Effect of hen age, body weight, and age at photostimulation. 1. Egg, incubation, and poult characteristics of commercial turkeys

Effect of Hen Age, Body Weight, and Age at Photostimulation. 1. Egg, Incubation, and Poult Characteristics of Commercial Turkeys1 T. J. APPLEGATE and M. S. LILBURN2 Department of Animal Sciences, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691 lated at 31 wk had 18.7 g heavier ovaries 3 wk after PS than hens photostimulated at 29 wk (P ≤ 0.06), primarily due to one additional follicle of ≥ 20 mm (P ≤ 0.04). During the first 10 wk of lay, egg weight increased 7.8 g, 4.4 g of which was due to increased yolk weight. Eggs from Normal BW hens weighed significantly less than those from Heavy BW hens only when hens were subjected to PS at 29 wk. Egg weight at transfer relative to egg weight at set was significantly increased from hens 4 to 6 wk after PS compared with the four older production ages (6 to 8, 8 to 10, 10 to 12, and 12 to 14 wk after PS). There was a significant increase in poult weight with increasing hen production age but no changes in poult weight relative to egg weight at set. In conclusion, hen BW at PS had minimal effects on egg component weights and subsequent poult weight at hatching.

ABSTRACT Turkeys from two BW groups (which averaged 11.8 and 12.9 kg, Normal and Heavy, respectively) were photostimulated at either 29 or 31 wk of age to determine what effects age-associated changes in hen carcass characteristics, egg weight, and egg components have on subsequent poult weight at hatching during the first 10 wk of production. Carcass measurements were determined from a subsample of hens 3 wk after photostimulation (PS). Subsamples of eggs from each PS age and BW group were selected for yolk and albumen measurements. All other eggs from these hens were individually weighed and incubated at 2-wk intervals during the first 10 wk of lay (4 to 14 wk after PS). All incubated eggs were reweighed at 25 d (transfer) and poults were individually weighed at hatch. Hen BW at PS had no effect on ovarian weight and follicular size or number 3 wk later. Hens photostimu-

(Key words: turkey, hen age, hen weight, egg, photostimulation) 1998 Poultry Science 77:433–438

(Leighton and Shoffner, 1961a,b; Shoffner et al., 1962; Wilson et al., 1962; Leighton and Potter, 1969; Woodard et al., 1974). Present-day commercial turkey hens can reach their reproductive BW target well before 30 wk of age, yet reproductive performance is still poor if hens are photostimulated at too young an age. Siopes (1992) reported that when hens were PS at 24 vs 30 wk of age, egg production was similar during the first 20 wk of lay, but age at PS was positively correlated with egg weight and poult weight during the first 11 wk. There was no mention of hen BW in this study, however. Hocking (1992) reported that hens photostimulated at 18 or 24 wk of age produced a higher proportion of poults with splayed legs and unhealed navels than hens photostimulated at 30 wk of age. After the onset of egg production, there is a positive correlation of hen age with egg weight and egg weight with poult weight (Reinha rt and Moran, 1979; Shanawany, 1987). Breeder age and hatchling weight may not share the same degree of relatedness, however

INTRODUCTION Commercial turkey hens are typically exposed to a photoinhibitory lighting schedule (8 h light:16 h dark) beginning at approximately 18 wk of age. They are subsequently photostimulated (≥ 14 h light; PS) between 29 and 31 wk of age. Within the industry, there exists a concept that PS at younger ages will have negative effects on reproductive performance, including delayed onset of sexual maturity after PS, decreased egg production, and decreased hatchability. In the few controlled studies that have been reported, noncommercial turkey strains have been used and these strains weigh considerably less than the Large White commercial strains prevalent in the industry today. The results of these studies suggest that hens achieve their optimal reproductive BW at approximately 30 wk of age

Received for publication March 3, 1997. Accepted for publication October 21, 1997. 1Salaries and research support provided by State and Federal funds appropriated to the Ohio Agricultural Research and Development Center. Manuscript Number 27-97. 2To whom correspondence should be addressed: [email protected]

Abbreviation Key: PS = photostimulation.

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(McNaughton et al., 1978, Applegate and Lilburn, 1996a). When adjustments were made for initial egg weight, Applegate and Lilburn (1996a) reported that poults from young turkey hens (36-wk-old) weighed less than those from older hens (55-wk-old). They attributed this reduced weight partly to differences in the maternal investment in the form of yolk deposition. In that study, the yolk to albumen ratio increased from 0.47 to 0.63 between 36 and 55 wk of age. The hypothesis of the current experiment was that hen age at PS and hen BW at PS have independent effects on selected carcass traits 3 wk after PS. To further test this hypothesis, we also studied the subsequent effects of hen age at PS and hen BW at PS on poult weight at hatching with consideration given to age associated changes in egg weight through the first 10 wk of production.

MATERIALS AND METHODS Commercial turkey hens (British United Turkeys of America,3 1995) were hatched and reared at the Ohio Agricultural Research and Development Center (OARDC), Wooster, OH 44691. All hens were exposed to a photoinhibitory lighting period (8 h light:16 h dark) beginning at 18 wk of age. The experimental design included two BW classes at PS (Normal, 11.8 + 0.5 kg; Heavy, 12.9 ± 0.5 kg) and two ages at PS (29 and 31 wk of age). These BW groups reflect the range of target BW of hens at PS by commercial turkey breeders, and were created by selecting hens within these ranges from a larger population of hens. At each of the two PS ages, 11 hens from each BW treatment were allocated to three breeder pens with litter floors (total n = 33 hens per BW class and PS age). Three weeks after PS, five hens per BW treatment and PS age were randomly selected for BW and carcass measures, including the weight of the Pectoralis major and Pectoralis minor muscles, abdominal fat pad weight, including fat around the gizzard, and weight of the ovary. The number and diameter of vitellogenic follicles (≥ 8 mm) was also recorded. Hens were inseminated weekly commencing 2 wk after PS with semen from a randombred Large White strain (RBC-3, Noble et al., 1995). Eggs were collected twice daily by pen and saved in 2-wk intervals prior to setting. Therefore, the hen production age data are reported in relation to PS as follows: 4 to 6, 6 to 8, 8 to 10, 10 to 12, and 12 to 14 wk after PS. Prior to setting, 5 eggs per pen (15 total per hen BW and age at PS) were individually weighed and hard-cooked in shell for albumen and yolk measurements and yolk DM determinations. Other eggs were individually weighed prior to setting in a Robbins incubator4 the day after the last day of the 2-wk egg collection period. Incubator temperature

3British United Turkeys 4Robbins Incubator Co.,

of America, Lewisburg, WV 24901. Denver, CO 80239.

was maintained at 37.5 C and 60% RH and hatcher temperature maintained at 36.9 C and 80% RH. After 25 d of incubation, eggs were reweighed and placed within individual pedigree baskets. At hatch, poults were individually weighed, wing-banded, and brooded. Mortality data were then recorded through 2 wk of age. The data were analyzed by analysis of variance using the General Linear Models procedure of SAS (SAS Institute, 1986). The main effects tested were age at PS, BW at PS, hen production age, and their interactions, whereby a pen of hens represented an experimental unit. Analysis of percentage data was done after arc sine transformation. One objective of this experiment was to differentiate between the effects due to egg size vs hen production age. At the end of the study, all eggs were assigned to one of eight egg weight classes for further statistical analyses. Egg weight at set, transfer weight (25 d), and poult weight were reanalyzed using a model that included egg weight class, hen production age, and their interactions.

RESULTS Age at PS had no effect on hen BW, P. major weight, P. minor weight, or abdominal fat weight 3 wk after PS (Table 1). Hen BW was still significantly different between the two BW groups 3 wk after PS (averaged across ages at PS, P ≤ 0.002). Neither the absolute nor relative weight of the P. major or P. minor were statistically different between Normal and Heavy BW hens. Heavy BW hens, however, had 71 g more abdominal fat (P ≤ 0.03) than Normal hens. Ovarian weights (3 wk after PS) were 18.7 g or 1.5% heavier (P ≤ 0.06) when hens were PS at 31 vs 29 wk (Table 2). This was largely a function of one additional follicle of ≥ 20 mm in hens PS at 31 wk. Hen BW at PS had no effect on absolute or relative ovary weight or on the size or number of follicles 3 wk after PS. Over the 10-wk production period, there was a significant increase in the weight of the eggs randomly selected for yolk and albumen measurements (P ≤ 0.0001; Table 3), primarily due to a significant increase in yolk weight (4.4 g; P ≤ 0.0001). Yolk DM percentage significantly decreased (P ≤ 0.001) over the course of the first 10 wk of lay. Absolute albumen weight did not significantly change with hen production age; thus there was a significant decline in albumen weight relative to egg weight (P ≤ 0.0003). When hens were PS at 31 wk of age, eggs selected for yolk and albumen measurements were heavier, had heavier yolks (absolute and relative weight), and had relatively lighter albumen weight over the 10-wk production period (P ≤ 0.03). Hen BW at PS had no consistent effects on egg weight or egg component weights. With increasing hen production age, there were significant increases in egg weight (P ≤ 0.0001), transfer egg weight (P ≤ 0.0001), and poult weight (P ≤ 0.0023) and a significant decline in transfer weight relative to

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EGG AND POULT CHANGES WITH HEN AGE TABLE 1. Turkey breeder hen carcass characteristics 3 wk after photostimulation Age at photostimulation (wk) 29 31

Hen BW1

Hen BW

Normal Heavy Normal Heavy

(kg) 11.875 12.65 11.82 12.74 0.22

SEM Source of variation Age at photostimulation Hen BW Age × BW Main effect means Age at photostimulation 29 wk 31 wk Hen BW at photostimulation Normal Heavy

Pectoralis major2 (g) 934 940 1,005 1,022 49

0.94 0.002 0.75

(%) 7.87 7.42 8.53 8.02 0.36

0.13 0.82 0.91

0.09 0.24 0.77

Pectoralis minor3 (g) 222.5 232.1 248.6 243.6 13.2 Probability 0.16 0.87 0.59

Abdominal fat4

(%) 1.87 1.83 2.11 1.91 0.09

(g) 283.9 336.5 239.4 328.8 29.1

0.12 0.23 0.44

0.38 0.03 0.54

(%) 2.39 2.66 2.01 2.59 0.23

0.35 0.09 0.54

12.26 12.28

937 1,014

7.65 8.28

227.3 246.1

1.85 2.01

310.2 284.1

2.53 2.30

11.85 12.69

970 981

8.20 7.72

235.6 237.9

1.99 1.87

261.7 332.7

2.20 2.63

1Average

hen BW at photostimulation: Normal = 11.8 kg, Heavy 12.9 kg. major. P. major percentage = (left P. major weight/BW) × 100. 3Left Pectoralis minor. P. minor percentage = (left P. minor weight/BW) × 100. 4Abdominal fat includes the fat disassociated from the gizzard. Abdominal fat percentage = (abdominal fat weight/BW) × 100. 5Means represent five hens per BW group and age at photostimulation. 2Pectoralis

egg weight at set (P ≤ 0.0001; Table 4). There were no significant differences in poult weight as a percentage of initial egg weight. When egg weight from all hen production ages were stratified into egg weight classes, there was a significant increase in egg weight at 25 d transfer (P ≤ 0.0001), transfer weight relative to egg weight at set (P ≤ 0.004), and poult weight at hatch (P ≤

0.0001), but there was a significant decline in relative poult weight (P ≤ 0.0001, relative to egg weight at set) with increasing egg weight class. Age at PS had no effect on initial egg weight or transfer weight (Table 5). Relative transfer egg weight (P ≤ 0.0001), absolute poult weight (P ≤ 0.05), and relative poult weight (P ≤ 0.03) were increased when hens were

TABLE 2. Turkey breeder hen reproductive characteristics 3 wk after photostimulation Follicles

Age at photostimulation Hen BW1 (wk) 29 31

Normal Heavy Normal Heavy

SEM

Ovary2 (g) 147.43 129.3 153.0 161.1 9.2

(%) 1.24 1.03 1.29 1.26 0.07

≥8 mm

≥20 mm

13.5 13.6 13.6 14.0 0.7

8.3 7.8 9.2 9.6 0.6

Probability Source of variation Age at photostimulation Hen BW Age × BW Main effect means Age at photostimulation 29 wk 31 wk Hen BW at photostimulation Normal Heavy 1Average

0.06 0.60 0.18

0.06 0.10 0.19

0.74 0.74 0.84

138.4 157.1

1.14 1.28

13.6 13.8

8.1 9.4

150.2 145.2

1.27 1.15

13.6 13.8

8.8 8.7

hen BW at photostimulation: Normal = 11.8 kg, Heavy 12.9 kg. percentage = (ovary weight/BW) × 100. 3Means represent five hens per BW group and age at photostimulation. 2Ovary

0.04 0.97 0.49

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APPLEGATE AND LILBURN TABLE 3. Egg weight, yolk weight, relative weight, dry matter, albumen weight, and relative albumen weight from turkey breeder hens during the first 10 wk of production1

Variable

Egg weight

Yolk weight (g)

Weeks after photostimulation 4 to 6 wk 6 to 8 wk 8 to 10 wk 10 to 12 wk 14 to 16 wk Age at photostimulation 29 wk 31 wk Hen BW4 Normal Heavy SEM Source of variation Hen age Age at photostimulation Hen BW

Relative yolk weight

Yolk DM

Albumen weight

Relative albumen weight

(%)

(% DM)

(g)

(%)

78.6 80.5 81.8 85.7 86.4

23.1 23.7 24.9 27.2 27.5

29.4 29.6 30.4 31.9 31.9

52.5 52.0 50.8 48.1 48.8

46.5 46.9 47.3 47.7 47.6

59.1 58.3 57.8 55.5 54.9

81.8 83.4

24.6 26.0

30.1 31.2

50.4 50.4

47.5 46.9

58.0 56.3

82.0 83.3 0.8

25.3 25.3 0.3

30.8 50.3 30.5 50.6 0.4 0.2 Probability

46.6 47.8 0.9

56.9 57.4 0.7

0.0001 0.03 0.07

0.0001 0.0001 0.74

0.0001 0.008 0.32

0.0001 0.88 0.055

0.86 0.48 0.12

0.0001 0.005 0.44

1Means

based on 15 eggs per hen BW and age at photostimulation (60 total) per age. percentage = (yolk weight/egg weight) × 100. 3Albumen percentage = (albumen weight/egg weight) × 100. 4Average hen BW at photostimulation: Normal = 11.8 kg, Heavy = 12.9 kg. 2Yolk

TABLE 4. Egg weight, weight at 25 d of incubation (transfer weight), relative transfer weight, poult weight at hatching, and poult weight relative to initial egg weight from turkey breeder hens during the first 10 wk of production

Variable

Egg weight1

Transfer weight (g)

Weeks after photostimulation 4 to 6 wk 6 to 8 wk 8 to 10 wk 10 to 12 wk 12 to 14 wk SEM Egg size, g4 ≤ 79.9 80.0 to 82.9 83.0 to 85.9 86.0 to 88.9 89.0 to 91.9 92.0 to 94.9 95.0 to 97.9 ≥ 98.0 SEM Source of variation Hen age Egg size

81.0 82.0 84.1 86.7 87.6 0.7

71.9 71.7 73.8 75.8 76.8 0.7

75.4 81.5 84.4 87.3 89.9 93.3 96.3 99.9 0.2

65.9 71.5 74.1 76.3 79.1 82.1 84.4 87.4 0.3

0.0001 0.0001

0.0001 0.0001

Relative transfer weight

Poult weight

Relative poult weight

(%)

(g)

(%)

88.5 87.3 87.5 87.7 87.0 0.2

52.8 52.6 54.5 54.8 55.6 0.6

64.3 64.2 64.6 63.6 63.2 0.4

49.6 52.7 54.1 55.1 56.4 58.2 58.7 62.0 0.5

65.0 64.5 64.0 63.3 62.5 62.7 61.0 62.4 0.6

87.5 87.5 87.8 87.4 88.0 88.0 87.7 87.8 0.3 Probability 0.0001 0.0007

0.0023 0.0001

0.13 0.0001

1Egg weight, transfer weight, and transfer percentage means based on 860, 777, 530, 555, and 455 eggs for each production age, respectively. 2Transfer percentage = (egg weight at 25 d incubation/egg weight at set) × 100. 3Poult weight and poult percentage means based on 303, 421, 261, 323, and 280 poults for each production age, respectively. Poult percentage = (poult weight at hatch/egg weight at set) × 100. 4Egg size means based on 849, 569, 580, 510, 353, 182, 76, and 58 eggs for each weight class, respectively.

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EGG AND POULT CHANGES WITH HEN AGE TABLE 5. Egg weight, egg weight at 25 d of incubation (transfer weight), poult weight, and poult weight relative to egg weight at set from turkey breeder hens during the first 10 wk of production1

Age at photostimulation

Hen BW2

(wk) 29

Normal Heavy Normal Heavy

31 SEM Source of variation Age at photostimulation Hen BW Age × BW Main effect means Age at photostimulation 29 wk 31 wk Hen BW at photostimulation Normal Heavy

Egg weight 83.1 85.4 84.2 84.3 0.7

0.95 0.056 0.07

Transfer weight (g) 73.3 75.2 73.4 73.6 0.7

0.19 0.14 0.24

Relative transfer weight (%) 88.1 88.1 87.0 87.2 0.2 Probability 0.0001 0.40 0.76

Poult weight

Relative poult weight

(g) 54.2 54.9 53.7 53.4 0.6

(%) 64.7 64.2 63.8 63.3 0.4

0.05 0.79 0.37

0.03 0.33 0.83

84.3 84.3

74.3 73.5

88.1 87.1

54.6 53.6

64.5 63.6

83.7 84.9

73.4 74.4

87.6 87.7

54.0 54.2

64.3 63.8

1Egg weight and transfer weight means based on at least 700 eggs per hen BW and age at photostimulation. Poult weight means based on at least 400 poults per hen BW and age at photostimulation. 2Average hen BW at photostimulation: Normal = 11.8 kg, Heavy = 12.9 kg. 3Transfer percentage = (egg weight at 25 d incubation/egg weight at set) × 100. 4Poult weight = (poult weight/egg weight at set) × 100.

PS at 29 wk of age. Egg weight at set from Heavy hens PS at 29 wk of age was increased and this resulted in an overall effect of hen BW at PS (P ≤ 0.056). There were no significant differences in percentage transfer weight, poult weight, or percentage poult weight due to hen BW at PS. The aforementioned increase in egg weight by Heavy hens PS at 29 wk resulted in a hen PS age by BW at PS interaction (P ≤ 0.07). Poult mortality through 2 wk of age was unaffected by hen production age, hen age at PS, or hen BW at PS (data not shown).

DISCUSSION Hens that were PS at 31 wk of age had enhanced ovarian development primarily due to an additional large follicle (≥ 20 mm). Applegate et al. (1997) reported that baseline luteinizing hormone concentrations were increased in hens PS at 24 to 25 wk of age compared with hens PS at 27 to 28 or 31 to 32 wk of age. Applegate et al. (1997) concluded that the differences in luteinizing hormone response to PS was as dependent upon chronologic age as it was on differences in body composition and supports the age-associated responses in ovarian development reported here. As egg weight increased during the initial 10 wk of production, there was a concomitant increase in the yolk to albumen ratio from 0.50 to 0.58. Similar changes in the relative proportion of egg components with increasing hen production age have also been reported in chickens (Cunningham et al., 1960 a,b; O’Sullivan et al., 1991) and in previous studies with turkeys (Moran and

Reinhart, 1980; Reidy et al., 1994; Applegate and Lilburn, 1996a). While studying hen production age-associated changes in egg weights from Nicholas hens, Applegate and Lilburn (1996a) reported an increase in the yolk to albumen ratio from 0.53 to 0.62 from their earliest two hen production ages (36 to 41 wk of age) with only a 0.1-g increase in egg weight over this production period, approximately the period of lay reported in the current experiment. The differences reported in hen production age-associated changes in egg weights and egg component weights between these studies may be largely a reflection of measuring different strains over differing hen production periods. Egg transfer weight percentage was greatest during the hen production period 4 to 6 wk after PS. The similarity in transfer percentages over the last four hen production ages, however, is in contrast to other reports in the literature, in which transfer weight percentage increased with increasing hen production age (Christensen and McCorkle, 1982; Lerner et al., 1993; Applegate and Lilburn, 1996a). Applegate and Lilburn (1996a) had previously reported that in eggs collected from Nicholas hens over an entire 19-wk production period and stratified according to egg weight, there was also no difference in transfer weight percentage due to differences in initial set weight. In the report by Applegate and Lilburn (1996a), poults from 55-wk-old hens were significantly heavier (3%) than poults from younger hens (36-wk-old) when initial egg weight was adjusted. They attributed part of this weight difference to differences in yolk size and

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yolk sac weight together with proportional reductions in residual yolk sac lipid at hatch. In the current study, poult weight at hatch increased during the first 10 wk of lay, but relative poult weight did not change. As the present experiment covered less than half of the production cycle with a different strain of hen, realistic comparisons with Applegate and Lilburn (1996a) are not appropriate. It is interesting, though, that the weight of the poult as a percentage of egg weight in the current study is similar to the data presented by Wilson (1991) but considerably lower than that reported by Applegate and Lilburn (1996a). Absolute and relative yolk-free embryo weight at 25 d did increase with age of hen (Applegate et al., 1996b), so there is some merit to the hypothesis that hen production age will influence embryonic development independent of differences in initial egg weight. In conclusion, hens PS at 31 wk had increased ovarian development primarily due to one additional large follicle (≥ 20 mm) and these eggs had larger yolks than eggs of hens PS at 29 wk of age. Only when hens were PS at 29 wk of age did BW have any bearing on egg weight during the first 10 wk of lay. Hen BW at PS had no consistent effect on egg component weights, incubation measures, or newly hatched poult weight. With increasing hen production age, there was proportionately more yolk deposited in the egg at the expense of albumen, although this did not appear to influence the poult weight at hatch relative to egg weight at set.

ACKNOWLEDGMENTS The authors wish to thank British United Turkeys of America, Lewisburg, WV 24901 for their generous donation of fertile eggs used in this experiment. The authors gratefully acknowledge the technical assistance of John Nixon and the farm staff at the OARDC Turkey Research Center.

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