D.O. Noble*, K.E. Nestor*, and D.M. Denbow+
*Department of Animal Sciences and
+Department of Animal and Poultry Sciences
Virginia Polytechnic Institute and State University
A condition occurs in a line of turkeys (E) selected for increased egg production in which poults flip onto their backs and cannot right themselves to stand without assistance. The same condition has been observed in commercial turkeys. Poults from the E line have a greater occurrence of flip-overs than their randombred control (the base population for the E line). Several potential causes of this condition were examined over 2 years. Estimates of heritability (the extent the problem is controlled by genetics) for the occurrence of flip-overs were low (4 to 5%). Poults that hatch late have a greater occurrence of flip-overs than those that hatch early, and occurrence of flip-overs declines as the production season progresses. Occurrence of flip-overs does not appear to be affected by beak trimming, poult moisture, or brain neurotransmitter (the chemicals which translate nerve impluses to chemical signals) levels. It is concluded the increased occurrence of poult flip-overs is a correlated response to long-term selection for increased egg production.
Early poult flip-overs can be a problem in commercial turkey production (Sandstrom, 1995). Poults that flip onto their backs cannot turn over and right themselves without assistance. Poults may flail their legs wildly while attempting to stand and exhibit twitching, possibly indicative of nervous system involvement. The flip-over condition has been observed in the E line of turkeys, which was selected for increased egg production (E; Anthony et al., 1991). Mortality from this condition can be high and was attributed to dehydration, as postmortem examinations and culturing revealed no evidence of infectious agents (Y.M. Saif, Food Animal Health Research Program, Ohio Agricultural Research and Development Center, Wooster, OH 44691, personal communication). Poults either recover from this condition or die by 5 days of age. Lacking in current literature is information on the potential causes of early poult flip-overs.
Studies were conducted over 2 years. In both years, eggs were stored for a maximum of 2 weeks prior to incubation. Upon hatching, poults were generally wing-banded by full-sib family and placed in floor pens with wood shavings litter. Feed and water were provided for ad libitum consumption, and supplemental heat during brooding was supplied by heat lamps.
Poults were observed at least twice daily from 0 to 4 days of age for poults that flipped over. Poults that flipped over were removed from the heat source, given a drink of water, and placed on their feet. The current study examined the influence of several factors on occurrence of early poult flip-overs, including genetic growth potential, inheritance, beak trimming, hatching time, poult moisture content, and brain neurotransmitter levels. In the report that follows, the methods of research into these potential causes and their results will be discussed.
Two different comparisons were made to investigate the influence of genetic growth potential on occurrence of poult flip-overs. Hatch 1 of Year 1 utilized Line E poults and a cross between males from a line selected for increased body weight (F; Nestor, 1984) and females from Line E.
In the remaining hatches of this experiment, the occurrence of poult flip-overs was compared in Lines E and the randombred control from which E originated (RBC1; McCartney, 1964; Nestor, 1977; Noble et al., 1995). Occurrence of poult flip-overs was analyzed by Chi square for each hatch to determine if lines differed in occurrence of flip-overs. Data are presented as percentage of poults in each line exhibiting this condition.
In six of eight comparisons, Line E had a significantly greater incidence of flip-overs than the faster growing line with which it was compared (Table 1). Even though poults from Line E and the F X E cross did not differ in body weight at hatching (1.49 and 1.46 ounces, respectively), the difference between the lines was significant at 13 days of age (5.54 vs 8.31 ounces for Lines E and F X E, respectively). The comparison of Lines E and F X E indicated that body weight at hatching may not be related directly to the occurrence of poult flip-overs. There also may be an effect of hybrid vigor on viability and appetite.
|Table 1. Occurrence of early poult flip-overs (%) by year, hatch number, and line.|
|Year||Hatch||RBC1||E||F X E|
|1||1||. . .||32.83 **||6.85|
|2||0.65 **||17.28||. . .|
|3||0.20 **||18.97||. . .|
|4||0.34 *||10.58||. . .|
|5||0.23 **||23.86||. . .|
|2||1||3.77 NS||7.63||. . .|
|2||1.81 NS||5.66||. . .|
|3||0.00 **||8.43||. . .|
|1 RBC1= a randombred control population developed
in 1956 which served as the base population for E; E = a line selected
for increased egg production; F X E = a cross of males from a line
selected for increased body weight and females from Line E.
* P < 0.05.
** P < 0.01.
Heritability (h2) of early poult flip-overs was estimated in Line E based on the variation between full-sib families, and h2 estimates were obtained for Years 1 and 2 using data from Hatches 2 through 5 in Year 1 and Hatches 2 and 3 in Year 2. The h2 estimate for the occurrence of poult flip-overs was 4.4% in Year 1 and 5.2% in Year 2. Estimates of h2 obtained from full-sib data contain dominance and maternal effects, if present (Falconer, 1989), which are not passed from parent to offspring; thus, h2 estimates from full-sib data provide an upper limit of the progress which can be made by selection.
In conjunction with a study on the effects of beak trimming on body weight and mortality, the influence of arc beak trimming at hatching on occurrence of poult flip-overs in Line E was examined. Poults were assigned within full-sib families to be arc beak trimmed 1.5 mm from the nostrils (Renner et al., 1989) or left with beaks intact. Hatches 3, 4, and 5 of Year 1 were used for this trial. Data were analyzed by Chi square to determine if beak treatments (intact vs trimmed) differed in occurrence of poult flip-overs.
Beak trimming did not affect the occurrence of poult flip-overs of Line E in any hatch measured (Table 2). The arc beak trimming method and severity of beak trimming used generally does not influence early mortality of turkeys (Renner et al., 1989; Cunningham et al., 1992; Noble et al., 1994).
|Table 2. Occurrence of early poult flip-overs (%) in Line E by hatch number and beak treatment.1|
|1Beak treatment did not affect the occurrence of poult flip-overs (P > 0.05).|
The effect of hatching time on the occurrence of poult flip-overs in Line E was studied in Hatch 1 of Year 2. Poults were sprayed with an alcohol-based dye while in the hatcher at 648 hours of incubation. All poults were removed from the hatcher at 672 hours of incubation. Those that were colored with the dye were considered "early" hatchers, and those without the dye were considered "late" hatchers. Chi square was used to determine if early and late hatchers differed in occurrence of poult flip-overs. Data are presented as percentage of poults flipping over. Poults that hatched late had a higher incidence of flip-overs than those that hatched early (15.45 vs 4.21%, respectively). Further studies are planned to determine if increased hatching time leads to increased occurrence of flip-overs.
Line E poults from the same hatch as the hatching time study were utilized to study the effect of poult moisture on occurrence of flip-overs. In Year 2, poults that flipped over at 0 or 1 day of age were removed from the pens, euthanized using carbon dioxide, weighed, and placed in a lyophilizer (Model 10-100, The Virtis Co., Gardiner, NY) and freeze-dried to a constant weight. An equal number of normal poults were treated in a similar manner as the affected poults to serve as a control. Data were analyzed by analysis of variance with condition (normal vs affected) as the source of variation.
Normal and flipped-over poults did not differ in carcass moisture (76.08 and 75.32%, respectively). In previous years, mortality of flipped-over poults was attributed to dehydration. The present study sampled poults before they died to see if dehydration led to flip-overs. While flip-overs may lead to dehydration, dehydration does not appear to lead to flip-overs. Further studies are planned to determine if lack of feed and water may lead to flip-overs.
Neurotransmitters are involved in converting the electrical signal of nerve cells into a chemical signal that can be used by another part of the body (Ganong, 1995). It was thought that the nervous symptoms of the flip-over condition we observed may have been caused by altered levels of brain neurotransmitters. Whole-brain levels of seven neurotransmitters, namely dihydroxyphenylalanine, norepinephrine, epinephrine, dihydroxyphenylehtylamine, 5-hydroxyindoleacetic acid, and 5-hydroxytryptamine, were determined as described by Myers et al. (1986) and Zhu et al. (1991) on a sample of poults from Line E. Poults utilized were from Hatch 1 of Year 2 and were either 0 or 1 day of age. An equal number of normal and flipped-over poults were used in this analysis (34 poults total). Levels of brain neurotransmitters were analyzed by analysis of variance with condition (normal vs affected) as the source of variation.
Normal and flipped-over poults did not differ in levels of any brain neurotransmitter levels measured (Table 3). The difference between normal and flipped-over poults in level of brain epinephrine approached significance (P = 0.08), possibly indicating a physiological response to stress. Use of epinephrine as an physiological indicator of stress, however, has met with only limited success in domestic animals (Craig, 1981). We plan to continue to examine the role of brain neurotransmitters on poult flip-overs in the future.
Of the potential factors influencing poult flip-overs, only hatching time and genetic growth potential appeared to be important influences. Crossing Line E with the fast-growing Line F greatly reduced the occurrence of poult flip-overs. The heritability of the trait appeared to be low, so selection would not be very effective in reducing the occurrence of flip-overs.
Selection for increased egg production has led to changes in other traits in Line E, including body weight, fertility, average clutch length, egg weight, days lost to broodiness (Anthony et al., 1991; Nestor et al., 1996), and changes in egg composition (Nestor and Noble, 1995). From the current study, it appeared that increased occurrence of poult flip-overs was another correlated response to long-term selection for increased egg production.
|Table 3. Mean1 levels of brain neurotransmitters (in parts per million of brain tissue) in normal and flipped-over turkey poults.2|
|1 Values (parts per million) were transformed to
common logarithms prior to analysis and presented on the original scale.
2 Normal and flipped-over poults did not differ in levels of any neurotransmitter (P > 0.05).
3 (P = 0.0808).
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