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ANIMAL NUTRITION |
* Prairie Swine Centre Inc., Saskatoon, Canada S7H 5N9; and
and
Department of Animal Science, University of Saskatchewan, Saskatoon, Canada S7N 5A8
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Key Words: pig • digestible energy • segregated weaning
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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). Because of this limitation, amino acids in the growing pig diet are formulated as a ratio to energy (NRC, 1998). However, the information available in the current literature on the response of the weaned pig to changes in dietary energy density is inconclusive.
Nutritional, physiological, environmental, and social stressors are imposed upon a pig concurrently at weaning (Pluske, 1995); consequently, the weaning period is associated with problems such as low feed consumption, poor growth rate, increased incidence of diarrhea, and high incidences of social vices (Gatnau, 1999). Weaning the pigs into a facility that is isolated from the sow herd has become widespread throughout the pork industry (Fangman and Tubbs, 1997). The response to site of weaning may be affected by age of weaning. Pigs weaned at 12 d of age to an off-site nursery had improved feed intake and 56-d BW relative to those weaned on-site at either 12 or 21 d of age (Patience et al., 2000). There is less conclusive evidence, however, on the impact of weaning system when pigs are weaned at 17 to 21 d of age (Fangman et al., 1996a).
Given the apparent reduction in stressors imposed on piglets weaned to off-site facilities and the improvement in feed intake (Patience et al., 2000), it is possible that the weanling pig’s response to dietary energy concentration may differ between on-site and off-site weaning.
The overall objectives of the current study were to evaluate the potential interactive effects of weaning environment and varying dietary DE concentrations on weaned pig performance. The herd of origin was reflective of many commercial herds located in western Canada.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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).
Dietary Treatments.
Ingredient and nutrient composition of the experimental diets are listed in Table 1. The phase III and IV diets, provided to the pigs in pelleted form, were formulated to contain 3.6 and 3.1 g of apparent ileal digestible lysine/Mcal of DE, respectively. These concentrations were previously determined in this herd to be nonlimiting for pigs of this age (Oresanya, 2005). All other nutrients were provided above NRC (1998) requirements. Canola oil was limited to a maximum of 5.0% to maintain pellet quality.
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; Smith et al., 1999), which is typical of commercial practice in western Canada. The range of energy between DE treatment concentrations was 150 kcal/kg; this range exceeds the variability within cereal grains of 1.5%, or 53 kcal (Fairbairn et al., 1999), allowing differences to be more readily attributed to treatment and not to ingredient variability.
Experiment 1
Animals and Management.
Before the beginning of each of 3 replications, a total of 136 pigs (Camborough-15 x Canabrid, PIC Canada Ltd., Airdrie, AB) were weighed at 6 and 1 d before weaning. For each replication, which consisted of a nursery fill, 42 barrows and 42 gilts were selected based on BW, sex, and ADG from 11 to 16 d of age. Selected pigs were weaned at 17 x 2 d of age (5.3 x 0.2 kg) and randomly assigned to 1 of 2 nursery facilities: on-site or off-site. Half of the selected pigs, 21 barrows and 21 gilts, were transported to the off-site nursery by a truck that had been washed and disinfected with Clinicide (Bimeda-MTC, Cambridge, ON).
Within site, pigs were reweighed (d 0 BW), blocked by sex and BW, and sorted to provide 7 pigs of common sex per pen. Pens were assigned to 1 of the 3 DE treatment diets providing a total of 3 pens per sex per treatment at each site. Nontreatment commercial phase I (Ultrawean Unlimited, Federated Cooperatives Ltd., Saskatoon, SK) and phase II (Ultrawean 21, Federated Cooperatives Ltd.) starter diets were fed from 17 to 19 and 20 to 25 d of age, respectively. Both diets contained LS-20 (providing 22 mg of lincomycin/kg and 22 mg of spectinomycin/kg; Bio Agri Mix, Ltd, Mitchell, ON). Dietary energy treatments were initiated on d 9 after weaning and continued through to d 56.
Pigs were also weighed at the change of each diet phase (d 3, 8, and 25), at the midpoints of phases III (d 17) and IV (d 32), and at 56 d of age (d 39). Feeders were emptied and feed weighed back before weighing of the pigs.
Weaning Site.
The herd from which the pigs were obtained possessed antibody titers for porcine reproductive and respiratory syndrome (PRRS) and Streptococcus suis type 9, but was considered free of other respiratory and gastrointestinal diseases, as well as internal and external parasites. The on-site nursery was a bio-secure facility that housed the farrowing as well as a grower/finisher unit. The off-site nursery was located in a research facility on the University of Saskatchewan campus; no other pigs were housed in this facility. To ensure that the physical environment did not confound the response of the pigs to site, extensive attention was paid to housing, daily management, and ventilation. The off-site nursery was extensively modified such that penning, feeders, and drinkers were identical at both sites. Personnel at the off-site nursery followed strict standards of hygiene and did not come into contact with pigs other than the experimental animals. The technicians at the on-site nursery were exposed to pigs at all stages of production. A footbath containing a 1% Betadine solution (Purdue Pharma, Pickering, ON) was placed outside each nursery room. Personnel at each site communicated daily to ensure that all activities, including feeding, weighing, health treatments, and sample collection were conducted at the same time and in the same manner at each site. Other personnel were restricted from entering the nurseries.
Each pen measured 1.8 x 1.2 m and was equipped with a multiple-space dry feeder (0.9 m in length, Staco, Schaefferstown, PA), and a single bowl drinker (Balpi J.P., Soubry Distribution Representation Ltd., Repentigny, QC). The front 60% of the floor was plastic-covered, expanded metal; the rear 40% was woven wire. Both nursery facilities were equipped with a preheat air space (preheat hallway, on-site; and plenum chamber, off-site). Air was drawn into the nursery rooms through manual air inlets (Robbco, Winnipeg, MB) from the preheat air space. Air for the preheat space was supplied from the attic in the on-site nursery and directly from the outside at the off-site nursery. The control of temperature and fan speed at both nurseries was accomplished with identical proportional environmental control panels (model PEC; Phason, Winnipeg, MB). Relative humidity (psychrometer; Cole-Palmer, Anjou, Quebec), and CO2 and NH3 (Colorimetric Dredger; Matheson Gas Products Inc.) were measured twice weekly at 0800. To reduce variation in air quality between sites, ventilation rates and temperature set points were adjusted at each site based on CO2, NH3, and relative humidity measurements.
Air was sampled onto MacConkey Agar (Becton Dickinson Microbiology Systems, Cockeysville, MD) for coliform counts and onto Plate Count Agar (Difco Laboratories, Detroit, MI) for total aerobic counts using the Burkard Portable Air Sampler (Burkard Manufacturing Co., Ltd., UK). Samples were incubated aerobically at 37°C for 24 h. Visible colonies were counted and were expressed as cfu per liter of air.
Statistical Analysis.
Pen was the experimental unit to test the effects of DE concentration and sex. Data were analyzed as a split plot design using the GLM procedure of SAS (SAS Inst., Inc. Cary, NC). Site was the main plot, and DE concentration and sex were considered subplots. The statistical model included the effects of nursery site, DE, sex, replication, and all interactions. Weaning weight was used as a covariate. The replication x site term was used as the error term to test the effect of site. Contrasts for linear and quadratic effects were used to detect differences among DE concentrations. Values were reported as least squares means.
Experiment 2
Animals and Management.
The experiment was conducted using a 3 x 2 factorial arrangement of treatments (3 DE concentrations x 2 diet phases). Eighteen pigs were restricted-fed at 5.5% of BW in 2 equal meals at 0800 and 1600 (initial BW, 5.7 x 1.1 kg). Another group of 18 pigs was allowed ad libitum access to feed (initial BW, 7.3 x 0.6 kg). Because of the range in initial BW, restricted-fed pigs were blocked by weight percentile.
For each feeding regimen, an initial group of 30 cross-bred barrows (Camborough-15 x Canabrid, PIC Canada Ltd.) was weaned at 17 d of age and housed in 2 nursery pens. From 17 to 25 d of age, temperature set points and phase I and II diets were similar to those used in Exp. 1. Pigs were weighed at 17 and 25 d of age. To provide a uniform group, a total of 18 pigs per feeding regimen were selected based on BW and ADG (17 to 25 d of age).
Pigs and DE treatments were randomly assigned to pens within the room. Pigs were placed into individual metabolism pens (0.56 x 1.17 m) fitted with trays for urine collection. Collection vessels under the trays contained 20 mL of concentrated HCl. Bags attached to the pigs’ hindquarters were used for fecal collection (van Kleef et al., 1994). Pigs received phase III diets from 25 to 41 d of age and phase IV diets from 42 to 50 d of age, which mimicked the timing of diet changes in Exp. 1.
All pigs were weighed weekly, and feed allowance for the restricted-fed pigs was adjusted based on BW. Intake was not based on multiples of maintenance because the differing diet energy concentrations would have resulted in different daily feed allowances (kg/d) among dietary treatments.
Sample Collection.
Within each phase, the first 5 d were used for diet acclimation, followed by a 3-d collection of feces and urine. Pigs continued to receive phase III diets until 41 d of age although no further fecal or urine samples were collected.
Dry matter of feed and freeze-dried fecal samples was determined according to AOAC (method 930.15, AOAC, 1990). Gross energy of feed and fecal samples was determined by combustion in a Parr adiabatic bomb calorimeter (model 1281, Parr Instrument Co., Moline, IL). Feed, fecal, and urine samples were analyzed for N by a combustion method (method 968.06, AOAC, 1990) using a Leco protein/N determinator (model FP-528, Leco Co., St. Joseph, MI). The endogenous acid insoluble ash content of the diet was used as an indigestible marker (McCarthy et al., 1974).
Statistical Analysis.
Because they were housed separately, the individual pig was considered the experimental unit. Data were analyzed using the GLM procedure of SAS (SAS Inst., Inc. Cary, NC). The model included effects of DE, phase, DE x phase, DE x pig, and DE x block interactions. To detect differences between phases, pairwise comparisons of means were performed using the PDIFF procedure of SAS. The 2 studies with the different feeding regimes were designed to determine the actual DE content of the diets used in Exp. 1 by 2 different approaches. No attempt was made to compare the results of the studies. To detect differences among DE concentrations, contrasts for linear and quadratic effects were used. To determine the relationship between daily DE intake and N retention, the PROC REG procedure of SAS was used. Nitrogen retention (g/d) was regressed against daily DE intake (kcal/d) at each DE concentration. Digestible energy intake was calculated using ADFI and measured DE values. Values were reported as least squares means.
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RESULTS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Efforts were made to maintain similar environments at each site; however, CO2, (1,099 x 580 ppm), NH3 (8.4 x 5.0 ppm), and relative humidity (61.1 x 10.0%), were 74, 43, and 14% greater, respectively, at the off-site compared with the on-site nursery. Average daily temperature was 0.2°C greater at the on-site than the off-site nursery (28.4 vs. 28.2 x 2.4°C).
Sex affected performance only during the first 3 d postweaning, which was before the imposition of DE treatment. During this time, gilts had a greater ADG and ADFI than the barrows (0.12 vs. 0.10 kg/d, P < 0.05 and 0.19 vs. 0.13 kg/d, P < 0.05, respectively). Sex did not affect pig response to site of weaning or DE; thus all reported treatment means include both sexes. There was no interaction between site of weaning and DE concentration on ADG, ADFI, or G:F (P > 0.10). Therefore, all data are reported as main effects of site of weaning and DE concentration. The response of weaned pigs to weaning site and DE concentration are shown in Table 2.
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The coefficient of variation of pig final BW was similar between sites (12.7% off-site vs. 11.9% on-site).
Effect of Digestible Energy Concentration.
There was a linear decrease in BW (P < 0.01) and a quadratic response in ADG (P < 0.01) and ADFI (P < 0.001) from 25 to 56 d age, as DE concentration increased (Table 2
). Efficiency of gain improved linearly with increasing DE during this time period (P < 0.01). There was a quadratic response (P < 0.05) to DE for the phase III diets (25 to 41 d of age) with pigs fed the 3.35 Mcal of DE/kg of diet having the greatest ADFI and ADG. The linear decrease (P < 0.001) in ADFI and no difference in ADG (P > 0.10) resulted in a linear improvement in efficiency of gain (P < 0.001) with increasing DE for the phase IV diets (42 to 56 d of age). Overall (25 to 56 d of age) ADG and ADFI decreased (P < 0.01), and efficiency of gain was improved (P < 0.01) as DE concentration of the diets increased from 3.35 to 3.65 Mcal/kg.
As with site of weaning, dietary DE concentration had no effect on the CV of final BW (12.6, 13.9, and 12.5% for the 3.35, 3.50, and 3.65 Mcal/kg treatments, respectively).
Bacterial Counts.
Total aerobic bacterial counts increased from an average of 24 x 11 cfu/L of air during wk 1 to 57 x 19 cfu/L by wk 6 (Table 3). Coliforms increased from a mean of 0.03 x 0.03 to 0.67 x 1.5 during this same period.
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). The incremental improvement observed between the 3.50 and 3.65 Mcal/kg of DE concentrations was greater in phase III than in phase IV resulting in a phase x DE interaction (P < 0.05). Daily DE intake increased linearly with increasing DE concentration (P < 0.05). The measured DE values were lower than the formulated DE values for all diets.
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). Urinary N output was greater in phase IV than phase III (P < 0.05) but unaffected by DE concentration (P > 0.10). The N digestibility and calculated N retention increased linearly (P < 0.001) as DE concentration increased and was greater in phase IV than in phase III (P < 0.05). Nitrogen retention was highly correlated to daily energy intake at the 3 DE concentrations (3.35, R2 = 0.84; 3.50, R2 = 0.93; 3.65 Mcal of DE/kg, R2 = 0.95), and the slope of the line was similar for the 3 DE concentrations (data not shown).
Ad Libitum Fed Pigs.
Similar to results observed with the restricted-fed pigs, a linear increase in energy digestibility was observed with increasing DE concentration (P < 0.05; Table 5). The incremental improvement observed between the 3.50 and 3.65 Mcal of DE/kg concentrations was greater in phase III than phase IV (P < 0.05; phase x DE.). The measured DE values were lower than the formulated DE values for all diets. Daily DE and N intake were greater in phase IV than phase III (P < 0.05) but unaffected by DE concentration (P > 0.10). Nitrogen digestibility, fecal and urinary N output, and N retention were greater in phase IV than in phase III (P < 0.05). Nitrogen digestibility and urinary N output increased (P < 0.05) and fecal N output decreased (P < 0.05) as DE concentration of the diet increased. Nitrogen retention was highly correlated to daily energy intake at the 3 DE concentrations (3.35, R2 = 0.94; 3.50, R2 = 0.93, 3.65 Mcal of DE/kg, R2 = 0.80).
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DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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), the absence of internal and external parasites, and the low incidence of diarrhea, coughing, or other clinical symptoms of gastrointestinal or respiratory disease (Madec et al., 1998). However, the herd carried a titer for PRRS and regularly observes meningeal and arthritic symptoms of Streptococcus suis.
Site of Weaning
In the current study, pigs were weaned at 17 x 2 d of age to either an on- or off-site nursery. Dietary DE treatments were imposed at d 25 (i.e., 8 d postweaning). The results indicate that weaning pigs to the off-site nursery improves pig weight at 56 d of age, even when the herd of origin had a relatively high health status. There was an 11.5% improvement in ADFI and an 8.9% heavier BW at 56 d of age in pigs weaned to the off-site nursery. The current study is similar to reports in the literature; however, many of the studies that examined off-site weaning in comparison with conventional weaning systems were confounded by different weaning ages, different housing systems, or different management procedures. Drum et al. (1998) found that segregated early weaned (SEW) pigs (weaned at 10 d of age) were 17% heavier at 56 d of age compared with pigs weaned at 24 d of age to an on-site nursery. Walker and Wiseman (1994) reported a 16% improvement in ADG during the nursery period for SEW pigs (weaned at 10 d of age) compared with conventionally weaned pigs (weaned at 27 d of age to an on-site nursery), and weaning pigs at 14 d of age into a cleaner nursery resulted in improved growth and feed intake at 49 d of age compared with conventionally weaned pigs at 21 d of age (Bazinet et al., 2003).
Fangman et al. (1996b) found no difference in performance between pigs weaned at either 16 or 13 d of age, to an on- or off-site sanitized nursery or those remaining in their original nursery, commingled with older pigs. No information was provided on the effect of weaning age x nursery site interaction. In the current study, potential confounding due to age, genetics, or the preweaning environment was removed by obtaining the 2 treatment groups from the same farrowing group and randomizing according to BW and preweaning growth. Additionally, pigs were allowed to adjust to their nursery environments for 7 d before the imposition of dietary treatments.
Crowe et al. (1996) observed less dust and lower total and respirable endotoxins in the air of an off-site nursery compared with a conventional nursery. In the current study, extraordinary measures were taken to ensure that the physical environment and animal management procedures between the sites were comparable. The trend to greater coliform and total aerobic bacteria counts observed in the off-site nursery may be explained by a lower actual vs. estimated ventilation rate suggested by the greater CO2, NH3, and relative humidity measurements. Although identical environments were not maintained between weaning sites, the environmental concentrations were within the range where pig performance is unlikely to be affected by CO2 (<2500 ppm; CIGR, 1984), NH3 (<25 ppm, time weighted average; Zhang, 1994), or relative humidity (50 to 80%; ASAE, 2000). Therefore, we are able to conclude that the responses observed in the current study result from physical segregation from the herd of origin and not from a superior physical environment in an off-site nursery.
Pig response to off-site weaning seems to be greater at a younger weaning age. The 8.9% improvement in BW at 56 d of age in pigs weaned at 17 x 2 d of age to an off-site nursery in the current study is less than the 12.5% reported by Patience et al. (2000) using pigs weaned at 12 d of age. Fangman et al. (1996b) reported that pigs weaned at 8 to 13 d of age were 16% heavier at 56 d of age compared with pigs weaned at the same age to an on-site nursery, but the difference was only 11.4% when the pigs were weaned at 17 to 21 d of age. Average daily gain, however, was consistently greater in the older weaned pigs (Fangman et al. 1996b).
The difference in ADFI between off- and on-site pigs was not significant until 42 d of age. An improved ADFI in pigs weaned to an off-site nursery has been reported by others (Fangman et al., 1996b; Drum et al., 1998; Patience et al., 2000).
Boeckman (1996) hypothesized that the response to off-site weaning is due to a naïve immune system, a result of the reduced pathogen exposure. The results of the air bacteria count in our study showed no difference between weaning site; however, due to the low sampling frequency and high variability observed with these measurements, it was not possible to conclusively support or refute their hypothesis. The lower total fecal enterobacteria concentrations in SEW pigs compared with conventionally weaned pigs as reported by van Kessel et al. (1997), and the greater number of villi and villus height:crypt depth ratio in off-site compared with on-site pigs as reported by Tang et al. (1999) all suggest reduced pathogen exposure in off-site pigs. The greater villus height is suggestive of more mature and functional enterocytes (Hampson, 1986) indicative of improved digestive capabilities in the off-site pigs.
On-site pigs might respond to increased dietary energy density due to greater maintenance energy requirements because of a reduced efficiency of gain (Patience et al., 2000) or greater immune stimulation (Williams et al., 1997). Bazinet et al. (2003) reported increased whole body oxidation of linoleic and linolenic fatty acids and increased acute-phase protein in pigs weaned conventionally at 21 d of age compared with pigs weaned at 14 d of age into a segregated, cleaner nursery. However, in the current study, the interaction between the site of weaning and DE concentration was not significant. A repartitioning of energy and amino acids away from growth and to immune function may explain some of the response to pigs weaned on-site; however, the greater feed intake and marginal improvement in efficiency of gain in the off-site pigs suggests that additional factors need to be considered.
Digestible Energy
The effect of dietary energy density on weanling pig performance is conflicting. In some studies, increasing the dietary energy concentration resulted in improved gain (Hastad et al., 2001a). Others, in agreement with the current study, were unable to demonstrate a growth response to increased dietary energy density (Tokach et al., 1995; Hastad et al., 2001b).
Dietary energy concentration in this experiment was increased with the inclusion of canola oil and oat groats at the expense of barley. Consequently, the proportion of energy derived from fat increased from 6.6 to 14%. Differing ingredients and proportion of fat in the diet will affect both palatability and energy digestibility. Because of the decreased feed intake, energy intake was similar among treatments. Extrapolating to the growth study, the energy values determined in the digestibility study (Exp. 2) using ad libitum feed intake, overall DE intake was 2.34, 2.30, and 2.45 Mcal/d for the 3.35, 3.50, and 3.65 Mcal/kg treatments, respectively. The maintenance of a similar energy intake despite varying dietary energy density has been reported by others (Nam and Aherne, 1994; NRC, 1998) and allows us to conclude that palatability did not limit feed intake.
Energy digestibility increased as DE concentration increased. Fat digestibility coefficients were not determined in this study; however, Baidoo et al. (1996) calculated that the digestibility of canola oil by 20 to 30 kg growing pigs was not affected by inclusion amount when 2 to 8% was added to barley and wheat-based diets. The improvement in efficiency of gain with increasing DE density observed in phase IV (42 to 56 d of age) was not seen in phase III, supporting the conclusions of others (Tokach et al., 1995) that fat digestibility is limited in pigs under 35 d of age. Conversely, energy digestibility tended to plateau in phase IV at the greater DE treatment, whereas it continued to increase up to this treatment in phase III (resulting in a phase x DE interaction) indicating a greater contribution of the added fat to energy digestibility in the younger pigs.
Similar to what has been seen by others (Baidoo et al., 1996), we observed considerable difference between formulated and measured DE values, particularly with the lower energy density diets. The digestibility coefficients for cereal grains are based on grower pig data. These coefficients may not accurately predict digestibility in the weaned pig, especially when using high fiber ingredients such as barley. Increasing fiber content increases digesta passage through the intestinal tract (Potkins et al., 1991), and young pigs have a limited ability to digest fiber (Kyriazakis and Emmans, 1995). The increase in passage rate along with the limited fiber digestion capability may account for the greater difference between formulated and measured DE values when dietary DE concentration was reduced. Energy digestibility was lower in pigs with ad libitum feed intake, probably a result of the greater daily feed intake and rate of passage of digesta (Ewan, 2001; Casano, 2002).
Other studies (Lawrence et al., 1994; van Lunen and Cole, 1998; Smith et al., 1999) have examined the response of varying dietary energy density in young pigs in relation to other nutritional responses (i.e., lysine:energy ratio). The current study examined the effect of energy density on performance and digestibility under the assumption that no other nutrients were limiting. The lysine intake (g/d) required to support the daily gain that was observed in this study was estimated (NRC, 1998). The calculated, daily digestible lysine intakes were 3.2, 2.2, and 1.3% greater than the NRC (1998) estimated requirement for the 3.35, 3.50, and the 3.65 Mcal of DE/kg treatments, respectively. Based on these calculations, daily lysine intake was not likely limiting performance in the current study, assuming NRC (1998) is correct for this genetic line. All other nutrients were formulated to be in excess (NRC, 1998).
The CP content of the diet increased in both phases with increasing DE concentration. Excessive AA are deaminated, resulting in an increased heat production (Le Bellego et al., 2001), a loss not accounted for with the DE system. Therefore, we estimated the NE content of the experimental diets (CVB, 1998; Table 1). A value of 8.8 Mcal of DE/kg was used for canola oil (CVB, 1998). The DE/NE ratio was similar among diets. Therefore, the lack of a response to DE cannot be explained on the basis of heat increment due to the increased CP in the high-energy diets.
The distribution of dietary energy between protein and lipid accretion is determined by the relationship between energy intake and protein deposition (Whittemore and Fawcett, 1976). Nitrogen retention increased as daily DE intake increased in restricted-fed pigs, suggesting that at an equivalent daily feed intake, increasing DE concentration can improve pig performance, which is supported by Lawrence et al. (1994). However, when pigs were fed ad libitum, there was no increase in N retention with increasing energy density. The similar N retention among dietary energy concentrations in pigs with ad libitum access to feed suggests that in the current study, any observed difference in gain was an increase in body lipid rather than protein. Only a few studies have examined the effect of energy density on protein and fat deposition (van Lunen and Cole, 1998; Res de Souza et al., 2000). Res de Souza et al. (2000) found no improvement in performance and an increase in the energy and lipid content of the empty BW gain when tallow was added to the diet at 4 or 8%. A decrease in daily deposition of protein with increasing fat in the diet also was observed (Res de Souza et al., 2000). van Lunen and Cole (1998) reported an improvement in performance that was characterized by an increase in protein and lipid gain (g/d) with increasing energy density.
van Lunen and Cole (1998) suggested a maximum N deposition rate of 17 g/d over the weight range of 9 to 25 kg of BW when DE is supplied at 14.25 or 16.40 MJ of DE/kg (3.41 and 3.92 Mcal of DE/kg) and lysine is not limiting. This value is similar to the N deposition rate of 19 g/d over a weight range of 10 to 20 kg of BW observed in the current study. In our study, the slope of the linear relationship between daily DE intake and N retention was similar for all 3 diets regardless of feeding regimen.
Gut Capacity Limitation
The NRC (1987) suggests that pigs weaned at 14 to 21 d of age have a limited ability to regulate feed intake based on dietary energy density. In the current study, pigs in Exp. 1 compensated for reduced dietary DE concentration by increasing feed intake. These pigs were weaned at 17 d of age; however, the dietary DE treatments were not imposed until d 25. The ADFI of pigs in this study was approximately 90% of the NRC (1998) estimated voluntary feed intake for pigs less than 20 kg of BW. Results from Smith et al. (1999) support the regulation of feed intake based on DE content in pigs less than 25 kg. Conversely, van Lunen and Cole (1998) showed no decrease in feed intake with increasing energy density, and Black et al. (1986) suggested that pigs weighing less than 20 kg are unable to compensate for dietary energy when the energy density of the diet is below 3.82 Mcal of DE/kg.
Pigs from 12 to 25 kg of BW may be able to accommodate diets of increasing bulk that have an increased dietary fiber content and water holding capacity with changes in the gastrointestinal tract. The weight of the stomach, large intestine, and cecum increased with increasing dietary fiber (Kyriazakis and Emmans, 1995). Young pigs (12 to 32 kg of BW) adapt to fibrous feedstuffs within 14 d (Whittemore et al., 2001). When a control diet (3.20 Mcal of DE/kg, 2.64% ADF) was compared with high bulk diets based on 35 or 56% sugar beet pulp, ADFI and gain were greater in pigs fed the control diet compared with pigs fed either high bulk diet for the first 7 d (Whittemore et al., 2001). However, in the following 7 d period, feed intake was greater in pigs on the 35% sugar beet pulp diet compared with the control diet such that daily DE intake and live weight gain were also greater in pigs on this diet. Because the experimental diets were fed for a minimum of 31 d in the current study, the pigs on the lower energy diets may have developed increased gut capacity as a result of the dietary fiber content, and therefore the response to decreased dietary DE concentration was related to voluntary feed intake rather than gut capacity.
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONIMPLICATIONSLITERATURE CITED |
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Footnotes |
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2 Corresponding author: denise.beaulieu{at}usask.ca
Received for publication May 16, 2005. Accepted for publication December 15, 2005.
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6 and 18:23 in the pig varies markedly with weaning strategy and dietary 18:23. J. Lipid Res. 44:314–319.
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