Effects of aflatoxin ingestion on the development of Moraxella bovis infectious bovine keratoconjunctivitis

A study was conducted to determine whether measured doses of aflatoxin given under different schedules would influence the pathogenesis of Moraxella bovis induced infectious bovine keratoconjunctivitis (IBK). Calves were allotted to 4 groups (groups I-IV) of 9, 9, 9, and 8 calves, respectively. Group I calves were given aflatoxin for 11 consecutive days starting 5 days before their eyes were exposed to M. bovis. Group II calves were given aflatoxin for 5 consecutive days starting 7 days after their eyes were exposed to M. bovis. Group III calves were given aflatoxin for 5 consecutive days starting 21 days after their eyes were exposed to M. bovis. Group IV calves were not given aflatoxin; but their eyes were exposed to M. bovis on the same day as were the eyes of calves in groups I-III; these calves served as controls. Aflatoxin had little if any influence on the pathogenesis of IBK under the conditions of this study. The results did not rule out an exacerbating effect of M bovis infection on aflatoxicosis in calves. Calves with the highest concentration of aflatoxin in their blood had the more severe signs of aflatoxicosis. Possible reasons for the equivocal results are discussed.     

Restraint

The object of restraint is to limit, restrict, and keep under control the animal's movement while performing different procedures. The author discusses the importance of evaluating the horse and its owner prior to employing any type of restraint, various concepts of restraint, and examples of situations in which restraint may be required.     

Comparison of vaccination and treatment in controlling naturally occurring infectious bovine keratoconjunctivitis.

A vaccination study for infectious bovine keratoconjunctivitis was conducted on 108 newborn Hereford calves in the US Department of Agriculture Meat Animal Research Center cattle herd at Clay Center, Nebraska. Groups were allocated so that age of calf, sex of calf, and age of dam were equally distributed between the 54 vaccinated (group I) and the 54 nonvaccinated (group 2) control calves. The dams of both groups of calves were monitored as group 3 controls. An autogenous Moraxella bovis bacterin (formalin-killed, whole cells) was given IM at birth and at approximate intervals of 2 weeks for a total of 3 doses. Bacterial isolation rates for the cattle in groups 1, 2, and 3 during the summer were 92.6%, 92.6%, and 54.1%, respectively, and disease rates were 100%, 96.3%, and 70.6%. The rates were significantly (P less than 0.05) different between calves and cows. Vaccination of calves at birth permitted serum antibodies to develop before the calves were extensively exposed to infection; however, immunity to the disease did not develop. In a treatment study of other animals in the same herd, but in another pasture, the same criteria were used for allocation of 107 cow-calf pairs. Eye spray was applied to treated principals (group 4, 52 calves; and group 6, 53 cows) each week after examination and sample collection. Controls consisted of 54 calves (group 5) and 54 cows (group 7) that were examined and cultured bacteriologically in the same manner. The bacterial isolation and disease rates were less (P less than 0.05) in the treated calves (group 4) than in the nontreated controls (group 5). The differences in bacterial isolation rates between groups 6 and 7 were not significant, but group 6 had less (P less than 0.05) grade III lesions than did group 7. Weekly treatment appeared to be more effective in reducing the incidence of disease than did vaccination.     

Pathogenesis of corneal lesions caused by Moraxella bovis in gnotobiotic calves

Moraxella bovis was instilled into the conjunctival sac of gnotobiotic calves and corneas were sampled serially after infection. Lesions developed in seven of eight infected calves, but were absent in a noninfected control calf. Histologically, M. bovis was first seen in foci of swollen epithelium and within basal epithelial cells adjacent to ulcers. Corneal ulcers were severe in later stages of infection; fibrin deposits, neutrophils, and bacteria were present in the stromas. Examination of early lesions by scanning electron microscopy showed M. bovis in pits on the surfaces of dark epithelial cells, enmeshed in degenerate epithelial cells and within erosions and an ulcer; in later samples, bacteria were rare. Ultrastructurally, M. bovis was seen in surface pits in superficial epithelial cell processes and within swollen epithelial cells. In stroma, M. bovis was frequently seen among collagen fibrils, within neutrophil phagosomes, and associated with cellular debris. This study demonstrates that a virulent strain of M. bovis can invade bovine corneal epithelial cells and can cause keratitis in the absence of injurious ultraviolet irradiation or other known predisposing environmental factors.     

Infectious bovine keratoconjunctivitis: contact transmission

The transmission of Moraxella bovis was studied in calves in the absence of the face fly (Musca autumnalis) or environmental conditions that might insult the eye. Thirty calves were placed in 10 groups of 1 experimentally infected calf and 2 contact calves each. Over 40 days, only 1 eye in 1 contact calf developed clinical infectious bovine keratoconjunctivitis. The organism was recovered in only 8 of 20 contact calves, whereas infection and disease occurred in all experimentally infected calves. Transmission of M bovis occurring in the absence of some other intervening factor was probably of minimal importance. Seemingly, herd preventive treatment would be most effective when flies and environmental factors are at a minimum.     

Heritability and quantitative trait loci of composition and structural characteristics in sorghum grain

Breeding efforts in cereal crops directed toward developing or improving end-use products of grain require assessment of existing phenotypic variance and an understanding of the genetic control of grain quality traits. To this end, a grain sorghum [Sorghum bicolor (L.) Moench] mapping population consisting of 113 F_2:7 recombinant inbred lines (RILs) derived from a cross between Sureño and RTx430 was evaluated in multiple environments for grain composition (fat, fiber, protein, starch) using near-infrared reflectance spectroscopy (NIRS), and size estimates of grain parts (embryo, vitreous endosperm, floury endosperm, kernel area) using an image-based phenotyping software system. Estimates of broad-sense heritability of grain compositional traits ranged from 0.11 to 0.90, whereas those of grain size ranged from 0.16 to 0.72. Composite interval mapping (CIM) was applied to a single nucleotide polymorphism (SNP)-based linkage map to identify marker-trait associations, and through these efforts, a total of 37 quantitative trait loci (QTL) for grain quality were identified across environments. Each QTL explained between 7 and 23% of the phenotypic variation for a given grain trait. Three of the five QTL that colocalized were for traits with significant negative correlation, which included grain protein content that was negatively correlated with grain starch content. In addition, several traits that were positively correlated (e.g. fat and fiber content) also revealed colocalized QTL. Finally, we compared the present study with previous studies identifying grain composition trait loci in an effort to identify genomic regions controlling grain traits across a diversity of environments and sorghum genotypes.