The arginine supplementation levels in the late-gestating sows’ diet did not affect body weight, backfat thickness, and the lactation feed intake of sows (Table 2).

 

In reproductive performance, dietary arginine levels during late gestation had no influence on the number of piglets for total born, stillborn, mummy, and born alive (Table 3). However, piglet birth weight showed a quadratic response (p < 0.03) such that the piglet birth weight was decreased by the arginine levels from 0.72% to 1.0%, whereas it was increased by the arginine level from 1.0% to 1.5%. Additionally, increasing the inclusion level of dietary arginine tended to increase (p < 0.10) the alive litter weight linearly. Increasing the dietary arginine levels in late gestation did not affect the farrowing time, helping frequency, and placenta weight.

 

Increasing dietary arginine levels in late gestation linearly increased (p < 0.05) the litter weight at day 21, and the litter weight gain, such that litter weight and litter weight gain for ARG15 tended to be greater than those for CON (Table 4). The piglet weight at day 21 of lactation was linearly increased (p < 0.05) as the dietary arginine level increased in late gestation. Additionally, increasing the dietary arginine level in late gestation linearly increased (p < 0.05) piglet weight gain, such that the piglet weight gain for ARG15 tended to be greater than that for CON.

 

The effect of dietary arginine levels in late gestation on the piglet uniformity is presented in Table 5. The SD for piglet birth weight was linearly increased (p < 0.05), and the CV for piglet birth weight had a tendency of linear increase (p < 0.10) as the dietary arginine level increased in late gestation. The piglet BW distribution at birth showed a significant difference (p < 0.01) among dietary treatment (Figure 1). However, dietary arginine levels in late gestation did not affect the piglet uniformity and BW distribution at day 21 of lactation.

The blood concentration of AAs in the gestating sows is presented in Table 6. Increasing arginine supplementation to late-gestating sows linearly increased (p < 0.05) the blood concentrations of arginine and ornithine at day 90 and day 110 of gestation, respectively. On the other hand, the blood concentrations of alanine at day 110 of gestation for sows fed a diet with higher dietary arginine were linearly decreased (p < 0.03) compared to those for sows fed the isonitrogenous control diet. Additionally, glutamine concentration for sows at day 110 of gestation was quadratically increased (p < 0.05), as the dietary arginine level increased. There were no significant differences in blood concentrations of other AA, among dietary treatments. The plasma concentrations of arginine, lysine, and methionine for day 90 of gestation were greater (p < 0.05) than those for day 70 of gestation. The plasma concentrations of alanine and glutamine for day 110 of gestation were greater (p < 0.05) than those for day 70 of gestation, whereas the plasma concentrations of citrulline, glycine, leucine, ornithine, taurine, and valine for day 110 of gestation were less (p < 0.05) than those for day 70 of gestation. There were interactions (p < 0.05) between arginine and the date effect in the plasma concentration for ornithine such that there was no significant difference in the plasma ornithine concentration for day 70 of gestation, whereas plasma ornithine concentrations at day 90 of gestation for ARG10 and ARG15 treatments were greater (p < 0.05) than that for CON treatment, and plasma ornithine concentration at day 110 of gestation for ARG15 treatment was greater (p < 0.05) than those for CON and ARG10 treatments.

 

The dietary arginine levels for the late-gestating sows had no significant influence on the blood concentrations of BUN, creatinine, total protein, and urea for sows in the late gestation period (Table 7). The blood concentrations of BUN, creatinine, and urea for day 110 of gestation were greater (p < 0.05) than those for day 70 of gestation. There were no interactions between arginine and the date effect in the blood concentrations for BUN, creatinine, total protein, and urea. Increasing the dietary arginine levels for sows during late gestation did not affect the milk composition of colostrum and milk (day 21 of lactation) in lactating sows (Table 8).

 

Supplementing sow diet with L-arginine during the late gestation did not influence the gain of BW and BF in sows for the late gestation period and loss of BW and BF in sows for the lactation period. This was in agreement with the result of Quesnel et al. [39], who reported that dietary supplementation with 25.5 g/day L-arginine from day 77 to farrowing did not affect the BW after farrowing and BF before farrowing of sows. Additionally, Bass et al. [40] reported that dietary supplementation with 1% L-arginine for gestating sows from day 93 to day 110 had no influence on BW loss, following farrowing or during lactation. However, they observed that improved late gestation BW gain of sows fed a diet with 1% L-arginine was revealed in parity 0 and parity 1, whereas, there was no difference in late gestation BW gain compared to the control animals and 1% L-arginine-supplemented sows in parity 2+, implying that supplementation with 1% L-arginine partially met the arginine requirement in gilts or sows with parity 1 sows, not in sows with parity 2+. The difference between the current study and that of Bass et al. [40] with regard to the effect of dietary arginine in late gestation on the changes of BW or BF for sows could have been due to the difference in the parities of sows in the treatment group. Additionally, the lack of difference in the changes of BW and BF for sows during the whole experiment period could partly have been due to the same nitrogen content of diets among the dietary treatments, with the addition of L-Alanine as the isonitrogenous control.

 

Dietary effects of L-arginine was reported such that supplementation of L-arginine was found to increase nitric oxide, enhancing the delivery of essential nutrients from maternal to fetal blood [16,17,18], and increasing the polyamines necessary for embryogenesis and placental growth [14,15,20]. Since the nitric oxide and polyamines are important for angiogenesis and embryogenesis, arginine enhanced the growth of fetus and placenta development [19,20]. The litter size, including the number of total born or born alive was not affected by the dietary arginine effect in the present study, which was in agreement with the results from the studies of Quesnel et al. [39] and Nantapaitoon et al. [41], who reported that 1% L-arginine supplementation for late-gestating sows had no influence on the number of piglets at birth. However, previous studies reported that arginine supplementation enhanced conceptus survival or sow litter size in the period of early-gestation [33,42], or whole gestation [12,13,36]. The number of developing embryos is decided in early gestation, because most of the embryonic losses occurred during early gestation [43], and the dead embryos were not reabsorbed by the uterus after day 40 of gestation [44]. Thus, the differences among studies with regard to the effects of dietary arginine on the litter size of sows could have been due to differences in the supplemented period for the diet with L-arginine.

• Quesnel, H.; Quiniou, N.; Roy, H.; Lottin, A.; Boulot, S.; Gondret, F. Supplying dextrose before insemination and-arginine during the last third of pregnancy in sow diets: Effects on within-litter variation of piglet birth weight. J. Anim. Sci. 2014, 92, 1445–1450. [Google Scholar] [CrossRef]
• Bass, B.E.; Bradley, C.L.; Johnson, Z.B.; Boyd, R.D.; Usry, J.L.; Maxwell, C.V.; Frank, J.W. Influence of dietary L-arginine supplementation to sows during late gestation on sow and litter performance during lactation. Res. Ser. 2011, 597, 151–155. [Google Scholar]
• Nuntapaitoon, M.; Muns, R.; Theil, P.K.; Tummaruk, P. L-arginine supplementation in sow diet during late gestation decrease stillborn piglet, increase piglet birth weight and increase immunoglobulin G concentration in colostrum. Theriogenology 2018, 121, 27–34. [Google Scholar] [CrossRef]
• Bérard, J.; Bee, G. Effects of dietary L-arginine supplementation to gilts during early gestation on foetal survival, growth and myofiber formation. Animal 2010, 4, 1680–1687. [Google Scholar] [CrossRef]
• Foxcroft, G.R.; Dixon, W.T.; Novak, S.; Putman, C.T.; Town, S.C.; Vinsky, M.D.A. The biological basis for prenatal programming of postnatal performance in pigs. J. Anim. Sci. 2006, 84, E105–E112. [Google Scholar] [CrossRef]
• Town, S.C.; Patterson, J.L.; Pereira, C.Z.; Gourley, G.; Foxcroft, G.R. Embryonic and fetal development in a commercial dam-line genotype. Anim. Reprod. Sci. 2005, 85, 301–316. [Google Scholar] [CrossRef]