To be or not to be horned - Consequences in cattle
Knierim U., Irrgang N., Roth B.A.
Abstract
In cattle, both males and females of horned breeds have permanent horns which are directly connected with the frontal sinuses of the skull and are growing during their entire life. To date a large proportion of cattle is disbudded or dehorned, or increasingly bred for polledness. This review explores the possible consequences of cattle having horns or not, both for the cattle themselves and for the farmers. During natural selection horns may have provided advantages concerning predator defence or in competition for mates and resources. Additionally, there are indications that horns serve as honest signals in mate selection, as they reflect individual health. Presence or absence of horns will likely affect quality and quantity of social interactions as well as social relationships in a herd. It clearly affects the way of cattle fighting. Only few studies deal with social behaviour in horned herds in comparison to hornless herds, and they rely on single herd observations or need to be interpreted with caution because of confounding factors. However, it appears that horned cattle attempt to keep greater inter-individual distances and resort less to physical interactions than hornless cattle, leading to more stable social relationships under suitable environmental conditions and management. Cattle may, furthermore, use horns for self-grooming of body regions which are otherwise out of reach. Even less is known on possible physiological functions of horns. While there is good evidence regarding a thermoregulatory function, other claimed functions, e.g. concerning digestion, have not been scientifically investigated yet. Although farmers in favour of keeping horned cattle, for instance for ethical reasons, are able to reduce the increased risk of animal injuries and human accidents by providing improved housing and management conditions and maintaining a good human–animal relationship, it may be economically advantageous to keep hornless cattle. If disbudding/dehorning is carried out, the consequences in terms of stress and pain can be alleviated by a combination of local anaesthesia and anti-inflammatory treatment, as well as sedation of animals insufficiently used to handling. However, possible negative side effects of sedation should be addressed in future studies. Furthermore, the possibility of longer lasting pain after disbudding/dehorning is not sufficiently investigated yet. Finally, it is an open question whether the removal of horns alters the social behaviour of the animals, or is a mere symptomatic measure to adjust them to husbandry conditions that are insufficiently adapted to the species-specific needs of cattle.
Introduction
In cattle, both males and females of horned breeds have permanent horns, and all current populations of wild cattle are horned (Porter, 2007). This also applied to the ancestor of domestic taurine cattle, the near eastern local wild ox (Bollongino et al., 2012). The horn itself consists of dense keratin that is produced at the corium, the area of cells located at the junction of the horn and skin. The horn buds start to form during the first two months of life, when they are free-floating in the skin layer above the skull. As the calf grows older, the horn buds attach to the skull, more precisely to the periosteum of the frontal bones overlying the frontal sinuses, and massive bony horns then start to grow. Beginning around the age of 6 to 8 months these are increasingly pneumatised from the caudal frontal sinuses so that the hollow centres of the horn cores are directly connected with the frontal sinuses of the skull. The bony cores of the horns are supplied by blood vessels and nerves and will continue to grow during the entire life (Habel and Budras, 2003, Parsons and Jensen, 2006).
To date a large proportion of cattle is disbudded or dehorned, and in most cases without proper pain relief (Fulwider et al., 2008; Vasseur et al., 2010; De Boyer des Roches et al., 2014; Cozzi et al., 2015). A higher percentage of cattle in loose housing systems compared to tie-stall systems are dehorned (Cozzi et al., 2015). Thus, beside the welfare benefits of loose housing systems, the increased likelihood of cattle being subjected to disbudding or dehorning is a certain disadvantage. Breeding for polledness is one recommendation how to solve this dilemma and to improve cattle welfare (e.g. Stafford and Mellor, 2005, Stafford and Mellor, 2011, Windig et al., 2015). Other authors claim that under improved loose housing conditions, it is not necessary to dehorn cattle, and thereby it is possible to improve cattle welfare in general (e.g. Waiblinger and Menke, 2009). Improving pain relief during and after the operation is another approach to ameliorate the welfare problem (e.g. Mirabito et al., 2009; Stock et al., 2013). This review takes one step back and aims to look at the possible consequences of cattle having or not having horns for the cattle themselves, and also for the farmer.
Section snippets
Potential phylogenetic functions of horns
While for males there is general agreement that the main evolutionary benefit of horns relates to intrasexual competition for mates (e.g. Preston et al., 2003; Bro-Jørgensen, 2007), regarding horned female ungulates diverse hypotheses have been investigated and controversies discussed. They include that horns may provide advantages during evolution concerning predator defence (e.g. Bro-Jørgensen, 2007; Stankowich and Caro, 2009) or in resource competition (e.g. Roberts, 1996; Robinson and
Behavioural consequences
The presence of horns will likely affect quality and quantity of social interactions as well as social relationships in a herd. However, literature explicitly dealing with social behaviour in horned herds in comparison to hornless herds is scarce and recent studies are lacking. Often, in work on social behaviour of cattle it is not even stated whether animals were horned or not. It was, therefore, necessary to assume that they were dehorned unless stated otherwise.
Presence or absence of horns
Physiological consequences
In the ancient world Goddesses and Gods representing fertility and vitality were often associated with horns or horned cows or bulls (Cooper, 1998). Also among cattle breeders the relation of superior production traits to the presence of horns in the past appeared to be a regular perception (Koots and Crow, 1989), and horns were appreciated for selection purposes. Variations in level of nutrition of the animal are reflected in variations in rapidity of horn growth, resulting in a series of
Consequences on animal pain and stress in horned herds
When it comes to physical agonistic interactions in horned herds, the risk for injuries is higher than in hornless herds. Menke et al. (1999) found a mean of 13.6 supposedly horn-inflicted lesions per cow in the 35 investigated dairy farms; Schneider (2010) recorded in 62 herds on average 10.1 lesions. A large majority of such lesions are superficial scratches or hairless areas (Menke et al., 1999, Waiblinger et al., 2001, Schneider, 2010, Castro et al., 2012). However, the range of horn
Consequences on animal pain and stress when disbudding or dehorning is carried out
If it is decided to disbud/dehorn cattle, the procedure itself will inflict pain and stress depending on the way of implementation and application of pain and stress relieving medication (reviewed by Stafford and Mellor, 2005, Stafford and Mellor, 2011; Knierim et al. (2009) and Stock et al. (2013)). In short, there is broad agreement that dehorning has markedly stronger negative welfare effects than disbudding due to the type and extent of inflicted wounds. For disbudding there are indications
Consequences for the farmer
Farmers in earlier times favoured cattle with horns over hornless cattle because they were used as draught animals and the horns served to attach the harness (Rosenberger and Robeis, 2005), and even today in small-holder farms, horns are partly used for tying cattle.
Hornless cattle are considered less dangerous for stockpeople's on-the-job safety, and this is a topic of emotional and controversy among farmers (Kling-Eveillard et al., 2015). Statistical information about actual accidents with
Conclusions
Not much is known about the behavioural functions of horns for cattle. While they are used in species-specific ways in social and grooming behaviour, they may have negative and positive welfare effects, depending on the environmental conditions in which cattle are housed. Even less scientific evidence is available on possible physiological functions of horns. Both areas, behavioural and physiological functions, present challenging research opportunities for the future. For the farmer, it may be ....