Farm Table says:
What is the problem?
Hormonal growth promotants (HGPs) have been used in the Australian beef industry for the last 30 years. There is sufficient scientific evidence to establish that growth rate is increased by 10-30%, feed conversion efficiency by 5-15% and carcass leanness by 5-8% (1).
What did the research involve?
Functional life of different implant formulations
-For the purposes of this paper, the functional life of an implant is defined as the period of time for which the implant releases hormone. The duration of the anabolic response during which growth promotion occurs is a separate issue which will be considered later.
Duration of anabolic activity
-There is general consensus in the scientific literature that compressed pellet implants do not stimulate anabolic activity beyond about day 140 after implantation.
Mechanism of action
-There are different hormones with different roles in the metabolic functions of growth and reproduction used in HGPs.
-The growth response (10-30%) to implanting cattle with HGPs is immediate and on a whole mob basis reasonably predictable.
Treatment during periods of liveweight loss
-There is no published information to suggest that the liveweight performance of implanted cattle is disadvantaged during periods of liveweight loss. This applies even with oestradiol treatment which acts through the growth hormone axis to promote growth.
Genetic selection for growth and response to HGP treatment
-Using a variety of indicators, the overwhelming probability is that there has been no measurable diminution, or increase, in the growth response to HGP treatment associated with increased genetic selection for growth rate.
What were the key findings?
Effects on feed intake and efficiency of feed conversion
-A review of numerous feedlot experiments in the United States which included experiments with different implantation strategies concluded that the average increase in liveweight gain was 18 %, the average increase in feed intake expressed as kilograms per day was six % and the average increase in feed conversion efficiency was 8 %. (52).
Effects on carcass composition
-The anabolic actions of HGPs result in a greater proportion of the metabolisable energy intake being partitioned towards protein rather than fat deposition.
Treatment of early and late maturing cattle
-There are very few direct comparisons of the response to HGP treatment by cattle of different maturity type. Those that are available are consistent with the principles described above. HGP treatment increases frame size and mature bodyweight.
Effects on meat eating quality
-There has been considerable research interest over the last decade on the effect of HGP treatment on the eating quality of beef. In the early years of interest, there was uncertainty about whether there was, or was not, a negative effect and if there was, its magnitude.
Effects on fertility of breeding females
-The labels of most of the products registered for use in Australia with heifers carry the warning that the product should not be used in breeding females. This recommendation is sound because both oestrogenic and androgenic growth promoting hormones can impair ovarian development and function, and mammary gland development.
Implant strategies and implant programs for sustained growth promotion
-HGPs were first registered for use in cattle in the northern hemisphere where they were used as finishing agents. Cattle were implanted with a short-life implant about 3 months before slaughter. In these production systems, weaning weights were high and cattle were routinely slaughtered well before two years of age.
Effects on bulls husbanded for meat production
-The traditional practice of castration is intended to produce animals that are easier to manage and have a more marketable carcass. In general, castration minimises the lack of finish and tenderness problems that are often associated with bulls.
Behaviour and side effects
-Implanting cattle with oestrogenic and/or androgenic hormones causes minor changes to the animals’ physiology which can modify their appearance, their behavior or their social interactions with other animals. Some, like the suppression of oestrus in feedlot heifers, are desirable, but most others are unsightly to cattleman and in extreme cases can lead to the economic loss.
The approving effect of HGP use on the rate of live weight gain is extremely reliable and increased gains of about 0.1 kg/d routinely occur during the period of anabolic activity of the implant. This average live weight response may be reduced when cattle go through seasonal fluctuations in the quantity and quality of feed on offer.