Reproductive response of crossbred Bos taurus x Bos indicus cows to biostimulation by pre-pubertal and pubertal teasers

Although, the beneficial effect of biostimulation on reproduction has been reported, the influence of selectivity and social factors on the response to biostimulation has not received sufficient research attention in both, Bos indicus and Bos indicus influenced cattle. Moreover, "green and cheap" strategies to improve cattle reproduction are currently in demand while Bos indicus influenced cattle with inferior reproductive performance and farmers with economic limitations are common in tropical zones. Hence, to assess the reproductive response of crossbred taurus x indicus cows to biostimulation by pre-pubertal (PPM) or pubertal (PM) teasers males, two trials of two years each were conducted. Trial 1 n=187 cows (Year 1:85 cows exposed to PPM and Year 2:102 cows exposed to PM). Trial 2 n=196 cows (Year 1:101 cows exposed to PPM and Year 2:95 cows exposed to PM). The effect of exposing cows to PPM and PM on the intervals calving to first service (ICFS), calving to conception (ICC) and economic cost of days open (ECDO) was analyzed using Kruskal-Wallis ANOVA and the effect of exposing cows to PPM and to PM on reproductive status at 90d (RS90) and proportion of cows requiring hormonal protocols (PRH) was compared using χ² analysis. Both, ICFS and ICC were shorter (P<0.0001) for PM-exposed females (96.12±4.1 and 110.93±2.9 d; respectively) than for those PPM-exposed (134.41±3.3 and 135.64±2.4 d; respectively). With RS90, more (P<0.0001) PM-exposed cows (50.7%) were pregnant than PPM-exposed cows (16.1%). The PRH was greater (P<0.0001) in PPM-exposed cows (79.0 %) compared to PM-exposed (27.9%). The ECDO was less (P<0.0001) in PM-exposed cows (US$ 142.9±3.8) than PPM-exposed (US$ 176.3±2.9). In conclusion, cows exposed to PM had shorter ICFS and ICC than cows exposed to PPM. More cows exposed to PM were pregnant after 90d and PRH was less than cows exposed to PPM. Cows exposed to PM had a reduced ECDO than those exposed to PPM.

Effects of the SLICK1 mutation in PRLR on regulation of core body temperature and global gene expression in liver in cattle

The SLICK1 mutation in bovine PRLR (c.1382del; rs517047387) is a deletion mutation resulting in a protein with a truncated intracellular domain. Cattle carrying at least one allele have a phenotype characterized by a short hair coat (slick phenotype) and increased resistance to heat stress. Given the pleiotropic nature of prolactin, the mutation may affect other physiological characteristics. The liver is one organ that could potentially be affected because of the expression of PRLR. The mutation is a dominant allele, and heterozygous animals have a similar hair coat to that of animals homozygous for the mutation. Present objectives were to determine whether inheritance of the SLICK1 mutation affects liver gene expression and if animals homozygous for the SLICK1 allele differ from heterozygotes in liver gene expression and regulation of body temperature during heat stress. In one experiment, rectal and ruminal temperatures were less for Holstein heifers that were heterozygous for the SLICK1 allele compared with wildtype heifers. There were 71 differentially expressed genes in liver, with 13 upregulated and 58 downregulated in SLICK1 heterozygotes. Among the ontologies characteristic of differentially expressed genes were those related to immune function and fatty acid and amino acid metabolism. In a prospective cohort study conducted with adult Senepol cattle, body temperature and hepatic gene expression were compared between animals heterozygous or homozygous for the SLICK1 mutation. There were no differences in ruminal temperatures between genotypes, rectal temperature was higher in animals homozygous for the SLICK1 mutation, and there was only one gene in liver that was differentially expressed. It was concluded that inheritance of the SLICK1 allele can exert functional changes beyond those related to hair growth although changes in liver gene expression were not extensive. Results are also consistent with the SLICK1 allele being dominant because there were few differences in phenotype between animals inheriting one or two copies of the allele.

Genome-wide scan reveals important additive and non-additive genetic effects associated with resistance to Haemonchus contortus in Florida Native sheep

Florida Native sheep is among the sheep breeds best adapted to humid and hot climatic conditions such as those of Florida, USA, and have shown a superior ability to regulate nematode burdens. This is one of the oldest sheep breeds in North America and is an endangered species. To ensure genetic diversity and long-term survival of the breed, protection of the current genetic stock is critical and conservation efforts are required to promote its breeding and production. The objective of the present study was to investigate the importance of additive and non-additive genetic effects on resistance to natural Haemonchus contortus infections in Florida Native sheep using a whole genome scan. A total of 200 sheep were evaluated in the present study. Phenotypic records included faecal egg count (FEC, eggs/gram), FAMACHA® score, packed cell volume (PCV, %), body condition score and average daily gain (ADG, kg). Sheep were genotyped using the GGP Ovine 50K SNP chip and 45.2 k single nucleotide polymorphism (SNP) markers spanning the entire genome were available for quality control procedures. Mixed models were used to analyse the response variables and included the identity by state matrix to control for population structure. Bonferroni correction was used to control for multiple testing and a second arbitrary threshold (0.1 × 10^-3) was used. Fifteen SNPs with additive and non-additive genetic effects and located in Ovis aries chromosome OAR1, 2, 3, 6, 8, 10, 11, 12, 13 and 21 were associated with FEC, FAMACHA® score, PCV and ADG. These SNPs could be potential genetic markers for resistance to natural H. contortus exposure in Florida Native sheep.

Systemic humoral immunity in beef bulls following therapeutic vaccination against Tritrichomonas foetus

The utility of therapeutic vaccination of bulls against Tritrichomonas foetus has been advocated in previous studies, but anecdotal reports suggest this practice does not clear infections and may additionally confound diagnostic testing by reducing parasite burdens below detectable limits. The objective of this study was to characterize the systemic humoral immune response to therapeutic vaccination in T. foetus-infected bulls over a period of four months using an indirect ELISA and to compare the dynamics of this response to culture and PCR results to establish the existence of a relationship (or lack thereof) between immunization and infection status. A study population of 4- to 6-year-old T. foetus-infected beef bulls (n = 20) was divided equally into a treatment group and a control group. The treatment group received two doses of commercially prepared whole cell killed vaccine 2 weeks apart while the control group received injections of vaccine diluent. Blood samples were collected at each injection and at 4 subsequent dates every 4 weeks thereafter (i.e. 0, 2, 6, 10, 14, and 18 wks) to measure IgG₁ and IgG₂ antibody subisotype response via an indirect ELISA. Preputial smegma samples were collected at the four monthly intervals following vaccination for diagnosis of infection via InPouch™ culture, Modified Diamond's Medium (MDM) culture, and PCR. Humoral response for both IgG isotypes from week 2 through week 18 were significantly increased in vaccinates compared to controls. No significant decrease in infection prevalence was detected in the treatment group for any of the diagnostic methods used. The apparent lack of pathogen clearance during a stimulated immune response suggests that therapeutic vaccination may not be a useful T. foetus management practice.

Lymphatic fluid for the detection of Mycobacterium avium subsp. paratuberculosis in cows by PCR, compared to fecal sampling and detection of antibodies in blood and milk

Johne's disease (JD), caused by Mycobacterium avium subsp. paratuberculosis (MAP), can cause considerable economic losses in affected herds. Early diagnosis of JD is hampered by the chronic nature of the disease with a slow subclincal progression. The aim of the present study was to challenge the hypothesis that lymphatic fluid is of diagnostic value in the early stages of the disease. Lymphatic fluid from 122 animals was collected and tested for MAP by nested PCR for IS900 and compared to the results of testing for MAP in feces (culture), blood and milk (ELISA) in 110 of these samples. MAP was detected by PCR in 27.1% of the lymph samples. Agreement between the tests was poor: 6.9% of the lymph positive cows were also positive in all other tests applied, and 69.0% had negative results in fecal culture, blood and milk ELISA. Resampling of 25 cows after 8 to 12 and 16 to 20 months revealed 20.0% lymph positive animals at the first, 5.5% at the second and 27.8% at the third sampling, respectively. Only one cow showed positive lymph-PCR results at more than one sampling date. Lymph-positive cows had a 7.2 times greater likelihood of being culled within 8 to 12 months after sampling, compared to negative cows, mainly due to other health issues than JD. It can be concluded, that lymphatic fluid might be promising for the detection of early MAP-infection in cows, but further studies to elucidate the potential of this diagnostic approach are needed.

Subspecies differences in early fetal development and plasma pregnancy-associated glycoprotein concentrations in cattle

Inclusion of Bos indicus genetics improves production traits of cattle maintained in hot climates. Limited information exists detailing pregnancy-specific events as influenced by variable amounts of Bos indicus genetics. Three experiments were completed to examine the effect of Bos taurus and Bos indicus genotypes on fetal size and plasma pregnancy-associated glycoprotein (PAG) concentrations. In all experiments, cows were bred by AI after synchronization of ovulation. Fetal measurements were completed by transrectal ultrasonography and plasma PAG concentrations were quantified from plasma harvested the day of each fetal measurement. In Exp. 1, fetal size and plasma PAG concentrations were measured at d 53 of pregnancy in cows composed of various fractions of Angus and Brahman (n = 9 to 21 cows/group). Fetus size was greater in cows containing >80% Angus genetics compared with cows containing <80% Angus influence (3.40 ± 0.28 vs. 2.86 ± 0.28 cm crown-rump length; P < 0.01). Plasma PAG concentrations were reduced (P < 0.01) in cows containing >80% Angus genetics when compared with their contemporaries (6.0 ± 1.5 ng/mL vs. 9.4 ± 1.5 ng/mL). In Exp. 2, fetal measurements and plasma PAG concentrations were determined at d 35 and 62 of pregnancy in Angus and Brangus cows. Breed did not affect fetus size at d 35, but Angus cows contained larger fetuses than Brangus cows at d 62 [3.0 ± 0.03 vs. 2.8 ± 0.03 cm crown-nose length (CNL; P > 0.01)]. Plasma PAG concentrations were not different between breed at d 35 and 62 (P > 0.1). In Exp. 3, fetal measurements and plasma samples were collected at d 33/34, 40/41, 47/48, and 54/55 post-AI in Angus and Brangus cows. Fetus size was not different (P > 0.05) between genotypes on d 33/34, 40/41, and 47/48. Angus fetuses were larger than Brangus fetuses at d 54/55 (2.1 ± 0.03 vs. 1.9 ± 0.03 cm CNL; P = 0.001). Plasma PAG concentrations were less in Angus than Brangus cows at each time point (average 4.9 ± 0.9 vs. 8.2 ± 0.9 ng/mL; P = 0.005). In conclusion, these studies determined that the Bos taurus × Bos indicus genotype impacts fetal size and rate of fetal development by 7 wk of gestation. Plasma PAG concentrations were increased in cattle with Bos indicus genetics in 2 of 3 studies, suggesting that genotype is one of several determinants of PAG production and secretion in cattle.

The collection of lymphatic fluid from the bovine udder and its use for the detection of Mycobacterium avium subsp. paratuberculosis in the cow

The objective of the current study was to evaluate the feasibility of lymph collection from the bovine udder and to investigate if the lymphatic fluid might be of diagnostic value in cows infected with Mycobacterium avium subsp. paratuberculosis (MAP), the etiologic agent of paratuberculosis. Lymph fluid collection was attempted from 58 cows, and the reactions of the cows as well as the level of difficulty of the procedure were recorded in 56 animals. Lymph samples (51 in total) were tested for the presence of MAP by nested polymerase chain reaction. Collection of the lymphatic fluid caused no or mild signs of discomfort in 94.6% of the cows; in 51.8% of cows, lymphatic fluid was attained on the first attempt, while sample collection was unsuccessful in 12.1%. Mycobacterium avium subsp. paratuberculosis was detected in 43.1% of all lymph samples. The bacterium was present in 66.7% of cows with clinical Johne’s disease, in 42.8% of asymptomatic cows with a positive or suspicious enzyme-linked immunosorbent assay (ELISA) result in blood, and in 38.7% of cows with a negative ELISA result in blood. The present study shows that the procedure was well tolerated by most cows and can easily be performed on farm. The current report of the isolation of MAP from lymph fluid suggests that the present approach could be used for the early detection of Johne’s disease in cattle.

Evaluation of 2 sources of Angus cattle under South Florida subtropical conditions

The objective of this study was to compare performance and aspects of adaptability attributes of cattle from a Florida Angus bloodline (local source from a mostly closed herd for over 50 yr) to cattle that are representative of modern Angus bloodlines (outside source) in US subtropical conditions. Embryos from both sources were transferred to Brahman-crossbred cows in South Florida, and calves (n=82) were born in 3 yr. Before weaning, summer tympanic temperatures were recorded hourly for 3 d in each year. Heifers were placed with fertile bulls until diagnosed pregnant. Traits relative to sexual maturation of bulls were recorded at 1- or 2-mo intervals until approximately 17 mo of age. Calves from outside sources had greater hip height at weaning than calves from the local source (P<0.001; 108.8 ± 0.62 and 104.7 ± 0.68 cm, respectively). Local-source calves (n=37) had greater (P=0.03) exit velocity (2.7 ± 0.3 m/s) than outside-source (n=45) calves (2.0 ± 0.29 m/s), which may be indicative of more nervous or temperamental disposition. However, no source differences were detected for other assessments of disposition (chute or pen score, P>0.8). Few source differences for minimum, maximum, or range of daily tympanic (inner ear) temperatures were detected. At 17 mo of age, outside-source heifers were heavier (P = 0.05) and had greater (P<0.001) hip height than Angus heifers from the local source. Heifers from the outside source were younger (P<0.001) at the time of their first conception (454 ± 17.5 d) than heifers from the local source (550 ± 16.9 d). Outside-source heifers also had greater (P<0.02) pregnancy and calving rates (0.7 ± 0.119 and 0.62 ± 0.125, respectively) from exposure to bulls within a year from weaning than the heifers from the local source (0.29 ± 0.089 and 0.19 ± 0.077, respectively). Bulls from the outside source were heavier (P=0.05) at 320 d of age than local-source bulls. From 14 through 17 mo of age, outside-source bulls had greater (P≤0.05) scrotal circumference and tended (P≤0.15) to be heavier than local-source bulls. There appeared to be no performance or adaptation advantages for the local-source Angus through 17 mo of age. The large source difference for age at first conception in heifers merits additional attention and comparison with cow lifetime production performance for the 2 sources.

Diagnostic accuracy of methods for detecting Anaplasma marginale infection in lactating dairy cattle of Puerto Rico

Bovine anaplasmosis (BA) is a hemoparasitic disease of great importance in cattle within the tropical and subtropical regions of the world. Control programs for BA require accurate diagnostic assays but validation can be challenging because the true disease status of all animals is frequently not known with certainty. The objective of this study was to estimate the accuracy of assays for detection of Anaplasma marginale infection in lactating dairy cattle of Puerto Rico using Bayesian methods without a perfect reference test. There were 2,331 cattle with complete diagnostic results sampled from 79 herds, and the prevalence of BA was estimated as 22% (95% probability interval [PI]: 19-25%). The sensitivity (Se) and specificity (Sp) of a major surface protein 5 competitive enzyme-linked immunosorbent assay (MSP-5 cELISA) were estimated as 99% (95% PI: 96-100%) and 89% (95% PI: 87-92%), respectively. The Se and Sp of a quantitative polymerase chain reaction (qPCR) were 67% (95% PI: 60-74%) and 99% (95% PI: 99-100%). The Se and Sp of a card agglutination test were 34% (95% PI: 29-39%) and 99% (95% PI: 99-100%). Area under the receiver-operating characteristic curve for the MSP-5 cELISA was 0.748 (95% PI: 0.71-0.79). The MSP-5 cELISA appears to be the test of choice for screening cattle for subclinical BA based on the high estimated Se, rapidity of results, relative low cost, and ease of standardization.

Reproductive performance of beef heifers: effects of vulvo-vaginitis, Ureaplasma diversum and prebreeding antibiotic administration

A group of 450 heifers, 13 to 15 mo of age, were individually identified, vaccinated (IBR, PI(3), Leptospira, Campylobacter fetus), examined (body condition score, reproductive tract evaluation, assessment of vaginal lesions), and cultured for U. diversum . Heifers were randomly allocated to either a treated group given chlortetracycline (approximately 350 mg/hd/d for 30 d in a grain crumble) or a nontreated control group. Prebreeding, most heifers showed signs of vulvovaginitis, 44% cultured positive for U. diversum . Significant associations were found between the severity of vaginal lesions and ovarian activity (P < 0.05), and between BCS and ovarian activity (P < 0.02). The U. diversum vaginal culture (positive or negative) showed no significant association with BCS, severity of vaginal lesions, or ovarian activity (all were P > 0.5). At pregnancy examination (35 d following conclusion of a 61-d breeding season), treated compared with nontreated heifers showed 1) a slight but not significant (P > 0.25) decrease in vaginal colonization by U. diversum (46 to 34% and 41 to 37%, respectively); 2) an association between increased severity of vaginal lesions and increasing pregnancy rate, especially in treated heifers; and 3) an increased pregnancy rate (72 and 57%, respectively; P < 0.01). Prebreeding treatment with chlortetracycline appeared to improve pregnancy rates in beef heifers with endemic U. diversum infections, although the role of U. diversum in heifer fertility is still not clear.

Candidate gene polymorphisms (BoIFNG, TLR4, SLC11A1) as risk factors for paratuberculosis infection in cattle

Paratuberculosis (Johne's disease) imposes a significant problem to the world dairy and beef industries and today is considered a potential zoonosis. The disease is caused by Mycobacterium avium subsp. paratuberculosis and is characterized by progressive weight loss and profuse diarrhoea. Susceptibility to infection is suspected to have a genetic component, and moderated values for heritability of infection have been reported. Interferon gamma is an inducible cytokine with a crucial role in the innate host response to intracellular bacteria. Toll-like receptors are trans-membrane structures responsible for coordination of innate and adaptive immune responses. The solute carrier family 11 member 1 (SLC11A1, formerly NRAMP1) gene plays an important role in innate immunity, preventing bacterial growth in macrophages during the initial stages of infection. The objective of this candidate gene case-control study was to characterize the distribution of polymorphisms in three candidate genes related to the immune function; interferon gamma (BoIFNG), toll-like receptor 4 (TLR4), and SLC11A1 genes and to test their role as potential risk factors for paratuberculosis infection in cattle. The statistical analysis demonstrated significant differences in allelic frequencies between cases and controls for BoIFNG-SNP(1)2781 and SLC11A1 microsatellites, indicating a significant association between infection and variant alleles. In the analysis of genotypes, a significant association was also found between infection status and BoIFNG-SNP(1)2781 and SLC11A1-275-279-281 microsatellites. However, when variables such as breed and age were included in the multivariate logistic regression analysis, a tendency toward statistical significance for the effect of polymorphisms in the odds of infection was only found for alleles SLC11A1-275 and 279.

Association between cow reproduction and calf growth traits and ELISA scores for paratuberculosis in a multibreed herd of beef cattle

The objective of this research was to assess the association between 4 cow reproductive and weight traits, and 2 preweaning calf traits and ELISA scores for paratuberculosis (0 = negative, 1 = suspect, 2 = weak-positive, and 3 = positive) in a multibreed herd of cows ranging from 100% Angus (A) to 100% Brahman (B). Cow data were 624 gestation lengths (GL), 358 records of time open (TO), 605 calving intervals (CI), and 1240 weight changes from November to weaning in September (WC) from 502 purebred and crossbred cows. Calf data consisted of 956 birth weights (BWT), and 923 weaning weights adjusted to 205 d of age (WW205) from 956 purebred and crossbred calves. Traits were analyzed individually using multibreed mixed models that assumed homogeneity of variances across breed groups. Covariances among random effects were assumed to be zero. Fixed effects were year, age of cow, sex of calf, year x age of cow interaction (except WC), age of cow x sex of calf interaction (only for WC), and covariates for B fraction of sire and cow, heterosis of cow and calf, and ELISA score. Random effects were sire (except for TO and CI), dam, and residual. Regression estimates of cow and calf traits on ELISA scores indicated that lower cow fertility (longer TO), lower ability of cows to maintain weight (negative WC), lower calf BWT, and lower calf WW205 were associated with higher cow ELISA scores. Further research on the effects of subclinical paratuberculosis in beef cattle at regional and national levels seems advisable considering the large potential economic cost of this disease.

Association among results of serum ELISA, faecal culture and nested PCR on milk, blood and faeces for the detection of paratuberculosis in dairy cows

Paratuberculosis is a chronic, infectious disease of ruminants that entails a serious concern for the cattle industry. One of the main issues relates to the efficiency of diagnosis of subclinically infected animals. The objective of this field study was to analyse the association among results of a serum enzyme-linked immunosorbent assays (ELISA), faecal culture and nested PCR tests on milk, blood and faeces for Mycobacterium avium subsp. paratuberculosis detection in dairy cows. Faeces, blood and milk samples were collected from 328 lactating dairy cows in four known infected herds. Results were analysed to determine associations and levels of agreement between pairs of tests. A total of 61 animals (18.6%) tested positive when all the tests were interpreted in parallel. The agreement between results in different pairs of tests was poor, slight and fair in two, five and three of the 10 possible combinations respectively. Faecal culture and faecal polymerase chain reaction (PCR) resulted in the highest kappa coefficient (0.39; fair agreement), with the lowest agreement being for ELISA and blood PCR (-0.036; poor agreement). Fisher's exact test resulted in statistically significant associations (P < or = 0.05) between the following test pairs: ELISA : faecal culture; ELISA : faecal PCR; milk PCR : faecal PCR, blood PCR : faecal PCR and faecal culture : faecal PCR. Enzyme-linked immunosorbent assays showed the highest complementary sensitivity values for all the possible two-test combinations, followed by faecal PCR. The combined use of ELISA and faecal PCR has the potential to increase the overall sensitivity for the diagnosis of paratuberculosis infection.

Tritrichomonas foetus

Tritrichomonas foetus is a venereal disease of cattle that has a clear pattern of adverse reproductive sequela in the affected female, with a carrier state in the bull in which he shows no outward signs. Given sexual rest and symptomatic treatment, the female returns to reproductive viability. In contrast, the male remains infective and is a risk to other female contacts. Prevention of the disease relies on excluding infected males and females from the population of susceptible cattle. Control of this disease requires a plan to identify, isolate, and treat infected females, and eliminate or cull infected males. Improvements in culture technique and the application of newer methods, such as polymerase chain reaction, enhance the likelihood of detecting infected animals.

Factors associated with ELISA scores for paratuberculosis in an Angus-Brahman multibreed herd of beef cattle

Cow and calf genetic and environmental factors were evaluated for their association with ELISA scores for paratuberculosis in a multibreed population of beef cattle. The ELISA scores are a measure of the presence or absence of antibodies against Mycobacterium avium subsp. paratuberculosis in bovine serum. The linear mixed-model analysis used 352 ELISA scores from 238 cows: 51 Angus (A); 34 Brahman (B); 41 (3/4 A 1/4 B); 45 (1/2 A 1/2 B); 34 (1/4 A 3/4 B); and 33 Brangus (5/8 A 3/8 B). Cows were assumed to be unrelated. Year affected (P < 0.001) ELISA scores, but age of cow did not, which was expected to be significant because of the chronic progressive nature of this disease. Important regressions on fixed effects associated with cows were 1) a positive estimate of cow B breed effect (0.59 +/- 0.24; P < 0.017), indicating an upward trend of ELISA scores toward 100% B cows; 2) a negative estimate for weight change from before calving (late November) to the date of the blood sample in May (-0.0062 +/- 0.0019 score/kg; P < 0.002), indicating that poorer maintenance of cow weights was associated with higher ELISA scores; and 3) a positive estimate for days in lactation of cow on the date of the blood sample (0.0086 +/- 0.0034 score/d; P < 0.021), indicating the production of larger amounts of antibodies against Mycobacterium avium subsp. paratuberculosis as lactation progressed. Relevant regressions on fixed effects associated with calves were 1) calf birth weight (-0.022 +/- 0.010 score/kg; P < 0.035), and 2) calf gain from birth to the date of the cow blood sample (-0.0092 +/- 0.0027 score/kg; P < 0.001). These estimates indicate that cows that produced lighter calves at birth and/or calves with slower preweaning growth tended to have greater ELISA scores. Although the sensitivity (percentage of infected animals detected) of ELISA was only 50%, these results suggest that subclinical paratuberculosis may be negatively affecting cows and their offspring. Factors identified as associated with ELISA scores could help producers with culling decisions related to paratuberculosis control and eradication in beef cattle.

Effect of biostimulation on the expression of estrus in postpartum Angus cows

The objective of this study was to evaluate the effect of biostimulation by bull exposure on the expression of estrus in postpartum Angus cows. Ninety Angus cows and their calves were allocated by parity and body frame to three pens (30/pen). From 1-week post partum, one epididectomized mature Angus bull was placed with Groups A and B (BE), whereas Group C served as a Control (NE). Data for duration of estrus (DE), total mounts received (TMR), and intensity of estrus (IE) were recorded using HeatWatch. At either the first or second postpartum estrus, there were no differences between BE and NE cows for DE, TMR and IE. However, the period after onset of estrus, cow within treatment and the interaction treatment by period exerted a significant influence on IE. Overall, the greatest IE (P<0.0001) was observed during the first two periods (6h). At the first postpartum estrus, IE tended (P<0.11) to be greater in BE than NE cows during the first 3h after onset of estrus. However, IE was greater (P<0.02) in NE cows than BE cows during 4-6h after onset of estrus. At the second postpartum estrus, IE did not differ between BE and NE cows during the first 3h after onset of estrus. However, from 4 to 9h after onset of estrus, IE was greater (P<006) in NE cows than BE cows. From the results of this study, it was concluded that DE, TMR and IE were not influenced by biostimulation. However, the manner in which mounting activities were distributed across the duration of estrus was influenced by the presence of bulls.

Assessing Performance of Cow-Calf Operations Using Epidemiology

This article examines the epidemiologic tools available to the cow-calf beef veterinarian (and cattle producer) to assess the performance of the beef cow herd and to examine ways in which these tools may be used.

Effect of biostimulation on uterine involution, early ovarian activity and first postpartum estrous cycle in beef cows

The objective was to determine the effect of biostimulation (bull-exposure) on uterine involution (UI), plasma progesterone concentration (P4), size of largest follicle (LF), number of follicles larger than 5 mm ( F > or = 5 ), presence of fluid in uterine lumen (PF), presence of luteal tissue (LT), and length of the first estrous cycle postpartum (LEC). Ninety Angus cows with calves were allocated by parity and body frame into three groups (30 per group) 1 week postpartum. Two groups were exposed to bulls (BE) and one non-exposed group (NE) served as a control. Data were collected during weekly sessions of palpation per rectum, ultrasonography and bleeding on a subgroup of 30 cows (10 cows per group) for 6 weeks, and permanent surveillance of estrus with HeatWatch on all 90 cows. There were no significant differences between BE and NE cows for UI ( 17.1+/-1.1 days versus 20.1+/-1.6 days), LF ( 9.5+/-1.7 mm versus 11.0+/-2.4 mm), F > or = 5 ( 1.20+/-0.3 versus 1.47+/-0.09 ), and PF. However, LT was detected in more BE than NE cows (13 versus 2; P<0.001 ). Overall differences in P4 were found between BE and NE cows with detected LT ( 2.00+/-0.3 ng/ml versus 1.05+/-0.4 ng/ml, respectively; P<0.05 ). More BE cows resumed reproductive cyclicity with estrous cycles normal in length compared with NE cows (16/30, 53%; 16/30, 53%; and 8/30, 26.6%, for the two BE groups and the NE group, respectively; P<0.01 ). In conclusion, BE hastened luteal function but did not affect uterine involution.

Epidemiology of Tritrichomonas foetus in beef bull populations in Florida

The objectives of this study were to estimate the prevalence of herd and individual bull infection with Tritrichomonas foetus in a survey of beef bulls in the state of Florida and to perform an epidemiological investigation of risk factors for the disease. Bulls were tested for T. foetus colonization by a single preputial scraping and culture. Bull infection prevalence within herds was calculated and relationships with bull, herd factors, and production measurements were determined. The survey included 1984 beef bulls in 59 herds throughout Florida; nine bulls in three small herds (<100 cows) were later excluded from the models. An overall prevalence for T. foetus-infected bulls was 6.0% (within-herd prevalence ranged from 0 to 27%). The herd prevalence was 30.4% (i.e. at least one infected bull); infected bulls were found in 11.1 and 39.5% of herds sampled in North and South Florida, respectively. The likelihood of disease was greatest in larger herds in more extensive management settings (> or = 500 cows, 53.9% prevalence; medium-sized herds of 100-499 cows, 10.0% prevalence). Tritrichomonas foetus infection was associated with several bull factors, including age, breed, herd, and herd management practices (bull-to-cow ratio, bulls per breeding group). Tritrichomonas foetus infection continues to be prevalent in beef herds in Florida that use natural service.

Synchronization of Bos indicus x Bos taurus cows for timed artificial insemination using gonadotropin-releasing hormone plus prostaglandin F2alpha in combination with melengestrol acetate

Nonlactating Bos indicus x Bos taurus cows were used in three herds to determine the efficacy of different PGF2alpha treatments in combination with GnRH and melengestrol acetate (MGA) for a timed artificial insemination protocol. The start of the experiment was designated as d 0, at which time cows were assigned a body condition score and received 100 microg of GnRH. Cows were fed MGA (0.5 x mg x cow(-1) x d(-1)) on d 1 to 7. On d 7, cows received either a single injection of PGF2alpha (Lutalyse sterile solution; 25 mg; n = 297), a single injection of cloprostenol sodium (Estrumate; 500 microg; n = 297), or half the recommended dose of PGF2alpha (12.5 mg; n = 275) on d 7 and 8. On d 10, all cows were artificially inseminated and received 100 microg of GnRH. Pregnancy rates to the timed artificial insemination (39%) were not affected by treatment, herd, or treatment x herd. There was an effect (P < 0.01) of artificial insemination sire on timed artificial insemination pregnancy rate for one herd, but not the other two herds. Herd influenced (P < 0.05) 30-d pregnancy rates, but there were no treatment or treatment x herd effects as 72.3% of the cows became pregnant during the first 30 d of the breeding season. Results indicate that the type of PGF2alpha treatment administered 7 d after GnRH did not influence timed artificial insemination pregnancy rates in nonlactating Bos indicus x Bos taurus cows.

Effect of chlortetracycline in a trace mineral salt mix on fertility traits in beef cattle females in Florida

The study objective was to determine the effect of chlortetracycline in an ad libitum trace-mineralized salt mix given to heifers before and(or) during bull exposure on the proportion pregnant and the time to conception in a fixed breeding period. Heifers (n = 768), 13 to 15 mo of age, were individually identified, immunized (Leptospira, Campylobacter fetus), examined (body condition score, vaginal lesion score, BW), and randomly allocated within 2 x 2 factorial blocks of treatments where trace mineral salt with and without chlortetracycline medication was provided in similar but nonadjacent pastures either before and(or) during bull exposure. The chlortetracycline feeding period was about 30 d for each. In the 2 d immediately before bull exposure, heifers were examined (body condition score, vaginal lesion score, reproductive tract evaluation) and reallocated to treatment pastures. Pregnancy was determined by per rectal palpation at 45 d following bull removal. Mineral intake was below that expected for heifer groups and, as a result, chlortetracycline intake was estimated at less than one-third of that targeted. Many heifers were not cycling reproductively at the onset of bull exposure (n = 456, 60.3%, based on a reproductive tract score < 3). Despite these limitations, heifers receiving chlortetracycline treatment before breeding had a pregnancy percentage of 65% (chlortetracycline before and during breeding 67% and chlortetracycline before breeding 61.8%) compared to those receiving no treatment before breeding (53%, P < 0.03; no chlortetracycline before or during breeding 60.4% and chlortetracycline during breeding 47.4%). Heifers receiving chlortetracycline treatment before breeding were 57% more likely to become pregnant than those not treated before breeding. Change in vaginal lesion score was associated with the proportion pregnant, but neither body condition score nor average daily gain were.

Environmental, genetic and social factors affecting the expression of estrus in beef cows

Genetic, social and environmental factors affecting behavioral estrus were evaluated in Angus (n = 10), Brahman (n = 10) and Senepol (n = 10) cows during a PGF2alpha synchronized estrus and subsequent spontaneous estrus. Cows were equally stratified by breed to two groups of 15. Both groups were pre-synchronized with a modified two-injection PGF2alpha protocol. At the start of the experiment, cows were treated with 25 mg PGF2alpha followed by a second and third administration of 12.5 mg PGF2alpha, 11 and 12 days later to induce synchronized estrus. The subsequent estrus was designated as spontaneous estrus. Behavioral estrus data including the onset and end of estrus, estrous duration and the total number of mounts received for the synchronized and spontaneous estruses were collected using HeatWatch". Interval from the third PGF2alpha, treatment to the onset of a HeatWatch" estrus occurred earlier (P < 0.05) in Angus (31 +/- 5 h) than Brahman (53 +/- 7 h) or Senepol (53 +/- 4 h) cows, with dominant Senepol and Brahman cows taking longer to exhibit estrus after PGF2alpha than subordinate cows. The duration of the synchronized estrus tended to be shorter (P < 0.06) in Senepol (12 +/- 3 h) than in Angus (19 +/- 2 h) or Brahman (17 +/- 2 h) cows. Behavioral estrus data between the two periods were confounded by greater temperature-humidity index (THI) values during spontaneous estrus. The THI during spontaneous estrus appeared (P = 0.09) to affect the duration of estrus (9 +/- 1 h versus 16 +/- 1 h) and did affect (P < 0.0001) the total number of mounts received (8 +/- 4 mounts versus 34 +/- 4 mounts) during spontaneous estrus compared to synchronized estrus. Breed had no effect (P > 0.10) on the duration and total number of mounts received during synchronized and spontaneous estruses. In conclusion, type of estrus (synchronized or spontaneous), THI, social dominance and breed exerted significant effects on characteristics associated with behavioral estrus in beef cattle in subtropical environments.

Assessment of estrus detection by visual observation and electronic detection methods and characterization of factors associated with estrus and pregnancy in beef heifers

One hundred and sixty-four beef heifers representing Angus, Brahman and their crosses were subjected to estrus synchronization treatment following evaluation of weight, body condition score and reproductive tract. Heifers were assigned to 1 of 2 methods of estrus detection, either visual observation for signs of standing estrus or a rump-mounted pressure-sensitive detection device. All heifers were artificially inseminated during a 25d insemination period and then bred by a bull. The effectiveness of estrus detection and timely insemination were evaluated by the type of detection method, breed and breeding event resulting in a pregnancy. Although there was not a significant difference in first service conception for method of detection, at the end of a 25-d insemination period, 60.5% of the visually observed heifers were pregnant, while only 45.8% of the heifers detected by the mount detection device were pregnant (P = 0.05). The reduced 25-d conception rate in the pressure-sensitive detection group suggested that insemination of detected heifers may not have been optimal for pregnancy. The mean time to estrus after implant removal and the time of insemination were evaluated. Heifers pregnant at the first service had a shorter time to estrus (32.11 +/- 1.6 h, P=0.13), a longer mean interval from the start of estrus to insemination (12.10 +/- 1.2 h, P = 0.16) and a positive mean interval between the end of standing estrus and the time of insemination (3.17 +/-1.7 h, P=0.19) than heifers not conceiving at the synchronized estrus (38.5 +/- 2.1, 7.42 +/- 1.9 h and -2.04 +/- 2.1 h, respectively). Breed differences were observed in estrus durations (Angus 8.52 +/- 1.2 h, Brahman 6.65 +/- 1.2 h, crossbred 11.90 +/- 1.2 h; P = 0.03), number of mounts (19 +/- 3.6, 25 +/- 5.4, 37 +/- 5.5, respectively; P=0.02) and gestation length (281 +/- 1.2, 291 +/- 1.8, 286 +/- 1.1 d, respectively; P = 0.001).

Prevalence of Tritrichomonas fetus in a bull population and effect on production in a large cow-calf enterprise

OBJECTIVE

To determine prevalence of infection with tritrichomonas fetus in a bull population; assess influence of age, breed, and grouping; assess effects on measures of cow performance (pregnancy rate, weaning percentage, weaning weight); and estimate test sensitivity.

DESIGN

Epidemiologic study.

ANIMALS

1,383 bulls and records for 28,471 cows bred by these bulls in the immediate past breeding season.

PROCEDURE

Bulls in 11 cattle units on a large ranch were tested for T fetus colonization by vigorous preputial scraping and protozoologic culture until no newly infected bulls were identified. Bull infection prevalence within units was calculated and correlated to production measurements reported for each cattle unit.

RESULTS

Mean prevalence of T fetus-infected bulls was 11.9% (range, 0 to 35.9%). Significant difference was detected between mean age of infected bulls (5.5 years) and noninfected bulls (3.9 years). Difference in prevalence among breeds was found, although other factors may have influenced this finding. Cow performance measurements (weaning percentage, mean weaning weight, and adjusted mean weaning weight/exposed cow) for cows exposed by breeding to bull groups with the highest prevalence of infection (35.9%) were significantly different from mean values for the entire study population. Test sensitivity for this study (73%) was less than that reported in other studies.

CLINICAL IMPLICATIONS

T fetus infection in a natural service beef herd has an adverse impact on several production measures: Severity of impact is related to prevalence of infection in the bull population, where prevalence is bull age and population dependent.

Selenium toxicosis in a flock of Katahdin hair sheep

Selenium supplementation by injection is a common practice. Acute toxicosis from dosaging errors may occur. In this report, 23 of 56 ewes and all 24 lambs injected with selenium died. Tissue, whole blood, and serum concentrations aided in the diagnosis. Caution should be taken when supplementing selenium by injection.

Effect of exogenous insulin on plasma and follicular insulin-like growth factor I, insulin-like growth factor binding protein activity, follicular oestradiol and progesterone, and follicular growth in superovulated Angus and Brahman cows

Angus (n = 14) and Brahman (n = 14) cows were used to evaluate the effects of insulin administered concomitantly with FSH in a superovulation regimen. Cows were allotted to four pen replicates by treatment and breed, and received FSH (i.m.) twice a day for 5 consecutive days (first day of injections = day 0 of study) plus concomitant administration of either saline (control) or long-acting bovine insulin (0.25 iu kg-1 body mass; s.c.). Blood samples were collected at intervals of 6 h during the injection period and analysed for plasma insulin, glucose, insulin-like growth factor I (IGF-I) and IGF-I binding protein (IGFBP) activity. Cows were ovariectomized on day 5. The number and diameter of follicles were recorded. Follicular fluid was aspirated for determination of IGF-I, IGFBP activity, oestradiol and progesterone. Mean plasma concentration of glucose was lower in insulin-treated than in control cows averaged over days 1-5 (56 +/- 3 versus 82 +/- 3 mg dl-1; P < 0.01). Plasma concentration of IGF-I and IGFBP activity were not affected (P > 0.10) by treatment, but were higher in Brahman than in Angus cows (IGF-I: 41 +/- 6 versus 19 +/- 6 ng ml-1, P < 0.05; IGFBP activity: 17.5 +/- 0.4 versus 15.8 +/- 0.04% (10 microliters)-1; P < 0.03). Insulin treatment did not affect the number of small (1.0-3.9 mm), medium (4.0-7.9 mm) or large (> or = 8.0 mm) follicles. Brahman cows had a greater (P < 0.01) number of medium and total follicles (19.4 +/- 2.5 and 60.5 +/- 5.5, respectively) than did Angus cows (7.5 +/- 2.6 and 30.5 +/- 5.6, respectively). Diameter of large follicles was greater in insulin-treated than in control cows (11.4 +/- 0.2 versus 10.6 +/- 0.1 mm; P < 0.05). Follicular fluid IGF-I concentration in large follicles was higher in insulin-treated Brahman cows (60 +/- 2 ng ml-1) than in control Brahman cows (37 +/- 2 ng ml-1), but was lower in insulin-treated Angus cows (31 +/- 3 ng ml-1) than in control Angus cows (38 +/- 2 ng ml-1; treatment x breed interaction, P < 0.01). IGFBP activity in fluid from large follicles was not affected by insulin treatment in Brahman cows but was reduced (P < 0.05) by insulin treatment in Angus cows.(ABSTRACT TRUNCATED AT 400 WORDS)

Safety assessment of moxidectin 1% injectable on reproductive performance in beef cows

The safety of moxidectin 1% injectable anthelmintic (0.6 mg/kg of body weight, 3 times the recommended dose) was evaluated in 145 reproductively sound, beef cows undergoing estrous cycle. Five treatment groups received moxidectin 1% injectable at specific times relative to a synchronized estrus (day 0): preovulatory treatment (day -2, treatment group 1), treatment at ovulation (day 0, group 2), and treatment after ovulation (days 7, 14, and 28, group 3, 4, and 5, respectively). Two groups of control cows received an injection of vehicle only at times corresponding to treatment in the other groups (6 at days -2, 7, and 28; 7 at days 0, 7, and 14). A final control group (8) received neither product or vehicle. Adverse clinical reactions were not observed in moxidectin- or vehicle-treated cows. Cows were bred by artificial insemination between days -2 and 25 and, subsequently, by breeding-sound bulls through day 65 of the study. Treatment and control groups did not differ in pregnancy rate or time to conception. Moxidectin (at 3 times the therapeutic dose) did not have deleterious effects on cow reproductive performance as examined (eg, at folliculogenesis, ovulation, and the early embryonic phase of development).

Relationship of parity and body condition score to pregnancy rates in Florida beef cattle

Pregnancy rates, determined by per rectum palpation, were analyzed with respect to cow parity (range 1 to >8 calvings) and body condition score (BCS, 1=thin to 9=fat) at pregnancy examination for 3734 beef cattle females on 3 commercial beef operations (8 herds) in 3 Florida counties in 1989 and 1990. The means and standard deviations for the herds were the following: pregnancy rate, 81.3 +/- 39% (range 62.1 to 91.5%); BCS, 4.7 +/- 0.6 (range 4.3 to 4.9); and parity, 3.9 +/- 2.3 (range 2.8 to 4.8). Significant associations were found between pregnancy rate, parity, BCS and herd (P < 0.001); and between the variable interactions, parity with BCS, herd with BCS, and herd with parity (P < 0.001). Cows with a BCS </=4 had a pregnancy rate of 59%; those with a BCS >/=5 had a pregnancy rate of 90%. Cows having a parity of <4 had a PR of 80%, while cows having a parity >/=4 had a PR of 85%. The interaction of parity with BCS was significant, resulting in pregnancy rates as follows; parity <4 and BCS </= 4 was 51%; parity < 4 and BCS >/= 5 was 88%; parity >/=4 and BCS </= 4 was 66%; and parity >/=5 and BCS >/= 5 was 93%. Body condition, parity, and the interaction of body condition and parity play important roles in the reproductive performance of commercial beef cows in Florida.

Impact of trichomoniasis on the cow-calf producer's profitability

Using current knowledge of bovine trichomoniasis, a computer spreadsheet simulation model was developed to contribute to the understanding of the disease dynamics and the disease's impact on calf crop, weaner calf production, and revenue returns. Two disease prevalence simulations were generated with the model. In each simulation, 200 susceptible cows were confined with 5 fertile bulls. In simulation 1, one bull was infected with Tritrichomonas foetus (prevalence, 20%); in simulation 2, 2 bulls were infected (prevalence, 40%). The remaining bulls in these groups were designated noninfected. The disease simulation outcomes for breeding and calving variables were compared with a similar but noninfected model group, simulation 0. The disease model predicted a reduction of 14 to 50% in annual calf crop, a prolonged breeding season, a reduction of 5 to 12% in the suckling/growing period, a reduction of 4 to 10% in pounds of marketable calf crop at weaning, a reduction of 4 to 10% in monetary return per calf born, and a substantial reduction of 5 to 35% in the return per cow confined with a fertile bull.