A static model to analyze carbon and nitrogen partitioning in the mammary gland of lactating sows

Quantitative estimates of mammary nutrient inputs, outputs and metabolism in sows are scarce, despite being critical elements to identify parameters controlling milk synthesis central for the feeding of lactating sows. The objective of this study was to quantify the mammary gland input and output of nutrients as well as the intramammary partitioning of carbon and nitrogen with the purpose to identify mechanisms controlling mammary nutrient inputs, metabolism and milk production in lactating sows. A data set was assembled by integration of results from four studies. The data set included data on litter performance, mammary arterial-venous concentration differences (AV-difference) of energy metabolites and amino acids, and the contents of lactose, fat and amino acids in milk. Milk yield was estimated based on average litter size and litter gain, and mammary plasma flow (MPF) was estimated using the sum of phenylalanine and tyrosine as internal flow markers. The yield and composition of milk were used to estimate mammary nutrient output in milk, and MPF and AV-difference were used to estimate net mammary input of carbon and nitrogen and output of CO₂. Carbon and nitrogen used for the synthesis of lactose, fat and protein in milk and CO₂-yielding processes were represented in a static nutrient partitioning model. The origin of mammary CO₂ output was calculated using theoretical estimates of carbon released in processes supporting mammary synthesis of de novo fat, protein and lactose in milk, mammary tissue protein turnover and transport of glucose and amino acids. Results indicated that total input of carbon from glucose and lactate was partitioned into lactose (36%), fat (31%) and CO₂-yielding processes (34%). Theoretical CO₂ estimates indicated that de novo fat synthesis, milk protein synthesis and mammary tissue protein turnover were the main processes related to mammary CO₂ production. More than 90% of mammary gland amino acid input was used for milk protein. The quadratic relationship between AV-difference and mammary input of essential amino acids indicated that both changes in AV-difference and MPF contributed to the regulation of mammary input of essential amino acids. The impact of the arterial supply of amino acids on mammary input may be greater for the branched-chain amino acids, arginine and phenylalanine than for other essential amino acids. In conclusion, relationships between input and output parameters indicate that AV-difference and MPF regulate mammary nutrient input to match the supply and demand of nutrients for the mammary gland.

Comparison of plasma tryptophan-related metabolites in crossbred Piétrain and Duroc pigs

Besides being incorporated into proteins, Trp, an indispensable AA, is involved in numerous metabolic pathways. Previous data showed that Trp conversion into kynurenine (Kyn) and nicotinamide (Nam) differs among studies, and such differences cannot be explained by different dietary niacin supplies. We hypothesized that pig genotype influences Trp metabolism and thus the conversion of Trp into its metabolites. The objective of this study was to compare plasma appearance of Trp and related metabolites in 12 Duroc and 12 Piétrain crossbred postweaning pigs fed 2 contrasting dietary Trp levels. Within each genotype, 6 pigs were fed a basal (B-Trp: 17% and 15% standardized ileal digestible [SID] Trp:Lys for starter and prestarter diets) or supplemented (S-Trp: 24% and 23% SID Trp:Lys for starter and prestarter diets) Trp diet. Growth was monitored, and plasma fasted concentrations were measured over 4 wk, and then pigs were fitted with a jugular catheter for frequent blood samplings. After overnight fasting, 350 g of the experimental diets were offered to each pig, and plasma concentrations of Trp, Kyn, Nam, and 5-hydroxytryptamine (5-HT) were measured for 6 h. The activities of Trp-degrading enzymes were measured in different tissues collected after pig slaughtering. Plasma Trp fasted concentrations did not differ between B-Trp and S-Trp diets and increased from weaning to 2 and 4 wk after weaning for Piétrain but not for Duroc crossbred pigs (time × genotype, = 0.001). Plasma Kyn concentrations were greater 4 wk after weaning ( = 0.002) than at weaning and for Piétrain compared to Duroc genetics ( = 0.008). Plasma Nam concentrations were greater for pigs fed the S-Trp diet than for those fed the B-Trp diet ( = 0.0001) and for Duroc than for Piétrain genetic lines ( = 0.001); this difference tends to be greater at weaning than after ( = 0.055). Our data showed an increase in plasma concentrations of Trp, Kyn, Nam, and 5-HT according to time after a meal and to the dietary Trp content. However, postprandial plasma concentrations of Trp metabolites and enzyme activities were not significantly different between Duroc and Piétrain crossbred pigs. In conclusion, our results suggest that Nam endogenous synthesis capacity from Trp is greater in Duroc than in Piétrain crossbred pigs, but this was apparent only at weaning.

Effect of added dietary threonine on growth performance, health, immunity and gastrointestinal function of weaning pigs with differing genetic susceptibility to Escherichia coli infection and challenged with E. coli K88ac

Threonine (Thr) is important for mucin and immunoglobulin production. We studied the effect of added dietary Thr on growth performance, health, immunity and gastrointestinal function of weaning pigs with differing genetic susceptibility to E. coli K88ac (ETEC) infection and challenged with ETEC. Forty-eight 24-day-old weaned pigs were divided into two groups by their ETEC susceptibility using mucin 4 (MUC4) gene as a marker (2 MUC4(-/-) , not-susceptible, and 2 MUC4(+/+) , susceptible, pigs per litter). Within genotype, pigs were fed two different diets: 8.5 (LThr) or 9.0 (HThr) g Thr/kg. Pigs were orally challenged on day 7 after weaning and slaughtered on day 12 or 13 after weaning. Before ETEC challenge, HThr pigs ate more (p < 0.05). The diet did not affect post-challenge growth, but HThr tended to increase post-challenge feed efficiency (p = 0.087) and overall growth (p = 0.087) and feed efficiency (p = 0.055). Before challenge, HThr pigs excreted less E. coli (p < 0.05), while after challenge, diet did not affect the number of days with diarrhoea and ETEC excretion. MUC4(+/+) pigs responded to the challenge with more diarrhoea, ETEC excretion and anti-K88 IgA in blood and jejunal secretion (p < 0.001). HThr pigs had a higher increase of anti-K88 IgA values in jejunal secretion (p = 0.089) and in blood (p = 0.089, in MUC4(+/+) pigs only). Thr did not affect total IgA and IgM values, morphometry of jejunum, goblet cells count in colon, total mucin from jejunum and colon, but varied jejunal goblet cells counts (p < 0.05). In the first two post-weaning weeks, 8.5 g Thr/kg diet may be not sufficient to optimize initial feed intake, overall feed efficiency and intestinal IgA secretion and to control the gut microbiota in the first post-weaning week, irrespective of the pig genetic susceptibility to ETEC infection.