What is the Feed Conversion Ratio for Turkey

Arch.Geflügelk., 73 ( 1). S. 13- 20 , 2009, ISSN 0003-9098. © Verlag Eugen Ulmer, Stuttgart

Comparison of growth performances of American Bronze, Large White turkeys and their crosses under intensive and semi-intensive management conditions

Vergleich der Wachstumsleistung von amerikanischen Bronze- und Large White Puten sowie ihrer Kreuzungen unter intensiven und semi-intensiven Haltungsbedingungen

Dept. of Animal Science, Faculty of Agriculture, University of Ankara, Ankara, Turkey

Manuskript eingegangen am 17. Oktober 2007, angenommen am 14. März 2008

Summary

This experiment was conducted to evaluate growth performance of five turkey genotypes, namely American Bronze (AB), Large White (LW) and their crosses F ₁, F ₂ and backcross to LW (BC ₁). The five genotypes were compared for body weight, feed conversion ratio and livability and were reared either under intensive (IMG) or semi-intensive (SIMG) management conditions. The assessment was carried out using performance records from 0 to 18 wk for IMG and 0 to 25 week for the SIMG.

At the end of the experiment, significant differences in mean body weights (P�<�0.05) were observed for all genotypes under IMG condition except between F ₁ and F ₂ crosses (P�>�0.05). Similarly, distinct differences in mean body weights between all genotypes under SIMG condition occurred (P�<�0.05). Feed conversion ratios were only calculated for different periods of IMG treatment. The best FCR was reached by LW turkeys, whereas, only minior differences could be observed between the other genotypes. Livability under IMG condition was not significantly different between genotypes (P�>�0.05), however, significant differences for relative livability were recorded under SIMG conditions (P�<�0.05) in some periods. Especially, livability of LW turkeys F ₂ turkeys was worse under SIMG condition, indicating the necessity for a more careful and stringent flock management for turkeys reared under field conditions.

Key words

Turkey, body�weight, feed�conversion�ratio, livability, management system, interaction

Zusammenfassung

Vergleich der Wachstumsleistung von amerikanischen Bronze- und Large White Puten sowie ihrer Kreuzungen unter intensiven und semi-intensiven Haltungsbedingungen

Der Versuch wurde durchgeführt, um die Wachstumsleistung von fünf Putengenotypen (Amerikanische Bronze­pute – AB, Weiße Breitbrustpute – LW, Kreuzung zwischen LW-Hahn und AB-Henne – F ₁, Kreuzung F ₁-Hahn x F ₁-Henne – F ₂, Rückkreuzung LW-Hahn x F ₁-Henne – BC ₁) unter intensiven (IMG) und semi-intensiven (SIMG) Haltungsbedingungen in der Türkei zu vergleichen. Hierzu wurden für IMG im Zeitraum 0. bis 18. Lebenswoche und für SIMG im Zeitraum 0. bis 25. Lebenswoche die Lebendgewichtsentwicklung, die Futterverwertung und die Überlebensrate der Puten getrennt für die Geschlechter ermittelt.

Die Lebendgewichte der geprüften Genotypen unterschieden sich in der Haltungsumwelt IMG am Versuchs­ende außer für die F ₁- und F ₂-Kreuzungen (P�>�0,05) signifikant (P�<�0,05). In ähnlicher Weise wurden auch bei der Haltungsumwelt SIMG am Versuchsende signifikante Gewichtsunterschiede festgestellt. Die Futterverwertung wurde nur für die Behandlung IMG für die verschiedenen Mastabschnitte ermittelt. Die beste Futterverwertung wurde von den LW Puten erzielt. Die anderen Genotypen unterschieden sich dagegen nur wenig in der Futterverwertung. Während für die Behandlung IMG keine Unterschiede in der Überlebensrate zwischen den Genotypen beobachtet werden konnten (P�>�0,05), traten bei der Behandlung SIMG in einzelnen Mastabschnitten signifikante Unterschiede auf (P�<�0,05). Insbesondere zeigten die LW-Puten eine schlechtere Überlebensrate unter den SIMG Bedingungen, was auf die Notwendigkeit eines vorsichtigeren und effektiveren Herdenmanagements bei der extensiven Putenmast hindeutet.

Stichworte

Pute, Lebendgewicht, Futterverwertung, Überlebensrate, Haltungsverfahren, Interaktion

Introduction

Between 1970 and 2005 turkey meat production in Turkey increased from 4.66 to 12.1 thousand tons or by 2.59 fold. Within this period, global turkey meat production increased from 1,224 to 5,767 thousand tons or by approximately five times ( FAO, 2008 ). Over a long period of time native American Bronze turkeys were used for meat production in Turkey. However, during the last 10 years, high demands for poultry meat in Turkey made the use of foreign genotypes necessary. Therefore, hybrid genotypes, especially hybrid large white turkeys, replaced the traditional use of American Bronze turkeys. These Hybrids are the result, as it is for Large White turkeys, of 3- or 4-line crosses ( Nestor et al., 2005 ). American Bronze turkeys which are still the predominant breeds in Turkey are characterized by small body size, lower egg production and hatchability ( Turkoglu et al., 1990 ; Turkoglu et al., 2005 ).

The objective of this study was to compare and assess the growth performances of the American bronze, foreign hybrid large white turkey (Hybrid Converter) and different combinations of their crosses raised under intensive and semi-intensive management conditions.

Materials and Methods

The study was carried out at the Faculty of Agriculture, Department of Animal Science, Ankara University, Ankara, Turkey. Large White (Hybrid Converter; LW) and American Bronze (AB) turkeys were used as pure lines and as crosses (Table�1). In total, 5 different genotypes were included in the experiment: LW, AB, the cross between LW toms and AB hens (F₁), the cross of F₁ toms and F₁ hens (F₂) and the backcross of LW toms x F₁ hens (BC₁). Semen was collected by dorso-abdominal massage ( Burrows and Quinn, 1937 ). Thoroughly mixed fresh pooled semen was diluted with dextrose solution (5%) in the ratio of 1:1. All hens were inseminated in the first week twice and thereafter once a week with 0.05 ml of diluted pooled semen. Eggs were collected two times daily and stored for maximum 14�d at 17˚C and 60% RH in a storage cabin.

Table 1. Turkey genotypes used in study for both intensive (IMG) and semi-intensive management groups (SIMG)

In der Studie verwendete Putengenotypen für die Haltung unter intensiven (IMG) und semi-intensiven (SIMG) Managementbedingungen

Genotypes	Toms		�	Hens		Matings1
	N	Genotypes	�	N	Genotypes
AB	6	Local American Bronze	�	20	Local American Bronze	AB x AB
F1	6	Large White (Hybrid Converter)	�	20	Local American Bronze	LW x AB
F2	6	F1 (LW x AB)	�	20	F1 (LW x AB)	F1 X F1
BC1	6	Large White (Hybrid Converter)	�	20	F1 (LW x AB)	LW X F1
LW	Purchased hatching eggs from commercial producer
1 All matings are carried out using artificial insemination.

The crosses were obtained by artificial insemination of 40 mature American Bronze hens (AB), 40 F₁ cross female turkeys and six toms of each progeny group from AB, F₁ and LW (Hybrid Converter) turkeys. The AB and F₁ cross females were separated into 2 mating groups to produce 4 genotypes as shown in Table�1. Hatching eggs of LW were purchased from commercial producer and were stored for 3 d and eggs of all groups were set into the incubator at the same time. For the treatment groups (IMG and SIMG; description see below) incubation was started at two weeks intervals resulting in 14 d difference between the two management groups. Hatchability results of the two groups were combined and are given in Table�2.

Table 2. Hatchability results of five genotypes

Schlupfergebnisse der verwendeten Genotypen

Genotype	Total Eggs1, n	Fertility, %	Hatchability of fertile eggs, %	Hatchability %
Large white	180	91.1	87.8	80.0
Bronze	265	80.0	64.2	51.3
F1	219	73.1	73.8	53.9
F2	245	80.0	66.8	53.5
BC1	283	74.2	62.4	46.3
1) Numbers were combined of SIMG and IMG

Intensive Management Groups (IMG)

A total of 150 poults were used in the research with thirty turkeys for each genetic group. Prior to sexing, each genetic group was randomly divided into three groups of 10 poults as replicate. After sexing at the end of week 8, for each sex group three replicates and in total six replicates were formed of each treatment group. The birds were reared in a littered floor house on deep wood-shavings with a space allowance per pen of 2 x 1 m. Birds were offered feed ad libitium using one tube feeder with 12�kg capacity per pen, and water was offered by one bell-type drinker per pen. Lighting was provided 23�h / d for the first week and subsequently was reduced to 14�h / d till the end of the experiment (18^th week). The following vaccination program was applied: HB1 live vaccine against ND at hatch (intra ocular), TRT / SHS live vaccine on day 7 (intra ocular), Lasota in 7^th week of life (by drinking water), TRT / SHS second vaccination in week 11, Lasota second vaccination in weeks 13–14.

Individual bird body weights were recorded at 0, 2, 6, 8, 10, 14 and 18 wk of age. Feed conversion ratio (FCR) was calculated by dividing average feed intake by average weight gain (g / g) and determined for three different periods (0–2, 3–8 and 9–18) per group. Mortality and culled birds were recorded as they occurred. Livability was calculated from daily mortality record data and expressed as percentage of initial number of birds in each period. Nutrient composition of the feed for the different periods used for the two management groups is shown in Table�3. Fattening duration for IMG treatment was 18 weeks.

Table 3. Nutrient content of diets for the different fattening periods

Nährstoffgehalte der Futterrationen für die verschiedenen Mastabschnitte

Nutrients	Weeks
	0–4	5–8	9–12	13–16	17–20	21–25
Crude protein (%)	28.08	26.08	22.30	19.35	16.80	14.30
Crude cellulose(%)	5.15	4.79	4.43	3.76	3.24	3.18
Crude fat (%)	5.00	5.77	6.15	7.63	8.22	9.00
M.E. (cal / kg)	2811	2905	3012	3120	3221	3350
Metionin (%)	0.77	0.63	0.49	0.43	0.28	0.30
Met.+ Cys (%)	1.14	0.99	0.82	0.73	0.56	0.54
Lysine (%)	1.62	1.52	1.30	1.00	0.80	0.70
Tryptophan (%)	0.32	0.30	0.24	0.21	0.18	0.14
Arginine (%)	1.87	1.74	1.43	1.22	1.01	0.80
Linoleic acid (%)	2.25	2.86	3.19	4.26	4.66	5.25
Ca (%)	1.42	1.10	0.85	0.79	0.81	0.70
P (total) (%)	1.25	0.90	0.80	0.77	0.70	0.61
Ca / P	1.14	1.22	1.06	1.03	1.16	1.15
Na (%)	0.19	0.17	0.16	0.15	0.15	0.12
Cl (%)	0.29	0.27	0.25	0.23	0.23	0.18
– Vitamin premix contained the following per 2,5 kilogram of the diet: Vitamin A, 15.000 IU, Vitamin D3 1.500 IU, Vitamin E 50 IU, Vitamin K3 5.000�mg, Vitamin B1 3.000�mg, Vitamin B2 6.000�mg, Niacin 25.000�mg, Vitamin B6 5.000�mg, Vitamin B12 30�mg, Folic acid 750�mg, D-Biotin 75�mg, Choline chloride 400.000�mg. – Mineral premix contained the following in milligrams per kilogram of the diet: Manganese 80�mg, Iron 30�mg, Zinc 60�mg, Copper 5�mg, Cobalt 5�mg, Iodine 2.0�mg, – 5000�mg Coccidiostat (Maduramicine ammonium) supplied per kg of feed except 13–18 and 21–25 week for IMG and SIMG respectively.

Semi-intensive Management Group (SIMG)

Two hundred and fifty poults were used for SIMG (50 birds per genetic group) and reared as described for IMG from hatch to the age of 6 weeks. From 6^th to 10^th week a period of transition between feeding under intensive management (provided feed) and grazing on the field by the birds themselves was introduced. During these periods, turkeys were allowed to graze on the field from 8.30 am to 5.00 pm. After 5 pm the birds were taken into the house where whole grains mixed with standard feed were provided in order to allow birds to adapt to feeding on fallen grains and other food materials on a newly harvested wheat crop field (15.5 hectares). Water was provided in the field and in the house. From the beginning of week 11 to the end of week 18, turkeys were reared as in the transition period except no feed was given in the house. Sample counts were conducted to determine the amount of grains in the field using sample squares sized 20 x 20�cm and thrown randomly in the field each time. Total number of wheat grains in the area covered by sample square was counted at every throw and average of total throws was computed. There was a total of 7.04�g (calculated) of wheat grain per m² of the field. At the beginning of week 19 to the end of week 25, turkeys were confined in pens according to their respective genetic groups. During these periods birds had access to unlimited feed (nutrient content of the feed given in Table�3) and water. Body weights were recorded at 0, 2, 6, 8, 10, 14, 18, 22 and 25 week of age. Duration of fattening period for treatment SIMG was 25 weeks.

The climate of the region where turkeys were grazed can be classified as semi-arid type of the Mediterranean climate, located between 39.36˚N and 32.41˚E. The region has an altitude of 1,050 m above sea level. The experiment was carried out between August and December.

Statistical analysis

Two-way analysis of variance (ANOVA) was performed to determine the effects of sex and genotype and their interactions on body weight for periods in which sex was determined (10 to 18 wk). For periods before sexing, only differences among mean values of genotypes were determined. In this case, sex and interaction terms were removed from the model below. Duncan's multiple range test procedure ( SAS Institute, 1999 ) was used to compare differences between means of genotypes at 5% level of significance.

ANOVA estimation of the effect of genotype and sex on body weight and FCR were performed using the following model:

y_ijk = µ + b_i + c_j +(bc)_ij+ e_{ijk .} Where;

y_ijk: value for each animal (each replicate for FCR)

µ: population mean

b_i: effect of ith genotype (Genotype: LW, AB, F_1, F₂ and BC₁)

c_j: effect of jth sex (Sex: male and female)

(bc)_ij : effect of interaction of ith genotype and jth sex

.e_ijk: : random residual error

Statistical analysis for livability was carried out using Minitab 13.0 packet program incorporating 2P application. Z-Test was employed to determine the existence of differences between two proportional values for the genetic groups.

Results

Body Weight (BW)

Mean body weight values for all the genetic groups reared under IMG at different age periods are presented in Table�4. Mean body weight differences (at 6, 10, 14 and 18�weeks) among the genetic groups were significant (P�<�0.05). LW genotype reached the highest while AB genotype the lowest body weight (13,317�g and 6,092�g) at 18 weeks of age, respectively. As expected, for all genetic groups toms were heavier than hens. The BC₁ crosses with mean body weight value of 10,470�g at 18 weeks have been the heaviest of all three crosses in the experiment (P�<�0.05). Differences between F₁ and F₂ genotypes for 18 week mean BW (8,270�g and 8,539�g) were not significant (P�>�0.05).

Table 4. Average body weight of genotypes for different fattening periods under intensive management condition (IMG; g ± SE)

Mittleres Körpergewicht der Putengenotypen in den einzelnen Mastabschnitten unter intensiven Haltungsbedingungen (IMG; g ± SE)

Age (wk)	Sex1	Large white			Bronze			F1			F2			BC1
0 (day)	All	57.8	±	0.52	58.7	±	0.64	58.4	±	0.73	59.01	±	0.71	60.2	±	0.73
6	All	1729	±	30.2ª2	1009	±	29.2 d	1277	±	33.8 c	1225	±	30.9 c	1405	±	35.3 b
10	F	5150	±	97.1	2510	±	103.8	3421	±	112.1	3544	±	97.1	3947	±	122.8
	M	6328	±	106.3	3168	±	89.9	4023	±	103.8	4375	±	112.1	4861	±	112.1
	All	5739	±	72.0ª	2839	±	68.6 d	3722	±	76.4 c	3959	±	74.1 c	4404	±	83.1 b
14	F	8314	±	141.8	3990	±	154.2	5182	±	186.8	5599	±	175.5	6184	±	154.2
	M	11321	±	175.5	5177	±	139.2	6859	±	147.7	7084	±	144.7	8662	±	200.7
	All	9818	±	112.8ª	4583	±	103.9 d	6021	±	119.1 c	6342	±	113.7 c	7423	±	126.5 b
18	F	10572	±	185.7	5263	±	206.7	6803	±	244.5	7211	±	229.7	8162	±	201.9
	M	16062	±	229.7	6920	±	182.3	9737	±	201.9	9967	±	193.3	12778	±	262.7
	All	13317	±	147.7ª	6092	±	137.8 d	8270	±	158.6 c	8589	±	150.1 c	10470	±	165.7 b
1) F: Female, M: Male, All: (Female+Male) 2) a,b,c,d Values with unlike superscripts in the same row differ significantly (P�<�0.05),

Table�5 shows mean body weight values for all genetic groups raised under SIMG condition for different age periods. Obviously, the highest mean BW was achieved by LW (P�<�0.05) followed by BC₁ and F₁ turkeys for all study periods with the exception of weight at hatch. At the end of week six which marks the beginning of transition period, mean BW for all genetic groups ranged between 1,170 and 2,121�g. Similarly, mean BW for the genetic groups ranged from 2,205 to 3,600�g at the end of the adaptation and / or transition period (wk 10). The turkeys were grazed on wheat field for eight weeks in total (from 10 to 18 week). At the end of wk 18 LW genotype had the highest mean BW while AB turkeys had the lowest ones with 5,905 and 4,243�g (P�<�0.05), respectively. When comparing the changes in mean BW till 10^th week and after week 18 with mean BW during grazing phase on the field (11 to 18 wk), a decline in mean body weight differences among the genetic groups under field conditions was observed. At the end of the 8 weeks grazing phase, birds were re-confined in the poultry house where they were provided with ad libitum feed (nutrient content of feed given in Table�3) and water which lasted for seven weeks. During this period, rapid increase in body weight was observed for all the genetic groups. For instance, there was a more than two fold increase in mean BW for LW genotypes. This rapid increase in mean BW may be explained with possible compensatory growth. Furthermore, mean BW differences among all the five genetic groups under semi-intensive management for both 22 and 25 weeks periods were found to be significant (P�<�0.05). LW turkeys had the highest mean BW followed by BC₁, F₁, F₂ and American Bronze genotypes, in that order.

Table 5. The average body weight of genotypes for different fattening periods under semi-intensive management condition (SIMG; g ± SE)

Mittleres Körpergewicht der Putengenotypen in den einzelnen Mastabschnitten unter semi-intensiven Haltungsbedingungen (IMG; g ± SE)

Age (wk)	Sex1	Large white			Bronze			F1			F2			BC1
0	All	58.3	±	0.81	57.8	±	0.67	56.9	±	0.74	57.5	±	0.69	56.5	±	0.67
6	All	2121	±	33.8a2	1170	±	27.2d	1486	±	29.8b	1268	±	26.2c	1557	±	27.7b
10	F	3233	±	59.9	1945	±	44.9	2526	±	54.2	2374	±	41.8	2507	±	49.8
	M	3966	±	55.4	2466	±	50.8	3109	±	48.0	2926	±	56.8	3277	±	48.0
	All	3600	±	40.8a	2205	±	33.9d	2817	±	36.2b	2650	±	35.3c	2892	±	34.6b
14	F	3799	±	86.0	2613	±	65.5	3199	±	77.8	3048	±	65.5	3047	±	91.2
	M	4523	±	105.3	3193	±	73.0	3908	±	69.0	3723	±	77.8	3915	±	65.5
	All	4161	±	68.0a	2903	±	49.0d	3554	±	52.0b	3385	±	50.9c	3841	±	56.2b
18	F	5458	±	122.7	3745	±	92.7	4764	±	114.4	4405	±	94.1	4804	±	137.1
	M	6353	±	182.8	4741	±	125.8	5618	±	112.0	5383	±	146.6	5616	±	98.5
	All	5905	±	110.1a	4243	±	78.2d	5191	±	80.0b	4894	±	87.1c	5210	±	84.4b
22	F	8702	±	248.1	5113	±	162.4	6469	±	204.8	6256	±	172.6	6916	±	240.2
	M	11826	±	303.8	7499	±	220.4	9009	±	192.2	8411	±	248.1	9314	±	172.6
	All	10264	±	196.1a	6306	±	136.9e	7739	±	140.4c	7334	±	151.1d	8115	±	147.9b
25	F	9819	±	266.9	5803	±	182.7	7706	±	220.4	6938	±	179.9	7764	±	258.4
	M	15149	±	326.8	9371	±	237.1	11501	±	206.7	10583	±	276.2	11698	±	185.6
	All	12484	±	211.0a	7587	±	149.7e	9604	±	151.1c	8760	±	164.8d	9731	±	159.1b
1) F: Female, M: Male, All: (Female+Male) 2) a,b,c,d Values with unlike superscripts in the same row differ significantly (P�<�0.05),

Body Weight Gain (BWG)

Figure�1 presents the weekly mean body weight gain for the different rearing periods for both IMG and SIMG treatment. Interesting values for BWG during grazing periods (11–18 week) and at 19 to 25 weeks were observed in the SIMG treatment. For instance, the calculated weekly body weight gain in the first 4 weeks of the grazing period (11–14 weeks) fluctuated between 140�g (LW) and 237�g (BC₁) while in the second 4 weeks period (15–18 weeks) weekly gain ranged from 335 to 436�g for AB and LW genotypes, respectively. Hence, the increase in mean BWG during the second four weeks of grazing period may be attributed not only to increases in growth of turkeys but also of turkeys' adaptation to grazing under field conditions. Furthermore, except for BC₁ genotypes the highest increase in body weight gain for all the genetic groups in IMG was observed during weeks 7 to 14 as compared to the other growth periods. Except for BC₁ cross there was a decline in body weight gain for all genotypes of IMG treatment in particular for LW (from 1,020�g to 875�g) from 15 to 18 weeks of age (Figure�1). Birds of SIMG treatment were sheltered and fed ad libitum in the poultry house from 18 to 25 weeks. The average weekly gain within the first four weeks (19–22 week) fluctuated between 516 to 1,090�g for AB and LW, respectively. The achieved increase in weekly gain slightly decreased to a lower level for all genetic groups during the last 3 weeks (23 to 25 week) of the trial periods (Figure�1).

Figure 1. Average weekly body weight gain (g) of turkey genotypes for different fattening periods under intensive (IMG) and semi-intensive (SIMG) management conditions

Mittlere wöchentliche Gewichtszunahmen (g) der Putengenotypen in den verschiedenen Mastabschnitten unter intensiven (IMG) und semi-intensiven (SIMG) Haltungsbedingungen

Feed Conversion Ratio (FCR)

Average feed conversion ratio (FCR) in periods determined for the genetic groups is presented in Table�6. It is obvious that FCR was higher for American Bronze turkeys than for the other four genetic groups for the 3–8 weeks period (P�<�0.05). In addition, it was also found that more than 80% of total feed (throughout 18 weeks = 126 days) was consumed by the birds between 9^th and 18^th week (last 70�days). At the end of the 18 weeks study period, the calculated FCR for all genetic groups ranged from 2.63 to 3.24 with LW and AB turkeys having the lowest and highest values, respectively (Table�6).

Table 6. Feed conversion ratio (g / g) of genotypes for different fattening periods under intensive management condition (IMG)

Futterverwertung (g / g) der Putengenotypen in den verschiedenen Mastabschnitten bei intensiven Haltungsbedingungen (IMG)

Age periods (week)	Sex1	Large White			Bronze			F1			F2			G1
0–2	All	1.26	±	0.062	1.54	±	0.088	1.29	±	0.072	1.46	±	0.088	1.50	±	0.072
3–8	All	1.69	±	0.059 a2	2.05	±	0.059 b	1.77	±	0.059 a	1.82	±	0.059 a	1.85	±	0.059 a
9–18	F	3.53	±	0.126	3.88	±	0.126	4.20	±	0.126	3.71	±	0.126	3.53	±	0.126
	M	2.69	±	0.126	3.76	±	0.126	3.26	±	0.126	3.61	±	0.126	3.47	±	0.126
	All	3.11	±	0.089 a	3.82	±	0.089 c	3.73	±	0.089 bc	3.66	±	0.089 bc	3.50	±	0.089 b
0–18	All	2.63			3.24			3.11			3.10			3.05
1) F: Female, M: Male, All: (Female+Male) 2 a,b,c, Values with unlike superscripts in the same row differ significantly (P�<�0.05)

Livability

Table�7 shows the livability values for the different trial periods for all five genetic groups reared both under IMG and SIMG conditions. Also, comparisons were made between livability values for the period 7 to 18 weeks within IMG and SIMG treatments. It was observed that livability for the period 0 to 18 weeks did not differ significantly between genetic groups in the IMG treatment. In contrast, F₁ genotypes showed the highest livability in the SIMG group (P�<�0.05) for 0 to 25 weeks period. Highest mortality rate was recorded in LW and F₂ genotypes for turkeys of the SIMG treatment (when 7–18, 7–25 and 0–25 week trial periods are considered). However, for the period 7 to 18 weeks livability between the genotypes did not differ significantly (P�>�0.05), with the exception of F₁ and AB genotypes. Comparison for livability was also made between the two management systems within the 7 to 18 weeks period when the turkeys from SIMG treatment were reared in the field, as shown in Table�7. Moreover, of the five genetic groups only livability for the AB and F₁ genotypes did not differ according to management system (P�>�0.05). Livability of the LW genotypes felt sharply from 100% to 74.4% in the 7 to 18 weeks period under intensive and semi-intensive management conditions, respectively. With the exception of F₁, no significant differences in relative livability were observed for all the other genotypes in the SIMG system (0 to 25 wk period; P�>�0.05).

Table 7. Livability (%) of turkey genotypes for different fattening periods under intensive (IMG) and semi-intensive (SIMG) management conditions

Überlebensrate (%) der Putengenotypen in den verschiedenen Mastabschnitten unter intensiven (IMG) und semi-intensiven (SIMG) Haltungsbedingungen

Management groups	Age periods (week)			LW	AB	F1	F2	BC1
Intensive	0	–	6	89.4	90.5	83.7	84.3	89.6
	7	–	10	100.0	100.0	97.6	97.7	97.7
	11	–	18	100.0	98.0	97.5	100.0	97.6
	7	–	18	100.0A	98.0A	95.1A	97.7A	95.3A
	0	–	18	89.4	88.6	79.6	82.4	85.4
Semi–intensive	0	–	6	94.0 ab	87.7 b	98.3 a	94.2 ab	91.8 ab
	7	–	10	100 a	95.0 ab	100 a	87.7 b	93.1 ab
	11	–	18	74.4 b	94.7 a	94.0 a	84.2 ab	87.0 ab
	19	–	25	93.1	98.1	100	97.9	100
	7	–	18	74.4aB	90.0bcA	94.0bA	73.8aB	81.0acB
	7	–	25	69.2a	88.3bc	92.0bc	72.3a	81.0ac
	0	–	25	65.1 a	77.5a	92.4 b	68.1 a	74.4 a
1) a,b,c, Values with unlike superscripts in the same row for any two genetic groups differ significantly in livability (P�<�0.05) AB Within 7–18 week age period values with unlike capital superscripts in the same column differ significantly (P�<�0.05)

Discussion

Body Weight

In this study, the performances of five genetic groups of turkeys were compared under two different management conditions. All comparisons between genetic groups for average performance characteristics were made within the same management system. The results obtained showed that LW had the highest mean body weight followed by BC₁, F₁, F₂ and AB turkeys (lowest). This coincides with the fact that American Bronze is a small sized native turkey breed in Turkey, reared by rural population under extensive management (or free scavenging field) conditions. But, rearing of AB turkeys under improved management conditions with access to high quality feed and good shelter did not significantly increase their average body weight (Table�4). Body weight of AB turkeys was only 46% and 61% of LW turkeys at 18 and 25 weeks of age, respectively (Table�4 and 5). Mean body weights for AB and LW turkeys in both experiments in the present study were broadly within the range of those reported in other studies conducted in Turkey ( Türkoglu et al., 1990 ; Testik and Çelen, 1993 ; Anonymous, 2006 ). Furthermore, 18-wk mean BW for male and female AB turkeys obtained in this experiment were much higher than values reported by Ersoy et al. (2006). Significant difference for mean body weight was observed between F₁ and F₂ crosses under semi-intensive condition (25 weeks of age), whereas, the difference was not significant under intensive condition (18 weeks of age). In addition, mean BW of the two parental genotypes (LW and AB) was higher than mean BW of their F₁ cross genotype, both under SIMG (10,035�g vs 9,604�g at 25 wks of age) and in IMG (9,705�g vs 8,270�g at 18 wks of age) condition, indicating the absence of heterosis for BW. Negative heterosis for BW at 8, 16 and 20 wk of age in both male and female reciprocal crosses was also reported by Nestor et al. (2004) in an experimental turkey line reciprocally crossed with a commercial dam line (BD) and selected long term (40 generations) for increased egg production. This research and the previous study are not in agreement with an earlier study by Emmerson et al. (2002) who reported heterosis for BW at 8, 16 and 20 week of age of 3.9%, 2.6% and 3.2%, respectively, in an experimental turkey line reciprocally crossed with its random bred control population. Nestor (1985) and Emmerson et al. (1991) reported that the occurrence of heterosis for BW in line and breed crosses in turkeys is inconsistent and specific for crosses with diverse genetic constitution. Similarly, the amount of heterosis in a particular cross depends on, among other things, differences in gene frequency ( Falconer, 1981 ), and lines exhibiting large differences in body conformation are likely to differ greatly in gene frequency.

Mean body weight of turkeys reared for 25 week under SIMG condition nearly matched mean body weight of turkeys reared for 18 weeks under IMG condition. The heaviest genotype was LW (12,484�g) followed by BC₁, F₁, F₂ and the AB turkeys. In contrast, mean BW at 25 weeks of age of AB and F₁ cross turkeys reared under SIMG was 24% and 16% higher than under IMG, respectively. Hence, these genotypes could be regarded as slow growing or in other words as genotypes with a slow growth potential. Naturally, there were differences in growth rate between turkeys reared under intensive and semi-intensive management system due to the different environmental conditions. Indeed, it was clear from this experiment that turkeys reared under semi-intensive management conditions for 18 weeks gained only between 44% (LW) and 70% (AB) of final body weight of turkeys reared under intensive management conditions. The reactions of these genetic groups to different environmental conditions may be attributed to the overall genotype x environment interaction. For the two systems of management, the highest and least difference in mean BW at 18 weeks of age was found within LW and AB turkeys, respectively. Hence, it can be concluded from the comparison of AB and LW genotypes, that LW turkeys were most affected by the unfavorable extensive management condition, including grazing on the field.

Feed Conversion Ratio (FCR)

The period from 9 to 18 weeks constitutes the most important part of growth (68–73% of 18^th week BW) of the turkeys and also of feed consumed (approx. 80–85%) under IMG condition. For this reason no statistical analysis was carried out with respect to the 0–18 weeks FCR values, which were only presented to give additional information. In addition, the parallelism of FCR values for the 3–8 and 9–18 weeks periods (Table�6) are believed to validate the information presented. In general, lowest FCR value was obtained for LW followed by BC₁ genotypes. The results obtained for FCR in this study were consistent with the values of 3.18 and 2.51 obtained by Sarica et al. (1991) and Anonymous (2006) for AB and LW turkeys, respectively, and with the value 2.638 obtained by Havenstein et al. (2007) for 2003 male turkeys on 2003 feed at 20 weeks of age. Mean FCR for AB was higher than that of the other four genetic groups (P�<�0.05) for the 3 to 8 weeks period. However, values among the AB, F₁ and F₂ genotypes did not differ significantly for the 9 to 18 weeks period.

Livability

Table�7 shows the livability values for the different trial periods for the five genetic groups reared both under intensive and semi-intensive management conditions. The livability for the period 0–18 weeks for the intensive mana­gement treatment ranged between 79.6% and 89.4% (P�>�0.05). The livability for the semi-intensive management treatment for the period 0–25 weeks fluctuated between 65.1% and 92.4%, and differences between the livability values of F₁ cross and other genetic groups were significant (P�<�0.05). Also, the higher livability observed at both the 11–18 and the 0–25 week periods for F₁ cross genotypes under semi-intensive management condition may be due to heterosis. In general, the missing differences in livability between genotypes of the IMG treatment and the observed differences in livability between genotypes of the SIMG treatment due to heterosis confirm the existence of genotype x environment interactions.

Livability values for the period 7 to 18 weeks under IMG condition were slightly lower for AB and F₁ crosses, which was consistent with the values of 91.2% and 86.2% reported by Testik and Çelen (1993 ). Testik and Çelen (1993 also observed a lower relative livability in crosses between AB and foreign Hybrid turkeys. Calculated livability values (Table�7) indicated that F₁ crosses and AB turkeys adapted better to the unfavorable conditions of hot summer weather and poor feeding under field conditions when compared to the other genotypes (P�<�0.05).

Conclusions

This study confirms in agreement with other animal species clear genotype x environment interactions for the tested turkey genotypes. Despite the achieved superior body weight of LW turkeys under the two different management conditions in comparison to the other tested genotypes a distinct decrease in livability was observed.

The mean BW of BC₁ approaching 80% (due to absence of heterosis for BW, presumably a result of additive genetic effects) of BW of the LW genotype and with its slightly lower FCR may be an alternative to commercial breeders for rearing under intensive management conditions. Lastly, the change in livability from one period to another under the SIMG condition, especially the increase in mortality rates during the grazing period, indicates the necessity for a more careful and stringent flock management for turkeys reared under field conditions.

Acknowledgement

The authors wish to thank The Scientific and Technology research council of Turkey (TUBITAK) for their financial support of this research work.

References

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