J. Anim. Sci. 2003. 81:209-216
© 2003 American Society of Animal Science
Impact of energy intake and pregnancy status on rate and efficiency of gain and backfat changes of sows postweaning
G. C. Shurson*,1,
G. W. Libal
,2,
J. Crenshaw
,
C. R. Hamilton,3,
R. L. Fisher*,4,
D. D. Koehler*,5 and
M. H. Whitney*
* Department of Animal Science, University of Minnesota, St. Paul 55108;
and
Department of Animal and Range Science, South Dakota State University, Brookings 57007; and
and
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
1 Correspondence:
E-mail:
shurs001{at}umn.edu.
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Abstract
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A collaborative study was conducted to evaluate factors related to determining optimal feeding and management programs for increasing net returns from marketing cull sows. A total of 269 multiparous sows averaging 192 kg of body weight were weaned, moved to individual gestation crates, and assigned to one of eight treatment combinations in a 2 x 2 x 2 factorial arrangement for a 42-d postweaning feeding experiment. Factors included limited (L) (1.8 kg/sow/d) or ad libitum (AL) access to feed during wk 1 postweaning, a corn–soybean meal (corn) or barley–sunflower meal (barley) diet, and pregnant or nonpregnant status. All sows were provided ad libitum access to feed from wk 2 to 6 postweaning. Gain and feed intake (FI) data were collected weekly for each sow and used to calculate gain:feed (G/F). Ultrasonic backfat (BF) data were collected on d 0, 21, and 42 postweaning. Sows on the AL treatment had greater FI (P < 0.05) but similar gain (P = 0.80) for the 42-d postweaning period compared to sows on the L treatment. Most of this response was due to lower sow body weight loss during wk 1 postweaning (P < 0.01) when sows were provided AL (-7.2 kg) vs L (-13.2 kg) access to feed. Sows fed the corn diet had higher gain (P < 0.01), improved G/F (P < 0.01), and increased BF (P < 0.01) over the 42-d feeding period than sows fed barley. The corn diet resulted in less sow BW loss (P < 0.01) during wk 1 (-8.8 kg) than the barley diet (-11.6 kg). Pregnant sows had higher gain, FI, G/F, and BF (P < 0.01) than nonpregnant sows over the 42-d feeding period. Most of this advantage occurred during wk 4 postweaning when FI and gain of nonpregnant sows was lower (P < 0.01) than for pregnant sows. An economic analysis indicated that, when cull sow prices are relatively high and feed prices are moderate to low, maintaining and managing cull sows for an additional 6 wk postweaning may be economically advantageous compared to 0 or 3 wk. Pregnant sows fed the corn diet produced the greatest economic return. These results suggest that mating sows as they return to estrus postweaning and providing ad libitum access to a corn–soybean meal diet improves growth performance and feed efficiency, and may thereby provide increased returns when marketing cull sows.
Key Words: Energy • Feed Intake • Postweaning Interval • Pregnancy • Sows
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Introduction
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The sale of cull sows represents a small but significant economic contribution (4 to 6 %) to the swine industry. Unfortunately, little research has been conducted to evaluate feeding, management, and marketing strategies to improve the economic value of this derivative of pork production. Previous studies have shown variable performance levels of cull sows fed corn–soybean meal diets for various lengths of time postweaning. Shurson et al. (1991) showed that sow BW, condition, and previous level of performance contribute to expected performance of sows during a postweaning feeding period.
Sows can be either sold immediately after weaning as wet sows, or fed for a period and marketed as dry sows. Economic returns from feeding cull sows prior to market are dependent on a number of different factors, including feed cost, rate and efficiency of weight gain, facility costs and/or availability, market price, and discounts for wet sows. Evaluating feeding programs and diet composition that may improve feed efficiency or weight gain may offer significant opportunities for swine producers to increase economic returns by feeding cull sows prior to marketing.
This study was conducted to test several postweaning feeding strategies that may be implemented prior to marketing cull sows. The objectives of this study were to evaluate the impact of dietary energy density, feeding level, and pregnancy status postweaning on the rate, efficiency, and composition of weight gain in sows. In addition, an economic analysis was conducted to determine which strategy or combination of strategies provides the greatest net economic return, and if a 3- or 6-wk postweaning period provides additional return compared to marketing wet sows.
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Materials and Methods
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Animals and Measurements
A total of 269 multiparous sows from three different herds (University of Minnesota, North Dakota State University, and South Dakota State University) were used. The genetic composition of sows in Minnesota and South Dakota were Yorkshire x Landrace F1, and Yorkshire x Hampshire x Duroc in North Dakota. Sows were individually housed in confinement gestation facilities and fed in individual gestation stalls throughout the experimental feeding period.
Animals were weighed immediately following weaning and assigned to one of the eight treatments based on weight, body condition, and parity. All sows were weighed weekly until the conclusion of the 42-d study to determine growth performance. Individual sow feed consumption was also measured on a weekly basis. Average backfat measurements were taken on all sows using a backfat probe (Renco LeanMeater) at weaning, d 21, and d 42 postweaning in an attempt to measure body composition change. Sows assigned to pregnant treatments were mated as they returned to estrus (3 to 7 d postweaning) to provide comparative differences in rate, efficiency, and composition of gain. Sows that were mated but returned to estrus 4 wk postweaning were removed from the trial. Those sows assigned to restricted (R) feeding levels were limit-fed 1.8 kg/d for the first week postweaning, and then allowed ad libitum access to feed for the remaining 5 wk of the trial.
Experimental Diets and Treatments
All sows were fed either a corn–soybean meal- or barley–sunflower meal-based diet (Table 1
) to study the effects of dietary energy density on growth rate, efficiency, and composition of gain. Separate vitamin and trace mineral premixes were used by each participating station, but all premixes were included to ensure that vitamins and minerals were provided to exceed NRC (1988) minimum recommendations. Corn–soybean meal diets were formulated to contain 3,172 kcal of ME/kg, 12.2% crude protein, and 0.52% lysine. Sows were assigned to one of eight treatments arranged in a 2 x 2 x 2 factorial of pregnancy status (pregnant or nonpregnant), feeding level during the first week postweaning (ad libitum [AL] or limit fed [L]), and diet composition (corn–soybean meal [corn] or barley–sunflower meal [barley]). Barley diets were formulated to contain 2,754 kcal of ME/kg, 14.6% crude protein, and 0.52% lysine. Diets were estimated to contain 2.8 and 6.4 % crude fiber, respectively, and were equivalent in Ca and P content.
Statistical Analysis
The experiment was a 2 x 2 x 2 factorial arranged in a randomized complete block design. The data were statistically analyzed using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC). Individual sow measurements were considered the experimental unit. Least squares means were calculated and used to evaluate responses to first-week feeding level, diet fed (energy level), and pregnancy status for ADG, ADFI, gain:feed ratio (G/F, weekly and total), and change in backfat (wk 1 to 3, wk 4 to 6, and wk 1 to 6). Initial sow BW at weaning was used as a covariate for ADG, ADFI, and G/F responses, whereas initial sow backfat at weaning was used as a covariate to evaluate changes in backfat depth. Location (station) did not appreciably affect (P > 0.15) growth or backfat responses to first-week feeding level, diet, or pregnancy status, and therefore those interactions were not included in the model.
Economic Analysis
An economic analysis was conducted using growth performance and feed intake data obtained from this experiment, based on the model used by Plain and Shurson (1999). Least squares means for ADG and ADFI were used to determine BW gain and feed intake over 3- and 6-wk postweaning periods, dependent on pregnancy status, feeding level wk 1 postweaning, diet fed, and all interactions between these dietary and management factors. An initial sow weaning weight of 190 kg and fixed nonfeed cost of $1.50/wk for each sow marketed were assumed. A low or high ($ 0.10 and $0.15/kg) feed cost, low or high ($0.70 and $0.90/kg of live BW) cull sow market price, and presence or absence of a $0.07/kg wet sow market price discount were included in the model. Differences in diet cost, expense for breeding, and any additional nonfeed costs were not considered since these costs may be quite variable dependent on individual operation. A pregnant sow discount at the time of marketing was not considered since most procurement facilities would not consider a difference at 6-wk gestation. In addition, many cull sows are marketed on a carcass-yield basis, and therefore would account for the presence of conceptus.
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Results and Discussion
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Sow Responses to Dietary Energy Density Postweaning
Sows fed the lower-energy barley diet gained an average of 0.18 kg•d-1•sow-1 less (P < 0.01) than sows fed the higher-energy corn diet throughout the entire 42-d postweaning feeding period (Table 2). Except during wk 3, 4, and 6, sows fed the corn diet had increased daily gains throughout the trial, but especially during wk 1 (P < 0.01) and 5 (P < 0.05). This resulted in an 18.2% increase in BW gain and 3.8% increase in ending sow weight (P < 0.05).
Feed intake was depressed for sows fed the lower-energy diets during wk 1 and 2 postweaning (P < 0.01). Even though sows fed the barley diet had a numerical decrease in feed intake (5.74 kg/d) and energy consumption (15.81 Mcal ME/d) than sows fed the corn diet (5.88 kg/d and 18.65 Mcal ME/d, respectively) over the 42-d feeding period (Table 2
), they were also less efficient (0.17 kg gain/kg feed) compared to sows fed the corn diet (0.20 kg gain/kg feed) (P < 0.01) for the 42-d study. This was due in part to lower feed efficiency rates during wk 1 (-0.65 vs -0.41, P < 0.10) and 4 (0.21 vs 0.26, P < 0.10) postweaning. Negative growth and feed efficiency values were observed for most sows during the first week postweaning due to high levels of water loss during the postsuckling period.
As expected, sows fed the lower-energy barley diet tended to accumulate less backfat from weaning to d 21 postweaning (0.86 mm, P < 0.05) and over the entire 42-d feeding period (1.46 mm, P < 0.01) compared to sows fed the higher-energy corn diet.
These results are in agreement with those reported from a previous study (Fernandez et al., 1986) that showed that sows are relatively efficient in utilizing high-fiber feedstuffs (barley and sunflower meal) compared to growing pigs. However, another study (Pollman et al., 1979) indicated that as the fiber content of the diet increases, digestibility of fiber, energy, and nitrogen decreases when comparing diets with sun-cured alfalfa, tall wheat straw, and corn–soybean meal. These two studies suggest that both source and level of dietary fiber need to be considered when developing feeding programs to optimize nutrient (energy) utilization in sows.
Results from this study suggest that a lower-energy, higher-fiber diet, such as the barley diet provided in this experiment, allows reasonable gains and efficiency of gain with less backfat gain over a 42-d feeding period. However, the feeding of a corn–soybean meal diet results in heavier sows at the end of the feeding period.
Sow Responses to Feeding Level the First Week Postweaning
There were no differences in overall ADG between sows that were L- or AL-fed the corn or barley diet during wk 1. During wk 1 postweaning, L sows lost an average of 1.88 kg/d, whereas AL sows lost an average of 1.03 kg/d (Table 2), a 45% reduction in BW loss (P < 0.01). However, the 6.0-kg difference in total BW loss between L and AL sows at the end of wk 1 was almost completely recovered at the end of the 42-d experimental period (239.4 vs 235.0 kg; P > 0.20). This suggests that sows that are nutrient-restricted during the first week postweaning achieve compensatory gain during subsequent feeding periods.
Sows that were limit-fed during the first week after weaning had similar increases in backfat accretion (8.24 mm) during the 42-d feeding period compared to sows that were full-fed during wk 1 (8.32 mm) (P = 0.89). Sows that were limit-fed during the first week after weaning, however, ate 13.4 kg less feed (237.3 vs 250.7 kg) (P < 0.05) than full-fed sows during the entire 42-d feeding period, and appeared to be slightly more efficient in converting feed to BW gain (0.182 vs 0.191 kg of gain/kg feed, respectively; P = 0.12). These results suggest there may be a slight advantage to limit-feeding sows during the first week after weaning to reduce overall feed cost/kg of gain.
Sow Responses to Pregnancy Status Postweaning
Sows that were mated as they returned to estrus after weaning, and that remained pregnant over the 42-d feeding period, gained an average of 0.26 kg/(sow•d) more (P < 0.01) than sows that were not pregnant during the study (Table 2). Much of this weight-gain advantage occurred during wk 4 of the feeding period when pregnant sows gained 1.09 kg/d, whereas nonpregnant sows gained only 0.10 kg/d (P < 0.01). The minimal weight gain experienced by nonpregnant sows during wk 4 can most likely be attributed to the fact that those sows returned to estrus during that week and consumed 8.05 kg less feed than pregnant sows (P < 0.01). However, the majority of the weight gain advantage of pregnant sows was due to higher average daily feed consumption (6.04 vs 5.58 kg/d; P < 0.01) over the 42-d feeding period. Pregnant sows also were more efficient (P < 0.01) in converting feed to BW gain (0.202 kg gain/kg feed) than nonpregnant sows (0.171 kg gain/kg feed). However, pregnant sows had an increased (30%) rate of backfat deposition, resulting in a greater proportion of BW gain being attributed to backfat deposition (P < 0.01).
Nutrient utilization, BW, and compositional changes are different between pregnant and nonpregnant sows (Close et al., 1984, 1985; Noblet et al., 1985). In the pig, there is conflicting evidence on the extent to which maternal nutrition influences fetal growth. If there is a range of feed intakes over which fetal growth and development are independent of maternal nutrition, then there is likely to be a range in which nutrients are partitioned between maternal and reproductive tissues (Close et al., 1984). Net maternal gain and the differences between pregnant and nonpregnant animals have been shown to vary with both feeding level and stage of gestation (Close et al., 1984).
These results may suggest that hormonal patterns associated with pregnancy have a large effect on BW gain, ad libitum feed intake, and gain efficiency, and that increased nutrient partitioning toward maternal growth appears to occur.
Sow Responses to Feeding Level, Dietary Energy Density, and Pregnancy Status Postweaning
Despite the fact that sows lose BW after weaning while consuming considerable amounts of feed (Shurson et al., 1991), feeding a low metabolizable energy density barley-sunflower meal diet further increases BW loss (Tables 2, 3, and 4), regardless of whether sows are limit- or full-fed during the first week postweaning (P < 0.01). As expected, no effect on weight loss during wk 1 postweaning can be attributed to whether sows are mated since they normally return to estrus within that time period (Table 2). Pregnancy status, however, significantly affects growth, feed intake and efficiency, and backfat accretion during the first 6 wk postweaning (Table 2), regardless of diet (Table 4) or feeding level wk 1 postweaning (Table 5) (P < 0.10). One study has shown that loss of body water at weaning is considerable, but is significantly less than that which occurs in the fasted animal, and depletion of body tissue (including protein) occurs in the newly weaned sow (Zoiopoulos, 1983). Therefore, in order to minimize sow weight loss during the first week postweaning, sows should be fed a corn–soybean meal diet ad libitum. Mating sows further improves growth performance and feed conversion.
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Table 3. Effects of a diet type x feeding level interaction on ADG, ADFI, gain:feed, and change in backfat thickness values of cull sows d 0 to 42 postweaning
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Table 4. Effects of a diet type x pregnancy status interaction on ADG, ADFI, gain:feed, and change in backfat thickness values of cull sows d 0 to 42 postweaning
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Table 5. Effects of a feeding level x pregnancy status interaction on ADG, ADFI, gain:feed, and change in backfat thickness values of cull sows d 0 to 42 postweaning
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Economic Analysis of Different Management Regimes on Marketing Cull Sows at 3 or 6 wk Postweaning
Results of an economic analysis of the results achieved from this trial are presented in Tables 6 to 9. Net profitability per sow marketed is presented for each factor included, in addition to the estimated feed consumed and BW gained that is assumed in the model. Including the presence of a wet sow discount of $0.07/kg of live weight in the model resulted in an additional $1.12 to $3.83/cull sow marketed, dependent on feeding and/or management factors and the feed costs and sow prices included, but did not guarantee a net profit for marketing cull sows at 3 or 6 wk postweaning. In general, feeding for 6 wk postweaning was advantageous compared to 3 wk only when sow price was high ($0.90/kg) and feed cost low ($0.10). When net return was near or below break-even, feeding for 3 wk was more economically advantageous than feeding for 6 wk. This indicates that if market prices are such that it is economically justified to feed cull sows, then a 6-wk period is preferable to a 3-wk period.
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Table 6. Economic analysis of different feeding and management regimens over a 3-wk postweaning period, assuming no wet sow discount, on net profitability per cull sow marketeda
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Table 9. Economic analysis of different feeding and management regimens over a 6-wk postweaning period, assuming a $0.07/kg of live weight sow discount, on net profitability per cull sow marketeda
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Sows that were mated and pregnant, and sows that were fed the corn diet had the greatest economic returns. There was no appreciable difference in feeding level during the first week postweaning on net profitability. Combining the pregnancy and corn factors resulted in additional increases in net profitability. However, this economic model does not consider a difference in feed cost between the corn and barley diets, nor does it consider the cost associated with breeding a sow. Although these costs should be relatively low, they will decrease the expected net return for each of these strategies. The least profitable scenarios occurred when sows were not mated and/or were fed the barley diets.
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Implications
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Ad libitum feeding during the first week postweaning increased overall average daily feed intake, but did not affect average daily gain, sow body weight, backfat accretion, or net return per cull sow marketed. Feeding a barley–sunflower meal diet decreased average daily gain and feed efficiency, and lowered average daily feed intake slightly. Mating sows immediately postweaning had increased average daily gain, average daily feed intake, gain:feed ratio, and backfat levels for the 42-d trial. Sows that were pregnant and/or fed a corn–soybean meal had the greatest net returns when fed for 3 or 6 wk postweaning. These results suggest that maximal growth and gain:feed ratio of cull sows can be achieved by mating sows as they return to estrus postweaning and by providing a corn–soybean meal diet. Maximal net economic returns may be achieved by implementing this strategy for 6 wk postweaning. It is a combination of other factors, including feed cost and sow price (wet and dry), that determines whether to market cull sows wet, and which diet to feed and for what period of time if marketing cull sows dry.
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Table 7. Economic analysis of different feeding and management regimens over a 3-wk postweaning period, assuming a $0.07/kg of live weight wet sow discount, on net profitability per cull sow marketeda
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Table 8. Economic analysis of different feeding and management regimens over a 6-wk postweaning period, assuming no wet sow discount, on net profitability per cull sow marketeda
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Footnotes
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2 Current address: 9101 Riverstone Ct., College Station, TX 77845. 
3 Current address: Darling Int., 251 O’Connor Ridge Blvd., Ste. 300, Irving, TX 75038.
4 Current address: Vigortone Ag Products, Inc., 5264 Council St. NE, P.O. Box 1230, Cedar Rapids, IA 52406.
5 Current address: VitaPlus Corp., P.O. Box 259126, Madison, WI 53725.
Received for publication October 17, 2001.
Accepted for publication September 20, 2002.
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Literature Cited
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Close, W. H., J. Noblet, and R. P. Heavens. 1984. The partition of body-weight gain in the pregnant sow. Livest. Prod. Sci. 11:517–527.
Close, W. H., J. Noblet, and R. P. Heavens. 1985. Studies on energy metabolism of the pregnant sow: The partition and utilization of metabolizable energy intake in pregnant and non-pregnant animals. Br. J. Nutr. 53:267–279.[Medline]
Fernandez, J. A., H. Jorgensen, and A. Just. 1986. Comparative digestibility experiments with growing pigs and adult sows. Anim. Prod. 43:127–132.
Noblet, J., W. H. Close, and R. P. Heavens. 1985. Studies on the energy metabolism of the pregnant sow: Uterus and mammary tissue development. Brit. J. Nutr. 53:251–265.[Medline]
NRC. 1988. Nutrient Requirements of Swine. 9th ed. Natl. Acad. Press, Washington, DC.
Plain, R. L., and G. C. Shurson. 1999. Marketing cull sows. Pork Ind. Hand. No. 123. Purdue Univ. Coop. Ext. Serv., West Lafayette, IN.
Pollman, D. S., D. M. Danielson, and E. R. Peo, Jr. 1979. Value of high fiber diets for gravid swine. J. Anim. Sci. 48:1385–1393.
Shurson, G. C., G. A. Isler, K. M. Irvin, and G. A. Peterson. 1991. Traits affecting postweaning weight gain and feed intake of primiparous sows. J. Anim. Sci. 69:3487–3493.[Abstract]
Zoiopoulos, P. E., J. H. Topps, and P. R. English. 1983. Losses in weight and body water in sows after weaning. Br. J. Nutr. 50:163–172.[Medline]
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Abstract
Introduction
