Y. Z. Li

Strand Length-Dependent Antimicrobial Activity and Membrane-Active Mechanism of Arginine- and Valine-Rich β-Hairpin-Like Antimicrobial Peptides

ABSTRACT Antimicrobial peptides with amphipathic β-hairpin-like structures have potent antimicrobial properties and low cytotoxicity. The effect of VR or RV motifs on β-hairpin-like antimicrobial peptides has not been investigated. In this study, a series of β-hairpin-like peptides, Ac-C(VR)nDPG (RV)nC-NH2 (n = 1, 2, 3, 4, or 5), were synthesized, and the effect of chain length on antimicrobial activity was evaluated. The antimicrobial activity of the peptides initially increased and then decreased with chain length. Longer peptides stimulated the toxicity to mammalian cells. VR3, a 16-mer peptide with seven amino acids in the strand, displayed the highest therapeutic index and represents the optimal chain length. VR3 reduced bacterial counts in the mouse peritoneum and increased the survival rate of mice at 7 days after Salmonella enterica serovar Typhimurium infection in vivo. The circular dichroism (CD) spectra demonstrated that the secondary structure of the peptides was a β-hairpin or β-sheet in the presence of an aqueous and membrane-mimicking environment. VR3 had the same degree of penetration into the outer and inner membranes as melittin. Experiments simulating the membrane environment showed that Trp-containing VRW3 (a VR3 analog) tends to interact preferentially with negatively charged vesicles in comparison to zwitterionic vesicles, which supports the biological activity data. Additionally, VR3 resulted in greater membrane damage than melittin as determined using a flow cytometry-based membrane integrity assay. Collectively, the data for synthetic lipid vesicles and whole bacteria demonstrated that the VR3 peptide killed bacteria via targeting the cell membrane. This assay could be an effective pathway to screen novel candidates for antibiotic development.

Effects of environmental temperature on heat production associated with food intake and on abdominal temperature in laying hens

An experiment was carried out to verify the relationship between the heat production associated with food intake and environmental temperature. Four laying hens were trained to eat two meals per day and were kept under artificial illumination with dark, dim and light periods. 2. Metabolic heat production was measured using two open-circuit respiratory chambers. Abdominal temperatures were measured, using thermocouples, at environmental temperatures of 12, 16, 20, 24, 28, 32 and 36 degrees C and at food intakes of 90, 60, 30 and 0 g/d. 3. The rate of heat production was dependent on both environmental temperature and food intake. Increasing environmental temperature resulted in a decrease in total metabolic rate at any food intake, indicating that heat production associated with food intake was not directly linked with thermoregulation at low environmental temperatures. 4. Abdominal temperature varied little with either food intake or environmental temperature below 28 degrees C. Above 28 degrees C, abdominal temperature increased with both environmental temperature and quantity of food, indicating that the heat production associated with food intake adds to the heat load at high environmental temperatures. 5. Both heat production and abdominal temperature declined with decreasing light intensity and increased before feeding time. These effects were considered to result from changes in physical activity.

Diurnal variation in heat production related to some physical activities in laying hens

1. Heat production, standing and eating activities, and hourly food intake of 4 laying hens were observed simultaneously and the effects of activity and food intake on heat production were studied. 2. Average heat production during the dark period (20.00 to 06.00 h) was 18.9 kJ/kgW0.75 h which was 33% lower than that during the light period. About 76% of the light-dark difference in the rate of heat production was probably associated with activity and posture. 3. Standing time, which included a range of behavioural activities, occupied 90% of the light period and the increased rate of heat production associated with standing was estimated to be about 18% of daily heat production. 4. Eating time occupied 40% of the light period; the heat production associated with eating activity represented about 5% of daily heat production or 3% of ME intake. 5. Because the regression of heat production on time spent eating agreed with the regression of heat production on hourly food intake, it is suggested that the energy expenditure associated with ad libitum feeding can be estimated for hens from the regression of heat production on hourly food intake.

Sorting by parity to reduce aggression toward first-parity sows in group-gestation housing systems

Young sows are subordinate and vulnerable in group-housing systems because they usually lose most fights and suffer more injuries than mature sows at mixing. This study was conducted to evaluate effects of sorting by parity on reducing aggression and associated stress with the aim to improve welfare and performance of first-parity sows in a group-housed system. Sows and gilts (n = 180) from 6 breeding groups were used. Within each group, 2 groups of 15 females were mixed in each of 2 treatment pens after weaning and remained there throughout the entire gestation period. The control pen consisted of 11 multiparous and 4 first-parity sows, and the treatment pen consisted of 11 gilts and 4 first-parity sows. Before mixing and at the end of the gestation period, sows and gilts were weighed individually, assessed for BCS, and measured for backfat thickness. Injury scores were assessed before and 48 h after mixing and wean-to-mating intervals, farrowing rate, and litter performance at the subsequent farrowing were recorded for all females. Aggressive interactions involving first-parity sows were video recorded for 72 h immediately after mixing in each pen. Data were analyzed using the Glimmix procedure of SAS with a Poisson regression model for count data and a Gaussian model for continuous data. All females in treatment pens sustained fewer scratches (P = 0.01) after mixing than females in control pens. First-parity sows in treatment pens fought more frequently (P = 0.01), tended to fight for longer periods (P = 0.08), and won more fights (P = 0.04) of parallel pressing but had fewer injures (P = 0.03) after mixing, gained more BW (P = 0.01) during gestation, and had greater farrowing rates (P = 0.03) compared with first-parity sows in control pens. The results suggest that sorting by parity shielded first-parity sows from severe injuries caused by mixing-induced aggression so that their welfare and performance can be improved in group housing systems.

Behavior and performance of pigs previously housed in large groups

A study was conducted to evaluate the effects of social familiarity and initial BW variation at mixing on performance and welfare of pigs born to group-housed lactating sows. A total of 180 pigs from 24 litters were used in a random design with 4 treatments in a 2 x 2 (social familiarity x initial BW uniformity) factorial arrangement. Pigs were born in group-farrowing rooms where they mingled in large groups of 66 to 80 pigs from 10 d of age. At 8 wk of age (BW=23+/-3.1 kg), pigs were allocated to 20 pens of 9 pigs (5 castrated males and 4 females) in a grow-finish room, with 5 pens assigned to each of 4 treatment combinations without consideration of relatedness. Familiar groups consisted of pigs from 1 farrowing room, and unfamiliar groups consisted of 3 pigs from each of 3 different farrowing rooms. Uniform BW groups were formed by using the middle 2 quartiles, and variable BW groups by using the heaviest and lightest quartiles of pigs. Aggression and activity behavior were directly observed by scan or continuous sampling during a period of 4 h on the first 3 d, d 7, and d 14 after grouping. Injury scores were assessed on all pigs immediately before and 48 h after grouping. Body weight gain and apparent feed intake were measured every 2 wk for 14 wk. Aggression in familiar groups was minimal throughout the observation periods. Compared with that in familiar groups, total duration of fighting was greater in unfamiliar groups on d 0 (upon grouping, 48.5 vs. 0.5+/-10.88 s/pig(-1).4 h(-1); P<0.001) and on d 1 (10.8 vs. 0.4+/-3.24 s/pig(-1).4 h(-1); P<0.05) after grouping. Unfamiliar pigs had greater injury scores (6.6 vs. 1.8+/-0.28; P<0.001) and spent less time eating on d 0 (5.1 vs. 8.8+/-0.92% of total observation time; P<0.01) after grouping compared with familiar pigs. The ADG and ADFI were decreased in unfamiliar groups during the initial 6 wk, but not for the entire 14-wk period in comparison with familiar groups. Body weight variation did not affect behavior and performance in familiar groups but increased aggression-induced injuries in unfamiliar groups. The results indicated that grouping unacquainted pigs derived from large groups induced overt aggression, associated injuries and initial reduction in performance, which causes welfare concerns on mixing pigs born to group-housed lactating sows.

Biochemical property and membrane-peptide interactions of de novo antimicrobial peptides designed by helix-forming units

Typical peptides composed of Phe, Ile, and Arg residues have not been reported, and the effect of the helix-forming unit (HFU) composed of the tripeptide core on biological activity remains unclear. In this study, multimers of the 3-residue HFU were designed to investigate the structure–function relationships. The in vitro biological activities of the peptides were determined. We used synthetic lipid vesicles and intact bacteria to assess the interactions of the peptides with cell membranes. The well-studied peptide melittin was chosen as a control peptide. The results showed that the antimicrobial and hemolytic activities of the peptides increased with the number of HFUs. HFU3 had optimal cell selectivity as determined by the therapeutic index. HFU3 and HFU4 exhibited strong resistance to salts, pH, and heat. CD spectra revealed that the peptides except HFU2 displayed α-helix-rich secondary structures in the presence of SDS or trifluoroethanol (TFE). The peptides interacted weakly with zwitterionic phospholipids (mimicking mammalian membranes) but strongly with negatively charged phospholipids (mimicking bacterial membranes), which corresponds well with the data for the biological activities. There was a correlation between the cell selectivity of the peptides and their high binding affinity with negatively charged phospholipids. Cell membrane permeability experiments suggest that the peptides targeted the cell membrane, and HFU3 showed higher permeabilization of the inner membrane but lower permeabilization of the outer membrane than melittin. These findings provide the new insights to design antimicrobial peptides with antimicrobial potency by trimers.

Savaging behaviour in gilts and sows

This study investigated the effects of parity, prior experience, and environmental conditions on the incidence of savaging on seven commercial farms. Results indicated that 3.40% of gilts and 1.22% of sows killed one or more piglets (P < 0.05). Fourteen percent of sows that savaged as gilts also savaged during their second farrowing, compared to 0.8% of sows that had not reviously savaged. The incidence of savaging was similar among gilts during the first (all gilt herd) and second (gilt/sow herd) farrowing cycles. Key words: Savaging, gilts, sows, pigs, maternal behaviour

Effects of a beta-adrenergic agonist (L-644,969) on performance and carcass traits of growing lambs in a cold environment

A 2 × 2 factorial experiment was conducted to study the effects of the beta-adrenergic agonist L-644,969 (BAA, supplied at 0.28 vs. 0 mg kg−0.75 d−1) on growth performance, carcass traits and nitrogen balance of lambs at two environmental temperatures (0°C vs. 20 °C). Sixteen Suffolk-Cross wether lambs (30.2 ± 2.06 kg BW) were randomly divided into four groups and exposed to each of four experimental treatments (20 °C with control diet; 20 °C with BAA-supplemented diet; 0 °C with control diet; and 0 °C with BAA-supplemented diet) for 5 wk. The collection period for nitrogen balance was 4 d during the 4th week of treatment. The low temperature decreased efficiency of feed utilization and increased backfat thickness by 20.8% (P < 0.01) and 35.1% (P < 0.05), respectively. L-644,969, on the other hand, increased daily gain, feed efficiency and hot carcass weight by 22.5% (P < 0.05), 17.2% (P < 0.05) and 9.6% (P < 0.05,) respectively. Dressing percentage (P < 0.01), biceps femoris weight (P < 0.01) and rib eye...

Effects of tryptophan supplementation on aggression among group-housed gestating sows

The objective of this study was to determine the effects of dietary Trp supplementation on mixing-induced aggression and the associated stress, and on reproductive performance in gestating sows. After weaning, sows were mixed in pens with electronic sow feeders on concrete-slatted floors. Each pen housed 21 ± 2.8 sows, with approximately 2.7 ± 0.43 m(2)/sow of floor space allowance. Multiparous sows (n = 168) from 8 breeding groups were used, with 4 groups assigned to a control diet and 4 groups assigned to a high-Trp diet. Control sows received corn- and soybean meal-based diets throughout gestation (0.15% Trp) and lactation (0.21% Trp). Three days before and after mixing, sows assigned to the high-Trp treatment received approximately 2.3 times the dietary Trp (0.35% in the gestation diet and 0.48% in the lactation diet) fed to control sows. Six focal sows (2 sows from each of parity 1, 2, and 3 or greater) in each pen were designated and videotaped for 72 h after mixing to determine the type and number of aggressive interactions among sows. Before and 48 h after mixing, saliva samples were collected from focal sows, and scratches were assessed on all sows. Data were analyzed using the FREQ and GLIMMIX procedures (SAS Inst. Inc., Cary, NC). Aggression among sows was intense during the initial 6 h and decreased between 6 and 72 h after mixing. The initial aggression caused scratches and increased cortisol concentrations (P < 0.05). Mature sows tended to fight for longer periods (112 vs. 52 s/h per sow, SE = 23.8; P < 0.10) but had fewer scratches caused by aggression (injury score = 4.3 vs. 6.5, SE = 1.13; P < 0.01) than parity-1 sows. Supplementation of dietary Trp reduced the total duration of head-to-head knocking (P < 0.05) but did not affect other aggressive behaviors. There was no difference between dietary treatments in injury scores or saliva cortisol concentrations. Sows in the high-Trp treatment had more total piglets born (12.5 vs. 10.5 pigs/litter, SE = 0.55; P < 0.05) and more stillborn piglets (1.5 vs. 0.8 pigs/litter, SE = 0.20; P < 0.05), but had no significant change (P = 0.12) in piglets born alive (10.8 vs. 9.7 pigs/litter, SE = 0.42) compared with control sows. The results indicate that the initial aggression after mixing caused more injuries in young sows than in mature sows. Supplementation of dietary Trp at 2.3 times the control amount for a short period did not effectively reduce aggression and the associated stress in sows at mixing.

Effects of stall width and sow size on behaviour of gestating sows

The adequacy of gestation stalls to accommodate the postural behaviour of sows is an important welfare concern. The behaviour of 184 sows from parity 0 to 9 was studied in stalls of four widths (55, 60, 65, and 70 cm). Postures, frequency of posture changes, contact with the stall and udder extension beyond the stall were observed for 24 h at 4 and 14 wk of gestation. Injuries were assessed based on number and severity at four 5-wk intervals. Sows spent less time standing and more time sitting in the narrower compared with wider stalls (P < 0.05). The proportion of lying time spent in lateral recumbancy was greater for larger than for smaller sows (P < 0.05) and larger sows made fewer postural changes (P < 0.05). The proportion of sows touching both sides of the stall, or with their udder extending into the adjacent stall, was affected by the interaction of stall width and sow size. Sows rarely touched both sides of the stall, nor did their udders extend into the adjacent stall, when the ratio of stall wi...