Effects of Gestational Housing on Reproductive Performance and Behavior of Sows with Different Backfat Thickness

Response to environmental enrichment of weanling pigs on growth, behaviour and welfare after weaning

The experiment was carried out to examine the growth, behaviour, and welfare response of weaning pigs to environmental enrichment from d 1 to d 28 after weaning. A total of 240 weaning pigs with average initial body weight (BW) 6.56 ± 0.17 kg were randomly allotted to one of the four treatments on the basis of initial BW. A completely randomized design was used to conduct this study. There were ten pigs per pen, with 6 replicates for each treatment. The experimental treatments were control, EE-1 (inclusion of play object until one week after weaning), EE-2 (inclusion of play object until two weeks after weaning), and EE-4 (inclusion of play object until four weeks after weaning). The pigs raised the EE-2 and EE-4 treatments had greater average daily gain (p = 0.002). The average daily feed intake (p = 0.016) was increased in the EE-2 treatment in phase 1. The pigs in the EE-4 treatment had greater average daily gain (p = 0.039) and average daily feed intake (p = 0.030) in phase 2 than pigs raised in the control treatment, and overall (average daily gain: p = 0.006, average daily feed intake: p = 0.014). The pigs under enriched environment treatments (EE-2 and EE-4) decreased BW uniformity in phase 1 (p = 0.006) and phase 2 (p < 0.001) than pigs in the control treatment. The incidence of diarrhea was lowered (p < 0.001) in early phase 1 (d 7 after weaning) under environmental enrichment treatments (EE-2 and EE-4). Behaviour traits exhibited reduced agonistic behaviour, such as biting (p = 0.018), tail biting (p = 0.001), and ear biting (p = 0.016) under environmental enrichment treatments (EE-2 and EE-4) in phase 1. The skin lesion score was reduced (p = 0.015) in the EE-4 treatment in phase 1. Hair cortisol was reduced in the EE-4 treatment (p = 0.032) at the end of phase 2, however, there were no significant differences in salivary cortisol concentration. These findings demonstrated beneficial effects on growth, group uniformity, behaviour, incidence of diarrhea, skin lesions, and concentration of hair cortisol through exposure to environmental enrichment after weaning.

Improvement of weanling pigs immune status and metabolic condition using ultraweak light

Weaning stress is the most common issue in swine farms, which increases mortality and morbidity. The use of artificial light is an option for modifying the immune system and metabolic pathways. This study aimed to evaluate the influence of ultraweak light (Photonia) on growth performance, immune system and metabolism of weanling pigs, and the carry-over effect on the growth performance in postweanling growing stages. A total of 30 weaned pigs with an average initial body weight of 7.06 ± 0.11 kg (age: 21 days) were allotted two treatments (Control and Photonia) with 15 replicates. The pelleted form diets were prepared for pigs in three phases including phase 1 (Days 0-14), phase 2 (Days 15-28) and phase 3 (Days 29-48). The gain-to-feed ratio (G:F) of pigs was significantly greater in the Photonia treatment. On Day 28, a higher concentration of immunoglobin A (IgA) (p < 0.01) and IgG (p < 0.01) was observed in the Photonia pigs. On Day 48, the Photonia treatment showed a greater serum IgA (p < 0.01) and IgG (p < 0.05). The concentration of interleukin (IL)-6 was decreased (p < 0.05) in the Photonia treatment. At Day 48, the concentrations of tumour necrotic factor-α, IL-1β and IL-6 in serum were decreased (p < 0.05) in pigs in the Photonia treatment. Metabolic pathways analysis showed that the Photonia treatment increased the d-glutamine, d-glutamate, alanine, aspartate, glutamate and phenylalanine compared with the control treatment. In conclusion, the use of Photonia for weanling pigs is recommended due to improved G:F, immune status and activation of amino acids metabolic pathways including d-glutamine, d-glutamate, alanine, aspartate, glutamate and phenylalanine.

Effects of Backfat Thickness on Oxidative Stress and Inflammation of Placenta in Large White Pigs

The purpose of this study was to evaluate the impact of the backfat thickness of sows on reproductive performance and on lipid metabolism, oxidative stress, and inflammation. At farrowing, 60 sows were assigned to three groups: the low-backfat-thickness group (LBF, n = 20): sows’ backfat thickness was between 9 and 12 mm; the medium-backfat-thickness group (MBF, n = 20): sows’ backfat thickness was between 13 and 20 mm; and the high-backfat-thickness group (HBF, n = 20): sows’ backfat thickness was between 21 and 25 mm. Maternal and fetal blood and placental samples were collected. Compared with the LBF and HBF groups, the MBF group delivered a significantly greater number of live piglets than the LBF or HBF groups. The different backfat thicknesses of sows had different effects on the lipid-related hormones and adipokines of maternal and fetal serum and placenta. Sows with poor or excessive backfat displayed higher levels of oxidative stress and higher levels of pro-inflammatory cytokines. According to these data, the thickness of a sow’s backfat affects the characteristics of farrowing piglets and their lipid metabolism, as well as placental inflammation, maternal inflammation, and oxidative stress. A moderate backfat thickness (between 13 and 20 mm) was associated with greater reproductive performance in sows.

Metabolic Responses of Dietary Fiber during Heat Stress: Effects on Reproductive Performance and Stress Level of Gestating Sows

Heat stress is an important issue, and the addition of fiber to the diet is an option in modifying intestinal health. This study evaluated the effect of acid detergent fiber (ADF) levels on reproductive performance, intestinal integrity, and metabolism of gestating sows, and its carry-over effect on the lactation period during heat stress. The diets included 4.3% (Low fiber; LF), 5.4% (Medium fiber; MF), and 6.5% (High fiber; HF) ADF. Sows fed the HF diet showed a lower respiratory rate, hair cortisol concentration, and farrowing duration compared with the LF treatment. The HF diet increased the pyruvate, citrate cycle, glyoxylate, dicarboxylate, and thiamine metabolism compared with the MF. The concentration of acetate and total short-chain fatty acids were increased in the sows fed the HF diet. The gene expression of glucose transporter 3 and glucose transporter 4 was increased in the HF treatment. The gene expression of heat shock protein 70 was decreased in the HF treatment. The HF diet during gestation increased feed intake, constipation index, piglet weight, and litter weight compared with the LF. Sows in the LF treatment showed the greatest digestibility of crude protein and the lowest digestibility of ADF. In conclusion, a 6.5% ADF level is recommended for gestating sows during heat stress.

Effects of Selenium as a Dietary Source on Performance, Inflammation, Cell Damage, and Reproduction of Livestock Induced by Heat Stress: A Review

Heat stress as a result of global warming has harmful consequences for livestock and is thus becoming an urgent issue for animal husbandry worldwide. Ruminants, growing pigs, and poultry are very susceptible to heat stress because of their fast growth, rapid metabolism, high production levels, and sensitivity to temperature. Heat stress compromises the efficiency of animal husbandry by affecting performance, gastrointestinal health, reproductive physiology, and causing cell damage. Selenium (Se) is an essential nutritional trace element for livestock production, which acts as a structural component in at least 25 selenoproteins (SELs); it is involved in thyroid hormone synthesis, and plays a key role in the antioxidant defense system. Dietary Se supplementation has been confirmed to support gastrointestinal health, production performance, and reproductive physiology under conditions of heat stress. The underlying mechanisms include the regulation of nutrient digestibility influenced by gastrointestinal microorganisms, antioxidant status, and immunocompetence. Moreover, heat stress damage to the gastrointestinal and mammary barrier is closely related to cell physiological functions, such as the fluidity and stability of cellular membranes, and the inhibition of receptors as well as transmembrane transport protein function. Se also plays an important role in inhibiting cell apoptosis and reducing cell inflammatory response induced by heat stress. This review highlights the progress of research regarding the dietary supplementation of Se in the mitigation of heat stress, addressing its mechanism and explaining the effect of Se on cell damage caused by heat stress, in order to provide a theoretical reference for the use of Se to mitigate heat stress in livestock.

A deep learning-based approach for feeding behavior recognition of weanling pigs

Feeding is the most important behavior that represents the health and welfare of weanling pigs. The early detection of feed refusal is crucial for the control of disease in the initial stages and the detection of empty feeders for adding feed in a timely manner. This paper proposes a real-time technique for the detection and recognition of small pigs using a deep-leaning-based method. The proposed model focuses on detecting pigs on a feeder in a feeding position. Conventional methods detect pigs and then classify them into different behavior gestures. In contrast, in the proposed method, these two tasks are combined into a single process to detect only feeding behavior to increase the speed of detection. Considering the significant differences between pig behaviors at different sizes, adaptive adjustments are introduced into a you-only-look-once (YOLO) model, including an angle optimization strategy between the head and body for detecting a head in a feeder. According to experimental results, this method can detect the feeding behavior of pigs and screen non-feeding positions with 95.66%, 94.22%, and 96.56% average precision (AP) at an intersection over union (IoU) threshold of 0.5 for YOLOv3, YOLOv4, and an additional layer and with the proposed activation function, respectively. Drinking behavior was detected with 86.86%, 89.16%, and 86.41% AP at a 0.5 IoU threshold for YOLOv3, YOLOv4, and the proposed activation function, respectively. In terms of detection and classification, the results of our study demonstrate that the proposed method yields higher precision and recall compared to conventional methods.

How Housing Conditions Determine the Welfare of Pigs

Humans who care for pigs prefer an environment that not only allows the pigs to express their natural behaviors but also limits the development of aggression and stereotypes. Most of the behavioral and health problems encountered by pigs in barren, conventional conditions are solved by alternative housing systems. However, it is not known whether these systems are advantageous in terms of the performance of pigs. In this work, we review the effects of housing systems on pigs' behaviors and performance, which are among the major indicators of the welfare of these animals. Research results point out that outdoor systems are more ideal for sows and fatteners than buildings. Nonetheless, outdoor housing is associated with two major effects in both groups: increased activity due to environmental exploration and higher space allowance, and increased incidence of injuries compared to indoor systems. Sows are more active when housed in groups, but they experience an increased frequency of injuries. According to the literature, group-housed sows give birth to healthy piglets with good daily weight gains. The difference in the fattening and slaughter performance of pigs raised indoors vs. outdoors remains unclear, and the results reported so far are inconsistent. Outdoor systems seem to be associated with a higher incidence of osteochondrosis and lesions of elbow and hock joints, whereas indoor systems cause a greater degree of body soiling in pigs. Based on the reviewed literature, it may be concluded that outdoor housing helps to solve behavioral issues in pigs but leads to other problems in pig production.

Effects of Dietary Monoglyceride and Diglyceride Supplementation on the Performance, Milk Composition, and Immune Status of Sows During Late Gestation and Lactation

Monoglyceride and diglyceride (MGDG) have antiviral and antibacterial properties and act as emulsifiers to increase dietary lipid digestibility. The primary aim of this trial was to investigate the effects of dietary MGDG supplementation on the reproductive performance and health status of sows during late gestation and lactation. One hundred sows (Landrace × Large White, mean parity of 4.59) were randomly allocated to groups receiving two different diets with 4% soybean lipids or 4% MGDG from day 85 of gestation to day 21 of lactation. Milk samples were collected on the day of farrowing (colostrum) and on day 14 of lactation, and blood samples were collected from the sows on days 0, 14, and 21 of lactation. Compared with control sows, sows fed MGDG showed no significant differences in reproductive performance (P > 0.05), but sow back fat thickness loss decreased during lactation (P < 0.05). There was a significant decrease in TNF-α concentrations in colostrum in the MGDG-supplemented sows compared with that in the soybean lipid-supplemented sows (P < 0.05). Dietary MGDG supplementation decreased sow plasma IL-8 concentrations on day 0 of lactation and IL-18 concentrations on days 14 and 21 of lactation (P < 0.05). Administration of MGDG increased the glucose and total cholesterol concentrations in sow plasma on day 14 and day 21, respectively (P < 0.05). The findings in this study suggest that MGDG supplementation could be effective in reducing back fat loss, decreasing inflammatory factor levels, and controlling total cholesterol (TCHO) concentrations during lactation.

Hot-Melt Extruded Selenium: a Highly Absorbable Nano-Selenium in Lactating Sows Exposed to High Ambient Temperature

To study the role of hot-melt extruded (HME) selenium (Se) and in the lactating sows' reproductive performance and litter growth, a total of 60 crossbred sows (Yorkshire × Landrace; average body weight, 245.3 kg) were allotted to one of four treatments according to a 2 × 2 factorial arrangement. The performance of lactating sows was investigated in the different average room temperatures (high temperature (HT), 28.1 °C vs. low temperature (LT), 24.6 °C), and different selenium sources (INO, 0.15 mg common sodium selenite/kg diet; HME, 0.15 mg nano-sodium selenite/kg diet) during the summer season. At days 10 and 21, the serum glutathione peroxidase (GPx) activity and Se concentration were greater in lactating sows fed HME compared with sows fed INO diet. The concentration of Se in the serum was greater in piglets from the HME treatment compared with piglets from the INO treatment. The HT treatment had a significantly higher body weight loss, backfat thickness loss, and weaning-to-estrus interval. The piglets' survivability, total weight gain, daily feed intake, and average daily gain during the lactation were greater in the LT sows compared with the HT sows. A higher blood cortisol concentration was observed in the HT sows compared with the LT. Selenium contents of milk at days 10 and 21 postpartum were increased by dietary supplementation of HME. In conclusion, the results of the present study demonstrated that there are no performance differences between sows fed different Se sources; however, HME supplementation increased serum and milk Se content, resulting in increased serum GPx concentration in sows and a greater serum Se in the litters.

Effect of farrowing pen size on pre-weaning performance of piglets

Litter sizes in commercial pig production have increased substantially over recent years; however, farrowing pen sizes have generally not changed over the same time period. The objective of this study was to evaluate the effect of farrowing pen size on piglet pre-weaning growth and mortality. Differences in pen size were created by varying the width of pens of the same length, increasing the creep area available to the piglets. The study used a total of 1,786 litters in a randomized complete block design to compare two farrowing pen size treatments (FPS): Standard (pen width 1.52 m) and Increased (pen width 1.68 m). Litter sizes were equalized across treatments (12.9 ± 1.95 piglets) at 24 h after birth using cross-fostering. Litter weights were collected at birth and weaning (21.3 ± 2.08 d); pre-weaning mortality was recorded. The experimental unit was the litter; models for statistical analysis included FPS and replicate. Farrowing pen size had no effect (P > 0.05) on litter size at birth (12.8 and 13.0 for the Standard and Increased FPS, respectively), after cross-fostering (12.9 for both treatments), or at weaning (11.2 and 11.3, respectively). There was no effect (P > 0.05) of FPS on total litter or average piglet weight at birth, after cross-fostering, and at weaning. These results suggest no benefit in piglet performance from increasing the width of farrowing pens. As litter sizes continue to increase in commercial production, further research is warranted to re-evaluate the impact of farrowing pen size on pre-weaning mortality.

Coping with large litters: management effects on welfare and nursing capacity of the sow

A number of management issues can be used as drivers for change in order to improve animal welfare and nursing capacity of the hyperprolific sow. Group housing of sows during gestation is a recommended practice from the perspective of animal welfare. Related health issues include reproductive health and the locomotor system. It appears that management of pregnant sows in groups is challenging for a producer and considerable skill is required. We explored the benefits and challenges of group housing, including feeding issues. Increasing litter size requires additional attention to the mammary gland and its ability to provide sufficient nursing for the growing litter. We discuss the fundamentals of mammary development and the specific challenges related to the hyperprolific sow. We also address challenges with the farrowing environment. It appears that the old-fashioned farrowing crate is not only outdated in terms of welfare from the public’s perspective, but also fails to provide the environment that the sow needs to support her physiology of farrowing, nursing, and maternal behaviour. Studies from our group and others indicate that providing the sow with a loose housing system adequate in space and nesting material, along with reasonable chance for isolation, can be considered as fundamental for successful farrowing of the hyperprolific sow. It has also been shown that management strategies, such as split suckling and cross fostering, are necessary to ensure proper colostrum intake for all piglets born alive in a large litter. We thus conclude that welfare and nursing capacity of the sow can be improved by management. However, current megatrends such as the climate change may change sow management and force the industry to rethink goals of breeding and, for instance, breeding for better resilience may need to be included as goals for the future.

Improving behavior characteristics and stress indices of gestating sows housed with group housing facility

This study was conducted to investigate the effects of group-housing facility (GHF), compared to an individual confinement stall (CON), on the reproductive performance, behavior, and stress hormones of gestating sows. A total of 50 primiparous sows (Landrace × Yorkshire) were randomly allocated into either CON (n = 25) or GHF (n = 25) during the gestation period. One week before parturition, the sows were transferred into conventional farrowing crates, and cross-fostering was conducted within 1 d of delivery. Blood was collected for analyses of stress indices at 75 d of gestation and postpartum. Reproductive performance was estimated during the period of birth to weaning. Behavior patterns were identified at 90 d of gestation. Litter size was not different between the CON and GHF treatments. Weaning to estrus interval, however, tended to be lower in the GHF than in the CON (p < 0.1). Activity, treating, belly nosing, and exploring behaviors were observed only in the GHF group, whereas rubbing was shown only with the CON. Serum cortisol concentration was lower in the GHF than in the CON at 75 d of gestation (p < 0.05). Sows housed in the GHF showed lower epinephrine and norepinephrine concentrations than those housed in the CON at postpartum (p < 0.05). The GHF sows demonstrated more natural behavior characteristics associated with stress relief than the CON sows with no adverse effects on reproductive performance. Therefore, these results suggest that GHF could be applied as an alternative housing facility to improve animal welfare on swine farms.

Comparison of the Productivity of Primiparous Sows Housed in Individual Stalls and Group Housing Systems

Simple Summary

Recently, South Korea amended the respective laws and will be enforcing that sows must be kept in group housing after 6 weeks from insemination by the year 2030. Accordingly, the comparison of productivity of sows in individual stalls and group housing systems was investigated in order to provide information on group housing systems for sows to pig farms. Primiparous sows were divided into four groups and housed in equal number in pen stalls, in short stalls with non-gated feeding stalls, in free access stalls, or with access to electronic sow feeders after 8 weeks from artificial insemination. Sows were transferred to farrowing crates at 110 days of gestation. No differences were found in sow productive performance, reproductive performance, and colostrum composition among housing types. Therefore, it was concluded that group housing systems could be used to replace individual stalls in commercial sow units.

Abstract

This study was conducted to provide commercial pig farms with information about group housing systems for sows in accordance with the amendment of the prohibition law for individual stalls for sows in South Korea. Therefore, this experiment was performed to compare the effects of individual stalls (IS) and group housing systems (GS) on the productivity of sows to investigate the feasibility of replacing individual stalls with group housing systems in commercial sow units. Forty primiparous sows (Landrace × Yorkshire; 210.67 ± 2.22 kg average initial body weight) were randomly assigned to four treatments with restricted feeding after 8 weeks from artificial insemination. The four treatments were (i) individual stalls (IS; housed in pen stalls), (ii) short stalls (SS; sows housed in pens with non-gated feeding stalls), (iii) free access stalls (FAS; a non-competitive housing system), and (iv) electronic sow feeders (ESF; used with radio frequency identification technology to allow individual sow management without individual confinement). All sows were transferred to farrowing crates at 110 days of gestation. There were no differences in sow productive performance, reproductive performance, and colostrum composition between IS and GS and among GS. The considered GS did not negatively affect any productivity parameters of primiparous sows compared with IS; the GS could replace IS in commercial sow units.

Effects of free feeding time system and energy level to improve the reproductive performance of lactating sows during summer

The reproductive performance of lactating sows was investigated by using different feeding methods including conventional feeding (CF, 3 times/d) or free feeding (FF), and different dietary energy level including low energy (LE: 3,300) or high energy (HE: 3,400 kcal/kg) during the hot season. A total of twenty-eight crossbred (Yorkshire × Landrace) sows were distributed into four treatments as a 2 × 2 factorial arrangement. Sows in the FF group showed lower body weight and backfat loss (p < 0.05) compared with the CF group. Backfat loss during lactation was lower (p < 0.05) in sows fed HE diet than in that fed LE diet. There were no significant differences in litter survival rate and weaning to estrus interval, but the litter weight at weaning was improved (p < 0.05) in FF and HE sows. Hence, it is concluded that using the free-feeding system or increased dietary energy density leads to improved sow performance during hot ambient temperature.

Effects of loose farrowing facilities on reproductive performance in primiparous sows

The present study investigated the effects of loose farrowing type during gestation and after farrowing on reproductive performance and of lactating sows. A total of 22 primiparous sows (Landrace; average initial body weights [BW], 228.54 ± 12.79 kg) were allotted to one of two treatments on the basis of body weight. Sows were divided into two experimental groups, conventional farrowing crates (CON), and loosed-farrowing pens (LFP). The experiment duration was around 38 days ranging from 10 days before parturition to 28 days after parturition. Gestating sows at the age of 105 d were placed in gestational stalls (group housing). All the sows were fed a common diet according to the National Research Council requirements for lactation. Cross-fostering was performed within 1 day of parturition. From 1 day after weaning, estrus detection was performed twice-daily (0900 and 1730 h) for 10 min by boar exposure. There were significant effects of LFP housing type on the farrowing duration, and farrowing interval. At the farrowing time, none of the litter parameters including total born, stillborn, mummy, born alive piglets and total litter weight and piglet weight were affected. There were no effects of housing type on the mortality of piglets at d 1, 3, 7, 21, and 28. In conclusion, the result of this study showed that there is no performance difference between the crated or LFP sows, which indicate that the LFP housing has the potential to be used as an alternative to the crated house without any detrimental effects in reproduction performance of lactating sows.

Excessive backfat of sows at 109 d of gestation induces lipotoxic placental environment and is associated with declining reproductive performance

This study investigated the influence of sow backfat thickness at 109 d of gestation on sow and piglet performance. Data from 846 farrowing multiparous Yorkshire sows with parity from 3 to 5 were collected from a pig breeding farm. Sows were divided into six groups based on backfat thickness (≤16, 17-18, 19-20, 21-22, 23-24, and ≥25 mm) at 109 d of gestation. The evaluation of reproductive performance included the litter size, litter weight at birth and at weaning of 21 d, weight of placenta at parturition, placental efficiency, and sow daily feed intake of lactation. Parameters related to plasma lipids and the placental-lipid concentration were measured. Data were analyzed to determine the relationships among backfat thickness, placental lipids, and piglet performance. No differences were observed in the number of piglets born, born alive, after cross-foster, and at weaning among groups (P > 0.05). The litter weight at birth and weaning, piglet birth weight, weaning weight, placental efficiency, and the number and percentage of piglets born with weight of <800 g showed a significantly quadratic effect of the backfat thickness (P < 0.05). During lactation, sow daily feed intake linearly decreased with increased backfat thickness at 109 d of gestation (P < 0.05). Although triglycerides and low-density lipoprotein cholesterol (LDL-C) showed no significant difference, cholesterol and high-density lipoprotein cholesterol (HDL-C) and free fatty acid (FFA) concentrations significantly increased (P < 0.05) in both maternal and umbilical cord blood with increased backfat thickness of sow. Placental-lipid concentrations also significantly increased (P < 0.05) with increased backfat thickness. Moreover, backfat thickness and placental-lipid concentration were positively correlated with the number of piglets weighing <800 g (P < 0.01) but negatively correlated with birth weight, litter birth weight, and piglet weaned weight (P < 0.01). In conclusion, backfat thickness of sow at end of gestation correlates with birth and weaning weight of piglets. Placental ectopic lipid accumulation-induced lipotoxicity is likely responsible for such correlation.

Comparative study on the relations between backfat thickness in late-pregnant gilts, mammary development and piglet growth

The potential relation between body condition of gilts in late-pregnancy and litter BW gain as well as mammary development was studied using 2 sets of data. Gilts either from a commercial herd (Part 1, n = 182) or from a series of trials looking at mammary development (Part 2, n = 172) were separated in 3 groups according to backfat thickness (BF) on d 110 of gestation. Group categorization was similar for Parts 1 and 2 of the study and was: low (LOW), 13.6 ± 1.6 mm (mean ± SD); medium (MED), 17.6 ± 1.0 mm (mean ± SD); and high BF (HIGH), 21.8 ± 1.8 mm (mean ± SD) for Part 1, and LOW, 14.2 ± 1.3 mm (mean ± SD); MED, 18.1 ± 1.0 mm (mean ± SD), and HIGH 23.4 ± 2.6 mm (mean ± SD) for Part 2. The effects of BF group on piglet BW gain (Part 1) or on various mammary gland characteristics (Part 2) were determined using ANOVA. Litters from HIGH sows tended to have a greater lactation BW gain than those from LOW sows (P < 0.10). Sows with HIGH BF had more mammary parenchymal tissue and more total protein and total DNA than MED and LOW sows (P < 0.05), which led to greater total protein and total DNA contents (P < 0.05). There were strong positive correlations (P < 0.0001) between parenchymal weight and total protein, total DNA, and total RNA. Results suggest that it is beneficial for primiparous sows to have greater BF (i.e., 20 to 26 mm) at the end of gestation to achieve optimal mammary development and greater litter BW gain in the subsequent lactation.