The effects of weaning weight and rate of growth immediately after weaning on subsequent pig growth performance and carcass characteristics

Transcription

1 The effects of weaning weight and rate of growth immediately after weaning on subsequent pig growth performance and carcass characteristics B. F. Wolter and M. Ellis 1 Department of Animal Sciences, University of Illinois, Urbana 61801, USA. Received 3 November 2000, accepted 28 March Wolter, B. F. and Ellis, M The effects of weaning weight and rate of growth immediately after weaning on subsequent pig growth performance and carcass characteristics. Can. J. Anim. Sci. 81: Effect of accelerated weight gain immediately after weaning on subsequent performance was evaluated in pigs with heavy and light weaning weights. The study was carried out as a randomized complete block design with a factorial arrangement with the treatments being weaning weight (Heavy vs. Light), post-weaning growth rate (Accelerated vs. Conventional) and sex (Barrow vs. Gilt). Pigs were weaned at 18 to 22 d of age, weighed and classified as either Heavy or Light (5.4 vs. 3.9 kg, SE ± 0.04). During the first 14 d after weaning, pigs on the Accelerated growth treatment were housed in a specialized nursery and provided with liquid milk replacer and a dry diet; pigs on the Conventional treatment were housed in a standard nursery and provided with a dry diet only. Subsequent to the 14 d post-weaning treatment period, pigs from all treatments were housed in standard accommodation and provided the same dietary regimen to slaughter weight (110 kg). Pigs on the Accelerated treatment were heavier (P < 0.01) than pigs on the Conventional treatment at the end of the treatment period (9.2 vs. 8.1 kg, SE ± 0.13) and at 56 d of age (19.6 vs kg, SE ± 0.28). Early growth rate did not affect growth from 35 d of age to slaughter weight, or days to reach slaughter weight. Pigs on the Conventional treatment had greater (15.6 vs mm, SE ± 0.47, P < 0.01) backfat depths at slaughter than those on the Accelerated treatment. Heavy pigs at weaning were heavier (P < 0.001) at birth and 56 d of age than light pigs, and reached slaughter weight 8.6 d earlier (P < 0.001). In summary, weaning weight, but not growth rate in the first 2 wk after weaning, influenced age at slaughter. Key words: Pigs, weaning weight, post-weaning growth rate, weaning management Wolter, B. F. et Ellis, M Incidence du poids au sevrage et du taux de croissance après le sevrage sur la croissance des porcs et les caractéristiques de la carcasse. Can. J. Anim. Sci. 81: Les auteurs ont évalué les effets d un gain de poids plus rapide immédiatement après le sevrage sur le rendement subséquent de porcelets lourds et légers. Il s agissait d une étude en blocs aléatoires complets avec combinaison factorielle pour les traitements «poids au sevrage» (lourd ou léger), «taux de croissance après le sevrage» (accéléré ou normal) et «sexe» (castrat ou truie nullipare). Les animaux ont été sevrés entre l âge de 18 et de 22 jours, pesés et séparés en deux groupes, lourds ou légers (5,4 kg contre 3,9 kg, ET ± 0,04). Au cours des 14 jours suivant le sevrage, les porcelets du groupe «croissance accélérée» ont été gardés dans un enclos spécial où ils ont reçu un aliment d allaitement liquide et une ration sèche; les autres ont été placés dans un enclos ordinaire où on les a nourris d un aliment sec. Ensuite, tous les porcelets ont été logés dans un enclos normal et engraissés de la même façon jusqu à ce qu ils atteignent leur poids d abattage (110 kg). Les animaux du groupe «croissance accélérée» étaient plus lourds (P < 0,01) que ceux du groupe classique à la fin du traitement post-sevrage (9,2 kg contre 8,1 kg, ET ± 0,13) et à 56 jours (19,6 kg contre 18,3 kg, ET ± 0,28). Une croissance accélérée en bas âge n a aucune incidence sur la croissance du 35 e jour à la date où les animaux atteignent leur poids d abattage, ni sur le nombre de jours jusqu au poids d abattage. La couche de gras dorsal était plus épaisse chez les porcs engraissés de la manière traditionnelle que chez ceux soumis à une croissance accélérée (15,6 mm contre 14,1 mm, ET ± 0,47, P < 0,01), à l abattage. Les porcelets lourds avaient un poids plus élevé (P < 0,001) que les porcelets légers à la naissance et à 56 jours, et ont atteint leur poids d abattage 8,6 jours plus tôt (P < 0,001). En résumé, c est le poids au sevrage, pas le taux de croissance au cours des deux premières semaines, qui influe sur l âge à l abattage. Mots clés: Porcs, poids au sevrage, taux de croissance après le sevrage, gestion du sevrage Variation in weight gain within groups of pigs under commercial conditions can have a high associated cost to pork producers, particularly for all-in, all-out management systems. Mahan (1995) reported that large variation in weight in groups of pigs normally occurs at weaning. Lighterweight pigs have lower feed intakes and reduced weight gains during the immediate period after weaning than those of a heavier weight (Himmelberg et al. 1985; Mahan et al. 1998). Mahan (1995) reported that, relative to heavier pigs, lighter pigs at weaning reared under a typical management 1 To whom correspondence and request for reprints should be addressed ( m-ellis7@uiuc.edu). 363 Abbreviations: ADG, average daily gain; ADFI, average daily feed intake; BW, body weight; G/F, gain to feed ratio

2 364 CANADIAN JOURNAL OF ANIMAL SCIENCE system are unable to achieve compensatory growth rates during the grow-finish periods and take longer to reach market weight. Increasing nutrient intake and accelerating pig growth rate immediately after weaning could be one strategy to increase the performance of light-weight pigs and may subsequently decrease variation in weight within a group of pigs. The use of liquid milk rather than dry diets has been shown to increase pig growth rate immediately after weaning (Braude and Newport 1977; Pluske et al. 1996). However, there is limited research evaluating the impact of this increased early growth rate on subsequent performance to slaughter weight. The objective of this study was to evaluate the effect of accelerating the early growth rate, using a liquid milk-based feeding system, of pigs with Heavy and Light weaning weights on subsequent performance to slaughter weight. MATERIALS AND METHODS The experiment was conducted using a randomized complete block design with a factorial arrangement of treatments with five replicates blocked by week of weaning. The factors evaluated were: post-weaning growth rate (Accelerated vs. Conventional), weaning weight (Light vs. Heavy), and sex (Barrow vs. Gilt). The research was carried out at the Swine Research Center at the University of Illinois and the experimental protocol was approved by the University of Illinois Animal Care Advisory Committee. Animals and Management Animals The experiment used a total of 160 pigs from 20 litters farrowed over a 4 wk period. The pigs were from Pig Improvement Company (Franklin, KY 42135) Line 355 sires C-22 dams (4 litters) for the first block, and PIC Line 326 sires C-22 dams (16 litters) for subsequent blocks. Within 24 h of parturition, pigs were weighed, and crossfostering was carried out to achieve standardized litters of 10 pigs with similar mean pig birth weight and sex distributions across litters. Pigs were weighed and weaned at 18 to 22 d of age and assigned within litter and sex to either a Heavy (mean = 5.4, SD = 0.66 kg) or Light (mean = 3.9, SD = 0.73 kg) weight group of four pigs. An attempt was made to randomly assign one pig from within each litter to one of the eight treatment combinations, but due to piglet mortality this was not achieved for three litters. Therefore, pigs (n = 5) were chosen at random from the pool of extra pigs originating in other experimental litters (i.e., litters weaning 9 or 10 pigs) based on sex and weight classification to achieve groups of four pigs of each treatment combination. Between-litter variation was controlled by the use of a single sire per week and the use of dams that were hybrids of inbred lines. Each group of four pigs was randomly allotted to either the Accelerated or Conventional growth treatment. Management of Pigs for 2 wk Treatment Period after Weaning Pigs were placed into one of two separate nursery facilities immediately after weaning. Pigs assigned to the Accelerated treatment were housed in a specialized nursery (Intensive Care Nursery, Inc. Colfax, IL) for a 2 wk period. The nursery was equipped with mechanical ventilation and a supplemental heater. Because of limited capacity within the specialized nursery, barrow and gilt groups of four pigs were placed in similar-weight pens of eight animals (two like-weight experimental units). Pens in the specialized nursery had woven wire floors, solid side walls, two nipple drinkers (Lixit, Napa, CA) with an accompanying trough to minimize wastage, and two 2-hole nursery feeders (Farmweld, Teutoplois, IL) providing 50 cm of trough space in total. Half of each pen ( m) had a hover fitted with a 250 W radiant heat lamp. Within the hover the temperature was maintained at 32 C, whereas the temperature outside the hover was maintained at 18 C. Liquid milk replacer and a dry pelleted phase I diet (Table 1) were available ad libitum outside the hover during the first week. Milk replacer powder was mixed with heated water (37 C) in a mixing compartment (0.5 L capacity) and the milk was distributed by gravity to the nipple drinkers in each pen via plastic tubing. Volume in the mixing compartment was electronically controlled to ensure that an unlimited supply of freshly mixed milk was available to the pigs. In the second week following weaning, fresh cold water was delivered via the nipples, and the phase I diet remained available ad libitum for the duration of the period. After the 2 wk treatment period (i.e., at approximately 35 d of age) pigs on the Accelerated treatment were moved to a conventional nursery and penned in treatment groups of four animals. Pigs assigned to the Conventional treatment were housed from weaning in groups of four pigs per pen in a conventional nursery. Pens ( m) consisted of expanded metal floors and solid side walls, and were equipped with a 5-hole feeder (Farmweld, Teutoplois, IL), providing 60 cm of trough space in total, and a nipple drinker (Lixit, Napa, CA). Temperature within the nursery was thermostatically set at 28 C for week 1 and then lowered 2 C for weeks 2, 3 and 4 until it reached 22 C. Fresh water and a phase I diet were available ad libitum for the 2 wk treatment period. Management of Pigs Post-treatment to Market Weight At 35 d of age, pigs from both growth rate treatments were housed in the conventional nursery accommodation and given ad libitum access to a pelleted phase II diet for 2 wk, followed by a meal-form phase III diet to 56 d of age via the 5-hole nursery feeder. At 56 d of age, pigs were placed in a naturally ventilated grow-finish facility (group integrity was maintained from the nursery) and given ad libitum access to a two-stage dietary regimen (Table 1) from 56 d of age to 50 kg BW and 50 to 110 kg BW, respectively. Pens ( m) had partially solid, partially slatted concrete floors and were equipped with a nipple drinker (Lixit, Napa, CA) and a 2-hole feeder (Pannier Inc., McLean, IL). Diets provided during the nursery and growing-finishing periods were corn and soybean meal based and formulated to meet or exceed NRC (1998) nutrient requirements. Dietary phases, duration of phases, diet form and calculated analysis of the diets are presented in Table 1.

3 WOLTER AND ELLIS WEANING WEIGHT AND EARLY GROWTH RATE IN PIGS 365 Table 1. Dietary phases, feeding duration of phases, diet form and composition of diets Dietary phase Item Milk replacer z Nursery I Nursery II Nursery III Grower Finisher Feeding duration 21 to 28 d 21 to 35 d 35 to 49 d 49 to 56 d 56 d of age to 50 to 110 kg of age of age of age of age 50 kg live wt. live wt. Diet form Liquid Pellet Pellet Meal Meal Meal Ingredient composition (%) y Corn Soybean meal Dried whey Lactose Sprayed-plasma White grease Limestone Dical-phosphate CSP 250 x Zinc oxide Copper sulfate 0.08 Trace mineral salt w Salt Vitamin mix v L-Lysine-HCl DL-Methionine Calculated nutrient composition (%) Crude protein Lysine Calcium Phosphorus ME (MJ kg 1 ) z Littermilk commercial milk replacer supplied by Land O Lakes, Webster City, IA. y On an as-fed basis. x Provides 110 mg of chlortetracycline, 110 mg of sulfamethazine, and 55 mg of penicillin per kilogram of complete diet. w Each kilogram of mix contained the following: Se, 85.7 mg; I, 100 mg; Cu, 2.3 g; Mn, 5.7 g; Fe, 25.7 g; Zn, 28.6 g; and NaCl, 855 g. v Each kilogram of mix contained the following: vitamin A, IU; vitamin D3, IU; vitamin E, IU; vitamin K, 2.2 g; vitamin B 12, 17.9 mg; riboflavin, 4.4 mg; d-pantothenic acid, 12.1 g; niacin, 16.5 g; and choline chloride, 165 g. Pigs and feeders were weighed weekly in the nursery (21 56 d of age) and at 2 wk intervals for the duration of the experimental period to determine average daily gain (ADG), average daily feed intake (ADFI), and gain:feed ratio (G/F). The coefficient of variation for pig weight within each pen was calculated. Pens of pigs were taken off test when the average pig weight was 110 ± 2.5 kg. Pigs were ultrasonically scanned at the end of the study using an Aloka Model 500V B-mode scanner fitted with an Aloka 5011 probe (Corometrics Medical Systems, Wallingford, CT) with the image being taken longitudinally and anterior to the last rib, 5.5 cm off the midline. From the ultrasound image, backfat and loin depth were measured automatically using the AUSKey /AutoD automated measuring system (Animal Ultrasound Services, Inc., Ithaca, NY 14850). The percentage of fat-free lean in the carcass was predicted using an equation based on liveweight, backfat depth and loin depth derived using the same ultrasound procedure and measurements (Cisneros et al. 1996b). Statistical Analysis Data were analyzed as a randomized complete block design using the PROC GLM procedure of SAS Institute, Inc. (1994). Pen was considered the experimental unit. The model included effects of week of weaning (block), weaning weight, post-weaning growth rate, sex and two- and three-way interactions. Means were evaluated using the PDIFF and STDERR options of SAS Institute, Inc. RESULTS AND DISCUSSION No significant (P > 0.05) treatment interactions were found for any of the variables; therefore, only main effects are reported. Effect of Early Growth Rate on Performance and Carcass Characteristics Mortality rates were similar for the growth rate treatments (one vs. two deaths for the Accelerated and Conventional treatments, respectively); however, one pen of pigs on the Conventional treatment was removed from the study on the sixth day after weaning because they had failed to consume the dry diet and were undernourished. Pigs assigned to the Accelerated treatment were heavier (1.1 kg, P < 0.001) and tended to have reduced (P = 0.10) variation in pig weights within a pen at the end of the 2 wk treatment period (i.e., at approximately 35 d of age) than those on the Conventional treatment (Table 2). The pigs from the Accelerated treatment were also 1.3 kg or 7% heavier (P < 0.01) at the end of the nursery period (approximately 56 d of age) than Conventional pigs (Table 2).

4 366 CANADIAN JOURNAL OF ANIMAL SCIENCE Table 2. Effects of post-weaning growth rate, weaning weight and sex on pig liveweight, and variation in pig liveweight from birth to 110 kg liveweight z Post-weaning growth rate y Weaning weight Sex Avgerage Probability of main effects Trait Conventional Accelerated Heavy Light Barrows Gilts SEM Growth Weight Sex No. of pens Weight (kg) Birth (1 d) Weaning (21 d) End of treatment period (35 d) End of nursery (56 d) End of grower phase Final CV, (%) x Birth (1 d) Weaning (21d) End of treatment period (35 d) Final (110 kg) z Least squares means. y Growth rate for 2 wk period immediately after weaning. x CV = coefficient of variation values were determined from pig weights within pen. Table 3. Effects of post-weaning growth rate, weaning weight and sex on pig performance from 2 wk after weaning to 110 kg liveweight z Post-weaning growth rate y Weaning weight Sex Avgerage Probability of main effects Trait Conventional Accelerated Heavy Light Barrows Gilts SEM Growth Weight Sex No. of pens Daily weight gain (g) 35 d to 56 d d to 50 kg kg to 110 kg d to 110 kg Daily feed intake (g) 35 d to 56 d d to 50 kg kg to 110 kg d to 110 kg Gain:feed ratio 35 d to 56 d d to 50 kg kg to 110 kg d to 110 kg Days to market (birth to 110 kg) z Least squares means corrected to a live end weight of kg using covariate analysis. y Growth rate for 2 wk period immediately after weaning. During the period from 35 to 56 d, pigs on the Accelerated treatment had similar (P > 0.05) growth performance to those on the Conventional treatment (Table 3). In the growing and finishing periods, post-weaning growth treatment did not affect (P > 0.05) pig performance; moreover, the advantage in liveweight for pigs on the Accelerated treatment was not maintained, and days required to reach final weight were similar (P > 0.05) to the Conventional treatment. However, at market weight, the variation in pig weights within a pen for the Accelerated treatment tended to be less (P = 0.10) than that of the Conventional treatment (Table 2). Previous research at this center using the same liquid milk feeding facility conducted by Zijlstra et al. (1996) and Fisher et al. (1997) reported that the milk-replacer system used for the first 7 d after weaning in combination with splitweaning (i.e., weaning heavier pigs in a litter at 14 d of age and lighter pigs at 21 d of age) resulted in a heavier total litter weights at 28 d of age than litters weaned at 21 d of age and placed into a conventional nursery system. Heo et al. (1998) also found that feeding liquid milk replacer immediately after weaning using a nursery facility similar to that used in the present study increased live-weight gain relative to pigs fed a dry diet in a conventional nursery. Other

5 WOLTER AND ELLIS WEANING WEIGHT AND EARLY GROWTH RATE IN PIGS 367 Table 4. Effects of post-weaning growth rate, weaning weight and sex on ultrasound carcass measurements, and predicted lean content at 110 kg live weight z Post-weaning growth rate y Weaning weight Sex Avgerage Probability of main effects Item Conventional Accelerated Heavy Light Barrows Gilts SEM Growth Weight Sex No. of pens Carcass measures (mm) Fat depth Loin-eye depth Predicted fat-free lean (%) x z Least squares means corrected to a live end weight of kg using covariate analysis. y Growth rate for 2 wk period immediately after weaning. x Calculated percentage of fat-free lean in the carcass using an equation based on fat depth and loin-eye depth derived by Cisneros et al. (1996b). authors have found that the use of liquid milk feeding rather than dry starter diets immediately after weaning enhanced weight gain (Leece et al. 1979; Ellis and Rowlinson 1989). A limited number of studies have been conducted to determine the impact of increasing growth rate immediately after weaning using improved feeding strategies on growth in subsequent production stages, and these have produced variable results. Kim et al. (2001) reported that pigs fed a liquid diet rather than a dry diet with an identical nutrient profile for 14 d immediately after weaning had 44% higher ADG during that period and reached 110 kg liveweight 4 d earlier. However, the majority of other studies have increased the nutrient availability and palatability of dry diets using complex ingredient mixtures in an effort to accelerate pig performance immediately after weaning. Generally, these studies have reported relatively modest improvements in pig performance in the initial nursery phases with increases in diet complexity resulting in heavier pig weights at the end of the nursery period; however, performance in the subsequent growing-finishing period has not been improved (Hancock et al. 1994; Dritz et al. 1996). Nonetheless, these authors did report as much as a 4 d reduction in the time required to reach market weight from the use of feeding strategies that increased growth rates during the nursery period. In contrast, Whang et al. (2000) observed that pigs reared on a feeding regimen using complex rather than simple diets in the nursery were heavier at the end of the nursery period, but had a similar liveweight at the end of the test period (152 d post-weaning). Inconsistencies of this sort conceivably could be due to factors such as ingredients used, environmental management at weaning, duration of feeding of starter diets and animal health status (Ball and Aherne 1982; Chiba 1995; Mahan et al. 1998). One of the proposed uses of an accelerated growth strategy is to increase the weights of the lighter pigs after weaning as a means of reducing the variation in pig weights within the weaning group. However, results of the present study indicate a numerically small reduction in the coefficient of variation in liveweight at the end of the study for the combined group of pigs made up of the Conventional Heavy and Accelerated Light pigs (10.7%) relative to the combined group of Heavy and Light pigs on the Conventional treatment (11.2%). Pigs on the Conventional treatment had greater (P < 0.01) backfat thickness and lower (P < 0.01) predicted lean content at 110 kg liveweight than pigs on the Accelerated treatment (Table 4). Previous reports, evaluating nursery feeding strategies, have found no differences in carcass lean and fat measurements resulting from modest increases in early growth rate (Himmelberg et al. 1985; Dritz et al. 1996). In the current study, the greater backfat thickness (1.5 mm) and lower predicted lean content (0.6 percentage units) for the Conventional relative to the Accelerated treatment, in part, may be due to the increase in dietary energy intake resulting from numerically higher ADFI (3%) for the Conventional treatment during the finishing period (i.e., 50 to 110 kg liveweight), although these differences were not statistically significant (P = 0.30, Table 3). Effect of Weaning Weight on Performance and Carcass Characteristics Light compared with Heavy pigs at weaning were lighter (P < 0.001) at birth and remained lighter throughout the study (Table 2). Subsequent to the 2 wk post-weaning treatment period, from 35 to 56 d of age, the Light pigs had a lower (P < 0.01) ADG (8%) and ADFI (8%), and a similar (P > 0.05) gain:feed ratio (G/F) as for Heavy pigs (Table 3). Weaning weight did not affect (P > 0.05) ADG, ADFI, and G/F during the grow-finish period or from 35 d of age to 110 kg liveweight. This resulted in the Heavy pigs requiring 8.6 fewer days (P < 0.001) to reach slaughter weight (Table 3). Previous experiments have also demonstrated that feed intake and rate of gain during the nursery period increased with weaning weight (McConnell et al. 1987; Mahan 1993). Studies on the effects of weaning weight on ADG and ADFI in the growing and finishing periods have produced inconsistent results. Mahan and Lepine (1991) and Mahan et al. (1998) reported a slightly greater ADG and ADFI during the growing period for heavier than for lighter pigs at weaning; however, weaning weight did not affect performance in the finishing period. Himmelberg et al. (1985) found no effect

6 368 CANADIAN JOURNAL OF ANIMAL SCIENCE of weaning weight on ADG or ADFI over the whole growfinish period. Previous research has also demonstrated a limited effect of weaning weight on feed efficiency during the growing and finishing periods (Mahan and Lepine 1991; Mahan 1993; Mahan et al. 1998). In support of the current study, other studies have found a decrease in the number of days for heavier pigs at weaning to reach market weight (Mahan and Lepine 1991; Mahan et al. 1998). At slaughter weight, heavy pigs had similar (P > 0.05) loin and backfat depths and predicted lean content as light pigs (Table 4). Similarly, Himmelberg et al. (1985) and Powell and Aberle (1980) reported similar loin-eye area and backfat depth at approximately 100 kg liveweight for heavier as for lighter pigs at weaning. Therefore, the effect of weaning weight on carcass composition at slaughter appears small. Effect of Sex on Performance and Carcass Characteristics Sex did not affect (P > 0.05) pig performance during the nursery and grower periods (Table 3). However, barrows had a higher (P < 0.01) ADG and ADFI than gilts during the finishing period (i.e., 50 to 110 kg liveweight) (Table 3). Gain:feed was similar (P > 0.05) for both sexes during all phases of the study. Barrows required 5.8 d (P < 0.01) fewer than gilts to reach market weight, and had a higher (P < 0.001) backfat thickness with a lower (P < 0.001) predicted carcass lean content. Other studies have found limited differences in growth performance between barrows and gilts below 50 kg liveweight (Hyun and Ellis 2000), but have generally shown faster growth rates during the finishing period, resulting largely from higher feed intakes for barrows than for gilts (Cisneros et al. 1996a; Ellis et al. 1996). In addition, barrows have generally been found to have fatter carcasses than gilts (Friesen et al. 1994; Cisneros et al. 1996a). CONCLUSIONS These results suggest that a liquid milk-based system may be used to accelerate growth rate immediately after weaning and increase pig weights out of the nursery, but advantages in growth are not sustained to slaughter weight. In support of previous findings, pigs that are lighter at weaning have a lower growth rate during the nursery phase and consequently require significantly more days to reach market weight. Therefore, strategies that increase weaning weight may have a greater impact on overall pig performance than feeding and management strategies that aim to accelerate growth rate immediately after weaning. ACKNOWLEDGMENT The authors gratefully acknowledge Cenex Land O Lakes, Inc., Webster City, IA, for donation of milk replacer, and Intensive Care Nursery Inc., Colfax, IL, for loan of the specialized nursery system. Ball, R. O. and Aherne, F. X Effect of diet complexity and feed restriction on the incidence and severity of diarrhea in earlyweaned pigs. Can. J. Anim. Sci. 62: Braude R. and Newport, M. J A note on a comparison of two systems for rearing pigs weaned at 2 days of age, involving either a liquid or a pelleted diet. Anim. Prod. 24: Chiba, L. I Effects of nutritional history on the subsequent and overall growth performance and carcass traits of pigs. Livest. Prod. Sci. 41: Cisneros, F., Ellis, M., McKeith, F. X., McCaw, J. and Fernando, R. L. 1996a. Influence of slaughter weight on growth and carcass characteristics, commercial cutting and curing yields, and meat quality of barrows and gilts from two genotypes. J. Anim. Sci. 74: Cisneros, F., Ellis, M., Miller, K. D., Novakofski, J., Wilson, E. R. and McKeith, F. K. 1996b. Comparison of transverse and longitudinal real-time ultrasound scans for prediction of lean cut cut yields and fat-free lean content in live pigs. J. Anim. Sci. 74: Dritz, S. S., Owen, K. Q., Nelssen, J. L., Goodband, R. D. and Tokach, M. D 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. J. Anim. Sci. 74: Ellis, M. and Rowlinson, P A note on the influence of an acidified liquid sow-milk replacer on the performance of suckling and early-weaned piglets. Anim. Prod. 49: Ellis, M., Webb, A. J., Avery, P. J. and Brown, I The influence of terminal sire genotype, sex, slaughter weight, feeding regime and slaughter-house on growth performance and carcass and meat quality in pigs and on the organoleptic properties of fresh pork. Anim. Sci. 62: Fisher, B. A., Meiners, D. and Easter, R. A Effect of split weaning into NEW Nursery on piglet growth and weight. J. Anim. Sci. 75 (Suppl. 1): 57 (Abstr.). Friesen, K. G., Nelssen, J. L., Unruh, J. A., Goodband, R. D. and Tokach, M. D Effects of the interrelationship between genotype, sex, and dietary lysine on growth performance and carcass composition in finishing pigs fed to either 104 or 127 kilograms. J. Anim. Sci. 72: Hancock J. D., Hines, R. H., Mills, C. G. and Nichols, D. A Effect of nursery diets on growth of pigs to market weight. J. Anim. Sci. 72 (Suppl. 2): 64 (Abstr.). Heo, K. N., Odle, J., Oliver, W., Jones, E. and Han, I. K Effects of liquid-diet feeding and segregated-temperature housing on growth of 14-day-old, early weaned pigs. The 8th World Conference on Animal Production 1: Himmelberg, L. V., Peo, E. R. Jr., Lewis, A. J. and Crenshaw, J. D Weaning weight response of pigs to simple and complex diets. J. Anim. Sci. 61: Hyun, Y. and Ellis, M Effect of group size and feeder type on growth performance and feeding patterns in growing pigs. J. Anim. Sci. 79: (In press). Kim, J. H., Heo, J. N., Odle, J., Han, I. K. and Harrell, R. J Liquid diets accelerate the growth of early-weaned pigs and the effects are maintained to market weight. J. Anim. Sci. 79: Leece, J. G., Armstrong, W. D., Crawford, P. C. and Ducharme, G. A Nutrition and management of early weaned piglets: Liquid vs. dry feeding. J. Anim. Sci. 48: Mahan, D. C 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. J. Anim. Sci. 71: Mahan, D. C Feeding for maximum lean growth. Illinois Pork Industry Conference. pp

7 WOLTER AND ELLIS WEANING WEIGHT AND EARLY GROWTH RATE IN PIGS 369 Mahan, D. C. and Lepine, A. J Effect of pig weaning weight and associated nursery feeding programs on subsequent performance to 105 kg body weight. J. Anim. Sci. 69: Mahan, D. C., Cromwell, G. L., Ewan, R. C., Hamilton, C. R. and Yen, J. T Evaluation of the feeding duration of a phase 1 nursery diet to three-week-old pigs of two weaning weights. J. Anim. Sci. 76: McConnell, J. C., Eargle, J. C. and Waldorf, R. C Effects of weaning weight, co-mingling, groups size and room temperature on pig performance. J. Anim. Sci. 65: National Research Centre Nutrient requirements of swine. 10th ed. National Academy Press, Washington, DC. Pluske, J. R., Williams, I. H. and Aherne, F. X Villous height and crypt depth in piglets in response to increases in the intake of cows milk after weaning. Anim. Sci. 62: Powell, S. E. and Aberle, E. D Effects of birth weight on growth and carcass composition of swine. J. Anim. Sci. 50: SAS Institute, Inc SAS user s guide statistics. SAS Institute, Inc., Cary, NC. Whang, K. Y., McKeith, F. K., Kim, S. W. and Easter, R. A Effect of starter feeding program on growth performance and gains of body components from weaning to market weight in swine. J. Anim. Sci. 78: Zijlstra, R. T., Wang, K. Y., Easter, R. A. and Odle, J Effect of feeding a milk replacer to early-weaned pigs on growth, body composition, and small intestinal morphology, compared with suckled littermates. J. Anim. Sci. 74:

8