Impact of arginine supplementation on serum prolactin and mRNA abundance of amino acid transporter genes in mammary tissue of lactating sows.

This study was conducted to test the hypothesis that supplemental dietary Arg to late-pregnant and lactating sows increases serum prolactin concentrations and mRNA abundance of SLC7A1, SLC7A2, and SLC6A14 in mammary parenchymal tissue. From day 108 of gestation and until day 21 of lactation, sows were fed a diet either supplemented with 0.10 g of l-Arg/kg body weight (BW) per day (n = 10, ARG) or 0.34 g of l-Glu/kg BW per day (n = 10, control). Litters were standardized to 10 piglets on day 1 of lactation and piglets were weighed on days 1, 7, 14, and 21 of lactation. Sow BW was recorded on day 108 of gestation and days 1, 10, and 21 of lactation. Lactation sow feed intake was recorded daily. Mammary parenchymal tissue was biopsied on day 5 of lactation to measure mRNA abundance SLC7A1, SLC7A2, and SLC6A14. On days 4 and 18 of lactation, blood samples were collected from sows at 2, 4, and 6 hr postfeeding to measure serum prolactin concentrations. Milk samples were collected on days 4, 10, and 18 of lactation to measure fat, lactose, urea N, and true protein concentrations. Sow BW, backfat, and feed intake over all sampling days did not differ between treatments. Piglet BW on d 1 tended to be greater for the ARG treatment than the control treatment (P = 0.12). Sow milk yield and composition (fat, protein, lactose, and urea N) and mammary mRNA abundance of candidate genes did not differ between the ARG and the control group. Compared to controls, serum prolactin concentrations tended to be greater (P = 0.08) in ARG sows on day 4 of lactation, and did not differ on day 18. Current findings show a potential beneficial effect of dietary supplementation with Arg to late-pregnant multiparous sows on BW of their piglets on day 1. Dietary Arg supplementation at a rate of 0.10 g/kg BW during late pregnancy and lactation tended to increase serum prolactin concentrations with no increase in mammary transcript abundance of SLC7A1, SLC7A2, and SLC6A14 in early lactation.

Nitrogen utilization of lactating sows fed increasing dietary protein1.

The objectives of the study were 1) to quantify dietary N utilized for milk N and N loss in urine and feces, in sows fed increasing dietary CP with a constant amount of Lys, Met, Thr, and Trp to meet their standardized ileal digestible (SID) requirement and 2) to determine the optimal dietary CP concentration based on dietary N utilization for milk production. Seventy-two sows were fed 1 of 6 dietary treatments, formulated to increase the SID CP as followed: 11.8, 12.8, 13.4, 14.0, 14.7, and 15.6% and formulated to be isocaloric (9.8 MJ NE/kg). Diets were fed from day 2 after parturition until weaning at day 28 (± 3 d). Litters were equalized to 14 piglets and weighed within 48 h following parturition. Sows were weighed and back fat scanned, at day 18 (± 3 d) and day 28 (weaning; ± 3 d). Litter weight was recorded at day 11, 18 (± 3 d), and 28 (± 3 d). Nitrogen balances were conducted on approximately day 4, 11, and 18 (± 3 d). Daily milk yield was estimated from recorded litter gain and litter size. To calculate sows mobilization of fat and protein, body pools of fat and protein were estimated by D2O (deuterated water) enrichment on day 4 and 18 (± 3 d). No linear, quadratic, or cubic effects of increasing dietary CP was observed for sows total feed intake, sow BW, body pools of protein and fat, protein and fat mobilization, total milk yield, and piglet performance. The protein content in milk increased linearly with increasing dietary CP in week 1 (P < 0.05), week 2 (P < 0.05), and week 3 (P < 0.001). Urine production did not differ among treatments and N output in urine increased linearly with increasing dietary CP concentration in week 1 (P = 0.05), week 2 (P < 0.001), and week 3 (P < 0.001). Urine N excretion relative to N intake increased linearly with increasing dietary CP (P < 0.001). Milk N utilization relative to N intake decreased linearly from 77.8% to 63.1% from treatment 1 through 6 (P < 0.001). Corrected milk N utilization decreased from 68.6% to 64.2% from treatment 1 through 6 (P < 0.05). In conclusion, a low dietary CP concentration for lactating sows with supplemented crystalline AA improved the efficiency of dietary N utilization and reduced the N output in urine without affecting lactation performance.

Whole-body nitrogen utilization and tissue protein and casein synthesis in lactating primiparous sows fed low- and high-protein diets.

Twenty-eight lactating Yorkshire and Yorkshire × Landrace primiparous sows were used to test the hypothesis that feeding a diet with reduced CP concentration and supplemented with crystalline AA (CAA) does not decrease milk protein yield and litter growth but improves apparent N utilization for milk protein production. Sows were assigned to 1 of 2 dietary treatments: 1) control (CON; 16.2% CP; analyzed content) or 2) low CP with CAA to meet estimated requirements of limiting AA (LCP; 12.7% CP) over a 17-d lactation period. A N balance was conducted for each sow between days 13 and 17 of lactation. On day 17, a 12-h primed continuous infusion of l-[ring-2H5]-Phe was conducted on 12 sows (n = 6) with serial blood and milk sampling to determine plasma AA concentrations and Phe enrichment, and milk casein synthesis, respectively. Thereafter, sows were sacrificed and tissues were collected to determine tissue protein fractional synthesis rates (FSR). Litter growth rate and milk composition did not differ. Sows fed the LCP diet had reduced N intake (122.7 vs. 153.2 g/d; P < 0.001) and maternal N retention (13.5 vs. 24.6 g/d; P < 0.05) and greater apparent efficiency of using dietary N intake for milk production (85.1% vs. 67.5%; P < 0.001). On day 17 of lactation, all plasma essential AA concentrations exhibited a quartic relationship over time relative to consumption of a meal, where peaks occurred at approximately 1- and 4-h postprandial (P < 0.05). Protein FSR in liver, LM, gastrocnemius muscle, mammary gland, and in milk caseins did not differ between treatments. Feeding primiparous sows with a diet containing 12.7% CP and supplemented with CAA to meet the limiting AA requirements did not reduce milk protein yield or piglet growth rate and increased the apparent utilization of dietary N, Arg, Leu, Phe+Tyr, and Trp for milk protein production. The improved apparent utilization of N and AA appears to be related exclusively to a reduction in N and AA intake.