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High fiber diets are known to have many benefits to sows (e.g., improving reproductive performance such as vitality of piglets, stimulating gut health, and improving well-being), and due to their fermentation properties, they may have different functions in lactating sows. Fast fermentable fiber favors the growth of beneficial microbiota which contributes to improved gut health, and slow fermentable fiber increases the fecal mass and provides a delayed release of some nutrients which benefits the farrowing process of sows. On the other hand, high fiber diets may reduce feed intake and nutrient digestibility. The objective of this study was to investigate the effects of dietary fiber concentration and fermentation rate on lactating sow performance, nutrient digestibility, and immunity. Four diets were formulated with increasing fast fermentable fiber, with diets 1 and 2 formulated at low (15%) total dietary fiber (TDF) and diets 3 and 4 at high (25%) TDF. The proportion of fast fermentable fiber in total diet of 4 treatments were 1.25%, 2.5%, 3.75%, and 5% respectively. The main fiber sources were sugar beet pulp, oat hull, and barley. Digestible energy, crude protein, and lysine levels were comparable among each treatment group. A total of 136 lactating sows (Landrace × Large White) were blocked by parity, body weight (BW), and back fat (BF), and then randomly assigned to each block (8 blocks). Feed allowance was set to increase from 3 kg/d (primiparous) or 3.5 kg/d (multiparous) at farrowing to a maximum of 7 kg/d or 8 kg/d at 7d or 8d post farrowing. Results showed that sows in high fiber groups had an increased litter weight gain and BF loss (P < 0.05), and sows in fast fiber groups showed a decreased BW and protein loss (P < 0.05). Low fiber fed sows showed a significantly increased digestibility of protein, gross energy (GE), and dry matter compared with high fiber ones (P < 0.05). Sows fed with slow fermentable fiber in the low fiber groups showed greater digestibility of GE, protein, and dry matter compared with the ones fed with fast fermentable fiber; however, the opposite was true in high fiber groups. Fiber concentration and fermentation rate did not show significant effects on serum IL-8, IL-10, TNF-a, or endotoxin of sows (P > 0.05). In conclusion, high fiber diet increased BF loss and negatively influenced nutrient digestibility while having positive effects on litter growth. The negative effects of fiber were partially compensated by increasing the soluble fraction. Based on the current study, when feeding lactating sows a diet with high fiber, a relative increase of fast fermentable fiber is the most favorable feeding strategy. [ABSTRACT FROM AUTHOR]

Simple Summary: The first month of gestation in the pig is characterised by many changes, such as entry of the embryos into the uterus, increased secretion of the pregnancy hormone, progesterone, and the implantation of the embryos into the uterus. Before implantation, embryos have not yet attached to the uterus, and are reliant on nutrients and signals in the uterine fluids, which are controlled by progesterone, among others. High feed intake has a positive effect on progesterone secretion and supports the establishment and development of pregnancy. Very low feed intakes, such as in sows competing for feed in group housing, can be detrimental to embryo survival and even the maintenance of pregnancy. After implantation, specific nutrients that improve the vascularisation of the placenta, such as arginine, can support the capacity of the uterus to support a litter of developing embryos since in this stage competition between embryos starts to play a role. In the pig, the establishment and maintenance of luteal function in early gestation is crucial to endometrial function, embryo development, and survival. The level of feed intake has a positive effect on formation of luteal tissue and progesterone secretion by the ovaries in the pre-implantation period, which is important for endometrial remodeling and secretion. These effects are independent of luteinising hormone (LH) and probably driven by metabolic cues, such as insulin and insulin-like growth factor (IGF-1), and seem to support progesterone secretion and delivery to the endometrium, the latter which occurs directly, bypassing the systemic circulation. Even after implantation, a high feed intake seems to improve embryo survival and the maintenance of pregnancy. In this stage, luteal function is LH-dependent, although normal variations in energy intake may not result in pregnancy failure, but may contribute to nutrient supply to the embryos, since in this phase uterine capacity becomes limiting. Feed incidents, however, such as unintended fasting of animals or severe competition for feed, may result in embryo or even pregnancy loss, especially in periods of seasonal infertility. Specific nutrients such as arginine have a role in the vascularisation of the placenta and can improve the uterine capacity in the period after implantation. [ABSTRACT FROM AUTHOR]

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 (Δ = 1.3 kg, P = 0.09). On Day 14 post-farrowing, HH diet led to higher plasma urea both pre-feeding and post-feeding (Δ = 2.3 mmol/L, P < 0.01, Δ = 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 (β = 0.03 mm/kg, P < 0.01, β = 0.04 mm/kg, P < 0.01, respectively). At Day 8 post-ovulation, plasma progesterone concentration was negatively related to loin muscle loss (β = −0.67 ng/ml · mm−1, P = 0.02), backfat loss (β = −2.33 ng/ml · mm−1, P = 0.02), and estimated body fat loss (β = −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 (β = 0.03 ng/ml · ME MJ−1, P = 0.01, β = 0.01 CL/ME MJ, P = 0.02, respectively). The conceptus size at Day 8 post-ovulation was negatively related to body weight loss (β = −0.01 mm/kg, P = 0.01), estimated body fat loss (β = −0.02 mm/kg, P = 0.03) and estimated body protein loss (β = −0.06 mm/kg, P = 0.04), and was positively related to the energy balance during lactation (β = 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. • Lactational body condition loss impairs conceptus development at Day 8 post-ovulation. • A higher body condition loss relates to a lower plasma P4 at Day 8 post-ovulation. • A higher body weight on Day 1 or 21 post-farrowing relates to a larger follicle size. [ABSTRACT FROM AUTHOR]