Wool Growth Rate Research Articles

Mineral supplementation and wool production of young Merino sheep on the south coast of Western Australia

Wool-free liveweight change (LWC), wool growth rate, annual wool production, and wool characteristics of young Merino wethers fed supplements of lupins with gypsum or a multi-element mineral lick were examined in 12 experiments at 5 farms between 1989 and 1992. The source of sheep varied between experiments; age was 4.5-6.5 months and liveweight 28-37 kg at the beginning of supplementation. Sheep were fed lupins, lupins coated with gypsum (15-20 g/kg lupins), or lupins along with access to the mineral lick (offered at 140 g/sheep.week). The amount of lupins offered in all treatments within any experiment was the same. Supplementary feeding varied between experiments from 150 to 240 days. The sheep grazed annual pastures at stocking rates of 8-1 6.7ha. Average lick intake was 12-18 g/sheep. day. During supplementary feeding, there was considerable variation in LWC (-80 to +110 g/day) and clean wool growth rates (3.8-15.1 g/day) within and between experiments. However, there was no significant positive effect of gypsum or mineral lick supplementation on LWC or clean wool growth rates during or after supplementary feeding in any experiment. There were positive (P<0.01) relationships between LWC and clean wool growth rates during supplementation. Also, for some spring-shorn sheep types, staple strength of wool was linearly related (P<0.01) to LWC in the period before the position of break in the wool staple. Annual wool production, average fibre diameter, and staple strength of midside wool were not significantly increased by supplements of gypsum or mineral lick in any experiment.

A biotechnological approach to improving the nutritive value of alfalfa.

The postruminal supply of the sulfur-containing amino acids, methionine and cysteine, has been reported to be a major limitation to wool growth in sheep. We aim to improve the protein quality of forage for ruminants by introducing into alfalfa chimeric genes encoding a ruminally stable, sulfur amino acid-rich protein from sunflower seeds. Four gene constructs were transferred to Australian commercial cultivars of alfalfa using Agrobacterium tumefaciens-mediated transformation and selection with phosphinothricin (PPT). Modification of the sunflower seed albumin protein-coding region by addition of the coding information for an endoplasmic reticulum (ER) retention signal was found to greatly increase the level to which the sulfur amino acid-rich protein accumulated in the leaves of transgenic alfalfa plants. The Cauliflower Mosaic Virus (CaMV) 35S promoter and two light-regulated plant gene promoter regions were compared for their ability to direct high-level expression of the introduced genes in alfalfa leaves. The highest expression of sunflower seed albumin was found in transformants bearing a gene incorporating the promoter from the Arabidopsis thaliana ats1A gene, which encodes the ribulose bisphosphate carboxylase small subunit. The highest level of sunflower seed albumin found in transgenic alfalfa leaves was estimated to constitute .1% of soluble leaf protein. This level of accumulation of the foreign protein would be predicted to supply an extra 40 mg of sulfur amino acids daily to sheep fed the modified forage. Published studies in which wool growth rates were significantly increased employed supplementation of approximately 1 to 2 g of sulfur amino acids daily.

Effect of selection for wool growth on seasonal patterns of yield, fibre diameter, and colour in Romney lines

Seasonal wool growth and associated wool characteristics were measured in a Romney line selected for high fleece weight and an unselected control line in 1990 and 1991. Both had a significant (P<0.01) decline in wool growth rate in winter compared with summer. The wool growth rate advantage (P<0.001) of the selected line over the control averaged 19 and 33% for ewes, and 24 and 36% for hoggets, in summer and winter, respectively. Staple strength, yield, and fibre diameter differences were closely associated with wool growth. Colour analysis showed no difference between lines in either brightness (Y) or yellowness (Y - Z). However, both the Y and Z values were lower in spring and summer, while Y - Z was highest in summer. The results suggest that selection for high fleece weight also improves major wool characteristics and reduces the relative winter wool growth decline in Romneys.

Some comparative studies of sulfate metabolism in Merino sheep genetically different in wool production

Several aspects of sulfate metabolism were compared in sheep from two selection flocks, selectively bred for either high (Fl+) or low (FI-) clean fleece weight per head. These were studied within a 23 factorial design: 2 flocksx2 levels of formaldehyde treated casein in diet (0 or 80 g day-1)x2 levels of subcutaneous L-thyroxine (0 or 1 mg day-1) with 4 sheep per cell. The treatments influenced the rates of wool growth and the output of sulfur in wool (P < 0.05), but with interactive effects (P < 0.05). The F1+ sheep produced 24 and 32 8g sulfur in wool cm-2 day-1at the midside when consuming the control and casein supplemented diet. The outputs of sulfur in wool by F1- sheep consuming these two diets were 16 and 17 8g cm-2 day-1. The thyroxine treatment increased the rate of growth of wool by 11% (P < 0.05), but did not increase average fibre diameter or the sulfur content of wool. Sulfate was cleared more rapidly (P < 0.05) from the plasma of sheep consuming the casein supplemented diet, with a rate constant of 0.134 h-1, compared to 0.099 h-1for the control sheep. The rate constants for Fl+ and F1- sheep were 0.102 and 0.131 h-1 respectively (P < 0.05). The concentration of sulfate in plasma was similar in all treatment groups: 1.3 mmol L-1The differences in the clearance of sulfate from plasma were reflected in similar differences in the proportion of the injected 35S-sulfate excreted in urine during the following 24 h. The sheep of the F1- flock and those consuming the casein-supplemented diet excreted significantly greater proportions of the injected 35S in urine (P < 0.05). In a second experiment, adult sheep (n = 24), the progeny of F1+ or F1- rams mated with a flock of medium wool Merino ewes, were randomly allocated to a low (c. 0.8 maintenance, 1 g sulfur day-1) or high (c. 2xM, 3 g sulfur day-1) dietary regime. [35S] sodium sulfate was again injected intravenously. There were no significant differences between the genetic groups for (i) sulfate concentration in plasma, (ii) total and net rates of irreversible loss of sulfate from plasma, (iii) the proportion of the injected [35S] sodium sulfate excreted in urine, (iv) the proportion of the excreted 35S present in urine as sulfate, and (v) the quantity of sulfate excreted in urine daily. However, the dietary treatments significantly influenced all these traits, except the concentration of sulfate in plasma. The direction of these effects was consistent with the proposition that sheep regulate excretion of sulfate from kidneys to maintain homeostasis of sulfate within the body. The smaller phenotypic difference in wool production between the two half-bred flocks in the second experiment, probably limited the chances of detecting any differences in the metabolism of sulfate.

Reduction of mitotic rate in the wool follicle by cortisol

Cortisol reduces wool growth at the systemic and local level, but the minimum time for a response to take place has never been reported because the methods used to measure the changes require at least 4 days of wool growth. A technique using local intradermal colchicines to estimate mitotic rate in wool follicles has been used in the present study, and can measure changes in mitotic rate over periods as short as 2 h. Within the dose range 0 to 1000 8g, intradermal injections of cortisol into adrenalectomized sheep had no effect on mitotic rate in wool follicles within 6 h. Stimulation of endogenous release of cortisol using exogenous adrenocorticotrophic hormone in entire sheep, was similarly ineffective within 5 h. Further investigations using adrenalectomized sheep revealed that bolus injections of hydrocortisone also had no effect on mitotic rate within 5 h. A fourth experiment was conducted, in which 15 adrenalectomized sheep were infused with: a control infusate for 4 days, followed by this infusate containing cortisol at a rate equivalent to 0, 0.87 or 1-82 mg kg-1 day-1 for 4 days, followed by a further 4 days of control infusate. Five hours after the change from control to the cortisol infusate, there was no significant difference in mitotic rate between treatment groups when adjusted using mean mitotic rate in the pre-cortisol period as a covariate (P = 0.887). However, 29 h of infusion with cortisol was sufficient to bring about a significant reduction in mitotic rate (P = 0.034). During the following 3 days of cortisol infusion, mitotic rate was maintained at a significantly lower level in the treated groups (P = 0.018), with the greatest effect apparent in the group which received the highest dose of cortisol. At 53 h post-cortisol infusion, there was a significant recovery in both cortisol treated groups to mitotic rates significantly above those recorded in the pre-cortisol infusion period (P = 0.003), while mitotic rate remained unchanged in the group which received no cortisol. It is concluded that acute changes in plasma cortisol concentration are not likely to produce acute changes in wool growth, but a sustained elevation of plasma cortisol concentration will reduce the rate of wool growth by reducing mitotic rate in wool follicles.

Productivity and cold resistance in ewes pre-lamb shorn by standard or cover comb

The cover comb has been developed in New Zealand as a means of increasing residual fleece depth after shearing and so increasing the resistance of shorn sheep to cold-stress. The effects of pre-lamb shearing ewes with cover or standard comb, and of leaving ewes unshorn until after weaning, on their feed intake, productivity, and cold resistance were studied. Border Leicester x Romney ewes were divided into three groups balanced for pregnancy status, ewe age and liveweight. Two groups of ewes were shorn, by either cover comb or standard comb, on day 114 of pregnancy (P114) and one group left unshorn until weaning on day 84 of lactation (L84). Ewes were managed under the same conditions during pregnancy and lactation. Ewes shorn pre-lamb by cover comb had lower mortality from shearing to lambing, and lower organic matter intakes and biting rates at P123-126 than ewes shorn by standard comb. These parameters did not differ between ewes shorn pre-lamb by cover comb and unshorn ewes except biting rate which was greater in the cover comb-shorn group. Twenty days after shearing (P134), the liveweights of ewes were greater in the unshorn group than in the cover comb-shorn group (P < 0.05), which was in turn heavier (P < 0.05) than ewes shorn by standard comb. Midside clean wool growth rates were greater in standard comb- and cover comb-shorn ewes during the post-shearing period (to day 40 of lactation) than in unshorn ewes ( P < 0.05). Similarly, the yield and brightness of wool were superior (P < 0.05) in pre-lamb shorn groups. Lamb liveweights at birth, docking and weaning, and lamb survival, were similar between shearing policies. Rectal temperature (RT) was significantly (P < 0.05) lower in both pre-lamb shorn groups than in the unshorn group on day 3 post-shearing (S3), but by S5 only the ewes shorn by standard comb had lower RT. These results suggest that the greater amount of residual wool in cover comb- vs standard comb-shorn ewes provides a low cost practical method for reducing the two important disadvantages of pre-lamb shearing, namely increased cold-stress and feed intakes post-shearing.

Nutrient partitioning in Merino rams with different wool growth rates

AbstractThe aim of this experiment was to determine whether there is any physiological basis for concerns that selection for fleece mass may decrease fitness by increasing the partitioning of nutrients to wool at the expense of other body functions.Forty-five Merino rams (24 months old) were given food at an ad libitum and a maintenance level of nutrition. Animals were grouped into high, average or low clean fleece growth-rate categories on the basis of measurements made during the ad libitum feeding period. During ad libitum feeding, high producers grew proportionately 0·42 more clean fleece, and deposited proportionately 0·36 more energy and 0·42 more nitrogen (N) as greasy fleece than average producers. This was achieved by partitioning a higher proportion of N consumed to wool (0·08 v. 0·06), and not by increased energy or N retention. High producers adapted to the maintenance diet by decreasing clean wool growth rate proportionately by 0·32. There were no differences between high and average wool producers in clean wool growth rate or the percentage of N or energy intake partitioned to wool at the maintenance level of feeding. Although there were no differences in initial live mass between groups, low producers gained proportionately 0·45 more live mass during the experiment than average producers.It was concluded that Merino rams of high clean-wool production potential are not more efficient, but partition more of the available nutrients to wool production at the cost of body tissue deposition.

Effect of sward surface height on herbage intake and performance of lactating ewes lambed in winter and continuously stocked on pasture

SUMMARYThirty-six 4-year-old Border Leicester × Romney (BR), Poll Dorset × BR (PBR) and Suffolk × BR (SBR) ewes balanced for litter size were assigned, 6 days after the mid-point of lambing (29 June 1989), to one of three sward surface height (SSH) treatments replicated twice (six ewes/1 ha paddock). The mean SSH during the 54 days of the trial were 2·6, 4·4 and 7·8 cm. Herbage organic matter intake (OMI) was measured using intraruminal chromium controlled release capsules during weeks 3, 4, 7 and 8 of lactation. Ewe OMI was not influenced by SSH during week 3 of lactation. During weeks 4 and 7 of lactation, ewe OMI increased with SSH up to a SSH of 7·8 cm. In week 8 of lactation there was no significant difference in OMI between ewes grazing the 4·4 or 7·8 cm SSH treatments, suggesting maximum intake at this stage of lactation is reached at 4·4 cm SSH. A maximum OMI of 2·6±0·1 and 3·0±0·1 kg OM/ewe per day (P< 0·05) was reached in week 4 of lactation on the 4·4and 7·8 cm SSH treatments, respectively. Ewes grazing the 2·6 cm swards had a relatively constant OMI throughout the experiment (range 1·8±0·1 to 2·0±0·1 kg OM/ewe per day). However, these ewes lost 10·5 kg of liveweight while those on the 4·4 and 7·8 cm SSH treatments maintained a constant liveweight. Sward surface height had no effect on ewe midside wool growth rate or mean fibre diameter (measured at day 60 of lactation) or on lamb liveweight gain. Ewe breed cross had no effect on ewe OMI or midside wool growth. Lambs reared by SBR ewes were heavier (20·4±0·5 kg) at day 60 of lactation than lambs reared by PBR (18·7±0·6 kg) or BR (18·4±0·6 kg) ewes (P< 0·05). These results suggest that for Winter(June)-lambing ewes in good condition a SSH of 4·0 cm under continuous stocking should ensure near to maximum ewe and lamb performance. However, ewes in good body condition at lambing stocked on a SSH down to 3 cm will rear lambs to acceptable weaning weights but at the expense of ewe liveweight loss and possible long-term carry-over effects on future productionif compensatory weight gains are not achieved during the spring pasture growth period.

Effects of stocking rate in spring on liveweight and wool production of sheep grazing annual pastures

Two experiments examined the effects of different stocking rates in spring, and hence the availability of annual pastures, on changes in liveweight and wool production in Merino wethers (Experiments 1 and 2 respectively: age 5 and 2+-year-old; liveweight 63.8 � 0.64 (s.e.m.) kg and 43.8 � 0.34 kg; condition score 3.9% 0.14 and 3.l � 0-08). In Experiment 1, stocking rates were 8, 16, 24, 32 and 40 sheep/ha from 8 August, 1989 f9r 122 days; Experiment 2 involved an additional stocking rate of 48 sheep/ha from 23 August, 1990 for 98 days. Feed on offer (FOO kg DM/ha) declined (P < 0.01) linearly as stocking rate increased. Stocking rate and initial FOO (ranging between 1100 and 7000 kg DM/ha) had no significant effects on pasture growth rate (PGR) through most of spring. Late in spring, increased stocking rates resulted in greater (P < 0.05) PGR. The total amount of pasture produced in the grazing period was not significantly affected by stocking rate (Expt 1, 7530 to 8200 kg DM/ha; Expt 2, 6390 to 6860 kg DM/ha). The relationships between liveweight change (LWC) or wool growth rates (WGR) and FO, during the period until pasture wilting at the lowest stocking rate (83 days in Expt 1; 76 days in Expt 2), were described by Mitscherlich equations. More than 74% of the variation in LWC or WGR was explained by differences in green FOO. In Expts 1 and 2 respectively, more than 90% of the maximum liveweight gain (66 and 192 g/day) was achieved at a FOO of 4000 or 3000 kg DM/ha, and sheep maintained weight at 2000 or 1000 kg DM/ha. More than 90% of the maximum WGR (22.3 and 19.0 g/day) was achieved at a FOO of 3000 or 2000 kg DM/ha. More than 70% of the variation in WGR was explained by LWC in both experiments. The slopes of the linear relationships were 0.047 g wool/g LWC in Expt 1, and 0.024 g wool/g LWC in Expt 2. At liveweight maintenance, sheep produced 15% less (Expt 1) or 25% less (Expt 2) wool than those grazed under conditions which allowed maximum rates of liveweight gain. Fibre diameter (FD) and length of wool grown were affected in the same manner as WGR by increases in FOO and hence LWC. In Expts 1 and 2 respectively, total clean wool weights were reduced by 17 and 9 g, mean FD by 0.05 and 0.02 microns and staple length by 0.35 and 0.13 mm, for each increase of one sheep/ha during the spring treatment periods. The effects of stocking rate in spring on annual wool production, mean FD and staple length were described by linear (P < 0.05 to P < 0.01) relationships. Standard deviation of midside FD (Expt 2), staple strength and position of break (both experiments) did not change significantly with stocking rate. These results indicate that grazing to a lower FOO during spring can be used to manipulate the amount and characteristics of wool produced by Merino wethers grazing annual pastures in Mediterranean climates with 600-700 mm rainfall.

Transgenic sheep and wool growth: possibilities and current status.

Merino wool is the result of generations of selection, yet improvements in wool quality and performance are still being sought. Through gene manipulation, sheep transgenesis offers possibilities of understanding the relationship between wool keratin protein composition and fibre structure and properties and of introducing novel changes to fibre properties and growth rates. We have established an efficient sheep transgenesis programme with an overall transgenic rate of 2.1% of zygotes injected. However, by incorporating in vitro culture and assessment of injected zygotes, this equates to a transgenic rate of 13% from 516 lambs born. With the first keratin gene construct, a wool keratin type II intermediate filament gene, four live F0 transgenic sheep have been produced and all express the transgene. In one of them, the highest expressor, phenotypic and ultrastructural changes were evident in the fleece. To improve wool growth rate by increasing the supply of cysteine to the follicle, transgenic sheep are being produced carrying the two genes necessary for endogenous cysteine synthesis. Three promoters have been tested driving the cysteine synthesis genes: two general promoters, the Rous sarcoma virus long terminal repeat and mouse phosphoglycerate kinase promoter, and a rumen-specific promoter from the sheep small proline-rich protein gene. To date, one transgenic sheep (bearing the small proline-rich protein promoter constructs) has produced cysteine in the rumen, although the amount was low at 3 months of age and not detectable at 6 months.

Nutritional responses in wool growth by four Merino genotypes of differing wool growth performance

Sheep from four Merino flocks, different in annual clean fleece production when grazed together, were offered a range of nutritional treatments to compare their ability to digest dietary organic matter (experiment 1) and to compare the relationships of wool growth and fibre diameter with nutrient intake (experiment 2). The sheep were selected from a finewool (Fl), a strong wool (S), and two medium-Peppin (MP6 and MP10) flocks. The nutritional treatments varied intakes of two pelleted diets-B and F. Diet B consisted of oat grain, lucerne chaff, and oaten straw, while diet F was as for B but fortified with fishmeal. The digestibility of both diets was negatively related to the level of intake, and there were some differences between the flocks in their ability to digest organic matter. Clean wool growth per unit area of skin was curvilinearly related (P < 0.001) to N intake, but was not influenced by diet per se. The regression coefficient for the relationship of clean wool growth with N intake and the estimated maximum wool growth rate of flock F1 were less than the other flocks. However, flock MP10 grew less wool than flocks S and MP6 at any given intake. Variation in (fibre diameter)2 accounted for 0.6 of the variation in wool growth, with responses in fibre diameter to intake being similar to those observed in wool growth. The responses in plasma cystine of the flocks to N intake differed, with the relationship for flock F1 being curvilinear and reaching a maximum at an intake of 27 g N day-1, while the responses of the other flocks were essentially linear. The relationships between plasma cystine level and wool growth differed between the flocks such that wool growth of sheep from flocks S and MP6 was more responsive to increased plasma concentration of cystine.

Wool production and blood supply to skin and other tissues in sheep.

Quantitative measurements of blood flow (BF) to skin and several other tissues were made using radioactive microspheres in conscious sheep. The sheep were from established flocks that had been selectively bred for greater (Fleece plus) or lesser (Fleece minus) wool production. The BF rate per unit area of wool-bearing skin was significantly greater in the Fleece plus (n = 9) than in the Fleece minus (n = 6) group, but the correlation between skin BF and the wool growth rate in individual animals was modest (r = .581). There was a strong, positive correlation (r = .813) between wool production and pineal BF. Other tissues that exhibited significant BF differences between the two groups included adrenal glands and fat, which were greater in Fleece plus sheep, and thyroid glands, reticulum, rumen, and extremity skin (non-wool-bearing), which were lesser in Fleece plus sheep.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of feed intake with cystine availability and wool growth in Merino wethers

Two experiments were conducted to characterize the relationship between nutrient supply and the rate of wool growth. We concentrated on the accepted view that the rate of wool growth in Merino sheep is primarily limited by the availability of sulfur amino acids, which are largely determined by diet intake and its interaction with microbial fermentation in the reticulo-rumen. In the first experiment, the effects of variable intakes of two diets (one including 10% fishmeal) by sheep on the rate of irreversible loss of cystine and plasma cystine concentration were investigated. Nitrogen intake (N) was positively and linearly related to both the irreversible loss rate and the plasma concentration of cystine, with no effects of diet per se. In the second experiment, the same dietary treatments were imposed on 39 wethers for 16 weeks following an 8 week pre-experimental period. The monthly rates of wool growth, average fibre diameter and sulfur content of the wool were measured and related to various components of intake. The rate of wool growth responded in a positive curvilinear decreasing manner to changes in intake, the response requiring 2 months to stabilize. There was no significant effect of diet when daily intake was expressed as g N kg-0.75 liveweight. Including the covariate (wool growth when fed the standard diet), the quadratic linear model accounted for 90% of the total variation in wool growth. Responses in fibre diameter and its variation, and wool sulfur content were similar to those of wool growth, in that they were positive and did not equilibrate quickly. A saturation kinetics model of the relationship between daily N intake (g N kg 0.75 liveweight) and wool growth accounted for a similar proportion of the variation as did a linear (with quadratic term) model without the covariate. It is concluded that the saturation kinetics model may be useful for more comprehensive comparisons of both the genetic potential and the sensitivity of wool growth to environmental changes.

Simulation of wool growth rate and fleece characteristics of Merino sheep in Southern Australia. Part 2—Assessment of biological components of the model

The first paper in this series described the development of procedures for predicting the effect of management changes on wool growth rate and fleece characteristics. A model of a self-replacing flock of Merino ewes was modified to provide weekly predictions of wool growth rate, fibre diameter, staple length and staple strength. This paper presents the results of a comparison of biological predictions of the model with field observations collected under a range of seasonal conditions and stocking rates. The results of the comparisons demonstrated the ability of the model to mimic the seasonal pattern of events and the trends in pasture and sheep performance generated by a wide range of stocking rates. The model successfully predicted the direct effects of stocking rate and changing seasonal conditions, as well as the interactions between them. For most of the fleece data, the model predictions were well within one standard deviation of the field observations. No major biases in the predictions of the model were evident.

Changes in plasma amino acid patterns and wool growth during late pregnancy and early lactation in the ewe

Pregnancy and lactation result in depressed growth, fibre diameter and tensile strength of wool. Competition for nutrients between wool follicles, maternal tissues and the foetus may cause these changes. Changes in the concentrations of individual free amino acids in plasma, during late pregnancy, were used as indicators of limiting amino acids in this experiment. A group of pregnant ewes was maintained in the animal house during late pregnancy and early lactation and measurements made on amino acids in plasma. Liveweight, wool growth and quality characteristics and sulfur in wool were also measured. Comparisons were made between the different time periods in pregnancy and lactation and between the reproducing ewes and a group of non-reproducing ewes maintained under the same conditions. During the last 3 weeks of pregnancy, there was a 31% decline in the concentration of the total, free essential amino acids in plasma. There was also a significant decline in the concentration of arginine (60%), lysine (55%) and threonine (48%). The concentrations of these amino acids increased during the first 3 weeks of lactation. There was no change in concentration of methionine or cystine. Wool growth rate was lowest in the last 3 weeks of pregnancy and the reproducing ewes had significantly lower wool growth, fibre diameter, staple strength and sulfur in wool than the non-reproducing ewes. The results indicate that a lack of the sulfur-containing amino acids is unlikely to be limiting, but a lack of arginine, lysine or threonine may be limiting wool growth and protein deposition in late pregnancy.

Supplementation of young Merino sheep grazing annual pastures with lupin, barley grain, or silage

We examined the effects on liveweight change and wool production of supplements of lupin, barley grain, or silage given to Merino weaners (age 5-7 months; starting weight about 30 kg) grazing dry annual pastures. In experiment 1, each supplement was offered at 5 rates (g/sheep.day): lupin, air-dry, 75-450; barley, air-dry, 80-480; silage, fresh, 430-2580. Sheep on all treatments gained weight in the first 29 days of supplementary feeding, with no effect of rate of supplementation (lupin 97 g/day; barley 57 g/day; silage 74 g/day). Those receiving no supplement also gained weight (40 g/day). Different supplements were not compared because the energy levels of lupin and barley were not measured. Over the next 48 days, liveweight changes increased (P<0.001) linearly with rate of feeding of lupin (25 � 2.1 g/100 g) and barley (12 � 0.8 g/100 g). The trend with silage (11 � 5.0 g/kg) was not significant. Taken over the 77 days, liveweight changes increased (P<0.01) linearly with rate of feeding for lupin (20 �. 1.8 g/100 g), barley (8 �. 1.7 g/100 g), and silage (10 �. 2 g/kg). There were no significant (P>0.05) differences associated with the rate of supplementation for annual clean fleece weight (lupin 3.43 kg, barley 3.37 kg, silage 3.30 kg) or mean fibre diameter of the 12-month fleece (lupin 22.2 �m, barley 22.6 �m, silage 22.1 �m). In experiment 2, sheep were given no supplement, lupin, barley, or lupin and barley mixtures (metabolisable energy ratio, 1:3,1:1,3:1). All supplements increased liveweight change (P<0.01) and clean wool growth rates (P<0.05) compared with no supplement. There was also a trend towards an increase in total wool grown by supplemented sheep (3.8 - 4.00 v. 3.73 kg). Liveweight change during the first 71 days of feeding increased (P<0.01) as the proportion of lupin in the supplement increased, with no effects in the final 70 days of supplementation. During supplementation, clean wool growth rate increased (P<0.05) as the proportion of lupin in the mixture increased, but there was no significant effect on the total amount of wool grown over 12 months or on mean fibre diameter. Supplements resulted in increased (P<0.001) staple strength when compared with controls (21-25 v. 14 N/ktex).

Effect of sward height during late pregnancy on intake and performance of continuously stocked June- and August-lambing ewes

Herbage organic matter intake (OMI), grazing behaviour and ewe and lamb production were measured during the last 4 weeks of pregnancy in 2-year-old and mixed-age Border LeicesterxRomney ewes due to lamb in June (winter) or August (spring). The intake of herbage (averaged across lambing date groups) was 1.4�0.1, 1.71�0.1, 1.7�0.1 and 1.9 9�0.1 kg OM ewe-1 day-1 (mean � s.e.m., P < 0.01) for ewes continuously stocked on 10-year-old ryegrass (L. perenne) and white clover (T. repens) pastures maintained at sward surface heights (SSH) of 2.0, 4.0, 6.0 and 8.0 cm respectively. Ewes that were in a good body condition score achieved their required daily intake of energy at a SSH of 2.0 cm. Relative to ewes on the 8.0 cm SSH treatment, those on the 2.0, 4.0 and 6.0 cm SSH treatments attempted to increase intake by increasing grazing duration rather than biting rate. Ewe liveweight, condition score, midside wool growth rate and mean fibre diameter were not affected by sward surface height in either lambing group. There was no within season effect of SSH on lamb birthweight, but lambs born in June were lighter than lambs born in August (4.4k0.2 v. 5.3�0.2 kg, P < 0.001). This trial has shown that, at the same SSH, June-lambing pregnant ewes achieve a similar daily herbage intake to that of August-lambing ewes. A target SSH of 2.0 cm during the last month of pregnancy was shown to be appropriate for both August- and June-lambing ewes in good condition. However, for August-lambing ewes in poor condition, a SSH of 2.0 cm at this stage of pregnancy would be detrimental to overall production, particularly in terms of ewe liveweight loss.

Simulation of wool growth rate and fleece characteristics of Merino sheep in Southern Australia. Part 1—Model description

A simulation model of a breeding ewe flock was extended to facilitate the evaluation of management strategies for improving the quality of Merino wool. The model extensions described in this paper were designed to improve the prediction of wool growth rate and to provide procedures for predicting the four most important clean wool characteristics of Merino sheep, namely fibre diameter, staple length, stample strength and vegetable matter level.

Effect of condensed tannins upon body growth, wool growth and rumen metabolism in sheep grazing sulla (Hedysarum coronarium) and perennial pasture

SUMMARYAreas of sulla (Hedysarum coronarium) and pasture (Lolium perenne/Trifolium repens/Holcus lanatus) were grazed by young sheep (29·5–34·8 kg initial liveweight) in four experiments, and effects upon body growth, wool growth and rumen metabolism were measured.Sulla contained 40–50 g condensed tannins (CT)/kg DM, whilst the pasture contained small amounts of CT (2–6 g/kg DM). After chewing during eating, a lower proportion of total CT was readily extractable and greater proportions were protein-bound and fibre-bound. Nutritional effects attributable to CT were assessed by oral administration of polyethylene glycol (PEG), which binds and inactivates CT, to half the animals grazing each forage. Rates of body growth were consistently higher for lambs grazing sulla than those grazing pasture, with the CT concentration in sulla being neither stimulatory or inhibitory to body growth or voluntary feed intake (VFI). The action of CT reduced carcass fatness in sheep fed both diets, in the one experiment where this was measured. CT present in both sulla and pasture decreased rumen ammonia concentration and decreased molar proportions of iso-butyrate and iso and n-valerate. During spring and early summer, when wool growth rates were highest, CT present in both pasture and sulla increased wool growth rate; when wool growth rates were low during winter, CT had no effect upon the wool growth of sheep grazing either forage. Numbers of protozoa and molar proportions of n-butyrate in rumen fluid were increased by CT in sheep grazing sulla but not pasture.It was concluded that the higher rates of body growth and VFI in lambs grazing sulla was most likely to be due to its very high ratio of readily fermentable: structural carbohydrate.

Coexpression of the cys E and cys M genes of Salmonella typhimurium in mammalian cells: a step towards establishing cysteine biosynthesis in sheep by transgenesis.

The Salmonella typhimurium genes for serine acetyltransferase (cys E) and O-acetylserine sulphydrylase B (cys M) were isolated and characterized in order to express these as transgenes in sheep to establish a cysteine biosynthesis pathway and, thereby, to achieve an increased rate of wool growth. Comparison of the S. typhimurium and Escherichia coli genes showed considerable homology, both at the nucleotide and amino acid sequence levels. The in vitro and in vivo expression studies showed that both genes could be transcribed and translated in eukaryotic cells and that their products could function as active enzymes. The cys M gene of S. typhimurium possessed a GUG initiation codon, like its E. coli counterpart, but translation could be initiated using this codon in eukaryotic cells to give an active enzyme product. Chinese hamster ovary cells, stably transfected with a tandem arrangement of the two genes, showed a capacity to synthesize cysteine in vivo, indicating the establishment of a cysteine biosynthesis pathway in these cells. The measured levels of activity of the gene products suggest that improved wool growth is possible by transgenesis of sheep with these genes.