Chlortetracycline Supplementation Research Articles

Supplementation of Paraformic Acid as a Substitute for Antibiotics in the Diet Improves Growth Performance and Liver Health in Broiler Chickens.

Simple SummaryParaformic acid (PFA) is a hyperpolymer formed by polymerization of formic acid monomers, and PFA has a lower pungent smell and corrosiveness to the gastrointestinal tract compared with formic acid. The liver is a crucial metabolic organ, playing a momentous role in nutrients biosynthesis and metabolism, defense against bacterial invasion, and endotoxin clearance. However, in the condition of intensive poultry husbandry, the broiler’s liver is susceptible to inflammatory damage. Our results showed that PFA supplemented to the diet improved growth performance, inhibited inflammatory response, and benefited liver protection, which provided a direction for the use of PFA in broiler production.The current study aimed to explore the effects of supplementing paraformic acid (PFA) into broilers’ diet on growth performance, inflammatory responses, and liver protection. A total of 567 healthy one-day-old broilers were used in a 42-d study, and they were randomized into three groups. Broilers were fed a basal diet (CON group) or the basal diet supplemented with either 50 mg/kg aureomycin (AB group) or 1000 mg/kg PFA (PFA group). The results showed that the PFA and AB groups had a higher feed conversion rate than the CON group from day 21 to 42 (p < 0.05). Dietary PFA or aureomycin supplementation decreased serum levels of interleukin (IL)-1β, IL-6, IL-10, alanine transaminase, diamine oxidase, and D-lactate, and significantly increased serum concentrations of immunoglobulin (Ig) A, IgM, and complement C4 (p < 0.05). Moreover, dietary PFA or aureomycin supplementation decreased hepatic levels of caspase-1, NOD-like receptor family pyrin domain containing 3 (NLRP3), tumor necrosis factor-alpha, IL-6, and IL-18, as well as NF-κB mRNA expression (p < 0.05). Above all, PFA supplementation into the broilers’ diet improved growth performance, inhibited inflammatory responses, and benefited liver protection. The protective effects of PFA on the liver might be related to inhibition of caspase-1-induced pyroptosis via inactivating the NF-κB/NLRP3 inflammasome axis in broiler chickens.

Effects of dietary Bopu powder supplementation on intestinal development and microbiota in broiler chickens.

This study aimed to investigate the effect of dietary supplementation with Bopu powder on intestinal development and bacterial community composition in broiler chickens. A total of 486 1-day-old arbor acres broilers were fed a basal diet (CON group), a basal diet supplemented with 50 mg/kg aureomycin (AB group), or a basal diet supplemented with 40 mg/kg Bopu powder (BP group). The results showed that the BP group had significantly lower serum tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and diamine oxidase concentrations and had significantly higher serum IL-10 concentrations than CON group (p < 0.05). Groups AB and BP had a significantly higher weight per unit length of the small intestine and villus height than the CON group (p < 0.05), and BP group had a significantly higher ratio of villus height to crypt depth than groups CON and AB (p < 0.05). Compared to the CON group, dietary Bopu powder or aureomycin supplementation significantly increased transforming growth factor-α concentration and mRNA expressions of zonula occludens-1 (ZO-1) and occludin, and decreased intestinal mucosal concentrations of TNF-α, IL-6, IL-10, caspase-3, and caspase-8 and mRNA expressions of nuclear factor-kappa-B and Bax/Bcl-2 ratio in the intestinal mucosa (p < 0.05). Meanwhile, BP group had significantly higher ZO-1, secretory immunoglobulin A, interferon-γ concentrations, and mRNA expressions of glucose transporter type-2 and sirtuin-1, and significantly lower IL-1β concentration than groups CON and AB in intestinal mucosa (p < 0.05). Dietary Bopu powder supplementation significantly increased the concentration of trefoil factor family member and mRNA expressions of superoxide dismutase-1 and bcl-2 associated X, and significantly reduced casepase-9 concentration and myeloid differentiation primary response-88 expression in the intestinal mucosa of broiler chickens relative to CON group (p < 0.05). Moreover, results of high-throughput sequencing showed that broilers in the BP group had microbial community structure distinct from that in CON group, and the addition of Bopu powder increased the abundances of Faecalibacterium and Colidextribacter (p < 0.05). Therefore, our study suggests a synergic response of intestinal development and microbiota to the Bopu powder, and provides a theoretical basis as a potential substitute for antibiotics.

Effects of Dietary Macleaya cordata Extract Containing Isoquinoline Alkaloids Supplementation as an Alternative to Antibiotics in the Diets on Growth Performance and Liver Health of Broiler Chickens.

This study aimed to investigate the effects of dietary supplementation with Macleaya cordata extract (MCE) containing protopine and allotypotopine on the growth performance and liver health in broiler chickens. A total of 486 1-day-old male AA broiler chickens were randomly assigned to the following three groups: (1) control (CON) group, broiler chickens fed a basal diet; (2) AGP group (positive control), broiler chickens fed a basal diet supplemented with 50 mg/kg aureomycin; (3) MCE group, broiler chickens fed a basal diet supplemented with 0.6 mg/kg MCE including 0.4 mg/kg protopine and 0.2 mg/kg allotypotopine. The results showed that the MCE group had significantly higher final body weight and average daily gain from d 0 to 42 than the other groups (p < 0.05), and groups MCE and AGP both had significantly lower feed-to-gain ratio from d 0 to 42 than the CON group (p < 0.05). Serum total protein, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol, glucose, immunoglobulin A, immunoglobulin M, and complements (C3, C4) concentrations in the MCE group were significantly higher than in the CON group (p < 0.05). Dietary MCE or aureomycin supplementation significantly reduced the hepatic contents of 8-hydroxy-2'-deoxyguanosine, malondialdehyde, interleukin (IL)-1β, IL-6, NLRs family pyrin domain containing 3 (NLRP3), and caspase-1 in the liver (p < 0.05). Moreover, MCE or aureomycin supplementation significantly inhibited mRNA expressions of Toll-like receptor 4, myeloid differentiation factor 88, nuclear factor-κB, and NLRP3, as well as the expression ratio of Bax to Bcl-2 mRNA (p < 0.05). Therefore, our study suggested that dietary supplementation with 0.6 mg/kg MCE containing protopine and allocryptopine improved growth performance and benefited liver health in broiler chickens possibly through inhibiting caspase-1-induced pyroptosis by inactivating TLR4/MyD88/NF-κB/NLRP3 signaling pathway, and provided support for the application of MCE containing protopine and allocryptopine as an alternative to antibiotics in the feed industry.

Effects of chlortetracycline on growth performance and intestinal functions in weaned piglets.

Weaning stress can cause serious damage to piglet's health. Chlortetracycline (CTC) is widely used to ameliorate weaning stress and prevent infectious diseases in weaned piglets. However, antibiotics as growth promoters have to be limited because of increased antimicrobial resistance. In this study, we evaluated the effects of CTC on growth performance and intestinal functions in order to provide evidence for seeking antibiotic substitutes in weaned piglets. A total of 20 weaned piglets were fed a basal diet or a diet supplemented with 75mg/kg CTC. CTC decreased the crypt depth and increased the ratio of villus height to crypt depth, whilst failing to affect growth performance and serum biochemical parameters and cytokines. 16S rRNA sequencing suggested that CTC supplementation had no effect on the diversity and composition of colonic microbiota. We speculated that gut microbiota is no longer sensitive to a low concentration of CTC due to the long-term use and low bioavailability of CTC in weaned piglets.

Effects of replacing dietary Aureomycin with a combination of plant essential oils on production performance and gastrointestinal health of broilers

The objective of this study was to investigate the effects of replacing antibiotics with a combination of plant essential oils on the growth performances and gastrointestinal health of broilers. A total of 720 1-day-old male AA broilers were randomly divided into 3 treatments: the control treatment (CON), the Aureomycin supplementation treatment (AGP), and the combined plant oils supplementation treatment (POC), with a 42-D period feeding procedure. Growth performances, carcass performances, intestinal sections, and cecal microbiota were investigated. Results indicated that POC supplementation decreased the feed conversion ratio compared with CON and AGP treatments, though not significantly. No significant differences were found for feed intake, BW gain, and culling rate among the 3 treatments (P > 0.05). In addition, no significant differences were seen on carcass performance. For the aspects of intestinal section, POC supplementation did not make significant effects on intestinal wall thickness, villus heights, crypt depths, and the ratio of villus heights/crypt depths compared with CON and AGP treatments. Cecal microbiota results demonstrated that bacterial diversity and some representative probiotic bacteria were significantly increased in numbers (P < 0.05) after POC supplementation. In conclusion, the combination of essential oils promoted intestinal health through improving gut bacterial diversity and probiotic bacteria, as well as improving feed conversion ratio of broilers. These results indicated that the combination of essential oils may benefit the gastrointestinal health and be applied as an antibiotic alternative.

Macleaya cordata extracts suppressed the increase of a part of antibiotic resistance genes in fecal microorganism of weaned pigs

This study was designed to evaluate the effects of Macleaya cordata extracts (Chinese herbal medicine extracts) and antibiotics combination with chlortetracycline (CTC) on the antibiotic resistance genes in fecal microorganism. Compared with the group without antibiotics, the relative abundances of all six tetracycline resistance genes were increased after 75 mg kg−1 CTC supplementation. Interestingly, M. cordata extracts in feed suppressed the increase of a part of tetracycline resistance genes in fecal microorganism of weaned pigs.

Effects of chlortetracycline and copper supplementation on the prevalence, distribution, and quantity of antimicrobial resistance genes in the fecal metagenome of weaned pigs

Use of in-feed antibiotics such as chlortetracycline (CTC) in food animals is fiercely debated as a cause of antimicrobial resistance in human pathogens; as a result, alternatives to antibiotics such as heavy metals have been proposed. We used a total community DNA approach to experimentally investigate the effects of CTC and copper supplementation on the presence and quantity of antimicrobial resistance elements in the gut microbial ecology of pigs. Total community DNA was extracted from 569 fecal samples collected weekly over a 6-week period from groups of 5 pigs housed in 32 pens that were randomized to receive either control, CTC, copper, or copper plus CTC regimens. Qualitative and quantitative PCR were used to detect the presence of 14 tetracycline resistance (tet) genes and to quantify gene copies of tetA, tetB, blaCMY-2 (a 3rd generation cephalosporin resistance gene), and pcoD (a copper resistance gene), respectively. The detection of tetA and tetB decreased over the subsequent sampling periods, whereas the prevalence of tetC and tetP increased. CTC and copper plus CTC supplementation increased both the prevalence and gene copy numbers of tetA, while decreasing both the prevalence and gene copies of tetB. In summary, tet gene presence was initially very diverse in the gut bacterial community of weaned pigs; thereafter, copper and CTC supplementation differentially impacted the prevalence and quantity of the various tetracycline, ceftiofur and copper resistance genes resulting in a less diverse gene population.

Effects of chlortetracycline and copper supplementation on antimicrobial resistance of fecal Escherichia coli from weaned pigs

Feed-grade chlortetracycline (CTC) and copper are both widely utilized in U.S. pig production. Cluster randomized experiment was conducted to evaluate the effects of CTC and copper supplementation in weaned pigs on antimicrobial resistance (AMR) among fecal Escherichia coli. Four treatment groups: control, copper, CTC, or copper plus CTC were randomly allocated to 32 pens with five pigs per pen. Fecal samples were collected weekly from three pigs per pen for six weeks. Two E. coli isolates per fecal sample were tested for phenotypic and genotypic resistance against antibiotics and copper. Data were analyzed with multilevel mixed effects logistic regression, multivariate probit analysis and discrete time survival analysis. CTC-supplementation was significantly (99% [95% CI=98–100%]) associated with increased tetracycline resistance compared to the control group (95% [95% CI=94–97%]). Copper supplementation was associated with decreased resistance to most of the antibiotics tested, including cephalosporins, over the treatment period. Overall, 91% of the E. coli isolates were multidrug resistant (MDR) (resistant to ≥3 antimicrobial classes). tetA and blaCMY-2 genes were positively associated (P<0.05) with MDR categorization, while tetB and pcoD were negatively associated with MDR. tetA and blaCMY-2 were positively associated with each other and in turn, these were negatively associated with both tetB and pcoD genes; which were also positively associated with one another. Copper minimum inhibitory concentration was not affected by copper supplementation or by pcoD gene carriage. CTC supplementation was significantly associated with increased susceptibilities of E. coli to copper (HR=7 [95% CI=2.5–19.5]) during treatment period. In conclusion, E. coli isolates from the nursery pigs exhibited high levels of antibiotic resistance, with diverse multi-resistant phenotypic profiles. The roles of copper supplementation in pig production, and pco-mediated copper resistance among E. coli in particular, need to be further explored since a strong negative association of pco with both tetA and blaCMY-2 points to opportunities for selecting a more innocuous resistance profile.

Competitive effect of commensal faecal bacteria from growing swine fed chlortetracycline-supplemented feed on β-haemolytic Escherichia coli strains with multiple antimicrobial resistance plasmids

To determine the differences in competitive fitness among Escherichia coli strains with different plasmid profiles when grown in suspension with commensal faecal bacteria from growing swine fed chlortetracycline-supplemented or unsupplemented diets. Five multiple drug-resistant (MDR) E. coli strains that possessed 0, 2, 6 or 8 plasmids were inoculated into anoxic faecal cultures from swine fed an unsupplemented (control) or chlortetracycline (50 g ton(-1))-supplemented (experimental) diet. On days 21 of chlortetracycline supplementation, faecal growth competition studies were performed. MDR E. coli were enumerated at 0, 6 and 24 h. The plasmid-free strain was below culturable limits in both the control and experimental cultures by 24 h. For each plasmid-bearing strain, there was no statistically significant difference in population CFU ml(-1) (P < 0.05) between the control and experimental cultures. There was no significant effect on the faecal microflora, owing to the inclusion of chlortetracycline, in the swine diets, that affected the growth of E. coli in the competition studies employed. Furthermore, these results suggest that the cost of maintaining plasmids in these E. coli strains had little influence on survivability. Mutations that led to antimicrobial resistance may have a greater impact on survivability than multiple plasmid carriage.

Effects of dietary polysavone (Alfalfa extract) and chlortetracycline supplementation on antioxidation and meat quality in broiler chickens

1. A total of 360 1-d-old male commercial Arbor Acre broiler chickens were randomly assigned to 5 groups (6 replicates of 12 birds each) to evaluate the dietary effects of polysavone (0·5, 1·0 and 1·5 g/kg), a natural extract from alfalfa, and 0·15 g/kg chlortetracycline (CTC) on growth performance, antioxidation and meat quality of broiler chickens. 2. Over the 6-week study, feed intake increased significantly with CTC supplementation and final body weight (BW) was significantly higher for 1·0 g/kg polysavone and 0·15 g/kg CTC treatments. Feed:gain ratio was not significantly affected by the dietary treatments. 3. At 3 weeks of age, serum total superoxide dismutase (T-SOD) activity for all polysavone treatments was significantly higher than controls, liver T-SOD activity in 1·5 g/kg polysavone group was significantly higher than the control and CTC groups, and serum glutathione peroxidase (GSHPx) activity for 1·5 g/kg polysavone and liver GSHPx activity in all polysavone groups were significantly higher than CTC. 4. At 6 weeks of age, serum and liver T-SOD activity in 1·5 g/kg polysavone group and liver GSHPx activity for all polysavone treatments were higher significantly than the control and CTC groups, and serum malondialdehyde (MDA) content for all polysavone treatments was significantly lower than CTC. 5. Breast muscle T-SOD activity and pH value at 6 weeks of age were significantly higher and MDA content was significantly lower in 1·0 and 1·5 g/kg polysavone groups than in the control and CTC groups. Breast muscle shear force was significantly lower in l·5 g/kg polysavone group compared with the control, and drip loss for all polysavone treatments was significantly lower than CTC. 6. It was indicated that polysavone modulates antioxidation and modifies meat quality, but with no adverse effect on performance of broiler chickens, and that CTC can be beneficial to performance but has no beneficial effect on antioxidant function or meat quality.

Chlortetracycline supplementation of yearling dairy heifers1,2

Chlortetracycline is an antibiotic that is used to increase weight gain, efficiency of gain, carcass grade, and conception rates. The objective of this experiment was to evaluate the effects of supplementation of 350 mg/d of chlortetracycline on ADG, G:F, BCS, thyroxine, and systemic glucose concentrations in yearling dairy heifers. Forty 12-mo-old Holstein heifers (initial BW = 363 +/- 21 kg) were housed in a free-stall barn with ad libitum access to feed and water for 104 d. A transition period was begun 14 d before the age of 12 mo to acclimate the heifers to the diet. The chlortetracycline-fed group (n = 20) consumed 328 +/- 8.2 mg of chlortetracycline/heifer daily. Measurements for BW, withers and hip heights, BCS, and health score were recorded weekly. Dry matter intake was measured daily. Blood was sampled every 4 d to determine plasma thyroxine and glucose concentrations and every 2 d to determine progesterone concentrations. Heifers were artificially inseminated on the first observed standing heat after 13 mo of age. There were no effects of chlortetracycline on ADG, G:F, withers and hip heights, BCS, blood glucose concentrations, peak progesterone concentrations, health, or conception rate. There was an interaction between treatment and time for chlortetracycline on serum thyroxine concentration. In the beginning of the experiment, serum thyroxine concentration was lower in heifers supplemented with chlortetracycline. There was no difference between treatments in thyroxine concentration at the end of the experiment. Chlortetracycline supplementation was not beneficial for yearling dairy heifers.

EFFECT OF THE FEED ADDITIVES CHLORTETRACYCLINE, MONENSIN AND LASALOCID ON FEEDLOT PERFORMANCE OF FINISHING CATTLE, LIVER LESIONS AND TISSUE LEVELS OF CHLORTETRACYCLINE

Charolais-sired, three way cross steers and heifers (n = 209) were fed ground high-forage diets for 56 d and then were finished on rolled grain based diets. Both diets were supplemented with chlortetracycline (CTC), monensin (MON) or lasalocid (LAS). Cattle fed the high-forage diets supplemented with MON or CTC gained faster (P &lt; 0.05) than those fed an unsupplemented (CON) diet. Dry matter intake was also increased (P &lt; 0.05) by CTC over animals fed the CON diet. Feed efficiency was not affected by CTC but was improved over CON by supplementation with MON or LAS. During the high-concentrate feeding period, inclusion of feed additives did not significantly improve average daily gain or dry matter intake when compared with CON. Of the carcass characteristics, only carcass weight was greater (P &lt; 0.05) and only with CTC supplementation. Monensin and LAS inclusion significantly decreased the acetic to propionic acid ratio in rumen contents. There was no evidence that the incidence of liver lesions differed among the treatments. Analyses of liver, muscle and kidney samples from 61 animals fed CTC and 14 animals fed the CON diet produced no repeatably detectable traces of CTC. Averaged across sex and weight group, returns to labor per animal were $25.83, $61.46, $48.52 and $41.10 for the CON, CTC, MON and LAS treatments, respectively. Key words: Chlortetracycline, monensin, lasalocid, beef steers, heifers, tissue residue

Effect of chlortetracycline supplementation during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival and fetal development in gilts

A total of 166 crossbred gilts weighing approximately 87 ± 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 ± 1 d of age until 15 d after breeding. These gilts were slaughtered at 31 ± 1 or 71 d ± 1 d of gestation for evaluation of reproductive performance. Age (190 ± 3 d vs 195 ± 3 d) and body weights (106 ± 2 kg vs 106 ± 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 ± 0.7 vs 12.9 ± 0.9, P = 0.31) and 71 d (13.9 ± 0.6 vs 12.4 ± 0.5, P = 0.10) of gestation. There was an increase (P = 0.04) in the number of live embryos for CTC-fed gilts at 31 d (12.1 ± 0.7 vs 9.7 ± 0.7) but not at 71 d (10.0 ± 1.1 vs 9.6 ± 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding CTC during prebreeding and early gestation did not influence the proportion or age of gilts at puberty. However, CTC feeding may have influenced a trend to-ward an increased ovulation rate and increased number of live embryos in gilts.

Mineral, Rumensin®, and chlortetracycline supplementation for steers on native bluestem pasture (1985)

Mineral, Rumensin®, and chlortetracycline supplementation for steers on native bluestem pasture (1985)

THE NUTRITION OF THE VEAL CALF; THE EFFECT OF ANAEMIA AND OF IRON AND CHLORTETRACYCLINE SUPPLEMENTATION ON THE PERFORMANCE OF CALVES GIVEN LARGE QUANTITIES OF WHOLE MILK.

THE NUTRITION OF THE VEAL CALF; THE EFFECT OF ANAEMIA AND OF IRON AND CHLORTETRACYCLINE SUPPLEMENTATION ON THE PERFORMANCE OF CALVES GIVEN LARGE QUANTITIES OF WHOLE MILK.

Chlortetracycline and bone demineralization in the rachitic rat.

SummaryWeanling male rats were maintained on the U.S.P. rachitogenic diet, with and without chlortetracycline supplementation, for a period of 35 days. Representative animals were sacrificed at intervals and the femurs removed, extracted and ashed under comparable conditions. The resulting data show that incorporation of 1 g chlortetracycline per kg in the rachitogenic diet slowed the rate of mineral depletion from the bones (femurs) as measured by the conventional bone-ash procedure.

Dietary Factors Affecting Volatile Fatty Acid Production in the Rumen

Sodium bicarbonate and calcium carbonate additions to high concentrate-low roughage type diets were without effect in altering acetate-propionate ratios and total volatile fatty acid levels in lambs. Supplementary sodium bicarbonate tended to elevate ruminal Ph. Concurrent sodium bicarbonate and lactic acid supplementation produced ruminal propionate levels no higher than produced by lactic acid alone. Sodium bicarbonate and calcium carbonate additions had no effect on growth and carcass characteristics of fattening wether lambs. Chlortetracycline supplementation of a high urea-high roughage lamb fattening ration tended to overcome the depressing effects of urea on carcass grade. Where no urea was included in these rations, chlortetracycline additions tended to widen acetate-propionate ratios and to elevate butyric acid levels. There appears to be an interaction between chlortetracycline and urea on acetate-propionate ratios and ruminal acetate levels. Narrowed acetate-propionate ratios, higher butyric acid levels, lower total volatile fatty acid levels and lower pH's were produced in the 80% concentrate as compared to the 50% concentrate diets. While overall weight gains were similar between the two types of rations, higher carcass grades, higher dressing percent and higher percent separable fat resulted in the higher concentrate rations. In the second intact lamb trial, correlation was shown be-between ruminal butyric acid levels and carcass grade. Rumen fluid buffering capacity measurements support the hypothesis that substances can enter the rumen from the blood stream or peritoneal cavity in the same manner that they are absorbed through the rumen wall.

The Effect of Cold and Debeaking upon the Adrenal Ascorbic Acid Concentration of Chickens Fed Aureomycin Supplement

INJECTIONS of adrenocorticotropic hormone (ACTH) into various animal species causes depletion of their adrenal ascorbic acid (Torrance, 1940; Sayers, Sayers, Liang and Long, 1946; Sayers and Chang, 1949). Severe cold was also reported to produce such an effect together with hypertrophy of the adrenal gland, in rats and guinea pigs (Therien and Dugal, 1949; Bacchus, 1951). In chickens, however, ACTH failed to elicitate adrenal ascorbic acid depletion (Bates, Riddle and Miller, 1940; Jailer and Boas, 1950; Zarrow and Zarrow, 1950; Howard and Constable, 1958; Elton, Zarrow and Zarrow, 1959), and birds were regarded as differing from mammals in this respect. Nevertheless, Perek, Eckstein and Eshkol (1959) succeeded in obtaining adrenal ascorbic acid depletion in one year-old hens, following ACTH injections; they were unsuccessful with 3 month-old pullets. After surgical removal of the bursa of Fabricius (Bursa), Perek and Eilat (1960) achieved adrenal ascorbic acid depletion in ACTH-injected chicks. They showed …

The influence of aureomycin on chick-rearing results using East African feedingstuffs with special reference to importance of experimental design for accurate statistical analysis

Groups of Rhode Island Red chicks were fed a mash made up from East African feedingstuffs or that diet supplemented with a high level rate of aureomycin—97 g. aureomycin hydrochloride per ton of feedingstuff. The chicks were kept on wire for 8 weeks. The initial improved growth rate of the chicks fed the aureomycin supplemented feedingstuff was not maintained, nor was there any statistical indication that the addition of aureomycin improved the feed conversion rate.Although the mortality rate appeared to be very much lower in the chicks fed the aureomycin supplement, the evidence was too limited to allow this to be attributed solely to the effects of the aureomycin.The experiment illustrates the need for careful design in order that the effect of the factors to be tested may be separated from the effects of other factors contained in the experiment and not confounded with them. Moreover, advanced statistical analysis should be used as an invaluable aid to, but not a substitute for, visual or graphical examination of results, for such examination often yields valuable indications of possible lines of analysis and may avoid the drawing of unjustified conclusions.

Urea Utilization by Young Dairy Calves as Affected by Chlortetracycline Supplementation

Summary Forty-eight two-day-old male and female calves representing the Holstein and Jersey breeds were raised to 86 days of age on a limited milk-hay-starter system to study the effect of chlortetracycline on urea utilization at three levels of protein equivalent intake. Four experimental starters ranging from 6.5 to 15.3% protein equivalent were fed with and without chlortetracycline supplementation. Highest average daily gains were made by calves on the 12.1% protein equivalent starter with chlortetracycline. The growth of calves increased as the protein equivalent level of the starter increased up to the 12.1% protein equivalent starter. Chlortetracycline did not spare dietary nitrogen in this study, but did significantly increase average daily gains, skeletal growth, and feed efficiency. Chlortetracycline had no significant effect on apparent digestibility of any ration nutrient, nitrogen retention, or blood levels of plasma protein and urea nitrogen. Coefficients of dry matter and crude protein digestibility, as well as nitrogen retention values, were significantly lower for calves on the 6.5% protein starter than for any of the other groups. The trend was for increased protein digestibility as the level of protein equivalent in the starter increased.