Emerging cytopathic and antigenic simian immunodeficiency virus variants influence AIDS progression.

Genetic variants of human and simian immunodeficiency virus (HIV and SIV) that evolve during the course of infection and progression to AIDS are phenotypically and antigenically distinct from their progenitor viruses present at early stages of infection. However, it has been unclear how these late variants, which are typically T-cell tropic, cytopathic and resistant to neutralizing antibodies, influence the development of clinical AIDS. To address this, we infected macaques with cloned SIVs representing prototype variants from early-, intermediate- and late-stage infection having biological characteristics typical of viruses found at similar stages of HIV infection in humans. These studies demonstrate that sequential, phenotypic and antigenic variants represent viruses that have become increasingly fit for replication in the host, and our data support the hypothesis that emerging variants have increased pathogenicity and drive disease progression in SIV and HIV infection.

Coccidia-induced mucogenesis promotes the onset of necrotic enteritis by supporting Clostridium perfringens growth.

This study tested the hypothesis that a host mucogenic response to an intestinal coccidial infection promotes the onset of necrotic enteritis (NE). A chick NE model was used in which birds were inoculated with Eimeria acervulina and E. maxima and subsequently with Clostridium perfringens (EAM/CP). A second group of EAM/CP-infected birds was treated with the ionophore narasin (NAR/EAM/CP). These groups were compared to birds that were either non-infected (NIF), or infected only with E. acervulina and E. maxima (EAM), or C. perfringens (CP). The impact of intestinal coccidial infection and anti-coccidial treatment on host immune responses and microbial community structure were evaluated with histochemical-, cultivation- and molecular-based techniques. Barrier function was compromised in EAM/CP-infected birds as indicated by elevated CFUs for anaerobic bacteria and C. perfringens in the spleen when compared to NIF controls at day 20, with a subsequent increase in intestinal NE lesions and mortality at day 22. These results correlate positively with a host inflammatory response as evidenced by increased ileal interleukin (IL)-4, IL-10 and IFN-gamma RNA expression. Concurrent increases in chicken intestinal mucin RNA expression, and goblet cell number and theca size indicate that EAM/CP induced an intestinal mucogenic response. Correspondingly, the growth of mucolytic bacteria and C. perfringens as well as alpha toxin production was greatest in EAM/CP-infected birds. The ionophore narasin, which directly eliminates coccidia, reduced goblet cell theca size, IL-10 and IFN-gamma expression, the growth of mucolytic bacteria including C. perfringens, coccidial and NE lesions and mortality in birds that were co-infected with coccidia and C. perfringens. Collectively the data support the hypothesis that coccidial infection induces a host mucogenic response providing a growth advantage to C. perfringens, the causative agent of NE.

Skeletal muscle alpha-actin synthesis is increased pretranslationally in pigs fed the phenethanolamine ractopamine.

Ractopamine [1-(4-hydroxyphenyl-2-(1-methyl-3-(4-hydroxyphenyl)propylamino)ethanol] enhances protein accretion in skeletal muscle (sm) of pigs. Experiments were conducted to elucidate fractional protein synthesis (FSR) and mRNA abundance for alpha-actin in sm of pigs fed a 16% protein diet containing 20 parts/million ractopamine for 21 days. Pigs were infused for 6 h with [14C]lysine (80 microCi/h.pig); after infusion pigs were killed, and longissimus dorsi muscle samples were obtained for RNA isolation and measurement of [14C]lysine incorporation. FSR was determined in vivo by incorporation of [14C]lysine from the muscle free amino acid pool into purified sm alpha-actin. FSR of sm alpha-actin was 55% greater in ractopamine-treated pigs than in controls. Relative mRNA abundance of alpha-actin was determined by dot blot hybridization of 0.1-0.4 microgram RNA to human sm alpha-actin [32P]cDNA probe. Longissimus dorsi alpha-actin mRNA abundance was 2-fold greater in pigs fed ractopamine. Sm RNA was translated in vitro using a cell-free assay to determine pretranslational effects on other muscle proteins. Effects of ractopamine on muscle protein synthesis are not specific to sm alpha-actin, because other muscle proteins also were increased using the in vitro translation assay. These results indicate that the increase in sm accretion in pigs fed ractopamine is due in part to an increase in myofibrillar protein synthesis and that some of the increase can be accounted for by an increase in mRNA abundance for sm alpha-actin.

Trade-off among antiherbivore defences in a south american blackberry (Rubus bogotensis).

The idea of trade-offs among antiherbivore defences in plants is examined using data from a South American blackberry (Rubus bogotensis). Two distinct morphs of R. bogotensis, one with glandular trichomes and one without, were compared with respect to leaf toughness, number of prickles and prickle length. The two morphs were sympatric and grew under similar environmental conditions. The morph lacking trichomes had significantly tougher leaves and also tended to have more and longer prickles. Bioassay showed that Ithomiid larvae fed to a lesser extent on tough leaves than on more tender ones. Correlations between antiherbivore defences within each phenotype revealed three significant or almost significant negative relationships. The comparisons support the hypothesis that trade-offs exist among antiherbivore defences.

Improved reproductive performance from dairy cows treated with dinoprost tromethamine soon after calving.

The first-service conception rate for 74 commercial dairy cows that were given a single injection of dinoprost tromethamine (prostaglandin F(2)alpha THAM) between 14 and 28 d after calving was 56%. For 74 untreated control herdmates the rate was 47%. The average interval from calving to first oestrus was 57 d for treated cows and 70 d for the control group. The difference is significant at the P = 0.017 level. The advantage in the conception rate of treated over control group cows occurred mostly in cows with a blood progesterone concentration of less than 0.5 ng/ml at the time of treatment; this numbered about two-thirds of the cows in the trial. The results support the findings of a previous study.

Changes in pars esophageal tissue appearance of the porcine stomach in response to transportation, feed deprivation, and diet composition.

Experiment 1 used 48 pigs to evaluate the effect of diet particle size, fat content, and a 24-h fast (FST) on pars esophageal (PE) tissue damage. Following a FST, a 750-microm, 550-microm, or 550-microm diet with 7.9% added fat was fed for 28 d. Additional pigs were fed the 550-microm fat-added diet with a FST every 7 d. The initial FST induced erosion (EROS) of the PE (P < .05). A 550-microm diet maintained the FST-induced EROS (P < .05). The 750-microm diet allowed the PE to heal. Sixteen pigs were used in Exp. 2 to evaluate transportation and FST-induced changes in PE. A FST following transportation induced keratinization (KERT) and EROS of the PE (P < .05). In Exp. 3, restraint and a FST followed by a 750-microm diet on PE was investigated using 48 pigs. A FST induced PE KERT and EROS, which was reduced to pre-FST levels ( P < .05) within 3 to 14 d by a 750-microm diet. In Exp. 4, 70 pigs were fed 750-microm or 550-microm diets following transportation and subsequent FST. Within 7 d, healing (P < .05) of FST-induced PE damage was observed with a 750-microm diet. A 550-microm diet maintained (P < .05) the transportation/FST-induced PE damage. Thirty pigs were used in Exp. 5 to investigate the effect of restraint for 24 h and FST on PE. A FST and the combination of restraint and FST induced similar levels of PE damage that were greater than pre-restraint/FST levels (P < .05).

Effect of ractopamine on insulin sensitivity and response of isolated rat adipocytes.

In vitro effects of the phenethanolamine ractopamine on basal and insulin-stimulated lipid metabolism were determined in adipocytes isolated from epididymal fat pads of Sprague-Dawley rats. Ractopamine appeared to be equipotent to the catecholamine isoproterenol in stimulating basal lipolysis and inhibiting basal lipogenesis, producing maximum effects at 10(-6) M. Addition of a half-maximally stimulating dose of ractopamine (5 x 10(-8) M) to the incubation media decreased insulin sensitivity but not insulin responsiveness of the cells, stimulating lipolysis and inhibiting lipogenesis only in the presence of low media insulin concentrations. This effect was totally reversed by 10 microM/propranolol. Maximally effective concentrations of ractopamine (10(-6) M) significantly decreased both the sensitivity and responsiveness of the isolated adipocytes to insulin. Addition of 10 microM propranolol to the incubation media effectively reversed the lipolytic and anti-lipogenic effects of 10(-6) M ractopamine observed at media insulin concentrations greater than 25 microU/ml, whereas it only partially reduced the ractopamine-induced effects observed at lower insulin concentrations. The results demonstrate 1) that ractopamine has concentration-dependent effects on adipose tissue insulin sensitivity and responsiveness and 2) that these effects may be mediated, in part, through beta-adrenergic receptors.

The effect of various levels of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine.

Six trials involving 888 pigs (Study 1) and three trials involving 360 pigs (Study 2) were conducted at various geographical locations in the U.S. and Canada to evaluate the effect of ractopamine hydrochloride on the performance and carcass characteristics of finishing swine. All trials were conducted using a randomized complete block design. Trial data were pooled within study for statistical analysis. Pigs averaged approximately 64.5 kg (Study 1) and 65.9 kg (Study 2) initially and had ad libitum access to a 16% crude protein corn-soybean meal or barley-soybean meal diet. Ractopamine was included in the diet at 0, 2.5, 5, 10, 20 or 30 ppm (Study 1), or at 0, 5, 10, 15 or 20 ppm (Study 2); diets were fed for an average of 45 d (Study 1) and 50 d (Study 2) to a final weight of about 104.3 kg (Study 1) and 106.6 kg (Study 2). Carcass dissection data were collected in three of the six trials in Study 1 (0, 5 and 20 ppm ractopamine) and in all three trials in Study 2 (0, 5, 10, 15 and 20 ppm ractopamine). All ractopamine levels improved (P less than .05) ADG and feed: gain (Studies 1 and 2) above those of control pigs. Ractopamine levels of 10 to 30 ppm (Studies 1 and 2) improved (P less than .05) dressing percentage over controls. Pigs fed ractopamine at 5 and 20 ppm (Study 1) and 10, 15 and 20 ppm (Study 2) had increased (P less than .05) dissected leanness compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of a specific mRNA in longissimus muscle of steers fed ractopamine.

To address the hypothesis that some classes of growth promoters stimulate muscle protein synthesis in growing cattle, 23 crossbred steers were fed diets containing the phenethanolamine growth promoter ractopamine in a 140-d feeding trial. Steers received either no ractopamine, .18 or .36 mg.kg BW-1.d-1 ractopamine for 140 d or .36 or .72 mg.kg BW-1.d-1 ractopamine for 56 d. Longissimus muscle was obtained at slaughter and frozen in liquid N2. RNA was extracted by homogenization of pulverized frozen muscle in guanidinium isothiocyanate and centrifugation through cesium chloride. Polyadenylated mRNA was extracted by capture on oligo-dT columns. Ractopamine had no effect on total RNA or mRNA concentrations (P greater than .25). Hybridization of the RNA to a putative myosin light chain-1/3 (MLC-1/3) cDNA clone in a Northern blot indicated one heavy band (approximately 1 kb) with no evidence of extensive destruction of the RNA. A second, minor band (approximately 3 kb) also was observed in some samples. The MLC-1/3 cDNA clone was hybridized to 1- or 5-micrograms samples of total RNA, and the intensity of the resultant autoradiographs was quantified by laser densitometry. There was a statistical correlation between MLC-1/3 mRNA-micrograms RNA-1 and longissimus cross-sectional area (P less than .05) and average daily gain (P less than .025). The results suggest that ractopamine either increased the transcription of the putative MLC-1/3 gene and(or) increased the stability of MLC-1/3 mRNA in bovine longissimus muscle, either of which could result in an increase in specific myofibrillar protein synthesis.

Paylean alters myosin heavy chain isoform content in pig muscle.

Feeding beta-adrenergic agonists promotes muscle growth. Early histological techniques failed to show precisely how feeding ractopamine-HCl (Paylean) alters muscle growth in pigs. To understand these effects, an indirect enzyme-linked immunosorbent assay (ELISA) was used to determine the abundance of each adult skeletal muscle myosin heavy chain isoform, one means of assigning muscle fiber type, in fast and slow muscles of pigs fed Paylean. Sixty growing pigs (-85 kg) were randomly assigned to three Paylean doses (0, 20, or 60 ppm). At 3, 7, 14, 28, and 42 d of treatment, four pigs per dose were harvested and white (WST) and red (RST) semitendinosus and longissimus (LM) muscles were removed and processed, and myosin heavy chain was quantified by ELISA. Feeding Paylean enhanced (P < 0.05) pigs' average daily gain. Muscle myosin heavy chain (slow, 2A, 2AX, and 2B) composition differed (P < 0.05) across muscles. Compared with LM, RST contained approximately five times more (P < 0.0001) slow and type 2A myosin heavy chain and three times more 2AX myosin heavy chain but nearly undetectable amounts of 2B myosin heavy chain. Myosin heavy chain composition of the WST closely resembled that of the LM (i.e., greater 2AX and 2B and less slow and 2A). After 42d of 60 ppm Paylean, the amount of slow, 2A, and 2AX myosin heavy chain decreased (P < 0.05) across the three muscles whereas the amount of 2B myosin heavy chain increased (P < 0.05). In contrast, relative amounts of 2A and 2AX myosin heavy chain increased (P < 0.05) in muscle of control pigs at 42d. Changes associated with the 20-ppm dose were intermediate to and different from (P < 0.05) control and 60 ppm treatments. Correlations (P < 0.05) among various myosin heavy chain within muscles suggest that slow, type 2A, and 2X decrease with increases in 2B myosin heavy chain. These data show that administration of Paylean affects myosin heavy chain isoform composition in a time- and dose-dependent manner and provides a mechanism of action for Paylean altering animal growth.

Effects of amperozide and azaperone on aggression and productivity of growing-finishing pigs.

Levels of aggression, activity and performance were determined in 270 pigs (initial wt 29.8 kg) injected with amperozide (1.0 mg/kg i.m.), azaperone (2.2 mg/kg i.m.) or saline (.1 ml/kg i.m.) immediately prior to mixing. Pigs had ad libitum access to feed in pens of 15, and six pens were allotted to each treatment. Each pen was video-taped for 48 h after injection. Aggression was determined by continuous observation and summarized for each 2-h period. Injuries on the ears and shoulders of each pig were scored prior to injection and 1, 2, 3 and 7 d after treatment. Eating, drinking and lying were determined by scan sampling at 2-min intervals and summarized for each 2-h period. Weight gain, feed consumption and efficiency were determined for periods ending on d 3, 7, 14, 28, 42, 56, 70 and 84. Both drugs reduced total fighting from 309.8 min for saline to 190.7 and 189.6 min for amperozide- and azaperone-treated pens, respectively (P less than .01). Treatment differences in aggression and lying were evident during the initial 6 h only. Amperozide resulted in fewer fights involving two pigs (197.3/pen) than did azaperone (260.2/pen) or saline (298.3/pen) (P less than .05). Injuries to the ears (P less than .01) and total injuries (P less than .05) were less severe in amperozide-treated pigs than in pigs on the other treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

In-vivo analysis of serum-borne growth factors in developing co-twinned fetuses.

Double-muscled fetuses develop more muscle fibers than normal-muscled fetuses. To examine whether serum growth factors modulate muscle development in cattle, twin pregnancies were induced in eight Holstein heifers using embryos from Belgian Blue and Holstein genetics representing heavy (HM) and light (LM) muscled cattle, respectively. Twin combinations were 1) two pairs of Belgian Blue fetuses that were designated as HM (HM), 2) two pairs of Holstein fetuses that were designated as LM (LM), and 3) four pairs of mixed fetuses; the four Holstein fetuses were designated as LM (HM) and the four Belgian Blue fetuses were designated as HM (LM). Pregnancies were terminated at 175 +/- 5 d after conception and fetuses, with evidence of vascular anastomosis, were dissected. Carcass weights were greatest (P < .05) for HM fetuses. Total bone and individual femur weights were greatest (P < .05) for LM (LM) fetuses. Total skeletal muscle mass and mass of semitendinosus, quadriceps femoris, infraspinatus, and longissimus muscles were in the order of HM (HM) > HM (LM) > LM (HM) = LM (LM) (P < .05). Estimated apparent muscle fiber number determined from a cross-section of semitendinosus muscle was in the order of HM (LM) > HM (HM) > LM (HM) = LM (LM) (P < .05). These data show that the presence of a co-twinned fetus with a lower genetic propensity for muscle development reduces the capacity of heavily muscled fetuses to develop muscle mass by 175 d after conception and strongly support the idea that blood-borne factors regulate muscle hypertrophy in fetal cattle.

The effect of narasin on apparent nitrogen digestibility and large intestine volatile fatty acid concentrations in finishing swine.

The effect of narasin on apparent nitrogen and dry matter digestibilities and large intestine VFA concentrations in finishing swine was investigated. The study used 21 crossbred barrows averaging 72 kg. Seven blocks were formed on the basis of pretreatment dry matter digestibility, and barrows were randomly assigned to three treatments in each block. Treatments consisted of a control (C) and narasin (N15 and N30) applied at 15 and 30 ppm, respectively. Fecal and urine samples were collected. Upon the completion of the digestibility work, intestinal samples were taken from three locations, and VFA concentrations for each animal were measured. Weight gains for the N15 and N30 treatments were increased 3.0 and 6.0% (not significant), respectively, over control. Fecal nitrogen was decreased (P < .05) in the narasin-fed barrows, and apparent nitrogen digestibility was increased (P < .05). Neither nitrogen retention nor urinary nitrogen excretion was altered (P > .05) due to narasin. There were no increases (P > .05) in apparent dry matter digestibility due to narasin. Analysis of pooled colon samples showed an increase (P < .05) in the concentration of propionic acid in relation to acetic and butyric in the narasin-fed barrows. Butyric acid was reduced (P < .05) in the transverse colon of narasin-fed barrows. In summary, narasin administration to finishing barrows resulted in improved apparent nitrogen digestibility, thus decreasing fecal nitrogen, and increased relative concentrations of propionic acid in the large intestine.

Estimation of 3-methylhistidine production in pigs by compartmental analysis.

Direct in vivo methodology is not available to accurately evaluate muscle turnover in pigs. Urinary 3-methylhistidine (3MH) excretion, which is used as an in vivo marker of muscle protein breakdown in humans and cattle, is not a valid indicator for pigs. The present study proposes that data from a single bolus dose of 3-[methyl-2H3]methylhistidine tracer can mathematically describe 3MH metabolism in pigs. Plasma concentration of the tracer is described by a linear time-invariant three-compartment model by using the SAAM/CONSAM computer modeling program. The model defines masses and fluxes of 3MH within the pigs and, in particular, the intracellular de novo production of 3MH, which should reflect muscle proteolysis. The de novo production of 3MH as calculated by the model was 621 mumol/d, corresponding to a fractional breakdown rate of 2.28%/d, which is similar to values reported by using indirect methodology. These data also suggest that certain model compartments may be indicators of body muscle mass (mass of compartment 3, r = .59, P = .006). The mathematical model developed does not depend on urine collections and can be used to assess changes in muscle proteolysis in vivo.

Effect of various levels of avilamycin on the performance of growing-finishing swine.

A series of 12 trials involving 1,710 crossbred pigs was conducted at eight geographical locations in the United States to determine the effect of avilamycin on average daily gain (ADG), average daily feed (ADF) and feed-to-gain ratio (F/G) of growing-finishing swine. Eight of 12 trials evaluated avilamycin concentrations at 0, 5, 10, 20, 40 and 60 ppm, while an additional four trials evaluated avilamycin concentrations at 0, 10, 20 and 40 ppm in swine grower and finisher diets fed ad libitum. All trials were conducted using a randomized complete block design with data from the 12 trials pooled for statistical analysis. Pigs fed 5, 10, 20, 40 or 60 ppm avilamycin had increased (P less than .05) ADG over control pigs. No differences were detected for ADF between control and avilamycin-fed pigs. Pigs fed 10, 20, 40 or 60 ppm avilamycin had improved (P less than .05) F/G over control animals. Average daily gain, ADF and F/G for pigs fed 0, 5, 10, 20, 40 or 60 ppm avilamycin were: 749, 763, 767, 769, 771 and 771 g; 2.38, 2.40 2.39, 2.41, 2.38 and 2.38 kg; and 3.17, 3.15, 3.12, 3.13, 3.09 and 3.09, respectively. Linear plateau procedures showed that the effective dose range of avilamycin for the growing-finishing phase is 5 to 10 ppm for improving ADG and 10 to 60 ppm for improving F/G.

Limitations of ractopamine to affect adipose tissue metabolism in swine.

To determine the temporal effect of ractopamine (Rac), a phenethanolamine, on adipose lipogenic enzyme activity and gene expression, 20 crossbred barrows were fed Rac (20 mg/kg of diet) for 0, 1, 8, or 24 d before slaughter (105 +/- 1 kg). Ractopamine had no effect (P > .05) on the activity of acetyl-coenzyme A carboxylase or malic enzyme in either the middle or outer layers of subcutaneous adipose tissue. Similarly, mRNA abundance for acetyl-coenzyme A carboxylase and the glucose transport proteins Glut 1 and Glut 4 were not affected by Rac in either adipose depot. Despite the inability of Rac to affect adipose tissue metabolism, Rac increased nitrogen retention, longissimus muscle area, and alpha-actin gene expression in skeletal muscle. Results indicate that Rac was not a functional beta-adrenergic agonist toward adipose tissue in this study. We suggest that the response to Rac in adipose tissue is masked by a combination of factors including tissue insensitivity, Rac-dose limitation, inherent partial agonism of Rac, and beta-adrenoceptor down-regulation.

The effect of ractopamine on beta-adrenoceptor density and affinity in porcine adipose and skeletal muscle tissue.

We have evaluated the effect of feeding ractopamine (Rac), a phenethanolamine lean enhancer being developed for commercial use in finishing pigs, on beta-adrenoceptor (beta-AR) number and ligand-receptor binding affinity in adipose and muscle tissues. Pigs weighing 78 +/- 1 kg were fed Rac (20 mg/kg of diet) for 0 (control), 1, 8, or 24 d before being killed at 105 +/- 1 kg BW. beta-adrenoceptor density (per milligram of protein) was decreased by Rac up to approximately 50% in both the middle and the outer layers of subcutaneous (SQ) adipose tissue. Orthogonal contrasts indicated significant (P < or = .05) linear effects of Rac in middle and outer SQ adipose tissue, and also a significant (P < or = .05) quadratic effect of Rac in the middle layer. Ractopamine did not affect the maximal binding (Bmax) of longissimus muscle. The relative affinity with which the beta-AR population of the tissues examined bound the radioligand ([3H]dihydroalprenolol) was not influenced by Rac. Likewise, feeding Rac had no effect on the affinity of the beta-AR for Rac. The data indicate that a Rac-induced reduction in the Bmax of adipose tissue may account for the diminished in vitro lipolytic potency of exogenous Rac after prolonged periods of Rac feeding, and that Rac-induced desensitization differs between adipose and skeletal muscle tissues.

Muscle protein metabolism in finishing pigs fed ractopamine.

Forty crossbred barrows (average initial weight, 66.4 kg) were utilized to determine the effects of ractopamine (a phenethanolamine/beta adrenergic agonist) on protein accretion and synthesis, activities of cathepsins B, H, L and calcium-dependent proteinase and nucleic acid content of semitendinosus muscle (ST). All pigs were offered a 16% protein, mineral and vitamin fortified corn-soybean meal diet supplemented with either 0 or 20 ppm ractopamine for 14, 21, 28, 35 or 42 d. Protein synthesis (fractional rates) was studied in pigs at d 21 and 35; ST protease activities, protein and nucleic acid content were measured on d 14, 28 and 42. Ractopamine increased (P less than .01) ST total protein content and maintained RNA muscle concentration and total ST muscle RNA content. DNA content (mg/g ST) declined (P less than .05) upon ractopamine feeding, but total DNA per muscle remained unchanged except for d 42, when the ST muscles were largest. Fractional accretion rates (FAR) were 1.0 and 1.2% for control and ractopamine-fed pigs, respectively. Fractional protein synthesis rate (FSR) was higher (P less than .06) in ractopamine-fed pigs (6.1%/d) than in control pigs (4.4%/d). Fractional protein synthesis rate could account for the observed muscle hypertrophy and increased FAR. Estimated fractional breakdown rates (FBR = FSR - FAR) were 3.4%/d and 4.9%/d for control and ractopamine-fed pigs, respectively. The activities of the catheptic proteases and calcium-dependent proteinase were not affected by the treatments.

Molecular ecological analysis of porcine ileal microbiota responses to antimicrobial growth promoters.

Cultivation-independent microbial molecular ecology approaches were used to examine the effects of antibiotic growth promoters on the pig ileal microbiota. Five-week-old barrows were fitted with a simple T-cannula at the distal ileum. Three diets meeting or exceeding the minimum nutrient requirements were fed for 5 wk and supplemented as follows: 1) negative control (no antibiotic; n = 5), 2) continuous tylosin administration (n = 5), and 3) an antibiotic rotation sequence (wk 1, chlorotetracycline sulfathiazole penicillin; wk 2, bacitracin and roxarsone; wk 3, lincomycin; wk 4, carbadox; wk 5, virginiamycin; n = 5). Ileal luminal contents were collected for DNA isolation at the end of each of the 5 wk of the testing period. The V3 region of 16S rDNA was amplified by PCR and analyzed via denaturing gradient gel electrophoresis (DGGE) and quantitative polymerase chain reaction (qPCR). Resulting PCR-DGGE band numbers (bacterial species) were counted, and the banding patterns analyzed by calculating Sorenson's pairwise similarity coefficients (C(S)), an index measuring bacterial species in common among samples. Band numbers and total bacterial DNA concentrations decreased (P < 0.05) temporally in antibiotic-treated pigs compared with controls. Comparisons between treatments yielded low intertreatment C(S) indices, indicating treatment-dependent alterations in banding patterns, whereas intratreatment comparisons revealed increased homogeneity in antibiotic-treated vs. control pigs. Sequence analysis of treatment-specific bands identified three Lactobacillus, one Streptococcus, and one Bacillus species that were diminished with antibiotic rotation treatment, whereas tylosin selected for the presence of L. gasseri. Lactobacillus-specific qPCR was performed and analyzed as a percentage of total bacteria to further evaluate the effects of antibiotic administration on this genus. Total bacteria were decreased (P < 0.05) by tylosin and rotation treatments, whereas the percentage of lactobacilli increased (P < 0.05) by d 14 and through d 28 in tylosin-treated pigs. The decrease in total bacteria by antibiotics may reduce host-related intestinal or immune responses, which would divert energy that could otherwise be used for growth. Conversely, the ability of tylosin to improve animal growth may relate to its apparent selection for lactobacilli, commensals known to competitively exclude potentially pathogenic species from colonizing the intestine.

Increased conception rate in dairy cows after early post partum administration of prostaglandin F2 alpha THAM.

Commercial dairy cows were given a routine injection of dinoprost tromethamine (prostaglandin F2 alpha THAM) in the early post partum period. The first service conception rate of 64 cows given a single 25 mg injection of dinoprost during the period 14 to 28 days after calving was 68 per cent, that of 64 untreated controls was 43 per cent. The difference was highly significant at the level P = 0.007. In cows with no blood progesterone and with basal progesterone concentrations at the time of treatment, indicating absence of an active corpus luteum, the mean conception rates for 30 treated and 38 control cows were 70 and 44 per cent, respectively, demonstrating that this is not a luteolytic effect. Although that implies a positive myometrial effect, the interval from calving to first service was not shortened in treated cows.