Last update: August 15, 2011 08:44:51 AM E-mail Print


The effect of steroid treatment of pre-weaned Merino Iambs on subsequent growth and fertility

J J Olivier, P J Griessel, A P Pretorius, P R King & J A Roux*

Grootfontein ADI, Middelburg, South Africa, 5900


It is alleged that steroids are used in the small stock stud industry to enhance growth when preparing the animals for sales and shows. Due to the detrimental effect of these hormones on testes development, it is suspected that the hormones are administered at a very young age in order to allow the testes to recover before the age of 12 to 18 months. To determine the effect of steroid administration at a young age, experimental animals (consisting of both ram and ewe lambs) were treated with either nine mg testosterone propionate (Sinovax-HR) per animal or 0.007 mg/kg live mass nandrolone laurate (LarabolinR) at 13, 37, 70 and 98 days of age. Experimental animals and a control group were pen fed. Body mass and testes circumference were recorded monthly. At 8 and 12 months of age libido and semen tests were carried out on all rams. The incidence of oestrus was determined in ewes by means of teaser rams at 12 months of age. Average body mass at 12 months of age was 72.08 ± 2.36, 69.04 ± 2.28 and 69.81 ± 2.72 kg for Sinovax-H, Larabolin and control rams respectively. The corresponding body mass for ewes was 66.56 ± 2.49, 58.78 ± 2.66 and 62.44 ± 2.59 kg. No significant difference in body mass was found between the treatment and control groups at all ages for both rams and ewes. Testes circumference from three to eight months differed significantly (P<0.05) between experimental and control animals. However, these differences had disappeared at 12 months of age with testes circumference being 6.11 ± 0.26, 5.62 ± 0.24 and 6.18 ± 0.31 cm for the Sinovax-H, Larabolin and control groups respectively. Similarly, at eight months of age the percentage normal sperm cells of the Sinovax-H group (21.1 ± 14.8) differed significantly (P<0.05) from that of the control group (74.7 ±15.8), but at 12 months of age this difference was insignificant (78.4 ± 7.7 vs. 77.7 ± 8.2). All ewes displayed overt oestrus at 12 months of age. It is concluded that the pre-weaning treatment of lambs with steroids does not have a beneficial effect on growth. Although testes growth was inhibited during the prepubertal period, this effect disappeared soon thereafter. The use of steroids at a young age to enhance growth rate in prospective show and sale animals therefore seems to be unwarranted.





Proceedings 12th SASAT congress, Proceedings 33rd SASAS congress