The use of hormones for caponising and finishing cockerels has become a well-established practice in the poultry industry. During the last decade, increasing interest has been shown in the use of synthetic oestrogens and androgens for stimulating the growth and fattening of beef cattle and sheep. This work has found great commercial application in the United States of America, where millions of cattle are fed stilboestrol treated rations in the feed lot. More recently it was shown that the subcutaneous implantation of stilboestrol pellets significantly increased the gain of grazing lambs (Perry et al. 1951 and Cleex et al., 1955) and of grazing steers (O'Mary and Cullison, 1956, and Lamming, 1956).
It is apparent that any large-scale application under the Australian environment will be with grazing stock; and hence by the implantation method. Experiments were initiated by the N.S.W. Department of Agriculture at Leeton and Temora Experiment Farms, and with private co-operators at Willbriggie and Canowindra, to assess the effect of implanting stilboestrol and hexoestrol. Work also has been undertaken at a number of other centres throughout the Commonwealth.
The overall effect of the hormone treatment is to make the animal younger physiologically. In other words, he puts on weight more quickly and efficiently. Much of this weight gain is due to extra growth of bone and muscle at the expense of the later developing fatty tissues. For instance, Aitken and Crichton (1956) found that the 43 lb. extra weight in a 783 lb, carcase from a treated steer was made up of about 9.5 lb. more bone, 6.7 lb. more protein, 28 lb. more moisture and 3.4 lb. less fat. Treated carcases are generally not as well finished.
A review of the literature as well as some of the results from local experiments will be presented firstly with respect to beef cattle; and secondly fat lamb production.
Liveweight gain for steers on pasture has been increased by approximately ½lb. per day over the first two to three months following implantation. Generally, the greatest response is apparent in the early post-treatment period. However, the magnitude and period over which it is obtained has varied greatly in the experiments reported. Table 1 presents the liveweight increases produced in a series of experiments undertaken by the N.S.W. Department of Agriculture. In at least one of these experiments this added gain of treated animals over controls, which was apparent at an early stage, was held for as long as 8 months. However, in another case (experiment 1) the initial satisfactory response was lost by 132 days post-treatment; at which time treated animals were only 19 lbs. heavier than the untreated controls.
|TREATMENT - Drug||Stilboestrol||Stilboestrol & Hexoestrol||Stilboestrol & Hexoestrol||Hexoestrol||Hexoestrol||Hexoestrol||Hexoestrol|
|- Level (mgm)||24 to 48||24 & 36||36||30 & 60||60||60||60|
|Initial Liveweight (lb)||1044||949||1095||921 & 921||725||604||531|
|Time of maximum recorded response (days)||42||107||78||112 & 142||70||278||171|
|Increased gain due to treatment - in lb. per day||0.7||0.4||0.5||0.3 & 0.5||0.9||0.2||0.4|
|Increased gain due to treatment - in lb.||26||42||40||37 & 71||62||49||72|
Carcase data from experiments 1 and 4 show that treatment causes an increase in this respect also. In experiment 1 this increase was 1 lb. only: but at the two levels of treatment in experiment 4, increases in carcase weight of 16 and 32 lbs. were recorded. Likewise there was an increase in "eye muscle" depth of 3, 6 and 14% respectively, and a decrease in fat depth of 5, 9 and 29% respectively, from experiment 1 and the two levels of treatment in experiment 4. The treated animals showed less "marbling" and also less caul fat; thus confirming overseas findings mentioned above. Treated carcases also showed an increase of the fore end of the carcase relative to the hind end.
Side Effects. In cattle, there is often a raising of the tail head and depression of the loin, probably due to a relaxation of the pelvic ligaments. (See photographs.) In the carcase the lumbo-sacral angle is much more acute (Cahill et al., 1956). However, while yard appeal may thus be reduced, there appears to be little adverse effect on the carcase. Overseas reports also mention restlessness and coital mimicry following implantation. An increase in rudimentary teat length is generally observed. Vaginal prolapse and lactation have been reported in treated heifers (Clegg et al., 1954).
Liveweight gain for sheep is frequently reported as being increased by approximately 0.1 lb. per day over the first 6 weeks or so. In a series of eight experiments undertaken by the Department of Agriculture this response to treatment has been most variable; in fact in a number of cases no significant increase has been recorded. In three experiments, however, an increase of 4 lbs. has resulted. These findings are confirmed from Victoria by McHugh and Cannon (1958) and from New Zealand by Lambourne (1958).
Carcase appraisal of one experimental group has not shown significant differences. Slaughtermen reported, though, that the pelts of treated animals were noticeably more difficult to remove. There was marked enlargement of accessory sex glands in treated wethers; on this basis 33% of carcases being rejected from export grade.
Other side effects are a marked increase in teat length and mammary development, including secretion. In lambs, implantation has caused in some cases vaginal and rectal prolapse, as well as urinary blockage resulting in death (Jordan 1953; Clegg et al., 1955). These findings have been supported by local experience; where implantation under some conditions has had some serious results.
The drug of choice for implantation is hexoestrol, which appears to have less side effects on the animal. It is also less toxic to humans; having only about one eigtheenth the oral potency of stilboestrol (Bishop (et al., 1948). The human hazard appears to be infinitesimal provided the drug is administered correctly. It has been reported from the United States that even with high level dosage the detectable level of stilboesrol in edible meat is something less than 1 part per 10 million (it would take 22 lb. of such meat to supply one daily therapeutic dose to man). Veterinary Record, 1957).
The following points should be emphasized:
(1) These hormones could be dangerous to human health if accidentally ingested.
(2) Pellets must be administered subcutaneously behind the ear. This insures that any unabsorbed hormone is dressed off the carcase at slaughter.
(3) Do not exceed recommended dose, which on present indications appears to be 60 mgm. for steers and 15 mgm. for lambs. Also, no added response could be expected from repeated implantation of the animal.
(4) Treat only animals destined for slaughter. Work is currently in hand to investigate the possible effect of implantation on subsequent fertility.
(5) Hormone implantation is not a substitute for feed and good husbandry.
(6) Do not implant backward stores in a short fattening season. Present indications are that animals are best treated towards the end of the fattening period. For steers this is 2 to 4 months prior to slaughter; and for sheep one to two months prior to slaughter.
(7) Hormone implantation appears to hold some promise with cattle but not with sheep.
Finally, it should be realised that there are considerable interactions between sex, age, plane of nutrition and rates of the hormone for both cattle and sheep.
This is emphasised by the variety of results obtained so far. Much more work is needed under the variety of conditions presented by the Australian environment before one can be clear as to just when implantation can be recommended with confidence.
(ACKNOWLEDGMENT: The photographs reproduced were supplied by the author, with original blocks supplied by courtesy of the Division of Information Services, Dept. of Agriculture, N.S.W-Editor).