By Stefan Guizot
The urgent need for a global expansion of food supplies, especially of high quality protein, to meet the requirements of a rapidly growing world population, has focused the attention of the meat industry on methods of increasing output.At the same time, meat producers must satisfy the demands of the consumer. Consumer preferences are changing and demand is moving away from traditional heavily fatted animals towards smaller and leaner joints.
It is well known that male animals have a lower body fat content than females and, since lean meat has a much lower energy value than fat, a lower input is needed to grow the same weight. The feed conversion efficiency of the male meat animal over the female has been thoroughly established experimentally and has also been confirmed in comparison to castrates. Castration also results in excess fat deposition (Campbell and Taverner, 1988; Dunshea et al., 1993b). It is thus economically sound to raise entire males for meat rather than castrates.
Unfortunately, the meat from boars frequently emits a strong unpleasant urine- or perspiration-like odour during heating, making it unacceptable to many consumers. Meat inspection regulations in the United States specify that carcasses with “strong odour” must be condemned and those exhibiting “slight odour” may only be used in comminuted sausage products. Canadian meat inspection regulations require the condemnation of all boar and stag carcasses. Since boar odour is exhibited by about two-thirds of all sexually mature boars, 1.35 million pigs (or 125 million kg of pork) could conceivably be subject to either condemnation or restricted usage if these regulations were enforced in the United States (Thompson, 1975). Current European Community legislation (Directive 64/433/EEC) provides that male carcasses over 80 kg may be allowed for human consumption provided that they bear a special mark and undergo treatment (i.e. processing) before entering the food chain.
If the problem of boar odour in pork could be eliminated, castration of male pigs would no longer be necessary. Up until recently most pig producers have castrated their male animals, probably to take advantage of the greater tractability of the castrated animal and the consumers’ demand for a fat carcass. However, there is growing pressure from animal welfare groups and veterinarians to cease this practise and it has already been outlawed in some European countries, notably Ireland and the UK. Recommendations that entered into force on 2 June 2005 in Europe provides that the ‘mutilation of pigs shall be generally prohibited and that measures shall be taken to avoid the need for such procedures in particular by changing the environmental factors or management systems by enriching the environment or by selecting appropriate breeds and strains of pigs’. A viable alternative to castration is therefore becoming a necessity.
In general the effect of castration is to modify the secondary sex characteristics of an animal. Sexual drive and aggression is reduced or abolished making handling easier. Castration also results in modification of body form and composition, resulting in different carcass characteristics. The balance between fore- and hindquarters is changed and the amount and distribution of fat in the carcass is also changed (Turton, 1969). In recent years there has been increased interest in the production of meat from entire males. This is mainly due to the greater efficiency of feed conversion and the possibility of higher edible carcass yields. Rearing of boars rather than barrows would result in production of 8-10 % more lean meat per pig and would increase feed efficiency by 12-15 % (Pearson, unpublished data). Numerous studies on the effect of castration of male pigs have suggested that large economic advantages would result from the rearing of intact male pigs for meat production if the problem of boar taint could be circumvented (Walstra and Kroeske, 1968; Martin, 1969; Turton, 1969; Siers, 1975).
Castration is not only laborious and distasteful, but it also retards growth and increases the risk of infection. Boars grow faster, achieve more efficient weight gains and produce longer, leaner carcasses that have less back fat than those from either barrows or gilts (Martin, 1969; Turton, 1969). Thus, procedures for preventing boar odour so as to enable the marketing of boar pigs for meat would be of great economic importance to the swine industry.
The quality of meat obtainable from male carcasses is, however, a matter of concern to both the retail side of the meat trade and the consumer. In the past, meat from boars originated mainly from discarded breeding animals of advanced age and was of poor quality and low commercial value, giving a poor reputation to boar meat. Boar meat from pork and bacon weight animals has become more common in recent years and is attractive in its leanness. The problem is that the fat carries an unpleasant odour which becomes apparent on cooking.
Attempts to identify the chemical compounds responsible for boar odour in pork date back to the early efforts of Lerche (1936) who demonstrated that the unpleasant odour emanating from heated boar meat first became apparent at the onset of sexual maturity and disappeared following castration. While unsuccessfully attempting to isolate testosterone from boar testes, Prelog and Ruzicka (1944) isolated C19 D16 steroids (Sa androst-16-en-3a0 and 5 androst-16-en-3b-ol), which they described as possessing musk-like odours. Brooks and Pearson (1957) later reported that the undesirable odour occurred predominantly in the meat from boars, but that the meat from some gilts, sows and barrows was also “tainted”. Williams et al. (1963) reported the incidence of boar odour to be much higher for boars (65 %) than for cryptorchids (35 %), barrows (5 %) or sows (1%). Craig and Pearson (1959) and Craig et al. (1962) conducted one of the earliest investigations on the chemical components responsible for boar odour. They established that the undesirable “urine-like” or “perspiration-like” odour was associated with the adipose tissue and was concentrated in the non-saponifiable fraction of the fat. Williams and Pearson (1965) eliminated several of the constituents present in the non-saponifiable fraction as contributors to boar odour, but failed to identify the responsible components.
Patterson (1968a), utilizing gas chromatography-mass spectrometry, isolated 5a androst-16-en-3-one as the “perspiration-like” component in boar fat. Other researchers (Beery and Sink, 1971; Beery et al., 1971; Thompson et al., 1972) confirmed this finding and identified other C19 D16 – steroids (5aandrost-16-en-3a-d and 5aandrost-16-en-3b-ol) as contributors to boar taint.
The object of this review is to investigate the origins and implications of boar odour and to discuss ways and means of overcoming this problem, so as to take advantage of the benefits accruing from the use of entire male pigs for meat production.
The influence of boar taint on consumer acceptance of boar meat has received widespread attention and a great amount of research has been conducted into the control and / or elimination of boar taint in pork. It would be informative to conduct research into South African consumer opinions on pork meat and to test sensitivity to boar taint-causing compounds
Although many of the compounds thought to be responsible for boar taint have been isolated and identified, more research needs to be conducted into the steroid hormone pathways responsible for the production of these compounds. With a clearer knowledge of these pathways it may be possible to develop chemical agents to block the production of C19 D16 steroids. Development of a suitable chemical blocking agent to prevent formation of the C19 D16 steroids without inhibiting production of androgenic and estrogenic sex hormones would be extremely valuable (Brooks and Pearson, 1986).
While androstenones and skatole have been thoroughly researched, there are other volatile compounds that could contribute towards boar taint that should be investigated. This area of research seems to be relatively neglected.
The auto-immunization of boars against 5a androst-16-en-3-one offers a potentially valuable procedure for exploiting the growth advantages of boar pigs and would be of economic benefit to the pork industry. The feeding of pigs to reduce boar taint deserves further attention, especially feeding to reduce the levels of Lactobacilli in the gut of pigs thought to be responsible for the production of skatole.
Methods of controlling the amount of skatole in boars, such as cleaning pigs and pens of faeces a week before slaughter could be a valuable low cost method of reducing boar taint. Further research on environmental influences on levels of boar taint-causing compounds needs to be conducted, as this area appears to be somewhat neglected.
The evaluation of boars for boar taint on the slaughter line is a useful way of reducing the amount of boar tainted meat reaching the consumer. Methods must be low cost and quick to be viable.
There are many avenues that need to be explored in the pursuit of realistic control of boar taint and some solutions have already been presented. With more research the problems associated with the production of meat from entire male animals will hopefully become problems of the past.