Broiler Performance, Bodyweight Variance, Feed and Water Intake, and Carcass Quality at Different Stocking Densities

Broiler Performance, Bodyweight Variance, Feed and Water Intake, and Carcass Quality at Different Stocking Densities J. J. R. Feddes,*,1 E. J. Emmanuel,* and M. J. Zuidhof *Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada, T6G 2P5; and Livestock Development Division, Alberta Agriculture, Food and Rural Development Edmonton, Alberta, Canada, T6H 5T6 ABSTRACT The effects of four stocking and water nipple yield of broilers per unit of floor space was highest (46.0 densities on broiler performance and carcass traits were measured in two trials. The stocking densities of kg/m 2 ). The coefficient of variation for BW was higher in the treatment with 11.9 birds/m 2 (15.3 %) than in the 23.8, 17.9, 14.3, and 11.9 birds/m 2 corresponded to 260, other treatments (13.0%). The birds in the treatment with 195, 156, and 130 birds per pen, respectively. The water 11.9 birds/m 2 consumed the least feed (2,993 g/bird) and nipple densities were 5, 10, 15, and 20 birds per water those in the 14.3 birds/m 2 treatment consumed the most nipple. Birds in Trial 1 were processed at Day 39 and feed (3,183 g/bird). The amount of water consumed and those in Trial 2 were processed at Day 42. Water and feed the water to feed ratio was highest in the 23.8 birds/m were provided ad libitum and light was provided 23 h/ d. Water nipple density had no effect on broiler performance or carcass quality. Birds grown at 23.8 birds/m 2 had no effect on mortality, breast yield, treatment (5,546 ml/bird and 1.85 ml/g, respectively). had lower BW (1,898 g) and carcass weights (1,334 g), carcass grading, incidence of scratches, or carcass quality. whereas birds grown at 14.3 birds/m 2 had the highest It was concluded high yield per unit area with good BW (1,985 g) and carcass weights (1,432 g). Although the treatment with 23.8 birds/m 2 gave the lowest BW, the carcass quality could be achieved when ventilation rate and air circulation were adequate. (Key words: broiler management, stocking density, body weight, water, feed consumption) 2002 Poultry Science 81:774 779 INTRODUCTION To achieve their genetic potential for growth, broilers must be provided with optimal environmental conditions. Any deviation from optimal conditions can result in decreased performance. High stocking densities can contribute to reduced performance due to a number of factors. One key factor affecting performance is high environmental temperature in the microclimate of the bird. In a high stocking density situation, airflow at the level of the bird is often reduced, resulting in reduced dissipation of body heat to the air. Other factors associated with high stocking densities that may contribute to reduced performance include poor air quality due to inadequate air exchange, increased ammonia, and reduced access to feed and water. The overall effect on broiler chickens of reducing floor space can be reduced growth rate, feed efficiency, liveability, and, in some cases, carcass quality (Puron et al., 1995). 2002 Poultry Science Association, Inc. Received for publication May 15, 2001. Accepted for publication December 28, 2001. 1 To whom correspondence should be addressed: john.feddes@ ualberta.ca. Assuming no change in performance, increasing stocking density will result in higher profitability per kilogram of chicken produced (Figure 1). At stocking densities ranging from 10 to 20 birds per m 2, Puron et al. (1995) observed a linear reduction in BW and feed intake of male broilers but no differences in feed conversion (FCR) or mortality by 7 wk of age. They demonstrated a similar, but nonsignificant, response in female broiler BW. In order to maximize profit, Puron et al. (1995) recommended a stocking density of 17 and 19 birds/m 2 for males and females, respectively. Due to reductions in fixed costs there is, however, an optimium stocking density that will maximize profitability because bird performance is negatively affected at higher stocking densities. The effect of various stocking densities on carcass quality remains to be determined. This study was undertaken to investigate the effects of stocking and water nipple density on BW, water consumption (WC), and carcass quality. MATERIALS AND METHODS Experimental Design A4 4 factorial design was used, with four levels of stocking density and four water nipple densities (Table Abbreviation Key: FC = feed consumption; FCR = feed conversion ratio; WC = water consumption. 774

BROILER STOCKING DENSITY 775 In the center of each pen, a polyvinyl chloride water nipple system was installed. The number of evenly spaced water nipples varied from pen to pen to obtain a bird per water nipple ratio of 5, 10, 15, or 20 (Table 1). A calibrated, 200-L plastic barrel was connected to each pen. Ad libitum WC was recorded daily by reading the level of the water remaining in the barrel. The barrel was manually refilled when the level decreased below the anticipated WC of the next day. A margin of safety was included. Stocks and Housing FIGURE 1. Sensitivity of total cost of production to stocking density of broilers, assuming no reduction in the performance of the birds (M. J. Zuidhof, 2001, unpublished data. Chickcop broiler chicken production cost model. Alberta Agriculture, Food and Rural Development and Alberta Chicken Producers, Edmonton, AB, Canada). 1). The experiment was repeated over time. Water nipple densities were 5, 10, 15, and 20 nipples per bird. The four stocking densities were 23.8, 17.9, 14.3, and 11.9 birds per m 2. The inverse of these densities represents a linear change in space allocation to the birds (0.042, 0.056, 0.070, and 0.084 m 2 /bird, respectively). Thirty-two pens were used for each of two trials. The pens measured 2.43 5.79 m. was calculated by subtracting 3.0 m 2 of unusable space (feeder area and 15 cm along the walls) from the total floor area. In order to maintain the correct stocking density, a 0.6 m high moveable partition was installed at the rear of the pen, which was moved to adjust the stocking density whenever the stocking density changed by 0.005 m 2 /bird due to mortality. Source of variation TABLE 1. Experimental design 1 Bird density (D) 2 3 Nipple density (N) 3 3 Replicate pens (P) 4 1 Replicate experiments (T) 1 D N 9 D P 3 D T 3 N P 3 N T 3 P T 1 D N P 9 D N T 9 D P T 3 N P T 3 D N P T (error) 9 Total 63 1 Four levels of stocking density and four levels of water nipple density in a 4 4 factorial experimental design replicated over time. The entire experiment was replicated in two successive 8-wk periods. 2 Four levels of stocking density: 23.8, 17.9, 14.3, and 11.9 birds/m 2. 3 Four levels of water nipple density: 5, 10, 15, and 20 birds/nipple. 4 Pen dimensions 2.43 5.79 m. Total feed pan and water line area subtracted from pen area. df The care of the birds was according to the guidelines of the Canadian Council of Animal Care (CCAC, 1999). A total of 12,000 Ross Ross broiler female chicks was grown in two replicate trials. The parent flock of these birds was 46 and 54 wk of age for Trials 1 and 2, respectively. The broilers were brooded together, and at 1 wk of age, the chicks were randomly assigned to treatment groups (Table 1). A photoschedule of 23L:1D was used for the duration of both trials. Feed was provided ad libitum via four tube-type pan feeders per pen. A starter diet (3,200 kcal ME/kg, 22% crude protein) was fed from 0 to 21 d, followed by a grower diet (3,200 kcal ME/kg, 20% crude protein). The diets included zinc-bacitracin (0.75 g/kg) to prevent necrotic enteritis. Total feeder space was 450 cm per pen. Body weights and feed consumption (FC) were recorded weekly to determine FCR. Each 16-pen room was ventilated by four, 600-mm exhaust fans (capacity of 3,000 L/s) and four, 450-mm exhaust fans (capacity of 1,200 L/s). A fan was mounted at one end of each pen and provided additional air movement and cooling for the birds. To allow for a sufficient amount of inlet air, four air inlets per room were available in the roof. At full capacity, the ventilation rate was estimated at 16,800 L/s (5.6 L/s per bird) at a negative pressure of 30 Pa between inside and outside of the bird airspace. This rate was higher than the recommended rate of 2.4 L/s (Canadian Farm Building Handbook, 1988). Temperature control was achieved through thermostatically controlled fans and a central forced-air heating system. Daily maximum and minimum temperatures inside and outside the barn were recorded during both trials. In Trials 1 and 2, the mean daily maximum temperatures for the last 20 d were 25.7 and 29.3 C, respectively. All mortalities were weighed, tagged, and examined by a veterinarian to determine the cause of death. Broilers that failed to thrive were culled, weighed, tagged, and also examined by a veterinarian. Birds were individually weighed on Day 37 in Trial 1 and on Day 39 in Trial 2. In both trials, 224 broilers were selected (eight per pen) within a range of 1,800 to 1,899 g, and were processed to examine carcass quality. The data recorded from these broilers included carcass weight, breast yield and area, thighs, legs, and wing measurements. On Day 38 of Trial 1 and Day 42 of Trial 2, the

776 FEDDESETAL. remaining broilers were shipped to a processing plant. 2 At the plant, birds were processed as 32 separate lots (pens). On the processing line, the number of birds with severe (deep) scratches, light (surface) scratches, old (occurred before shipping) and new (occurred during shipping) scratches were recorded for each lot. The number of carcasses that were condemned, contaminated, or requiring trimming was recorded for each lot. After air chilling of the carcasses, the number of birds and eviscerated carcass weights were recorded. Statistical Analyses Trials 1 and 2 were identical replicates, except for the environmental temperatures and the dates of processing. Data from Trial 1 and 2 were treated as separate blocks, and are presented separately in the tables, to demonstrate these block effects. A two-way analysis of variance was used to analyze the data, with each replicate trial treated as a block. The general linear models procedure of SAS software (SAS Institute, 1992) was used. Sources of variation were stocking density and nipple density. Differences among treatment and interaction means were separated by t-tests, using the pdiff option of the least squares means statement of the general linear models procedure of SAS software (SAS Institute, 1992). In any analysis of variance, an assumption that needs to be satisfied is that the sample data submitted for analysis are normally distributed. In order to satisfy this assumption, percentage data are often transformed by an arcsin-square root transformation. The univariate procedure of SAS software (SAS Institute, 1992) was used to test for normality. Because the arcsin square root transformation did not improve the normality of the percentage data reported in this experiment, the data were analyzed and are presented as untransformed. Correlation coefficients for WC, feed intake, BW, eviscerated weight mortality, and condemnations were computed with the REG procedure of SAS software (SAS Institute, 1992). Differences were considered significant at P < 0.05. RESULTS AND DISCUSSION Stocking Density and Live Performance At 37 d of age in Trial 1 and 39 d of age in Trial 2, the average BW were almost identical at 1,944 and 1,924 g, respectively (Table 2). The average BW of the birds from Trial 2 were lower than those from Trial 1 (Table 2), even though birds in Trial 2 were 2 d older at time of individual weighing. According to target growth curve (Ross Breeders, 1999) the birds in Trial 2 at Day 39 should have been 124 g heavier (2,068 g) than those in Trial 1 (Day 37). The lower BW in Trial 2 may be attributed to higher environmental temperatures that occurred during Trial 2 compared to Trial 1. Because the decreased performance 2 Lilydale Cooperatives Ltd., Calgary, AB, Canada. in Trial 2 occurred in all four treatments, it appears that birds in the high stocking density (23.8 birds/m 2 ) treatment were no more affected by high temperature than those in the other treatments, likely because of the high ventilation rate used and air movement at the level of the birds. Production (live bird mass) per unit area was 46.0, 34.6, 28.6, and 22.9 kg/m 2 for densities of 23.8, 0.56, 14.3, and 11.9 birds/m 2, respectively. In Trial 1, birds housed at a stocking density of 14.3 birds/m 2 had significantly higher BW (1,995 g) than those in the other treatments (Table 2). Although not significant in Trial 2, live performance appeared similar to that observed in Trial 1. Birds housed at 14.3 birds/m 2 were almost 100 g heavier than those in the 23.8 birds/m 2 treatment. In Trial 2 and overall, the CV for BW (relates inversely to flock uniformity) was higher (15.3%) in the lowest stocking density treatment than in the other three stocking density treatments, in which the CV for BW ranged from 13.0 to 13.6 (Table 2). The lower BW in the 23.8 birds/ m 2 treatment may be explained by the close proximity of the birds during growth. Bolton et al. (1972) reported a similar result. The higher variability in BW in the 11.9 birds/m 2 treatment might have resulted from the greater floor space allowing the fast-growing birds to grow to their potential; however, the mean BW was not significantly higher in the lowest stocking density treatment as compared to the highest stocking density treatment. Live performance was not affected by water nipple density (data not shown). Feed and Water Consumption Shanwany (1988) indicated that as stocking density increases, feed intake decreases, because physical access to feed and water is impeded. However, in this study, increasing stocking densities did not decrease FC. In this experiment, the maximum distance from a feeder was less than 1.5 m. When some birds may have to travel farther to access a feeder, or if feeder space is limiting, FC may be negatively affected by increased stocking density. Birds in the 14.3 birds/m 2 treatment consumed more feed (3,183 g/bird) than birds in all other treatments (Table 3). This increase in intake was likely in response to the increased growth expressed in the 14.3 birds/m 2 treatment. The effect of stocking density on FCR (Table 3) was not significant. The FCR of the birds for all the treatments (Day 7 to end) was 1.71. Cravener et al. (1991) also reported that FCR is not affected by stocking density. The effect of stocking density on WC (Table 3) demonstrates that WC increases at higher stocking densities. Birds housed at 11.9 birds/m 2 consumed less water (5,093 ml/bird) than those in the other treatments (range 5,390 to 5,546 ml/bird). Some of this effect might have been due to lower FC. However, the WC:FC ratio demonstrates clearly that as the stocking density increases, WC increases independently. Although there was a trend toward a decrease in water intake with increasing water nipple scarcity, the effect of water nipple density treat-

BROILER STOCKING DENSITY 777 TABLE 2. The effects of stocking density on production per unit floor area, body weight, and coefficient of variation (CV) 1,2 Yield per unit area (kg/m 2 ) Live weight (g) CV in BW (%) (birds/m 2 Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined 23.8 47.5 a 46.3 a 46.9 a 1,911 b 1,884 1,898 b 12.3 13.7 b 13.0 b 17.9 34.9 b 34.4 b 34.6 b 1,943 b 1,917 1,931 b 13.2 14.0 b 13.6 b 14.3 28.8 c 28.5 c 28.6 c 2,004 a 1,985 1,995 a 13.3 13.5 b 13.4 b 11.9 22.9 d 22.9 d 22.9 d 1,917 b 1,912 1,915 b 14.2 16.4 a 15.3 a Mean 33.5 33.5 1,944 1,924 13.3 14.4 P 0.0001 0.0001 0.0001 0.008 0.0685 0.0006 0.2386 0.0065 0.0023 a-d Means within each column with no common superscript are significantly different (P < 0.05). 2 Trial 1, birds were individually weighed at 37 d and shipped at 38 d of age; Trial 2, birds were weighed at 39 d and shipped at 42 d of age. ment on WC was not significant (Table 4). It was hypothesized that decreasing the number of water nipples available to the birds would decrease the water intake. This was not observed, however, indicating that one water nipple per 20 birds was adequate, in that water intake was not significantly restricted. Mortality The effect of stocking and water nipple density on mortality was not significant. Overall mortalities in Trials 1 and 2 were 2.0 and 4.3%, respectively. The range in mortalities for the treatments in these trials ranged between 1.7 and 2.2% and 3.1 and 5.3%, respectively. Processing Yield Carcass yields of the birds in Trial 2 were higher than in Trial 1 because the birds were shipped 4 d later. There was no difference in breast muscle yield and breast muscle area among the four treatments. The mean breast muscle weight was 336 g (range between 332 and 341g) and the mean breast muscle area was 201 cm 2 (range between 200 and 203 cm 2 ). The breast muscle yield as a percentage of carcass weight was 24% for each of the treatments. This result is consistent with the data of Bilgili and Hess (1995), who concluded that stocking density had no effect on breast meat yield. Birds in the 14.3 birds/m 2 treatment had the thickest breast muscle (27.7 mm), whereas the birds in the 11.9 birds/m 2 treatment had the lowest breast thickness (26.4 mm) (Table 5). An increase in stocking density was expected to decrease breast muscle thickness, as the more crowded birds were not expected to grow to their full potential, but was related more to BW than stocking density in this trial. The breast muscle yield was approximately 19% of live weight. The average BW of the birds on the day of commercial processing was 2.01 kg for Trial 1 and 2.14 kg for Trial 2. The distribution of eviscerated body weights and the coefficient of variation followed the same trend as the live weight data. Overall, the 14.3 birds/m 2 treatment had the highest eviscerated BW (1,432 g) (Table 6). The CV in eviscerated BW showed that the 11.9 birds/m 2 in the combined trial data had the highest degree of variability (14.6 %), whereas the CV values for the 23.8, 17.9, and 14.3 densities were not significantly different (ranged from 12.9 to 13.4%). These values were similar to the CV values of BW indicating that eviscerated carcass weight CV can be used as a good indicator of BW uniformity. Carcass Quality had very little effect on grade or removal of carcasses from the processing line due to contamination and condemnation (Table 7). Percent grade A carcasses in the two trials were 78.8, 77.1, 73.7 and 75.4% for the stocking densities of 23.8, 17.9, 14.3 and 11.9 birds/ m 2, respectively (Table 7). These values are not consistent with those of Proudfoot et al. (1979) who indicated that as stocking density increased, the percentage of grade A carcasses decreased. However, the grading systems have likely evolved significantly in 20 yr. had no effect on the grade of the carcass or the percentage of birds removed from the line. The percentage of condemned carcasses in the 14.3 birds/m 2 treatment in Trial 2 was the lowest (0.8%) whereas the 23.8 birds/m 2 treatment had the highest percentage (4.0%). For the combined trials, there were no differences in the percentage of condemned carcasses. The higher number of condemned carcasses in Trial 2 was primarily due to fecal contamination. Elfadil et al. (1996) reported that an increase in the incidence of scratches was directly associated with increases in stocking density. However, in this study the effect of stocking density on scratches was not significant (Table 8). Summary In contrast to our hypothesis, water nipple density had no significant effects on broiler performance or carcass traits. One water nipple per 20 birds appeared to be sufficient to provide adequate water to broiler chickens to 6 wk. Distribution of the water nipples may be important; however, in these experiments, the birds were unable physically to be more than 1.3 m from the nearest water nipple. In contrast, there was a significant effect of stocking density on broiler performance and carcass traits. Maximum growth was observed at a stocking density of 14.3 birds/m 2. Yield (and gross return) per unit of floor area

778 FEDDESETAL. TABLE 3. The effects of stocking density on feed and water consumption, feed to gain ratio, and water to feed ratio 1,2 Feed consumption Feed conversion Water consumption (g/bird) (feed/gain; g/g) (ml/bird) Water/feed (ml/g) (birds/m 2 ) Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined 23.8 3,039 b 2,967 b 3,003 b 1.72 1.72 1.72 5,505 a 5,588 a 5,546 a 1.81 a 1.88 a 1.85 a 17.9 3,112 ab 3,023 b 3,068 b 1.73 1.72 1.72 5,440 a 5,399 ab 5,420 a 1.75 b 1.76 b 1.75 b 14.3 3,204 a 3,162 a 3,183 a 1.73 1.73 1.73 5,483 a 5,315 ab 5,399 a 1.71 bc 1.68 c 1.70 c 11.9 3,026 b 2,961 b 2,993 b 1.71 1.68 1.70 5,040 b 5,147 b 5,093 b 1.66 c 1.74 bc 1.70 c Mean 3,095 3,028 1.72 1.71 5,368 5,362 1.73 1.77 P 0.0081 0.0125 0.0001 0.3839 0.2805 0.092 0.0003 0.1105 0.0001 0.0014 0.0016 0.0001 a-c Means within each column with no common superscript are significantly different (P < 0.05). 2 Trial 1, birds were shipped at 38 d of age; Trial 2, birds were shipped at 42 d of age. TABLE 4. The effect of water nipple density on water consumption 1,2 Water consumption (ml/bird) Water nipple density (birds/nipple) Trial 1 Trial 2 Combined 5 5,472 5,422 5,447 10 5,394 5,428 5,411 15 5,325 5,330 5,327 20 5,277 5,209 5,243 Mean 5,367 5,347 P 0.1268 0.2453 0.1720 1 Results are presented for each individual trial and combined. 2 Water intake was recorded for 30 d in Trial 1 and for 32 d in Trial 2. was highest at the highest stocking density. Flock uniformity was low at the lowest stocking density. FC decreased as bird density increased from 14.3 to 23.8 birds/m 2 ; however, FCR did not significantly differ among treatments. also affected the WC:FC ratio, with the highest ratio of 1.85 occurring in the highest stocking density treatment. The birds in the second trial only consumed 0.04 ml of water/g of feed more than those in the first trial even though maximum barn temperatures were, on average, 4 C higher in Trial 2 during the last 3 wk of the growing cycle. The effect of stocking density on carcass traits was negligible in this study. Breast yield and carcass quality (% grade A, condemnations, scratches) were not affected by stocking density, in contrast with the results of Proudfoot et al. (1979). Some of the contrast in results may be a function of the ventilation rates used. The high ventilation rate of 5.6 L/s per bird and the air circulation fans were able to remove the heat from the bird microclimate to reduce possible heat stress, even at the highest stocking density. ACKNOWLEDGMENTS The authors acknowledge the financial support of the Alberta Chicken Producers, Lilydale Cooperatives Ltd. and Alberta Agricultural Research Institute. The care and management provided by the staff at the Poultry Research TABLE 5. Effects of stocking density on breast muscle thickness 1,2 Breast muscle thickness (mm) (birds/m 2 ) Trial 1 Trial 2 Combined 23.8 25.4 b 28.4 a 26.9 ab 17.9 25.8 b 27.9 ab 26.8 ab 14.3 27.0 a 28.4 a 27.7 a 11.9 26.1 ab 26.7 b 26.4 b Mean 26.3 28.3 P 0.026 0.035 0.027 a,b Means within each column with no common superscript are significantly different (P < 0.05). 1 Results are presented for each individual trial and combined. 1 Birds in Trial 1 were processed at 38 d of age and at 42 d of age in Trial 2.

BROILER STOCKING DENSITY 779 TABLE 6. The effects of stocking density on eviscerated weight and variation in eviscerated weight 1,2 Eviscerated body weight (g) CV of Eviscerated body weight (%) (birds/m 2 ) Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined 23.8 1,327 b 1,420 b 1,373 b 11.5 14.1 12.9 b 17.9 1,332 b 1,448 ab 1,391 b 12.0 14.5 13.4 b 14.3 1,377 a 1,485 a 1,432 a 13.4 14.3 13.9 b 11.9 1,314 b 1,445 ab 1,380 b 12.0 15.9 14.6 a Mean 1,337 1,450 12.3 14.7 P 0.0062 0.046 0.0005 0.187 0.279 0.04 a,b Means within each column with no common superscript are significantly different (P < 0.05). 1 Data are reported for each individual trial and combined. 2 Birds in Trial 1 were processed at 38 d of age and at 42 d of age in Trial 2. TABLE 7. The effect of stocking density on broiler carcass quality 1,2 Birds removed from Grade A carcasses (%) processing line (%) Condemned carcasses (%) (birds/m 2 ) Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined 23.8 76.1 81.4 78.8 2.2 7.9 5.1 0.5 4.0 a 2.3 17.9 72.8 81.4 77.1 2.4 6.5 4.5 0.7 2.0 b 1.3 14.3 71.2 76.1 73.7 2.2 7.0 4.6 0.6 0.8 b 0.7 11.9 72.7 78.1 75.4 1.5 7.0 4.3 0.2 2.4 ab 1.3 Mean 73.2 79.3 2.1 7.1 0.5 2.4 P 0.55 0.81 0.056 0.7 0.68 0.7 0.55 0.02 0.2 a,b Means within each column with no common superscript are significantly different (P < 0.05). 2 Birds in Trial 1 were processed at 38 d of age and at 42 d of age in Trial 2. TABLE 8. The effect of stocking density on the incidence of scratches 1,2 Light scratches (%) Severe scratches (%) Total scratches (%) (birds/m 2 ) Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined Trial 1 Trial 2 Combined 23.8 29 9 19 3 22 12 32 31 31 17.9 29 11 20 3 21 11 31 32 31 14.3 27 9 18 3 13 8 30 22 26 11.9 24 11 18 4 20 12 28 31 30 Mean 27 10 3 19 30 29 P 0.3 0.84 0.76 0.65 0.29 0.26 0.44 0.5 0.43 2 Birds in Trial 1 were processed at 38 d of age and at 42 d of age in Trial 2. Center was invaluable to the study. The cooperation of the staff at Lilydale Cooperatives Ltd. in Calgary, Alberta was appreciated as the plant operation was altered to accommodate the 32 individual groups on two occasions. REFERENCES Bilgili, S. F., and J. B. Hess. 1995. Placement density influences broiler carcass grade and meat yields. J. Appl. Poult. Res. 4:384 389. Bolton, W., W. A. Dewar, and R. M. Jones. 1972. Effect of stocking density on performance of broiler chicks. Br. Poult. Sci. 13:157 162. Canadian Farm Building Handbook. 1988. Agriculture Canada Research Branch. Canadian Government Publishing Center, Hull, QC, Canada. CCAC. 1999. Guide to the Care and Use of Experimental Animals. Council of Animal Care, Ottawa, Ontario, Canada. Cravener, T. L., W. B. Roush, and M. M. Mashaly. 1992. Broiler production under varying stocking densities. Poult. Sci. 71:427 433. Elfadil, A. A., J. P. Vaillancourt, and A. H. Meek. 1996. Impact of stocking density, breed and feathering on the prevalence of abdominal skin scratches in broiler chickens. Avian Dis. 40:546 552. Proudfoot, F. G., H. W. Hulan, and D. R. Ramey. 1979. The effect of four stocking densities on broiler carcass grade, the incidence of breast blisters, and other performance traits. Poult. Sci. 58:791 793. Puron, D., R. Santamaria, J. C. Segaura, and J. L. Alamilla. 1995. Broiler performance at different stocking densities. J. Appl. Poult. Res. 4:55 60. Ross Breeders. 1999. Ross 508 Ultimate Yield. Ross Breeders, Huntsville, AL. SAS Institute. 1992. SAS/STAT User s Guide, Version 6. ed. Vol. 4. SAS Institute Inc., Cary, NC. Shanwany, M. M. 1988. Broiler performance under high stocking densities. Br. Poult. Sci. 29:43 52.