 2015).

Effect of Hatching Time on Yolk Sac Percentage and
Broiler Live Performance at 7 d compared to Early and Middle chicks but the effect was not apparent thereafter.These data were consistent with the BW data.The present data clearly demonstrated a negative effect of late hatching, which was obviously related to poor feed consumption at 7 d.Early hatch groups have been reported to consume more feed at 4 d as compared to middle and late hatch groups (Lamot et al., 2014).Additionally, Løtvedt & Jensen (2014) reported that early male hatched chicks displayed a higher response to novelty, as well as a tendency of lower passivity.In this study for the overall period at 35 d, there were no significant differences in feed consumption in a manner similar to previous studies (Casteel et al., 1994;Joseph & Moran, 2005;El Sabry et al., 2013;Lamot et al., 2014).Further, the Early chicks exhibited an improved (p≤0.05) FCR at 21 d of age but not thereafter (Table 3).Effects on FCR due to hatch time have also not been apparent at market age in other studies (Casteel et al., 1994;Joseph & Moran, 2005;El Sabry et al., 2013).--------(Feed Consumption, g/chick) --------- Joseph & Moran (2005) reported that the mean incubation length of early hatching chicks was 497 h (480-504 h) compared with 509 h (506-512 h) for late hatching chicks resulting in an average postemergent holding duration of 15 h versus 3 h in the hatcher, respectively.At 512 h of incubation, all of the chicks were removed, weighed, and kept in the hatchery for an additional 9 h before placement.Although greater BW and yolk sac weight at hatch time were associated with late emergence, decreased holding time in the hatcher had no effect on live performance or carcass yield at 42 d of age.In another study, chicks that hatched early (480 h), or in the middle of the hatching period (492 h), and were held in the hatcher for 12 to 24 h lost 11.5% and 6.7% of their BW, respectively, and exhibited lower initial BW as compared to chicks that hatched during late incubation (504 h).However, the percentage BW gain during the first 7 d was 76.6%, 76.2%, and 74.1% for the early, middle, and late hatching groups, respectively, so that differences in initial hatching BW disappeared.All hatch time groups exhibited a similar BW, feed intake, and mortality at 41 d of age (Almeida et al., 2006).Pinchasov & Noy (1993) and Tong et al. (2015) found that BW loss and yolk sac utilization were increased when chicks had extended holding period.Therefore, posthatch BW loss may not be exclusively the result of dehydration.Dehydration as a result of extended post-hatch holding has been associated with poor post-hatch performance (Joseph & Moran 2005;Almeida et al., 2008).It has been reported that chick BW at pull time was significantly influenced by time of emergence from the shell as chicks that hatched early lost BW while waiting to be pulled and subsequently weighed less than later hatching chicks at pull time (Reis et al., 1997;Sklan et al., 2000;Joseph & Moran, 2005;El Sabry et al., 2013).------------------------------------------------------(BW, g) ---------------------------------------------- 2 Placement time was 518h.
3 SEM for mean of 9 pens of 9 male plus 9 female chicks at placement.Elibol O, Brake J

Effect of Hatching Time on Yolk Sac Percentage and Broiler Live Performance
Using a different experimental protocol, Casteel et al. (1994) divided chicks after 528 h of incubation into two groups that were either placed in floor pens or returned to the hatcher for an additional 24 h.Chick BW was reduced after holding for 24 h as chicks lost approximately 5% of their BW compared with initial hatch BW.At 21 d post-placement the broilers held were significantly heavier than their controls but were similar by 43 d of age when birds were weighed at the same age relative to placement on feed and water.Obviously, hatched chicks underwent complex metabolic processes as they decreased in BW at a rate of about 4 g per 24 h due in part to moisture loss as well as utilization of reserves available from the yolk and pectoral muscle (Noy & Sklan, 1998b;Halevy et al., 2003;Tona et al., 2003;Careghi et al., 2005).This process appeared to be necessary to prepare the chick to consume feed and complete the absorption of the yolk sac (Chamblee et al., 1992) as late hatching chicks that had not undergone this BW loss did not consume feed as well as did the early hatching chicks.The present data clearly demonstrated a positive effect of early hatching, which was obviously related to BW loss and yolk sac utilization while being held under optimum conditions in the hatcher.Some authors have found chick weight to be an accurate predictor of final BW (Sklan et al., 2003) while others have not (Ulmer-Franco et al., 2010).The current study showed no positive relationship between day old chick BW and final BW at 35 d.As expected, males exhibited greater BW than females after 7 d post-hatch (data not shown; p≤0.05).
1 Early hatch time was 471-477 h, Middle hatch time was 480-486 h, and Late hatch time was 494-510 h.

CONCLUSIONS
This study demonstrated that Late hatching chicks had a greater yolk sac percentage and BW at placement but that was followed by poorer feed consumption at 7 d, decreased BW at 35 d, and increased mortality compared to Early and Middle hatching chicks.Overall, live performance of Late hatching chicks, judged by mortality and BW at 35 d, was reduced compared to Early hatching chicks.Under optimum hatcher conditions, chicks could be held approximately 30 h without detrimental effect on subsequent broiler performance.

Table 1 -
The effect of hatch time on yolk percentage at time of emergence from the shell (initial hatch) and at placement on feed.BWthan Late chicks with Middle chicks intermediate at 35 d.The effect of hatch time on feed consumption, and feed conversion ratio from placement on feed to at 35 d of age are shown in Table 3.Late chicks consumed less feed (p≤0.05) a,b Means within a column with different superscripts differ significantly (p<0.05).1 Early hatch time was 471-477 h, Middle hatch time was 480-486 h, and Late hatch time was 494-510 h.2 Placement time was 518 h.3 SE for mean of 10 chicks.

Table 3 -
Feed consumption, and feed conversion ratio of broiler chickens from placement on feed at 35 d of age as affected by hatch time. - a,b Means in a column with different superscripts differ significantly (p<0.05).1 Early hatch time was 471-477 h, Middle hatch time was 480-486 h, and Late hatch time was 494-510 h. 2 SEM for mean of 9 pens.

Table 2 -
Body weight, BW loss of broiler chickens from hatch and placement on feed at 35 d of age as affected by hatch time.
Early hatch time was 471-477 h, Middle hatch time was 480-486 h, and Late hatch time was 494-510 h. 1

Table 4 -
Effect of hatch time on mortality.