Effect of feed form, formulation, and restriction on the performance of laying hens

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1 Effect of feed form, formulation, and restriction on the performance of laying hens T. A. Scott 1,4, F. G. Silversides 2, D. Tietge 3, and M. L. Swift 3 1 Pacific Agri-Food Research Centre, Agassiz, British Columbia, Canada V0M 1A0; Piercy Road, Denman Island, British Columbia, Canada V0R 1T0; and 3 Pro-Form Feeds, P.O. Box 1000, Chilliwack, British Columbia, Canada V2P 6J6. Contribution no. 600, received 21 July 1998, accepted 8 February Scott, T. A., Silversides, F. G., Tietge, D. and Swift, M. L Effect of feed form, formulation, and restriction on the performance of laying hens. Can. J. Anim. Sci. 79: A laying trial was performed with 1440 DeKalb hens caged at 18 wk of age to test the effect of feed form (expanded pellets or mash) and type of formulation (for crude protein [CP] or for specific amino acids[aa]), and five levels of feed restriction applied at either 24 wk or 32 wk of age. Formulation for CP rather than AA content resulted in 4.4% greater egg production and 7.1% greater production of egg mass in hens fed mash and 4.0% better feed efficiency in hens fed both mash and pellets. Hens fed mash had 2.3% higher feed consumption, suggesting that the hens may prefer mash. Feed restriction reduced body weight and hen day egg production proportionate to the restriction level, but egg weight was reduced only slightly. These data suggest that care should be exercised in formulating for AA content rather than for CP, especially if feed intake is reduced. This strain of hens was very successful at regulating its feed intake for maximum production, and even a slight feed restriction produced a negative effect on production. Key words: Laying hens, feed restriction, feed form, feed formulation, protein level Scott, T. A., Silversides, F. G., Tietge, D. et Swift, M. L L effet de la forme, la formulation, et la restriction de l aliment sur la performance des poules pondeuses. Can. J. Anim. Sci. 79: Un essai de ponte a été realizé en utilisant 1440 poules DeKalb mises en cage à 18 semaines d âge pour vérifier l effet de la forme de l aliment (agglomérée ou farine), le type de formulation (pour protéine brute ou pour des acides aminés spécifiques), et cinq niveaux de restriction alimentaire appliqués à 24 ou 32 semaines d âge. La formulation pour la protéine brute en lieu de celle pour des acides aminés a produite une production d œufs 4,4% plus elevée et de masse d œuf 7,1% plus elevées pour les poules alimentées avec la moulée de forme farine et une efficacité alimentaire meilleur de 4,0% pour les poules alimentées avec les deux formes. Les poules alimentées avec la moulée de forme farine ont consumé 2,3% plus, suggérant ainsi une préférence. La restriction alimentaire a réduit le poids corporel et la production d œufs par jour en relation directe avec le niveau de restriction, mais le poids de l œuf a été reduit moins. Ces données suggèrent qu il faut faire attention avec la formulation pour les acides aminés surtout avec une consommation reduite d aliment. Cette souche de poule a réussi trés bien de régler sa consommation pour une production maximale et même une restriction légère a produit un effet negatif sur la production. Mots clés: Poules pondeuses, restriction alimentaire, forme de l aliment, formulation d aliments, niveau de protéine Laying hens are much better than broilers at controlling their feed intake, but feed restriction can be used during rearing to control mature BW and reduce feed costs (Gous and Stielau 1976; Summers and Robinson 1995). Feed restriction during the egg-production cycle can also be used to control BW gain. Restriction before the peak of egg production may reduce the BW to less than the ideal for maximum egg production (Summers and Robinson 1995). Restriction after the production peak has been the subject of much scientific and commercial interest. Experimental feed restriction has been carried out by limiting time of access to feeders (Snetsinger et al. 1973; Kuney and Enos 1980; Cerniglia et al. 1984), restricting the amount of feed (Snetsinger et al. 1973; Gerry and Muir 1976; Kari et al. 1977; Matsoukas et al. 1980; Cunnigham and Polte 1984; Okonkwo et al. 1994), and restricting the energy in the feed (Snetsinger et al. 1974). In most cases restriction 4 To whom correspondence should be sent. scotta@ em.agr.ca. 171 has been accompanied by a decrease in egg production, egg weight, egg mass, or one or more of these, depending on the strain of bird and the level of restriction. However, it can result in increased economic efficiency (Cunnigham and Polte 1984) in at least three ways. Feed efficiency may be improved (Snetsinger et al. 1973; Gerry and Muir 1976; Kari et al. 1977), as a greater proportion of the nutrient intake is used for egg production. Mortality may be reduced (Singsen et al. 1958; Snetsinger et al. 1973), especially for heavy strains. Finally, egg size can be reduced at the end of the cycle, which provides an advantage if there is no price differential between large and extra-large eggs, because it increases feed efficiency and reduces egg breakage. While energy is the major feed component controlling voluntary feed intake (Summers and Robinson 1995), it is not the only nutrient needed for egg production. Laying hens Abbreviations: AA, amino acids; ANOVA, analysis of variance; BW, body weight; CP, crude protein; ME, metabolisable energy; SBM, soybean meal; SE, standard error; TSAA, total sulfur amino acids

2 172 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 1. Ingredients and calculated percentage of nutrients contained in diets wk wk HP z LP HM LM HP LP HM LM % Ingredients Corn Wheat SBM (46% CP) Meat meal (18% CP) Limestone Feed fat Alfalfa pellets Canola meal Celite Dicalcium phosphate Salt Avizyme y Novo Biofeed x Liquid choline w Alimet v L-lysine HCl L-threonine L-tryptophan Vitamin mineral mix u Calculated composition ME (kcal kg 1 ) Ca Available P CP Lysine Methionine TSAA Tryptophan Threonine z H represents high CP; L represents low protein; P represents pelleted; and M represents mash. y Finfeeds International, Box 777, Marlborough, Wiltshire, United Kingdom SN8 1XN. Avizyme 2300 was used except for pelletted diets in the second period, when liquid was used. x Hoffmann-La Roche Ltd., th St., S. E., High River, AB, Canada T1V 1M7. w 70% choline chloride. v Novus International (Canada) Inc., 2430 Meadowpine Blvd., Mississauga, ON, Canada L5N 6S2. Liquid-methionine analogue with a methionine value of about 85%. u To supply per kilogram diet: IU vitamin A; IU vitamin D3; 50 IU vitamin E; 1.5 mg vitamin K; 15 ug vitamin B 12 ; 1 mg thiamine; 5 mg pyrodoxine; 5 mg riboflavin; 7.5 mg niacin; 8.0 mg pantothenic acid; 0.5 mg folacin; 80 ug biotin; 90 mg manganese; 80 mg iron; 10 mg copper; 80 mg zinc; 0.5 mg iodine; 0.3 mg selenium. require a minimum level of CP and of essential AA. Methionine and TSAA are most often cited as limiting (Novacek and Carlson 1969). According to the National Research Council (1994), the requirement of laying hens for CP can be lowered if a minimum of 300 mg of methionine and 580 mg of TSAA is supplied, although others (Calderon and Jenson 1990; Cao et al. 1992; Schutte et al. 1994) suggest higher minimum levels. Reducing the level of CP may reduce feed costs, and it has been shown to reduce nitrogen and phosphorus excretion (Priesmann and Peterson 1995). Feed formulation can balance the ration according to the level of CP, or to meet minimum levels of specific AA, especially methionine and TSAA. According to Ahmad et al. (1997), suppliers of synthetic AA suggest a formulation based on TSAA content, and breeding companies recommend a formulation based on CP. Which of these is more economical depends on the relative cost of the major energy and protein sources. Laying hens are often fed their rations in a mash form because their total ad libitum feed intake is not a limitation to nutrient intake. Nevertheless, pellets can be used for layers because they facilitate feed handling, and the pelleting process can alter the availability of some nutrients (Scott et al. 1976). A trial was performed with commercial laying hens between 20 and 70 wk of age to investigate the effects of (1) moderate feed restriction after the production peak or for the entire laying period; (2) a diet formulation based on CP or TSAA, and 3) the form of the feed, either mash or pellets. MATERIALS AND METHODS Eighteen-week-old DeKalb pullets were purchased from a commercial source. They were raised in a single-deck cage system and fed a 19% CP crumble starter diet until 8 wk of age and a 17% CP rolled pullet grower diet afterward. Day length during rearing was reduced gradually from 22 h at

3 placement to 10 h at 3 wk of age where it remained for the remainder of the growing period. At 18 wk of age, 1440 pullets were housed three hens to a cage providing 12 cages per treatment. All mortality was replaced from spare birds maintained on identical treatments. Each cage had a floor space of 2064 cm 2 and was provided with two nipple drinkers and a feeder. Day length was increased gradually to reach 16 h just after peak production where it was maintained until the end of the experiment. Experimental conditions were in accordance with guidelines described by the Canadian Council on Animal Care (1993), and the protocol was approved by the Animal Care Committee of the Pacific Agriculture Research Centre at Agassiz, British Columbia. Four factors of the feeding program were investigated: restriction level (five levels, including the control), restriction period (two treatments), feed form (two treatments), and protein formulation (two treatments). The weekly feed consumption of a control group of birds given ad libitum access to feed was used to determine the amount of feed to be given the restricted birds in the following week. Feed restriction began at either 24 or 32 wk of age. Restriction levels were set at 97.5, 95.0, 90.0, and 85.0% of ad libitum intake, with these levels being applied after 32 wk of age. Between 24 and 32 wk, restriction levels for the earlyrestriction group were only half as severe (98.25, 97.5, 95.0, and 92.5% of ad libitum intake). A skip-a-day feeding program was used for the restricted groups. A 17% CP prelay mash diet was fed from 18 to 20 wk. Experimental diets were formulated by a commercial feed manufacturer (Pro-Form Feeds, Box 1000, Chilliwack, BC) on the basis of percent CP or the content of specific AA, resulting in high and low protein treatments, and were fed as expanded pellets or as mash. Diets fed from 20 to 34 wk and from 35 to 70 wk are shown in Table 1. Xylanase enzyme (Table 1) was added to the mash diets in dry form and to the pelleted diets in liquid form. The flock reached 10% egg production during their 19th week, before the start of the experimental treatments, and further measures of sexual maturity were not made. Egg production per cage was recorded for 5 d wk 1 and was extrapolated to 7 d. Each week, all the eggs produced on one day were weighed, which, combined with egg production, allowed for the calculation of the egg mass produced. Weekly feed consumption was recorded to allow for the calculation of feed efficiency. In addition, eggs produced on one day at 24, 32, and 70 wk of age were weighed. After storage overnight, the eggs were broken onto a flat surface; albumen height was measured with a tripod micrometer; and shell weights were determined after drying for 2 d at 60 C. All hens were weighed at 20, 24, 32, and 70 wk of age. Differences in mortality between restriction levels and feed form were tested using contingency chi-square (Steel and Torrie 1980). Other data were analyzed by ANOVA using the JMP statistical software of SAS Institute, Inc. (1995), with the effects of feed form, protein level, restriction level, and restriction period as fixed effects. Initial analyses included all the two-way interactions between these effects. The final models were simplified to include SCOTT ET AL. RESTRICTED FEEDING OF LAYERS 173 Table 2. Laying hen mortality from 20 to 70 wk of age z Restriction period Restriction level wk y wk Total % of ad libitum Total z The number of hens in each restriction level was 288. No difference between restriction levels or restriction periods was significant when tested by chi-square. y Restriction between 24 and 32 wk was only one half of that shown. only the feed-form protein-level and the restriction-level period interactions. Where appropriate, the feed form and protein level were combined to give four levels of feed type, which allowed for valid multiple comparisons of feed types using the Tukey Kramer test (SAS Institute, Inc. 1995). RESULTS Mortality during the trial was 6.5%, with no significant differences between restriction treatment groups (Table 2). Mortality of hens fed expanded pellets was higher than that of hens fed mash diets (61 vs. 33, χ 2 = 8.3, 1 df, P < 0.01). The F ratios for each source of variation in the ANOVA are presented in Table 3. When the diets were fed as expanded pellets, diet formulation had no effect on egg production or egg mass (Table 4). When the same diets were fed as mash, hens fed diets formulated on the basis of CP produced more eggs and a greater egg mass than did hens fed diets formulated on the basis of AA. The hens consumed more of the mash diets than the pelleted diets. There was a significant interaction between the form of the feed and the protein level, but the differences between protein level within form were not significant. The protein level and the feed form also affected feed efficiency. Hens produced egg mass more efficiently on high-protein diets than on low-protein diets and they produced egg mass more efficiently when the diets were fed as expanded pellets. In initial analyses including all two-way interactions, an interaction was seen between the diet formulation and the restriction level (F = 2.8, P < 0.05) for daily egg-mass production between 32 and 50 wk of age. With ad libitum feed intake, there was no difference (data not shown) between formulation types, while at all restriction levels, egg mass produced on the low-cp diets was less than that produced on the high-cp diets. The form of the feed, the protein level, and the interaction between the form and the protein level were significant for the average egg weight (Table 5). Eggs produced by hens fed the pelleted diets and the high-protein mash diet were of similar weight (except at 24 wk, when eggs from the highprotein mash diet were heavier than those from the high protein pelleted diet). Eggs produced by hens on the low-protein mash treatment weighed less than the others but not significantly less than those produced by hens on the high-protein pelleted diet.

4 174 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 3. ANOVA z for the performance of laying hens fed diets formulated according to CP or AA levels as either mash or expanded pellets at five levels of feed restriction and one of two periods of restriction F ratio Form Protein Form protein Period Level Period level Hen d % ** 16.1** ** 0.3 Egg mass ** 41.1** 7.2** 105.7** 0.2 Feed consumed 65.0** ** 9.7** 229.0** 1.1 Efficiency 35.4** 48.7** 12.3** ** 0.1 Egg wt 24 wk * 14.7** wk ** ** wk * ** 0.7 Percent shell 24 wk 85.1** ** * 32 wk 155.7** ** wk 8.0** 4.8* ** 1.2 Albumen height 24 wk ** wk 22.1** 6.9** wk ** 1.2 BW 20 wk wk 7.1** wk 33.4** ** wk ** ** 0.2 z Hen d and egg mass production, feed consumption, and feed efficiency used the cage averages (n = 480), n = 1440 for BW, and n = 571 to 625 for egg quality at 24, 32 and 70 wk. *,**Significant at P < 0.05 and P < 0.01, respectively. Table 4. Egg production, egg mass, and feed efficiency of hens fed diets formulated for CP or AA as expanded pellets or mash (x ± SE) Expanded pellets Mash High protein Low protein High protein Low protein Production (hen d %) z wk ± 0.007a ± 0.007a ± 0.007a ± 0.007a wk ± 0.007ab ± 0.007ab ± 0.007a ± 0.007b wk ± 0.006b ± 0.007b ± 0.007a ± 0.007b wk ± 0.005b ± 0.006b ± 0.005a ± 0.005b Egg mass (g bird 1 d 1 ) wk ± 0.36a ± 0.40a ± 0.37a ± 0.36a wk ± 0.46a ± 0.49a ± 0.43a ± 0.43b wk ± 0.44b ± 0.49b ± 0.43a ± 0.45c wk ± 0.33ab ± 0.38b ± 0.33a ± 0.33c Feed consumption (g d 1 ) wk 92.6 ± 0.6b 93.0 ± 0.6ab 95.1 ± 0.6a 92.9 ± 0.6ab wk 94.8 ± 0.6b 95.3 ± 0.6ab 97.0 ± 0.6a 96.0 ± 0.6ab wk 95.4 ± 0.6bc 98.0 ± 0.6c ± 0.6a 99.6 ± 0.6ab wk 94.5 ± 0.5c 95.8 ± 0.5bc 98.1 ± 0.5a 96.7 ± 0.5ab Feed efficiency (feed egg 1 ) wk 2.14 ± 0.02a 2.14 ± 0.03a 2.16 ± 0.02a 2.14 ± 0.02a wk 1.90 ± 0.01b 1.92 ± 0.02b 1.92 ± 0.01b 2.05 ± 0.01a wk 1.96 ± 0.01c 2.04 ± 0.02b 2.00 ± 0.01bc 2.17 ± 0.01a wk 1.97 ± 0.01b 2.01 ± 0.01b 1.99 ± 0.01b 2.11 ± 0.01a z Each mean represents 120 cages with three hens in each. a c Means within a row with different letters are significantly different at P < Tables 3 and 5 also show that period and the period restriction-level interaction were significant for shell percentage at 24 wk, suggesting that the effects of restriction were very rapid. The level of restriction was significant at 32 and 70 wk, but the effect was small. Shell percentage for the 85% restriction level was significantly greater than that for the 90% level at 32 wk and that for the 97.5% level at 70 wk. Percentage shell was also affected by the feed form and protein level. Eggs produced by hens fed mash diets had a greater percentage of shell than eggs from hens fed pellets at all three times, and hens fed low-protein diets had higher values at 70 wk.

5 SCOTT ET AL. RESTRICTED FEEDING OF LAYERS 175 Table 5. BW and egg weight, shell percentage, and albumen height of eggs from hens fed diets formulated for CP or AA as expanded pellets or mash (x ± SE) Expanded pellets Mash High protein Low protein High protein Low protein Egg weight (g) 24 wk ( ) 51.6 ± 0.4bc 52.4 ± 0.5ab 53.4 ± 0.5a 50.8 ± 0.4c 32 wk ( ) 57.0 ± 0.4ab 57.9 ± 0.4a 58.4 ± 0.4a 56.1 ± 0.3b 70 wk ( ) 62.0 ± 0.5ab 62.5 ± 0.5a 62.5 ± 0.4a 60.8 ± 0.4b Shell (% of egg weight) 24 wk ( ) 9.16 ± 0.07b 9.31 ± 0.06b 9.81 ± 0.07a 9.86 ± 0.07a 32 wk ( ) 8.63 ± 0.09b 8.57 ± 0.06b 9.52 ± 0.06a 9.39 ± 0.06a 70 wk ( ) 8.61 ± 0.06b 8.72 ± 0.06ab 8.75 ± 0.06ab 8.92 ± 0.06a Albumen height (mm) 24 wk ( ) 6.67 ± 0.10bc 6.99 ± 0.09a 6.59 ± 0.07c 6.90 ± 0.08ab 32 wk ( ) 6.72 ± 0.08b 7.01 ± 0.07a 6.49 ± 0.07b 6.58 ± 0.06b 70 wk ( ) 5.41 ± 0.10a 5.62 ± 0.11a 5.38 ± 0.10a 5.38 ± 0.10a BW (g) 20 wk (360) z 1483 ± 7a 1475 ± 7a 1468 ± 7a 1469 ± 7a 24 wk (358, 359) 1510 ± 7a 1506 ± 7a 1530 ± 7a 1524 ± 7a 32 wk (360) 1554 ± 8b 1564 ± 8b 1611 ± 8a 1597 ± 8a 70 wk (360) 1650 ± 10bc 1682 ± 11ab 1693 ± 10a 1630 ± 11c z The number of samples represented by each number is given in parentheses following the character. a c Means within a row with different letters are significantly different at P < Table 6. Feed consumption, BW, egg mass, and egg-production efficiency of hens between 32 and 70 wk with five levels of feed restriction (x ± SE) Restriction (% of ad libitum consumption) Feed consumption (g) ± 0.7a ± 0.2b 98.6 ± 0.2c 93.6 ± 0.2d 88.8 ± 0.2e % of ad libitum Egg production (hen d %) ± 0.006a ± 0.006ab ± 0.005b ± 0.006c ± 0.006d % of ad libitum Egg weight (g) 62.4 ± 0.3a 61.3 ± 0.2b 61.1 ± 0.2b 60.0 ± 0.2c 60.1 ± 0.2c % of ad libitum Egg mass (g d 1 ) 53.3 ± 0.4a 51.0 ± 0.4b 50.2 ± 0.3b 47.2 ± 0.4c 43.8 ± 0.4d % of ad libitum Feed efficiency (feed egg 1 ) 1.96 ± 0.01b 1.98 ± 0.02ab 1.97 ± 0.01b 1.99 ± 0.02ab 2.04 ± 0.02a % of ad libitum BW at 70 wk (g) 1780 ± 14a 1707 ± 10b 1681 ± 10b 1612 ± 9c 1537 ± 8d % of ad libitum a e Means within a row with different letters are significantly different at P < The albumen height was greater at 24 and 32 wk when hens were fed low-protein diets and greater at 32 wk when the diets were fed as pellets (Table 5), but there was no interaction between these factors. At 70 wk, the albumen height was greatest (5.77 ± 0.13 mm) with the most severe feed restriction, and it decreased progressively with increasing feed allotment to 5.00 ± 0.10 mm for ad libitum consumption (P < 0.05). The form of the feed had a significant effect on BW, with mash diets producing heavier birds at 24 and 32 wk (Table 5). Protein level did not affect BW except at 70 wk, when there was a significant interaction between the feed form and protein level and birds fed low-protein mash diets weighed the least. At 32 wk, early-restricted hens weighed less than those restricted only after peak production (1571 ± 5 and 1592 ± 6 g, respectively, P < 0.05). Over the 51-wk trial, early-restricted hens consumed slightly less feed than those restricted later (95.7 ± 0.4 and 96.5 ± 0.3 g d 1, respectively, P < 0.05) and produced slightly less egg mass per day (47.6 ± 0.3 g d 1 vs ± 0.2 g d 1, P < 0.05). As expected, the level of feed restriction affected many of the variables measured. The period of restriction was of only minor importance for most of these variables, and the only interaction between period and level was for egg specific gravity. To simplify presentation of the results, feed consumption, egg production, egg weight (average weekly weight), egg mass, and feed efficiency only after the imposition of the restriction at 32 wk are shown in Table 6, along with BW at 70 wk. Feed consumption at each level of restriction was significantly different from the others and followed the experimental design very closely. Egg production, egg mass produced, and BW at 70 wk followed feed-

6 176 CANADIAN JOURNAL OF ANIMAL SCIENCE Fig. 1. Egg production (A) and egg weight (B) from 32 to 70 wk of hens with five levels of quantitative feed restriction ( is 100%; n is 97.5%; m is 95%; Ò is 90%; and l is 85%); 2-wk periods are identified on the axis without a dividing slash. consumption levels and were also different for each group, except that the 95.0 and 97.5% restriction groups were the same for all three variables and the 100 and 97.5% restriction groups were the same for egg production. Egg weight was lower with feed restriction, but to a lesser degree than feed consumption, particularly at the 90 and 85% restriction levels. With greater restriction, egg mass was depressed slightly more than feed consumption or egg production. Feed efficiency was not improved by restriction and was significantly worse when hens were restricted to 85% of ad libitum consumption. A slight decline in egg production occurred at wk in the four restricted groups (Fig. 1A) but not in the control group. Thereafter, egg production declined gradually, but in the 85% restricted group, production leveled off and actually increased slightly near the end of the experiment. The difference in egg weight between the five groups (Fig. 1B) increased between 32 and 70 wk for all groups. DISCUSSION Hens consumed more of the mash diets than the pelletted diets, suggesting a preference for the mash form, and possibly explaining differences in production, especially early in production. Alternatively, the feed may have differed nutritionally. The pelleting process may have altered the availability of some nutrients, and the pelleted and mash diets were formulated and mixed separately and used different enzyme sources or forms. This resulted in a confounding of effects, and conclusions on the effect of the feed form cannot be drawn. Albumen height was greater with low-protein diets and with increased restriction. The literature is nearly silent

7 (Hunton 1995) on the effects of nutrition on albumen quality, but Williams (1992), in a review, mentioned that dietary changes influencing the rate of lay cause an inverse change in the Haugh unit score, as was seen here. Cerniglia et al. (1984) and Cunningham and Polte (1984) found that early feed restriction reduced egg production. The restriction before 32 wk, as applied here, did not affect hen day egg production, but it produced a slight reduction in BW at 32 wk and reduced egg-mass production. These results show that even moderate restriction before the peak of production can limit growth and subsequent overall eggmass production. The type of formulation resulted in different levels of CP. In the AA formulation, wheat replaced SBM, with slightly altered levels of meat meal and canola meal. The calculated content of specific AA was similar for all diets, and all diets supplied greater than 300 mg d 1 methionine and 580 mg d 1 TSAA, as is recommended by the National Research Council (1994), even at the most severe restriction level. If actual requirements are higher, as suggested by Calderon and Jensen (1990), Cao et al. (1992), and Schutte et al. (1994), then methionine and TSAA consumption may not have been sufficient for maximum production on restrictedfeeding treatments. The restriction-level protein interaction was significant for egg mass per day between 32 and 50 wk, but not for other production variables, possibly supporting this hypothesis. The National Research Council (1994) estimated the energy requirements of a 1.5 kg hen laying at 70% production to be 264 kcal ME d 1 and 276 kcal ME at 80% production. Between 32 and 70 wk, the full-fed hens obtained about 278 kcal ME d 1. This is in close agreement with the National Research Council (1994) estimates and agrees with various authors on the ability of the hen to control energy intake. Restricted hens received correspondingly less energy, with the 85%-restriction group receiving only 240 kcal ME d -1, which is clearly below the requirement. The restricted birds suffered a slump in egg production just after the peak in egg production, suggesting inadequate feed intake, while the full-fed birds did not. Most reports of feed restriction for layers after the eggproduction peak describe a reduction in BW and egg weight (Snetsinger et al. 1974; Gerry and Muir 1976; Kuney and Enos 1980; Matsoukas et al. 1980; Cunningham and Polte 1984; Cerniglia et al. 1984). A reduction in BW might result in increased feed efficiency, and a reduction in egg weight could improve the economic efficiency. Many markets pay no more for extra-large eggs than for large eggs, even though extra-large eggs require more feed to produce and are subject to higher rates of breakage during handling. Even at the end of the egg-production cycle, eggs from the 85%-restriction group averaged only 61.7 g, nearly 3 g less than those of full-fed hens, which would result in a shift of eggs from the extra-large category to the large category. The benefits of feed restriction (Snetsinger et al. 1973; Kari et al. 1977), including improved livability and feed efficiency as a result of decreased feed intake with no change in egg production, may have disappeared with continued selection for more efficient layers (Summers and SCOTT ET AL. RESTRICTED FEEDING OF LAYERS 177 Robinson 1995). Results shown here and those of Gerry and Muir (1976) and Okonkwo et al. (1994) suggest that this may be true. In data shown here, BW, egg production, and egg-mass production were reduced in direct proportion to the feed restriction, while egg weight was reduced to a lesser degree. It is significant that feed restriction as slight as 2.5% caused a reduction in egg weight and egg mass produced, confirming that hens are able to control their feed intake to meet their nutrient requirements (Summers and Robinson 1995) to a remarkable degree. The effects of feed restriction on production undoubtedly depend, at least in part, on the strain of laying hen, and economic effects depend as well on the market. ACKNOWLEDGMENTS We gratefully acknowledge the financial support of the British Columbia Egg Marketing Board, Agro Pacific Industries Ltd., and Agriculture and Agri-Food Canada. We also thank Lee Struthers and the poultry staff of The Pacific Agricultural Research Centre (Agassiz) for their dedication and hard work in maintaining the birds and collecting and analyzing the data. Ahmad, H. 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M. and Stielau, W. J Growth and laying performance of light hybrid pullets subjected to quantitative food restriction. Br. Poult. Sci. 17: Hunton, P Egg production, processing and marketing. Chapter 20 in Hunton, P., ed. Poultry Production, Elsevier, New York, NY. Kari, R. R., Quisenberry, J. H. and Bradley, J. W Egg quality and performance as influenced by restricted feeding of commercial caged layers. Poult. Sci. 56: Kuney, D. R. and Enos, H. L Time-limited feeding of Leghorn layers in California open-housing. Poult. Sci. 59: Matsoukas, J., Scoglund, W. C. and Whittaker, D Feed restriction in laying hens. Poult. Sci. 59: National Research Council Nutrient requirements of poultry. 9th ed. National Academy Press, Washington, DC. Novacek, E. J. and Carlson, C. W Low protein cage-layer diets and amino acids. Poult. Sci. 48: Okonkwo, A. C., Igwebuike, J. U. and Isaac, L. J The

8 178 CANADIAN JOURNAL OF ANIMAL SCIENCE effects of feed restriction on the performance of laying hens. East Af. Agric. For. J. 59: Priesmann, T. and Peterson, J Effect of controlled feeding of laying hens on the performance and the amount of nitrogen and phosphorus in faeces. Arch Gefluegelkd 59: SAS Institute, Inc JMP statistics and graphics Guide. SAS Institute, Inc., Cary, NC. Schutte, J. B., DeJong, J. and Bertram, H. L Requirement of the laying hen for sulfur amino acids. Poult. Sci. 73: Scott, M. L., Nesheim, M. C. and Young, R. J Nutrition of the chicken. 2nd ed. M. L. Scott and Associates, Ithaca, NY. Singsen, E. P., Matterson, L. D., Tlustohowicz, J. and Potter, L. M The effect of controlled feeding, energy intake and type of diet on the performance of heavy-type laying hens. Poult. Sci. 37: Snetsinger, D. C., Zimmerman, R. A. and Greene, D. E Limited feeding of egg strain layers. Poult. Sci. 52: Snetsinger, D. C., Zimmerman, R. A. and Greene, D. E Limited feeding of egg strain layers as influence by cage density and social order. Poult. Sci. 53: Steel, R. G. and Torrie, J. H Principles and procedures of statistics: a biometrical approach, 2nd edition. McGraw-Hill Book Company, Toronto, ON. Summers, J. D. and Robinson, F. E Comparative feeding programs for poultry production. Chapter 15 in Hunton, P., ed. Poultry production. Elsevier, New York, NY. Williams, K. C Some factors affecting albumen quality with particular reference to Haugh unit score. World s Poult. Sci. J. 48: 5 16.