Growth and Development of Leghorn Pullets Subjected to Abrupt Changes in Environmental Temperature and Dietary Energy Level

Growth and Development of Leghorn Pullets Subjected to Abrupt Changes in Environmental Temperature and Dietary Energy Level S. LEESON and L. I. CASTON Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, NIG 2W1, Canada (Received for publication November 19, 1990)

1991 Poultry Science 70:1732-1738 INTRODUCTION

Leeson and Summers (1989) concluded that pullet growth is most responsive to energy intake, and that with consumption of 1 kg of balanced protein to 20 wk, there is little benefit from additional protein intake. These effects are most pronounced under hot weather conditions, where pullets often fail to achieve their growth potential. Under hot-cyclic conditions, Leeson and Summers (1989) indicate the advantage of providing diets of >2,850 kcal ME/kg so as to ensure energy intakes of >20 Meal ME/kg to 20 wk of age. In warm environments it is often difficult to maintain desired nutrient intake. There is a suggestion that nutrient self-selection under these environmental conditions may be beneficial (Scott and Balnave, 1988), although the major response appears to be in terms of normalizing protein rather than energy intake. In field situations, birds often adapt to environmental conditions such that growth in hot weather may not be as retarded as recorded in more short-term research studies. However, under field conditions, major fluctuations in

environmental temperature are thought to be most detrimental to growth and development, although pullets will adjust feed intake in relation to energy requirements. For example, Muramatsu and Isariyodom (1989) suggest that the ME intake response of layers to changes in ambient temperature is quite rapid, with a delay period to normalization of only some 6 days. However, the feed intake response is more severely delayed (35 to 42 days), with this effect perhaps related to normalization of protein intake. Similarly, Scott and Balnave (1988) suggest that under conditions of nutrient self-selection and high ambient temperature, birds attempt to normalize uieir intake or energy:protein. There are few reports of pullet response to major changes in ambient temperature. Sudden and severe changes in temperature are expected to have large effects on feed intake and growth, and so should serve as a useful model for the study of pullet growth. Coupling such changes in ambient temperature with increases or decreases in dietary energy should enhance or ameliorate such growth responses, depending upon direction of temperature change.

1732

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ABSTRACT Four trials were conducted to note the response of pullets to changes in environmental temperature and energy level at 56 days of age. In each trial, birds were fed diets providing either 2,500 or 3,000 kcal ME/kg throughout rearing, or with a single diet change from 2,500 to 3,000 and 3,000 to 2,500 kcal ME/kg occurring at 56 days. Each of the four diet scenarios was tested with six replicate caged groups each containing 10 pullets. In Trials 1 and 2 environmental temperature was maintained at 18 and 30 C, respectively, to 126 days. In Trials 3 and 4, temperature was changed at 56 days from 18 to 30 C and 30 to 18 C, respectively. Regardless of environmental temperature conditions, diet change per se had minimal effect on growth and development. Rather dietary energy level used from 56 to 126 days had the greatest effect on growth, with birds fed the highest energy content diet generally being heaviest. However, this effect was not significant (P>.05) in all trials, which is probably related to a lack of effect on energy intake under such conditions. Final body weight was more closely associated with energy intake than with protein intake and energy intake was maximized when high-energy diets were used after 56 days of age. Consumption of high-energy diets after 56 days, regardless of trial conditions, always resulted in increased carcass fat content at 126 days. It was concluded that abrupt and major changes in environmental temperature or dietary energy as used in these trials have little deleterious effect on pullet development. Conditions prevailing during later stages of growth have a far greater effect than changes per se in these parameters. {Key words: pullet, energy, environmental temperature, body weight, carcass fat)

1733

DIETARY ENERGY AND PULLET GROWTH MATERIALS AND METHODS

TABLE 1. Diet composition Ingredients and analysis

Starter 1

Grower 3

Starter 2

Grower 4

\wj

Corn Oats Barley Wheat shorts Soybean meal (48% CP) Animal-vegetable fat Limestone Dicalcium phosphate (20% P) Iodized salt DL-methionine Vitamin-mineral premix Analysis Crude protein, %^ ME, kcal/kg Calcium, V? Available phosphorus, %

71.72

64.20 30.00 25.90 17.00 22.00 1.00 1.55 1.40 .30 .10 .75 100.00 20.20 2,503 1.04 .44

30.00 1.50 1.60 1.60 .30 .05 .75 100.00

30.00 35.38 19.00 10.50 1.00 1.50 1.50 .30 .07 .75 100.00

4.00 19.00 1.00 1.60 1.60 .30 .03 .75 100.00

19.85 3,020 1.00 .44

16.20 2,508 1.00 .45

16.05 3,025 .96 .43

Supplied per kilogram of diet vitamin A, 8,000 IU; vitamin D, 1,600IU; vitamin E, 11.0IU; vitamin K (Hetrezeen), 1.5 mg;riboflavin,9.0 mg; d calcium pantothenate, 11.0 mg; vitamin B 1 2 , 13.0 |ig; niacin, 26.0 mg; choline CI, 900 mg; folic acid, 1.5 mg; biotin, .25 mg; santoquin, 125 mg; manganese, 50 mg; selenium, .1 mg; zinc, 50 mg; copper, 5.0 mg; iron, 30 mg. Determined; other values calculated.

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Nine-hundred and sixty day-old White Leghorn pullets of a commercial strain were wing-banded, weight-sorted, and randomly distributed to cages maintained in one of two identical environmentally controlled rooms. These 960 pullets were used in one of four separate trials. For the first 48 h, birds were subjected to constant light at 100 lx, and thereafter daily photoperiod was reduced to 8 h at 10 lx. After a conventional brooding period of 28 days, the environmental temperature in one room was reduced to 18 C, whereas the alternate room was maintained at 30 C to trial termination at 126 days. These room temperatures were maintained by varying degrees of supplemental heating. Four separate trials were conducted, involving potential change in environmental temperature at 56 days. Temperature changes, where appropriate, were accommodated by moving birds between the two rooms. Because rooms were not replicated, there is no statistical inference across these trials. In Trials 1 and 2, birds were maintained at constant 18 and 30 C, respectively, to 126 days. In Trials 3 and 4, birds were subjected to environmental changes at 56 days, involving 18 to 30 C and 30 to 18 C, respectively.

Within each of the four trials, birds were assigned one of four dietary treatments. These treatments were consistent across trials, and involved diets providing different levels of energy. Birds in Treatments 1 and 2 were offered diets providing 2,500 and 3,000 kcal ME/kg, respectively, throughout the 126-day rearing period. In Treatments 3 and 4, birds were subjected to diet changes at 56 days of age. In treatment 3 birds were moved from the low- to high-energy diet series; the reverse was adopted for Treatment 4. In each trial, birds were fed starter diets to 56 days of age, and corresponding grower diets thereafter to 126 days (Diets 1 to 4, Table 1). Within each trial, each treatment was replicated with six groups of 10 birds per 60 x 50 cm cage. Birds had free access to feed and water throughout the trial period. Birds were group weighed at 28 days, and thereafter individually at 14-day intervals. Birds were also weighed at 63 days of age, which was 7 days after the diet or environmental changes, so as to more closely observe effects of diese treatments. Feed intake was recorded over the entire starter (0 to 56 days) and grower periods (56 to 126 days). Shank length was also measured at 56 and 126 days.

1734

LEESON AND CASTON

At 126 days, two birds from each replicate cage were selected at random for whole-body chemical analysis. Birds were killed by cervical dislocation without loss of blood and frozen prior to grinding and freeze-drying to constant weight. Following regrinding of dry samples, analyses were conducted for crude protein (Kjehl-Foss, Association of Official Analytical Chemists, AOAC, 1975) and etherextractable hpid (AOAC, 1975).

For each trial, cage was considered the experiment unit and a one-way ANOVA (SAS Institute, 1981) was carried out for both performance and calculated response variables. These included body weight comparisons made before temperature change, at Days 1, 28, 42, and 56 and after temperature change at Days 63, 70, 84, 98, 112, and 126. Shank length measurements were made and compared at 56 and 126 days, and carcass protein and fat were compared at 126 days. Nutrient intake was assessed in terms of feed intake, energy intake, and protein intake between 0 to 56 days, 56 to 126 days, and 0 to 126 days. Means of response variables having a significant F test were further analyzed using Duncan's multiple range test (Duncan, 1955). RESULTS

Body weights of the growing pullets from the four trials are shown in Table 2. In Trial 1, pullets maintained at constant 18 C and fed the higher energy diets were heavier at 56 days of age. At 126 days, pullets were smaller (P<.01) when subjected to a diet change of 3,000 to 2,500 kcal ME/kg at 56 days. In Trial 2, when birds were held at constant 30 C throughout rearing, dietary energy level generally had little effect on growth. There was an indication of increased early growth rate with higher energy diets, although this effect was lost after 42 days of age. In Trial 3, birds were maintained in the cool 18 C environment to 56 days, and then subjected to 30 C through to 126 days. As in Trial 1, birds reared in a cooler environment to 56 days were heavier during the time they were offered diets of higher energy level (P<.01), although this effect was lost when birds were moved to a

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Statistical Analysis

warmer environment (30 C) regardless of dietary energy level. Conditions in Trial 4 were comparable with those used in Trial 2 during 0 to 56 days. Again there was an indication of increased early growth rate (42 days) in response to higher diet energy, although this effect reversed by 56 days such that birds reared on 2,500 kcal ME/kg were heavier. Data from Trial 2 (P>.05) confirmed this trend. However, after environmental temperature was reduced from 30 to 18 C at 56 days, the heaviest pullets at 126 days were those offered the highest energy diets from 56 to 126 days (P<.01). Because protein level of diets was fixed, variation in protein intake relates to corresponding changes in feed intake (Table 3). When the dietary energy level was held constant to 126 days, there was a consistent trend across all trials for birds to consume less feed when the dietary energy level was at 3,000 versus 2,500 kcal/kg. However in Trials 1, 3, and 4, such reduced feed intake of the high-energy feed was associated with increased energy intake (P<.01). In view of these results, changing diet energy level from 2,500 to 3,000 kcal ME/kg and vice versa caused predictable changes in feed intake (P<.01) suggesting no prolonged effect of prior levels of satiety or gut-fill. Because birds normally consume more feed from 56 to 126 days of age than they do from 0 to 56 days of age, it is not too surprising that energy level of the diet offered from 56 to 126 days has a major influence on intake over the 0- to 126-day period. Only in Trial 3 was there an apparent effect of diet change on 0- to 126-day energy intake. Thus, birds consumed more energy when offered a high-energy diet from 0 to 126 days, compared with birds fed the diets that were changed from 2,500 to 3,000 kcal/kg. Regardless of environmental conditions, birds fed a diet of 2,500 kcal ME/kg throughout rearing were consistently leaner than contemporaries fed the higher energy feed throughout (Table 4). This effect was significant in Trial 1 (P<.01) and Trial 3 (P<.05). Pullets fed the low-energy versus high-energy diet from 56 to 126 days were also leaner at 126 days (P<01 for Trials 1 and 4) again suggesting that nutrient intake in the later part of growth overwhelms any effect of early nutrition in terms of carcass composition around the time of maturity.

1735

DIETARY ENERGY AND PULLET GROWTH

DISCUSSION

Leeson and Summers (1989) concluded that under hot daily cyclic (32 to 22 C) conditions, pullet growth was maximized with high-energy diets related to increased energy intake, especially as birds approached maturity. In the

TABLE 2. Effect of dietary energy and environmental temperature on body weight of Leghorn pullets Dietary ME (kcal/kg) 0 to 56 days

56 to 112 days

1

42

28

63

56

Day!s of age 70

84

98

112

126

1,398* 1,434* 1,386* l,322 b

f\r-nrAn,

Trial 1 18 C 2,500 3,000 2,500 3,000 Significance

vg; 2,500 3,000 3,000 2,500 SD

Trial 2 30 C 2,500 3,000 2,500 3,000 Significance

2,500 3,000 3,000 2,500 SD

b

31.2

724 733 705 716 NS 23.6

830 842 816 822 NS 26.0

1,024 1,015 977 996 NS 37.9

1,180 1,184 1,162 1,145 NS 36.0

1,292 1,303 1,274 1,254 NS 37.5

8.4

409 399 383 410 NS 23.6

577 552 578 569 NS 22.9

665 641 670 659 NS 25.9

762 728 753 753 NS 27.0

921 882 909 928 NS 35.3

1,042 1,008 1,036 1,051 NS 36.4

1,145 1,122 1,143 1,149 NS 32.3

1,266 1,218 1,245 1,228 NS 38.1

38.3 38.3 39.0 38.1 NS .9

278 b 244* 220 b 246*

409*b 418*b 398b 431*

587° 623*b 593 bc 638*

**

*

**

26.4

685 710 683 713 NS 22.7

772 785 762 797 NS 24.2

940 948 918 950 NS 29.8

1,073 1,053 1,047 1,087 NS 33.6

1,177 1,163 1,160 1,191 NS 34.7

1,270 1,271 1,263 1,271 NS 49.1

38.9 38.2 38.3 38.1 NS 1.2

231 239 233 218 NS 21.0

399b 494* 402 b 461*

565* 549*b 572* 515 b

658* 665* 686* 601 b

763*b 776* 793* 720 b

937*b 967* 973* 905 b

*

*

*

1,223 1,242 1,245 1,175 NS 46.6

U86b 1,371* 1,366* l,251 b

**

1,080 1,122 1,135 1,070 NS 48.5 39.0

39.3 39.5 39.2 39.3 NS 1.3

234 237 224 239 NS 11.8

423 426 406 433 NS 17.7

608* 630* 577 b 644*

38.4 38.2 38.8 38.3 NS .9

236 b 245*b 236 b 255*

**

**

**

48.5

Trial 3 18 to 30 2,500 3,000 2,500 3,000 Significance

2,500 3,000 3,000 2,500 SD

Trial 4 30 to :18 C1 2,500 2,500 3,000 3,000 2,500 3,000 3,000 2,500 Significance SD

12.8

20.0

28.3

34.2

40.1

41.0

*

"^Means within columns and trials with no common superscripts are significantly different (P<05). temperature changed at 56 days. *P<05. **P<.01.

** 56.7

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present trials, when birds were held at a constant high temperature of 30 C, the dietary energy level generally had no effect on body weight throughout rearing. As suggested by Leeson and Summers (1989) this situation may relate to almost perfect adjustment of feed intake in relation to maintaining constant energy intake in this 30 C environment (Table 2, Trial 2). Final 126-day body weight did not seem to relate to protein intake and, as suggested by Leeson and Summers (1989), it seems unlikely that excessive protein intake, as occurs with lower energy diets, is useful in stimulating growth of the pullet. When birds were reared in a constant cool environment of 18 C (Trial 1) high-energy diets were obviously advantageous in promot-

Few differences were observed in shank length, which is assumed to be a measure of skeletal development, and so only data recorded at 56 and 126 days are shown in Table 5. Birds fed the high-energy diets to 56 days generally exhibited greater shank length (P<.01, Trials 1 to 3) although by 126 days, diet treatment had no effect (P>.05) on this parameter.

1736

LEESON AND CASTON

TABLE 3. Feed and nutrient intake of Leghorn pullets subjected to various environmental temperatures and fed diets of varying energy levels Protein intake per bird

Energy intake per bird

Feed intake per bird

0 to 126 0 to 126 0 to 56 56 to 0 to 56 56 to Dietary ME 56 to 0 to 126 0 to 56 56 to 126 days days 126 days days days days 126 days days 0 to 56 days 126 days days (Va\

(kcal/kg) Trial 1 18 C 2,500 3,000 2,500 3,000 Significance

2,500 3,000 3,000 2,500 SD

Trial 2 30 C 2,500 3,000 2,500 3,000 Significance

2,500 3,000 3,000 2,500 SD

Trial 3 18 to 2,550 3,000 2,500 3,000 Significance

30 C 1 2,500 3,000 3,000 2,500

SD Trial 4 30 to 18 C 2,500 2,500 3,000 3,000 3,000 2,500 2,500 3,000 Significance SD

- (Meal)

\<^&)

— (kg)-

2.09* 1.96b 2.00b 1.95b

5.90* 5.02c 4.95 c 5.43 b

7.99* 6.98c 6.95° 7.38 b

5.24b 5.91* 5.02c 5.90*

14.80* 15.16* 14.95* 13.59b

20.04b 21.07* 19.97b 19.49b

.39* .36 b .36 b .36 b

.94* .80° .79° .86 b

1.33* 1.16c 1.16= 1.23b

**

**

**

**

**

**

**

**

**

1.87* 1.61b 1.89* 1.68b

4.18* 3.58b 3.58b 4.11*

6.05* 5.19° 5.47 b 5.79*

4.69 b 4.88 b 4.73 b 5.07*

.67* .57 b .57 b .66*

1.01* .87s .92 b N.97 b

**

**

**

**

**

**

.16

15.17 15.69 15.55 15.36 NS .60

.35* .30 b .35* .31 b

**

10.48 10.81 10.82 10.29 NS .50

.01

.03

.04

.69* .59 b .60 b .69*

1.06* .95 b .97 b 1.05*

.46

.37 .36 .37 .35 NS .01

.06

.13

.16

.16

.37

.45

.01

.03

.02

.06

.19

.24

2.01 1.94 2.00 1.92 NS .07

4.31* 3.69b 3.75 b 4.33*

6.31* 5.64b 5.76 b 6.25*

5.03b 5.87* 5.01 b 5.81*

10.78* 11.15b 11.34b 10.84*

15.81° 17.02* IMS 1 * 16.65*b

**

**

**

*

**

1.83* 1.66b 1.85* 1.60b

5.28* 4.74 b 4.85 b 5.07*

7.10* 6.41 b 6.71 b 6.67b

4.57° 5.02* 4.64 bc 4.83*b

13.22b 14.33* 14.66* 12.70*

17.78b 19.35* 19.30* 17.53b

.34* .31 b .34* .30 b

.84* .76 b .78 b .81*

1.18* 1.09b 1.12b l.llb

**

**

**

**

**

**

*»

**

**

.07

.12

.17

.16

.23

.21

.21

.33

.49

.64

.01

**

.02

.03

.03

""^Means within columns and trials with no common superscripts are significantly different (P<05). temperature changed at 56 days. *P<05. **P<.01.

**

.04

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difference in body weight and nutrient intake of birds reared at 18 versus 30 C. Likewise, the environmental temperature from 56 to 126 days seemed to have the greatest effect on these parameters when changing environmental conditions are considered (Trial 3 versus 4, Tables 2 and 3). It was originally assumed that pullet growth may be most impeded by a combination of elevated environmental temperature and reduced diet energy level, because the pullets' energy requirements should be reduced and birds would be accustomed to consuming very little feed. In fact, such changes in diet and environment had no significant effect on pullet growth (Table 2), with birds showing only

ing growth. The worst scenario for growth occurred with birds moved from high- to lowenergy diets at 56 days, as these birds exhibited a 15% reduction in 56- to 126-day growth relative to birds maintained on the high-energy diet during this period. This reduced growth from 56 to 126 days was directly associated with reduced energy intake (P<.01, Table 3). This slower growth was associated with increased protein intake (P<.01, Table 3) relative to birds fed 3,000 kcal ME/kg diet throughout rearing. These data again confirm the concept that energy intake is a major correlate to growth in the immature pullet. Although statistical comparisons across trials are not valid, it is of interest to note the

1737

DIETARY ENERGY AND PULLET GROWTH

TABLE 4. Effect of diet energy level and environmental temperature on carcass characteristics of Leghorn pullets at 126 days of age Dietary ME 0 to 56 days

56 to 126 days

Protein

Fat

Protein

Fat

60.2" 53.0 b 56.3 ab 59.9 s

34.8bc 42.0a 38.8 ab 33.5C

59.9 56.4 57.2 59.9

34.1 37.9 37.0 33.9

**

**

NS 2.7

NS 3.2

3.4

3.5

Trial 3 18 to 30 C 1

Trial 4 30 to 18 C 1

Protein

Fat

Protein

Fat

33.6" 38.2a 36.7•ab 33.6b

62.0 s 55.7b 55.1 b 64.5a

33.8 ab 38.0 s 38.6a 29.5 b

2.8

3.9

4.0

(% DM) • 60.1a 56.1 b 58.5;ab 60.8a 2.4

a_c

Means within columns with no common superscripts are significantly different (P<05). temperature changed at 56 days. *P<05. **P<01.

slightly depressed energy intake on 2,500 versus 3,000 kcal ME/kg diet after 56 days (Trial 3, Table 3). Similarly, it was anticipated that pullet growth would be maximized in Trial 4, when after 56 days birds were subjected to low temperatures and a change from a low- to high-energy diet (Table 2). Again, the diet effect had no influence (P>.05) on body weight at 126 days or on energy intake from 56 to 126 days (Trial 4, Table 3). These data suggest that dietary or environmental temperature changes or both as used in these trials have little effect on early growth of die pullet, and it is the actual conditions that prevail during late growth that are most

influential in tfiis regard. Contrary to the results of Mowbray and Sykes (1971), the data reported here tend to support the observation of Okumura et al. (1988) with laying hens, that the adaptation of birds to changing environmental temperature in terms of energy intake adjustment, is quite rapid. Sykes (1977) intimates that adjustments of feed intake to sudden changes in environmental temperature may in fact be a correlate of the efficiency of adaptation of water intake under such conditions. Altfiough diet and environmental treatment did not always have significant effects on growtii and development, mere were often

TABLE 5. Effect of diet energy level and environmental temperature on shank length of Leghorn pullets Dietary ME 0 to 56 days

56 to 126 days

(kcal/kg) 2,500 2,500 3,000 3,000 2,500 3,000 3,000 2,500 Significance SD

Trial 2 30 C

Trial 1 18 C 56 days

126 days

56 days

126 days

72.3C 81.l a 71.2C 78.2b

99.3 100.5 101.6 100.3

81.6" 82.2'ab 80.8b 83.4 s

101.4 100.9 100.4 101.6

1.4

NS 1.3

**

NS 1.5

Trial 3 18 to 30 C 1

Trial 4 30 to 18 C 1

56 days

126 days

56 days

126 days

101.5 100.9 100.8 101.8

80.9 81.4 82.2 80.9

100.1 99.4 99.3 100.2

NS 1.1

NS 1.9

NS 1.5

(mm) 73.8 b 81.8a 72.5 b 81.2 a

1.2

1.1 "^Means within columns with no common superscripts are significantly different (P<05), temperature changed at 56 days. *P<05. **P<01.

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(kcal/kg) 2,500 2,500 3,000 3,000 3,000 2,500 2,500 3,000 Significance SD

Trial 2 30 C

Trial 1 18 C

1738

LEESON AND CASTON

ACKNOWLEDGMENT

This work was supported by the Ontario Ministry of Agriculture and Food.

REFERENCES Association of Official Analytical Chemists, 1975. Official Methods of the Association of Official Analytical Chemists. 11th ed. Association of Official Analytical Chemists, Washington, DC. Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1-42. Leeson, S., and J. D. Summers, 1989. Response of Leghorn pullets to protein and energy in the diet when reared in regular or hot-cyclic environments. Poultry Sci. 68:546-557. Mowbray, R. M., and A. H. Sykes, 1971. Egg production in warm environmental temperatures. Br. Poult. Sci. 12:25-29. Muramatsu, T., and S. Isariyodom, 1989. Computersimulated growth prediction of replacement pullets with special reference to seasonal changes in feed intake. Poultry Sci. 68:771-780. Okumura, J., N. Mori, T. Maramatsu, and I. Taskaki, 1988. Analysis of factors affecting year-round performance of Single Comb White Leghorn laying hens reared under an open-sided housing system. Poultry Sci. 67:1130-1138. SAS Institute, 1981. SAS® for Linear Models. SAS Institute, Inc. Cary, NC. Scott, T. A., and D. Balnave, 1988. Comparison between concentrated complete diets and self-selection for feeding sexually-maturing pullets at hot and cold temperatures. Br. Poult. Sci. 29:613-625. Soller, M., Y. Eitan, and T. Brody, 1984. Effect of diet and early quantitative feed restriction on the minimum weight requirement for onset of sexual maturity in White Rock broiler breeders. Poultry Sci. 63: 1255-1261. Sykes, A. H., 1977. Nutrition-environment interactions in poultry. Pages 17-29 in: Nutrition and the Climatic Environment. W. Haresign, H. Swan, and D. Lewis, ed. Butterworths, London, England.

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changes observed in carcass composition of the 126-day-old bird, suggesting possible effects on subsequent maturity and reproductive characteristics (Table 4). Birds with the most carcass fat, regardless of environmental temperature, were those fed high-energy diets from 56 days of age. The dietary energy level used up to 56 days had little effect on 126-day carcass composition, and there was little variation in results for any treatment across the various trials. The question of carcass composition at maturity as it affects subsequent reproductive fitness is open to question, as both fat and lean body mass have been suggested as meaningful correlates to onset of maturity in poultry (Soller et al., 1984). The present data suggest that the magnitude of changes in dietary energy or environmental temperature or both, at 56 days as used in these trials have relatively minor effects on growth and development of the Leghorn pullet. Absolute diet or environmental conditions prevailing during the 56- to 126-day growing period overwhelm any prior effects or any response to changes per se in diet or environment.