Effects of dietary energy and lysine levels on physiological responses, reproductive performance, blood profiles, and milk composition in primiparous sows

Abstract

The adequate intake of energy and lysine for primiparous sows are necessary for maternal growth of sows and growth of their progeny. This study was conducted to evaluate the effects of dietary energy and lysine levels on primiparous sows and their progeny. A total of 48 gilts (Yorkshire × Landrace), with an initial body weight (BW) of 168.1 ± 9.71 kg and at day 35 of gestation, were allotted to eight treatment groups with a 2 × 4 factorial arrangement. The first factor was metabolizable energy levels in diet (3,265 or 3,365 kcal of ME/kg), and the second factor was lysine levels in diet (gestation 0.55%, 0.65%, 0.75%, 0.85%, lactation 0.70%, 0.85%, 1.00%, 1.15%). The BW gain (p = 0.07) and backfat thickness (p = 0.09) in the gestation period showed a tendency to be increased in sows fed the high-energy diets. In the lactation period, sows fed the high-energy diets tended to be greater BW (p = 0.09) and less BW loss (p = 0.05) than those of sows fed the low-energy diets. Sows fed high-energy diets had a tendency of greater piglet weight at day 21 of lactation and greater piglet weight gain (p = 0.08 and p = 0.08, respectively). Although the blood urea nitrogen (BUN) was increased linearly as dietary lysine level increased at day 110 of gestation (Linear, p = 0.03), the BUN was decreased linearly as dietary lysine level increase at day 21 of lactation (Linear, p < 0.01). In the composition of colostrum, sows fed high-energy diets had greater casein, protein, total solid, solid not fat, and free fatty acid concentrations than those of sows fed low-energy diets (p < 0.05). Supplementation of total lysine 0.75% for gestation and 1.00% for lactation with 3,365 kcal of ME/kg energy level could be applied to the primiparous sows' diet to improve performance of sows and growth of their progeny.

INTRODUCTION

The recent genetic improvement in sows have resulted in a high litter size and low piglet birth weight and uniformity [1–3]. The modern sows need higher nutrient intake to support the maternal body reserve and maintain the growth requiremnet of their progeny during the gestation and lactation periods rather than ordinary sows due to the increased growth rate and number of fetuses.

The adequate intake of nutrients such as energy and lysine are an important part of the nutrition for sows [4]. Deficient energy intake during gestation has been identifeid as the major reason for decreased body fat reserve at farrowing or weaning, which prolongs the weaning-to-estrus interval (WEI) and decreases the conception rate [5,6]. On the other side, the excessive energy intake in gestating sows increased body weight of sows at farrowing [7] and the excessive weight gain could have a negative influence on litter size, lactation feed intake, and subsequent parity performance [8– 10]. Several studies have reported that low lysine intake in lactation period had negative influences on metabolic status, reproductive hormone secretion, and WEI [11–13]. On the other hand, high lysine intake improved the metabolic status of sows and increased the total litter weight at birth and piglet weight at weaning [14–16].

Although there have been several studies on dietary energy and lysine levels in first parity [10, 12, 17, 18], the research on amino acid utilization in primiparous sows was limited. The amino acids utilization for primiparous sows should be considered with the maternal growth, development of mammary gland, and fetal growth during gestation and milk production and maternal nutrient mobilization during lactation [19], hence the amino acids requirement for primiparous sows is greater than multiparous sows [19,20]. Furthermore, it is very important to provide adequate energy and amino acids to primiparous sows because body status and performance of primiparous sows have a significant impact on later productivity and longevity [21,22].

The lysine requirement of primiparous sows has been estimated to be 2.1 g/d for maintenance, 5.5 g/d for maternal growth, and 4.4 g/d for growth of the conceptus and reproductive tissues [23,24]. As reported by the NRC [25], the total lysine requirement increased from 0.57% to 0.80% in gestation and from 0.91% to 0.93% in lactation. Also, NRC [25] suggested that the optimal lysine intake was 12.4/19.3 g/d (< 90 d, > 90 d) and 52.6 to 56.5 g/d in gestation and lactation of primiparous sows, respectively.

Therefore, it was hypothesized that adequate intake of energy and lysine during gestation and lactation will improve the reproductive performance and litter performance of primiparous sows. Thus, this experiment was conducted to investigate the effect of the dietary energy and lysine levels on the physiological response, reproductive performance, blood profiles, and milk composition of primiparous sows.

Materials and methods

All experimental procedures were reviewed and approved by the Institutional Animal Care and Use Committee at Seoul National University (SNU-160819-9).

Animal preparation

A total of 48 gilts (initial body weight [BW] of 90 kg; F1, Yorkshire × Landrace; Darby, Korea) were obtained from a research farm of Seoul National University (Eumseong, Korea). They were group-housed in a separate pen (11 m × 14 m) and offered feed and fresh water ad libitum until reaching 120 kg BW. When the BW of gilts reached 120 kg, the gilts were moved to a breeding barn and housed in the gestation stalls (2.20 m × 0.65 m) with a concrete slatted floor. The sows were fed a gestation diet of 800 g/d for an average daily gain of 750 g/d. The estrus and heat detection for gilts were diagnosed twice a day with two mature boars (Duroc) using the back-pressure test. After three or four estrus cycles, the gilts with average BW from 135 to 140 kg were given artificial insemination with fresh diluted semen (Darvy AI center, Chungju, Korea) twice in 12 hrs intervals. The confirmation of pregnancy was performed at 21 days of gestation by re-estrus checks and at 35 days of gestation by an ultrasound diagnostic device (Easyscan, Dongjin BLS, Gwangju, Gyeonggi-do, Korea).

Experimental animals and housing

The 48 primiparous sows (average BW of 168.1 ± 9.71 kg) with confirmed pregnancy were used for a feeding trial. The pregnant sows were allotted to eight treatments based on BW and backfat (BF) thickness at day 35 of gestation in a completely randomized design (CRD) with six replicates. The gestating sows were housed in an individual gestation stall (2.20 m × 0.65 m) equipped with a feeder and a water nipple until day 110 of gestation. On day 110 of gestation, the pregnant sows were moved into the farrowing barn after washing their body and placed in individual farrowing crates (2.50 m × 1.80 m). Each farrowing crate was equipped with a cup drinker and a feeder and a piglet house with a heating lamp and a waterer. The room temperature was maintained at an average of 20 ± 3℃ and 28 ± 2℃ for gestating and lactating sows, respectively. The piglet houses under heating lamps were kept at 32 ± 2℃. The gestating sows were fed 2.0 kg/d of the experimental diet for gestation period once per day (08:00), and feed was reduced gradually by 0.2 kg/d for 5 days before the due date of farrowing. After farrowing, the amount of feeding lactation diet was gradually increased from 1 to 5 kg/d during the first 5 days of lactation; then, sows were fed the experimental diet for lactation period ad libitum until weaning.

Experimental design and diets

The experiment was designed as a 2 × 4 factorial arrangement with the metabolizable energy level and the total lysine level in diet as the main factors. The experimental diets for gestation period contained two energy levels [3,265 or 3,365 kcal of metabolizable energy (ME)/kg] and different total lysine levels (total lysine 0.55%, 0.65%, 0.75%, 0.85% or 11.0 g/d, 13.0 g/d, 15.0 g/d, and 17.0 g/d). The lactation diets contained two energy levels (3,265 or 3,365 kcal of ME/kg) and different total lysine levels (total lysine 0.70%, 0.85%, 1.00%, and 1.15%). All nutrients of the experimental diets met or exceeded the recommendations of the NRC [12]. The diet formulation and chemical composition for the experimental diets were presented in Tables 1 and 2.

Table 1. The formulas and chemical composition of experimental gestation diet¹⁾

¹⁾Experimental diet was formulated with corn-soybean meal (SBM) based diet and adjusted lysine content.

²⁾Provided per kg of diet: vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D₃, 1,600 IU; vitamin E, 32 IU; d-biotin, 64 g; riboflavin, 3.2 mg; calcium pantothenic acid, 8 mg; niacin, 16 mg; vitamin B₁₂, 12 μg ; vitamin K, 2.4 mg.

³⁾Provided per kg of diet: mineral per kg of complete diet: Se, 0.1 mg; I, 0.3 mg; Mn, 24.8 mg; Cu, 54.1 mg; Fe, 127.3 mg; Zn, 84.7 mg; Co, 0.3 mg.

⁴⁾Calculated value.

ME, metabolizable energy; Lys, lysine; MDCP, mono-dicalcium phosphate.

Table 2. The formulas and chemical composition of experimental lactation diet

¹⁾Provided per kg of diet: vitamins per kg of complete diets: vitamin A, 8,000 IU; vitamin D3, 1,600 IU; vitamin E, 32 IU; d-biotin, 64 g; riboflavin, 3.2 mg; calcium pantothenic acid, 8 mg; niacin, 16 mg; vitamin B12, 12 μg ; vitamin K, 2.4 mg.

²⁾Provided per kg of diet: mineral per kg of complete diet: Se, 0.1 mg; I, 0.3 mg; Mn, 24.8 mg; Cu, 54.1 mg; Fe, 127.3 mg; Zn, 84.7 mg; Co, 0.3 mg.

³⁾Calculated value.

ME, metabolizable energy; Lys, lysine; MDCP, mono-dicalcium phosphate.

Sample collection and analysis

The sow BW and BF thickness were measured at 35 and 110 days of gestation, 24 hrs postpartum, and 21 days of lactation. The BW was measured by an electric scale (CAS, Yangju, Korea) and BF thickness was measured at P₂ position by an ultrasound lean meter (Anyscan BF, Songkang GLC, Seongnam, Korea). In lactation period, the feed supply and wastage were recorded to measure the voluntary feed intake of lactating sows. The days from weaning to first estrus of sows were recorded to calculate the weaning to estrus interval (WEI).

Within 12 hrs postpartum, the number of piglets in total born, born alive, stillborn, and mummy, and their BWs were recorded, respectively. At 21 days of lactation, the BW of piglets were measured for litter weight gain and piglet weight gain. The piglet birth weights and piglet BWs at 21 days of lactation from one litter was used for calculating piglet uniformity, such as coefficient of variation (CV) and standard deviation (SD).

The 10 mL of blood sample (n = 4 for each treatment except two sows from the highest BW and the lowest BW) was collected from the jugular vein of each sow with a serum tube (SST^TMII Advance, BD Vacutainer, Becton Dickinson, Plymouth, UK) and centrifuged at 1,957×g and 4℃ for 15 minutes (5810R, Eppendorf, Hamburg, Germany). Then, the serum was transferred into microtubes (Axygen, Union City, CA, USA) and stored frozen at –20℃ for further analysis. The concentration of total protein (colorimetry, TP2, Roche, Germany), creatinine (kinetic colorimetry assay, CREJ2, Roche, Germany), blood urea nitrogen (BUN; kinetic UV assay, UREAL, Roche, Germany).

Colostrum at 12 hrs postpartum and milk at day 21 of lactation were collected from the first and second teats of sows (n = 4 for each treatment with the same sows for blood sampling) after a 5 IU oxytocin injection (Komi oxytocin inj., Komipharm International, Siheung, Korea) in the ear vein. Collected milk samples were stored frozen at –20℃ until later analysis. The composition of colostrum and milk (day 21) were analyzed by using Milkoscan FT 120 (FOSS, Hillerod, Denmark) in the National Institute of Animal Science (Wanju, Korea).

Statistical analysis

Data were analyzed by least squares mean comparisons and were evaluated using PDIFF option with the general linear model (GLM) procedure of SAS (SAS Inst., Cary, NC, USA). Individual sows and their litters were used as the experimental units. Orthogonal polynomial contrasts were used to detect the linear and quadratic responses to lysine levels when the significance of lysine effect was detected. To test the hypotheses, p < 0.05 was considered significant. If pertinent, trends (0.05 ≤ p < 0.10) are also reported.

Results

The effects of dietary energy and lysine levels on BW and BF thickness of primiparous sows were presented in Table 3. The BW gain (p = 0.07) and backfat thickness (p = 0.09) in the gestation period showed a tendency to be increased in sows fed the high-energy diets. However, the BW loss of sows fed the high-energy diets tended to be less than that of sows fed the low-energy diets in lactation period (p = 0.05). The sows fed high energy diets had greater BF thickness than that of sows fed low energy diets on 24 hrs postpartum (p = 0.04), and showed a tendency to be increased in BF thickness on day 21 of lactation (p = 0.07). However, the lactation daily feed intake was not affected by dietary energy and lysine levels. Sows fed the Lys 0.55%/0.70% and Lys 0.75%/1.00% diet showed a shorter WEI than sows in the other treatment groups (p = 0.03).

Table 3. Effects of dietary energy and lysine levels on physiological changes, feed intake, and WEI in primiparous sows

¹⁾Factors: energy level (3,265 or 3,365 kcal of ME/kg) and lysine level (total lysine 0.55/0.70%, 0.65/0.85%, 0.75/1.00%, 0.85/1.15%) in gestation/lactation diet.

WEI, weaning-to-estrus interval; ME, metabolizable energy; Lys, lysine; SEM, standard error of the mean; E, energy effect. L, lysine effect. I, interaction between energy and lysine effects.

The effects of dietary energy and lysine levels on reproductive performance and growth of their progeny were shown in Tables 4 and 5, respectively. Dietary energy and lysine levels tended to interact on the number of total born and born alive such that sows fed low energy diets decreased the number of total born and born alive piglets, but sows fed high energy diets increased the number of total born and born alive piglets (p < 0.01, and p = 0.04, respectively). The number of mummy was greater in the Lys 0.65/0.85 group and lower in the Lys 0.85/1.15 group (p = 0.01). There were no significant differences in total litter weight and alive litter weight. However, alive piglet weight was decreased in the high-energy group and increased in the low-energy group (p = 0.02). The piglet uniformity, such as SD and CV of piglet weight, and ratio of irregular birth weight at farrowing, were not affected by dietary energy and lysine levels for gestation diets. Litter weight and litter weight gain during lactation were not affected by dietary energy and lysine levels. However, piglet weight on day 21 of lactation and piglet weight gain for high energy diets tended to be increased than those for low energy diets (p = 0.08). As the result of piglet uniformity at farrowing, there were no significant differences in SD and CV of piglet weight within the same litter at day 21 of lactation.

Table 4. Effects of dietary energy and lysine levels on reproductive performance in primiparous sows

¹⁾Factors: energy level (3,265 or 3,365 kcal of ME/kg) and lysine level (total lysine 0.55/0.70%, 0.65/0.85%, 0.75/1.00%, 0.85/1.15%) in gestation/lactation diet.

ME, metabolizable energy; Lys, lysine; SEM, standard error of the mean; E, energy effect; L, lysine effect; I, interaction between energy and lysine effect; SD, standard deviation; CV, coefficient of variation.

Table 5. Effects of dietary energy and lysine levels on growth of progeny in primiparous sows

¹⁾Factors: energy level (3,265 or 3,365 kcal of ME/kg) and lysine level (total lysine 0.55/0.70%, 0.65/0.85%, 0.75/1.00%, 0.85/1.15%) in gestation/lactation diet.

ME, metabolizable energy; Lys, lysine; SEM, standard error of the mean; E, energy effect; L, lysine effect; I, interaction between energy and lysine effect; SD, standard deviation; CV, coefficient of variation.

In blood profiles of primiparous sows (Table 6), blood creatinine was greater in Lys 0.65/0.85 and Lys 0.75/1.00 groups on 24 hrs postpartum (p = 0.04). The BUN was increased linearly as lysine level increased at day 110 of gestation (Linear, p = 0.03), However, the BUN was decreased linearly as lysine level of diets increased at day 21 of lactation (Linear, p < 0.01) and were significantly lower in the Lys 0.75/1.00 and Lys 0.85/1.15 groups (p = 0.02).

Table 6. Effects of dietary energy and lysine levels on blood profiles in primiparous sows

¹⁾Factors: energy level (3,265 or 3,365 kcal of ME/kg) and lysine level (total lysine 0.55/0.70%, 0.65/0.85%, 0.75/1.00%, 0.85/1.15%) in gestation/lactation diet.

²⁾Linear response (p < 0.05) to dietary lysine levels when significance of lysine effect was detected.

³⁾Linear response (p < 0.01) to dietary lysine levels when significance of lysine effect was detected.

ME, metabolizable energy; Lys, lysine; SEM, standard error of the mean; E, energy effect; L, lysine effect; I, interaction between energy and lysine effect

In the composition of colostrum (Table 7), sows fed high energy diets had greater contents of casein, protein, total solid, solid not fat, and free fatty acid than those of sows fed low energy diets (p = 0.03, p = 0.03, p = 0.03, p = 0.03, and p < 0.01, respectively). Otherwise, the lactose level of colostrum was lower in the high-energy group (p = 0.02); however, the lactose level in milk on day 21 of lactation was higher in the high-energy group (p = 0.04). For the lysine effect, the free fatty acid level of milk for Lys 0.75/1.00 and Lys 0.85/1.15 groups were greater than that for Lys 0.65/0.85 (p = 0.01).

Table 7. Effects of dietary energy and lysine levels on milk composition in primiparous sows

¹⁾Factors: energy level (3,265 or 3,365 kcal of ME/kg) and lysine level (total lysine 0.55/0.70%, 0.65/0.85%, 0.75/1.00%, 0.85/1.15%) in gestation/lactation diet.

ME, metabolizable energy; Lys, lysine; SEM, standard error of the mean; E, energy effect; L, lysine effect; I, interaction between energy and lysine effect.

Discussion

In the current study, high energy intake resulted in greater BW gain during gestation, and greater BW, BF thickness, and less BW loss during lactation. Increased energy intake from 3,100 to 3,400 kcal of ME/kg during gestation in primiparous sows resulted in greater BW gain [26,27]. Heo et al. [18] showed that dietary energy levels (3,265, 3,330, and 3,400 kcal of ME/kg) did not affect the gestation BW and BF thickness, but there were greater BW loss and BF loss of sows for low energy treatment during the lactation period. Thus, the high energy diet led to greater BW and BF gain during gestation compared to the low energy diet. There were no lysine effects on BW and BF thickness during gestation in primiparous sows, which was in agreement with the Cooper et al. [28] study. They reported that the level of dietary lysine (average of 10.6 and 13.2 g total lysine/d) during gestation did not affect gestation BW gain. Otherwise, supplementation with 16 g/d of lysine increased BW gain in primiparous sows during gestation compared with sows fed 4 or 8 g/d of lysine [29]. Total lysine intake during gestation in the current study was 11, 13, 15, and 17 g/d; these values were at or above the nutrient recommendations (9.4–11.4 g and 12.4–19.3 g of total lysine/ d) of the 1998 NRC guidelines [24] and the 2012 NRC guidelines [25], respectively. Thus, the current results demonstrated that the recommendations of the NRC in both 1998 [24] and 2012 [25], with respect to daily lysine intake, were adequate. Although there was no significant difference in BW and BF changes during lactation in the current study, Yang et al. [14] demonstrated that high-lysine intake (1.6% vs. 1.0% vs. 0.4%) during lactation reduced BW loss; and, lysine intake during lactation did not affect BF change during the entire lactation period. Also, Knabe et al. [30] demonstrated that various lysine diets (0.6%, 0.75%, and 0.9% total lysine) had no influence on BW and BF loss during lactation. According to the results that were reported by Jones and Stahly [13] and Yang et al. [14], low lysine intake had no significant influence on BF loss during lactation, but muscle protein degradation for sows tended to be increased due to the insufficient protein intake for milk production. Moreover, Prunier et al. [31] observed that the energy and nitrogen contents in milk were similar in primiparous sows fed 2.5 or 5.5 kg of feed per day during lactation, which was in accordance with the observation in primiparous sows fed 67.3 or 40.1 kJ ME/d during lactation; however, these low intakes of energy and feed resulted in severe BW and BF loss of primiparous sows.

In the current study, there was an interaction between energy and lysine effect in the number of piglet birth and alive piglet weight. These results were from the lower number of piglet birth in Lys 0.85/1.15 with 3,265 kcal of ME/kg treatment and Lys 0.65/0.85 with 3,365 kcal of ME/kg treatment. There were some possible reasons for these results; one possibility is that these results were not from the dietary factors, but were influenced by the ovulation rate and fetal survival of individual primiparous sows before the experiment started. Cooper et al. [28] reported that increased lysine intake in the gestation diet had no significant effects on litter size and growth; however, total births and total litter weight were affected by parities. They observed that gestation energy intake showed a positive relationship with the number of piglets born alive and litter weight at birth in multiparous sows, but not in primiparous sows because primiparous sows were still growing to mature size. The other possibility was that the amino acid imbalance affected the results. The total lysine levels of the diets were adjusted on each treatment with the same amount of limiting amino acids (methionine, threonine, and tryptophan). This imbalance of amino acids may result in an unexpected number of piglet births and piglet birth weight. Touchette et al. [32] demonstrated that increasing lysine levels with the constant ideal amino acid ratios to first parity sows reduced the number of total born and born alive piglets on subsequent parity. Cooper et al. [28] reported that different lysine intake (0.44% or 0.55% total lysine) did not affect litter size for total born and born alive, litter birth weight, nor piglet birth weight. Thus, various energy and lysine intake during gestation had no significant effect on litter size, litter weight, and piglet weight at birth in primiparous sows.

Litter growth was improved by greater milk production with the high energy diet [12,33] and greater lactation feed intake [34]. In the current study, the dietary energy effect was observed in piglet weight gain and piglet weight on day 21 of lactation, not in litter weight and gain. Considering the results for colostrum content, lactation feed intake, and BW loss during lactation, the 3,365 kcal of ME/kg diet met the energy requirement of sows for milk production and maternal gain and the growth of their progeny rather than the 3,265 kcal of ME/kg diet. In addition, these results suggested that the energy effect on litter weight was not observed due to litter size during lactation and feeding ad libitum.

In the present study, sows fed 0.7%, 0.85%, 1.0%, or 1.15% total lysine with different energy diets (3,265 or 3,365 kcal of ME/kg) consumed, on average, 33.7 g/d, 46.3 g/d, 52.1 g/d, and 56.5 g/d of total lysine, respectively, on the 3,265 ME kcal/kg diet, and 36.3 g/d, 44.1 g/d, 52.1 g/d, and 50.8 g/d of lysine, respectively, on the 3,365 ME kcal/kg diet. Previous studies had reported that the maximal response in litter weaning weights or piglet weaning weights was detected at 47 g/d of lysine ([35]; sows consumed 20–47 g/d lysine and 10.5 weaned pigs per litter), or 55 g/d of lysine ([36]; sows consumed 35–55 g/d lysine and 11.1 weaned pigs per litter). According to the NRC [24], total lysine intake during lactation (35.3 g/d or 48.6 g/d) met the lysine requirement of lactating sows. According to the NRC [25], total lysine intake during lactation for primiparous sows was 48.7 to 56.5 g/d (the daily weight gain of piglets was 190–270 g), and sows were weaning 11 pigs per litter. Taken together, lysine intake that ranged from 33.7 to 52.1 g/d met or supported piglet growth with no negative effects. The weaning weight of the piglets in the present study was similar to the results that observed by Touchette et al. [32], Thaler et al. [37], and Santos et al. [38], who reported no improvement in litter performance with increasing lysine intake during lactation. In accordance with Knabe et al. [30], the piglet weights at day 21 of lactation were not increased by feeding a corn-SBM-based diet with 0.9% lysine and they concluded that a 0.75% lysine diet met the nutrient needs of the sows or nutrient deficiency limited the sow’s ability to respond to the higher lysine intake. In addition, the lack of response to increasing levels of lysine on litter performance (even with the addition of DL-methionine, L-threonine, and L-tryptophan to achieve balance in the diets) could be related to a lack of other limiting amino acids [32,38]. Thus, lysine intake during lactation met the minimum lysine requirement or induced amino acid imbalance of lactating sows and did not show any significant differences in litter growth as a result of the lysine effect.

Piglet birth weight and litter uniformity are important to the growth and mortality of piglets before weaning [39] because low-weight piglets could not intake the sufficient colostrum and have low passive immunity or nutritional status [2], and litters with greater BW variation had more variable weight at weaning and slaughter [40]. There was no significant difference in the SD and CV of piglet weight at birth and day 21 of lactation because of pre-mating factors and maternal nutrition during gestation [41,42]. Before gilts mate, the development and uniformity of embryos and placenta ultimately affecting litter uniformity can be affected by insufficient restoration of follicle development and increased developmental variation within the preovulatory follicle pool [42]. In addition, Campos et al. [41] reported that maternal nutrition during gestation, such as insulin, IGF-1, and dietary protein or amino acid levels, had an effect on piglet uniformity. Also, the CV of the mean BW was positively related to the BF gain of the sow during gestation [3], but dietary effects were not observed in BF gain during gestation and piglet uniformity in the current study.

The concentration of BUN is known as an indicator of protein mobilization, nitrogen balance [43], and amino acid requirements [44] in sows. Also, creatinine is an indicator of muscle catabolism [18]. Based on the concentrations of creatinine, 0.65% and 0.75% lysine in gestation diets had a high efficiency of protein utilization in lactating sows at 24 hrs postpartum. According to the results of BUN, high lysine intake induced excess nitrogen at day 110 of gestation, and the 0.75%/1.00% lysine group showed high efficiency of nitrogen utilization in lactating sows on 24 hrs postpartum and day 21 of lactation.

Many previous studies reported that the chemical compositions of colostrum and milk were not affected by dietary energy intake during gestation because sows utilize their internal reserves to compensate for deficient nutrients [15,27]. Beyer et al. [45] indicated that colostrum and body reserves were major determinants of milk yield in early lactation, whereas the feed intake of sows becomes important in the later lactation due to the greater exhaustion of their body reserves [45]. The body condition of the sow at farrowing and during lactation plays an important role in milk composition such that the milk fat content was 20% greater in sows with a high body fat content compared with lean sows [46]. Thus, the high deposition of protein and fat mass in primiparous sows before lactation resulted in high milk components, except lactose, which was delivered from the dam to their progeny using body reserves. Some researchers reported that a high-lysine diet does not affect milk composition [47,48], whereas others insist that a high-lysine diet increases milk components [13, 18, 29]. In the current study, the lysine effect was observed only in free fatty acids of colostrum. Milk fat was manufactured in the mammary gland from glycerol and free fatty acids [49], and the lysine requirement to maximize the milk production was increased as ME intake increased [12]. Therefore, the high-energy group had greater free fatty acid content in colostrum compared with the low-energy group, and sows fed the 0.75% lysine diet had the highest free fatty acids content in the colostrum.

Conclusion

In conclusion, the primiparous sows fed the diet containing 3,365 kcal of ME/kg had more gain of BW and BF compared with sows fed the diet containing 3,265 kcal of ME/kg. Also, piglets from sows fed the 3,365 kcal of ME/kg diet showed greater piglet weight gain during lactation. Although significant differences were not observed in reproductive performance and piglet uniformity, total lysine 0.75% for gestation and 1.00% for lactation showed higher nitrogen utilization in the blood profile of sows. Moreover, the WEI was decreased in the Lys 0.75/1.00 group. Thus, the supplementation of total lysine 0.75% for gestation and 1.00% for lactation in 3,365 kcal of ME/kg could be applied to the primiparous sows’ diet to improve sow performance and piglet growth.

Competing interests

No potential conflict of interest relevant to this article was reported.

Funding sources

This research was supported by "Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ011617)" Rural Development Administration, Korea.