Genetic Background of Lameness

It is not only the cows’ environment that has (been) changed during recent years, cows themselves have been changed genetically in order to increase their productivity – milk yield or feed conversion. For generations dairy cattle have been bred and selected for a number of characteristics, all of which aimed at improving productivity (LOGUE 1997). What has not

been considered in this context is the fact that genes coding for high milk yield do not neces-sarily code for healthy legs and claws. For economic reasons, genetic selection for animal welfare is neglected in favour of selection for increased milk yield (OLTENACU and AL-GERS 2005; similarly VAN DORP et al. 1998).

AMSTUTZ (1987), MCDANIEL (1994) and VERMUNT and GREENOUGH (1995) de-scribe the desired characteristics of a cow’s feet: the conformation of the cow’s foot should be short, steeply angled, high in the heel, and evenly clawed. The sole should be somewhat con-cave. The most common claw traits were discussed by the EAAP Working Group ‘Claw Quality in Cattle’ (POLITIEK et al. 1986; DISTL et al. 1990): these traits consisted of an evaluation of the claw shape, the quality of the claw horn and features of the inner structure of the claw. As was demonstrated by several studies, these traits had sufficiently high additive genetic variation to achieve genetic improvement. Claw measurements are significantly corre-lated genetically and phenotypically to the prevalence of claw disease, longevity and lifetime performance (GREENOUGH 1996). So, most lameness could be prevented if proper attention was paid to selecting breeding animals with correct foot and leg conformation; in other words, any animal with a serious genetic defect of the feet should not be used for breeding purposes (AMSTUTZ 1987).

DISTL (1990) showed a genetic component of lameness and of foot and leg shape in German Simmentals. BOETTCHER et al. (1998) describe highly significant correlations be-tween lameness and phenotype traits such as foot angle, rear legs and rump width, as do van der WAAIJ et al. (2005). Also, overly straight hocks, splay toes, or overlapping toes are commonly seen with an increase in the rate of lameness. The heritability of lameness ranks from 0.14 to 0.22 (MCDANIEL 1994; VAN DER WAAIJ et al. 2005); PRYCE et al. (1998) report the heritability of lameness to be 0.015 to 0.005 only, whereas VAN DORP et al.

(1998) found the heritability of lameness to be 0.16. Several claw disorders seem to have a partially genetic basis; the heritability of heel horn erosions is set to be between 0.13 and 0.15, that of interdigital dermatitis to be 0.13, of sole ulcer to be 0.39, and of white line dis-ease to be 0.17 (MCDANIEL 1994). The total number of lesions observed on the feet of Fri-sian cows is reported to be 0.39 (SMIT et al. 1986; CALAVAS et al. 1996).

The heritability of lameness seems to be influenced by other factors associated with a cow’s body traits as well, like breed, body weight, claw horn colour, and milk yield. In a

Dan-ish study carried out by ALBAN (1995), the author found that the DanDan-ish Jersey breed had a lower risk of lameness than did the Red Danish, the Danish Black and White and the Danish Red and White, as the latter breeds are all heavy breeds, while Danish Jersey is a light breed.

ENEVOLDSEN and GROEHN (1991) found that body weight was positively associated with sole ulcer. Claw horn colour seems to be associated with the occurrence of lameness as well, as white claws seem to be more susceptible to lameness than are black ones (CHESTERTON 1989). Selection for high milk yield tends to increase lameness (WARD 2001); large breeds have a high milk yield, which might predispose them to lameness (ALBAN 1995).

In recent years, not only bulls have shown to be a possible risk factor (WARD 1999) in passing their possibly defective genes onto their progeny. With embryo transfer becoming more and more popular, so that hundreds of calves can stem from only one cow, the cow too is recognised as a possible threat to the integrity of the genetic pool (AMSTUTZ 1987). Nev-ertheless, breeding organizations now publish the shape of feet and legs in bulls, which should help reduce the risk of lameness; it was in 1987 already that Russell showed that the daugh-ters of some bulls were much more likely to suffer from foot lameness than those of other sires. Managers of dairy herds with a high prevalence of lameness should be encouraged to consider selection of bulls, which sire shorter, steeper claws in addition to high milk yield (VERMUNT and GREENOUGH 1995).

Genetic selection of certain traits seems to be a practical way of improving locomotion in dairy cattle (MCDANIEL 1994; BOETTCHER et al. 1998). DISTL (1994) believes that ge-netic improvement of claw and leg conformation should enable animals to resist influences of the environment without suffering from diseases or reducing their performance ability. The author proposes a certain guideline as to what should be considered when defining the genetic traits to be preferred. He suggests that claw and leg traits for breeding objectives should be carefully defined and the traits chosen should be tested for their usefulness in practical breed-ing work and in respect to the environment the animals are exposed to. Possible other side effects on the musculoskeletal or other system should be avoided. Traits to be used in breed-ing work should consequently be related to susceptibility for claw and leg diseases on the one hand, and to management requirements such as low need for claw care and to functional as-pects of locomotion on the other hand.

This implies that the traits necessary seem to be of a complex nature and seem to depend on and respond to the exposure to environmental effects (DISTL 1994). Phenotypic traits to be used in genetic improvement of claw and leg characteristics should contribute to the de-crease of the lameness problem in the future. As the most common cause of lameness is lo-cated in the claw, more selection pressure should be put on claw traits. Nonetheless, accord-ing to DISTL (1994), WEBSTER (1995) and BOETTCHER et al. (1998), target traits for claw and leg quality should be defined carefully. They should include the incident of all rele-vant claw and leg diseases and of correlated diseases as well as production traits that are re-lated to claw and leg quality.

There are a number of consequent challenges to breeders and geneticists. It will be impor-tant to maintain the fitness of very high producing animals by recording health, fertility, lon-gevity and parlour traits and to use these data to give them appropriate weight in selection decisions (HILL et al. 1995; similarly VAN DORP et al. 1998). The ultimate goal in breeding programs for dairy cattle should be to produce animals with a high yield and high claw quality (VERMUNT and GREENOUGH 1995); thus, the longevity and lifetime performance of the animals could both be improved (DISTL 1994), and the quality of dairy cow life could be enhanced (OLTENACU and ALGERS 2005).

6.5.1. Conclusions for Genetic Background of Lameness

Breeding programs for healthy feet should be encouraged.

Animals with correct claw and leg angles need to be selected for breeding.

Bulls should be considered in terms of giving their genes to their progeny; cows are important, too, especially with modern techniques like embryo transfer on the rise.

Claw and leg traits for breeding objectives should be carefully defined.

The traits chosen should be tested for their usefulness in practical breeding work and according to the environment the animals are exposed to.

Possible side effects on the musculoskeletal or other system should be avoided.

Traits to be used in breeding work should consequently be related to susceptibility for claw and leg diseases on the one hand, and to management requirements such

as low need for claw care and to functional aspects of locomotion on the other hand.

As the most common cause of lameness is located in the claw, more selection pressure should be put on claw traits.