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* Department of Animal Sciences, University of Illinois, Urbana 61801 and
and
United Feeds, Inc., Sheridan, IN 46069
2 Correspondence:
216 Animal Sciences Laboratory, 1207 W. Gregory Dr. (phone: 217-333-6455; fax: 217-333-7861; Email:
mellis7{at}uiuc.edu).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Key Words: Feed Troughs • Floor Space • Growth • Pigs
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResults and DiscussionImplicationsLiterature Cited |
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The experiment was carried out in a randomized complete block design with a 2 x 2 x 2 factorial arrangement of treatments with four replicates, blocked by day of weaning. Treatments were: 1) floor space (high [0.630 m2/pig] vs. low floor space [0.315 m2/pig]), 2) feeder trough space (unrestricted [4 cm/pig] vs. restricted feeder trough space [2 cm/pig]), and 3) treatment period (duration of imposing floor and feeder trough space treatments [12 vs. 14 wk postweaning]). From the end of the treatment period to market weight, pigs on all treatments were managed identically and provided the same floor and feeder trough space allocations (0.630 m2 and 4 cm per pig, respectively).
Animals
A total of 1,728 crossbred pigs (Ausgene Line 5 sires x Ausgene Line 13 dams; Ausgene, Gridley, IL) were weaned at 17 d of age (mean BW = 5.0 ± 0.01 kg) and allotted to treatments after weaning. Pigs were formed into single-sex (barrow or gilt) outcome groups of eight animals of similar BW and were randomly allotted from within outcome group to treatment groups to form mixed-sex pens of 54 pigs. The ratio of barrows to gilts was kept constant across treatments within replicate.
Diets and Housing
Pigs were fed on a 10-phase dietary regimen. Diets were formulated to meet or exceed NRC (1998) recommendations for nutrient requirements. Pigs were fed according to a feeding budget that allowed every pen of pigs to consume a similar quantity per pig of each dietary phase (Wolter et al., 2001).
The study was carried out in an insulated, tunnel-ventilated, wean-to-finish house. The flooring was comprised of concrete slats and pen divisions and gates consisted of horizontal steel rods. Pen dimensions (length x width) were 5.74 x 6.10 m and each pen contained a six-place, two-sided feeder (Jumbo Wean-to-Finish Feeder, Farmweld, Teutopolis, IL) accessible from both sides. The feeder had solid space divisions and dimensions (width x depth) of 36.0 x 30.5 cm. Therefore, each pen provided 0.630 m2/pig floor space and 4 cm/pig feeder trough space. The recommended floor space allowance for finishing pigs is 0.74 m2/pig (Fritschen and Muehling, 1986). For the low floor-space treatment, gates were used to divide pens in half (5.74 x 3.05 m), which allowed access to only one side of the feeder (i.e., three places), however, an additional three-space feeder (Jumbo Wean-to-Finish Feeder, Farmweld, Teutopolis, IL) was placed in these pens to provide the equivalent feeder configuration and floor space per pig in each pen. For the restricted feeder space treatment, three adjacent feeder places were blocked; therefore, only 2 cm/pig of feeder trough space was available. Each pen contained hanging water drinkers, located at three quarters of the distance from the center aisle to the outside wall of the pen, which provided one waterer per 13.5 pigs. At the end of the treatment period, pen dividers and additional feeders were removed from low-floor-space pens so all treatments had the same floor and feeder space per pig for the subsequent period. The barn had a center aisle and was separated into two rooms. Each replicate was located in the same area of one room, and treatments were randomly allocated to adjacent pens within that area.
The temperature inside the building was maintained with thermostat-controlled heating and fan ventilation systems. The thermostat was set at 24°C for wk 1 and 2 and then lowered by 2°C per week until it reached 18°C, where it remained for the remainder of the experiment. During wk 1 postweaning, a rubber floor mat (0.91 x 1.52 m) and supplementary heat were provided in each pen by one propane brooder suspended 120 cm above the mat.
Growth Measurements
All pigs were weighed individually at the start, the end of the treatment period, and the end of the experiment (wk 25). The coefficient of variation in individual pig BW was calculated for each pen. Pigs experiencing health problems or injuries that did not respond to therapeutic treatment were removed from the study; the date and BW at removal were recorded and used to calculate growth performance.
Feed data were collected using a computerized feed-mixing (L.O.M.A.N. Systemtechovik, Bremerhaven, Germany), -delivery (AZA International, Medolago, Italy), and -recording (Fancom B.V., Pannigen, The Netherlands) system. The mixer was fitted with a load cell that recorded the weight of the feed dispensed to each feeder. The load cell was calibrated and the feed-recording system was validated each week (Wolter et al., 2001). Feed remaining in each feeder was measured on each pig weigh day to determine feed intake and gain:feed ratio.
Carcass Measurements
Pigs were ultrasonically scanned at the end of the treatment period (12 or 14 wk postweaning) and at the end of the study (wk 25 postweaning) with an Aloka model 500V B-mode scanner fitted with an Aloka 5011 probe (Corometrics Medical Systems, Wallingford, CT) with the image taken longitudinally and anterior to the last rib, 5 cm off the midline. From the ultrasound image, backfat and longissimus depth were measured automatically using the AUSKey system (Animal Ultrasound Services, Inc., Ithaca, NY), and percentage carcass lean for the pigs at wk 25 was predicted using an equation published by Liu and Stouffer (1995).
Statistical Analysis
Pig performance data were analyzed as a randomized block design with a 2 x 2 x 2 factorial arrangement of treatments, and the pen was considered the experimental unit. All data were tested for normality using the PROC UNIVARIATE procedures of SAS (SAS Inst. Inc., Cary, NC). Data for the percentage of pigs removed from study did not conform to the normal distribution; consequently, the Friedman’s 
2 rank-based test (Steel and Torrie, 1980) was carried out using the PROC RANKS procedures of SAS. Data meeting criteria for normality (Steel and Torrie, 1980) were analyzed using the GLM procedure of SAS. The model used included effects of floor space, feeder trough space, treatment period, room, and day of weaning (block) nested within room, and all two- and three-way interactions. The residual mean square error was used as the error term and an F-test was used. Least squares means were compared using the PDIFF and STDERR options of SAS.
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Results and Discussion |
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. Results relating to pig growth performance and carcass measures are presented in Tables 2 and 3 , respectively.
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). Pigs given low floor space had lower ADFI (5.2%; P < 0.01), ADG (6.8%; P < 0.001), and gain:feed ratio (2%; P < 0.01) than those given high floor space during the postweaning treatment period (Table 2). Pigs with low floor space had lower (P < 0.001) backfat depth, but similar (P > 0.05) longissimus depth at the end of the treatment period as those with high floor space (Table 3).
At the end of wk 25 postweaning, BW and variation in BW within a pen were similar (P > 0.05) for the two floor-space treatments (Table 1). In the period from the end of treatment through the end of wk 25, there was an interaction (P < 0.05) between floor space and treatment period for ADG and gain:feed ratio (Table 2). The increase in ADG and G/F for pigs on low vs. high floor space was relatively greater for the 14-wk (5.5 and 5.7% for ADG and gain:feed ratio, respectively) than the 12-wk (2.3 and 2.8% for ADG and gain:feed ratio, respectively) treatment period. During the period from the end of treatment to the end of wk 25, ADFI was similar (P > 0.05) for both floor-space treatments. Carcass measures of pigs were similar (P > 0.05) between these treatments at the end of study (Table 3).
Results of this study agree with previous findings that indicated pigs that have experienced a decrease in early growth rate due to restricted access to floor space, feeder space, or both will have increased growth rate and feed efficiency when provided adequate space in the subsequent grow-finish period (Wolter et al., 2002a,c). However, Wolter et al. (2003) reported that reduced postweaning growth resulting from the feeding of simple rather than complex diets during the nursery period had little impact on subsequent pig growth performance. Similarly, other studies that have reported variation in pig growth in earlier postweaning periods have found little impact of restricted growth on subsequent growth performance to market BW (Brumm et al., 2001; Wolter and Ellis, 2001). Many factors, including the cause of the growth restriction as well as its length and severity, are likely to interact to determine the extent of any increase in growth rate following a period of restriction.
In the current study, applying the restricted floor space treatment for 12 or 14 wk postweaning resulted in improvements in feed efficiency in the subsequent period to wk 25 of 2.5 and 6.0%, respectively. Prince et al. (1983) suggest that both severity and duration of restriction impact the level of increased growth rate and efficiency of growth following a period of restricted feed intake and concomitant lower BW gain. Obviously, in the present study, the severity of floor-space restriction and of growth reduction increased with increasing duration of treatment.
Similar to results of the current study, Mersmann et al. (1987) found pigs had less carcass fat, but not less longissimus area after a period of restricted feed intake and growth rate. However, following a realimentation period, there was little difference in carcass fat and longissimus measures at market BW. Other studies also have reported no effect of increased growth performance following early growth restriction on backfat and longissimus measures at market (Critser et al., 1995; Wolter et al., 2002a, 2003). Previous research results suggest that growth of pig body fat and food-processing organs (e.g., liver, kidney, gastrointestinal tract) are reduced during periods of low voluntary feed intake during early growth (Tullis and Whittemore, 1986; Whang et al., 2000), whereas growth of protein in the empty pig body appears to be maintained during modest feed-intake restrictions (Stamataris et al., 1991).
In the current study, low floor space allowance increased (P < 0.01) the rate of pig removal due to injury, poor health, or death during the treatment period (Table 1). However, previous floor space treatment did not impact rate of pig removal in the subsequent period ending at market weight. Wolter et al. (2002c) reported a similar increase in the rate of pig removal due to restricted space allowance. In contrast, other studies have reported no effect of decreased space allowance resulting from increasing the number of pigs per pen on number of pigs that died or were removed due to injuries or poor performance (Brumm et al., 2001; Wolter et al., 2002a). There is evidence, however, that decreasing floor-space allowance per pig can lead to increased aggressiveness (Ewbank and Bryant, 1972; Randolph et al., 1981). The effect of floor space on rate of pig morbidity and mortality remains unclear and may depend on other environmental factors that require further study with larger numbers of animals.
Effect of Feeder Trough Space
Restricting access to feeder trough space did not affect (P > 0.10) pig BW or variation in BW at any point (Table 1). Pigs on restricted feeder space had similar ADG (P > 0.10), but lower ADFI (2.9%; P < 0.05) and greater gain:feed ratio (2.0%; P < 0.01) than those on urestricted feeder trough space during the postweaning treatment period (Table 2). However, previous feeder trough space experience did not impact (P > 0.05) subsequent growth performance from the end of treatment to the end of study (Table 2). Carcass backfat and longissimus depth measures and predicted lean content were similar (P > 0.05) regardless of feeder-trough treatment at both the end of treatment and the end of study (Table 3).
Contrary to expectation, these results suggest that restricting feeder trough space to 2 cm per pig slightly lowered feed intake, but had little effect on pig growth rate over the entire period from weaning to the end of treatment. In a previous study conducted in the same facility, Wolter et al. (2002b), using a larger group size (108 pigs/pen), reported pigs with access to 2 cm per pig had a similar feed intake, but lower growth rates, than those with 4 cm after wk 6 postweaning. Brumm and Carlson (1985) found there was no effect on growth performance from reducing feeder trough space from 5.2 to 1.7 cm per pig from weaning (28 d of age) to the end of wk 5 postweaning; however, variation in pig BW within a pen increased at the lower trough space. Research also has shown that pigs may adapt by altering preferred patterns of feeding when trough space per pig is decreased (Laitat et al., 1999; Hyun and Ellis, 2002). This may explain, in part, inconsistencies in effects of decreased trough space on pig growth performance. Gonyou and Lou (2000) suggested the form of diet, feeder design features, and BW range of pigs evaluated may impact any effect of feeder trough space on pig performance, so current results may not be repeated across all production systems.
In the current study, restricting feeder trough space reduced feed intake, but had no effect on ADG-results that suggest either an increase in efficiency of feed utilization or a reduction in feed wastage for the restricted feeder trough space treatment. Defining the optimal feeder trough space is obviously a complex issue, but one that warrants further research.
A significant (P < 0.05) interaction was observed between feeder trough space and treatment period for rate of pig removal during the postweaning treatment period (Table 1). During the 14-wk treatment period, pigs on restricted feeder trough space had a higher rate of removal than pigs on unrestricted feeder trough space, whereas pigs on both restricted and unrestricted feeder trough space had similar rates of removal during the 12-wk treatment period. For the 14-wk treatment period, the percentage of pigs removed was higher during the first 10 wk of the study for restricted vs. unrestricted feeder trough space (1.85 vs. 0.92%, respectively). This suggests that the higher removal rate for the restricted vs. unrestricted feeder trough space on the 14-wk treatment period may in part be due to chance. The relationship between feeder trough space and morbidity and mortality warrants further investigation.
Effect of Treatment Period
Pigs on the 12- and 14-wk treatment periods had similar (P > 0.05) BW at the end of study (Table 1). Pigs on the 12-wk treatment period had lower (P < 0.01) ADG and ADFI, but higher (P < 0.001) gain:feed than those on the 14-wk treatment (Table 2). Similarly, daily feed intake, on average, was lower (P < 0.001) for pigs on the 12-wk treatment during the subsequent growth period to the end of study (Table 2). At the end of the postweaning treatment period, pigs on the 12-wk treatment had similar (P > 0.05) backfat depths, but lower (P < 0.001) longissimus depths than those on the 14-wk treatment (Table 3). However, carcass measures were similar (P > 0.05) between treatments at the end of study (Table 3). These results generally agree with those of other studies that have reported increasing ADG and ADFI and decreased gain:feed ratio with increased time postweaning (Andersen and Pedersen, 1996; Wolter et al., 2002a), as well as similar changes in carcass composition (Shields et al., 1983) in growing pigs.
Results of this study and others suggest a similar increase in feed efficiency for finishing pigs experiencing a modest growth restriction due to decreased space during the nursery and/or growing periods, and this observation has a significant, positive implication for the economics of pig production. Interestingly, for the entire growth period from weaning to the end of wk 25 postweaning, the overall growth performance of pigs on all treatments was quite similar (Table 2). But producers still may be able to exploit the potential to reduce production costs by using strategies that manipulate the growth curve of the animal using a range of nutritional and environmental approaches. However, given the level of complexity by which a number of animal and environmental factors can interact following a period of growth restriction (Lawrence and Fowler, 1997), it is difficult to determine with certainty whether pigs show a systematic increase in growth rate and feed efficiency following an earlier period of growth restriction. The results reported here require validation across a wider range of production systems, and deeper understanding of the impact of the degree of restriction on pig growth at various stages of development is needed.
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Implications |
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Footnotes |
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Received for publication July 3, 2002. Accepted for publication November 26, 2002.
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