Influence of organic iron complex on sow reproductive performance and iron status of nursing pigs

Livestock Science 160 (2014) 89–96

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Influence of organic iron complex on sow reproductive performance and iron status of nursing pigs Jun Wang, Desheng Li, Lianqiang Che, Yan Lin, Zhengfeng Fang, Shengyu Xu, De Wu n Key Laboratory for Animal Disease-Resistance Nutrition of Sichuan Province of China, Institute of Animal Nutrition, Sichuan Agricultural University, Ya'an 625014, China

a r t i c l e i n f o

abstract

Article history: Received 19 December 2012 Received in revised form 6 November 2013 Accepted 27 November 2013

This experiment was conducted to evaluate the effects of organic iron complex on sow reproductive performance and iron status of nursing pigs. At day 84 of gestation, a total of 58 PIC sows at five-parity were randomly assigned to two groups receiving diets containing organic iron complex (n ¼ 33) and ferrous sulfate (n ¼ 25). According to a 2  2 factorial design of treatments, nursing pigs (2.09 7 0.34 kg) within a given litter were divided into two groups and given either an injection with or without iron (0 vs. 200 mg/pig) on day three of lactation. The feeding trial lasted for 51 days, including 30 days of gestation and 21 days of lactation. The results showed that organic iron complex did not improve the reproductive performance of sows or the growth performance of piglets. In particular, nursing pigs injected with iron had greater individual body weight at day 21 of lactation compared to pigs that were not treated with iron (P o0.05). Compared with ferrous sulfate, organic iron complex significantly increased the Cu content in mature milk (P o0.01), and the serum iron concentration at day one of lactation (P o 0.05), as well as ceruloplasmin activity at day 21 of lactation (P o 0.01). Piglets from sows fed organic iron complex tended to have a greater total iron binding capacity (P ¼0.08) and ceruloplasmin activity (P¼ 0.05) at day 10 of lactation, and tended to have a higher concentration of hemoglobin (P ¼0.08), total iron binding capacity (P o 0.01) and serum iron (Po 0.01) at day 21 of lactation compared with piglets from sows fed ferrous sulfate. Piglets injected with iron had a greater red blood cell count (P o 0.01), hemoglobin (P o 0.01), serum iron (Po 0.01) and total iron binding capacity (P o0.05) at day 10 and 21 of lactation compared to piglets that were not treated with iron. In conclusion, organic iron complex had minor positive effects on the iron status of sows and nursing pigs, but did not significantly improve the performance of sows and their offspring. Therefore, attempts to replace the commonly used Fe injection with a maternal organic iron complex dietary supplement failed to prevent iron-deficiency anemia of nursing pigs. & 2013 Elsevier B.V. All rights reserved.

Keywords: Organic iron complex Ferrous sulfate Fe injection Sow Piglet

1. Introduction Historically, ferrous sulfate has been used as an oral supplement in swine diets (Kegley et al., 2002). Hown Corresponding author. Tel.: þ86 835 2885107; fax: þ86 835 2885056. E-mail address: [email protected] (D. Wu).

1871-1413/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.livsci.2013.11.024

ever, recent studies have emphasized the biological effects of organic iron over the iron salt, which has low bioavailability (Spears et al., 1992; Henry and Miller, 1995; Pineda and Ashmead, 2001). Organic iron improves iron absorption and iron status of animals (Ashmead, 1993; Yu et al., 2000). In particular, Ashmead (1993) and Du et al. (1996) proposed that organic iron limits interactions with dietary factors that prevent absorption through a special

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uptake mechanism in the intestine. Feeding organic iron to pregnant sows has been shown to increase newborn and weaning weight, reduce stillbirths and postnatal mortalities, as well as improve iron status of piglets (Close, 1998, 1999). In rats and humans, substituting iron glycine chelate (Fe-Gly) for ferrous sulfate improved iron absorption and bioavailability (Layrisse et al., 2000; Pineda and Ashmead, 2001). Similar to Fe-Gly, iron methionine chelate and iron lactate are better absorbed in nursing pigs under experimental conditions (Spears et al., 1992; Svoboda et al., 2004). Likewise, ferrous fumarate has been added to infant food to prevent and treat iron deficiency (Davidsson et al., 2000). However, previous studies have primarily focused on the bioavailability of single organic iron sources, while detailed bioavailability and biological responses to organic iron complexes are still unknown. In sows, iron is essential for embryonic and fetal development. During late pregnancy and lactation, the iron requirement rapidly grows due to increasing iron storage by the fetus and needs of the newborn (Mahan and Shields, 1998; Mahan et al., 2009). Fetal growth and development relies entirely on the maternal supply of nutrients, including trace mineral elements (Van Saun, 2008). Mineral deficiency in the fetus induced by inadequate transfer of these elements from the maternal system can result in poor growth and health of the conceptus with negative effects continuing well into the neonatal period (Hostetler et al., 2003). In particular, organic iron has been reported to increase the quantity of iron transferred across the placenta to the fetus (Ashmead and Graff, 1982). On the other hand, feeding organic minerals to sows could improve micro-mineral output in mature milk and increase mineral retention in weaning pigs (Peters et al.,

2010). Therefore, we hypothesized that feeding an organic iron complex to sows could improve the iron status of their offspring. Finally, since it had been shown previously that high dietary iron did not improve iron absorption (Hansen et al., 2009), 80 mg/kg iron was provided for gestating and lactating sows according to NRC (1998) recommendations. Thus, we compared the effect of organic iron complex and ferrous sulfate on the reproductive performance of sows and the growth performance of piglets, as well as tested whether supplementation of an organic iron complex to sows improved the iron status of sows and their offspring. 2. Materials and methods 2.1. Materials The composition of the organic iron complex included ferrous fumarate (35%), iron lactate (25%), iron glycine chelate (37%) and iron methionine chelate (3%). The measured value of Fe2þ in the organic iron complex and ferrous sulfate was 20.84% and 30%, respectively. 2.2. Experimental design Experimental design, animal care, and animal handling procedures were approved by the Biosafety and Animal Care and Use Committees at Sichuan Agricultural University. A total of 58, five-parity PIC sows, which had a similar sized number of piglets (10–12 pigs/sow) from parity 1 to parity 4, were assigned to the experiment at day 84 of gestation. Sows in ideal body condition (body condition score¼3) were randomly allotted to receive diets

Fig. 1. The experimental design and the timing of the different treatments and procedures. O and F represent sows fed the organic iron complex and ferrous sulfate, respectively. OI and ONI represent piglets injected with or without iron under the condition of nursing sows fed organic iron complex, respectively; FI and FNI represent piglets injected with or without iron under the condition of nursing sows fed ferrous sulfate, respectively.

J. Wang et al. / Livestock Science 160 (2014) 89–96

containing organic iron complex (n¼33) and ferrous sulfate (n ¼25) as iron sources, respectively. After farrowing, 91 piglets from eight sows previously receiving an organic iron complex, and 56 piglets from five sows previously receiving ferrous sulfate were selected to receive an intramuscular neck injection of either 0 mg or 200 mg of Fe (dextran iron) on day three of lactation. For each sow, half of the nursing pigs were injected with iron and the other half were control animals. The sucking piglet experiment was therefore conducted as a two by two factorial arrangement of treatments. The experimental design is detailed in Fig. 1. The experiment began with 62 sows, but one sow in the organic group and three sows in the inorganic group were removed from the study due to reproductive failure during gestation. 2.3. Diets and feeding A basal corn–soybeans meal diet (Table 1) was formulated to meet or exceed the NRC requirements of gestating and lactating sows, with the exception of iron content. Eighty milligrams/kilograms iron were provided into the basal diet during gestation and lactation. Sows were provided 3.5 kg of feed daily on day 84–107 of gestation, and restricted gradually (0.5 kg each day) for the last week of gestation. Cross-fostering was performed within 24 h after farrowing. The sows were given 1.5 kg of feed for the first day after farrowing and the amount was increased gradually (0.5 kg each day) for the first week. Sows were then fed ad libitum until weaning at day 21 of lactation. The sows had ad libitum access to water during gestation and lactation. The detected iron content in the basal diet (not adding ferrous sulfate or organic iron complex) for gestating and lactating sow was 103 and 107 mg/kg, respectively. After iron incorporation, dietary iron content was 186 and 191 mg/kg for gestating and lactating sows, respectively.

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Table 1 Compositions and nutrient content of basal diet (as-fed basis). Ingredient

Gestation (%)

Lactation (%)

Corn Soybean meal Fish meal Soybean oil Wheat L-lysine D-methionine Valine Tryptophan L-threonine Calcium carbonate Dicalcium phosphate Chloride choline Salt Saleratus Vitamin premixa Mineral premixa Total Calculated value CP (%) DE (Mcal/kg) Total lysine (%) Calcium (%) Phosphorus (%) Nonphytate phosphorus (%) Analyzed value Ironb (mg/kg)

64.00 14.80   16.60 0.26 0.08  0.01 0.11 1.00 1.60 0.15 0.40 0.44 0.05 0.50 100

65.00 20.00 2.50 3.00 5.00 0.24 0.11 0.14 0.03 0.11 1.10 1.29 0.15 0.40 0.38 0.05 0.50 100

14.00 3.00 0.80 0.80 0.70 0.45

17.00 3.30 1.10 0.90 0.66 0.45

103

107

a Provided the following vitamins and trace minerals per kilogram of diet: Cu (as copper sulfate), 30 mg; I (as potassium iodide), 0.25 mg; Mn (as manganese sulfate), 40 mg; Se (as sodium selenite), 0.25 mg; Zn (as zinc sulfate), 100 mg; Cr (as chromium picolinate), 0.3 mg; 25,000 IU vitamin A; 5,000 IU vitamin D3; 12.5 IU vitamin E; 2.5 mg vitamin K; 1 mg vitamin B1; 8 mg vitamin B2; 3 mg vitamin B6; 0.015 mg vitamin B12; 17.5 mg niacin; 12.5 mg pantothenic acid; 0.25 mg folacin. b The detected iron content in the basal diet for gestating and lactating sow was 103 and 107 mg/kg, respectively. After iron incorporation, dietary iron content was measured of 186 and 191 mg/kg for gestation and lactation, respectively.

2.4. Data and sample collection

2.5. Chemical analyses

Data of performance (total litter size, live litter size, litter birth weight) was immediately recorded after farrowing. At day 10 and 21 of lactation, nursing pigs were weighed and 10 mL of blood was collected via the precaval vein. At day 1 and 21 of lactation, 10 mL of blood was collected from sows via ear venipuncture. A portion of the blood (2–3 mL) was collected into 5 mL heparinized vacutainer tubes to analyze the red blood cell count and hemoglobin concentration, as described below. Another portion of the blood samples was collected into vacuum blood collection tubes (10 mL) and allowed to coagulate at room temperature for 30 min. Serum was harvested by centrifuging collection tubes at 3000g for 10 min at 4 1C. Thereafter, serum was aliquoted into cryovials (0.2 ml) and stored at  20 1C. A colostrum sample was collected within 2 h of farrowing by hand-expression from several glands. At weaning, 10 IU oxytocin (10 IU/ml) was injected via ear venipuncture to let milk down, and 20–30 mL of colostrum or mature milk was collected into three tubes (10 mL) and frozen at 20 1C.

The concentrations of serum iron (SI), hemoglobin (Hb), red blood cell (RBC) amount, and the total iron binding capacity (TIBC) were measured using commercially available kits (purchased from Guang Zhou BGH Biochemical CO., LTD.) according to the manufacturer's instruction by automatic biochemical analyzer (Hitachi Model 7020, Kyoto, Japan). Ceruloplasmin (Cp) activity in serum was measured using a commercially available Cp activity assay kit (Nanjing Jiancheng Bioengineering Institute) according to the manufacturer's instruction on a UV-1100 spectrophotometer (Mapada, Shanghai, China). The wet ashing method was applied to determine the mineral concentration of the feed and milk (AOAC, 2000). Diet was ground fine enough to pass through a 1 mm sieve and analyzed for dry matter (DM). The milk sample (10 mL) or the representative sample of diets (approximate 0.5 g) was added to a mixture of nitric acid and perchloric acid (4:1) for digesting overnight. The solution was boiled until the mixture became clear, and then diluted with deionized water. Concentrations of Fe, Cu, and Zn were

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analyzed with flame atomic absorption spectrophotometry (Analytik Jena-novAA400, Germany). All analyses were performed in duplicate and certified mineral reference solutions (National Analysis Center for Iron and Steel, China) were used as standards. The precision of the analytical method, calculated as the relative standard deviation of metal concentrations in two digests of the same sample, were between 0.52% and 7.33%. Mineral concentrations of the feed were conducted on a DM basis, whereas milk mineral concentrations are reported as mg/L in Table 4. 2.6. Statistical analysis Statistical analysis was performed using the General Linear Model procedure of SPSS 16.0 software (SPSS, Inc., Chicago, IL, USA), arranged as a 2  2 factorial in a randomized complete block design. The individual sow or litter of piglets was used as the experimental, and the average piglet weight of each litter was used in the analysis. Litters divided in half by injection with or without iron were analyzed separately. Moreover, colostrum, milk, and serum measurements were considered as experimental units. T-test and Duncan's test were conducted to determine the differences among treated groups of sows and piglets, respectively. Po0.05 was used for determination of significant differences and P o0.10 was considered to represent tendencies among treatments. 3. Results 3.1. Performance of sows and nursing pigs The reproductive performance response to iron sources is presented in Table 2. No difference was observed in the number of total pigs born and the number of live births between the inorganic and organic groups (P40.05). There was no difference in individual body weight and litter weight between the organic and inorganic groups (P40.05). Piglets injected with iron had greater individual

body weights compared to piglets without Fe injection at day 21 of lactation (Table 3, P o0.05). 3.2. Mineral concentrations in colostrums and mature milk Analyzed values of Fe, Cu, and Zn for colostrum and mature milk samples are presented in Table 4. Compared with ferrous sulfate, organic iron complex significantly increased Cu content in mature milk (Po0.01). However, Fe and Zn concentrations in colostrum and mature milk were not significantly affected by dietary iron source (P40.05). 3.3. Iron-related blood parameters in sows The effect of dietary iron sources on sow iron-related blood parameters is shown in Table 5. Compared with ferrous sulfate, organic iron complex significantly increased SI concentration at day 1 of lactation and Cp activity at day 21 of lactation (Po0.05). However, no significant differences were observed in RBC value, Hb concentration or TIBC at day 1 and 21 of lactation between the organic and inorganic groups (P40.05). 3.4. Iron-related blood parameters in nursing pigs Table 6 displays the effect of sow dietary iron sources and Fe injection treatments on iron-related blood parameters of nursing pigs. Piglets injected with iron had a greater RBC value and increased Hb and SI concentrations at day 10 and 21 of lactation compared to the control group (P o0.01). Piglets injected with iron had a greater TIBC at day 10 (Po0.05) and 21 of lactation (Po0.01) compared to the control group. Piglets from sows fed organic iron complex tended to have a greater TIBC (P¼0.08) and Cp (P¼ 0.05) at day 10 of lactation, and tended to have a higher concentration of Hb (P¼0.08), TIBC (Po0.01) and SI (P o0.01) at day 21 of lactation. Furthermore, there were significant interactions between the SI and TIBC response at day 21 of lactation (Po0.01).

Table 2 Reproductive performance of sows fed organic and inorganic iron. Item

Number of sows Number of total born Number of born alive Number of born dead Number of piglets at day 10 of lactationb Number of piglets at day 21 of lactationb Individual weight (kg) Day 1 of lactation Day 10 of lactationb Day 21 of lactationb Litter weight (kg) Day 1 of lactation Day 10 of lactationb Day 21 of lactationb a b

RSDa

Supplemental iron source

P-value

Inorganic

Organic

25 12.68 11.68 1.00 10.80 9.85

33 12.21 11.48 0.67 10.48 9.80

2.799 2.290 1.175 1.028 1.498

0.53 0.75 0.29 0.31 0.91

1.48 3.22 5.84

1.47 3.44 5.75

0.228 0.728 1.255

0.76 0.33 0.81

17.24 35.22 58.97

16.68 35.93 57.79

3.528 8.626 15.860

0.55 0.78 0.80

Residual standard deviation. n ¼20 and 25 in the inorganic and organic group, respectively.

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Table 3 Effect of sow dietary iron sources and Fe injection treatment on individual weight of nursing pigsa (kg). Item

Day 3 of lactation Day 10 of lactation Day 21 of lactation a b c

RSDb

Inorganic (n¼ 5 sows)

Organic (n ¼8 sows)

Not injected (n¼ 27 pigs)

Injected (n¼ 29 pigs)

Not injected (n¼ 43 pigs)

Injected (n¼ 48 pigs)

2.13 4.06 6.47b

2.12 4.27 7.21a,b

2.10 4.25 6.61a,b

2.11 4.48 7.77a

0.266 0.616 0.922

P-value Iron source

Fe injection

Interactionc

0.86 0.45 0.37

0.99 0.39 0.02

0.91 0.98 0.59

In the same row values with different small letter superscripts mean significant difference (Po 0.05). Residual standard deviation. Iron source  Fe injection interaction response.

Table 4 Effects of sow dietary iron sources on milk Fe, Cu and Zn concentrations of sows. Itema

Supplemental iron source

Colostrums (mg/L) Fe Cu Zn Mature milk (mg/L) Fe Cu Zn a b

SEMb

P-value

Inorganic

Organic

4.08 4.79 23.07

3.93 5.02 20.96

0.217 0.243 1.769

0.73 0.64 0.41

3.88 1.87 6.41

4.66 2.64 6.10

0.402 0.128 0.266

0.33 o 0.01 0.29

Colostrums: n¼ 16 or 18 in each group; mature milk: n¼ 15 in each group. Standard error of the mean.

Table 5 Effect of sow dietary iron sources on iron-related blood parameter of sows. Itema

Supplemental iron source

SEMb

P-value

Inorganic

Organic

Day 1 of lactation RBC (1012/L) Hb (g/L) SI (μmol/L) TIBC (μmol/L) Cp (IU/L)

5.25 107.43 10.84 42.95 59.08

5.25 107.13 12.11 43.40 53.40

0.076 1.321 0.350 0.377 3.434

0.96 0.89 0.04 0.53 0.18

Day 21 of lactation RBC (1012/L) Hb (g/L) SI (μmol/L) TIBC (μmol/L) Cp (IU/L)

5.80 122.46 14.02 37.25 45.83

5.86 121.74 14.65 37.22 68.49

0.085 1.918 0.652 1.184 4.459

0.66 0.80 0.63 0.96 o0.01

a Response variables: RBC ¼red blood cell; Hb ¼ hemoglobin; SI¼ serum iron; TIBC ¼total iron binding capacity; Cp ¼ ceruloplasmin activity (n ¼13-18 per treatment). b Standard error of the mean.

4. Discussion Iron is a micronutrient essential for many biochemical processes, including oxygen delivery, regulation of cell growth and differentiation, electron transfer reactions, etc. (Beard, 2001). Iron is required for the normal growth

of animals, and plays a critical role in embryonic and fetal survival and development (Hostetler et al., 2003). In particular, organic iron has been shown to improve sow reproductive performance (Close, 1998, 1999). Therefore, we hypothesized that an organic iron dietary supplement given to sows in late pregnancy and during lactation would enhance the growth rate of sucking piglets (Tummaruk et al., 2003). However, organic iron complex failed to improve the reproductive performance of sows and the growth performance of piglets in the present study. Although, the growth performance of nursing pigs injected with iron was enhanced. This finding is consistent with a previous report by Peters and Mahan (2008b). Milk is considered as the main mineral source for sucking piglets. Colostrum is largely synthesized before farrowing, and mineral supplement during late gestation could influence its mineral composition. Consistently, postpartum mineral intake can alter mineral compositions of mature milk (Peters et al., 2010). However, in the present study, organic iron complex did not improve milk iron output, but did enhance Cu output in mature milk. It is well known that antagonism can occur between trace minerals (O'Dell and Sunde, 1997). Specially, inorganic minerals tend to interact with various ingredients in the gastrointestinal tract, leaving the minerals susceptible to other mineral antagonisms that impair absorption (Richards et al., 2010). In contrast, organic mineral help ensure the stability of minerals to limit the interactions with other ingredients (Richards et al., 2010). Mechanisms involving peptide or amino acid uptake in the intestine

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Table 6 Effect of sow dietary iron sources and Fe injection treatment on iron-related blood parameter of nursing pigsa. Itemb

Inorganic

SEMc

Organic

Not injected

Injected

Not injected

Injected

Day 10 of lactation RBC (1012/L) Hb (g/L) SI (μmol/L) TIBC (μmol/L) Cp (IU/L)

3.58b 51.42b 3.18b 35.31b 42.84a,b

4.85a 95.57a 17.66a 36.24b 38.27b

3.41b 50.30b 2.84b 35.82b 45.35a,b

4.57a 99.89a 18.23a 41.53a 47.39a

Day 21 of lactation RBC (1012/L) Hb (g/L) SI (μmol/L) TIBC (μmol/L) Cp (IU/L)

3.54b 44.20c 2.44c 35.63b 31.85b

5.75a 110.5b 11.82b 37.67b 37.50b

3.51b 43.23c 2.61c 35.75b 52.35a

6.09a 121.14a 17.83a 43.68a 33.20b

P-value Iron source

Fe injection

Interactiond

0.070 1.266 0.373 0.802 1.473

0.11 0.53 0.88 0.08 0.05

o 0.01 o 0.01 o 0.01 0.04 0.67

0.69 0.29 0.54 0.14 0.27

0.084 1.340 0.455 0.361 2.458

0.35 0.08 o0.01 o0.01 0.11

o 0.01 o 0.01 o 0.01 o 0.01 0.18

0.28 0.04 o 0.01 o 0.01 0.02

a

In the same row values with different small letter superscripts mean significant difference (Po 0.05). Response variables: RBC ¼red blood cell; Hb¼ hemoglobin; SI¼ serum iron; TIBC ¼total iron binding capacity; Cp ¼ ceruloplasmin activity (n ¼10–16 per treatment). c Standard error of the mean. d Iron source  Fe injection interaction response. b

have been proposed as the means of organic minerals absorption, rather than normal metal ion uptake mechanisms (Ashmead, 1993). Therefore, it is feasible that organic minerals may be able to minimize mineral losses to antagonists. In the present study, increased milk Cu was likely induced by the reduction of antagonism between iron and copper. Iron is a vital component of Hb, which is necessary for the transfer of oxygen from the bloodstream to tissue. Correspondingly, Hb levels are useful for evaluating the biological response to iron (Amine et al., 1972). Likewise, SI and TIBC are specific biomarkers signaling iron deficiency or iron overload in circulation (Furugouri, 1972; Gottschalk et al., 2000). In particular, SI is considered as a marker of iron entering and leaving the blood stream, and has been used for qualitative measurement of bioavailability of iron supplements (Ferreira da Silva et al., 2004). TIBC has been used for assessing the sum of all iron binding sites on transferrin (Soldin et al., 2004). Iron metabolism can be altered by Cp which catalyzes the conversion of Fe2 þ to Fe3 þ and helps load Fe3 þ onto transferrin for iron transport in the plasma (Cherukuri et al., 2005). Therefore, Hb, SI, TIBC and Cp are sensitive indicators of iron absorption. Our results reveal that organic iron complex has a positive effect on SI content and Cp activity for sows, and Hb, SI content, and TIBC for piglets. These alterations indicate that organic iron complex improved the iron status of sows and their offspring. However, these positive effects were too small to improve the growth performance of nursing pigs. Iron-deficiency anemia in suckling pigs is a serious problem in the swine industry (Svoboda et al., 2005). In past years, neonatal pigs were most frequently given an injection with iron to prevent iron-deficiency anemia (Svoboda et al., 2004). Many studies have proposed there is the potential for negative effects of intramuscular injection, for example, increasing the acute toxicosis rate (Ness et al., 2010), impairing macrophage activity and

phagocytosis (Morris et al., 1995), stimulating bacterial growth (Knight et al., 1983), or the risk of polymyositis, rhabdomyolysis and myoglobulinuria (Foulkes et al., 1991). However, attempts to replace the Fe injection with a single organic iron source (ferrous fumarate or iron amino acid chelate) or with parenteral iron administration have largely been unsuccessful (Pond et al., 1961; Veum et al., 1965; Brady et al., 1978). Therefore, the present study examined the effects of replacing the Fe injection with an organic iron complex. Contrary to the expected results, the organic iron complex fed to sows failed to prevent irondeficiency anemia of nursing pigs without an additional neonatal Fe injection, using a Hb value lower than 70 g/L as an indicator of anemia (Zimmerman, 1980). The iron transfer barrier in the placenta and breast tissue, as well as the rapidly increasing iron requirements during the nursing period, might account for these results. Interestingly, the organic iron complex improved SI concentration, but did not alter the iron output in sow milk, which suggests that maternal iron did not effectively transfer to piglets via milk. Therefore, the increased Hb and SI concentration in offspring from sows fed organic iron complex was not induced by the iron status of the sows. A previous study demonstrated that oral and intramuscular iron supplementation did not improve the iron status in copper-deficient swine with impaired iron absorption and anemia (Lee et al., 1968). In contrast, copper-deficient, anemic swine could be successfully treated by copper supplementation or an injection of Cp (Lee et al., 1968; Ragan et al., (1969)). These results indicate that copper may be required for adequate “hemoglobin building” (Eisenstein, 2000). Therefore, in the present study, we concluded that organic iron complex increased milk copper content by reducing antagonism between iron and copper, and further, concluded that increasing the serum Cp content of piglets improved the transport capacity of iron in milk to improve the iron status of nursing pigs. However, the mechanisms involved require further investigation.

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5. Conclusion Our results indicate that organic iron complex had minor positive effects on the iron status of sows and nursing pigs, but did not improve sow reproductive performance and the growth performance of piglets. Replacing the Fe injection with an organic iron complex dietary supplement for sows was not successful in preventing anemia in nursing pigs. Interestingly, maternal supplementation with an organic iron complex was successful at improving Cu output in mature milk. Conflict of interest statement Neither the entire paper nor any part of its content has been published or has been accepted elsewhere. All other authors have read the manuscript and have agreed to submit it in its current form for consideration for publication in the journal. Disclosure summary The authors have nothing to disclose.

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