SummaryThe use of functional amino acids during pregnancy has been linked to improved reproduction in mammals. In this context, arginine is a precursor in the synthesis of numerous molecules, such as nitric oxide and polyamines, which play an important role during reproduction. However, contradictory studies are found in the literature, particularly regarding the amount of supplementation and the period of pregnancy in which it is used. The objective of this study was to evaluate the effects of dietary arginine supplementation for pregnant sows on foetal development via a systematic review. The search for papers was performed during the month of December 2015, in the databases ISI Web of Science, Science Direct, Scopus, and SciELO. From a total of 5675 returned studies, only 13 papers were selected after applying selection criteria.Most (47%) of the studies that evaluated the effects of dietary arginine supplementation on foetal development in pigs used 1% arginine. Supplementation was initiated in the first third of pregnancy in 47% of tests, including in both primiparous and multiparous sows. These studies showed positive results for embryo survival and foetal development, evidenced by the increase in placental weight and the number and weight of piglets born alive. Of all evaluated studies, 53% showed benefits on foetal development. It is concluded that supplementing dietary arginine in gestating sows can benefit embryo survival and foetal development. However, to establish a supplementation plan with this amino acid, aspects related to the period of pregnancy, supplementation levels, and source of arginine must be well defined. K E Y W O R D Sfoetal weight, functional amino acid, litter, reproduction, swine conceptus

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The use of functional nutrients has been proposed to reduce the occurrence of intrauterine growth retardation in animals at birth in several mammalian species. The objective of this study was to verify the effectiveness of citrulline and N-carbamylglutamate (NCG) dietary supplementation as arginine precursors for mammalian species, and the effects on fetal development through a systematic review. The search for studies was performed during August 2018 in the PubMed, ISI Web of Science, Science Direct, and Scopus databases. The literature search was conducted using “arginine precursor”, “citrulline”, or “N-carbamylglutamate” as keywords, combined with “gestation”, “pregnancy”, “fetus”, “newborn”, or “reproduction”. Studies in which arginine precursors were evaluated in gestating mammals and their effects on parameters related to the intrauterine development of the conceptus were selected. Of 1,379 articles, 18 were selected, primarily based on the title and the abstract. Supplementation with NCG (0.5 g to 2 g/kg of feed) increased maternal plasma arginine concentrations in all studies that evaluated this variable. Fetal number increased in 55.56% of the studies that evaluated it, and fetal weight increased in the majority (62.5%) of the studies evaluating this variable. By supplementing citrulline, only fetal weight was improved, with an increase in maternal plasma arginine in 40% of the studies. In conclusion, N-carbamoyl glutamate seems to be an arginine precursor more effective than L-citrulline during gestation; however, both precursors, beside L-Arginine, should be evaluated in similar conditions to confirm the existence of specific particularities such as periods and levels of supplementation, which need to be considered for different species of animals. The supplementation of NCG increases arginine concentrations in maternal plasma, thus improving mammalian reproductive efficiency and fetal development, mainly by promoting higher birth weight.

The objective of the study was to evaluate the effects of litter size and supplementation of functional amino acids on the piglet birth weight variability through of a systematic review and meta‐analysis. PubMed, ISI Web of Science, Science Direct, Scopus and SciELO are the main used databases and were searched in January 2019 by using the following keywords and their combinations: within‐litter birth, weight variability, piglets, litter size, sow, amino acids, gestation, uniformity, CV and/or SD. Of the 64 pre‐selected articles, only articles presenting the coefficients of variation and/or standard deviations according to the litter size and different levels of amino acid supplementation in the sow diets during gestation were selected. The average birth weights of total and live piglets were 43% lower in litters from sows with high prolificacy than those from sows with low prolificacy. The weight variability was affected by high prolificacy sows, with increases of 4.04% and 4.54% in the coefficients of variation of total and born alive piglets respectively (p = .074; p = .009). The standard deviation increased by 180 g in born alive piglets to high prolificacy sows. The coefficients of variation of total and live piglets born from high prolificacy sows showed an increase of 4.04% and 4.54% respectively (p = .07; p < .05). There was a tendency for reduced weight variability with amino acids supplementation when considering the standard deviation of total born (p = .072). However, reproductive performance was not significantly influenced (p > .05). In conclusion, the average litter weight and the number of piglets born influence weight variability. Amino acids supplementation may reduce the birth weight variability between piglets. However, this effect depends on the amino acid used, the levels of supplementation and on other factors not completely addressed in this study. Thus, more research is necessary to fully elucidate this topic.

The study assessed the effects of dietary L‐arginine supplementation from days 85 to 115 of gestation on sow performance, litter quality, piglet physiology and survival variables in the first 24 hr of life. Twenty multiparous sows, with a history of hyperprolificacy (more than 14 piglets per litter), were used. A completely randomized experimental design was used, consisting of two treatments: feed supplemented or not with 1% L‐arginine from days 85 to 115 of gestation. The experimental unit consisted of the sow and its respective litter, using 10 replicates per treatment. The sows were distributed into the treatments based on body condition and parity. Supplementation with L‐arginine reduced the within‐litter standard deviation and the within‐litter coefficient of variation of piglet weight at 24 hr by 54 g and 4.14 percentage points respectively (p = .029; p = .035). Supplementation with 1.0% L‐arginine decreased the percentages of piglets weighing less than 800 g by 5.60 and 5.08 points at birth and at 24 hr of life respectively. Piglets from sows supplemented with L‐arginine had higher (p = .088) average rectal temperatures at birth and lower (p = .030) rectal temperature at 24 hr of life in comparison with control piglets. No significant differences in placental weight or estimated colostrum production and intake were observed in the first 24 hr of life. At 24 hr of life, piglets weighing less than 1,000 g and from supplemented sows had lower (p = .048) surface/mass ratios and higher body mass index (p = .070). Piglets from supplemented sows and who weighed 1601 to 1,800 g had lower body mass index and ponderal index (p = .002; p = .003). Supplementation with L‐arginine during the final third of gestation reduces the incidence of unviable piglets (<800 g) and improved litter uniformity and piglets’ body conformation within the first 24 hr of life.