The effect of human interferon alpha on replication of different bovine viral diarrhea virus strains.

Bovine viral diarrhea virus (BVDV) exists in two main biotypes: cytopathic (cp) and noncytopathic (ncp). Although some studies were done on the effect of interferon alpha (IFN-α) on BVDV, the effect of exogenous IFN against BVDV biotypes remains unclear. In the present study, we evaluated the comparative effect of exogenous human IFN-α (HuIFN-α) on different BVDV biotypes and genotypes. The results showed that exogenous HuIFN-α greatly inhibited the growth of different BVDV biotypes and genotypes. However, HuINF-α has a significant inhibitory effect on cp biotype compared to ncp one without significant variation between different genotypes. The effect of HuIFN-α on BVDV reached the maximum level at early stages of infection (0-20 h post infection) and increased in a dose-dependent manner (10-500 U/ml). Quantitative real-time RT-PCR was used to evaluate the effect of exogenous HuIFN-α on RNA synthesis of both BVDV biotypes. HuIFN-α reduced RNA production of cp by 4 logs compared to only 2 logs for ncp strains. Additionally, the antiviral effect of IFN-α against both BVDV biotypes seems to be independent of the RNA-dependent protein kinase (PKR) activation as assayed by direct analysis of in vivo phosphorylation of eIF2-α and by 2-aminopurine (2-AP) treatment. Collectively, these results indicated that the exogenous HuIFN-α treatment has an inhibitory effect not only on cp BVDV biotype but also on the ncp BVDV. The antiviral effect of exogenous HuIFN-α was biotype, time, dose but not genotype dependent. PKR has no role in the inhibitory effect suggesting that other IFN-antiviral pathways were involved. Keywords: BVDV biotypes; HuIFN-α; RNA synthesis; PKR-independent.

Kennedy, the early sixties, and visitation by the angel of death.

The inaugural issue of Pathologia Veterinaria in 1964 contained the first detailed account of lesions in aborted fetuses following natural, experimental, and postvaccinal infection with bovine herpesvirus 1 (BoHV-1). The article, written by pathologists Kennedy and Richards, described diagnostic gross and histologic features in 13 bovine fetuses. The authors provided clinical and epidemiologic features of 1 postvaccination outbreak, including the absence of clinical signs in infected dams and the propensity for abortions to occur after 6 months' gestation. Subsequent field and experimental studies corroborated and expanded these observations. As a result of this and later reports, veterinarians became alert to the association between infectious bovine rhinotracheitis and abortion, including the risks of exposing pregnant cattle to live vaccinal BoHV-1. Methods were developed to corroborate a morphologic diagnosis of herpetic abortion in cattle, including immunofluorescence, immunohistochemistry, and polymerase chain reaction methods. Outbreaks of postvaccinal BoHV-1 abortion in the United States began to be reported with apparently increased frequency in the early 2000s. This coincided with licensure in 2003 of modified live BoHV-1 vaccines intended for use in pregnant cattle, which are now sold by 3 manufacturers. Ten recent herd episodes of postvaccinal BoHV-1 abortion are reported. All 10 BoHV-1 isolates had single-nucleotide polymorphism (SNPs) profiles previously identified in a group of BoHV-1 isolates that contains vaccine strains, based on a BoHV-1 SNP classification system. They lacked SNP features typical of those in characterized field-type strains of BoHV-1.

The induction of a cell-mediated immune response to bovine viral diarrhea virus with an adjuvanted inactivated vaccine.

This study evaluated the induction of bovine viral diarrhea virus (BVDV) cell-mediated and humoral immune responses after vaccination with an adjuvanted inactivated product. In vaccinated animals, there was an overall treatment effect (P less than .05), for an increased percentage of BVDV-specific CD8 T cells expressing interferon-γ (IFN-γ). The percentages of IFN-γ producing γδ-T cells in the vaccinated group were increased on days 7 (P =.10), 14 (P =.09), and 31 (P = .12). CD4 T cells expressing IFN-γ were increased on day 42 (P = .05). Stimulated peripheral blood mononuclear cells of the vaccinated group had increased IFN-γ production on days 14 and 35 (P less than .05). Testing for BVDV types 1 and 2 titers began at day 14, with peak titers on days 42 and 35, respectively. In summary, the intracellular accumulation and release of IFN-γ, a T helper cell 1 cytokine, indicates that an adjuvanted inactivated BVDV vaccine is capable of invoking a cell-mediated response while delivering a targeted humoral response.

Influence of cow breed type, age and previous lactation status on cow height, calf growth, and patterns of body weight, condition, and blood metabolites for cows grazing bahiagrass pastures.

This study was initiated to evaluate performance and patterns of cow traits and blood metabolites of 3 breeds of cows grazing bahiagrass (Paspalum notatum Flügge) pastures in central Florida. Purebred cows (n = 411) of either Angus (Bos taurus), Brahman (Bos indicus), or Romosinuano (Bos taurus) breeding, rotationally grazed (moved twice weekly) bahiagrass pastures year-round, and received bahiagrass hay supplemented with molasses and soyhulls or legume hay supplemented with unfortified molasses from October to June each production year. At monthly intervals, all cows were weighed, measured at the hip (HH), scored for BCS, and blood samples collected by jugular puncture from 10 cows per cow breed/block group for plasma urea N (PUN), glucose and non-esterified fatty acids (NEFA). Data were analyzed on cows that calved with a statistical model that included fixed effects of year, cowage, cow breed, month, block, supplement group (n = 2, but not presented), and whether the cow weaned a calf the previous year. Cow was a repeated observation over mo. Three-way interactions involving monthly patterns for cowage x year, year x lactation status the previous year, cowage × cow breed, year × cow breed, and cow breed × lactation status the previous year were significant (P < 0.001) for BW and BCS. The interaction for cowage × month was also significant (P < 0.05) for glucose, and cow breed × month was important (P < 0.01) for PUN, glucose, and NEFA. Important differences included: 1) greater BW and BCS for older cows compared to 3-yr old cows; 2) greater BW and BCS before calving for cows that did not lactate the previous year; 3) PUN levels were above 11 mg/dl except for February, August and September, and was generally greater in tropically adapted breeds; 4) GLU was greatest in Brahman, lowest in Angus, and intermediate in Romosinuano cows; and 5) plasma levels of NEFA escalated at calving and then declined, but Brahman cows maintained greater (P < 0.05) levels from calving until weaning than the other breeds. Cows that lactated the previous year had less NEFA than those that did not lactate. Brahman cows were less fertile than Bos taurus breeds, and weaned heavier calves.

Evaluation of tropically adapted straightbred and crossbred beef cattle: Cortisol concentration and measures of temperament at weaning and transport.

The objective of this research was to evaluate circulating concentrations of plasma cortisol and measures of temperament at weaning in calves (steers and heifers) and at transport in steers. Calves ( = 993) were produced from a 3-breed diallel mating design that included calves from 3 consecutive years. Breed types of calves were straightbred Angus (A), Brahman (B), and Romosinuano (R) and all F crossbred combinations (AB, BA, AR, RA, BR, and RB). At weaning (d 0) and at 24 and 72 h after weaning, blood was sampled from calves and the plasma was stored for later cortisol assay. Additionally, at each of these times, temperament was assessed as chute score, exit velocity, and pen score. About 1 mo later, steer calves ( = 471) were sampled before shipment, at arrival, and at 24 h, 72 h, 2 wk, and 4 wk after shipment (2,025 km; Brooksville, FL, to El Reno, OK). At each of these sampling times, blood was collected and plasma was stored for subsequent cortisol assay and temperament was assessed by measurement of exit velocity. At both weaning and transport, plasma concentrations of cortisol did not significantly differ ( > 0.05) among straightbreds or among crossbreds. Significant ( < 0.05) positive genetic effects were observed for plasma concentration of cortisol at weaning (heterosis for BA and direct Romosinuano effect) and transport (heterosis for RA, BR, and BA; direct Romosinuano effect; and maternal Angus effect). Assessment of temperament using the objective measurement of exit velocity or the subjective measures of chute score or pen score (1 [lowest] to 5 [highest excitability] scale, based on behavior in chute and behavior in pen with human observer, respectively) generally provided similar results: Brahman was higher than Brahman crosses, which were higher than Angus, Romosinuano, and their reciprocal crosses. For exit velocity, however, Brahman did not differ from Brahman crosses and Angus did not differ from Romosinuano or Brahman crosses. At transport, sire breed and dam breed affected exit velocity of steers, with higher ( < 0.05) estimates for Brahman than for Romosinuano or Angus. These data suggest that weaned calves and shipped steers of various breed types show a similar response to stressors in cortisol concentration. In contrast, in assessing temperament or behavioral response to humans, Romosinuano and Angus had better temperaments and were less excitable than Brahman.

Protection against fetal infection with either bovine viral diarrhea virus type 1 or type 2 using a noncytopathic type 1 modified-live virus vaccine.

Two bovine viral diarrhea virus (BVDV) fetal protection studies were done using a monovalent noncytopathic (NCP) BVDV vaccine containing type 1 BVDV. In study 1, thirty-two fetuses (23 vaccinates and nine controls) were recovered following fetal challenge with the type 1a BJ strain. Twenty of twenty-three fetuses from the vaccinates were negative for BVDV type 1 while all of the controls (nine of nine) were infected. In study 2, twenty-two animals (14 vaccinates and eight controls) were challenged with the type 2 PA131 strain. Thirteen of the fourteen fetuses from the vaccinates were negative for BVDV type 2 while all of the nonvaccinated controls (eight of eight) were infected. These results indicate the efficacy of a monovalent NCP BVDV vaccine in providing excellent protection against either BVDV type 1 or 2 fetal infection.

Heterosis and direct effects for Charolais-sired calf weight and growth, cow weight and weight change, and ratios of cow and calf weights and weight changes across warm season lactation in Romosinuano, Angus, and F cows in Arkansas.

The use of Brahman in cow-calf production offers some adaptation to the harsh characteristics of endophyte-infected tall fescue. Criollo breeds, such as the Romosinuano, may have similar adaptation. The objectives were to estimate genetic effects in Romosinuano, Angus, and crossbred cows for their weights, weights of their calves, and ratios (calf weight:cow weight and cow weight change:calf weight gain) across lactation and to assess the influence of forage on traits and estimates. Cows ( = 91) were bred to Charolais bulls after their second parity. Calves ( = 214) were born from 2006 to 2009. Cows and calves were weighed in early (April and June), mid- (July), and late lactation (August and October). Animal was a random effect in analyses of calf data; sire was random in analyses of cow records and ratios. Fixed effects investigated included calf age, calf sex, cow age-year combinations, sire breed of cow, dam breed of cow, and interactions. Subsequent analyses evaluated the effect of forage grazed: endophyte-free or endophyte-infected tall fescue. Estimates of maternal heterosis for calf weight ranged from 9.3 ± 4.3 to 15.4 ± 5.7 kg from mid-lactation through weaning ( < 0.05). Romosinuano direct effects (of the cow) were -6.8 ± 3.0 and -8.9 ± 4.2 kg for weights recorded in April and June. Calf weights and weight gains from birth were greater ( < 0.05) for calves of cows grazing endophyte-free tall fescue except in mid-summer. Cow weight change from April to each time was negative for Angus cows and lower ( < 0.05) than other groups. Cows grazing endophyte-free tall fescue were heavier ( < 0.05) at all times but had more weight loss in late lactation. Angus cows had the lowest ( < 0.05) ratios (negative) of cow weight change:calf weight gain, indicating an energy-deficit condition. Cows grazing endophyte-free tall fescue had more negative ( < 0.05) values for this trait but not in early lactation ( < 0.05). Estimates of heterosis ranged from 12.8 ± 9.5 to 28.6 ± 9.4 kg for cow weight, 7.9 ± 3.0 to 15.8 ± 5.0 kg for cow weight change, and 0.07 ± 0.03 to 0.27 ± 0.1 for cow weight change:calf weight gain. Direct Romosinuano effects ranged from 14.8 ± 4.2 to 49.8 ± 7.7 kg for cow weight change and 0.2 ± 0.04 to 0.51 ± 0.14 for cow weight change:calf weight gain. The adaptive ability of Romosinuano in temperate fescue regions may be favorable with respect to relative cow and calf weight but may be a consequence of lower milk-producing ability.

Genetic parameters estimated at receiving for circulating cortisol, immunoglobulin G, interleukin 8, and incidence of bovine respiratory disease in feedlot beef steers.

Bovine respiratory disease complex (i.e., shipping fever and bacterial bronchopneumonia) is a multifaceted respiratory illness influenced by numerous environmental factors and microorganisms. Bovine respiratory disease (BRD) is just one component of BRD complex. Because BRD is moderately heritable, it may be possible to reduce the incidence of BRD through genetic selection. The objectives of this study were to determine the heritability and associative genetic relationships among immune system traits (i.e., cortisol, total IgG, IgG isotypes, and IL-8) in cattle monitored for BRD incidence. At an average of 83 d after weaning (219 d age and mean = 221.7 kg [SD 4.34]), crossbred steer calves ( = 2,869) were received at a commercial feedlot in southeastern Colorado over a 2-yr period. At receiving, jugular blood samples were collected at 212 (yr 1) and 226 d (yr 2) of age for immune trait analyses. The BRD phenotype was defined as a binomial variable (0 = no and 1 = yes) and compared with immune system traits measured at receiving (prior to illness onset). An animal identified as BRD positive exhibited ≥ 2 clinical signs (i.e., eye or nasal discharge, cough, lethargy, rapid breathing, acute interstitial pneumonia, or acute upper respiratory syndrome and/or a rectal temperature > 39.7°C). Heritability and genetic correlation estimates for categorical variable BRD, cortisol, IgG, IgG1, IgG2, and IL-8 were estimated from a sire model using ASREML. Heritability estimates were low to moderate for BRD (0.17 ± 0.08), cortisol (0.13 ± 0.05), IgG (0.15 ± 0.05), IgG1 (0.11 ± 0.05), IgG2 (0.24 ± 0.06), and IL-8 (0.30 ± 0.06). A moderate negative genetic correlation was determined between BRD and cortisol ( = -0.19 ± 0.32). Moderate positive correlations were found between BRD with IgG (0.42 ± 0.28), IgG1 (0.36 ± 0.32), and IL-8 ( = 0.26 ± 0.26). Variation in the BRD phenotype and immune system traits suggested herd health improvement may be achieved through genetic selection.

Detection and characterization of viruses as field and vaccine strains in feedlot cattle with bovine respiratory disease.

This study investigated viruses in bovine respiratory disease (BRD) cases in feedlots, including bovine herpesvirus-1 (BoHV-1), bovine viral diarrhea virus (BVDV), bovine respiratory syncytial virus (BRSV), bovine coronaviruses (BoCV) and parainfluenza-3 virus (PI3V). Nasal swabs were collected from 114 cattle on initial BRD treatment. Processing included modified live virus (MLV) vaccination. Seven BRD necropsy cases were included for 121 total cases. Mean number of days on feed before first sample was 14.9 days. Swabs and tissue homogenates were tested by gel based PCR (G-PCR), quantitative-PCR (qPCR) and quantitative real time reverse transcriptase PCR (qRT-PCR) and viral culture. There were 87/114 (76.3%) swabs positive for at least one virus by at least one test. All necropsy cases were positive for at least one virus. Of 121 cases, positives included 18/121 (14.9%) BoHV-1; 19/121 (15.7%) BVDV; 76/121 (62.8%) BoCV; 11/121 (9.1%) BRSV; and 10/121 (8.3%) PI3V. For nasal swabs, G-PCR (5 viruses) detected 44/114 (38.6%); q-PCR and qRT-PCR (4 viruses) detected 81/114 (71.6%); and virus isolation detected 40/114 (35.1%). Most were positive for only one or two tests, but not all three tests. Necropsy cases had positives: 5/7 G-PCR, 5/7 q-PCR and qRT-PCR, and all were positive by cell culture. In some cases, G-PCR and both real time PCR were negative for BoHV-1, BVDV, and PI3V in samples positive by culture. PCR did not differentiate field from vaccines strains of BoHV-1, BVDV, and PI3V. However based on sequencing and analysis, field and vaccine strains of culture positive BoHV-1, BoCV, BVDV, and PI3V, 11/18 (61.1%) of BoHV-1 isolates, 6/17 (35.3%) BVDV isolates, and 1/10 (10.0%) PI3V identified as vaccine. BRSV was only identified by PCR testing. Interpretation of laboratory tests is appropriate as molecular based tests and virus isolation cannot separate field from vaccine strains. Additional testing using sequencing appears appropriate for identifying vaccine strains.

Factors influencing tenderness in steaks from Brahman cattle.

The objective of this study was to identify a set of explanatory variables for Warner-Bratzler shear force and myofibril fragmentation indices after 7, 14, and 21d of aging; and sensory tenderness after 14d of aging of steaks from Brahman cattle. Insoluble collagen was negatively associated (P<0.001) with all tenderness traits across aging periods, and regression coefficients ranged from 5.69±0.49 to 9.12±0.29N for Warner-Bratzler shear force. The effect of lean color score (P<0.05) in analyses of unadjusted traits was diminished when data were adjusted for contemporary group (calves of the same sex, fed in one pen, and slaughtered the same day). Insoluble collagen may be of special importance and offer a unique opportunity to improve palatability of steaks from purebred Brahman cattle.

Comparison of the breadth and complexity of bovine viral diarrhea (BVDV) populations circulating in 34 persistently infected cattle generated in one outbreak.

Exposure to bovine viral diarrhea viruses (BVDV) results in acute and persistent infections. Persistent infections result from in utero exposure during the first trimester of gestation. Clinical presentation, in persistently infected cattle (PI), is highly variable. The reasons for this variation is largely unknown. The BVDV circulating in PI exist as quasispecies (swarms of individual viruses). An outbreak resulting in 34 PI cattle presented an opportunity to compare a large number of PI׳s. Methods were developed to compare the circulating viral populations within PI animals. It was found that PI animals generated in the same outbreak carry circulating viral populations that differ widely in size and diversity. Further, it was demonstrated that variation in PI viral populations could be used as a quantifiable phenotype. This observation makes it possible to test the correlation of this phenotype to other phenotypes such as growth rate, congenital defects, viral shed and cytokine expression.

Nested and multiplex polymerase chain reactions for the identification of bluetongue virus infection in the biting midge, Culicoides variipennis.

Two polymerase chain reaction tests for the detection of bluetongue viral (BLU) RNA in the principal North American insect vector, Culicoides variipennis, were developed. The BLU serogroup specific test used the highly expressed non-structural protein 1 gene as the target gene and two amplification steps. First a 1228 base pair product was amplified using an outer primer pair, then a second amplification using a nested or internal primer pair produced a 930 base pair product. This nested PCR test was found to be very sensitive detecting an equivalent to 1 plaque-forming unit of BLU viral RNA extracted from infected biting midges. The serotype specific test used a multiplex PCR approach in which five different primer pairs were used simultaneously. Each pair was based on the variable outer capsid protein VP2 gene of the five US serotypes generating specific product which were easily identified by size difference. The sensitivity of the multiplex PCR was less sensitive than the nested-PCR but sufficient for use with field collected samples. These tests provide valuable tools for epidemiologic studies of BLU disease.

Development of a fetal challenge method for the evaluation of bovine viral diarrhea virus vaccines.

A method to evaluate the efficacy of bovine viral diarrhea virus (BVDV) vaccines using a multiple challenge model was investigated. Four pregnant heifers were challenged intranasally with a type I and type II isolate of BVDV at 75 days of gestation. At 60 days postinoculation, virus isolation and RT-PCR from blood and tissues of fetuses indicated that all fetus were persistently infected with both type I and type II isolates. Differing results of detection by PCR and virus isolation between the type I and type II isolates were obtained. These preliminary studies may indicate differences in the level of replication between type I and type II BVDV as well as predilected sites of replication in certain tissues.

Escherichia coli O157:H7 prevalence in fecal samples of cattle from a southeastern beef cow-calf herd.

The proportion of fecal samples culture-positive for Escherichia coli O157:H7 was determined for samples collected from 296 beef cows on pasture in a single Florida herd in October, November, and December 2001. The overall proportion of samples that cultured positive was 0.03. The proportion of cows that were culture-positive on at least one occasion was 0.091. No effect of pregnancy status or nutritional regimen on the proportion of culture-positive samples for E. coli O157:H7 was detected. We detected a breed effect on the shedding of E. coli O157, with Romosinuano cows having a lower (P < 0.01) proportion of samples culture-positive than Angus or Brahman cows. This difference might have resulted from the presence of confounding variables; however, it also might represent evidence of breed-to-breed genetic variation in E. coli O157 shedding. Further research is warranted to evaluate breed as a possible risk factor for shedding of this important foodborne pathogen. Further substantiated findings could indicate that breed is a cow-calf-level critical control point of E. coli O157:H7.

Detection of bovine herpesvirus-1 in peripheral blood mononuclear cells eight months postinfection.

Peripheral blood mononuclear cells (PBMCs) from 5 calves (3 controls and 2 vaccinates) used in a bovine herpesvirus 1 (BHV-1) vaccine study with a BHV-1 Cooper strain challenge were collected 6 months after challenge. The PBMCs from the control animals were positive by immunofluorescence for the BHV-1 glycoprotein D (gD) while the vaccinates were negative. The PBMC samples from 4 of the 5 animals were examined for BHV-1 DNA by polymerase chain reaction (PCR) and for gD immunofluorescence at 8 months after challenge. The BHV-1 DNA and viral antigen were detected in PBMC samples at 8 months postinfection, but no virus was isolated.

Serotyping of Mannheimia (Pasteurella) haemolytica isolates from the upper Midwest United States.

Mannheimia (Pasteurella) haemolytica biotype A serotype1 (A1) is the primary bacterial agent responsible for the clinical signs and pathophysiologic events in bovine pneumonic pasteurellosis. The goal of this study was to determine the prevalence of other serotypes of M. haemolytica biotype A organisms obtained from the upper Midwest diagnostic laboratories. A total of 147 M. haemolytica isolates were collected from Minnesota, South Dakota, and Michigan. Isolates were tested against M. haemolytica antisera obtained from the National Animal Disease Center, Ames, Iowa. Results indicated that M. haemolytica serotype 1 represented approximately 60%, serotype 6 represented 26%, and serotype 2 represented 7% of the total examined isolates. In addition, 7% of the isolates were serotype 9, 11, or untypable. This finding suggests that M. haemolytica serotypes other than serotype 1 can be isolated from the lung lesions of diseased cattle and seem to be capable of causing the pathologic changes observed in the lung with pneumonic pasteurellosis.

Immunohistochemical and pathological study of Mycoplasma bovis-associated lung abscesses in calves.

Out of 45 cases of fatal chronic pneumonia in calves examined for Mycoplasma bovis infection from February to July 1994, 11 cases with pulmonary abscesses that were culture positive for M. bovis were encountered. The cases were studied in detail using a recently developed monoclonal antibody-based immunoperoxidase technique. Mycoplasma bovis organisms were detected in specific locations at all stages of abscessation observed. In bronchioles or terminal airways within which abscesses developed, M. bovis was located at the epithelial surface and in close association with infiltrating neutrophils and macrophages. Abscessed airways that had lost the epithelium were encapsulated and were seen as coagulative necrotic foci that stained intensely for M. bovis, especially at the periphery. Some foci stained weakly and such might have been resolving lesions. Mycoplasma bovis was also demonstrated at sites of mild mononuclear cell infiltration in the livers and kidneys of 2 calves. The mycoplasma was detected within bile ducts in the liver and in the tubular epithelium of the kidney. Abscesses not staining for M. bovis, presumably caused by other pathogens, were seen concurrently with M. bovis-associated abscesses in some lungs. Thirteen other M. bovis-positive cases showed no abscesses, possibly indicating heterogeneity among M. bovis strains. Three other cases with abscesses were negative for M. bovis by culture and immunoperoxidase staining. The monoclonal antibody-based immunohistochemical technique is efficient for specific detection of M. bovis in cases of enzootic pneumonia of calves with or without abscessation. Mycoplasma bovis is implicated in the pathogenesis of lung abscesses in some calves.

Effect of exogenous estradiol on plasma concentrations of somatotropin, insulin-like growth factor-I, insulin-like growth factor binding protein activity, and metabolites in ovariectomized Angus and Brahman cows.

To determine the effect of breed and estradiol-17 beta on selected hormones and metabolites, ovariectomized (> or = 3 mo) Angus (n = 14) and Brahman (n = 12) cows were paired by age and body weight and randomly assigned as either nonimplanted controls (CON) or implanted with estradiol (E2) for 45 d. After Day 7 and through Day 42, plasma concentration of somatotropin was greater for E2 than CON cows (treatment x day, P < 0.05). During an intensive blood sampling on Day 36, E2 cows tended (P < 0.10) to have greater somatotropin pulse amplitudes than CON cows, but other parameters of somatotropin release were not affected (P > 0.10) by E2 treatment. The effect of breed was apparent on Day 36 as Brahman cows had greater (P < 0.05) somatotropin pulse amplitude, basal secretion, and mean concentration than Angus cows. Overall, plasma concentration of IGF-I was greater (P < 0.01) for E2 than CON cows (158.3 vs. 104.2 ng/ml) and was greater for Brahman than Angus cows (164.1 vs. 98.4 ng/ml). However, there was a trend (P < 0.10) for a treatment x breed x day interaction for IGF-I (i.e., the magnitude of increase in IGF-I concentration was greater in E2-Angus than E2-Brahman cows). After Day 7 and through Day 42, total plasma IGF binding protein (IGFBP) activity was greater (P < 0.01) for E2 than CON cows. Ligand blotting revealed at least five forms of IGFBP activity, and E2 cows had greater (P < 0.05) binding activity of IGFBP-3 and the 30- and 32-kDa IGFBP than CON cows. Brahman cows had greater (P < 0.05) IGFBP-3 and the 32-kDa IGFBP than Angus cows. After Day 14 and through Day 42, concentration of urea nitrogen (PUN) was greater (P < 0.001) for CON than E2 cows (treatment x day, P < 0.001). Brahman had greater (P < 0.01) PUN than Angus cows (16.6 vs. 14.2 mg/dl). Plasma concentration of glucose was greater (P < 0.01) for E2 than CON cows (78.9 vs. 76.4 mg/dl) but was not affected (P > 0.10) by breed. In summary, these data suggest that some, but not all, of the positive effects of estradiol on peripheral concentration of IGF-I and IGFBP activity can be attributed to increased somatotropin. Moreover, breed influenced basal and E2-induced secretion of somatotropin and IGF-I such that differences between Brahman and Angus cows in plasma IGF-I concentrations were abated within 3 wk of estradiol implantation. Thus, breed influences the metabolite and hormonal response of cattle to estrogenic implants.

A novel phenotype for Lardon dwarfism in miniature Bos indicus cattle suggests that the expression of growth hormone receptor 1A in liver is required for normal growth.

Mutations within the growth hormone receptor (GHR) gene that lead to an inactivated or truncated GHR protein cause abnormal growth and small adult size in a variety of species (Laron dwarfism). We studied a line of miniature Bos indicus cattle that have phenotypic (small mature size) and endocrine (increased blood growth hormone and decreased blood insulin-like growth factor-I concentrations) similarities to Laron dwarfs. Liver mRNA from miniature and control cattle was used to amplify a cDNA within the coding region of the GHR. The miniature cattle had GHR mRNA size (determined by Northern blot) and cDNA sequence that were similar to control cattle and, therefore, were unlike most Laron dwarf genotypes in which the GHR gene is mutated. Amounts of mRNA from liver as well as muscle (superficial neck and longissimus) were analyzed by ribonuclease protection assay for IGF-I, total GHR, GHR 1A (inducible, liver-specific GHR mRNA), and GHR 1B (constitutive GHR mRNA). Four control and five miniature bulls were tested. As expected, liver IGF-I mRNA was decreased in the miniature cattle (approximately 12% of control; P < 0.01). The amount of the total GHR as well as GHR 1A mRNA were also decreased in liver (17% and 19% of control, respectively; P < 0.01). Other GHR mRNA, including GHR 1B mRNA, were similar for miniature and control cattle. In muscle, there was a tendency (P < 0.10) for decreased IGF-I mRNA and increased GHR mRNA in miniature compared with control cattle. In summary, a novel phenotype for Laron dwarfism in Bos indicus cattle was associated with underexpression of GHR 1A mRNA, but not other GHR mRNA variants in liver. In addition to decreased GHR 1A mRNA, the miniature cattle had decreased liver IGF-I mRNA. Full expression of GHR 1A in liver, therefore, may be required for full liver IGF-I expression and normal growth.

Differences between Brahman and Holstein cows in response to estrus synchronization, superovulation and resistance of embryos to heat shock.

Embryos from Bos indicus are more resistant to elevated culture temperature (i.e. heat shock) than embryos from some Bos taurus breeds. The present experiment was designed to determine if Brahman embryos have greater resistance to heat shock than Holstein embryos at a stage in development before the embryonic genome was fully activated. A second objective was to test breed effects on estrus synchronization and superovulation responses. A total of 29 Brahman and 24 Holstein cows were subjected to estrus synchronization using gonadotropin releasing hormone (GnRH) and prostaglandin F2alpha (PGF2alpha) superovulation. Embryos were collected at 48 h and day 5 after insemination. There was a tendency for a lower proportion of Brahmans to be detected in standing estrus than Holsteins. There were no differences between breeds in the proportion of cows detected in estrus using both tailpaint and standing estrus as criteria or in interval from PGF2alpha to estrus. The degree of synchrony in estrus was greater for Brahmans. Superovulation response was generally similar between breeds. At 48 h after insemination, there was a tendency for a greater proportion of Brahman oocytes to have undergone cleavage. Uncleaved oocytes were cultured for an additional 24 h-at this time, cleavage rate was similar between breeds. When embryos reached the 2-4-cell stage, they were heat-shocked for 4.5 h at 41 degrees C. This heat shock reduced the proportion of embryos that developed to the blastocyst stage but there was no breedxtreatment interaction. At day 5 after insemination, the number of embryos recovered was too low to allow comparison of breed effects. In conclusion, genetic effects on cellular thermotolerance that make Brahman embryos more resistant to heat shock are not expressed at the 2-4-cell stage. There were few differences between Brahman and Holstein in response to estrus synchronization and superovulation. The fact that cleavage tended to occur earlier in Brahman than Holstein embryos suggests breed differences in timing of ovulation, fertilization or events leading to cleavage.