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PRODUCTION, MODELING, AND EDUCATION |
* Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2P5; and Agriculture Research Division, Alberta Agriculture and Rural Development, Edmonton, Alberta, Canada, T6H 5T6
1 Corresponding author: frank.robinson{at}ualberta.ca
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: feather sexing • nutrient density • reproductive efficiency • turkey
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Egg production in slow-feathering (SF) compared with fast-feathering (FF) poultry has been found to vary (Chambers et al., 1993). Decreased egg production has been reported in SF compared with FF laying hens (Harris et al., 1984; Saleh et al., 1987), broiler breeders (O’Sullivan et al., 1991), and turkeys (Zakrzewska, 1995). In egg-type and broiler breeder hens, decreased production has been connected to the expression of the "ev21" viral gene, which is closely associated with the K+ allele and encodes for infectious lymphoid leukosis virus (Harris et al., 1984; O’Sullivan et al., 1991). Dunnington and Siegel (1986) and Katanbaf et al. (1989) concluded that reproductive factors were minimally affected by sex-linked feathering alleles in broiler breeder stock. These results may be due to differences in research techniques related to diet and environment, as well as changes in the genetic background in domestic poultry with time. Varying results also suggest interaction of the K gene with other genes present in the genome (Chambers et al., 1993).
The prelay period 4 to 6 wk before onset of lay is associated with increased nutrient and energy requirements (Cave, 1984; Brake et al., 1985). Sexual maturity (SM) is attained after certain thresholds have been met, including age, BW, and body composition (Soller et al., 1984). These indicators are reflective of metabolic signals initiating the cascade of the sexual development process (Renema et al., 1999) and require adequate nutrient reserves for reproductive processes to commence.
Increased dietary protein during the prelay period (Cave, 1984; Brake et al., 1985) and during production (Bowmaker and Gous, 1989) have been shown to increase egg production in broiler breeders. Although turkeys are quite lean, turkeys fed ad libitum have been reported to have more ovarian large yellow follicles (LYF) than feed-restricted turkeys due to increased follicular recruitment, as well as increased carcass fat levels (Hocking, 1992a).
With feed-restricted broiler breeders, modest delays in photostimulation (PS) allow smaller birds to increase in skeletal frame size, muscle mass, and organ development before onset of lay without negatively influencing egg numbers (Yuan et al., 1994; Renema et al., 2007). Woodard et al. (1974) found that delayed PS in turkeys increased egg production by decreasing the number of multiple ovulations. Hocking et al. (1988, 1992) reported reduced large ovarian follicle numbers at later PS ages. The number of small eggs early in the production period is reduced with delayed PS (Zuidhof et al., 2007). Hocking (1992b) reported increased egg production in turkeys with late PS because of a reduction in the incidence of multiple hierarchies of large follicles and a reduction in the number of nonsettable eggs. Delaying PS is thought to permit feed-restricted breeder hens to respond to light stimulation with entry into lay in a more uniform manner, which may increase BW uniformity and egg productivity by increasing early egg size, settable egg production, and persistency of lay.
A sex-linked gene for slow feathering was incorporated into a commercial line of Large White turkeys (Sikur et al., 2004). Successful development of feather-sexable lines could benefit the turkey industry by reducing sexing errors, poult handling, stress, and processing costs at the hatchery. The objective of the current research was to characterize parameters of reproductive efficiency and carcass morphology during lay in Hybrid standard FF and experimental SF turkey hens. An increased nutrient density has been reported to improve growth and feather coverage of this SF turkey strain (Sikur et al., 2004). Increased nutrient density and delayed PS were the experimental parameters applied in the current study in an attempt to improve reproductive efficiency traits.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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A total of 226 experimental SF turkey hens and 226 FF turkey hens (Hybrid grade Maker, Hybrid Turkeys, Kitchener, Ontario, Canada) from a described previously rearing trial (Sikur et al., 2004) were randomly distributed to 16 floor pens (measuring approximately 4 x 1.5 m) per strain in a light-tight facility (n = approximately 14 per pen). Each strain was fed either a control diet (CON), formulated as commercial hen diet to meet breeder-recommended nutrient levels, or a HIGH diet that contained 10% more energy and protein, including essential amino acids, than the CON diet throughout the breeding period (Table 1
). The diets were fed as a breeder 1 from PS to 36 wk, a breeder 2 from 36 to 46 wk, and a breeder 3 from 46 to 56 wk. Feed and water were provided ad libitum throughout the study. Pens were subdivided with a mesh wall and 2 trap-nests were added, creating 32 breeder pens measuring approximately 2 x 1.5 m. An equal number of birds remaining at PS ages within each strain x diet interaction were photostimulated at either 29 or 31 wk (total = 356 birds). Birds had been exposed to a 6L:18D lighting regimen from 16 d of age. At PS, this was increased to 14L:10D in a single step, with incandescent lights coming on at 0600 h and light intensity increased following breeder recommendations. Body weight and feed consumption were recorded every 2 wk to 56 wk of age. The experimental protocol followed the Guide to the Care and Use of Experimental Animals (Canadian Council of Animal Care, 1993) and was approved by the University of Alberta Animal Care and Use Committee for Livestock.
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At both PS and SM, 96 preassigned birds from each group were processed. The remaining 260 birds were processed at the end of the laying period (56 wk of age). At processing, hens were killed by cervical dislocation and individually weighed. Shank and keel lengths were measured to assess frame size as described by Sikur et al. (2004). Dissection measurements included weights of total breast (both pectoralis major and pectoralis minor), liver, fatpad, ovary, and oviduct. Each ovary was weighed and ovarian morphology traits assessed. The number of LYF (ovarian follicles >10 mm in diameter) was recorded. Oviduct contents were removed before weighing the oviduct.
Egg Production
Hens were trap-nested to record egg production data from individual birds. Hens were palpated to ascertain the presence of an egg in the shell gland at 0600 h, and a time of oviposition was estimated based on the interval from the previous oviposition and typical laying patterns of the hen. Within 1 h before the predicted time of lay, hens were placed in a trap-nest box if they had not already entered one. Hens were released from the nest box within 30 min after oviposition. Floor eggs were infrequent, but were successfully matched to a hen in every instance by palpation of hens in the pen still due to lay that day. Daily individual records of egg production, egg weight, and egg quality (settable vs. unsettable due to shell defects, integrity, or double-yolked) were collected. These data were used to calculate total hen-housed egg production, average sequence lengths, pause lengths, and number of ovulations, and to determine the time of cessation of lay. Proportion of birds in lay at the end of the study was determined through examination of individual production records. Ovarian morphology data were used to confirm reproductive status in cases where egg production ceased in the last 2 wk of the experiment. No management techniques were used to control incidence of broody behavior (characterized by cessation of egg production and in some cases aggression).
Statistical Analyses
Egg production records were analyzed for differences in total egg production, average sequence length and prime sequence length using the Egg Production and Sequence Analyzer (Version 3.00, 1999; Alberta Agriculture and Food, Edmonton, Alberta, Canada). The effects of age at PS, strain, diet, and their interactions on the parameters measured were assessed by 3-way ANOVA using the GLM procedure of SAS (SAS Institute, 2002), with treatment pens nested. Following a significant F-test (P < 0.05), means were separated using the t-test procedure of SAS (SAS Institute, 2002). Unless otherwise stated, significance was assessed at the P < 0.05 level.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Hens that were photostimulated at 31 wk were 2 to 5.5% (0.2 to 0.5 kg) heavier than birds photostimulated at 29 wk between 34 and 38 wk of age (Table 2). This effect extended through the peak egg production period, similar to results reported in broiler breeders (Joseph et al., 2002) and turkey breeder hens (Siopes, 1999) that had been delayed in PS. Overall, FF hens were approximately 8.0% (0.8 kg) heavier than in SF hens (28 to 56 wk of age). Whereas Katanbaf et al. (1989) observed no difference in BW between SF and FF broiler breeders, O’Sullivan et al. (1991) found that SF broiler breeders were heavier than FF birds at SM.
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Carcass Morphology
Exposing hens to PS at 31 wk compared with 29 wk had no effect on carcass parameters at time of PS or at SM (Table 3). By the end of lay, keel length and ovary and oviduct weights were 2.5, 20.7, and 17.3% greater, respectively, in birds photostimulated at 31 wk compared with 29 wk, whereas shank length was 2.3% longer in 29-wk birds. This agrees with Robinson et al. (1996a) and Renema et al. (2001a, b), who reported proportionately increased organ growth and frame size in broiler breeders photostimulated at a later age. The current findings are in contrast to results in broiler breeders that were photostimulated later and showed an increase in frame size estimates at SM and a decrease in frame size estimates at end of lay (Joseph et al., 2002). Long-term growth of the keel may be more representative of true changes in frame size than is shank length.
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). The similarity of relative fleshing and fatness indicated that the SF birds were simply growing more slowly to this point and were not compositionally different. By SM, both BW and other carcass morphology measures were similar (Table 3). At end of lay, FF hens had 2.1% longer shank length, 15.4% greater absolute liver weight, 53% heavier oviduct, and 49% heavier ovary that was maintaining 1.7 more LYF than the SF hens (Table 3). These results indicate that the FF hens were in superior condition for lay compared with SF hens at 56 wk of age. Despite birds of both strains having a similar BW and frame size at SM, ultimately the FF hens appeared to retain more carcass reserves of protein than SF birds, as indicated by increased skeletal and reproductive organ growth. This may be indicative of differences in overall efficiency, with the inferior feather cover of SF hens (Sikur et al., 2004) likely contributing to part of these differences.
Increased nutrient density had no effect on carcass morphology at PS or at SM (Table 3). By the end of the laying period, birds fed the HIGH diet had a 1.8% shorter shank length and a 13.1% lower absolute fat-pad weight (data not shown) compared with feeding the CON diet. Because keel length and relative breast muscle and abdominal fatpad weights were similar at this time, it shows that the additional nutrients supplied in the HIGH diet were not allocated to carcass stores during the breeder period. These results concur with those of Renema et al. (2001a, b), who indicated that additional nutrients were allocated toward body protein and egg production instead of carcass fat by the end of lay.
Reproductive Parameters
There were no differences in interval between PS and age of SM (mean number of days to first egg) in response to PS age, strain, or diet treatments, as birds attained SM 21.0 d after PS, on average, in all treatments (data not shown). Birds were responsive to the different PS ages, but did not mature any faster with the 31 wk vs. 29 wk PS age. The rates of maturation of the flocks were also similar, as indicated by the egg production profile (Figure 1). Siopes (1992, 1999) observed a slight acceleration in onset of lay of turkey breeder hens photostimulated at a later age.
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). Birds photostimulated later produced fewer double-yolked eggs (0.08 vs. 0.24 for 31- and 29-wk birds, respectively). Hens photostimulated at 31 wk were laying 8.1% better than the 29-wk birds during the last 2 wk of lay (Figure 1). Because the start of the egg production profile of 31-wk PS birds was delayed by several weeks, this may be a reflection of a phase-shifted production period. However, rate of lay of the PS 31-wk birds was also supported in the form of longer laying sequence lengths between 35 and 38 wk (approximately 0.5-d difference), 44 and 49 wk (approximately 0.4-d difference, except at 47 wk), and at 53 wk (approximately 0.5 d) compared with the PS 29-wk birds (Figure 2).
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). As ovary and oviduct weights were greater in PS 31-wk hens at end of lay (Table 3), these birds appear to have had more optimal support LYF and ovary development, allowing them to more strongly support the egg production process. Delaying PS has been shown to have no detrimental effect on egg output in broiler breeders, whereas it results in increased frame size, muscle growth, and organ development at SM (Yuan et al., 1994; Robinson et al., 1996b; Zuidhof et al., 2007). Delaying PS results in increased early egg size in broiler breeders (Joseph et al., 2002; Renema et al., 2007) and a reduction in the incidence of multiple ovulations in turkeys (Woodard et al., 1974). This decrease in non-settable eggs in the turkey was attributed to decreased multiple follicular hierarchies (Hocking, 1992b). Siopes (1992) observed a decrease in hen-day egg production to 54 wk in birds photostimulated later. This was attributed to the shorter laying period of the late-photo-stimulated hens.
Laying sequence lengths were longer in FF hens than in SF hens throughout lay (Table 4; Figure 2), with the maximum difference of 4.5 d occurring at 35 wk of age. Prime sequence length (11.9 vs. 8.0 d), total egg production (98.9 vs. 58.2), number of settable eggs (97.2 vs. 57.9), average sequence length (3.8 vs. 2.7 d), age at last egg laid (49.9 vs. 45.2 wk), and number of ovulations (99.2 vs. 58.3) were superior in FF hens compared with SF hens (Table 4). The number of eggs laid without shells were 0.13 and 0.66 in SF and FF birds, respectively. The FF hens laid more soft-shelled eggs than the SF hens (0.71 vs. 0.19, respectively). The number of double-yolked eggs was 0.02 in SF hens compared with 0.30 in FF hens. The SF hens laid fewer total defective eggs on absolute and percentage bases, but also had a much lower rate of lay and total number of eggs produced compared with the FF birds. Even though the number of LYF on the ovary at the end of lay was reduced by 1.7 in SF hens (7.1 vs. 8.8), ovary weight at that time was half that of the FF hens (Table 3), demonstrating the lack of support the SF hens were able to provide the ovary.
The FF hens had significantly greater average rates of lay (55.1 vs. 33.2%) and peak production (76.3 vs. 68.4%) compared with SF hens (Figure 1). There was a high incidence of broodiness (as evidenced by pale, dry vents with increased aggression and an enhanced commitment to nest occupation) observed in SF hens, as hens stopped laying and decreased in BW in conjunction with a markedly decreased feed intake. The proportion of the population that had gone broody was estimated at 5% of FF hens compared with 50% of SF hens. By the end of the experiment, 71.4% of FF hens were still in active lay compared with only 34.1% of SF hens. Most hens remained out of lay permanently once they ceased production, although a small group returned to lay after a 3- to 4-wk break in production (2 FF and 6 SF hens). These short pauses in production have also been reported in broiler breeders (Renema et al., 2001b).
Individual egg production calculations included assessment of the age at last egg laid, a measure that was 4.7 d later in FF compared with SF hens (Table 4). Zakrzewska (1995) reported decreased egg production and high incidence of broodiness in SF turkey hens compared with FF hens. The FF hens appeared more proficient at allocating nutrients to the support of egg production compared with SF hens. Factors associated with poorer egg production in chickens with advancing age include an increased occurrence of pauses longer than 33 h between sequences (Robinson et al., 1990) and an increased incidence of follicular atresia (Zakaria et al., 1983). There was no evidence that increased incidence of follicular atresia, defective egg production, or internal ovulation were reasons for reduced egg production in later lay in SF hens in the current study.
Comparison of a distribution of total egg production values for SF and FF hens reveals 2 distinct clusters within each population (Figure 3). The FF population had a large cluster of hens producing approximately 125 eggs. A second, smaller cluster of FF hens produced approximately 35 eggs; most of this smaller group were hens that ceased production part-way through the production phase. The SF hens had clusters of hens at approximately 25 eggs and at 105 eggs (Figure 3). In addition to both of these values being lower than FF values, many more SF hens were clustered at the lower peak. A key part of the strategy to improve overall egg production of SF hens will be to limit the number of birds spontaneously ceasing lay after only laying 20 to 30 eggs. It is not clear if these are exclusively broody birds, or a mix of birds that spontaneously ceased production or went broody. Sikur et al. (2004) showed that the SF hens were predisposed to grow breast muscle at the expense of feathers. It is less clear how feather coverage relates to reproductive traits, because many of these parameters were still quite variable in the current study.
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Unlike chicken lines with a slow-feathering gene, the inferior reproductive outcomes for the SF line suggest that more than just feather growth genes are affected in the females of this line. These birds require multiple generations of selection for feather coverage and production efficiency to reach a commercially comparable state to existing lines. The use of several generations of backcrossing between unrelated growth-selected and egg production lines has been demonstrated to be a viable way to increase BW of dam lines without badly sacrificing egg production (Nestor et al., 2006). However, in the SF line of the current study, maintenance of egg size and rate of lay are also of importance. A classic report demonstrated that egg weight affected BW up to 24 wk of age (Scott and Phillips, 1936).
Nutrient density had a minimal effect on egg production (Figure 1), although hens fed the CON diet exhibited a longer sequence length (7.5 vs. 7.0 d) at 35 wk compared with hens fed the HIGH diet (Figure 2). From 37 to 39 wk, hens fed the HIGH diet had approximately 0.5-d-longer sequence lengths than hens fed the CON diet. The numerical 4.7-egg increase in production in HIGH compared with CON hens was enough to affect laying patterns in the form of a shorter pause length between laying sequences (Table 4). Most of this difference was because of the effect of the HIGH feed early in lay. Variability among birds was greater than treatment variation for most production traits (see Figure 3, where total egg production ranged from 0 to 148, for example).
Comparison of an SF turkey strain to a normal, FF strain for the breeder period indicated that birds of the SF strain expressed different BW, carcass morphology, and reproductive efficiency compared with FF hens. The SF hens had reduced BW and egg production compared with commercial birds during lay. Delaying PS resulted in positive effects on BW, carcass morphology, and rate of lay, as egg production to 56 wk was similar in both PS groups. Nutrient density had minimal effects on production in this trial. With continued genetic research and efforts to improve reproductive efficiency in strains with the SF gene(s), it will be possible to have commercially viable, feather-sexable turkey strains.
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ACKNOWLEDGMENTS |
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Received for publication October 21, 2007. Accepted for publication April 24, 2008.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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