Wool Growth Rate Research Articles

Supplementation of young sheep with lupins plus sulfur and a complete mineral mix

Young Merino sheep (7-8 months of age, weighing about 40.5 kg) were given weekly supplements of 1050 gfsheep of lupins, lupins coated with potassium sulfate (25 g/kg lupins), lupins and access to a mineral lick (offered at 175 g/sheep.week), or lupins coated with potassium sulfate and access to the lick. The sheep grazed an annual pasture at a stocking rate of 15 sheepha and were given the supplements between 14 December and 5 April. The amount of pasture on offer in mid December exceeded 3000 kg DMha but declined to 1500 kg DMha in late March.There were significant amounts of green feed present in December and March (>20% of pasture DM), a small amount in January, and no green feed in February. Despite this the percentage of sheep licking the minerals was over 70% in January , February; and March, with average intake being about 10 g/sheep.day. No significant differences occurred between treatments for liveweights of sheep during the feeding period or at shearing. Over the feeding period sheep lost weight at about 30 g/day. Neither the additional sulfur nor the mineral lick had any significant effects on fleece weight, mean fibre diameter of the fleece, staple length, or staple strength. Wool growth rates were not different between treatments during the feeding period. These results indicate that under good pasture conditions with some green feed available, and when lupins are supplied, responses to mineral supplements are unlikely.

Factors associated with the rate of growth of clean wool on grazing sheep

In a grazing study that spanned 2.5 years, the rate of clean wool growth (Wi, g/day) in 4 week periods on Corriedale wether sheep was measured on each side of the animal with dyebands that were applied, alternately, at 2 week intervals. The observations (n = 224) on wool growth from 3 contiguous periods Wi = 1, 2 and 3 with the middle overlapping the other two periods, were related to either the daily rate of organic matter intake (OMI, g/day), the digestible organic matter intake (g DOMI/day), the hourly rate of OMI (IR, g OMI/h) or the hourly rate of digestible organic matter intake (DR, g DOMI/h) in linear or quadratic expressions. The intake data were collected every 4 weeks over the 3 days that correspond to days 6 to 8 of W1. The variance accounted for in each of W1, W2 and W3 increased in the order OMI<DOMI<IR<DR. DR accounted for 33.2% of the variance in W1 with a significant quadratic fit (P < 0.01) and 24.3% and 7.8% with linear fits against W2 and W3, respectively. A relationship that comprised five factors and accounted for 68% of the variance in W1 was developed by nonlinear regression. Three factors that were associated with nutritional aspects, the hourly rate of digestible organic matter intake (DR, g DOMI/h), the organic matter digestibility (OMD %) and the average organic matter intake in a grazing period (M, g OMI/grazing period) accounted for 54.9% of the variance in W1 while the other two factors that were associated with the physiological state of the animal, fleece-free liveweight change (C, g/day) and the fleece-free liveweight (L, kg) accounted for a further 13.1% of the variance of W1. The study suggests that factors associated with phenomena within a daily period may have important effects on wool growth. Management aspects are discussed.

Effects of abomasal protein and energy supply on wool growth in Merino sheep

The relative importance for wool growth of energy-yielding nutrients compared with amino acids required for incorporation into wool proteins was assessed in an experiment in which most nutrients were supplied via the abomasum. Nine nutritional treatments, providing three levels of protein (53, 99 and 145 g/day) to the intestines at three levels of energy (5.2, 7.5 and 9.7 MJ/day), were given to 12 Merino sheep during three consecutive periods of 3 weeks in a balanced lattice design. Abomasal nutrients consisted of varying proportions of casein, whole milk, glucose and glycerol. There was a large effect of protein supply on all components of wool growth, but there was no significant effect of energy. There was a significant interaction between the effects of protein and energy supply on diameter, length growth rate and volume of wool, but it was small relative to the main effect of protein. Extra energy appeared to enhance wool growth at the highest level of protein but reduce it at the lowest level of protein. The concentration of urea, cystine, methionine and other essential amino acids in plasma increased with protein level. Increasing energy supply reduced the concentration of urea and essential amino acids in plasma but not that of cystine or methionine. The experiment confirmed the major role of amino acid supply in controlling wool growth but indicated that there may be a small interaction with energy supply.

Simulation of life-cycle efficiency of lamb and wool production for genetic levels of component traits and alternative management options

A deterministic computer model was used to predict effects of genetic improvements in performance and of management options on life-cycle flock TDN input per unit of empty body weight (EBW) or carcass lean (CLN) equivalent value of market lamb, cull ewe, and wool output from a pure breeding system of sheep production for sheep fed to maintain normal weight. Relative values per kilogram for market lambs, cull ewes, and clean wool were 1 to .33 to 2.04 in lamb empty body equivalent, but 1 to .33 to 1 in lamb carcass lean equivalent. A 10% increase in lamb viability improved TDN/EBW or CLN by -15 to -20% for high to low lambing rates. Corresponding smaller gains were -7 to -11% for fertility, -3 to -13% for lambing rate, -1 to -3% for wool growth rate, -1 to -5% for milk production without creep feeding, -2 to -1% for mature size to about 70 kg, and -.6 to -.9% for precocity of fertility. Increasing leanness 10% improved TDN/CLN by -3 to -1% but increased TDN/EBW 3% because of higher maintenance requirements of leaner sheep. Higher protein requirements for increased lambing rate, milk production or leanness, or greater increases in non-feed than in feed costs, would mean only slightly less reduction of TDN/output than shown. Creep feeding was beneficial only for prolific, low-milking stock. Flushing reduced adverse effects of restricted feeding. Different values for wool vs meat or for costs of feed vs non-feed inputs would change results. These estimates for relative economic importance of traits apply to derivation of optimum criteria for selection among breeds or crosses, or within-breeds used in rotation crossbreeding, but would differ for specialized terminal-sire or maternal breed roles.

Wool sulfur concentration and output in fleeceweight-selected and control Romney rams

Wool sulfur concentration and output of Romney sheep from fleeceweight-selected and control lines were measured with a view to determining their potential use as genetic markers for fleeceweight. Midside wool samples were collected at 28 day intervals from 4 to 14 months of age from 35 fleeceweight-selected and 30 control rams. Clean wool growth during each sampling period was calculated. Wool samples were digested using an open wet digestion method and the wool sulfur concentration was determined by plasma emission spectrometry. Fleeceweight-selected rams had significantly greater midside wool growth than the control animals throughout the trial except on day 56. Average wool sulfur concentration in both lines increased over the sampling period to a peak at day 308. The wool sulfur concentration of control rams was significantly higher than that of fleeceweight-selected rams only on days 28 and 280. Total sulfur output (the product of midside wool growth rate and sulfur concentration) was significantly higher in the fleeceweight-selected than in the control rams on days 84-140 (March-May) and 196-308 (June-October). It is concluded that midside wool sulfur concentration and output of 4 to 14 month-old-Romney hoggets are unlikely to be useful genetic markers for fleece production.

The effect of energy malnutrition in ruminants on experimental infection with dermatophilus congolensis

The ability of malnourished and optimally fed animals to resist infection with D. congolensis was assessed by the dose-response to experimental inoculation. The severity of infection, as measured by scoring the lesions, was the same in both groups of lambs. However marked differences were seen between the two groups in the appearance of scabs and in the time taken for them to resolve. The malnourished animals had more persistent, chronic lesions compared with the more obvious, acute type lesions seen on the skin of the healthy controls. These results were probably related to the reduced rates of wool growth and lanolin production found in the malnourished lambs, which may reflect a reduction in the rate of cellular turnover in the skin of these animals.

Effect of a B agonist on the Partition of protein between wool and other tissues in sheep

In growing lambs a high proportion of protein retained (0.2-0.3) may be stored in wool. Protein retention is known to be increased by treating sheep with B agonists and there are indications that the extra protein is stored mainly in the carcass (Williams, 1987; Fiems, 1987). Wool growth rate at any time is determined by the relative availability of nutrients to all body tissues and is affected by, for example, pregnancy. It is also dependent on the kinetics of all competing biochemical reactions, which are altered by hormones (Black and Reis, 1979).To investigate the partition of protein between wool and other body tissues, a nitrogen balance trial was carried out with lambs fed on a diet with or without the B agonist, Cimaterol (Boehringer Ingelheim, Ingelheim, West Germany).

Estimation of Cell Birth Rate in the Wool Follicle Bulb using Colchicine Metaphase Arrest or DNA Labelling with Bromodeoxyuridine

The birth rate of cells in the wool follicle cells (CBR) was measured in two experiments on sheep differing widely in wool growth rate as a consequence of differences in nutritional regime. In Experiment 1, CBR was determined in one sheep on a high and one on a low plane of nutrition by two methods: the colchicine-metaphase arrest method, or from the product of total cell number and cell cycle time (the latter determined by DNA labelling with 5-bromo-2'-deoxyuridine (BrdU) and analysis of the fraction of mitoses labelled curve). CBR by colchicine was 0.73 and 0.56 of that determined using BrdU for the low- and high-plane sheep respectively. Cell cycle times were 26.5 h (low nutrition) to 18.6 h (high nutrition). In Experiment 2, CBR was again measured by the colchicine method, and from the rate of increase in labelled cells following a pulse dose of BrdU, in sheep on two levels of nutrition (n = 4llevel) and with a 3.7-fold difference in wool growth rate. Again, CBR by colchicine was only 0.41 (high nutrition) to 0.74 (low nutrition) of estimates made using the BrdU method, this difference being statistically significant only for sheep on the high plane of nutrition. Nutrition significantly altered CBR determined by colchicine (Pc0.001) and by BrdU (Pc0.034). The rate of fibre growth per follicle measured on two separate occasions was closely related to CBR measured using colchicine (r= 0.83, P< 0.01 and 0.8 1, P c 0.02) or BrdU (r= 0.73, P c 0.04 and 0.64, P< 0.08). It is concluded that CBR is a major determinant of fibre growth, but that colchicine depresses CBR. Previous estimates of mitotic activity in wool follicle bulbs have been made using colchicine and are thus probably underestimated. The technique using BrdU labelling and the subsequent rate of increase in labelled cells appears to be a useful one for estimating follicle cell kinetics.

The activity of the thyroid glands in relation to genetic differences in wool production

Twelve adult castrate male Merino sheep from each of two flocks, genetically different in their capacity for clean wool production, were allocated to a high (H: 0.81 kg digestible dry matter day-1; 26 g N day-1) or low dietary regime (L: 0.42 kg digestible dry matter day-1; 9.5 g N day-1). The sheep weighed 47 kg (s.e. =0.8) at the start of the experiment, with sheep from the two genetic groups having similar average liveweights. The dietary treatments were imposed for between 4 and 10 weeks before eight samples of venous blood were collected from each sheep during 24 h. Each sheep was then injected with thyroid stimulating hormone (TSH), (1.25 unit/sheep) before seven samples of blood were collected during the following 24 h. The plasma from these blood samples was assayed for total thyroxine (T4) and tri-iodothyronine (T3). There were no significant differences between the flocks in either T3 or T4 before or after the injection of TSH. We concluded that differences in the activity of the thyroid gland were not necessary for the establishment of genetic variation in the rate of wool growth. The circulating levels of both T4 and T3 were greater in the sheep receiving the H dietary regime (T4: 81.4 v. 55.8 nmol L-1; P<0.5 and T3: 1.8 v. 1.0 nmol L-1; P<0.05). These differences were maintained after the injection of TSH, which approximately doubled the pre-injection levels of T4 in plasma 9-10 h after the injection. The levels of T3 also increased after the injection, reaching a maximum which was 2.3 times the average pre-injection concentration after 4-5 h.

Studies of wool growth responses to 2-hydroxy-4-(methylthio) butanoic acid, Alimet, an analogue of methionine

An analogue of DL-methionine, Alimet, was evaluated for its commercial potential for increasing wool growth in Merino sheep in pen and grazing experiments. This was done by administering Alimet as a drench, in drinking water, or via rumen or abomasal fistula, and measuring wool growth rate and plasma methionine concentrations. In vivo data indicated that significant wool growth responses (23-35%) to Alimet as a drench or in drinking water occurred at low rates (estimated 5-6 g/sheep.day) of basal wool production when sheep were fed a lucerne diet to maintain liveweight. At higher rates of clean wool growth (10-12 g/sheep.day) when sheep were eating above-maintenance diets (lucerne ration or pasture), Alimet treatment was associated with variable and reduced response. A significant (P<0.05) negative correlation (r2 = 0.699, n = 11) between wool growth responses (x � s.d. = 0.11 � 0.067) to the 3 mL dose rate of Alimet and wool growth in control treatments (y �: s.d. = 0.70 � 0.202) confirmed the above trend. Four hours after administration of Alimet via either rumen or abomasal fistula, comparative plasma concentrations of methionine, 28 and 168 �mol/L respectively, suggest that Alimet is susceptible to degradation in the rumen. The corresponding values for DL-methionine, via either rumen or abomasal fistula, were 64 and 350 �mol/L, respectively. The small rises (40%) in plasma methionine values associated with significant increases in wool production indicate that a dose of 3 mL is as effective as 4 mL of Alimet when the basal nutritional regime is limiting. While administration of Alimet in drinking water during dry seasons is possible, the profitability of supplementation would need to be tested further.

Spring and summer and wool growth pasture feeding and ewe reproduction

Effects of pasture feeding level during lactation and over summer on ewe wool growth and ovulation rate were assessed in 1983-84 and 1984-85. Two levels of pasture feeding (lactation high and lactation low) from parturition to weaning (10 weeks) produced 8 to 10 kg liveweight difference in ewe liveweight at weaning. Groups (n = 40) were offered pasture allowances of 0.8, 1, 1.4, 2 or 5 kg DM/ewe/day from weaning until after the third synchronzied oestrus in April. Ewes on the lower allowances tended to reach a stable liveweight and those on 5 kg DM/ewe/day gained throughout. Other groups were offered low allowances during summer and then 5 kg DM/ewe/day after the first recorded oestrus. Mean dates for synchronised oestrus were 2 March, 19 March and 5 April. Ovulation rate increased by 0.15 corpora-lutea/ewe ovulating at each successive oestrus, and increased by 0.047 corpora lutes/ewe ovulating for each kg increase in liveweight at oestrus. These effects accounted for 77% of the variation in ovulation rate between treatments across years. The effects of flushing, lactation or summer liveweight change were small and generally non-significant. Lactation feeding affected wool growth during lactation as well and had carryover effects through the summer when lactation low ewes grew 10% less wool irrespective of the level of summer feeding. Keywords ewe, wool growth, ovulation rate, lactation, summer feeding, liveweight, flushing

Relationships between staple strength and other wool characteristics of Romney ewes

Abstract Romney ewes were offered pasture allowances of 0.7, l.2, l.7, or 2.2 kg dry matter (DM)/ewe per day for 6 weeks in June—July. Liveweight change, wool growth, fibre diameter, and staple length growth rate were measured during early and late winter and in spring. Fleeceweights were recorded at shearing in December and samples were collected for measurement of staple strength and assessment of soundness grade. Relationships between staple strength and subjectively assessed soundness grade and otherwqol measurements were examined. Increases in staple strength for a 1 gJday increase in wool growth in July—August were: Year 1,3.3 (SE = 0.5) N/ktex; Year 2, low allowance, l.8 (SE = l.2); Year 2, high allowance, 6.1 (SE = 0.9). There were also significant positive relationships between staple strength and both fibre diameter and clean fleeceweight. Ewes growing fleeces of low staple strength had a more pronounced seasonal pattern of wool growth than ewes growing sound fleeces, with the difference being most marked in July-August. Staple strength was not significantly associated with liveweight change, suggesting that variation in strength is caused by variation in the partitioning of nutrients to wool growth rather than to variation in intake.

Wool growth and sulfur amino acid entry rate in sheep fed roughage based diets supplemented with bentonite and sulfur amino acids

In two experiments, sheep were offered a roughage-based diet supplemented with either cysteine or bentonite as a solid, or bentonite, cysteine or methionine added to their drinking water. Supplementation with cysteine as a solid had no effect on wool growth, while supplementation via drinking water had no effect on wool growth or cysteine entry rate into the blood. Supplementation with methionine via drinking water increased the entry rate of methionine into blood by 69% (P< 0.05) as measured by a continuous infusion of [35S]-methionine. This coincided with subsequent increases in wool growth of 16% (P< 0.05) compared to sheep fed a basal diet alone. Compared with the basal diet alone, supplementation with 30 g/day bentonite as a dry powder or 60 g/day as a suspension in drinking water increased wool growth by 19 and 20% respectively. Bentonite given as sole supplement did not increase the entry rate of either cysteine or methionine into the blood of sheep. When bentonite and sulfur amino acids were complexed or mixed, wool growth was not increased above that for bentonite or the amino acid alone.

Evaluation of feed additives for increasing wool production from Merino sheep. 2. Flavomycin and tetronasin included in lucerne-based pellets or wheaten chaff fed ad libitum

The feed additives flavomycin, a glycolipid antibiotic, and tetronasin, an ionophore, were evaluated for their ability to improve wool growth and liveweight gains in Merino sheep. Each was included in 2 diets: one was a pelleted mixture of (g/kg) lucerne (590), lupins (250) and barley (1 50); the other diet was wheaten chaff. Flavomycin was included in each diet at 10 and 20 mg/kg feed; tetronasin at 5 and 10 mg/kg feed. During an 8-week experimental period, the diets were fed ad libitum to weaner Merino wethers, with 15 sheep receiving each treatment diet at each level of additive inclusion, and 30 sheep receiving each diet without additives. Liveweight changes, feed intake and wool growth were measured over 2 consecutive 4-week periods, and rumen fluid samples were taken from all sheep after 6 weeks. Feed intake, liveweight gain and wool growth rate were all higher for animals eating the pelleted diets compared with those eating chaff. Rumen volatile fatty acids (VFA) and ammonia (NH3) concentrations were also higher with the pelleted diet. On the pelleted diet, flavomycin and tetronasin inclusion significantly increased liveweight gains during the second 4-week period (296, 277, 231 g/sheep.day for flavomycin, tetronasin and controls respectively, P<0.001), but neither additive had any significant effect on feed intake. The amount of clean wool grown during both measurement periods was greater for animals receiving flavomycin or tetronasin with the pelleted diet compared with control animals. Neither additive had any significant effect on liveweight gains or wool growth of sheep eating chaff. Fibre diameter (FD) was measured on wool clipped in the second period, and was not significantly altered by either additive: mean FDs for animal receiving pellets were 25.1 �m, compared with 18.5 �m for animals receiving chaff. Total rumen VFA concentrations were lower with flavomycin or tetronasin treatments on both diets, and ammonia concentrations were lower with both additives on the pelleted diet and with tetronasin on the chaff diet. It is concluded that both flavomycin and tetronasin were able to increase liveweight gains and wool growth in rapidly growing sheep eating a high-protein diet, but had little or no consistent effects with animals eating a lower quality, low-protein diet.

Effects of defaunation of the rumen and supplementation with amino acids on the wool production of housed Saxon Merinos. 1. Lupins and extruded lupins

Six groups, each comprising 10 superfine Merino wethers ('Sharlea'), were individually penned indoors and hand-fed oats and wheat straw, either alone or with 10% (w/w) crushed lupins or extruded lupins. The rations were fed at maintenance level and were offered 3 times a week. Half of the sheep were defaunated by drenching with Alkanate 3SL3. Wool growth rates and wool quality were measured during a 5-month trial period. Defaunation resulted in a 6.5% increase in clean wool production, with a 3% higher sulfur content. The quality of the wool grown was unaffected by defaunation. Inclusion of lupins or extruded lupins in the ration resulted in a 10% increase in clean wool growth. Wool quality was largely unaffected, though a lower resistance to compression was apparent. It was concluded that a reasonable diet for 'Sharlea' production was 500g oats, 50g wheat straw, 50g lupins, 10.5g vitamin, mineral mix per sheep per day. This diet may be further improved by additional ingredients and defaunation of the sheep.

Utilization of clover diets by sheep. 2. Intake, digestion and utilization of nitrogen and sulfur

Nine mature Merino wethers were fed three clover diets at 95% of previously measured intake under steady state conditions. The diets were mature subterranean clover (MSC), green subterranean clover (GSC) and persian clover (PC). The utilization of dietary N and S was studied for each feed.The ratios of digestible organic matter (DOM) to crude protein (CP) in the diets ranged from 3.9 to 5.5 : 1. The flow of microbial crude protein (MCP) from the abomasum was only 34 g day-1 in sheep given MSC compared to 77 g day-1 for GSC and 85 g day-1 for PC. However, the calculated efficiencies of MCP synthesis were 230-250 g MCP per kg OM apparently digested in the rumen for the three clovers. Despite the similar efficiencies of MCP synthesis, the ammonia-N (30 mg l-1) and sulfide-S (220 8g l-1) concentrations in the rumen of sheep fed MSC were low. The concentrations for the the other clovers were ammonia-N 90-110 mg l-1 and sulfide-S 730-1770 8g l-1. The amount of CP apparently digested in the intestines (DCPi) was only 31 g day-1 in sheep given MSC compared to 100 g day-1 and 81 g-1 in those fed GSC and PC, respectively. While this indicates that protein insufficiency in the tissues may have limited the intake of MSC, the DCPi values per unit of DOM intake were 150,210 and 150 g kg DOM-1 for MSC, GSC and PC, respectively. Sheep excreted more N and S (% of intake) in faeces when given MSC compared to GSC or PC.The sheep were in positive apparent balance for N and S when fed GSC or PC, but were mobilizing these nutrients from tissues at the low intakes of DOM, N and S with MSC. The wool growth rates and amounts of N and S incorporated into wool when MSC was fed were about half the other two feeds.These results are discussed in relation to other work on the utilization of N and S by sheep and likely effects of this on the intake of the feeds.

PROSPECTS FOR BIOTECHNOLOGY IN ANIMAL PRODUCTION

Through recent advances in molecular and reproductive biology selected genes from one animal or species can be inserted into another animal's genome to produce a 'transgenic' animal. Striking increases have been achieved in the rate of growth of mice containing additional copies of the rat growth hormone gene. Such results raised the possibility of using similar techniques to modify the expression of existing genes and introduce novel gene(s) into domestic livestock for improved productivity. The introduction of multiple copies of the growth hormone genes into pig embryos has resulted in live births of pigs that grew 10-20X larger and reached market weight three weeks earlier than litter-mates. The introduced genes were passed from generation to generation. In sheep cysteine supplementation into the abomasum produced at 10.20% increase in wool growth rate. Genes responsible for cysteine biosynthesis have been isolated from yeast, and a modified gene suitable for expression in sheep produced. By engineering the cysteine biosynthetic pathway into the sheep genome there is scope to considerably increase wool production. Keywords: gene transfer, transgenesis. recombinant DNA, embryo manipulation.

The value of whole cottonseed in a wheat-based maintenance ration for sheep

The effects of fuzzy whole cottonseed (WCS) on the performance and health of sheep were examined. Thirty 2-year-old Merino wethers were divided into 3 equal groups and offered maintenance rations for 138 days, with whole wheat grain to WCS ratios of 100:O (diet A), 75:25 (B) and 50:50 (C). Liveweight changes for diets A, B and C were -0.3, +4.4 and +3.0 kg respectively, and were significantly (P<0.05) greater on WCS diets. Wool growth rates were also significantly (P< 0.01) improved by the addition of WCS, with treatment means being 0.65 (diet A), 0.82 (B) and 0.88 mg/cm2.day (C). Digestibility of DM in diet C (677 g/kg) was significantly (P< 0.001) lower than in diets A (782) and B (777 g/kg), perhaps because of increased fibre and oil in the ration. Subclinical anaemia and muscle damage were evident in animals given WCS by days 43 and 127 respectively. Post mortems and histological examination revealed renal haemosiderosis in sheep given WCS, with increased severity at 50% inclusion in the ration. Despite the reduction in digestibility and the subclinical effects on health, at least 25% WCS can be safely included in a wheat-based maintenance ration for wethers and this ration has production advantages over wheat alone. Caution is advised in feeding higher levels of WCS or feeding such a ration for more than 5 months.

A study of the characteristics of wool follicle and fibre in Merino sheep genetically different in wool production

Fourteen Merino ewes from each of two flocks, selectively bred for either high (Fleece Plus) or low (Fleece Minus) clean fleece weight per head, were randomly allotted to two feeding levels (17 v. 34 g kg-1 liveweight) of a good quality diet and offered these levels for 100 days. During the final 42 days, the rate of wool growth and its components were measured in each sheep. The Fleece Plus sheep had a greater density of wool follicles and produced more wool per unit area of skin. The latter trait interacted with the nutritional level; Fleece Plus sheep were more responsive to the higher nutritional level (45 v. 13%). Both the rate of growth of fibre length and the diameters of fibres produced in secondary follicles were the components associated with this interaction. The sulfur content of the wool was 12% less in wool from Fleece Plus ewes, but the difference between the two flocks was unrelated to the nutritional level. The average diameter (c. 83 8m) of the bulbs of the follicles did not differ between flocks or dietary levels, but follicles in the skin of Fleece Plus sheep were deeper (P < 0.05) below the skin surface (1.52 v. 1.38 mm). Despite the similar maximum bulb diameters, random longitudinal sections of follicles from Fleece Plus sheep had a 10% greater area of mitotically active tissue (P < 0.05). The difference was independent of nutritional level. When colchicine (10 8g) was injected intradermally, the number of cells revealing metaphase arrest within the mitotically active area of the follicle increased linearly with time to 6 h after the injection. The rate of increase in these cells expressed per unit volume of bulb tissue was not however influenced by either genotype or nutritional level. The average volume of cortical cells isolated from the fibres did not differ between genotypes or nutritional levels, but as with fibre volume, the volume of the cortical cells of the Fleece Plus sheep was more sensitive to a change in nutritional level (interaction: P < 0.05). Calculation of the rate of incorporation of cortical cells into fibre from both rate of production of fibre and the size of the cortical cells indicated that 20% more cells were incorporated by the Fleece Plus sheep and 17% more cells were incorporated by those sheep offered the greater dietary allowance. There was no significant interaction between genotypes and nutritional level for this trait.

Effect of chemical removal of grasses from pasture leys on pasture and sheep production

Pasture production, pasture composition and quality, and liveweight, body condition and wool growth of Merino weaner wethers were monitored over 2 seasons and at 2 stocking rates (4 and 8 sheep/ha) on a mixed annual grass-legume pasture sprayed with propyzamide to control grasses. Propyzamide virtually eliminated annual grasses from the pasture (less than 5 kg/ha of grass dry matter in spring v. 403 kg/ha on untreated pasture in 1981) and this carried over into the second season (61 kg/ha v. 647 kg/ha in spring 1982). Propyzamide treated pastures had less total dry matter (P = 0.05) throughout 1981: however, except for a single sample date, there was no effect of propyzamide on total available pasture in the second season. Increased growth of clover and capeweed compensated for the absence of the grasses. The higher stocking rate reduced available clover, capeweed and total dry matter (P = 0.05) throughout both years. Sheep grazing grass-free pastures had lower liveweights during winter in both years, but made compensatory gains during late spring and summer consistent with the higher quality (1.6 v. 1.07% nitrogen when sampled in January) of propyzamide treated pastures. In 198 1, wool growth rates were reduced at the higher stocking rate and total clean wool production was reduced from 4.55 kg/sheep at 4/ha to 3.65 kg/sheep at 8/ha. Pasture treatment had no effect on wool production in either year. The implications of using selective herbicides to remove the annual grass component of legume-based annual pastures in south-western Australia are dis cussed in relation to pasture and sheep production.