Microstructure of skeletal muscles of growing calves fed silage-based vs hay-based diets. II. Fibre type distribution.

As described in part I, samples of musculus longissimus dorsi, semimembranosus and semitendinosus were obtained post-slaughter from 2-week, 3-month and 10-month-old bull calves. The 2-week-old calves were fed milk only. All the remaining animals were fed grass silage or hay ad lib and a restricted amount of concentrate from 2 weeks of age onwards. Muscle fibres were differentiated according to Ziegan (1979) into fast-twitch glycolytic, fast-twitch oxidoglycolytic and slow-twitch oxidative fibres (FTG, FTO and STO, respectively). The percent distribution of individual types of fibres was estimated as related to the calves age and diet. The most numerous were always fast-twitch glycolytic fibres, the lowest values being observed in the 2-week-old calves. The effect of the diet on fibre percentage distribution in 3-month-old calves differed from that found in 10-month-old animals. This research suggests that a hay-free diet based on grass silage alters the microstructure of skeletal muscles, which thus might also affect the quality of meat.     

Effect of sex on muscular development of Muscovy ducks

Muscovy ducks display marked sexual dimorphism. The aim of our study was to analyse the consequences of dimorphism on muscular growth and, particularly, on the myofibrillar typology of the Pectoralis major and Sartorius muscles. In the Pectoralis muscle, we only found two fibre types: red fast-twitch oxido-glycolytic fibres (about 90%) and white fast-twitch glycolytic fibres. In the Sartorius, the innermost part contained both white (30%) and red (55%) fast fibres and red slow-twitch oxidative fibres (15%). For both muscles, neither sex nor age had a significant effect on the percentage of each fibre type. The cross-sectional areas of fibres increased with age. The difference in muscle weight observed between sexes could be explained by a higher size and/or total fibre number in the male muscles.     

Effects of anabolic steroids and high intensity exercise on rat skeletal muscle fibres and capillarization. A morphometric study.

The effects were investigated of high intensity short duration exercise and anabolic steroid treatment on the medial gastrocnemius muscle of female rats. Twelve rats were divided equally into four groups, exercise with and without steroid administration and sedentary with and without steroid administration. Animals were made to swim for 5 weeks, 6 days.week-1. Muscle fibres were classified as slow-twitch (ST), fast-twitch oxidative glycolytic (FOG) and fast-twitch glycolytic (FG). Muscle fibre size was measured as the equivalent circle diameter. Exercise (P less than 0.001) and steroid (P less than 0.05) treatments alone, significantly elevated FOG and decreased FG fibre proportions. Overall proportions of fast-twitch and ST muscle fibres did not vary with any of the treatments. Significant differences in the proportion of muscle fibres were found to exist between different areas within the gastrocnemius muscle (P less than 0.05). Exercise and steroid treatments alone did not alter muscle fibre diameters. Combined exercise and steroid treatments did significantly increase ST fibre diameters (P less than 0.05). Exercise only treatment resulted in significant increases in the number of capillaries surrounding ST fibre (P less than 0.05) and FOG fibre (P less than 0.01) types. In conclusion the main finding of this study indicated that anabolic steroids in conjunction with high intensity swimming instigated ST fibre hypertrophy. Exercise and steroid only treatments significantly elevated FOG fibre proportions while FG fibre proportions diminished. Exercise only treatment resulted in significant increases in the number of capillaries surrounding both ST and FOG fibre types.     

Proportion of insoluble fibre in the diet affects behaviour and hunger in broiler breeders growing at similar rates

With a view to alleviate the feeling of hunger in broiler breeders, different types of fibre sources were used in high-fibre diets to increase feed quantity while limiting growth to industry recommended levels. Using scatter feeding, three diets (C1: commercial control diet, 1 × fibre content, 80% insoluble fibre (ISF); H2: 2 × fibre content, 89% ISF; and L2: 2 × fibre content, 71% ISF) were each fed to 10 groups of 16 broiler breeder chickens. Similar growth rates were obtained on different quantities of food with all birds reaching commercial target weight at 15 weeks of age. In a hunger test, birds fed C1 ate significantly faster and showed a higher compensatory feed intake than birds on diets H2 and L2, indicating that the two high-fibre diets did reduce the level of hunger experienced by the birds. Behavioural observations carried out at 14 weeks of age showed high levels of tail pecking in birds fed C1 and almost none in birds fed L2, whereas birds fed H2 were intermediate. Stereotypic pecking at fixtures was seen twice as frequently in birds fed C1. Birds on diet L2 displayed behavioural signs indicative of discomfort, and the high water usage on this diet created problems with litter quality. Birds on diet H2 continued to show foraging behaviour throughout the day, and were more frequently engaged in dust bathing and other comfort behaviour. This experiment indicates that high-fibre diets can alleviate the feeling of hunger currently experienced by broiler breeders, and a high ratio of ISF may improve the well-being of the birds.     

The turnover of cytochrome c in different skeletal-muscle fibre types of the rat.

The turnover of cytochrome c was determined in the three skeletal-muscle fibre types of adult male rats by a kinetic analysis that followed the time course of cytochrome c content change. Confirming evidence was obtained with double-labelling studies using delta-aminolaevulinate. Cytochrome c turnover was most rapid in the low-oxidative fast-twitch white fibre [t1/2 (half-life) about 4 days], slowest in the high-oxidative fast-twitch red fibre (t1/2 9-10 days) and relatively rapid in the high-oxidative slow-twitch red fibre (t1/2 5-6 days). Thus cytochrome c turnover does not strictly conform to either the appearance (i.e. red or white) or the contractile characteristics (i.e. fast or slow) of the muscle fibres. The synthesis rates needed to maintain the corresponding cytochrome c concentrations, however, were similarly high in the two mitochondria-rich red fibre types. These data illustrate that both the synthesis and degradation processes are important in establishing the cytochrome c concentrations that distinguish the different skeletal-muscle fibre types.     

Growth and multiplication of white skeletal muscle fibres in carp larvae in relation to somatic growth rate

A morphometric analysis of white axial muscle of common carp Cyprinus carpio was undertaken in order to quantify increase in fibre size, fibre nuclei and fibre number in relation to somatic growth rate during early life. In fast-growing carp larvae fed zooplankton, length and height of fibres from the central part of dorsolateral muscle increased at the same rate (0.75) relative to the total length of the larvae during the first 2 weeks of feeding. During this period, the number of nuclei per fibre increased threefold while the number of nuclei per unit fibre surface remained constant. In fast-growing larvae fed a formulated diet, the total cross-sectional area of one epaxial quadrant of white muscle and the total area of white fibres increased at almost the same rate (3.15; 3.23) relative to larval total length during the first 28 days of exogenous feeding. The total number of white fibres increased faster (2.07) relative to the total length of larvae than the mean area of white fibres (1.16). Hyperplasia accounted for 64% of muscle growth in these larvae. The proportion of fibres with a width < 10 μm decreased from 72% at first feeding to 14% 28 days later, while the proportion of fibres with a width >20 μm which was 0% at first feeding increased up to 34% in the same time. The recruitment of new white fibres seemed to be almost the same in the whole muscle quadrant at first feeding and 18 or 28 days later but, 8 days after first feeding, a transient significant recruitment of new fibres was shown at the apex of the myotome. Comparisons between fast- and slow-growing groups of larvae showed that for a given larval total length: (1) the mean width of central white fibres was higher and the proportion of central fibres with a width <10 μm was lower in slow-growing larvae than in fast-growing ones; (2) the total number of white fibres was lower for a higher total cross-sectional area of white muscle in slow-growing larvae than in fast-growing ones. These results suggest that, in Cyprinus carpio larvae, slow-growing conditions are related to a decreased contribution of hyperplasia to muscle growth.     

The relationship of voluntary running to fibre type composition, fibre area and capillary supply in rat soleus and plantaris muscles

Twenty 4-week-old Wistar rats exercised voluntarily in running wheels each day for 45 days. Fibre type composition, fibre cross-sectional area and the number of capillaries around a fibre of the slow-twitch soleus and fast-twitch plantaris muscles were examined and compared with animals which had no access to running wheels. The exercise group had a higher percentage of fast-twitch oxidative glycolytic (FOG) fibres and a lower percentage of fast-twitch glycolytic (FG) fibres in the deep portion of the plantaris muscle. The area of FOG fibres in the surface portion of the plantaris muscle was also greater in the exercise group. In the exercised animals, there was a positive relationship between the running distance and the area of FOG fibres in both the deep and surface portions of the plantaris muscle. In addition, the running distance correlated positively with the percentage of FOG fibres and negatively with that of FG fibres in the deep portion of the plantaris muscle. There were no relationships between the running distance and fibre type composition, or fibre area and capillary supply in the soleus muscle. These results suggested that the increase in the percentage and area of FOG fibres in the fast-twitch muscle was closely related to voluntary running.     

Quantitative investigation of the neuromuscular junction of rat skeletal muscle fibres after double innervation

Summary In normal (untreated) rats the mean length ratio of postsynaptic to presynaptic membrane was 2.7±0.8 for neuromuscular junctions of slow-twitch soleus muscle fibres and 4.2±1.0 for neuromuscular junctions of fast-twitch extensor digitorum longus muscle fibres; this difference was significant (P<0.001). After experimental double innervation by fast and slow muscle nerves for four months, the ratio was (1) 2.9±0.8 for the original slow-twitch fibre end-plate and 2.8±0.8 for the newly established one, both not significantly different from that of the normal slow-twitch fibres; and (2) 2.2±0.5 for the original fast-twitch fibre end-plate and 2.2±0.7 for the newly established one, both significantly smaller than that of the normal fast-twitch fibres (P<0.001). This means that the double innervated slow-twitch muscle fibres retained their original neuromuscular junction type, whereas the doubly-innervated fast-twitch muscle fibres underwent a dramatic transformation of their neuromuscular junction from the fast-muscle to the slow-muscle type. In both doubly innervated fibres, the ultrastructural characteristics of neuromuscular junctions, whether altered or not, were identical at both end-plate regions.     

Occurrence of bifidobacteria in faeces of calves fed milk or a combined diet

The development of faecal bacteria composition in calves fed milk or a combined diet was investigated from 4 to 21 days of age. On day 7, bifidobacteria in faeces of milk-fed calves already increased from about 7.6 to 9.2 log CFU/g and did not change until the end of the study, whereas in calves fed the combined diet bifidobacteria only moderately increased to 7.9 log CFU/g and decreased slowly until day 21. The counts of bifidobacteria in calves on a combined diet were significantly (p < 0.01) lower compared to those in milk-fed calves. Bifidobacterial counts determined by cultivation or by fluorescence in situ hybridisation (FISH) did not differ significantly. Our results showed that the occurrence of bifidobacteria in calf faeces is highly dependent on the diet composition. Faecal bacteria flora of calves fed exclusively by milk is rich in bifidobacteria, but in calves on a combined diet coliforms dominated.     

Effects of sodium chloride and sodium bicarbonate in the diet on the performance of calves

Sixty male Friesian calves were weaned from milk at 5 weeks of age. From 3 to 11 weeks of age, the calves were offered a diet of barley, meat meal, urea and 15% oat straw, supplemented with sodium chloride (NaCl) or sodium bicarbonate (NaHCO₃). The sodium (Na) contents of the diets supplemented with NaCl were 0.3, 1.1, 1.9 and 2.8%. The sodium contents of the diets supplemented with NaHCO₃ were 1.1 and 1.9%.The performance of the calves fed on the diets containing 0.3, 1.1 and 1.9% Na from NaCl was similar, but the organic matter intake and weight gains of the calves fed on the diet containing 2.8% Na were significantly lower between 5 and 11 weeks of age. The feed intake of the calves fed on the diets containing 1.1 and 1.9% Na from NaHCO₃ was 8 and 15% greater than the feed intake of the calves fed on the diet containing 0.3% Na. However, there was no significant difference in the intake of organic matter, the efficiency of feed conversion ratios or the weight gains of the calves.The sodium treatments resulted in no significant differences in the concentration of volatile fatty acids in the rumen. The addition of NaHCO₃ to the diets altered in acid—base balance in jugular blood.     

Parvalbumin in mouse muscle in vivo and in vitro

Parvalbumin is a cytosolic calcium-binding protein found in adult fast-twitch mammalian muscle. Using an antibody to paravalbumin, we have shown that its distribution in adult mouse muscles is associated with certain fibre types. It is absent from slow-twitch type 1 fibres, is absent or at low levels in fast-twitch type 2A fibres, but is present at moderate or high levels in fast-twitch type 2B fibres. When adult mouse muscle is cultured with embryonic mouse spinal cord, the regenerated fibres become innervated, express the adult fast isoform of myosin heavy chain and appear histochemically as fast-twitch fibres. We therefore investigated whether these apparently mature fibres also contained parvalbumin. Parvalbumin was not found in any fibres of twenty mature cultures, suggesting that neurotrophic activity in the absence of specific adult nerve activity patterns was insufficient to cause the expression of parvalbumin in the cultures.     

Persistent Expression of Developmental Myosin Heavy Chain Isoforms in the Tapered Ends of Adult Pigeon Pectoralis Muscle Fibres

We have shown previously that in addition to the adult myosin heavy chain (MyHC) isoform present throughout the length of each fast-twitch glycolytic muscle fibre within the pectoralis of the mature chicken, the neonatal isoform is retained in the tapered ends of these fibres. This work, however, has been the only published report of this phenomenon. Here, we tested the hypothesis that similar to the chicken, the ends of mature pigeon pectoralis muscle fibres contain developmental MyHC isoform(s). A histological stain was used to visualize endomysium to assist in the analysis of transverse sections of pectoralis muscle from four mature pigeons. Immunocytochemical techniques were used to localize MyHC isoform(s) characteristic of pigeon pectoralis development. We show that within mature pigeon pectoralis, the ends of both fast-twitch glycolytic and fast-twitch oxidative-glycolytic fibre types express MyHC isoform(s) characteristic of their earlier development. Thus, we extend our findings on chicken to another species and an additional muscle fibre type. Retention of developmental MyHC isoform(s) within the tapered ends of mature muscle fibres may be more widespread than is currently appreciated.     

Effects of body suspension on soleus muscle fibres and spinal motoneurones in the rat.

1. After 14 days of body suspension, fibre type composition and fibre cross-sectional area in the soleus muscle of 17-week-old male Sprague-Dawley rats were investigated. Oxidative enzyme activity of soleus motoneurones in the spinal cord was also examined. 2. After suspension, soleus muscle weight decreased by 44.2%, the cross-sectional area of SO and FOG fibres decreased by 60.4% and 58.6%, respectively. 3. The percentage of fibre types was not changed by suspension. However, ATPase activity after alkaline preincubation was markedly inhibited in FOG fibres. 4. Oxidative enzyme activity of soleus motoneurones was not changed by suspension. 5. This study demonstrates that using mature animals body suspension induces atrophy of fast- and slow-twitch fibres accompanied with the selective inhibition in ATPase activity of fast-twitch fibres, and without changes in histochemical profiles of the corresponding motoneurones.     

Polymorphism of myofibrillar proteins of rabbit skeletal-muscle fibres. An electrophoretic study of single fibres.

Rabbit predominantly fast-twitch-fibre and predominantly slow-twitch-fibre skeletal muscles of the hind limbs, the psoas, the diaphragm and the masseter muscles were fibre-typed by one-dimensional polyacrylamide-gel electrophoresis of the myofibrillar proteins of chemically skinned single fibres. Investigation of the distribution of fast-twitch-fibre and slow-twitch-fibre isoforms of myosin light chains and the type of myosin heavy chains, based on peptide ''maps'' published in Cleveland. Fischer, Kirschner & Laemmli [(1977) J. Biol. Chem. 252, 1102-1106], allowed a classification of muscle fibres into four classes, corresponding to histochemical types I, IIA, IIB and IIC. Type I fibres with a pure slow-twitch-type of myosin were found to be characterized by a unique set of isoforms of troponins I, C and T, in agreement with the immunological data of Dhoot & Perry [(1979) Nature (London) 278, 714-718], by predominance of the beta-tropomyosin subunit and by the presence of a small amount of an additional tropomyosin subunit, apparently dissimilar from fast-twitch-fibre alpha-tropomyosin subunit. The myofibrillar composition of type IIB fast-twitch white fibres was the mirror image of that found for slow-twitch fibres in that the fast-twitch-fibre isoforms only of the troponin subunits were present and the alpha-tropomyosin subunit predominated. Type IIA fast-twitch red fibres showed a troponin subunit composition identical with that of type IIB fast-twitch white fibres. On the other hand, a unique type of myosin heavy chains was found to be associated with type IIA fibres. Furthermore, the myosin light-chain composition of these fibres was invariably characterized by a small amount of LC3F light chain and by a pattern that was either a pure fast-twitch-fibre light-chain pattern or a hybrid LC1F/LC2F/LC3F/LC1Sb light-chain pattern. By these criteria type IIA fibres could be distinguished from type IIC intermediate fibres, which showed coexistence of fast-twitch-fibre and slow-twitch-fibre forms of myosin light chains and of troponin subunits.     

Effects of dietary fibre on the intestinal absorption of dextrin, blood sugar level and growth of tilapia, Oreochromis niloticm × O. aureus

The roles of five different dietary fibres (cellulose, agar, guar gum, carrageenan and carboxy-methylcellulose) each as 10% wt/wt added into the diet, affecting the intestinal sugar absorption, blood sugar level and utilization of dextrin were studied in hybrid tilapia, Oreochromis niloticus × O. aureus ; dextrin and glucose were also included in the study as controls for comparison. There were seven dietary groups: each diet was fed to three aquaria each containing 15 fish. The experiment was carried out in a closed circulation, filtered, rearing system for 2 months. The results indicated that the weight gain percentage and food conversion ratio were significantly (P<0.05) lower in tilapia fed fibre-containing diets than those of tilapia fed dextrin or glucose diet. The intestinal absorption of carbohydrate and the blood sugar content of tilapia were low when diets contained fibre, regardless of the source.     

Indigestion in Young Calves

Fiftysix calves, in 2 similar experiments, were given 1 of 4 diets including a high lactose milk replacer: ground barley (GB), ground barley plus coarse hay (GB + GH), coarse hay (CH) and the liquid diet only (NS) ; the 2 last diets were held as controls. The calves were on the experimental diet from 1–2 weeks of age until slaughtered at 7-8 weeks of age. As observed by stereo-microscopy, the ruminai papillae in calves fed on GB were thickened, mostly finger- or club-shaped and sometimes nodular; nodular papillae were always arranged on prominent mucosal folds. Scattered nodular papillae had white coats. For calves fed on GB + CH the papillae were mostly finger- or tongue-shaped. Histologically papillae in calves fed on GB had hyperplasia of secondary papillae and epithelial layers. Microabscesses associated with penetrating hairs were frequent, and some calves had dyskeratosis with infiltration of polymorphonuclear leucocytes at the apex of papillae, identified as the white coats. For calves given GB+CH, abscesses and apical dyskeratosis were absent and the hyperplasia of epithelial layers milder than in the case of the GB diet. An ameliorative effect of hay on papillary changes caused by barley is indicated.     

Muscle fibre growth in undernourished reindeer calves (Rangifer tarandus tarandus L.) during winter.

To study whether moderate under-nutrition causes muscle wasting, reindeer (Rangifer tarandus tarandus L.) calves were fed either pelleted reindeer feed ad libitum (n=8) or restricted amounts of lichens (n=8). The restricted amount was 60% of ad libitum intake of lichens, and the feeding period was 6 weeks preceded by a 2-week adjustment period. Biopsy samples from the middle gluteal muscle (M. gluteus medius) for the analysis of fibre composition and area, as well as for the activity of cathepsin B were taken before the restriction period in November and January, and after the restriction period in April. In all calves the muscle fibre composition remained unchanged during the winter. In the lichen group, the fibre size also remained unchanged, whereas in control calves the cross sectional area of type I and type IIA fibres increased significantly from November to April. Cathepsin B activity decreased in all calves from November to January and remained at that low level for the rest of the study period, which suggests an attenuated rate of protein degradation. These results can be taken as an indication that moderate under-nutrition causes no muscle wasting in reindeer calves, and the decreased availability of nitrogen is partially compensated for by adaptive decrease in protein degradation. Interestingly the adaptive changes in protein metabolism are equally well seen in the well-fed controls as in the undernourished lichen-fed reindeer.     

Evolution of postprandial cholesterolemia and triglyceridemia with age in the preruminant calf; the effect of sorbitol ingestion

From birth to 10 weeks of age, 7 Friesian male calves were fed milk replacers containing 21 p. 100 tallow. The calves were divided into two groups: a control group (4 calves) and a "sorbitol" group (3 calves) receiving sorbitol in the milk replacer (0.6 g/100 g DM). At 2, 3, 5, 7 and 10 weeks of age, plasma concentrations of free cholesterol, cholesterol esters and triglycerides were determined in jugular blood 2 h before the morning meal and 1/2, 2, 3, 5 and 7 h after feeding. No significant variations were observed in the pattern of postprandial estercholesterolemia whatever the age or diet. Average estercholesterolemia was significantly higher (P less than 0.01) at 2-3 weeks of age than at 5, 7 or 10 weeks. Sorbitol supplementation decreased estercholesterolemia significantly (P less than 0.01) when the calves were 2 weeks old, but no effect was observed later. Similar variations in postprandial cholesterolemia were noted for both groups at all ages. Cholesterolemia was significantly higher (P less than 0.05) during the - 2h, + 1/2 hour-period than in the 2-5- hour period and rose significantly at 7 h (P less than 0.05) to the same pre-feeding level. Average cholesterolemia showed the same changes with age as estercholesterolemia in both groups. Changes in postprandial triglyceridemia were similar to those of cholesterolemia in both groups at all the ages studied. The decrease in triglyceridemia (P less than 0.01) 2 h after feeding was probably related to intense lipolysis, and the increase (P less than 0.05) 7 h after feeding was due to the arrival of new feed triglycerides. Triglyceridemia was significantly (P less than 0.05) lower when the calves were 10 weeks old than when they were younger, but no change was observed when sorbitol was added to the diet.     

Muscle growth in juvenile Atlantic salmon as influenced by temperature in the egg and yolk sac stages and diet protein level

Atlantic salmon Salmo salar eggs derived from a single family were incubated at two different water temperature regimes, with a mean temperature between fertilization and first feeding differing between 6 and 10° C (HT) and 2–6° C (LT). From first feed the fry were kept under the same rearing conditions and fed either high (50%) or low (45%) protein diet level of equivalent energy content until smoltification. All treatments were carried out in duplicate tanks. At first feeding the groups were similar in mass, but thereafter the HT‐fish were heavier and longer compared to the LT‐fish throughout the experiment. The groups fed the high protein diet were significantly heavier and longer compared with the corresponding low protein diet. A strong positive relationship was observed between L_F and total white muscle cross‐sectional area (CSA), white muscle fibre diameter and fibre number. There were also equivalent relationships with body mass. There were no significant differences in CSA, the mean diameter or the number of white muscle fibres per CSA between groups at first feed. Muscle fibre number and CSA increased in all groups during the experiment, whereas fibre diameter reached a plateau when the fish reached > 9 cm L_F. There were only minor effects of pre‐hatch and yolk sac stage temperature on CSA and fibre number per CSA during the juvenile stage. In short periods the LT‐group had larger CSA and higher fibre number than the HT‐groups, but this differences had disappeared by the end of the juvenile stage. No differences in mean fibre diameter were found between groups, except at the time of smoltification. When the fish approached smoltification a decrease in mean fibre diameter and an increase in muscle fibres <25 µm was seen and taken as an indication of recruitment of new fibres (hyperplasia). Only minor differences in CSA, fibre number or fibre diameter was observed between high and low protein diet groups.     

Effects of intravenous infusion of mimosine on wool growth of Merino sheep.

Merino sheep were given continuous intravenous infusions of L-mimosine for periods of 1 1/2, 2 or 21 days; efficacy as a defleecing procedure and effects on subsequent wool growth were measured. In addition, the amino acids tyrosine, phenylalanine and cystine were investigates as antagonists to the effects of mimosine. Infusions for 1 1/2 or 2 days at the daily rate of 80-120 mg/kg caused a cessation of wool growth by 1 1/2-2 days from the start of infusion, and all sheep were subsequently defleeced. It was estimated that, on average, fibre growth stopped for 10 1/2-13 days in four sheep after a 2-day infusion, and for 5 1/2 and 9 1/2 days in two sheep after an infusion for 1 1/2 days. There was considerable variation in the time taken for new fibres to recommence growth. During the period 3-5 weeks after infusion of mimosine, length growth rate was consistently greater than the pretreatment rate. Likewise, fibre diameter was greater in three out of the four sheep. As a result, the volume growth rate of fibres was greater post-treatment than it was pretreatment. Infusion for 3 weeks at the daily rate of 21-24 mg/kg did not stop wool growth. However, both length growth rate and fibre diameter were considerably depressed, and after 12 days' infusion, fibre diameter and volume growth rate were reduced to less than half the pretreatment values, and wool fibres were very weak. After the mimosine infusion stopped, fibre diameter increased to above pretreatment values and remained ther for the period of 2-3 weeks studied. The concurrent infusion of tyrosine, phenylalanine or cystine with mimosine failed to prevent any of the effects of mimosine on wool growth.