Low Stocking Density Research Articles

181 Effects of Moderate Exercise Regimen on Reproductive Development of Replacement Beef Heifers Reared in Drylots at a High Stocking Density

Abstract This experiment evaluated the physiological and reproductive responses of beef heifers reared at a high stocking density and provided with access to an exercise area. Ninety Angus × Brahman heifers were ranked by age (257 ± 2 days), body weight (BW; 216 ± 2 kg), and temperament score on day 0 and assigned to a) 1 of 6 drylot pens (10x14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m2/heifer (DENS), or b) 1 of 3 paddocks (2-ha paddocks; 10 heifers/paddock) resulting in a stocking density of 2,000 m2/heifer (CON). On day 15, 3 DENS pens were randomly selected and given access to an exercise area (DENS-EX) for 1 hour three times weekly. Negligible forage was available for CON heifers, whereas all heifers received the same limit fed diet which averaged 13 kg/heifer daily of a corn-based diet. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on days -3 and 225 for average daily gain calculation. On day 0, heifers were fitted with a pedometer behind their shoulder and an ear tag (CowManager, Select Sires, Plain City, OH) to record behavioral responses. Each week, pedometer results were recorded, and blood samples were collected for puberty evaluation via plasma progesterone. Heifers from CON had more (P < 0.05) steps per week compared with DENS and DENS-EX, and DENS-EX heifers had more (P < 0.05) steps per week compared with DENS. Heifers from CON spent more (P < 0.05) time ruminating and eating compared with DENS and DENS-EX. No treatment effects (P ≥ 0.12) were detected for heifer BW gain or temperament variables. Heifers from DENS experienced delayed puberty attainment given a greater (P < 0.05) proportion of CON heifers were pubertal by day 98 compared with DENS and DENS-EX, whereas a greater (P < 0.05) proportion of DENS-EX heifers were pubertal by day 154 compared with DENS heifers (treatment × day interaction, P < 0.01). Collectively, results from this experiment demonstrate that providing heifers reared at a high stocking density access to an exercise area does not result in similar reproductive responses as those reared on pasture at a low stocking density. This work is supported by the USDA National Institute of Food and Agriculture (#2021-67015-34083).

Determining overwintering performance and economic viability of monosex tilapia fingerling production in hapa cum cage aquaculture system for Bangladesh's haor fishers

Ensuring a consistent supply of uniformly sized fingerlings for tilapia cage aquaculture in Bangladesh's poses a significant challenge. This study assessed overwintering growth performance and economic viability of monosex tilapia fingerling production in haor waters. Nine hapas, each inside a designated treatment cage, were stocked with T1 (200), T2 (250) and T3 (300) tilapia fry, averaging 1.25±0.25 g, per m³ for 90 days. The most successful treatment continued for two subsequent crops over two years for economic viability assessment. Average final body weight gain was the highest at the lowest stocking density (T1, 58.86±7.23 g), but the most desirable biomass gain (222 kg cage⁻¹) occurred at medium stocking density (T2). Beyond biomass gain, T2 exhibited superior profitability, with 26% and 30% profitability in the second and third crops respectively, over total costs. In conclusion, overwintering tilapia fingerling production in the hapa-cum-cage system at a stocking density of 250 m⁻³ proved more profitable and sustainable than other treatments, offering a viable income-generating option for resource-poor haor fishers.

How the EU animal welfare legislation can tackle AMR – a One Health perspective

Abstract The development of antimicrobial resistance (AMR) is linked to the imprudent use of antimicrobials and is fuelled by industrial farming, accounting for 70% of antimicrobial use. Tackling AMR requires a One Health approach that addresses the root causes of high antimicrobials use in intensive farming and generates co-benefits for human, animal and environmental health. On intensive farms animals are mostly of high-yield breeds and are exposed to stressors, which leads to immunosuppression, increasing susceptibility to infections that need antimicrobial therapy. To combat AMR the EU Commission adopted legislation prohibiting the use of antimicrobials to compensate for poor husbandry and management. However, there is a gap in policy regarding animal welfare improvements necessary to reduce the need for antimicrobials. We assess how the EU animal welfare legislation, under revision, can contribute to filling this gap by providing the regulatory framework for improvements needed to reduce antimicrobial use. Methods include literature review and expert interviews in an approach that integrates knowledge across the human-animal-environmental sectors. Improvements in husbandry and management (lower stocking density, outdoor access, genetic diversity, etc.) positively impact animal health and welfare, consequently reducing susceptibility to infections and antimicrobial use. By prescribing these improvements the revised animal welfare legislation can have a synergistic effect with the Veterinary Products Regulation, in line with the Farm to Fork strategy, and provide the regulatory framework for higher animal welfare standards that reduce antimicrobial use. The positive correlation between higher animal welfare and the reduced need for antimicrobials demonstrates the urgency of improving welfare in farming as a key strategy to limit AMR. It builds the case for an ambitious revision of the EU animal welfare legislation to protect animal and human health in line with One Health. Key messages • The revised EU animal welfare legislation can become a relevant policy in tackling AMR by providing the regulatory framework for high animal welfare standards neded to reduce antimicrobials in farming. • Tackling AMR requires a One Health approach addressing the root causes of high antimicrobial use in intensive farming: the poor welfare of animals, which increases their susceptibility to infections.

Effects of Snail Bellamya purificata Farming at Different Stocking Densities on the Algal and Fungal Communities in Sediment

The snail Bellamya purificata is recognized as a potential bio-remediation species, and is commonly employed in polyculture to enhance resource utilization efficiency and realize culture environment regulation. In order to enrich the microbiome studies on elucidating the ecological effects of snail B. purificata farming, we assessed the effect of B. purificata farming activities, at varying stocking densities, on the algal and fungal communities in sediment. Four experimental groups were established in our study, each corresponding to a different stocking density: 0, 234.38, 468.75, and 937.5 g/m2, represented as CON, LD, MD, and HD, respectively. High-throughput sequencing based on ITS and 23S ribosomal RNA (rRNA) genes was employed to analyze the variations in algal and fungal communities under B. purificata farming activities at different stocking densities. B. purificata farming activities had no significant effect on the alpha diversities of fungal and algal communities, but significantly altered the compositions of fungal and algal communities in sediments, especially B. purificata farming activity at low stocking density. B. purificata farming activities at low stocking density could significantly increase the relative abundances of fungal genera Paraconiothyrium and Penicillium compared with the CON group. The promoting effect diminished with increasing density. B. purificata farming activities at low or medium stocking density also could enhance the relative abundances of algal genera Microchloropsis, Scenedesmus, and Auxenochlorella. Hence, B. purificata farming activity at low stocking density might be the optimum density to enhance resource utilization efficiency and minimize environmental pollution.

Effect of Stocking Density on the Post-larval Production of <i>Macrobrachium rosenbergii</i> in A Two-Phase Larval Rearing System

The effect of stocking density on the post-larval production of Macrobrachium rosenbergii has been studied. A two-phase larval rearing technique involving high-density rearing of early larvae for 10-12 days followed by low-density rearing of advanced larvae (stage VI) was followed. In the first phase of rearing, the stocking density did not show any effect on survival. However, in the second phase of rearing, percentage of survival decreased with increasing stocking density. Post-larval production per litre was found to be maximum at a stocking density of 55/1, and both higher and lower stocking densities resulted in decreased production per litre of the medium.

Replacing Fertilizer with Dried Distillers' Grains in Stocker Cattle Systems on Southern Great Plains Old World Bluestem, USA.

The objective was to examine the effects of dried distillers' grains supplementation and fertilization strategies on the cattle performance and resource use efficiency of stocker cattle grazing on Plains Old World bluestem. Over 4 consecutive years, heifers and steers (average n = 239) were randomly assigned to 1 of 4 treatments: (1) low input, low stocking density, and no fertilizer or distillers grains supplementation (LOW); (2) high stocking density and no fertilizer with distillers grains supplementation (DDGS); (3) high stocking density and 90 kg of nitrogen/ha with no distillers grains supplementation (NFERT); (4) high stocking density, 90 kg of nitrogen/ha, and 39 kg of phosphorus/ha with no distillers grains supplementation (NPFERT). Cattle grazed in the pastures from mid-May to mid-September each year, except for 2011, when the experiment ended in July due to lack of forage. Data were analyzed using a linear model with fixed effects of treatment, year, and treatment × year (R software). Nitrogen use efficiency (retained/inputs) was affected by a treatment × year interaction, where LOW had the greatest efficiency in all years and DDGS was greater than NFERT and NPFERT in all years except 2012, with NFERT and NPFERT being not different in all years. The estimated total carbon equivalent emissions were greater for DDGS, NFERT, and NPFERT than LOW, but the carbon footprint (kg CO2eq/kg weight gain) was lesser for LOW and DDGS, which were not different, than NFERT and NPFERT, which were also not different. Replacing nitrogen fertilizer with dried distiller's grains improved the cattle performance and the efficiency of resource use, and could be a viable economic alternative to traditional systems.

Effects of high stocking density on growth performance and expression of MyD88, and its temporal expression under the challenge of Vibrio parahaemolyticus in the noble scallop Chlamys nobilis

High stocking density has been regarded as an adverse factor in bivalve aquaculture. However, its subsequent molecular response to pathogenic bacteria has been little studied. In order to study the question, a novel MyD88 was first cloned using adult noble scallops Chlamys nobilis (CnMyD88), and its tissue distribution was investigated. Then, 1860 juvenile scallops were divided into two groups with two initial densities of high density (200 individuals/layer, HD) and normal density (110 individuals/layer, ND) and in-situ cultured for three months, in which their growth, survival, and the differential expression of CnMyD88 were examined, respectively. Finally, scallops were injected with the Vibrio parahaemolyticus to assess the temporal expression of CnMyD88. As the results show, CnMyD88 cDNA has a full length of 2241 bp and contains an 1107 bp ORF that encodes a 368-derived protein. It was widely expressed in examined tissues with a significantly higher level in hemolymph, intestine, mantle, and gonad than others. Besides, the HD group showed lower growth (0.39 ± 0.05 mm/day) and survival (37.00 ± 8.49%) than the ND group (0.55 ± 0.02 mm/day and 76.82 ± 5.78%). More importantly, the HD group exhibited significantly lower expression levels of CnMyD88 in their examined tissues than the ND group. After V. parahaemolyticus challenging, CnMyD88 had significantly lower expression levels in the scallops from the HD group than that of the scallops from the ND group at 6th, 24th, and 36th. The present results indicated that high stocking density not only made adverse impacts on growth and survival but also may induce immunosuppression in the noble scallop. Therefore, appropriate low stocking density may be worth considering to adopt in scallop aquaculture.

Compensatory growth and production economics of Silver pompano, Trachinotus blochii (Lacepede, 1801), fingerlings stunted by feed and space deprivation

The effect of stunting by feed and space deprivation on compensatory growth (CG) in Silver pompano,Trachinotus blochii, was investigated. A commercial pellet feed (45% protein and 10% fat) was fed two times a day, throughout the entire experiment. The 270-day experiment consisted of an initial 60-day stunting phase and a 60-day post-stunting phase carried out in 4 × 2 × 2 m3galvanized iron (GI) rectangular cages, and a 150-day grow-out phase carried out in 3-m diameter circular GI cages. During the stunting phase, the normal fish (in triplicates) were stocked at lower stocking density (17 fish/m3) and fed at 10% of body weight (BW), while stunted fish (one replication) were stocked at about three times higher stocking density (56 fish/m3) and fed at a three times lower feeding rate (3% of BW). The stunted and normal fish were reared in triplicates during the post-stunting phase, at uniform stocking density (15 fish/m3) with feeding at a higher rate (10% of BW) for stunted fish and normal feeding rate (8% of BW) was adopted for normal fish. During the grow-out stage, each replication from the post-stunting phase was shifted to 3-m circular cages with the same feeding rates. The lag in growth in stunted fish (5.56 g against 9.43 ± 0.13 g of normal) during the stunting phase was compensated during the post-stunting phase (36.88 ± 2.23 g against 38.13 ± 1.48 g of normal) by higher feeding rate. There were no significant (p> 0.05) differences in final harvest, biometry, morphometry, dressing yield, carcass nutritional composition, and serum biochemical markers at the end of grow-out stage. Because of the significant difference (p< 0.05) in the total feed provided (5.2 kg for stunted fish against 22.8 kg for normal fish) and the lesser unit cost for the production of stunted fingerling (USD 0.087 for stunted fish against USD 0.106 for normal), the farming of stunted fish brought about a higher net operational revenue and benefit:cost ratio.

Compensatory gain and oxidative response of tilapia rearing at high densities in a biofloc system and transferred to clear water system

Aquaculture has grown a lot in recent years, with tilapia being one of the species with the greatest growth potential. The use of intensive systems, with greater production, biosafety and environmentally correct have been the subject of recent research. The biofloc technology (BFT) has stood out in terms of fish production and performance. The aim of this study was to evaluate the use of a tilapia nursery in BFT for 30 days and/or direct stocking in a clear water system (CW) or 30 days in BFT and then transferred (TRN) to CW. The treatments were as follows: CW 100 (60 days in CW with 100 fish/m3), TRN 750; (30 days in BFT with 750 fish/m3 and 30 days in CW 100 fish/m3), TRN 1500 (30 days in BFT with 1500 fish/m3 and 30 days in CW 100 fish/m3), BFT 750 (60 days in BFT with 750 fish/m3) and BFT 1500 (60 days in BFT with 1500 fish/m3). Water quality, growth, body composition, biochemical and organosomatic parameters, nutrient deposition and thiobarbituric acid reactive substances (TBARS) were evaluated. High ammonia levels and lower pH were observed in the BFT system, this may be associated with a higher density. At 30 days there was a smaller growth of the fish reared at high densities in the BFT, but at 60 days there was a compensatory growth of the fish that were transferred from the BFT to the CW, while fish cultivated for 60 days in BFT with high density showed worse performance indices. There was improvement in the levels of deposition and protein and lipid efficiency in fish transferred from the BFT to CW. An increase in glycogen was also observed in fish cultured for 60 days on BFT and a decrease in proteins and amino acids in the liver of fish cultured for 60 days on BFT. There was a decrease in TBARS in fish cultured in BFT, showing that this system can act as a protector against lipid peroxidation. It is recommended to cultivate tilapia of approximately 2 g in BFT with high density for a period of 30 days and after that, transfer to a production system with lower stocking densities.

Long-term crowding stress induces chronic inflammatory response and declines the immunity of grass carp (Ctenopharyngodon idella)

This study is aimed to explore the mechanism of overcrowding stress on the immunity of grass carp Ctenopharyngodon idella. Fish were reared for 120 days at 10 kg/m3 (low stocking density, LSD), 15 kg/m3 (medium stocking density, MSD) and 20 kg/m3 (high stocking density, HSD). The results showed that HSD significantly increased the serum cortisol level, implying that fish reared at higher density were subjected to physiological stress. HSD led to a remarkable decline in serum lysozyme activity. The conspicuous decrease of serum complement 3 (C3) and immunoglobulin M (IgM) contents also appeared in the HSD group. The serum antioxidant enzymes activity included total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), glutathione peroxidase (GPx), and catalase (CAT) of fish reared at HSD group were clearly decreased. The serum glutathione (GSH) concentration of fish reared at HSD group was notably reduced. The malondialdehyde (MDA) level was obviously increased in HSD group. Long-term crowding stress gave rise to the constitution of melano-macrophage centers in spleen. The transcriptional levels of TLR4/NF-κB signaling pathway were notably up-regulated except for iκbα and mTOR pathway related genes were prominently down-regulated in fish reared at HSD group. The notably up-regulated pro-inflammatory cytokines (tnf-α, ifnγ2, il1-β, and il-8) except for il-6 and prominently down-regulated anti-inflammatory cytokines (il-10, il4/13a, il4/13b, tgf-β1 and tgf-β2) appeared in HSD group. All of the above results revealed that long-term overcrowding stress induced unbalanced inflammatory response via TLR4/NF-κB and mTOR signaling pathway and decreased the immunity in grass carp.

Ammonia and methane emissions from small herd cattle buildings in a cold climate

Ammonia (NH3) and methane (CH4) emission measurements that reflect local production conditions are required to track progress in national emission policies and verify emission factors. The findings can also be used to better understand key factors influencing emissions. This is especially important in Norway, which has long cold winters, and small cattle herds in mechanically ventilated buildings. However, until now, NH3 and CH4 emissions from Norwegian cattle buildings have not been reported in literature. Moreover, in other cold climates, NH3 and CH4 emissions are often taken from large dairy herds in naturally ventilated buildings, with less focus on suckler cows. The objectives were to assess indoor climate, report NH3 and CH4 emissions and examine the impact of climatic factors on NH3 and CH4 emissions in three small herd dairy and suckler cow buildings over three seasons. Three of the buildings had mechanical ventilation, while one was naturally ventilated. The suckler building had higher relative humidity (RH > 90 %) and NH3 concentrations (> 25 ppm) due to lower minimum air change rate (ACH = 1.2 h−1). The suckler building also had the highest NH3 emissions (2.04 g Livestock Unit (LU)−1 h−1) followed by the mechanically ventilated dairy building (1.92 g LU−1 h−1) with the highest ACH. These two buildings had the lowest stocking densities and floor areas. In contrast, the suckler building had the lowest CH4 emissions (6.8–10.7 g LU−1 h−1). Methane emissions from the dairy building with the supply-exhaust air mixing system (16.4–19.3 g LU−1 h−1) was higher than the other dairy buildings (11.7–13.8 g LU−1 h−1). Temperature influenced NH3 emissions however, the direction of association between temperature and NH3 emissions differed among buildings. Relationship between RH and NH3 emissions was positive, but the correlation coefficient (R2 = 0.67) was strongest in the building with the highest RH.

A needle in a haystack: strontium isotopes (87Sr/86Sr) in otoliths identify origin of largemouth bass from a large Southwest reservoir

Largemouth bass Micropterus salmoides, a popular warm water sport fish, is routinely stocked in reservoirs throughout the USA to augment wild populations. Evaluating if these supplementations are successful requires distinguishing hatchery-sourced fish from their wild counterparts. From 2011 to 2019, over 467 000 largemouth bass fingerlings were stocked from multiple hatchery sources into a large southwestern reservoir (Elephant Butte Reservoir, New Mexico, USA) to supplement the sport fish population. To identify hatchery-sourced largemouth bass, we measured strontium isotope ratios (87Sr/86Sr) and determined ages using otoliths and dorsal spines. Otolith analysis of 169 fish classified 92.9% ( n = 159) to the reservoir with few fish of hatchery origin (2 from Arkansas, 1.2%, and 1 from Montana, 0.6%). While stocking over 467 000 fingerlings across 8 years appears to reflect negligible stocking success, it is likely that low and variable stocking densities (average 3.0, range 0.29–7.77 fish·ha−1) contributed to the low stocking success in Elephant Butte Reservoir. Dorsal fin spines did not yield accurate age reconstructions and their 87Sr/86Sr values were affected by matrix interferences preventing source assignments.

Development and evaluation of an animal health and welfare monitoring system for veterinary supervision of pullet farms.

Regular welfare monitoring throughout rearing of pullets may help to identify problems early and take counteractions timely, which helps in guaranteeing good welfare. The aims of our observational study were (i) to establish and test a welfare monitoring system that can be used during (short) routine veterinary and technical staff visits for pullet flocks, (ii) to use the monitoring system to investigate variability between flocks and (iii) to analyse factors that potentially affect pullets' body weight, uniformity in body weight and mortality. The developed monitoring system tries to minimise the time required while not losing important information. Age-specific recording sheets comprise animal-based indicators of welfare and relevant environmental factors (housing, management, care) to allow for identifying causes of problems and targeted action. Finally, the system was implemented in a cross-sectional study and data collected in 100 flocks (67 organic, 33 conventional) on 28 rearing farms in Austria. Linear mixed models were used to identify factors influencing body weight, uniformity and mortality, both including all flocks (A) and only organic flocks (O) and a linear regression model with all flocks to investigate associations within animal-based indicators. High variability was found between flocks in animal-based indicators. Body weight was higher when the pre-rearing period was shorter (p≤0.001, A&O), with higher intensities of light (p=0.012, O), with only one compared to more stockpersons (p≤0.007, A&O), with a higher number of flock visits per day (p≤0.018, A&O), and a lower avoidance distance (p=0.034, A). Body weight uniformity increased, with age and decreased with the duration of the light period (p=0.046, A), and, amongst others, was higher on organic farms (farming type; p=0.041). The latter may reflect a more uniform level of welfare due to a lower stocking density and lowered effects of social competition. Within organic flocks mortality was lower if pullets had access to a covered veranda (p=0.025) resulting in an overall lower stocking density inside the barn, while in the model including all farms mortality was higher in cases where a disease had been diagnosed. We conclude that our monitoring system can easily be implemented in regular veterinary and technical staff visits, but could also be used by the farmers'. Several easy-to-record animal-based indicators of animal welfare could be analysed more frequently to increase early detection of problems. Implementation of such a routine-based monitoring system with easy-to-assess animal-based parameters and input measures can contribute to better animal health and welfare in pullets.

Rotational Grazing Strategies Minimally Impact Soil Microbial Communities and Carbon Dynamics—A Texas Case Study

The goal of our study was to evaluate the long-term (>12 years) influence of stocking density and herd rotation frequency on plant and soil microbial community and carbon dynamics in three working ranches in Texas. One ranch utilized a high stocking density and high-frequency (HIGH) rotation where cattle were moved multiple times each day; the second ranch used a medium stocking density and rotation frequency (MED) where herds were moved every 2–3 weeks; and the third ranch used a low stocking density with continuous grazing (LOW). Neither plant nor microbial diversity measures differed between the ranches, but plant functional and microbial community compositions differentiated management strategies. The MED ranch was characterized by a plant community dominated by little bluestem (Schizachyrium scoparium) and had the greatest soil organic matter content (2.8%) and soil respiration rates compared to the LOW (SOM = 2.2%) and HIGH (SOM = 2.1%) ranches. The HIGH ranch had a relatively high abundance and diversity of forbs and introduced grasses, and the LOW ranch had an even mixture of tall, introduced, and cool-season grasses. All three ranches had relatively high levels of Gram-positive bacteria (>70%) with MED having a higher relative abundance of bacteria important for carbon cycling. Furthermore, network analyses suggest that soil microbial communities at all ranches were highly synergistic and exhibited well-defined ecological niches. Differences in soil properties between ranches tended to be minor and suggest that grazing strategies can differ without any substantial shifts in soil and microbial function.

Reducing Stocking Densities and Using Cooling Systems for More Adapted Pigs to High Temperatures When Reared in Intensive Conditions.

This study is aimed at evaluating the effect of reducing stocking density and using cooling systems to mitigate the negative effects of high temperatures in growing pigs (females and castrated males) reared in intensive conditions (from 25 to 100 kg) during summer (June to October 2020). The experimental design was a 2 × 2 factorial where pigs were provided with an evaporative cooling system and/or raised at regular or at lower stocking densities (i.e., 0.68 to 0.80 m2/animal). Treatments were distributed in four different rooms containing sex-balanced pens with either castrated males or females. Temperature and humidity were recorded throughout the experiment, and the temperature-humidity index was calculated. Heat stress (HS) on pigs was measured through changes in animals' performance, animal-based indicators (dirtiness and activity budget) and physiological indicators (neutrophil/lymphocyte ratio and hair cortisol). The use of cooling, lowering stocking density and the combination of both strategies had positive effects on pigs' final body weight (+5 kg, +3 kg, +9 kg, respectively; p < 0.001). The prevalence of dirtiness was similar at the stocking densities tested, and no clear effect of the cooling system was found. Both mitigation strategies lowered the physiological indicators of stress, although only hair cortisone can be considered an indicator of HS. In conclusion, both mitigation strategies are effective in improving pig welfare and performance, especially when both are combined. The severity of the stocking density effect may depend on the severity of the temperature.

Impact of selection for growth and stocking density on Nile tilapia production in the biofloc system

Environmentally friendly aquaculture systems such as the biofloc technology (BFT) are gaining prominence, as well as the use of genetically superior fish and better adapted strains. However, sustainable systems must be economically efficient as well. According to literature, Nile tilapia takes a longer time to reach commercial weight in BFT if compared to traditional systems, reducing profitability. A better adapted strain, with faster growth, feed efficiency and tolerance to the intensive conditions of the BFT, should be an alternative to improve the profitability of the system. This study evaluated the economic and growth performance of Nile tilapia populations from two distinct generations, the base generation (G0) and generation 5 (G5), from a genetic improvement program based on genetic selection for body weight in BFT and recirculating aquaculture system, under two different stocking densities (12.5 and 37.5 ind. ‧ m−3) in BFT. A total of 320 male fingerlings (160 from G0 and 160 from G5) were randomly distributed in a factorial arrangement (2 × 2, four treatments) with four replicates (800 L tanks) for each treatment (16 sample units in total). The means were compared using two-way ANOVA and SNK's test (p < .05) and the confidence interval (95%) of the differences between them. The water management measures were enough to keep the water indicators within the acceptable ranges for tilapias. Survival rate was high (> 90%) for all treatments. The daily weight gain (DWG) was greater for G5 compared to G0 and resulted in a reduction of >57 days in slaughter time (750 g of harvested weight) for G5 compared to G0 and a 0.22 reduction in feed conversion ratio. The G5 promoted an average reduction of US$ 246.38 ‧ 100 m−3 for total operating cost and added US$ 275.97 ‧ 100 m−3 in operating profit compared to G0. Considering the economic analysis in relation to one ton of tilapia produced, G5 reduced the total operating cost and increased the operating profit only in the lowest stocking density. The increase in stocking density reduced the DWG for both generational groups, resulting in an increase of average time to slaughter of 43.61 days, however, 37.5 tilapia ‧ m−3 promoted a larger operating profit per 100 m−3 (+ US$ 832.60) and per ton of tilapia produced (+ US$ 338.90 for G0 and + US$ 148.39 for G5). This study demonstrates the importance of using genetically improved tilapia together with an adequate stocking density management to achieve better productivity and to make economically more viable an environmentally friendly system.

The gut microbiome and resistome of conventionally vs. pasture-raised pigs.

Conventional swine production typically houses pigs indoors and in large groups, whereas pasture-raised pigs are reared outdoors at lower stocking densities. Antimicrobial use also differs, with conventionally raised pigs often being exposed to antimicrobials directly or indirectly to control and prevent infectious disease. However, antimicrobial use can be associated with the development and persistence of antimicrobial resistance. In this study, we used shotgun metagenomic sequencing to compare the gut microbiomes and resistomes of pigs raised indoors on a conventional farm with those raised outdoors on pasture. The microbial compositions as well as the resistomes of both groups of pigs were significantly different from each other. Bacterial species such as Intestinibaculum porci, Pseudoscardovia radai and Sharpea azabuensis were relatively more abundant in the gut microbiomes of pasture-raised pigs and Hallella faecis and Limosilactobacillus reuteri in the conventionally raised swine. The abundance of antimicrobial resistance genes (ARGs) was significantly higher in the conventionally raised pigs for nearly all antimicrobial classes, including aminoglycosides, beta-lactams, macrolides-lincosamides-streptogramin B, and tetracyclines. Functionally, the gut microbiomes of the two group of pigs also differed significantly based on their carbohydrate-active enzyme (CAZyme) profiles, with certain CAZyme families associated with host mucin degradation enriched in the conventional pig microbiomes. We also recovered 1043 dereplicated strain-level metagenome-assembled genomes (≥90 % completeness and <5 % contamination) to provide taxonomic context for specific ARGs and metabolic functions. Overall, the study provides insights into the differences between the gut microbiomes and resistomes of pigs raised under two very different production systems.

Effects of single tree selection cutting on vascular plant species diversity components in temperate forests of Hyrcanian region

Temperate forests in northern Iran are one of the most important natural ecosystems with the highest economic value and a key role in the conservation of forest biodiversity in Iran. We studied vascular plant species diversity components (alpha, beta and gamma) of herb and tree layers on 120 plots at six sites in forests managed by single tree selection and forests that have been left unmanaged for more than 30 years in the Hyrcanian forest zone in northern Iran. Generalized linear mixed models (GLMM) were used to analyse the effect of management on stand properties, tree and herb layer local diversity and soil characteristics. Despite the differences in herb layer local α-diversity, forest management did affect neither community composition of the herb layer nor regional γ-diversity. Also, species richness as well as α- and γ-diversity of the tree layer was significantly higher in managed forests, while β-diversity showed no directional response across herb and tree layers. According to constrained ordination analysis, main drivers for explaining variance in plant species composition were soil organic matter, total nitrogen, potassium, phosphorous, pH and forest structural variables (basal area, number of trees per hectare and canopy cover) in herb and tree layers. We found that in Hyrcanian forests single tree selection management promotes environmental conditions that effectively contribute to increased diversity of the herb and tree layers at the local and regional scale compared to unmanaged forests. The higher diversity of herb and tree layers is likely being driven by higher within-stand heterogeneity, improved light availability in managed forests due to lower stocking density and larger canopy gaps, or also results from topsoil disturbances through wood extraction. This study indicated that single tree selection system has the potential to be used in order to improve biodiversity conservation, and these results can be useful for development of management guidelines and decision-making processes.Because it may not be specific enough to dismiss or prioritize forest management regimes, based only on their impact on plant diversity, further assessments of forest management effects on other crucial factors (such as fauna diversity, structural diversity and forest ecosystems services) are needed.

L-Tryptophan Mitigates Cannibalism and Improves Growth of Asian seabass, Lates calcarifer Reared in a RAS System

Severe cannibalism can result in a significant loss of productivity during the nursery phase of Asian seabass, Lates calcarifer. The present study aimed to determine the effect of dietary tryptophan on growth, feed utilization, cannibalism, survival, and muscle proximate composition of Asian seabass juveniles (initial size, 2.77 ± 0.04 cm in length and 0.29 ± 0.01 g in weight) in a recirculating aquaculture system (RAS) at different stocking densities. The tryptophan levels were set at 0.41% (control diet, standard dosage for normal growth and survival of Asian seabass), 1.00% (Diet 1), and 1.50% (Diet 2), while the stocking densities were set at 0.5 ind./L and 1.5 ind./L. The results indicated that dietary supplementation with L-tryptophan (TRP) and fish stocking density had a significant effect on fish growth parameters, feed utilization, cannibalism, survival, and muscle lipid content (p &lt; 0.05) over the 45-day trial. The maximum length, weight, WG, and SGR were 11.64 ± 0.35 cm, 22.93 ± 2.67 g, 22.64 ± 2.67 g, and 9.63 ± 0.27%, respectively, in the fish fed Diet 2, and 11.35 ± 0.22 cm, 24.38 ± 1.28 g, 24.09 ± 1.28 g, and 9.82 ± 0.11% at a 1.5 ind./L stocking density. The lower FCR (0.81 ± 0.04) and higher PER (2.98 ± 0.16) ensured better utilization of Diet 1 than the other diets. Moreover, significant interaction effects between diet and stocking density were observed in total yield, cannibalism, and survival of the Asian seabass. Significantly higher survival rates of 76.11 ± 3.90% in the Diet 1 group and 76.28 ± 2.88% in 0.5 ind./L stocking density were obtained, which is promising. The study concludes that dietary supplementation with 1.00% TRP was effective in reducing cannibalism and increasing the survival of the Asian seabass nursery reared in RAS at a lower stocking density (i.e., 0.5 ind./L), whereas 1.50% supplemental TRP at a higher stocking density (i.e., 1.5 ind./L) significantly increased the cannibalism and growth, which in turn reduced the survival rate.

Measuring Chronic Stress in Broiler Chickens: Effects of Environmental Complexity and Stocking Density on Immunoglobulin-A Levels

Commercial housing conditions may contribute to chronic negative stress in broiler chickens, reducing their animal welfare. The objective of this study was to determine how secretory (fecal) and plasma immunoglobulin-A (IgA) levels in fast-growing broilers respond to positive and negative housing conditions. In three replicated experiments, male Ross 708 broilers (n = 1650/experiment) were housed in a 2 × 2 factorial study of high or low environmental complexity and high or low stocking density. In experiments 1 and 3 but not in experiment 2, high complexity tended to positively impact day 48 plasma IgA concentrations. When three experiments were combined, high complexity positively impacted day 48 plasma IgA concentrations. Stocking density and the complexity × density interaction did not impact day 48 plasma IgA concentrations. Environmental complexity and the complexity × density interaction did not impact day 48 secretory IgA concentrations. A high stocking density negatively impacted day 48 secretory IgA concentrations overall but not in individual experiments. These results suggest that environmental complexity decreased chronic stress, while a high stocking density increased chronic stress. Thus, plasma IgA levels increased under high-complexity housing conditions (at day 48), and secretory IgA levels (at day 48) decreased under high-density conditions, suggesting that chronic stress differed among treatments. Therefore, these measures may be useful for quantifying chronic stress but only if the statistical power is high. Future research should replicate these findings under similar and different housing conditions to confirm the suitability of IgA as a measure of chronic stress in broiler chickens.