2 IDENTIFICATION OF CONTAMINANT SALE LOTS
SUMMARY A trial incorporating the testing of commercial core samples has provided further evidence of wool contamination arising from crossbreeding Merinos with Damara fat tail rams. The trial has also highlighted limitations of the CSIRO Dark Fibre Detector for this purpose in terms of both its subjectivity and the operator time required for a test. Core samples from bales of fleece wool from Merino ewes known to have reared Merino lambs (5 lots), or to have reared Damara crossbred lambs (14 lots), or to have been mated to Damara rams but failed to rear a lamb (6 lots), were tested for pigmented and for medullated fibres by 3 laboratory methods. The tests were performed at AWTA Ltd and SARDI. The wool from the 3 different farm management practices had significantly different (P<0.005) concentrations of pigmented and medullated fibre. The ewes rearing the Merino lambs showed the lowest contamination, those rearing the Damara crossbred lambs showed the greatest contamination, and the remaining 6 lots showed intermediate concentrations of pigmented and medullated fibre. The 2 laboratories were not significantly different (P≥0.05) in their reported concentrations of medullated fibres and of the darkest (CSIRO darkness levels 6 to 8) pigmented fibres. However, for the pale-pigmented fibres (CSIRO darkness levels 4 and 5) and the total pigmented fibre concentration there were differences between the laboratories.
Merino wool contamination from rearing of Damara crossbred lambs
Recent importations and promotion of Damara sheep has raised concerns and debate about potential for Merino wool contamination. This project examined Merino ewe wool contamination arising from the mating of Damara rams and rearing of Damara crossbred lambs. Shirley-blended core samples from 3 commercial greasy wool sale lots known to involve Merino ewes shorn with Damara crossbred lambs at foot (2 lots), or shorn 3 weeks after weaning, were assessed. Contaminant fibres were above commercial expectations for Merino wool and present in every core sample measured. There was no significant difference found between these sale lots. From an experimental flock, composites of fleece samples were carded and the effects of mating or rearing alone assessed. No detectable increase of pigmented or heavily medullated fibres, above very low background levels, were detected among the Merino ewes mated to Damara rams (1 ram per 65 ewes). However, high concentrations of contaminant fibres were found in the Merino ewe wool at weaning of their Damara crossbred lambs and also 3.5 months after weaning; with reduced levels post-weaning. The management strategy of restricting wool exposure to mating effects alone may offer advantage but delaying shearing of ewes after weaning to reduce the contaminant fibre burden was, in this case, not sufficient to overcome potential concerns for wool processing. However, in view of the many potential contributing factors, actual contamination may vary widely between cases and require the advancement of presale measurement to gain buyer confidence and accurate appraisals.
Effects of thyrotropin-releasing hormone and a thyrotropin releasing hormone analog on growth and selected plasma hormones in lambs.
An 8-wk growth trial was conducted to assess the effects of continuous infusion of thyrotropin-releasing hormone (TRH) and an active TRH analog less than Aad-His-Pro-NH2 (the less than Aad is L-pyro-alpha-aminoadipic acid) on growth trial performance, carcass composition and hormone profiles of growing lambs. Both drugs were infused at 600 micrograms X lamb -1 X d -1 with 16 lambs/treatment. Both TRH and less than Aad-His-Pro-NH2 decreased average daily gain (ADG; P less than .01) and increased feed conversion (FC; P less than .01) compared with saline infused controls. Average daily feed intake was not altered. Carcasses of lambs given TRH or less than Aad-His-Pro-NH2 contained fewer kilograms of moisture (P less than .05) and appeared to contain fewer kilograms of protein. Thyrotropin-releasing hormone and less than Aad-His-Pro-NH2 increased thyroid gland weights (P less than .05), but pituitary gland weights were not different. Plasma thyrotropin (TSH) concentrations were increased by both drugs compared with control lambs, peaking at 4 to 7 d after initiating infusion. However, by 14 d, TSH concentrations returned to control levels. Triiodothyronine (T3) and thyroxine (T4) were elevated by both drugs over the entire 8-wk trial, with peak levels reached at 10 d and maintained for the duration of the study. Both TRH and less than Aad-His-Pro-NH2 increased prolactin over the entire period. Growth hormone levels were not altered by either drug. The effects of less than Aad-His-Pro-NH2 infusion on growth trial performance, carcass composition and hormone profiles of growing lambs were very similar to TRH. The negative effects of TRH and less than Aad-His-Pro-NH2 infusion on ADG, FC and carcass protein appear to be the result of elevated T3 and T4 levels.