Long-Term Selection for Body Weight in Japanese Quail Under Different Environments

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1 Long-Term Selection for Body Weight in Japanese Quail Under Different Environments H. L. MARKS USDA, Agricultural Research Service, Southeastern Poultry Research Laboratory, c/o The University of Georgia, 107 Livestock-Poultry Bldg., Athens, Georgia ABSTRACT Long-term selection was conducted for high 4-wk BW in Japanese quail under different selection environments to investigate selection limits and to determine whether genetic parameters for growth are similar to those in chickens. Quail lines were selected under an adequate 28% CP diet (P line) and under a low 20% CP diet (T line). Mean realized heritabilities ranged from 0.32 (T line) to 0.49 (P line) during the first 10 generations. Although genetic variation remained following 97 generations of selection, realized heritabilities obtained agreed with theoretical predictions of loss of additive genetic variability with continuous selection. Similarity of heritability estimates indicates that Japanese quail are an excellent model for genetic studies of growth in meat-type chickens. Positive relationships accompanying selection for INTRODUCTION Genetic selection is a powerful means to increase BW and rate of gain in chickens (Siegel, 1962; Chambers, 1990) and turkeys (Nestor, 1984; Buss, 1990). Although there are limited data regarding moderate to long-term selection responses for BW in chickens (Siegel and Dunnington, 1987), and turkeys (Nestor, 1984) results from longer term (> 50 generations) selection studies in aves are unavailable. The practicality of such studies is limited because of the generation interval in most domestic avian species. Wilson et al. (1961) suggested Japanese quail (Coturnix japonica) as a pilot animal for genetic selection studies because of its short generation interval and the economy of production resulting from its size. Following development of a Japanese quail control population in the early 1960s with a wide genetic base, selection studies have been conducted to estimate genetic parameters for growth under different selection Received for publication August 16, Accepted for publication June 12, high 4-wk BW were increases in adult BW, age at first egg, and egg weight. Negative relationships were decreases in percentage fertility and hatchability, and egg production. Increased growth rate in selected lines was accompanied by an increase in feed and water intake, and by improvement in feed efficiency. Feed efficiency differences appeared to be important only immediately following hatch, whereas feed intake differences were present from 0 to 4 wk. Evidence of major physiological changes accompanying selection for growth were not observed. However, changes were observed in increased "resource allocations" to supply organs, during late embryonic stages and the 1st wk posthatch. Carcass composition was similar between unselected and selected lines except for higher fat and lower moisture levels in selected lines. (Key words: Japanese quail, body weight, growth, long-term selection, genotype by environment interactions) Poultry Science 75: environments. In addition, the influence of changing both selection environment and selection criterion on the ultimate long-term responses for increased BW have been investigated. Long-term selection is necessary to address the fundamental question of whether cessation of selection responses result from a ceiling (limit) or a plateau. The purpose of this paper is to summarize selection responses for BW in several Japanese quail lines selected long-term for BW to determine whether genetic parameters for growth are similar to those in chicken and turkeys. MATERIALS AND METHODS The primary objective of this paper is a review of long-term selection responses in Japanese quail lines (P and T) selected under different nutritional environments. Line P was selected on an adequate 28% CP diet, whereas Line T was selected on a 20% CP diet containing 0.2% thiouracil (TU). Selection criterion was high 4-wk BW in all lines, and progeny from the base control population (C) were available to serve as unselected controls (Marks, 1978).

2 SYMPOSIUM: THE EFFECTS OF LONG-TERM SELECTION ON GROWTH OF POULTRY H-CD -» S H-SD f! I I I I I I I I I I I I I I I I I I I I I I I I I I I I I FIGURE 1. Four-week body weights (g) of Japanese quail lines selected for high (H) and low (L) BW under complete- (CD) and split-diet (SD) environments. A second study involving divergent selection for 4-wk BW in Japanese quail under complete-diet (CD) and split-diet (SD) environments will also be reviewed. In this study, selection was conducted for 30 generations under a SD in which quail had the opportunity to selfselect feed from high protein or high energy diets, whereas under a CD, quail received a normal 28% CP diet (Darden and Marks, 1988). RESULTS AND DISCUSSION Genetic Parameters for Body Weight Divergent Selection for 4-wk BW (s 1 to 30). During initial generations (1 to 11), selection responses were similar and symmetrical within high and low lines (Figure 1). The BW of high and low lines continued to diverge through 30; however, the change was less pronounced in later generations. Realized heritabilities for 4-wk BW declined across generations L-CD L-SD (Table 1). Estimates (0.3 to 0.5) for s 1 to 11 were similar to those reported by Nestor et al. (1982). Estimates for s 21 to 30 were lower and agree with an earlier report that genetic variation declines following long-term selection for BW (Marks, 1978). Long-Term Selection for High 4-wk BW (s 1 to 97). Selection responses of P and T lines and their respective controls (PC and TC) for s 0 through 97 are shown in Figure 2. Initial responses (s 1 to 20) were large and similar in these lines (Table 2); however, subsequent responses were greater in the P than the T line. Response in the P line for s 81 through 97 was greater (1.89 g per generation) than during s 41 through 80 (1.3 g per generation) indicating the continued presence of additive genetic variation in this line. In the T line, there was little response to selection (< 1 g per generation) from s 21 through 60. Selection responses however, gradually increased in the T line from 51 through 80. Because of the lack of a positive response 1 to to to 30 TABLE 1. Realized heritability (h 2 ) estimates for 4-wk BW in high (H) and low (L) complete-diet (CD) and split-diet (SD) quail lines 1 H-SD 0.36 ± ± ± 0.06 Split-diet L-SD 0.30 ± ± ± 0.08 H-CD 0.52 ± ± ± 0.08 Complete-diet : h 2 = regression of corrected population mean on the cumulative selection differential. L-CD 0.57 ± ± ± 0.10

3 1200 MARKS to * * ^ \/ \X. ^'v' v^' V" "V*'*-^'*--.*,*' ri [ 111 r FIGURE 2. Four-week body weights for P and T lines and their respective controls (PC and TC) thru 97 generations of selection (P line selected under 28% CP diet; T line selected under 20% CP diet containing 0.2% thiouracil). from 80 to 89, the selection environment for the T line was changed in 90 by removing TU from the diet. Following this change moderate gains (1.8 g per generation) were observed from s 90 through 97. Response "waves" across 97 generations indicate that selection plateaus may be a common phenomenon encountered in long-term selection studies. Selection differentials (SD) for the P and T lines were significantly (P < 0.05) different in only 2 of 10 comparisons. Therefore, selection environment did not have a major impact on the magnitude of SD. Realized heritabilities for 4-wk BW by 20-generation intervals are shown in Table 2. Mean heritabilities in both lines for the first 10 generations ranged from 0.32 to 0.49 and were similar to heritabilities reported for juvenile growth in broilers (Siegel, 1962). Heritabilities in the P line declined in a more or less linear fashion across generation. In the T line, heritabilities declined through the first 60 generations and then increased from 60 to 80. Realized heritabilities obtained in this study are in agreement with theoretical predictions of loss of additive genetic variability with continuous selection. Responses in Sublines Following Change of Selection Environment. Several sublines were developed by subjecting progeny from the T and P lines to new selection environments to determine whether changing the selection environment would effect expression of genetic variation for BW. In 20, a subline (R) was established from the T line by creating a new environment consisting of a 20% protein diet. In 27, a subline (S) was established by subjecting progeny from the T line to a 28% protein diet containing 0.2% TU. In PC TC TABLE 2. Summary of responses (R) and realized heritabilitii :s (h*)! in P and T quail lines R W P Line T Line P Line T Line 1 to to to to to 972 J h ± ± ± ± ± 0.6 (g) ± ± ± ± ± ± ± ± ± 0.04 = regression of corrected population mean on the cumulative selection differential. 2 T line generations 81 to ± ± ± ± ± 0.07

4 SYMPOSIUM: THE EFFECTS OF LONG-TERM SELECTION ON GROWTH OF POULTRY , a subline (TR) was established from the T line and reverse selection was initiated for BW. In 47, a subline (TSP) was established from the S subline and selected under the 28% protein diet. In 68, a subline (PR) was developed from the P line by relaxing selection for high 4-wk BW. In 77, a subline (TP) was established from the T line by subjecting quail to the same selection environment as received by the P line. Sublines were reared contemporaneously with the P and T lines. Responses in sublines (S, TSP, and TP) established by creation of new selection environments were greater than responses in lines from which these sublines originated. Higher realized heritabilities indicate that increased responses were due to the expression of greater additive genetic variation rather than changes in selection differentials. These observations indicate that changing or modifying the selection environment may provide a desirable strategy to sustain or enhance long-term selection responses. Summary of Genetic Parameters for Growth in Japanese Quail. Both heritability estimates and realized heritabilities for 4-wk BW in Japanese quail appear to be very similar to heritability estimates for BW in chickens (Siegel, 1962; Kinney, 1969; Chambers, 1990) and turkeys (Nestor, 1984; Buss, 1990). In addition, other researchers (Collins et al, 1970; Chahil and Johnson, 1974; Nestor et al, 1982; Godfrey, 1968; Marks, 1990; Toelle et al, 1991) have reported heritabilities for BW in Japanese quail within the ranges observed in this study. Similarity of heritability estimates indicates that Japanese quail are an excellent model for genetic studies of growth in meat-type chickens. Correlated Responses Positive relationships accompanying selection for high 4-wk BW were increases in adult BW (16-wk), age at first egg (SM), and egg weight (EW). Increases in adult BW were greater in the P than T line, which was likely related to higher 4-wk BW in the P line. The delay in age at SM and increases in EW were not greatly different between the two lines (Marks, 1979). Negative relationships accompanying selection for high 4-wk BW were evidenced by declines in percentage fertility and percentage hatchability of total eggs. The decline in percentage hen-day egg production was relatively small and appeared to be greater in the P than the T line. Anthony et al. (1990) reported changes in adult BW, live weight, and egg weight in quail lines divergently selected for BW. Increased growth rate in Japanese quail is accompanied by an increase in feed intake and improvement in feed efficiency (Marks, 1980). In addition, selection for increased growth rate results in greater water intake and higher water to feed ratios in selected than in unselected control quail (Marks, 1981). These data agree with observations regarding the influence of selection for BW in chickens on both feed intake (Barbato et ah, 1980) and feed utilization (Siegel and Wisman, 1966). Although * 130 I 11 CO Diets (% protein) FIGURE 3. Mean 4-wk BW of P, T, and C quail lines fed 18,21,24, and 27% CP diets ( 39). there is substantial evidence that the increase in BW of selected chicken populations is mainly associated with increased appetite (McCarthy and Siegel, 1983), the role of feed efficiency in the expression of genetic variation is not fully understood. There is evidence, however, that when feed efficiency data are segmented into different periods, which allows for investigation at early ages, major differences are observed between genetically diverse populations (Marks, 1991). The expression of the greatest differences between stocks immediately after hatch indicates that early feed efficiency changes may set the stage for the increased feed intake observed in selected stocks at subsequent ages. Changes Following Selection Evidence of major physiological changes in Japanese quail accompanying selection for increased growth is sparse. Burke and Marks (1984) failed to detect higher levels of growth hormone, thyroxine, and triiodothyronine in growth-selected P and T quail lines than in the unselected C line. Also, DNA, RNA, and protein concentration of selected and unselected lines appears similar, as does the RNA, DNA, and protein:dna ratios (Fowler et al, 1980). In general, of all physiological traits investigated, there has been little evidence of differences between genetically diverse lines of Japanese quail. Lilja (1983) suggested that rate of growth after hatching is at least partly determined by the pattern of organ growth. He postulated that a high specific growth rate is possible through an organ growth pattern in which a large part of early resources are used for enlarging the food processing organs, thus making further rapid growth in selected lines possible. Percentages of total BW of the gizzard, intestines, and the digestive tube were found to be considerably larger in the P line quail at hatching and during the 1st wk of the growth period (Lilja et al, 1985). Because growth rate is linked to an increase in the relative size of digestive organs, overall growth rate is likely restricted by the capacity to ingest and digest food. 27

5 1202 MARKS C Line P Line CD -Q E 13 ± Body Weight (g) FIGURE 4. Four-week body weight in P and C quail lines following 80 generations of selection. Carcass changes (protein, ash, lipid, and water) were investigated in P and C quail following 51 generations of selection. Both percentage ash and protein increased from hatch to 14 d and thereafter remained constant. However, percentage water and total lipid demonstrated contrasting responses to increasing age; percentage water declined whereas percentage total lipid increased. The P line quail had less carcass water and protein, but had more lipid. Line differences for carcass traits were small from 0 to 21 d, but became larger at 28 and 42 d primarily due to higher fat and lower water levels in the P line (Marks, 1993a). Evaluation of P, T, and C quail lines on diets containing 18, 21, 24, and 27% CP demonstrated that P-line quail selected under a 28% CP diet required a high protein diet for maximum growth (Figure 3). However, T line quail selected on a 20% CP diet performed as well on low protein diets as on high protein diets (Marks, 1993b) and did not require high protein diets for full expression of their genetical potential for growth. However, when lines were evaluated across several environments, largest BW's within line were observed under their respective selection environment (Marks, 1993c). CONCLUDING REMARKS Barring the discovery of "major growth" genes, it appears that genetic engineering techniques will not be useful in the near future for improvement of quantitative growth traits in poultry. Therefore, techniques involving "cloning", "insertion" and "expression" may have limitations unless combined with quantitative genetic theory and practice. For example, Figure 4 shows the normal distribution of 4-wk BW in P and C line quail following 80 generations of selection. The mean of the C line is 88 g with the upper limit of 112 g. However, the mean of the P line is 253 g. Therefore, if the technology to "clone" had been available prior to the initiation of selection for BW in the P line, the maximum BW following cloning would be similar or the same as the largest bird in the C line. This finding would have resulted in a population approximately one-third as large as that resulting from traditional selection. These data indicate that quantitative genetics has played an important role in animal improvement and that there is a need to blend new and old technologies for continued improvement in animal breeding programs. REFERENCES Anthony, N. B., D. A. Emmerson, K. E. Nestor, and W. L. Bacon Divergent selection for body weight and yolk precursor in Cotumix japonica. 8. A summary of correlated responses. Poultry Sci. 69: Barbato, G. F., J. A. Cherry, P. B. Siegel, and H. P. VanKrey, Repeatabilities of feed and water consumption of growing chickens. Poultry Sci. 59: Burke, W. H., and H. L. Marks, Growth hormone, thyroxine and triiodothyronine levels of Japanese quail selected for four-week body weight. Poultry Sci. 63: Buss, E. G., Genetics of growth and meat production in turkeys. Pages in: Poultry Breeding and Genetics.

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