Allan J. Rintoul

Effects of pinealectomy on wool growth and wool follicle density in Merino sheep

Abstract: There is evidence to indicate that pinealectomy may enhance wool growth in the sheep. The aim of this study was to determine the effect of pinealectomy on wool growth and wool follicle density in Merino sheep.

The relative feeding value of a new pasture legume, eastern star clover (Trifolium dasyurum), compared with subterranean clover (Trifolium subterraneum)

An accession of eastern star clover (Trifolium dasyurum C. Presl.), a new species to agriculture, has been identified by the National Annual Pasture Legume Improvement Program for commercial release in Australia. This paper reports the findings of an experiment designed to assess the feeding value of eastern star clover compared with a commercial cultivar of subterranean clover (T. subterraneum L. cv. Dalkeith). The hypothesis tested in this experiment is that sheep grazing eastern star clover will have similar growth rates, condition scores, and wool production to sheep grazing subterranean clover. Additionally, it is hypothesised that the sheep grazing the different clover species will have similar health and meat quality. The relative feeding value of the 2 clover species was tested using 14-month-old Merino wethers, grazing 8 by 0.5 ha plots (4 of each species). Stocking rates were such that herbage mass availability would not have limited feed intake. Liveweight, wool growth, and animal health were monitored. After 10 weeks of grazing, 2 animals from each plot were slaughtered for sensory analysis of meat. Although there were generally no differences in liveweight change, condition, or wool growth between sheep grazing eastern star or subterranean clovers, sheep in the subterranean clover plots grew faster during the first month of grazing. There were no differences in meat eating quality (tenderness, juiciness, or flavour), animal health, or vegetable matter contamination of wool. The data suggest that the clovers had the same relative feeding value despite herbage mass from the eastern star clover plots having lower in vitro digestibility, crude protein, and higher fibre than herbage mass from the subterranean clover plots. Given that there was a minimum of 1000 kg/ha of herbage mass in the plots, it is likely that sheep gazing the two clovers were able to maintain the same weight by selecting the high quality components of the pasture. Differences in plant quality are associated with differences in reproductive strategies of the clovers.

Sheep Pineal Beta-Adrenoceptor Function – Interaction with Gamma-Aminobutyric Acid

To clarify the role and site of action of gamma-aminobutyric acid (GABA) in ovine pineal glands, we have investigated the effects of aminooxyacetic acid (AOAA), an inhibitor of GABA transaminase, on endogenous GABA content and beta-adrenoceptor mediated pineal function in Merino sheep. A significant elevation of endogenous GABA levels was noted in the glands, but no effect was observed on radioligand binding in vitro to pineal beta-adrenoceptors following in vivo administration of AOAA. Incubation of washed pineal membranes with GABA or AOAA had no effect on ligand binding to beta-adrenoceptors. Incubation of Merino pineal slices with GABA inhibited isoprenaline-stimulated but not basal serotonin N-acetyltransferase (NAT) activity. Incubation of whole pineal homogenates with GABA was without effect on either isoprenaline-stimulated or basal adenyl cyclase activity. Thus, Merino pineal glands resemble bovine pineals in that beta-adrenoceptor mediated melatonin biosynthesis in both species may be regulated in part by GABA. Our results indicate that GABA may exert its effect on Merino pineal NAT activity at a locus distal to the site of action of adenyl cyclase; however, the detailed mechanism and physiological role of this regulation remain to be elucidated.

Seasonal Changes in the Sensitivity of Ovine Pineal β- Adrenoceptors to Steroids

Immunoneutralization of endogenous gonadal steroids has recently been shown to modify pineal β-adrenoceptor function in intact Merino ewes. In the current study, interactions between gonadal steroids

Effects of modified circulating prolactin levels on seasonal wool growth in Romney ewes

The study investigated the effects of chronic elevation or suppression of circulating prolactin levels on seasonal wool growth in Romney sheep. Ewes (n=10/group) were housed indoors under natural lighting (latitude 34°S) and received either 50 mg bromocriptine i.m./ewe/28 days (Group B), 1 mg spiperone s.c./ewe/day (Group S) or no treatment (Group C) commencing in summer. Wool growth and liveweight were measured every 4 weeks and venous blood samples were collected for prolactin determination. Plasma prolactin levels (mean±S.E.) in Group C exhibited a gradual seasonal decline from 121±29 ng/ml to 35±9 ng/ml (.)

Sheep grazing bladder clover (Trifolium spumosum L.) had similar productivity and meat quality to sheep grazing subterranean clover (Trifolium subterraneum L.)

An accession of bladder clover, a new species to agriculture, was selected for commercial release in Australia with the cultivar name of AGWEST Bartolo. As part of a duty-of-care assessment, we tested the hypothesis that sheep grazing the bladder clover cultivar will have similar liveweight, condition scores and wool production to sheep grazing a widely adopted subterranean clover cultivar (cv. Dalkeith). Further, we hypothesised that sheep grazing bladder clover and subterranean clover will have similar meat quality (after 48 days of grazing) and health as indicated by muscle, liver and kidney panel analysis. The data supported the hypotheses. While there were significant initial differences in liveweight between the two groups of sheep, there were no significant differences in liveweight at later time points during the grazing period and no significant differences in mean daily growth rate between weighing times. There were no differences in wool growth between sheep grazing the bladder or subterranean clover cultivars. Sheep in the subterranean clover plots had significantly higher condition scores after the first 24 days of grazing; however, these differences were not apparent after another 24 days of grazing. There were some differences in indications of animal health; however, there were no significant detrimental effects associated with bladder clover and sheep grazing both species had mean plasma indicators that were deemed ‘healthy’. There were no differences in meat eating quality as estimated by a consumer panel for tenderness, juiciness or flavour. Dry seasonal conditions limited biomass growth and the sheep were removed from the subterranean clover plots on Day 48 of grazing. The sheep grazing the bladder clover plots remained on the plots for a further 26 days. The data indicate that, for the conditions of this experiment, the clovers had the same relative feeding value. Laboratory analysis of herbage from across the clover plots (bulked before analysis) suggest that the bladder clover had higher in vitro digestibility, crude protein and lower fibre than the herbage sample from the subterranean clover plots. The biomass data indicate that the bladder clover cultivar can support more grazing days per ha in a relatively dry season than the subterranean clover cultivar.