Growth and muscle development of steers implanted with hexoestrol

Abstract

A muscle biopsy technique was employed in an experiment designed to assess the effects of hexoestrol implantation on 2-year-old and 6-year-old Aberdeen Angus steers under New Zealand grazing conditions. This paper reports the results concerning live-weight gains, carcass weights and detailed analyses of samples of m. semitendinosus and associated subcutaneous fat.There was some evidence of an adverse effect of the biopsy operation on the older, less tractable, animals, despite the observation of no apparent effect of repeated muscle biopsies in a preliminary trial with sheep.Hexoestrol implantation, of four 15 mg. pellets for the 2-year-old steers and six 15 mg. pellets for the 6-year-olds, led to significant increases in live weight gains during the later part of the trial only, and reduced the dressing-out percentage of the younger animals. Although there were indications of a positive response in carcass weight to hexoestrol implantation, it was concluded that, under the conditions of this experiment, implantation of relatively large dosages was not economically justified in terms of increased meat production.Absorption of the implanted pellets varied from 42 to 85% of the total dosage, but evidenced little association with live weight changes.Deposition of subcutaneous fat appeared to be reduced under the hormone treatment, but the responses in this respect of the 6-year-old steers were highly variable.

Implantation of oestrogenic hormones in beef cattle

“…Such seasonal variation in the response of grass-fed steers to implanted sex hormones stresses once again the possibility of the growth of New Zealand grazing stock being affected by oestrogenic levels of pasture plants. Everitt and Carter (1961), using dosage levels of 60 mg of implanted hexoestrol in pasture-fed two-year-old Aberdeen Angus steers, and 90 mg in six-year-olds, found that only the younger cattle evidenced a real increase in liveweight gain over three months in the spring. Callow and Finney (1959), in a study of the implantation of 15 mg, 30 mg, or 60 mg of hexoestrol in steers reared under obviously poor, Argentinian, pastoral conditions, concluded that 30 mg gave the optimum response and that the 60 mg dose level may have actually depressed, rather than stimulated, growth.…”

“…Previous work (Everitt and Carter 1961) had shown the fasting losses of similarly-aged cattle implanted with 60 mg hexoestrol to exceed those of untreated steers. To check that observation in this experiment the cattle were yarded at 0800 hours on 21 November 1959, and were fasted, but with access to water, for 31 hours; four liveweights were recorded during this time, and the last of these weights (taken at 1500 hours on 22 November 1959) has been termed the Starved Liveweight.…”

“…The method of implantation has been discussed elsewhere (Everitt 1959). Liveweights were recorded when the cattle were removed from pasture at three hours after sunrise; the reasons for the choice of this time of weighing are based on the work of Tayler (1954) and have been reviewed by Everitt and Carter (1961).…”

“…Particularly for meat exporting countries, such as New Zealand, it is important that these conformation and physiological changes should not impair carcass quality; the possible increase in carcass weight must be considered in relation to the degree of "side-effects" concurrently elicited. In New Zealand, Everitt and Carter (1961) found that a dosage of 60 mg hexoestrol in two-year-old steers, and of 90 mg in six-year-olds, did not produce a significant increase in carcass weight, although there were indications of a small, positive response. Consideration of other published work (Casida et al 1959;Callow and Finney 1959;Davidson 1960) suggests that, in New Zealand, the optimum dose level of hexoestrol in grass-fed steers may be less than those employed by Everitt and Carter (1961), and the level may vary according to the season of the year and the plane of nutrition supplied to the cattle.…”

A Biopsy Technique for Sampling the Gracilis Muscle in the Baby Pig

“…Merkel et al (1954) and Wilson et al (1955) working with swine and cattle, respectively, described surgical procedures by which a sample was excised from the intact muscle. Everitt and Carter (1961) and Bray (1963) used an instrument similar to a cork borer to obtain a muscle sample; whereas, Harris and Bennett (1970) used a "muscle tissue extractor" to sample the semitendinosus and longissimus muscles of cattle. The above biopsy techniques were developed with larger, more mature animals, and thus may not be directly applicable to the young pig.…”