Twelve dairy heifers were used to examine the clinical response of an alimentary oligofructose overload. Six animals were divided into 3 subgroups, and each was given a bolus dose of 13, 17, or 21 g/kg of oligofructose orally. The control group (n = 6) was sham-treated with tap water. Signs of lameness, cardiovascular function, and gastrointestinal function were monitored every 6 h during development of rumen acidosis. The heifers were euthanized 48 and 72 h after administration of oligofructose. All animals given oligofructose developed depression, anorexia, and diarrhea 9 to 39 h after receiving oligofructose. By 33 to 45 h after treatment, the feces returned to normal consistency and the heifers began eating again. Animals given oligofructose developed transient fever, severe metabolic acidosis, and moderate dehydration, which were alleviated by supportive therapy. Four of 6 animals given oligofructose displayed clinical signs of laminitis starting 39 to 45 h after receiving oligofructose and lasting until euthanasia. The lameness was obvious, but could easily be overlooked by the untrained eye, because the heifers continued to stand and walk, and did not interrupt their eating behavior. No positive pain reactions or lameness were seen in control animals. Based on these results, we conclude that an alimentary oligofructose overload is able to induce signs of acute laminitis in cattle. This model offers a new method, which can be used in further investigation of the pathogenesis and pathophysiology of bovine laminitis.

Weakening of the suspensory tissue supporting the pedal bone is the central issue in the theory of acute bovine laminitis, but this aspect has never been tested. The objective of this study was to investigate the effect of laminitis on the suspensory tissue. The hypothesis was that clinical and histological signs of acute laminitis are associated with decreased strength of the suspensory tissue of the bovine claw. Nonpregnant dairy heifers (n=10) received oral oligofructose overload (17 g/kg of body weight) and were killed 24 (n=4) and 72h (n=6) after overload. Control heifers (n=6) received tap water and were killed at 72 or 96h. Clinical, orthopedic, and histological examinations were carried out to confirm the occurrence of laminitis. After euthanasia, 2 adjacent tissue samples including the horn wall, lamellar layer, dermis, and pedal bone were cut from the dorso-abaxial aspect of each claw. Tissue samples were kept on ice until mounted on a mechanical testing frame, fixed by horn and bone, and loaded to failure. A stress displacement curve was generated and measurements of physiological support (force needed to displace 1mm beyond first resistance) and maximal support (force needed to break the tissue) were recorded. Heifers treated with oligofructose developed clinical signs consistent with ruminal and systemic acidosis after treatment as well as acute laminitis, characterized by weight shifting (35% of observations vs. 6% in controls), moderate lameness (100 vs. 17%, score of 3 out of 5 at 72h), and reaction to hoof testing (30 and 50% at 48 and 72h, respectively, vs. 0% in controls). Histological examination of claws from heifers killed 72h after overload showed changes consistent with acute laminitis, including stretched lamellae, wider basal cells with low chromatin density, and a thick, wavy, and blurry appearance of the basement membrane. Biomechanical results showed no effect of oligofructose overload on physiological support of the suspensory tissue at 24 and 72h after overload; in contrast, overload increased maximal support of the tissue 72h after overload. Herd of origin and location of the sample had large effects on both physiological support and maximal support (herd=547 N/cm(2); location=531 N/cm(2)) of claw suspensory tissue (herd=260 N/cm(2); location=327 N/cm(2)). Despite clinical and histological signs of laminitis, no weakening of the suspensory tissue of the bovine claw was detected at 24 and 72h after oligofructose overload. Herd factors appeared to be important for claw suspensory tissue strength.

Histopathology of the dermo-epidermal junction in the lamellar region of front claws was examined in 6 dairy heifers given an alimentary oligofructose overload and compared with sections from a control group of 6 heifers. Four of the 6 heifers administered oligofructose developed clinical signs of acute laminitis before they were euthanized. Postmortem samples from front claws were processed for histology. Eleven histopathologic characteristics were selected from the existing literature and used in a blinded evaluation of sections. In total, 104 front claw samples, including 8 samples from 2 cows having spontaneously occurring acute laminitis, were evaluated histologically using hematoxylin and eosin as well as periodic acid-Schiff staining. The major morphological features associated with oligofructose-induced acute clinical laminitis were stretching of lamellae, dermal edema, hemorrhage, changes in basal cell morphology, presence of white blood cells in dermis, and signs of basement membrane detachment. Changes at the lamellar junction of claw tissue affected by oligofructose-induced clinical laminitis resembled tissue from the 2 cows suffering from spontaneous acute clinical laminitis, and generally were consistent with existing descriptions of laminitis histopathology. Important exceptions to existing descriptions in the literature were stretching of lamellae and basement membrane changes. Not previously described, we considered these early signs of acute laminitis. In conclusion, this study documents that oligofructose-induced clinical laminitis is associated with histopathological changes at the lamellar interface. A weakened dermo-epidermal junction is a possible intermediate stage in the pathophysiology of bovine sole ulceration at the typical site.

No abstract

Skeletal atavism in Shetland ponies is a heritable disorder characterized by abnormal growth of the ulna and fibula that extend the carpal and tarsal joints, respectively. This causes abnormal skeletal structure and impaired movements, and affected foals are usually killed. In order to identify the causal mutation we subjected six confirmed Swedish cases and a DNA pool consisting of 21 control individuals to whole genome resequencing. We screened for polymorphisms where the cases and the control pool were fixed for opposite alleles and observed this signature for only 25 SNPs, most of which were scattered on genome assembly unassigned scaffolds. Read depth analysis at these loci revealed homozygosity or compound heterozygosity for two partially overlapping large deletions in the pseudoautosomal region (PAR) of chromosome X/Y in cases but not in the control pool. One of these deletions removes the entire coding region of the SHOX gene and both deletions remove parts of the CRLF2 gene located downstream of SHOX. The horse reference assembly of the PAR is highly fragmented, and in order to characterize this region we sequenced bacterial artificial chromosome (BAC) clones by single-molecule real-time (SMRT) sequencing technology. This considerably improved the assembly and enabled size estimations of the two deletions to 160−180 kb and 60−80 kb, respectively. Complete association between the presence of these deletions and disease status was verified in eight other affected horses. The result of the present study is consistent with previous studies in humans showing crucial importance of SHOX for normal skeletal development.