Laying performance of six pure lines of chickens and four commercial hybrids at the Agassiz Research Centre

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1 Laying performance of six pure lines of chickens and four commercial hybrids at the Agassiz Research Centre F. G. Silversides Agriculture and Agri-Food Canada, Agassiz Research Centre, P. O. Box 1000, Agassiz, British Columbia, Canada V0M 1A0 ( Agassiz Research Centre Contribution no Received 19 February 2010, accepted 23 April Silversides, F. G Laying performance of six pure lines of chickens and four commercial hybrids at the Agassiz Research Centre. Can. J. Anim. Sci. 90: The Agassiz Research Centre keeps six pure lines of high-producing but noncommercial layers. Egg production, body weight, feed consumption and efficiency, and several characteristics of the eggs were measured to 60 wk of age and compared with those of four commercial white- and brown-egg hybrids. Egg production from 20 to 60 wk was highest for the four commercial hybrids, with no difference between them, and was 6 to 11% lower for the pure line white-egg layers, and 7 to 13% lower for the pure line brown-egg layers. The pure line and hybrid white-egg layers had similar body weights, but the pure line brown-egg layers weighed more than the commercial brown-egg hybrid. Feed efficiency was similar for the four hybrids and was generally better for the hybrids than the pure lines, based largely on higher egg production rather than increased feed consumption. The difference between industrial hybrids and the pure lines studied can be attributed to the selection that has been applied as well as to heterosis. Key words: Chicken, genetic resources, Agassiz layer lines Silversides, F. G Rendement de six lignées pures de pondeuses et de quatre ligne es hybrides commerciales a` la station de recherche d Agassiz. Can. J. Anim. Sci. 90: La station de recherche d Agassiz e lève six ligne es pures de pondeuses a` haut rendement, non commerciales. L auteur a mesure la production d œufs, le poids corporel, l ingestion d aliments et l indice de consommation, ainsi que plusieurs parame` tres des œufs jusqu a` ce que les poules atteignent 60 semaines, puis a compare les résultats à ceux des quatre ligne es hybrides commerciales produisantdes œufs blancs ou bruns. Chez les poules hybrides du commerce, le nombre d œufs pondus atteint un maximum entre l aˆ ge de 20 etde 60 semaines, sans variation entre les lignées. Il e tait de 6 à 11% plus faible pour les pondeuses pures d œufs blancs, etde 7 a` 13% plus faible pour les pondeuses pures d œufs bruns. Les ligne es pures etles ligne es hybrides qui pondentdes œufs blancs ontun poids corporel similaire, mais les sujets purs pondant des œufs bruns sont plus lourds que les poules hybrides commerciales. L indice de consommation e tait le même pour les quatre ligne es hybrides, celui des lignées pures étant lége` rementplus faible. On le doitdans une large mesure a` la production accrue d œufs, et non a` l ingestion d une plus grande quantite d aliments. Les diffe rences observées entre les hybrides industriels et les lignées pures re sultent vraisemblablement de la se lection et de l he térosis. Mots clés: Poulet, ressources géne tiques, ligne es de pondeuses d Agassiz In 1946, Canadian Record of Performance programs included 263 breeders of laying chickens (Silversides etal. 2007) but today only two breeding companies supply nearly all of the world s industrial laying hens, including those in Canada. Brands of laying hens are easily recognized as those that were sold by independent breeders several decades ago, but they are now consolidated under Erich Wesjohann (Hy-Line, Lohmann, and H & N) and Hendrix Poultry (ISA, Babcock, Shaver, Hisex, Bovans, and DeKalb). A similar consolidation has occurred in research institutions. Before its incorporation into a North American registry (Somes 1984), the last edition of Crawford s catalogue of poultry stocks kept in Canadian research institutions (Crawford 1981) listed 79 lines of chickens keptby 11 publicly funded research 341 institutions in Canada. Silversides et al. (2008) identified 33 lines of chickens representing 23 independent populations kept by five Canadian institutions. Six of the populations of chickens kept in Canadian research institutions are laying lines maintained at the Agassiz Research Centre, which were acquired by D. McQ. Shaver after his retirement and kept for a number of years before being transferred to Agassiz. These include three lines of White Leghorns (Burgundy, Black, Blue) and one each of Rhode Island Red Abbreviations: B300, Babcock 300; BPR60, Barred Plymouth Rock; CPR, Columbia Plymouth Rock; RIR50, Rhode Island Red; S579, Shaver 579; S2000, Shaver 2000; SW, Shaver White

2 342 CANADIAN JOURNAL OF ANIMAL SCIENCE (RIR50), Barred Plymouth Rock (BPR60), and Columbian Plymouth Rock (CPR). An initial description of the origins and performance of these lines is provided by Silversides etal. (2007). This reportgives a further description of the production characteristics of these lines and relates them to those of three commercial hybrid white-egg layers (Babcock 300, B300; Shaver White, SW; Shaver 2000, S2000) and one commercial hybrid brown-egg layer (Shaver 579, S579). MATERIALS AND METHODS The original populations that were received at the Agassiz Research Centre were reproduced by artificial insemination without selection using 64 males and between 166 and 225 females per line. Each of the males was mated to approximately three females but pedigree records were not kept. Fertile eggs were saved for 6 or 7 d, and incubated by Western Hatchery (Abbotsford, BC). Eggs from B300, SW, S2000 and S579 were obtained from George Ansah (ISA North America, Ithaca, NY 14850, USA) and incubated along with eggs from the pure lines. All chicks were obtained in a single hatch. Chicks were housed randomly by strain in groups of 60 in pulletgrowing cages in a single room with 200 cm 2 per bird. Groups were splitwhen the birds were approximately 6 wk of age to give 400 cm 2 per bird. At16 wk of age, pullets were housed randomly by strain in laying cages in a single room with three birds per cage providing 688 cm 2 per bird. Atapproximately 18 wk of age, 64 males per line were housed individually in cages that provided 1394 cm 2 per bird. Diets (Table 1) were formulated using an Excel Feed Formulation Spreadsheetdeveloped by Evan Thomas (University of New England, Armidale 2351, NSW, Australia) with ingredient nutrient profiles from the National Research Council (1994). Feed and clean water were provided to allow for ad libitum consumption. Chicks were vaccinated for Marek s disease, infectious bursal disease, Newcastle disease, infectious bronchitis, infectious laryngotracheitis, and avian encephalomyelitis. Chicks were exposed to a day length that decreased to 9 h at 2 wk of age and was increased to 14 h at 18 wk. Brooding temperature was initially 338C and was lowered 28C per wk until it reached 218C. All procedures were approved by the Animal Care Committee of the Agassiz Research Centre and followed principles described by the Canadian Council on Animal Care (2009). Data were recorded throughout the trial for 28 cages for each pure line (84 hens) and 26 cages for each hybrid line (76 hens) and on 64 males per pure line. Hens were weighed athousing and both sexes were weighed every 10 wk between 20 and 60 wk of age. Feed consumption was recorded for 1-wk periods atthe same ages for cages of three hens and groups of eight males. Egg production per cage was measured for 5 d per week and extrapolated to 7 d. Sexual maturity was Table 1. Ingredients and principal nutrients in diets fed to 10 strains of layers during the rearing and laying periods Ingredient (%) Wk 0 to 6 Wk 6 to 8 Wk 8 to 15 Wk 15 to 20 Wk 20 to 24 Wk 24 to 32 Wk 32 to 48 Wk 48 to 60 Corn Barley Wheat, hard red Canola meal Meatmeal Soybean meal (47.5% CP) CaP dibasic (18% Ca, 21% P) Vegetable oil Vitamin mineral premix z Limestone Celite y NaCl Lysine (98%) DL-Methionine Choline chloride Calculated nutrients ME (MJ kg 1 ) CP (%) Ca (%) AP (%) z Supplied per kilogram of diet to 20 wk of age: vitamin A, IU; vitamin D3, 2640 IU; vitamin E, 36 IU, choline, 480 mg; manganese, 168 mg; zinc, 216 mg; iron, 96 mg; niacin, 72 mg; ascorbic acid, 60 mg; copper, 18 mg; D-pantothenic acid, 12 mg; riboflavin, 7.2 mg; pyridoxine, 6 mg; menadione, 2.4 mg; thiamin, 1.8 mg; iodine, 1.38 mg; folic acid, 0.72 mg; selenium, 0.48 mg; cobalt, 0.3 mg; biotin, 0.18 mg; vitamin B 12, mg; sodium 960 mg. Supplied per kg of diet from 20 to 60 wk of age: vitamin A, 9600 IU; vitamin D3, 3120 IU; vitamin E, 36 IU; menadione, 2.4 mg; vitamin B 12, mg; riboflavin, 7.2 mg; pantothenic acid, 14.4 mg; niacin, 60 mg; thiamine, 1.2 mg; pyridoxine, 2.4 mg; folic acid, 0.72 mg; biotin, 0.10 mg; zinc, 100 mg; iron, 80 mg; manganese, 100 mg; copper, 12 mg; iodine, 1 mg; selenium, 0.3 mg. y Celite Corp. Lompar, CA

3 SILVERSIDES * PERFORMANCE OF AGASSIZ LAYER LINES 343 determined as the first weeks with 5 and 50% hen-day egg production. On 1 d per week, bulk egg weights per cage were recorded. Bulk egg weights, weekly egg production, and feed consumption data were used to calculate feed efficiency. Egg quality was measured on one egg per cage at30, 40, 50, and 60 wk of age. Eggs were stored overnight at 48C and after removal from the cooler were allowed to sit at room temperature for 1 h before breaking onto a flat surface. Egg weight, yolk weight, and shell weight (after washing in water and drying for several days at room temperature, then 4 h at 1008C) was recorded. Albumen heightwas recorded with a tripod micrometer, and albumen weight was determined by difference from egg, yolk, and shell weights. All data except mortality were analyzed using GLM (Version 9.1, SAS Institute, Inc., Cary, NC) with an ANOVA including the fixed effect of strain. Each threebird female cage or group of eightmale cages was a replicate for measures of egg production, feed consumption, and feed efficiency and individual birds and eggs were the replicates for body weight and egg characteristics. When the model was significant at P B0.05 the means were separated using Duncan s multiple range test. The significance of differences between lines in mortality was tested using contingency chi-square analysis (Zar 1999). RESULTS Of the commercial lines, the brown-egg layer (S579) had the earliest sexual maturity (Table 2) with little difference between the other three lines. Sexual maturity of the pure lines was similar to that of the white-egg commercial lines, with that of the BPR60, RIR50, and Black lines being slightly later. The early sexual maturity of S579 hens resulted in egg production before 20 wk being higher than that of all other lines, but production of all commercial lines after 20 wk was very similar. Hen-day egg production by the six pure lines did not Table 2. Sexual maturity and egg production of six pure lines and four commercial strains of laying hens z differ between week 20 and 48 and averaged 6.8 and 9.0% less than that of commercial lines between 20 and 32 weeks and 32 and 48 weeks, respectively. Late egg production was lower for the pure lines than the commercial lines and overall the hen day egg production of the pure lines was 9.9% lower than that of the commercial crosses. Mortality in each group is not shown, butranged from one S579 hen (of 78) to seven Blue hens (of 84), with no difference between lines being significant. As expected, males and females of the three brownegg pure lines were heavier than those of the White Leghorn lines or commercial crosses (Table 3). Females of the commercial brown-egg line (S579) weighed less than those of the BPR60 and RIR50 at 20 wk and less than all three brown-egg pure lines at 60 wk. Among the brown-egg pure lines, the CPR weighed the least, but gained more weight over the production cycle than any other line or cross. At 60 wk, the Blue line weighed least of the pure-line White Leghorns, and the S2000 was heaviest of the commercial white-egg layers. Although the S579 hens weighed substantially more than the commercial white-egg layers, they gained less than other lines over the production cycle, significantly less than S2000 hens and four of the six pure lines. Birds of both sexes ate less than 100 g per day with the exception of the S2000 and S579 hens, which ate slightly more (Table 4). Of the pure line females, the Black hens ate least, although not significantly less than the other pure line White Leghorns, and the RIR hens ate the most, but not significantly more than the other brownegg pure lines. Consumption by S2000 and S579 was significantly higher than that of other commercial lines, and that by S579 was significantly higher than all lines excepts2000. Feed efficiency was very similar for all four commercial crosses at all times measured with no clear difference between white-egg and brown-egg layers. Feed efficiency was higher for the pure lines than for the commercial crosses. Feed efficiency for the Hen-day egg production Age (wk) at5% Age (wk) at50% Line production production Wk16to20 Wk20to32 Wk32to48 Wk48to60 Wk20to60 Blue White Leghorn 19.3ab 20.5b 0.039cd 0.847cd 0.874b 0.805b 0.844b Burgundy White Leghorn 19.0bc 20.2b 0.070bc 0.854bcd 0.869b 0.745c 0.825bc Black White Leghorn 19.3ab 21.1a 0.028d 0.813d 0.864b 0.758c 0.814bcd Columbia Plymouth Rock 18.8c 20.4b 0.067bc 0.825d 0.835b 0.690d 0.786d Barred Plymouth Rock a 21.0a 0.015d 0.814d 0.832b 0.711cd 0.788cd Rhode Island Red a 20.9a 0.030d 0.852bcd 0.867b 0.752c 0.826bc Babcock bc 20.2b 0.067bc 0.900a 0.956a 0.901a 0.921a Shaver White 18.9c 20.3b 0.073bc 0.890abc 0.935a 0.870a 0.901a Shaver c 20.1b 0.078b 0.896ab 0.943a 0.890a 0.911a Shaver d 19.0c 0.253a 0.924a 0.952a 0.868a 0.917a SEM z Means represent 28 three-bird cages for pure lines and 26 three-bird cages for commercial lines. ad Means in a column followed by a different letter are different at PB0.05.

4 344 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 3. Body weights (g) of six pure lines and four commercial strains of layers Males Females Line Wk 20 Wk 60 Body weightchange Wk 20 Wk 60 Body weightchange n 64 59to63 59to63 78to84 75to82 75to82 Blue White Leghorn 1665c 2082e 403d 1453d 1696e 242de Burgundy White Leghorn 1785c 2324d 527c 1491d 1788d 297bcd Black White Leghorn 1761c 2274d 505c 1561c 1841d 280cde Columbia Plymouth Rock 2137b 2910c 760b 1710b 2108b 393a Barred Plymouth Rock Line a 3104b 837b 1837a 2171ab 339b Rhode Island Red Line a 3234a 956a 1875a 2210a 336b Babcock e 1666e 272cde Shaver White 1467d 1714e 246de Shaver d 1808d 309bc Shaver b 1976c 226e SEM ae Means in a column followed by a different letter are different at PB0.05. Table 4. Feed consumption and feed efficiency of hens of six pure lines and four commercial strains of laying hens CPR and BPR60 lines was the highest at all times measured, and of the pure lines, that for the Burgundy line was the lowest, except at week 60. Egg albumen height declined steadily with age of the hen (Table 5). Thatof eggs from commercial white-egg layers was uniformly high and only slightly higher than that of the pure-line White Leghorns. Albumen height of eggs from BPR60 hens was lower than that of all White Leghorns except the Black line, and that of the CPR, RIR50, and S579 was lowest. Shell and albumen weights increased with age, but by only 6 and 4%, respectively, between 30 and 50 wk (after which both had a slightnon-significantdecline), compared with an overall increase of 19% in yolk weightbetween 30 and 60 wk of age. The interaction between the line and age was significant for egg and yolk weights and is investigated further in Table 6. The principal cause for the interaction is that the eggs from S579 hens at 30 wk are heavier than those from all other lines, but the increase over the production cycle is less, and by 60 wk they are not different from those of any other line. This interaction is even clearer for yolk weight, which is greatestfor S579 hens at30 wk, butis less at50 and 60 wk than that of all pure lines and is not different from commercial crosses. Regressions of egg and yolk weights on age of the hen for each line (Table 7) may more effectively show this difference. All of the regressions for both egg and yolk weights were significant except that for egg weightof S579. Regressions of egg weighton age for the other nine lines were between and g per week with those for the BPR60 and RIR 50 being largest. The age of the hen accounted for and 0.304% of the variation in egg weight for these nine lines, but very little of the variation for eggs from S579 hens. Regressions of yolk weighton age of the hen Daily feed consumption (g) z Feed efficiency (g feed g egg 1 ) Males Females Line Wk 20 to Wk 60 Wk 20 to Wk 60 Wk 30 Wk 40 Wk 50 Wk 60 Blue White Leghorn 96.8a 95.8def 2.13cd 2.13b 2.18cde 2.20bcd Burgundy White Leghorn 97.2a 94.4def 2.04cde 2.11bc 2.26cde 2.44ab Black White Leghorn 92.7b 92.7f 2.10cd 2.16b 2.34abcd 2.31bcd Columbia Plymouth Rock 99.4a 97.3bcd 2.37a 2.37a 2.59a 2.54a Barred Plymouth Rock b 96.8cde 2.32ab 2.21ab 2.49ab 2.36ab Rhode Island Red a 99.7bc 2.20bc 2.10bc 2.35abc 2.31abc Babcock cd 1.97de 1.93cd 1.99e 1.98d Shaver White 93.7ef 1.92e 1.75d 2.08cde 2.02d Shaver ab 2.02de 1.90d 2.05de 1.94d Shaver a 1.99de 1.83d 2.12cde 2.07cd SEM z Feed consumption is daily feed per bird. Means represent 28 three-hen cages for pure lines and 26 three-hen cages for commercial lines and eight groups of eightroosters per line. af Means in a column followed by a different letter are different at PB0.05.

5 SILVERSIDES * PERFORMANCE OF AGASSIZ LAYER LINES 345 Table 5. Quality of eggs laid by six pure lines and four commercial strains of laying hens Albumen heightegg weightshell weightyolk weightalbumen weight n (mm) (g) Line Blue White Leghorn b 58.46cd 5.31c 16.17b 37.08def Burgundy White Leghorn b 59.39bc 5.39c 16.00bc 38.01bc Black White Leghorn c 58.68cd 5.26cd 16.26b 37.17cdef Columbia Plymouth Rock e 58.12d 4.98e 16.81a 36.33f Barred Plymouth Rock cd 59.84ab 5.15d 16.79a 37.89bcde Rhode Island Red de 60.29ab 4.99e 16.34b 38.97a Babcock a 58.08d 5.70b 16.09bc 36.30f Shaver White a 58.21d 5.71b 15.46d 37.04ef Shaver a 59.50bc 5.80b 15.75cd 37.95bcd Shaver e 60.92a 6.21a 15.98bc 38.74ab SEM Week a 56.68c 5.29c 14.40d 36.99b b 57.92b 5.35c 15.90c 36.71b c 61.02a 5.62a 17.06b 38.34a d 61.01a 5.51b 17.35a 38.15a SEM ANOVA P Strain B0.01 B0.01 B0.01 B0.01 B0.01 Age B0.01 B0.01 B0.01 B0.01 B0.01 StrainAge NS 0.02 NS B0.01 NS af Means in a column followed by a different letter are different at PB0.05. mirrored those of egg weight. All 10 regressions were significant but that for S579 was much lower than the others (0.043 versus to g per week of age). The R 2 for this regression was for S579 hens, but from to for the other nine lines. DISCUSSION Silversides et al. (2007) reported production data of the six pure lines kept at the Agassiz Research Centre, but their trial did not include any commercial lines for comparison, and they reported only briefly on management and data recording. Results from this trial Table 6. Egg and yolk weights (g) of eggs laid by six pure lines and four commercial strains of laying hens generally agree with those of Silversides et al. (2007) for egg production, body weight, and egg weight, and confirm that these hens produce eggs at a high rate. Management guides produced by the suppliers of the commercial hybrids include expectations for production (Hendrix Poultry 2010). Although a direct comparison is difficult because the measures reported here are not exactly the same as those reported in the guides (henhoused versus hen-day egg production and weekly egg production versus production over several periods) and the trial was conducted several years ago, whereas the guides are current, it appears that egg production was Egg weightyolk weight Line Wk 30 Wk 40 Wk 50 Wk 60 Wk 30 Wk 40 Wk 50 Wk 60 n 26to28 25to28 26to28 26to28 26to28 25to28 26to28 26to28 Blue White Leghorn 56.43bc bc 60.07bc 14.47b 15.87bc 17.13bc 17.24cd Burgundy White Leghorn 56.88b bc 62.10ab 14.20bc 15.78bc 16.91bcd 17.16cd Black White Leghorn 54.63c abc 60.16bc 13.80c 16.31ab 17.46ab 17.50bc Columbia Plymouth Rock 55.63bc bc 59.91bc 14.60b 16.73a 17.66ab 18.32a Barred Plymouth Rock bc a 62.25ab 14.50b 16.37ab 18.08a 18.26ab Rhode Island Red b ab 63.39a 14.62b 15.73bc 17.26b 17.79abc Babcock bc c 59.26c 14.48b 15.82bc 17.03bc 17.03cd Shaver White 56.04bc c 60.22bc 13.91c 15.14c 16.16d 16.61d Shaver b bc 61.53abc 14.17bc 15.33c 16.46cd 17.00cd Shaver a ab 61.16abc 15.28a 15.77bc 16.34cd 16.52d SEM ad Means in a column followed by a different letter are different at PB0.05.

6 346 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 7. Regression coefficients (b) and coefficients of determination (R 2 ) of egg and yolk weights (g) on age of the hen (weeks) between 30 and 50 wk of age z Egg weightyolk weight Line b R 2 b R 2 Blue White Leghorn 0.147* * Burgundy White Leghorn 0.187* * Black White Leghorn 0.193* * Columbia Plymouth Rock 0.160* * Barred Plymouth Rock * * Rhode Island Red * * Babcock * * Shaver White 0.145* * Shaver * * Shaver * z Sample size is 101 to 110 for each line. *PB0.01. slightly better than expected for these commercial hens. Eggs produced by all four lines were several grams smaller than expected throughout the production cycle. The S579 hens had earlier sexual maturity than other commercial lines, but overall egg production of the four commercial lines was very similar. There was no clear distinction between pure lines and commercial crosses for sexual maturity, but the commercial crosses all produced more eggs than the pure lines. Fairful (1990) summarized reports showing heterosis for egg laying from 3 to 40%, with many estimates being close to 10%, suggesting that the advantage of the commercial lines seen here in egg production may be due to heterosis in addition to the intense selection practiced by the breeding company. These lines had been subjected to mild selection for egg production, early egg size, and egg shell quality before arriving at the Agassiz Research Centre (Silversides et al. 2007) and the current data attest to the success of the breeder. Although it was not the primary aim of this research, the current data provide interesting comparisons between commercial white and brown-egg layers, especially in relation to the pure line White Leghorns and the BPR and RIR breeds that made major contributions to Brown egg commercial lines (Gowe and Fairfull 1995; Crawford 1990). That egg production of these commercial lines is approximately equal is not surprising because they are all subject to the same commercial pressures, and Silversides etal. (2006a, b) also showed that egg production by S579 is at least as good as that of white egg layers. Several differences between the BPR60 and RIR50 lines and the commercial brown-egg layer S579 that relate to the egg might be the result of selection. Washburn (1990) reported on a number of studies showing that the breeds that contributed to commercial brown-egg strains produced eggs with thinner shells than White Leghorns, which should have led to commercial brown egg lines being selected more intensely for shell quality. The data presented here supports this by showing that among the pure strains, the brown-egg strains had shells that weighed less than the white-egg strains, but among the commercial crosses, the brownegg strains had heavier shells than white-egg strains. The change in egg size over the production cycle is largely due to changes in yolk weight. Early egg size for the industrial brown-egg line was high, as would be expected because of the higher body weight, but over the production cycle, egg size increased less than that of other strains. This was also found by Scott et al. (2001), Silversides and Scott (2001) and Silversides et al. (2006b) for ISA Brown versus ISA White hens and by Silversides etal. (2006a) for ISA Brown versus Babcock B300 hens. The slow rate of increase in egg size with increasing age does not appear to be an inherent quality of brown-egg layers because itwas notseen for the pure brown-egg breeds that are thought to be major contributors to the commercial brown-egg layers. Instead, it suggests that breeders of the S579 and ISA Brown hens have attempted to alter the curve of egg size over the production cycle. Their relative success for brown-egg lines in relation to that for white-egg lines may relate to the contributing genetic variation. Brown-egg layers have been derived from several differentbreeds and white-egg layers from only one, with most commercial white-egg lines probably sharing at least part of their genetic background (Crawford 1990). The range of contributing genetic variation may allow greater genetic progress in brown-egg lines than white-egg lines because progress is dependent on the original genetic variation that contributes to the population (Falconer 1989). ACKNOWLEDGEMENTS I would like to thank Lee Struthers, Harold Hanson, Kathy Ingram, and Wendy Clark for the care of the birds, Beth McCannel for technical assistance, and Martin Fraser for preparation of the diets. In particular I would like to thank George Ansah for arranging the gift of the eggs from the commercial lines from ISA. Canadian Council of Animal Care Guidelines on: the care and use of farm animals in research, teaching and testing. [Online] Available: [2010 Feb. 16]. Crawford, R. D Catalogue of poultry stocks held at research and teaching institutions in Canada. 14th ed. University of Saskatchewan, Saskatoon, SK. Crawford, R. D Poultry genetic resources: evolution, diversity, and conservation. Chapter 2 in R. D. Crawford, ed. Poultry breeding and genetics Elsevier, New York, NY. Fairful, R. W Heterosis. Chapter 37 in R. D. Crawford, ed. Poultry breeding and genetics Elsevier, New York, NY. Falconer, D. S Introduction to quantitative genetics. 3rd ed. Longman, New York, NY.

7 SILVERSIDES * PERFORMANCE OF AGASSIZ LAYER LINES 347 Gowe, R. S. and Fairfull, R. W Breeding and genetics of egg laying chickens. Chapter 19 in P. Hunton, ed. Poultry production Elsevier, New York, NY. Hendrix Poultry Productperformance. [Online] Available: [2010 Feb. 16]. National Research Council Nutrient requirements of poultry. 9th rev. ed. National Academy Press, Washington, DC. Scott, T. A., Kampen, R. and Silversides, F. G The nutrient sparing effect of phytase enzyme in wheat- and cornbased diets fed to two strains of laying hens. Can. J. Anim. Sci. 81: Silversides, F. G. and Scott, T. A Effectof storage and layer age on quality of eggs from two lines of hens. Poult. Sci. 80: Silversides, F. G., Korver, D. R. and Budgell, K. L. 2006a. Effect of line of layer and age at sexual maturity on egg production, egg quality, and bone strength. Poult. Sci. 85: Silversides, F. G., Scott, T. A., Korver, D. R., Afsharmanesh, M. and Hruby, M. 2006b. A study on the interaction of xylanase and phytase enzymes in wheat-based diets fed to commercial white and brown egg laying hens. Poult. Sci. 85: Silversides, F. G., Shaver, D. McQ. and Song, Y Pure line laying chickens at the Agassiz Research Centre. Animal Genetic Resources Information 40: Silversides, F. G., Song, Y., Renema, R., Rathgeber, B. R. and Classen, H. L Cryopreservation of avian germplasm kept in Canadian research institutions. Can. J. Anim. Sci. 88: Somes, R. G International registry of poultry genetic stocks. Storrs Agricultural Experiment Station, Bulletin 469. Washburn, Genetic variation in egg composition. Chapter 32 in R. D. Crawford, ed. Poultry breeding and genetics Elsevier, New York, NY. Zar, J. H Biostatistical analysis. 4th ed. Prentice Hall, Upper Saddle River, NJ.