Lactation body condition loss impaired conceptus development and plasma progesterone concentration at day 8 post-ovulation in primiparous sows

The current study investigated effects of dietary amino acid (AA) availability on lactational body condition loss and metabolic status, in relation to reproductive parameters after weaning up to Day 8 post-ovulation. Primiparous sows (n = 35) were allocated to one of two lactation diets containing either low crude protein (CP, 140 g/kg) with a low percentage (8%) of slow protein in total protein (LL, n = 18) or high CP (180 g/kg) with a high (16%) percentage of slow protein (HH, n = 17). The HH diet was expected to improve AA utilization by supplying more AA, in a more gradual fashion. The diets did not affect sow body condition loss during lactation, while the HH diet tended to increase litter weight gain during the week 3 of lactation (Delta = 1.3 kg, P = 0.09). On Day 14 post-farrowing, HH diet led to higher plasma urea both pre-feeding and post-feeding (Delta = 2.3 mmol/L, P < 0.01, Delta = 2.4 mmol/L, P < 0.01, respectively), whilst plasma creatinine, NEFA and IGF-1 were similar. No dietary effects on reproductive parameters were found, however several relationships were found between body condition and reproductive parameters. Sows with higher body weight on Day 1 or Day 21 post-farrowing had greater follicle size on Day 3 post-weaning (beta = 0.03 mm/kg, P < 0.01, beta = 0.04 mm/kg, P < 0.01, respectively). At Day 8 post-ovulation, plasma progesterone concentration was negatively related to loin muscle loss (beta = -0.67 ng/ml mm(-1), P = 0.02), backfat loss (beta = -2.33 ng/ml mm(-1), P = 0.02), and estimated body fat loss (beta = -0.67 ng/ml mm(-1), P = 0.02). Both plasma progesterone and the number of corpora lutea were positively related to the energy balance during lactation (beta = 0.03 ng/ml ME MJ(-1), P = 0.01, beta = 0.01 CL/ME MJ, P = 0.02, respectively). The conceptus size at Day 8 post-ovulation was negatively related to body weight loss (beta = -0.01 mm/kg, P = 0.01), estimated body fat loss (beta = -0.02 mm/kg, P = 0.03) and estimated body protein loss (beta = -0.06 mm/kg, P = 0.04), and was positively related to the energy balance during lactation (beta = 5.2*10(-4) mm/ME MJ, P = 0.01). In conclusion, body protein and fat losses during lactation reduced subsequent plasma progesterone concentration and conceptus development at Day 8 post-ovulation.