Australian Journal of Agricultural Research

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1 Publishing Australian Journal of Agricultural Research Volume 53, 2002 CSIRO 2002 A journal for the publication of original contributions towards the understanding of an agricultural system All enquiries and manuscripts should be directed to: Australian Journal of Agricultural Research CSIRO Publishing PO Box 1139 (150 Oxford St) Collingwood, Vic. 3066, Australia Telephone: Fax: publishing.ajar@csiro.au Published by CSIRO Publishing for CSIRO and the Australian Academy of Science

2 etal Aust. J. Agric. Res., 2002, 53, Interactions between weaning age, weaning weight, sex, and enzyme supplementation on growth performance of pigs F. R. Dunshea AF, D. K. Kerton A, P. D. Cranwell B, R. G. Campbell C, B. P. Mullan D, R. H. King A, and J. R. Pluske E A Agriculture Victoria, Victorian Institute of Animal Science, 600 Sneydes Rd, Werribee, Vic. 3030, Australia. B P. D. Cranwell Consultants, PO Box 620, Rosanna, Vic. 3084, Australia. C Bunge Meat Industries, PO Box 78, Corowa, NSW 2646, Australia; present address: Ausgene International, PO Box 68, Gridley, IL, 61744, USA. D Agriculture WA, Locked Bag 4, Bentley Delivery Centre, WA 6983, Australia. E Division of Veterinary and Biomedical Sciences, Murdoch University, Murdoch, WA 6150, Australia. F Corresponding author; Frank.Dunshea@nre.vic.gov.au Abstract. Digestive capacity of early-weaned pigs may be insufficient to fully digest many ingredients currently used in weaner diets. The aim of this experiment was to determine whether an exogenous enzyme preparation with broad carbohydrase activity could benefit pigs that developmentally might be immature at weaning, especially with regard to gastrointestinal development. Eighty Large White Landrace pigs were used in a factorial experiment with the factors being: weaning age (14 or 24 days), weaning weight (heavy or light), sex (boar or gilt), and dietary Biofeed Plus CT (0 or 500 µg/g), which contained fungal xylanases, pentosanases, and β-glucanases. Pigs were housed individually and given a wheat-based (550 g/kg) diet containing 15.0 MJ DE and 15.9 g lysine/kg on an ad libitum basis for 21 days. The diet also contained 50 g/kg of soybean meal and 50 g/kg of lupin (Lupinus angustifolius) kernels. The liveweights of heavy (H) pigs weaned at 24 or 14 days and light pigs (L) weaned at 24 or 14 days were 7.9 and 5.3 and 5.2 and 3.9 kg, respectively. Pigs weaned at 14 days grew slower (157 v. 345 g/day) than those weaned at 24 days, although there was a suggestion of an interaction between age and weight at weaning (P = 0.081). Thus, H and L pigs weaned at 14 days grew at 148 and 166 g/day, whereas H and L pigs weaned at 24 days grew at 374 and 315 g/day, respectively. Although there was no main effect of enzymes on daily gain (248 v. 254 g/day, P = 0.80), feed intake (278 v. 284 g/day, P = 0.79), or feed conversion ratio (1.19 v. 1.25, P = 0.35), there were interactions with weaning age on daily gain (P = 0.050) and feed intake (P = 0.060). Pigs weaned at 14 days grew slower (176 v. 138 g/day) and ate less (206 v. 174 g/day), whereas pigs weaned at 24 days grew faster (321 v. 369 g/day) and ate more (351 v. 394 g/day), when supplemented with enzymes. During the third week after weaning there were interactions between dietary enzymes and sex (P = 0.060) and dietary enzymes and age (P = 0.023) on daily gain. Thus, pigs weaned at 24 days and supplemented with Biofeed Plus CT grew more quickly during the third week (559 v. 460 g/day), whereas the converse was true for pigs weaned at 14 days (286 v. 334 g/day). Also, enzyme-supplemented boars grew better over this period (457 v. 371 g/day), whereas the converse was true for gilts (388 v. 423 g/day). In conclusion, these data clearly indicate that the greatest determinant of post-weaning performance under the present conditions was the age of the pigs at weaning. Dietary enzyme supplementation appeared most efficacious in boars weaned at an older age, although benefits did not become apparent until 2 weeks after weaning. Additional keywords: growth, enzymes, pig, weaning. AR01197 Enzyme F. R. Dunshea supplementation for weanedpigs Introduction There is increasing interest in the use of early weaning management systems in the Australian pig industry. The main drive for this is the possibility of using segregated early weaning (SEW) to break the disease transfer cycle from sow to piglet. Another reason for early weaning is that, from about 14 days of lactation, sow milk yield and composition can limit piglet growth to well below their potential (Williams 1995; Toner et al. 1996). Sucking pigs grow at approximately 220 g/day between birth and weaning, but this CSIRO /AR /02/080939

3 940 F. R. Dunshea et al growth rate is far below the biological potential of the artificially reared pig, which can grow in excess of 400 g/day (Hodge 1974; Harrell et al. 1993; Dunshea and Walton 1995). The success of weaning at 14 days of age to make use of the enormous growth potential of the piglet will depend largely upon the development of appropriate diets, which will need to be designed to meet the digestive and physiological development of the piglet. In particular, the development of digestive enzyme activity may limit the use of traditional feedstuffs, particularly those high in non-starch polysaccharides (NSP) in the diets of early-weaned pigs. It is possible that supplementing the pig s endogenous enzymes with exogenous enzymes may be beneficial in increasing the digestibility of some feed ingredients. Enzyme supplementation has been very successful in improving nutrient digestibility in poultry (Choct 2001), particularly in young birds. Responses in pigs have not been as dramatic, perhaps because many studies have been conducted in more mature animals with better developed digestive systems. In addition, the digesta in pigs is less viscous than in chickens, and there is considerable hindgut capacity that might mask some of the effects of enzymes (Thacker et al. 1991; Mavromichalis et al. 2000; Partridge et al. 1999). Therefore, the aim of this study was to examine the effects of weaning age, weight, sex, and supplemental enzymes on growth performance of pigs fed a predominantly wheat-based diet. Materials and methods Animals and feeding Eighty (Large White Landrace) pigs were allocated to a factorial experiment with the respective factors being sex (male and female), age at weaning (14 and 24 days), size at weaning (heavy and light), and enzyme supplementation (0 or 500 µg/g of Biofeed Plus CT (Novozymes-Roche), which contained fungal xylanases, pentosanases, and β-glucanases. Pigs were weighed at weaning and then, within each sex, weight, and age group, randomly allocated to one of the 2 pelleted diets offered ad libitum (Table 1). All piglets were weaned on the same day and so pigs from different age groups were derived from different sows. However, all sows and litters were housed in the same shed. Pigs were weighed and feed intake was recorded at 3, 7, 14, and 21 days after weaning. Throughout the experiment the pigs were kept in individual pens at the R&D Unit at Bunge Meat Industries (Corowa, NSW, Australia). The room was maintained at 28 C, and heat lamps provided additional heat. Statistics Treatment effects were assessed by analyses of variance for a factorial design with the main effects being age at weaning, weight at weaning, sex, and dietary enzyme supplementation. All analyses were performed using GENSTAT (Payne et al. 1993). Results Growth rate The selection of heavy and light pigs at 14 and 24 days of age ensured that there were significant effects of age, weight, and an interaction between age and weight on weaning weight Ingredient Table 1. Composition of experimental diets (g/kg) g/kg Wheat (11%) A Lupin (L. angustifolius) kernels (34%) Soybean meal (48%) Meatmeal (55%) Fishmeal (67%) Skim milk powder Bloodmeal Whey powder Water Tallow Salt DL-Methionine Threonine Lysine.HCl Tryptophan Endoxacillin Vitamins and minerals B Estimated composition C Digestible energy (MJ DE/kg) Lysine (g/kg) A For the enzyme supplemented diet, 0.5 kg of wheat was replaced with 0.5 kg of Biofeed Plus CT. B Vitamin mineral premix provided the following nutrients per kg of air-dry diet (mg): retinol, 6.4; cholecalciferol, 0.083; tocopherol, 22; menadione, 0.60; riboflavin, 3.3; nicotinic acid, 16.5; pantothenic acid, 5.5; pyrodoxine, 1.1; biotin, 0.56; choline, 1100; cyanocobalamin, 0.017; Fe, 88; Zn, 55; Mn, 22; Cu, 6.6; I, 0.22; Se, 0.1. C Estimated from ingredients. (Table 2). Over the first 3 days post-weaning, the pigs weaned at 14 days lost 116 g/day, whereas those weaned at 24 days gained 30 g/day. There was an indication of an interaction between age and weight at weaning (P = 0.065), with the heavy pigs weaned at 14 days losing more weight than the light pigs ( 155 v. 77 g/day). This was not the case for heavier pigs weaned at 24 days of age (38 v. 22 g/day). Over the first 7 days after weaning there was a significant effect of age on growth rate, with pigs weaned at 14 days losing an average of 14 g/day, whereas those weaned at 24 days gained 168 g/day (P < 0.001). There was no effect of sex on growth rate, with males and females growing at 78 and 76 g/day, respectively (P = 0.94). In the second week post-weaning, growth rates were 161 and 341 g/day for the pigs weaned at 14 and 24 days, respectively (P < 0.001). Over the first 14 days post-weaning, daily gain averaged 81 and 263 g/day for pigs weaned at 14 and 24 days, respectively (P < 0.001). During the third week post-weaning the pigs weaned at 14 days had a lower daily gain than those weaned at 24 days (310 v. 509 g/day, P < 0.001), and heavy pigs tended to grow more quickly than light pigs (436 v. 383 g/day, P = 0.093). In addition, there was an interaction (P = 0.048) between age and weight at weaning such that there was no difference in growth rate over the second and third weeks post-weaning

4 Enzyme supplementation for weaned pigs 941 Table 2. Interactions between age and weight at weaning, sex, and enzyme supplementation on growth performance over the 3 weeks post-weaning Control Enzyme s.e.d. Significance A Female Male Female Male Day 14 Day 24 Day 14 Day 24 Day 14 Day 24 Day 14 Day 24 Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Liveweight (kg) Weaning A***, W***, S.W*, A.W*** 21 days post-weaning A***, W***, A.W**, A.D Daily gain (g/day) 0 3 days A***, A.W, S.A.W 0 7 days A*** 0 14 days A*** 0 21 days A***, A.W, A.D* 7 14 days A***, S.A days A***, W, A.W*, S.D, A.D* A A, Age at weaning; W, weight at weaning; S, sex; D, dietary enzyme supplementation. P < 0.1; * P < 0.05; ** P < 0.01; *** P < Table 3. Interactions between age and weight at weaning, sex, and enzyme supplementation on feed intake over the 3 weeks post-weaning Control Enzyme s.e.d. Significance A Female Male Female Male Day 14 Day 24 Day 14 Day 24 Day 14 Day 24 Day 14 Day 24 Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Heavy Light Feed intake (g/day) 0 3 days A*** 0 7 days A***, W**, S.W* 0 14 days A***, W* 0 21 days A***, W*, A.W*, A.D 7 14 days A***, W days A***, W*, A.W*, A.D* Feed conversion efficiency 0 7 days A***, S.D* 0 14 days A***, A.D 7 14 days S.A* 0 21 days A***, W* days A A, Age at weaning; W, weight at weaning; S, sex; D, dietary enzyme supplementation. P < 0.1; * P < 0.05; ** P < 0.01; *** P <

5 942 F. R. Dunshea et al between heavy and light pigs weaned at 14 days (305 v. 315 g/day), whereas for pigs weaned at 24 days the difference in growth rate between heavy and light pigs was substantial (568 v. 451 g/day). There was also a significant interaction (P = 0.023) between age at weaning and enzyme supplementation, with pigs weaned at 14 days growing at 286 and 334 g/day for pigs with and without enzyme supplementation, whereas the pigs weaned at 24 days grew at 559 and 460 g/day, respectively. Also, there was an interaction (P = 0.060) between sex and enzyme supplementation over the second and third weeks post-weaning such that males grew better with enzyme supplementation (457 v. 371 g/day), whereas this was not the case for females (388 v. 423 g/day). Over the full 3 weeks after weaning, the pigs weaned at 14 days had a lower daily gain than those weaned at 24 days (157 v. 345 g/day, P = 0.001). Although there was no overall effect of enzyme supplementation on growth over the full 3 weeks post-weaning (248 v. 254 g/day, P = 0.80), there was an interaction (P = 0.050) with age at weaning. Thus, pigs weaned at 14 days of age grew more slowly when supplemented with enzyme (176 v. 138 g/day), whereas for pigs weaned at 24 days, enzyme supplementation improved growth rate (321 v. 369 g/day). Effects on food intake and feed conversion ratio Feed intake followed a similar pattern to daily gain. Over the first 3 days post-weaning, pigs weaned at 24 days consumed more feed than pigs weaned at 14 days (69 v. 24 g/day, P < 0.001) (Table 3). This trend continued, and over the first 7 days post-weaning, the pigs weaned at 24 days ate nearly 3 times as much feed as those weaned at 14 days (159 v. 60 g/day, P < 0.001). Heavier pigs ate more than lighter pigs (124 v. 95 g/day, P = 0.010), although there was an interaction with sex (P = 0.067). Thus, light females ate more than light males (112 v. 77 g/day), whereas there was no real difference between heavy females and males (121 v. 127 g/day). During the second week after weaning, the older pigs ate more than the younger pigs (366 v. 292 g/day, P < 0.001), and heavy pigs tended to eat more than the light pigs (292 v. 253 g/day, P = 0.087). There were no main effects on feed:gain during the second week post-weaning. However, there was an interaction between sex and age at weaning (P = 0.037) such that female pigs weaned at 14 days had better feed:gain than their male counterparts (1.25 v. 1.46), whereas for pigs weaned at 24 days the converse was true (1.66 v. 0.99). Over the third week post-weaning, the older pigs ate more than the younger pigs (589 v. 324 g/day, P < 0.001), and heavy pigs ate more than the light pigs (498 v. 416 g/day, P = 0.017). However, there was an interaction (P = 0.019) between age and weight at weaning such that there was no difference in feed intake between the heavy and light pigs weaned at 14 days (325 v. 324 g/day), whereas feed intake was higher for the heavy pigs weaned at 24 days (670 v. 508 g/day). There was also an interaction between age and diet (P = 0.027) such that enzyme supplementation increased feed intake in the pigs weaned at 24 days (540 v. 637 g/day) but not in the pigs weaned at 14 days (351 v. 297 g/day). There were no main effects on feed:gain during the third week post-weaning. Over the full 3 weeks post-weaning, the pigs weaned at 24 d ate more than those weaned at 14 days (372 v. 190 g/day, P < 0.001). Also, heavier pigs ate more than the lighter pigs (305 v. 257 g/day, P = 0.017). However, there was an interaction (P = 0.046) between age and weight at weaning, with the heavy and light pigs weaned at 14 days eating similar amounts (194 v. 186 g/day), whereas for the pigs weaned at 24 days the heavy pigs ate more than the light pigs (416 v. 328 g/day). Although there was no overall effect of enzyme supplementation on feed intake over the full 3 weeks post-weaning (278 v. 284 g/day, P = 0.79), there was an interaction (P = 0.060) with age at weaning. Thus, pigs weaned at 14 days of age ate less when supplemented with enzyme (206 v. 174 g/day), whereas for pigs weaned at 24 days, enzyme supplementation increased feed intake (351 v. 394 g/day). Feed conversion efficiency (FCE) was lower in the pigs weaned early (0.78 v. 0.90, P < 0.001) and lower in heavy pigs (0.80 v. 0.90, P = 0.016). Discussion These data clearly indicate that the greatest determinant of post-weaning performance under the present conditions was the age of pigs at weaning. There have been very few studies designed to look specifically at the effect of age at weaning on subsequent growth rate, and those that have been conducted have often confounded weaning age with housing or other management factors. In one study, Dunshea (2002) reported that pigs weaned at 25 days of age grew faster over the first 3 weeks of weaning than pigs weaned at 17 days. Interestingly, the effects were not so pronounced during the first week post-weaning but became apparent in the second and third week post-weaning. Dritz et al. (1996) reported that pigs weaned at 9 days of age (3.4 kg) ate less feed per day and grew slower post-weaning than pigs weaned at 19 days of age (5.4 kg). These differences in performance, particularly feed intake, were diminished by increasing the complexity of the diets, achieved mainly by replacing soybean meal with spray-dried plasma and dried whey (Dritz et al. 1996). Although the statistical comparisons were not made, Patience et al. (2000) found that pigs weaned at 12 days of age grew slower (104 g/day) and had a lower FCE (0.67) over the first 9 days post-weaning than pigs weaned at 21 days over the first 5 (143 g/day and 0.89) or 12 days (223 g/day and 0.92) following weaning. In that study, Patience et al. (2000) reported that segregated weaning ameliorated these differences in performance. Therefore, although it is clear that pigs weaned at younger ages (14 days or less) do not grow as quickly as pigs weaned at approximately 3 weeks of age or

6 Enzyme supplementation for weaned pigs 943 more, early-weaned pigs can grow as well as, or even better than, conventionally weaned pigs when the right conditions (e.g. SEW, improved diets) are provided. Numerous workers have shown that heavier pigs grow faster than lighter pigs in the immediate post-weaning period (Himmelberg et al. 1985; Mahan and Lepine 1991; Mahan 1993; Mahan et al. 1998). For example, Himmelberg et al. (1985) found that heavy pigs (>5.6 kg at 21 days) grew faster and ate more than light pigs (<5.0 kg) when weaned at 21 days of age. In a very comprehensive multi-site study, Mahan et al. (1998) found that although heavy pigs (7.5 kg at 24 days) tended to grow slightly faster (171 v. 161 g/day, P =0.06) than light pigs (5.6 kg) over the first week post-weaning, the relative response was greater over the second (347 v. 303 g/day, P < 0.01) and third (497 v. 454 g/day, P < 0.01) weeks post-weaning. The results from the present study were not as clear. Certainly, heavier pigs ate more than their lighter counterparts, but there was no overall main effect of weaning weight on daily gain. However, there were interactions between weaning weight and age on both feed intake and daily gain such that the early-weaned heavy and light pigs ate similar amounts and grew at similar rates over the full 3 weeks of the study, whereas for the pigs weaned at 24 days, the heavy pigs ate more and grew faster than the light pigs. In general, there were very few main effects of sex on growth performance. However, there were a number of interactions between sex and either weaning age, weaning weight, or enzyme supplementation. For example, light female pigs ate more and grew faster over the first week post-weaning than light male pigs, whereas there was no difference between heavy male and female pigs. Previously, we have reported that female pigs eat more and grow faster than male pigs over the first few days post-weaning, particularly in pigs that are light for their age (Power et al. 1996). Also, Dunshea (2002) reported on two studies where female pigs grew faster than male pigs over the first 7 21 days post-weaning, regardless of weaning age (that occurred between 17 and 26 days of age). In a retrospective analysis of 58 studies conducted at the University of Kentucky, Cromwell et al. (1996) demonstrated that although barrows were heavier at weaning, gilts grew more rapidly over the subsequent 4 weeks. Given that the post-weaning performance of gilts is superior to both barrows and boars it appears that the factor(s) responsible are intrinsic to the gilt. Others have found that neonatal male rats were more susceptible than female rats to early dietary deficiencies, retardation, and handling stresses (Crutchfield and Dratman 1980). In addition to the possibility that the hormonal milieu stimulates the appetite and/or reduces stress of the gilt, it is also possible that there is further sexual dimorphism with respect to gastrointestinal size and function, as indicated by the responses, or indeed lack thereof, to exogenous enzymes. Although there were very few effects of enzyme supplementation on growth performance of weaner pigs, there were some interesting interactions between enzyme supplementation and sex, weaning age, and weaning weight. For example, enzyme supplementation was most beneficial for the heavy, male pigs weaned at an older age, whereas the converse was true for the light, female pigs weaned at an early age. Also, the response to enzyme supplementation did not become apparent until the third week post-weaning. The reasons for this are unknown but may be related to the fact that weaned gilts appear to have a larger, more developed gastrointestinal system and greater pancreatic enzymic capacity than boars (Cranwell et al. 1997; Pluske et al. 1997; RJ van Barneveld, P White, FR Dunshea unpublished data). Also, Hughes (2001) reported that the estimate of metabolisable energy (ME) was lower and more variable in male broiler chickens than in broiler hens for a given sample of wheat, suggesting a lower and more variable digestive capacity in males. In the present study, it was possible that enzyme supplementation was of little benefit where digestive capacity is not limiting performance, as may be the case for gilts or where feed intake per se is less in younger or smaller pigs. Alternatively, solubilisation of the NSP by the enzyme might have created conditions in the gut lumen, such as an increase in digesta water-holding capacity, that led to a delay in gastric emptying and/or a decrease in the rate of passage (Choct and Cadogan 2001). These events, in turn, could have caused a reduction in voluntary food intake. However, in the heavy and older boars with relatively high feed intakes during the third week and possibly longer, post-weaning endogenous enzymic capacity may limit digestibility and growth performance. In this case, sufficient development of the microflora and physiological mechanisms for handling NSP (e.g. water and acid absorption) would have occurred, such that pigs of this age were better able to handle the cleavage products of NSP hydrolysis by the enzyme. The relative lack of effect of exogenous enzyme supplementation is not unusual, and as more information is gathered about their modes of action, the circumstances (other than those outlined above) where enzymes may prove beneficial are becoming evident. For example, Mavromichalis et al. (2000) investigated the interactions between xylanase supplementation, stage of growth, and particle size of wheat, and found that enzyme supplementation only appeared to be beneficial in weaner pigs fed diets containing coarsely ground wheat. Cadogan et al. (1999) characterised a series of wheats as low to high DE wheats based upon the growth performance of weaner pigs fed diets containing these varieties. Subsequently, these workers reported that exogenous xylanase was beneficial in weaner pigs fed diets containing low DE wheats, but was of no benefit for pigs fed diets containing high DE wheats (Choct et al. 1999; Partridge et al. 1999; Cadogan et al. 2001). To further complicate matters, Cadogan (1999) found that the DE content of some low DE wheats could increase after storage for 3 months. Therefore, it appears that the type

7 944 F. R. Dunshea et al and form of wheat and other grains used in diets, as well as other factors such as storage time, may also determine whether pigs respond to exogenous xylanase and other enzyme supplementation. In conclusion, these data clearly indicate that the greatest determinant of post-weaning performance under the present conditions was the age of the pigs at weaning, with pigs weaned at 24 days eating more and growing faster than pigs weaned at 14 days of age. Pigs that were heavier at weaning performed better than those that were light for age, and gilts performed better than boars during the early post-weaning period. Dietary enzyme supplementation appeared most efficacious in boars weaned at an older age, although benefits did not become apparent until 2 weeks post-weaning. Acknowledgments The authors acknowledge the financial assistance of the Pig Research and Development Corporation. These data were presented in part at the 6th Biennial Meeting of the Australasian Pig Science Association [Dunshea FR, Cranwell PD, Harrison DT, Campbell RG, Kerton DJ, Pluske JR, King RH (1997) Enzyme (Biofeed plus) supplementation may be more beneficial in boars and older weaning age pigs. In Manipulating pig production VII. (Ed. PD Cranwell) p (Australasian Pig Science Association: Werribee, Vic.)]. References Cadogan DJ (1999) Agronomical and physiochemical factors of wheat affecting nutrient availability and performance of wheat. MSc thesis, The University of New England, Australia. Cadogan DJ, Choct M, Campbell RG, Kershaw S (1999) Effects of new seasons wheat on the growth performance of young male pigs. In Manipulating pig production VII. (Eds DP Hennessy, PD Cranwell) p. 40. (Australasian Pig Science Association: Werribee, Vic) Cadogan DJ, Ross G, Argent C (2001) Effects of increasing xylanase supplementation of diets containing high and low quality wheats. In Manipulating pig production VIII. (Ed. PD Cranwell) p (Australasian Pig Science Association: Werribee, Vic.) Choct M (2001) Enzyme supplementation of poultry diets based on viscous cereals. In Enzymes in farm animal nutrition. (Eds MR Bedford, GG Partridge) pp (CABI Publishing: Wallingford, UK) Choct M, Cadogan DJ (2001) How effective are supplemental enzymes in pig diets? In Manipulating pig production VIII. (Ed. PD Cranwell) pp (Australasian Pig Science Association: Werribee, Vic.) Choct M, Cadogan DJ, Campbell RG, Kershaw S (1999) Enzymes can eliminate the difference in the nutritive value of wheat for pigs. In Manipulating pig production VII. (Ed. PD Cranwell) p. 39. (Australasian Pig Science Association: Werribee, Vic.) Cranwell PD, Pierzynowsk SG, Rippe C, Pluske JR, Power GN, Campbell RG, Kerton DJ, King RH, Dunshea FR (1997) Weight and age at weaning influence pancreatic size and enzymic capacity. In Manipulating pig production IV. (Ed. PD Cranwell) p (Australasian Pig Science Association: Werribee, Vic.) Cromwell GL, Coffey RD, Aaron DK, Lindemann MD, Pierce JL, Monegue HJ, Pupard VM, Cowen DE, Parido MB, Clayton TM (1996) Differences in growth rate of weanling barrows and gilts. Journal of Animal Science 74(Suppl. 1), 187. Crutchfield FL, Dratman MB (1980) Growth and development of the neonatal rat: particular vulnerability of males to disadvantageous conditions during rearing. Biology of the Neonate 38, Dritz SS, Owen KQ, Nelssen JL, Goodband RD, Tokach MD (1996) Influence of weaning age and nursery diet complexity on growth performance and carcass characteristics and composition of high-health status pigs from weaning to 109 kilograms. Journal of Animal Science 74, Dunshea FR (2002) Female pigs better handle weaning and other transitions than male pigs. Asian-Australasian Journal of Animal Science (in press) Dunshea FR, Walton PE (1995) Potential of exogenous metabolic modifiers for the pig industry. In Manipulating pig production IV. (Eds DP Hennessy, PD Cranwell) pp (Australasian Pig Science Association: Werribee, Vic.) Harrell RJ, Thomas MJ, Boyd RD (1993) Limitations of sow milk yield on baby pig growth. In 1993 Cornell Nutrition Conference for Feed Manufacturers. pp (Cornell University: Ithaca, NY) Himmelberg LV, Peo ER Jr, Lewis AJ, Crenshaw JD (1985) Weaning weight response of pigs to simple and complex diets. Journal of Animal Science 61, Hodge RW (1974) Efficiency of food conversion and body composition of the preruminant lamb and young pig. British Journal of Nutrition 32, Hughes RJ (2001) Variation in the digestive capacity of the broiler chicken. Recent Advances in Animal Nutrition in Australia 13, Mahan DC (1993) Effect of weight, split-weaning, and nursery feeding programs on performance responses of pigs to 105 kilograms body weight and subsequent effects on sow rebreeding interval. Journal of Animal Science 71, Mahan DC, Cromwell GL, Ewan RC, Hamilton CR, Yen JT (1998) Evaluation of the feeding duration of a phase 1 nursery diet to three-week-old pigs of two weaning weights. NCR 42 Committee on Swine Nutrition. Journal of Animal Science 76, Mahan DC, Lepine AJ (1991) Effect of pig weaning weight and associated nursery feeding programs on subsequent performance to 105 kilograms body weight Journal of Animal Science 69, Mavromichalis I, Hancock JD, Senne BW, Gugle TL, Kennedy GA, Hines RH, Wyatt CL (2000) Enzyme supplementation and particle size of wheat in diets for nursery and finishing pigs. Journal of Animal Science 78, Partridge GG, Simmins PH, Cadogan DJ (1999) Influence of xylanase addition to diets containing wheat co-products and nutritionally-defined wheat on growing pig performance. In Manipulating pig production VII. (Eds DP Hennessy, PD Cranwell) p. 37. (Australasian Pig Science Association: Werribee, Vic.) Patience JF, Gonyou HW, Whittington DL, Beltranena E, Rhodes CS, Van Kessel AG (2000) Evaluation of site and age of weaning on pig growth performance. Journal of Animal Science 78, Payne RW, Lane PW, Genstat 5 Committee (1993) Genstat 5 reference manual. (Oxford Science Publications: Oxford, UK) Pluske JR, Power GN, Cranwell PD, Pierzynowski SG, Campbell RG, Kerton DJ, King RH, Dunshea FR (1997) Sex and age at weaning affect small intestinal histology and enzymatic capacity. In Manipulating pig production VI. (Ed. PD Cranwell) p. 67. (Australasian Pig Science Association: Werribee, Vic.)

8 Enzyme supplementation for weaned pigs 945 Power GN, Pluske JR, Campbell RG, Cranwell PD, King RH, Dunshea FR (1996) Effect of sex, weight and age on post-weaning growth in pigs. Proceedings of the Nutrition Society of Australia 20, 137. Thacker PA, Campbell GL, GrootWassink JWD (1991) The effect of enzyme supplementation on the nutritive value of rye-based diets for swine. Canadian Journal of Animal Science 71, Toner MS, King RH, Dunshea FR, Dove H, Atwood CS (1996) The effect of exogenous somatotropin on lactation performance of first-litter sows. Journal of Animal Science 74, Williams IH (1995) Sow milk as a major nutrient source before weaning. In Manipulating pig production IV. (Eds DP Hennessy, PD Cranwell) pp (Australasian Pig Science Association: Werribee, Vic.) Manuscript received 21 November 2001, accepted 14 March