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Our thanks to the author and Conference Organisers, a Committee consisting of both University and Industry colleagues.

The full paper will appear in the Conference Proceedings ('Recent Advances in Animal Nutrition - 2007', edited by Phil Garnsworthy and Julian Wiseman) published by Nottingham University Press in the autumn of 2007 www.nup.com

Courtesy of the 41st Annual University of Nottingham Feed Conference www.nottingham.ac.uk/biosciences/ah/research/conferences.php

This paper will consider the anatomical structures and tissues of the claw which are affected by lesions which cause lameness. It will review function in body-weight bearing in the context of complexities of cell, extracellular and molecular biology of important tissues. It will identify the composition of these tissues and discuss nutritional requirements necessary to support growth and maintenance to maintain health. Emphasis will be given to the limited studies under controlled conditions with some reference to data obtained from more applied investigations.


Lameness in dairy cattle is well recognised as a painful and internationally endemic production disease. It has been associated with selection of cows predominantly for milk yield and intensification of nutritional supply, housing environments and management systems. There is particular interest in lameness produced by “aseptic” claw horn lesions and related to poor quality horn, and infections due to digital dermatitis (Lamecow, 2007). Its aetiology is complex (Greenough et al., 1997).


Major symptoms of claw horn lesions include bruising and haemorrhage brought about by compression of the pedal bone on underlying soft tissues with apparent exacerbation by adverse underfoot environments. The causal mechanisms are poorly understood. They may relate to reductions in effectiveness of the normal suspensory apparatus supporting the weight of the animal caused by (i) inflammation of the vascular dermal tissue as in acidosis-related laminitis (Nocek, 1997) and/or (ii) breakdown of laminar dermal connective tissue, particularly around calving in suggested response to physiological signalling by systemic hormones (Tarlton, et al., 2002). Matrix metalloproteinases are typically associated with connective tissue degradation in claw dermis.


Important nutritional aspects include meeting requirements for production and maintenance of important anatomical structures including collagen-containing connective tissues, the systematic provision of substrate for production of horn and optimising dietary carbohydrate supply. Molecules such as enzymes and growth factors which are important in metabolic regulation also require nutritional inputs. Such provision concerns also the development of claw tissues in utero, post-natally and in response to homeorhetic mechanisms regulating reproductive and lactational states and determining partition of absorbed nutrients.


The major tissue components of the claw are the external (non-vascular) horn-forming epidermis and the underlying basement membrane, (vascular) dermis and hypodermis with the maintenance of integrity of all components necessary for weight-bearing and synthesis of good quality horn. Horn, specific to anatomical production site, is produced from soft tissue basal cells which divide and differentiate in migrating to form hard tissue cornified horn.


A range of keratin proteins are known to be expressed systematically as differentiation proceeds. These proteins, which contain ca 0.04-0.07 of the sulphur-containing amino acid cysteine, combine to form intermediate filaments (IFs). These react in turn with intermediate filament-associated proteins (IFAPS) which may contain up to 0.30 cysteine to form the cytoskeleton of horn cells.


Cysteine is essential for the formation of intra- and inter-molecular disulphide bonds. Cytoskeletal structures are inadequately formed in cells of poor quality horn in precalving heifers and may predict the propensity to formation of lesions after calving (Kempson and Logue, 1993). Methionine supply, as a means of improving provision of sulphur amino acids, has been studied in claw tissue explants in vitro (Hepburn et al., (2007).


Results showed that incorporation, which optimised at ca. 50μmol/litre (in the range of physiological concentrations in blood), was not limited by capacity for uptake and was not affected by cysteine concentrations.


Methionine was shown to support synthesis of normally-expressed proteins in explant tissues. Proteomic evaluation of extracts of explant tissues showed differences in presence of proteins according to location in claw and in response to different concentrations of methionine (Galbraith et al., 2006). Immunohistochemistry and peptide mass fingerprinting identified a range of proteins associated with structure, enzymic action, energy metabolism, lipid transport and steroid biochemistry.


Comparison of amino acids showed that cysteine was present in greater concentrations in claw horn than in dietary sources including rumen microbial protein. Methionine supplementation of diets designed to improve sulphur amino acid supply has had limited effects on claw horn characteristics.


Adhesion between epidermal cells is an important property indicating quality of horn and depends on synthesis of “intercellular cementing substance”. This material requires synthesis of glycoproteins and lipids to provide linking between cells. Lipids present in bovine claw horn were shown to include fatty acids with chain lengths in excess of 24. These are apparently elongated from shorter chain length molecules in situ.


There is considerable interest in the role of the B-vitamin biotin in carboxylation reactions in fatty acid elongation and there are questions of adequacy of supply from unsupplemented diets and microbial synthesis in digestive tract. Lipids are also an important component of the digital cushion of the claw which act as shock absorbers in locomotion. Their composition differs from other fat depots in containing higher concentrations of mono-unsaturates which may reflect physical requirement to deform under load. Anti-inflammatory n-3 polyunsaturated fatty acids may have a role in in modulating laminitis and the innate inflammatory responses in skin to infective digital dermatitis.


Whole animal models have shown that excessive ruminal lactic acid production can produce clinical laminitis and inflammatory effects on laminae and basement membrane of the suspensory system. These results appear to relate to ruminal endotoxin production with similarities to the equine laminitic model.


A range of other nutrients are important in supporting proliferation and differentiation of epidermis as a continually renewing tissue and dermis in synthesising connective tissue and in local regulation of epidermis. These include major and trace minerals and fat and water soluble vitamins (Tomlinson et al., (2004). Brief attention will also be given to requirements for future research to improve our knowledge of claw horn biology and the need to increase the priority for support by major funding organisations.



References

Lamecow (2007) http://template.bio.warwick.ac.uk/E+E/lamecow/public_html/lesions.html.

Galbraith, H. et al., (2006) Proteomic evaluation of tissues at functionally important regions in the bovine claw. Cattle Practice 14 127-137.

Greenough, P.R. et al., (1997) Basic concepts of bovine lameness. In Lameness in cattle, Third Edition, pp 71-86. Edited by P.R. Greenough and A. D. Weaver. W.B. Saunders, Philadelphia.

Hepburn, N. L. et al., (2007) Methionine uptake, incorporation and effects on proliferative activity and protein synthesis in bovine claw tissue explants in vitro. J. Agric. Sci. (in press).

Kempson, S.A. and Logue, D.N. (1993) Ultrastructural observations of hoof horn from dairycows - changes in the white line during the 1st lactation. Vet. Record 132 (21), 524-527.

Nocek, J.E. (1997) Bovine acidosis: implications on laminitis. J. Dairy Sci. 80, 1055-1028.

Tarlton, J.F. et al., (2002) Biomechanical and histopathological changes in the support structures of bovine hooves around the time of first calving. Vet. J. 163, 196-204.

Tomlinson, D. J. et al., (2004). Invited review: Formation of keratins in the bovine claw: Roles of hormones, minerals and vitamins in functional claw integrity. J. Dairy Sci. 87, 797-809.



Authors: H Galbraith¹ and J R Scaife^2
1 School of Biological Sciences, University of Aberdeen, 23 St Machar Drive, Aberdeen, AB24 3RY.
² School of Equine and Animal Science, Writtle College, Lordship Road, Chelmsford , CM1 3RR.

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