Research and Reviews: Poultry and Swine

Special Circular 164-99

Influence of Adult Body Weight and Egg Weight on Hatching Time in Selected and Randombred Control Lines of Turkeys

K. E. Nestor1
D. O. Noble
The Ohio State University
Department of Animal Sciences

1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 1680 Madison Ave., Wooster, OH 44691; 330-263-3757; Fax: 330-263-3949; e-mail: nester.1@osu.edu.

Abstract

An experiment was conducted to measure the hatching times of eggs and to estimate the relationships among adult body weight (BW50), egg weight, and hatching times in six experimental lines of turkeys. Lines utilized were selected for increased 16-week body weight (F), increased shank width (FL), increased egg production (E), or were unselected randombred control lines (RBC1, RBC2, and RBC3). The base populations for the F, FL, and E lines were RBC2, F, and RBC1, respectively.

The experimental turkey lines differed in hatching times indicating genetic differences exist in hatching time. The line differences in hatching time could not be explained by line differences in egg weight. Within lines, the regression of hatching time on egg weight was positive and significantly different from zero in only three of the six lines. Overall regression of hatching time on egg weight and BW50 was positive for egg weight and negative for BW50. However, only 4% of the variation in hatching times could be explained by variation in egg weight and BW50. Within lines, the regression coefficient of hatching time on BW50 was not significantly different from zero in any line but the sign was negative in five of six lines.

Introduction

Hatching times in chickens may be influenced by a number of factors including inheritance and egg weight. In chickens, the unweighted average for heritability estimates of hatching times was 0.29 (Crittenden and Bohren, 1961; MacLaury and Insko, 1969; Becker et al., 1966; Abdou and Ayoub, 1975; Palomares-Hilton and Bohren, 1981). Lines of chickens exhibiting longer or shorter incubation periods have been developed by divergent selection (Smith and Bohren, 1975; Palomeres-Hilton and Bohren, 1981). Selection for a shorter incubation period was associated with smaller egg weight (Smith and Bohren, 1975; Bohren, 1978) and larger body weight from hatching through six weeks of age (Vasquez and Bohren, 1978).

The relationship between egg weight and hatching time is inconsistent. In chickens, Crittenden and Bohren (1961) reported the genetic correlation between these two variables was 0.55 based on variation among sires and 0.20 based on variation among dams. Henderson (1950) found that the phenotypic correlation coefficient between egg weight and hatching time was 0.30 based on dam means but was not significant based on individual eggs. A small correlation coefficient of 0.11 was observed between these variables by Suarez et al. (1996). In turkeys, Olsen (1942) found that the hatching time was 637.6, 639.8, and 641.6 hours, respectively, in eggs weighing 70 to 80, 80 to 90, and 90 to 100 grams. Cherms (1969) found no association between egg weight and hatching time in turkey eggs.

Genetic increases in body weight and shank width in experimental lines of turkeys was associated with increased egg weight and reduced hatch of fertile eggs (Nestor and Noble, 1995; Nestor et al., 1996). In the same studies, genetic increases in egg production resulted in decreased egg weight with no change in hatchability. The purpose of the present study was to evaluate hatching times in the genetic lines and study the association of hatching time, egg weight, and adult body weight.

Materials and Methods

Six experimental lines of turkey lines were used. Lines RBC1, RBC2, and RBC3 were non-selected randombred control populations developed in 1956, 1966, and 1986, respectively. Line E originated from the RBC1 line and was selected for increased egg production. Line F originated from the RBC2 line and was selected for increased 16-week body weight. Line FL originated from Line F and was selected for increased shank width. Egg and reproduction traits for these lines have been described by Nestor and Noble (1995).

Eggs were stored in a cold room at 14.5öC and 75% relative humidity (RH) for no longer than seven days to avoid potential egg storage effects on hatching time. The eggs were trayed by line, and hen within line, and left at room temperature overnight prior to initiation of incubation. The eggs were set in a Robbins incubator (Model 14I) maintained at 37.5öC and 60% RH. At approximately 168 hours of incubation, eggs were candled and infertile eggs and those containing dead embryos were removed. The remaining eggs were transferred at a minimum of 576 hours of incubation to a Robbins hatcher (Model H5) set at 37öC and 80% RH. The hatcher was checked for hatched poults at intervals that varied by trial. Checking for hatched poults was performed by shutting off the hatcher fan to prevent excessive loss of moisture when opening the door, opening the hatcher door only wide enough to allow a person to enter, closing the door upon entering the hatcher, and turning the fan on when inside the hatcher. Poults that hatched were moved to separate hatching baskets and the remaining eggs placed in contact with one another.

Trial 1 (preliminary) took place when the selected Lines E, F, and FL were in the 34th, 29th, and 17th generation of selection, respectively. Hens were in the 10th week of production. Based on unpublished data from the lines, setting times were varied in order to synchronize the hatching of the various lines. The large-bodied lines (F, FL, and RBC3) were set 24 hours prior to, and the medium-bodied lines (RBC1 and RBC2) were set 15 hours prior to the small-bodied E line. At 25 days of incubation for Line E, eggs were transferred by line to the hatcher. Eggs were checked at 12-hour intervals starting at 612 hours of incubation for Line E and ending at 696 hours of incubation for Lines F, FL, and RBC3. Data were analyzed by analysis of variance with line as the source of variation and variation in individual poult hatching time as the error term. Duncan's multiple range test was used to separate the multiple means.

Trial 2 took place when Lines E, F, and FL were in the 35th, 30th, and 18th generations of selection, respectively. Two one-week settings of eggs were collected when hens were in the 11th and 12th week of egg production. Egg storage and incubation and hatching conditions were similar to Trial 1. Eggs were marked with the hen's number on both the large and small ends of the egg to facilitate identification. In each setting, each hen's eggs were group weighed and placed in incubator trays. Eggs were set simultaneously for all six lines to avoid possible confounding of different setting times. From 616 to 696 hours of incubation, eggs were checked at four-hour intervals for hatched poults using the same procedure for entering the hatcher described for Trial 1. Egg weight, hatching time, and body weight when the hens first achieved 50% production (BW50; a measure of adult body weight), were analyzed by analysis of variance with line and week of production as sources of variation. The error term was based on hen means to remove the possible bias caused by larger families. Means were separated using Duncan's multiple range test. In addition, hen mean hatching time was regressed on egg weight and BW50 using multiple regression analysis (SAS Institute, 1988).

Results

Lines differed in hatching time in Trial 1 when the hatching time was based on individual eggs and the eggs were checked every 12 hours (Table 1). In this trial, setting times were confounded with line differences. The E line had longer hatching times than its control (RBC1). No difference in hatching time was observed between the F line and its control (RBC2). The FL line had a longer hatching time than its base population, the F line. All three randombred control populations differed in hatching time. The coefficient of variation in hatching time was higher in the RBC1 and RBC2 lines than in the other lines.

Lines also differed in hatching time in Trial 2 when the eggs were set at the same time and the eggs were checked every four hours (Table 2). In this trial, the E line also had longer hatching times than the RBC1 line and FL had longer hatching time than the F line even though egg weight was similar in the F and FL lines. The randombred control lines also differed in hatching time but the order was different in Trial 2 (RBC2 >RBC1 > RBC3) than in Trial 1 (RBC2 > RBC3 > RBC1). In Trial 2, the F line had a shorter hatching time than the RBC2 line. Egg weights and BW50 differed greatly among lines.

The overall equation that described the relationships among hatching time, BW50, and egg weight was:

Hatching time = 635.4 hours of incubation + 0.17 hour/gram of egg weight - 0.62 hours/kilogram of BW50.

The regression coefficients for both egg weight and BW50 were different from zero (P <= 0.0001) but the coefficient of determination for the model was only 4%. Within lines, the regression of hatching time on egg weight was positive and significant only for the E, FL, and RBC3 lines. None of the regression coefficients of hatching time on BW50 within lines was significant.

Discussion

The question arises as to the effect of repeated opening of the hatcher door on hatching time. This question can not be answered in the present study, but Bohren et al. (1961) found that repeated opening of the hatcher had no effect on the hatching of chicken eggs, even when done at two-hour intervals. In the present study, unhatched eggs were placed back in contact with each other after removing hatched poults in order to synchronize hatching time (Pani et al., 1969).

It is clear from the results of the two trials that hatching times differed among the experimental lines of turkeys. The inconsistencies in the line comparisons of the two trials may be due, in part, to the confounding of setting time and line in Trial 1. The line differences in hatching time indicate that there is genetic variation in hatching time in the turkey as has been observed in chickens (Crittenden and Bohren, 1961; MacLaury and Insko, 1968, 1969; Becker et al., 1966; Abdou and Ayoub, 1975; Palomares-Hilton and Bohren, 1981).

Differences in hatching time among lines in the present study could not be explained by line differences in egg weight although egg weight and hatching times were positively associated in three of the six lines. The inconsistency in the relationship between hatching time and egg weight has previously been observed in chickens and turkeys. The genetic correlation coefficient between these two variables in chickens was 0.20 and 0.55 based on the dam and sire components of variance, respectively (Crittenden and Bohren, 1961). Henderson (1950) found that the phenotypic correlation coefficient between egg weight and hatching time in chickens varied from 0.05 to 0.21 in various genetic groups. Based on dam means, Bohren et al. (1961) reported a phenotypic correlation coefficient of 0.30 between egg weight and hatching time, but based on individual eggs the correlation coefficient was not significantly different from zero. In turkeys, Olsen (1942) reported that egg weight and hatching time were positively associated, but no association of these traits was reported by Cherms (1969).

Selection for increased body weight during the growing period of chickens (Anthony et al., 1989) and turkeys (Bray, 1965; Anthony et al., 1991) alters growth rate throughout life, including embryonic development as early as 16 days of incubation in chickens (Anthony et al., 1989) and 18 days of incubation in turkeys (Bray, 1965). Over all lines in Trial 2, there was a significant negative regression coefficient of hatching time on BW50, indicating that as growth rate increased, hatching time decreased. Two of the larger-bodied lines (RBC3 and F) had the fastest hatching times. The RBC1 line was heavier and had faster hatching times than the E line. Within lines, the regression coefficient of hatching time on BW50 was not significant for any line although the sign of the coefficient was negative in five of six lines.

In summary, hatching times differed among experimental lines of turkeys and the line differences could not be explained by line differences in egg weight. Over all lines, growth rate as indicated by BW50 was associated negatively with hatching time, but no significant relationship was observed within lines.

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