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ANIMAL NUTRITION |
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* Centro Nacional de Investigación Disciplinaria en Fisiología Animal–Instituto Nacional de Investigaciones Forestales Agrícolas y Pecuarias, Ajuchitlán, Qro., México C. P. 76280;
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University of Minnesota, Morris 56267;
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University of Minnesota, St. Paul 55108; and
JBS United, Sheridan, IN 46069
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: embryo survival • fiber • performance • sow
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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). However, the response to dietary fiber is not consistent. Other workers (Pond et al., 1985; Calvert et al., 1985; Holzgraefe et al., 1986) reported no beneficial effects of dietary fiber on litter size in swine. The quantity and characteristics of fiber used to elicit improved litter size were not adequately described in previously reported research. Consequently, nutritionists are unable to formulate high-fiber diets for sows that will predictably enhance litter size compared with typical diets containing relatively low levels of fiber This study was designed to test the hypothesis that type of dietary fiber affects reproductive performance of sows. Therefore, the objective of this study was to formulate diets with carefully controlled types and concentrations of dietary fiber to better understand the effects of high-fiber sow diets on reproductive performance and to increase our understanding of the components leading to increased litter size caused by high-fiber diets fed to sows.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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The protocol for this study was approved by the University of Minnesota’s Institutional Animal Care and Use Committee before initiation of the experiment.
Forty-eight gilts (Duroc x Imperial Swine Genetics-Line 422) were used in this study. Gilts were assigned randomly to 1 of the 4 experimental diets (Table 1). The experimental diets were a control diet (C) based on corn and soybean meal containing 1.16% soluble fiber (SF) and 9.98% insoluble fiber (ISF). A second diet high in soluble fiber (HS) included oat bran to contain about 2-fold the amount of SF present in C (3.02%) and concentration of ISF similar to C (10.06%). A third diet high in insoluble fiber (HIS) included wheat straw to contain a similar amount of SF (1.08%), but nearly 2-fold the amount of ISF (18.09%) as C. A fourth diet high in both soluble and insoluble fiber (HS + HIS) used soybean hulls to double the amount of SF and ISF (2.46 and 24.55%, respectively) compared with C. Soluble fiber and insoluble fiber content of feed were measured by a modification (Prosky et al., 1988) to the total dietary fiber procedures described by Prosky et al. (1985) at Medallion Laboratories, Minneapolis MN. All diets were fed to sows in mash form. The oat bran was Diamond Brand #8 Coarse Oat Bran (LaCrosse Milling Co., Cochrane, WI). Wheat straw was ground twice through a 16-mm screen in a commercial hammer mill.
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Gilts were inseminated artificially 12 h after the first sign of estrus then again 12 and 24 h later using pooled terminal line Duroc semen (D-100, Compart’s Boar Store Inc.). After the first mating, gilts were fed individually once daily to meet their calculated energy requirements according to the NRC (1998) gestation model assuming 40 kg of BW gain during gestation and expected litter size of 10 pigs.
Gilts were checked for signs of estrus using a mature boar from d 16 to 21 after insemination. Pregnant gilts were slaughtered at the University of Minnesota Meat Laboratory between d 28 and 35 of gestation. Immediately after slaughter, the reproductive tract from every gilt was removed and ovaries were grossly examined for the number of corpora lutea (CL), which was assumed to equal the number of ova ovulated. The ovaries were explored thoroughly through dissection to determine the presence of any hidden CL. Uterine horns were opened carefully to recover the embryos within their trophoblastic vesicles. The total number of embryos and the crown-rump length of each embryo were recorded. A crown-rump length of more than 2 SD less than the mean for that gilt’s embryos was used as an objective measure of abnormal development (Jindal et al., 1996), and normally developed embryos were considered viable. Total embryo survival rate was calculated as the total number of embryos divided by the total number of CL, and viable embryo survival rate was calculated as the number of viable embryos divided by the number of CL according to Jindal et al. (1996).
Data were analyzed as a completely randomized design using the general linear models procedure (SAS Inst. Inc., Cary, NC). All reported means are least squares means. The statistical model included the effects of diet with day of gestation as a covariate. Data for pregnancy rate were analyzed using chi-square analysis. Simple linear regression analyses were used to determine the effects of SF, ISF, and ME intakes on ovulation rate, number of viable embryos, and embryo survival. Pooled SEM were calculated using the mean squared error and the harmonic mean due to unequal replication among experimental diets (Steel et al., 1997).
Exp. 2
The protocol for this study was approved by the University of Minnesota’s Institutional Animal Care and Use Committee before initiation of the experiment.
A total of 716 (Large White x Landrace) mixed parity sows were used in 3 concurrent trials conducted at the T.C. Bache Farm research facilities of JBS United, Sheridan, IN. Initial BW, date, and BCS (1 = very thin to 5 = very fat) were recorded as females entered the breeding area from gilt acclimation pens or from farrowing rooms on the day of weaning. At estrus, females were inseminated artificially twice with fresh, pooled semen obtained from different boars (Large White x Duroc) housed on the farm. Two days after insemination, sows were moved to 1 of 3 gestation rooms where they were assigned randomly to the control diet or 1 of the 3 experimental diets (HS, HIS, or HS + HIS; Table 2). Within a gestation room, sows received the control diet or one of the experimental, high-fiber diets. Throughout the experiment, only 1 experimental diet and the control diet were fed to sows in a given gestation room.
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Data in this experiment were analyzed as 3 concurrent trials under a completely randomized design using the general linear models procedure (SAS Inst. Inc.). Sows were classified by parity into 4 groups. Sows that were entering their first or second parity constituted groups 1 and 2, respectively. Sows that were in their third to fifth parity constituted group 3, and sows of 6 or more parities constituted group 4. Season was determined by the month in which sows were bred. July through the first half of September was considered summer, whereas the second half of September through November was considered autumn. The statistical model included the effects of diet, parity group, genetic line, and season as well as the interaction among these effects. Chi-square analyses were used to determine the distribution of parity groups and genetic lines across dietary treatments. All reported means are least squares means. Pooled SEM were calculated using the mean squared error and the harmonic mean due to unequal replication among experimental diets (Steel et al., 1997). Statistically significant differences were assumed with P-values <0.05. Probability values between 0.06 and 0.10 were considered trends.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Forty-three (C, 12; HS, 10; HIS, 10; HS + HIS, 11) of the 48 gilts assigned to experimental diets were mated. Neither initial BW (Table 4) nor pregnancy rate were affected by experimental diets. The pregnancy rates for gilts fed the experimental diets were 75, 90, 100, and 81.8% for gilts fed the C, HS, HIS, and HS + HIS diets, respectively.
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Gravid uterus weight was different among females fed the experimental diets. Gilts fed the C diet had a heavier gravid uterus (P < 0.05) than gilts fed HS, HIS, and HS + HIS diets with no difference among gilts fed HS, HIS, and HS + HIS diets. These differences in weight of the gravid uterus could be explained by the greater number (P < 0.05) of total embryos (Table 4
) and the associated placental tissues and fluids found in gilts fed the C diet compared with gilts fed the other experimental diets. Diet had no effect on the weight of the empty uterus from gilts fed the experimental diets.
Ovulation rate was similar among gilts fed the experimental diets (Table 4). Regression analysis demonstrated that ovulation rate was independent of intakes of SF, ISF, and ME recorded from first mating until slaughter. The relatively small differences in ME intake realized did not affect ovulation rate.
Total number of embryos and viable embryos were different among gilts fed the experimental diets (P < 0.05). Gilts fed HIS and HS + HIS diets had a decreased number of total and viable embryos compared with gilts fed C. Results of regression analyses suggested that ISF intake tended to negatively affect the number of viable embryos (P = 0.07; R2 = 0.09), but only about 9% of the decrease in the number of viable embryos could be explained by ISF intake. There was no relationship (P = 0.10; R2 = 0.07) between the SF intake and the number of viable embryos.
Total embryo survival was less for gilts fed HS + HIS compared with gilts fed C and HS. However, viable embryo survival was not different among gilts fed the experimental diets. A high plane of feeding during early gestation increases metabolic clearance rate of progesterone in gilts and can decrease embryo survival (Ashworth, 1991; Prime and Symonds, 1993). Consequently, a regression analysis was performed to explore the effects of ME intake on embryo survival. There were no relationships between ME intake (R2 = 0.007) and embryo survival, which was likely due to the similarity of ME intake among gilts fed the experimental diets. Similarly, SF intake was not related (R2 = 0.04) to embryo survival. Insoluble fiber intake (P = 0.08; R2 = 0.08) tended to decrease embryo survival, but only a small portion of the effect (i.e., about 9%) on embryo survival could be explained by ISF intake.
Decreased total embryo survival when gilts were fed the HS + HIS diet in this study is consistent with our previous research (Holt et al., 2006) where sows fed a diet containing 40% soybean hulls from 1 d postweaning through d 109 of gestation had fewer total piglets born per litter than sows fed a control diet. The results reported herein suggesting a lower number of viable embryos due to elevated ISF intake contrast with those of other research groups that demonstrated increased litter size when feeding diets high in ISF (Carter et al., 1987; Ewan et al., 1996). Carter et al. (1987) fed gestating gilts increasing concentrations of ADF from alfalfa hay or sunflower hulls and reported increased litter size at farrowing. Likewise, Ewan et al. (1996) supplemented corn-soybean meal-based diets for gestating sows with ground wheat straw and reported increased litter size at farrowing. Positive effects of wheat straw were evident in the second and third farrowings but not the first.
Exp. 2
There were no interactions between diet and main effects of parity group, genetic line, and season; therefore, only effects of diet will be discussed. Initial condition score (2.9 vs. 2.9) and BW of sows were not different between sows fed C and HS diets (Table 5). Sows fed the HS diet had a greater weight gain during gestation (P < 0.01) than sows fed the C diet despite similar feed intake and estimated ME intake during the gestation period.
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) that included diets similar to the current experiment. In those studies, sows fed high levels of SF from oat bran displayed increased digestibility of energy compared with those fed C diet. In that study, intake of SF and ISF accounted for 78% of the variation in energy digestibility of the diet. Using the values for SF and ISF intake in Table 5, the calculated apparent digestibility of energy was 88.4% for the HS diet and 85.4% for the C diet. This difference in digestibility of energy could help explain the difference in gestation BW gain.
Sows fed the HS diet had a greater (P < 0.05) BW loss during lactation than sows fed the C diet, even though lactation length, litter size nursed, and feed intake during lactation were similar (Table 5). Weldon et al. (1994) reported that sows that gained more BW during gestation lost more BW during the subsequent lactation. Results of the present study support those of Weldon et al. (1994) that BW changes of sows during gestation and lactation are related inversely. Even though sows fed HS during gestation lost more weight during lactation than C sows, wean-to-estrus interval was not adversely affected likely because the magnitude of lactation BW loss did not exceed the critical level reported by Reese et al. (1982). The differences in SF and ISF intake between sows fed the C and HS diets during gestation had no effect on litter size and average pig BW at farrowing or weaning.
In the second trial of this experiment, sows fed the HIS diet had a greater feed intake (P < 0.01) during gestation than sows fed the C diet (Table 6). The difference in feed intake during gestation between sows fed C and HIS diets did not affect gestation BW gain or sow BW at the end of the gestation period. The similarity of sow BW during gestation was expected given the energy digestibility of the experimental diets (C, 85.2%; HIS, 83.0%) predicted by the equation of Renteria-Flores et al. (2008) and increased feed intake of sows fed HIS.
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). Similarity of gestation BW gain, litter size at farrowing and weaning, and pig weaning weight between sows fed C and HIS diets in Exp. 2 demonstrates that high-fiber diets can be fed to gestating sows successfully without compromising sow performance as long as appropriate adjustments in daily feed intake are implemented.
During the third trial of this experiment, sows fed the C diet gained more BW during gestation (P < 0.01) compared with sows fed HS + HIS (Table 7). These results suggest that the differences in calculated daily feed allowance were not enough to compensate for the energy dilution caused by increasing dietary fiber or that digestibility of energy in the HS + HIS diet was less than predicted or both. Based on the SF and ISF intake of sows, predicted apparent energy digestibility was 84.0% for the HS + HIS diet and 85.4% for the C diet (Renteria-Flores et al., 2008). This small difference in apparent energy digestibility was not adequately compensated for by the difference in feed allowance for sows assigned to the C and HS + HIS diets.
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showed similar effects when they fed gestating sows diets containing sugar beet pulp. They theorized that enhanced lactation feed intake of sows fed high fiber diets during gestation was due to increased physical capacity or other physical changes in the GI tract of sows. Increasing voluntary feed intake during lactation is important because excessive BW and body condition loss leads to suboptimal reproductive performance (Prunier et al., 1994).
Similar to the 2 previous trials, diet had no effect on litter size farrowed or weaned or on piglet BW at birth or weaning. These trials using 3 different high-fiber diets offered no evidence for an increase in total number of pigs born or born alive per litter when the dietary levels of SF or ISF or both were increased from 2 d after breeding until d 109 of gestation. These results contrast with other studies that reported that increasing fiber in the diets of gestating sows increased litter size (Everts, 1991; Ewan et al., 1996; Grieshop et al., 2001).
Increases in litter size at birth can only be realized with increased ovulation rate, improved fertilization rate, or improved embryo survival, or combinations of these responses (Ulberg and Rampacek, 1974). Nutrition has an important influence on sow reproductive performance and can affect ovulation rate (Ashworth, 1994). Nutrition during lactation and weaning in multiparous sows, as well as nutrition before the first mating in nulliparous sows can affect the ovulation rate (Beltranena et al., 1991a,b; Zak et al., 1997). Researchers (Cox et al., 1987; Beltranena et al., 1991b; Whitley et al., 1998) have demonstrated a positive relationship between circulating insulin concentrations in blood and ovarian function that resulted in increases in litter size. In humans, increased consumption of dietary soluble fiber has increased sensitivity of peripheral tissues to insulin, and improved glycemic control (Landin et al., 1992; Vuorinen-Markkola et al., 1992). Therefore, elevated levels of dietary fiber during the periovulatory period might increase circulating concentrations of insulin and enhance ovulation rate of sows ultimately leading to increases in litter size at farrowing.
The timing of fiber-feeding for enhanced litter size may be important. Nutritional interventions designed to affect ovulation rate in nulliparous and multiparous sows need to be imposed before mating (Ashworth, 1991; Beltranena et al., 1991a,b; Zak et al., 1997). Recruitment of preovulatory follicles occurs between d 14 and 16 of the estrus cycle in swine (Hunter and Wiesak, 1990), and there is evidence that the diet consumed before mating has a great impact on embryo survival (Zak et al., 1997; Ashworth et al., 1999). In the present experiment, nulliparous and multiparous sows did not receive experimental diets until 2 d after mating. Facility layout and management considerations prevented earlier introduction of experimental diets. This delay in introduction of experimental diets may be an important reason why the high-fiber diets did not increase litter size in this experiment. Alternatively, high-fiber diets should have been introduced during lactation, during the period of follicular recruitment. Nutrition during lactation can have important effects on embryo quality (Yang et al., 2000). Ferguson et al. (2007) reported an increase in subsequent litter size when sows were offered 20% sugar beet pulp diets during lactation. Possibly, dietary treatments in the present study needed to be imposed earlier in the reproductive cycle to elicit a litter size response.
If the periovulatory period is critical to increasing subsequent litter size, one would have expected a significant increase in litter size for gilts fed the high-fiber diets in Exp. 1 because they received these diets from 28 d before until 30 d after estrus and mating. This treatment duration covers the periovulatory period and should be enough time to elicit a response at the ovarian level (Flowers et al., 1989; Beltranena et al., 1991a,b; Ashworth, 1991).
In previous studies that have reported increased litter size, it is difficult to determine if the effect is due to fiber inclusion or energy dilution after mating. The increase on litter size might be attributable to lesser postmating energy intake due to the dilution effect of fiber (Kennelly and Aherne, 1980), which could reduce progesterone clearance. Reduced progesterone clearance favors embryo survival (Jindal et al., 1997), which might likely explain increased litter size at parturition. Furthermore, the fiber concentration of the diets in the present study may not have been high enough to elicit a litter size response. Intakes of NDF from experimental diets were 222, 391, and 420 g/d for HS, HIS, and HS + HIS diets, respectively. Johnston et al. (2002) summarized the inclusion levels of NDF in several experiments that showed an increased litter size in sows fed high fiber levels. A litter size response was reported when NDF intakes ranged from 520 to 1,010 g/d. Reese (1997) recommended that sows consume different levels of NDF according to the feedstuff used as a fiber source (i.e., alfalfa haylage, oat hulls, corn gluten feed, or wheat straw). Reese’s recommendations ranged from 368 to 515 g of NDF per day during gestation to improve the litter size.
Feed intake during lactation has important effects on sow productivity and longevity (Dourmad et al., 1994; Xue et al., 1997). Feed intake during gestation can affect lactation feed intake (Coffey et al., 1994; Weldon et al., 1994). Feeding high levels of dietary fiber during gestation can increase feed intake during lactation (Matte et al., 1994; Vestergaard and Danielsen, 1998; Danielsen and Vestergaard, 2001). The mechanism(s) by which dietary fiber increases feed intake during lactation has not been elucidated. One possible explanation for this increase in the feed intake during lactation is that the bulkiness of the diet facilitates the adaptation of the sows to the drastic increase of feed intake required during lactation (Matte et al., 1994; Danielsen and Vestergaard, 2001). In trial 3, sows fed increased levels of both SF and ISF (HS + HIS diet) during gestation had a 9.5% increase (P < 0.01) in ADFI during lactation compared with sows fed C diet during gestation. Danielsen and Vestergaard (2001) mentioned that high-fiber diets increased the physical capacity of the gastrointestinal tract, which may enhance feed intake capacity during the subsequent lactation.
The effects of soluble and insoluble fiber in the gastrointestinal tract are different. Increased intake of SF delays gastric emptying, whereas increased intake of ISF decreases the intestinal transit time (Anderson, 1985). This may help explain the differences between trials 2 and 3. Perhaps the results observed in the third trial may be a combination of the increased intake in SF and ISF and the interaction of these 2 fiber fractions. It could be that the increased levels of SF intake delayed gastric emptying, which compensated for decreased intestinal transit caused by the increased ISF intake, resulting in increased retention time of feed. This could cause the distention of the gastrointestinal tract responsible for the greater feed intake during lactation. One cannot discount the possibility that the difference in feed intake during lactation elicited by soybean hulls could be related to the reduced energy intake and the lower weight gain during gestation.
Feeding gestating gilts increased levels of dietary soluble or insoluble fiber (from oat bran, wheat straw, or soy hulls) did not affect ovulation rate or viable embryo survival. Feeding gestating sows high levels of fiber from 2 d after mating to d 109 of gestation did not affect litter size. Therefore, the examination of feeding multiparous sows increased levels of dietary soluble and insoluble fiber may need to focus on the period from weaning to d 2 after mating. The results of the present experiment suggest that feeding sows high dietary levels of both soluble and insoluble dietary fiber from soy hulls during gestation may promote increased voluntary feed intake during lactation and prevent lactation weight loss.
The present experiment demonstrates that high levels of dietary fiber can be included in diets of gestating sows without compromising sow productivity provided the influence of fiber on digestibility of nutrients is considered in diet formulation and calculation of daily feed allowance. Feeding gestating sows increased levels of SF and ISF from d 2 after breeding to d 109 of gestation did not increase litter size. Logistical challenges and waste management considerations of feeding high-fiber diets should be taken into consideration if pork producers plan to include high levels of fiber in sow diets under commercial conditions.
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Footnotes |
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2 Corresponding author: johnstlj{at}morris.umn.edu
Received for publication June 22, 2007. Accepted for publication May 27, 2008.
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LITERATURE CITED |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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