Wool Growth Rate Research Articles

Sulfur and Cystine Content in Various Sheep Wool Breeds and Their Correlation with Wool Growth and Strength

This scholarly article presents a comprehensive analysis of sulfur and cystine content in the wool of various sheep breeds, with a particular focus on their relationship with wool growth and strength. The breeds under scrutiny include the Askanian fine-wool, Prekos, Latvian dark-headed, Ukrainian Carpathian mountain, and Karakul breeds. Our research revolves around wool samples extracted from the scapula area before the spring shearing process. Our findings reveal that the highest sulfur content is observed in the wool of Karakul sheep (3.05 %) and Prekos sheep (2.90 %), whereas the lowest sulfur content is noted in Latvian dark-headed sheep (2.65 %). Conversely, the highest cystine content is exhibited in the wool of Askanian fine-wool sheep (11.87 %) and Prekos sheep (11.46 %), while the lowest cystine content characterizes the wool of Karakul sheep (8.99 %) and the Latvian dark-headed breed (10.10 %). The genetic factors, specifically breed-specific characteristics, impact on the rate of wool growth. The most rapid growth rates are observed in Karakul sheep (873 mg/cm/day) and Askanian fine-wool sheep (857 mg/cm/day). Slightly lower growth rates are noted in Prekos breed sheep (844 mg/cm/day) and Ukrainian Carpathian mountain breed sheep (766 mg/cm/day). The lowest growth rates are recorded in Latvian dark-headed sheep (742 mg/cm/day). Furthermore, we establish that the highest tensile strength values are associated with the coarse wool of Karakul sheep (9.6 cN/tex) and the semi-coarse wool of Ukrainian Carpathian mountain sheep (9.3 cN/tex), as these fibers possess the thickest cuticular layer. Conversely, the lowest tensile strength values are observed in the wool of Latvian dark-headed sheep (7.0 cN/tex) and Prekos breed (7.1 cN/tex). An examination of the data reveals that there is no statistically significant correlation between the content of sulfur and cystine and the rate of wool growth. However, a robust direct correlational relationship is identified between the sulfur content and fiber strength (with correlation coefficients of r = 0.831 for Karakul breed sheep wool, 0.713 for Latvian dark-headed, 0.698 for Ukrainian Carpathian mountain, 0.544 for Askanian fine-wool, and 0.460 for Prekos breed wool).

Wool production in Dohne Merino, Dormer, Merino and South African Mutton Merino lambs

In this study, the wool growth of Dohne Merino, Dormer, Merino and South African Mutton Merino (SAMM) lambs reared on a feedlot diet (10.62 MJ ME/ kg feed, 20.7% crude protein) was monitored from about two months old until the lambs were shorn as yearlings. The 100 cm2 patches on the left sides of the lambs were sheared monthly and the clippings were weighed to determine the wool growth rate. At approximately one year old, the lambs were shorn and the fleeces were weighed. A mid rib fleece sample was also retrieved from each lamb for quality analysis. Merino lambs presented the highest wool growth rates (12.943 g/day) and fleece weights (6.140 kg), whereas Dormer lambs exhibited the lowest values for these traits (8.487 g/day and 3.330 kg, respectively (P <0.05)). The lack of differences between Dohne Merino (9.720 g/day and 4.671 kg) and SAMM (10.553 g/day and 4.158 kg) lambs for these wool growth rate and fleece weight traits was attributed to disparities in live weight (86.8 kg and 105.2 kg, respectively (P <0.05), with heavier SAMM lambs offsetting the expected variations in fleece weight. Wool from Dohne Merino and Merino sheep had the finest fibre diameters (<21 μm), followed by SAMM wool (22–23 μm), with Dormers producing coarse wool (>27 μm). These results could be used as guidelines in sheep production to predict the income contribution of wool from these breeds.

Sheep wool cortisol as a retrospective measure of long-term HPA axis activity and its links to body mass

Hair cortisol analysis has been suggested as a powerful retrospective measure of long-term hypothalamic-pituitary-adrenal (HPA) axis activity in numerous mammal species. In contrast, research evaluating the use of wool as a marker of long-term HPA axis activity is still scarce, and wool differs from hair in a number of ways. Here, we assess repeatability and differences in wool cortisol concentrations (WCCs) across (i) the wool shaft, (ii) two body locations, and (iii) time, in 33 barren Welsh mountain ewes (Ovis aries). We also (iv) investigated effects of grazing-related changes in body mass on WCCs and (v) assessed effects of the washing procedure during sample preparation on WCCs. Cortisol concentrations were repeatable but differed significantly across the wool shaft indicating that, provided wool growth rate is known, a single sample per individual could be used as a retrospective cortisol “timeline.” WCCs were significantly higher in shoulder than in back samples, and no correlation between these two body locations was found, highlighting the importance of sampling from the same body location for repeated measures. An increase in body mass during grazing corresponded with a decrease in WCCs, which was significantly negatively correlated with body mass (and positively with age), suggesting that WCCs can be used as a marker of body condition and nutritional status in sheep. Interestingly, we found higher WCCs in washed compared with unwashed samples and discuss implications of this finding for future work. Overall, our study revealed significant within- and between-individual differences in WCCs and highlights a number of advantages but also methodological considerations of using WCCs as a retrospective measure of long-term HPA axis activity in sheep.

Seasonal pattern of skin follicles activity and fibre growth in grazing fat-tailed Kermani sheep in the South of Iran

Photoperiod is known to be important in regulating the pattern of wool growth in sheep. The aim of this study was to investigate the effect of natural changes in photoperiod on live weight, skin follicle activity and fiber characteristics of grazing Kermani sheep in the south of Iran, Jiroft (28° 40′ N and 57° 44′ E, elevation 650m). Ten male and 10 female Kermani sheep with initial live weights of 31.9±0.8 and 30.7±0.9kg (mean±s.e.) respectively, were used in a 365day study. Percentage of active primary (PAP) and percentage of active secondary (PAS) follicles, ratio of secondary to primary follicles (S/P) and follicle density (FD) were measured in skin samples, taken from the right mid-side of the animals at monthly intervals. Greasy and clean wool growth rates and fibre diameter were determined from patch samples (10cm×10cm) harvested at the end of every month. The value for PAP was greatest (p<0.05) in summer and spring and lowest (p<0.05) in winter (98.2±0.8, 84.1±0.9, 75.6±0.8 and 97.0±1.1% for summer, autumn, winter and spring, respectively); seasonal differences in PAS were similar (99.3±0.8, 88.5±0.7, 82.9±0.8 and 98.9±0.7% for summer, autumn, winter and spring, respectively). Clean wool growth rate was greatest (p<0.001) in summer and spring, and lowest (p<0.001) in winter (0.7±0.03, 0.4±0.04, 0.3±0.01 and 0.7±0.05mg/cm2/day for summer, autumn, winter and spring, respectively). Fibre diameter was greatest in spring (34.8±0.3μm) and lowest in winter (29.1±0.2μm). The values for wool growth rates and fibre diameter were greater (p<0.05) in male rather than those observed in female sheep. Fibre and skin follicle characteristics were not affected by a season×sex interaction. These results demonstrated that there is a seasonal pattern in fibre follicles activity and wool growth in grazing Kermani sheep.

Seasonal variation of fibre follicle activity and wool growth in fat-tailed Sanjabi sheep in west Iran.

This experiment was conducted to investigate the seasonal pattern of hair follicle activity, wool growth and fibre diameter (FD) in Sanjabi sheep in west Iran, Kermanshah (34° 18' N and 47° 3' E, elevation 1420 m). Ten male and 10 female Sanjabi sheep with an initial live weight of 32.1 ± 1.3 and 32.7 ± 1.5 (means ± SD), respectively, were used in a 365-day study. A diet was offered with an estimated concentration of 2.18 Mcal metabolizable energy and 130.0 g/kg DM crude protein. Body weight, average daily gain (ADG) and dry matter intake (DMI) were recorded weekly. The percentages of active primary and secondary wool follicles (PAP and PAS), follicle density and the ratio of secondary to primary follicles (S/P) were determined from skin biopsies, taken from the right mid-side of the sheep at monthly intervals. Raw and clean fibre growth rates and FD were measured from left mid-side patches (10 × 10 cm) harvested at the end of every month. There was a gradual increase in live weight throughout the experiment, while ADG and DMI changed in concert with day length. The greatest values for PAP and PAS were observed in summer, whereas lowest were obtained in winter (p < 0.001). Clean wool growth rate and FD were greatest (p < 0.001) in summer and lowest (p < 0.001) in winter. It is concluded that a seasonal cycle of feed intake, body growth, fibre follicle activity, wool growth and FD occur in fat-tailed Sanjabi sheep.

Influence of nutrition supplementation on the seasonal change in fiber growth and skin follicle activity in both male and female Sanjabi lambs

The present work aimed to investigate the effect of nutrition supplementation on skin follicle activity and wool growth rate in male and female Sanjabi lambs during the autumn and winter seasons, when the natural daylength is declining and being shortest. Twenty male (control and male (CM), n=10; treatment and male (TM), n=10) and 20 female (control and female (CF), n=10; treatment and female (TF), n=10) Sanjabi lambs were housed in individual pens, under natural daylength condition at west of Iran, Kermanshah (34°18′ N and 47°3′ E and 1420m above sea level). Lambs in control groups received a diet consisting of 80% alfalfa and 20% concentrate, providing 2.18Mcal and 130.0g per kg DM ME energy and crude protein, respectively. In treatment groups, lambs were fed a diet consisting of 65% alfalfa and 35% concentrate, providing 2.34Mcal and 160.0g per kg DM ME energy and crude protein, respectively. Raw and clean fiber growth rates and fiber diameter were measured from left mid-side patches harvested at the end of every month. Percentage of active primary and secondary follicles (PAP and PAS), follicular density (FD) and the ratio of secondary to primary follicles (S/P) were measured from skin biopsies, taken from the right mid-side of the lambs in monthly intervals. PAP and PAS in autumn were significantly (p<0.01) higher than those observed in winter season. There was a positive effect of feeding supplementation on both PAP and PAS but, similar values for S/P ratio and FD were observed in control and treatment groups. All hair follicle parameters viz. PAP, PAS, S/P ratios and FD were significantly greater in females compared to male lambs. The rate of wool growth was significantly lower in winter compared to autumn season, although similar fiber diameter was recorded in two seasons. Male lambs compared to females had greater body weight, DMI and the rate of wool growth. It is concluded that the fiber follicle activity and therefore wool growth in Sanjabi lambs is mainly under influence of nutrition, nonetheless little monthly fluctuation in follicle activity and fiber growth and diameter was observed. Likewise, there was a different pattern of wool production in male and female Sanjabi lambs.

Low ambient temperature elevates plasma triiodothyronine concentrations while reducing digesta mean retention time and methane yield in sheep.

Ruminant methane yield (MY) is positively correlated with mean retention time (MRT) of digesta. The hormone triiodothyronine (T3 ), which is negatively correlated with ambient temperature, is known to influence MRT. It was hypothesised that exposing sheep to low ambient temperatures would increase plasma T3 concentration and decrease MRT of digesta within the rumen of sheep, resulting in a reduction of MY. To test this hypothesis, six Merino sheep were exposed to two different ambient temperatures (cold treatment, 9 ± 1 °C; warm control 26 ± 1 °C). The effects on MY, digesta MRT, plasma T3 concentration, CO2 production, DM intake, DM digestibility, change in body weight (BW), rumen volatile fatty acid (VFA) concentrations, estimated microbial protein output, protozoa abundance, wool growth, water intake, urine output and rectal temperature were studied. Cold treatment resulted in a reduction in MY (p < 0.01); digesta MRT in rumen (p < 0.01), hindgut (p = 0.01) and total digestive tract (p < 0.01); protozoa abundance (p < 0.05); and water intake (p < 0.001). Exposure to cold temperature increased plasma T3 concentration (p < 0.05), CO2 production (p = 0.01), total VFA concentrations (p = 0.03) and estimated microbial output from the rumen (p = 0.03). The rate of wool growth increased (p < 0.01) due to cold treatment, but DM intake, DM digestibility and BW change were not affected. The results suggest that exposure of sheep to cold ambient temperatures reduces digesta retention time in the gastrointestinal tract, leading to a reduction in enteric methane yield. Further research is warranted to determine whether T3 could be used as an indirect selection tool for genetic selection of low enteric methane-producing ruminants.

Responses to betaine and inorganic sulphur of sheep in growth performance and fibre growth

Sulphur-containing amino acids (SAA) are essential and usually the first limiting amino acids for growth, milk and wool production. The keratin fibre that grows from epidermal tissue is rich in SAA. The rate of fibre growth and its S content are influenced by the availability of SAA. Betaine is a dietary source for a labile methyl group and actively participates in methionine metabolism by donating methyl groups for the remethylation of homocysteine to methionine. Ruminants are capable of synthesizing SAA from inorganic S sources, and most bacteria in the rumen can use inorganic S to meet their requirements for growth. The objective of this study was to examine whether betaine and an inorganic sulphur supplement could provide methyl groups and sulphur amino acids in a way that growth performance and wool production of ewes and lambs are improved. Treatments performed included betaine supplementation, sulphate supplementation and betaine plus sulphate supplementation with five replications for each treatment. The dry matter intake of the ewes was affected by betaine plus sulphate supplementation (p < 0.05). In the ewes, betaine plus sulphate supplementation increased (p < 0.05) the wool growth rate, wool yield, staple length and wool sulphur concentration, while decreasing wool wax and wool yellowness (p < 0.05). In the lambs, wool growth rate, wool yield, fibre diameter, staple length, staple strength, wool sulphur concentration, wool wax and fibre percentage did not differ (p > 0.05) between treatments. In the ewes, plasma methionine concentration increased (p < 0.05) with betaine plus sulphate treatment. No corresponding difference (p > 0.05) was observed in plasma methionine concentration in the lambs. It can be concluded that betaine plus sulphate supplementation has the potential to change wool characteristics in the ewes, while these compounds were without any effect on growth and wool production of the lambs. Combining the two supplements was advantageous.

Sheep of divergent genetic merit for wool growth do not differ in digesta kinetics while on restricted intakes

Sheep selected for high wool growth were previously shown to exhibit higher microbial protein outflow from the rumen and higher uptake of amino nitrogen in portal blood than those selected for low wool growth. This suggests that genetic selection for wool growth may induce changes in foregut physiology. This study was undertaken to determine whether differences in digesta kinetics, especially mean retention mime (MRT), are associated with differences in fleece production between sheep with low or high estimated breeding values (EBVs) for fleece weight. Twenty mature Merino wethers with uniform EBVs for liveweight were allocated to two groups of 10 animals on the basis of high or low EBVs for yearling fleece weight. Five sheep with low-EBVs and five sheep with high-EBVs for fleece weight groups were allocated in a crossover design to low and high feeding-level treatments, which comprised a blended hay diet fed at maintenance or 1.5 times maintenance. All sheep were given single doses of chromium-mordanted fibre and cobalt-EDTA as inert, non-digestible markers. Digesta kinetics was determined by analysis of the faecal marker excretion patterns using a compartmental model. Higher feed intakes from animals fed 1.5 times maintenance were associated with higher rates of wool growth and higher masses of indigestible fibre in the gut, but reduced MRT of digesta. Although sheep with higher EBVs for fleece weight had higher wool growth rates, there was no indication that these wool growth differences were associated with differences in digesta kinetics. The lack of interaction between feeding level and genotype suggests that MRT did not contribute to genotype differences in wool growth in sheep fed restricted intakes. The differences in wool growth among commercial Merino sheep with divergent fleece weight EBVs achieved by multi-trait selection are not attributable to differences in digesta kinetics, at least when feed is not available ad libitum.

Effect of added dietary nitrate and elemental sulfur on wool growth and methane emission of Merino lambs

The effects of dietary nitrate (NO3) and elemental sulfur (S) on nutrient utilisation, productivity, and methane emission of Merino lambs were investigated. Forty-four lambs were randomly allocated to four groups (n = 11) fed isonitrogenous and isoenergetic diets. The basal feed was supplemented with 1% urea + 0.18% S (T1), 1.88% NO3 + 0% S (T2), 1.88% NO3 + 0.18% S (T3), or 1.88% NO3 + 0.40% S (T4). Retention of S was improved by increasing the content of elemental S in the NO3-containing diet (P &lt; 0.001), yet the N retention (g/day) by the animal, and the N and S content of wool (%), were not altered by S supplementation (P &gt; 0.05). Dry matter intake, liveweight gain, and feed conversion ratio did not differ (P &gt; 0.05) between treatments. Replacing urea with NO3 improved the rate of clean wool growth by 37% (P &lt; 0.001, T1 vs T3). Clean wool growth increased by 26% (P &lt; 0.001) when the S content of the NO3-containing diet was increased from 0 to 0.18% (T2 vs T3). Methane production (g/day) and methane yield (g/kg DM intake) were reduced (P &lt; 0.05) by 24% when urea was replaced by NO3 (T1 vs T3). The addition of 0.4% S to a diet containing 1.88% NO3 also reduced methane production (P = 0.021) and methane yield (P = 0.028). In conclusion, the addition of 1.88% NO3 and 0.18% elemental S to a total mixed diet increased clean wool production and reduced methane production. However, there was no evidence of inter-relationships between NO3 and S.

Comparison of feeding value of a treated sea plant, Posidonia australis, with lucerne, pasture and wheat

An experiment was carried out to compare the effect of feeding posidonia australis as a non-conventional feedstuff with cereal straw for sheep maintenance; and to compare seagrass/chicken litter with lucerne hay and pasture for sheep production on a scale such as would be applicable to lot-feeding of sheep in the area of suthern Australia in case of short term feed scarcity. To approach this target a Randomized Completely Block Design with six treatments was applied on sixty adult merino. The six experimental diets were: (A) 75% treated seagrass+25% lucerne; (B) 75% treated wheat straw+25% lucerne; (C) 75% treated wheat straw+25% chicken litter (seagrass bed+chicken manure from a 7-week broiler raising period); (D) 50% treated wheat straw+50% treated seagrass; (E) 100% treated straw; (F) Green pasture, mixture of legume and graminea. To treat seagrass and straw a solution containing 8% fertilizer grade urea, 15% sugarcane molasses and 1% calcium-diphosphate was mixed with either seagrass or straw (1 Kg/Kg DM). The mixture was stored under anaerobic conditions for 3 weeks. The total experimental period of 109 days was used to measure the effect of experimental rations on the voluntary intake, body weight gain, fat score, feed efficiency and wool growth rate of sheep. There were different DMI of diets A, B and C during the experiment but these differences were not significant. Similar results were obtained for diets D and E as well. Among sheep of groups A, B and C total body gain of the sheep in group A was significantly less than that of the other two groups. The body weight gain of sheep grazed on pasture was significantly less than that of the sheep groups B and C, more than for the sheep in groups D and E (P<0.05) and equal that of the to sheep group A. In general there were few statistical differences, except that sheep on diet A showed consistently lowest values for greasy and clean fleece weight, staple growth rate, length: diameter ratio and staple strength. There was not a significant difference in clean fleece growth rate between sheep grazed on pasture and sheep in diet groups B, C, D and E, but this value was higher than for sheep in group A. It can be suggested that seagrass litter can be used proportionally in a mixed diet to provide enough nutrients and energy for sheep production in time of drought or feed scarcity. Meanwhile the cheaper diets D (seagrass containing) or E (straw only) could be used with equal efficiency in a lot-feeding system.

Yerba Mate (Ilex paraguarensis) as a novel feed supplement for growing lambs

Yerba Mate (Ilex paraguarensis), a plant known for its high antioxidant content, was fed to 20 of 40 lambs for 8 weeks. Lambs were randomly divided into two groups: one group (n=20) was fed the control diet and one group (n=20) was fed the control diet with 2.5% Yerba Mate. Lambs were group housed by treatment and fed ad libitum through automatic feeders that recorded individual food intake. Lambs received the dietary treatments for a total of 8 weeks and were monitored for live weight (LW), average daily growth rate (ADG), food conversion rate (FCR) and feed intake. Blood samples (8mL) were taken from all lambs, on weeks 0, 2, 4, 6, and 8 and plasma analysed for total antioxidant capacity (TAC), advanced oxidation protein products (AOPP), non-esterified fatty acids (NEFA), triglycerides and cholesterol. Wool growth and cell-mediated immune status (PHA) were also measured. Overall, Yerba Mate (YM) lambs ate more (mean±sem; 989±68g/d; P<0.001) pellet than the control (CTRL) lambs (759±63g/d), however, LW (YM: 33.5±1.1kg and CTRL: 33.5±1.2kg) and ADG (YM: 207±9.6g/day and CTRL: 191±8.4g/day) were not significantly different between the two groups. FCR (g VFI/g ADG) was higher (P<0.05) in the Yerba Mate supplemented lambs compared to the control ones (4.78±0.45 and 3.97±0.32, respectively). Wool growth rate was higher (P<0.01) in the YM lambs (0.09±0.005g/cm2 and 0.07±0.005g/cm2, respectively). There was a significant effect of the interaction diet×sampling time on plasma AOPP concentrations (P<0.05), with Yerba Mate lambs presenting higher AOPP levels than the control lambs on weeks 4 and 5. Overall, plasma NEFA and triglycerides concentrations were similar in the Yerba Mate and in the supplemented group (NEFA: 0.15±0.02 mmol/l and 0.17±0.02mmol/l, and triglycerides: 0.27±0.02mmol/l and 0.29±0.02mmol/l, respectively), however, a significant effect of the interaction time of sampling×diet on both metabolites (P<0.05) was noted, with Yerba Mate supplemented lambs presenting lower NEFA and triglycerides levels than the control lambs on weeks 3, 4, 5 and 6 and on weeks 3, 4 and 5. No significant effect of diet was noted for PHA test, cholesterol and TAC levels, fat depth, eye muscle depth and muscle score. Our study indicates that although Yerba Mate supplementation can increase feed intake and wool growth in lambs, it did not result in significant differences in LW, ADG or body composition and had a significant negative effect on FCR. Further work is required to investigate the effect of Yerba Mate supplementation on lambs production and health.

The effect of thyroxine on wool growth and lamb production

Summary In a series of trials over the period 1954-57 inclusive some 650 sheep of the Corriedale breed have been implanted with 1-thyroxine and the following observations made: — i. The rate of wool growth is stimulated if the implantations are made during the late summer and autumn period (January-April) but implantations made in the winter, spring, and early summer (June-December) are ineffective. ii. The optimum dose level appears to be in the region of 60–90 mg as a single implantation in sheep of 120–130 lb body weight. iii. 90 mg implants cause an 8 lb loss in body weight over the first month, which is slowly but not fully regained in subsequent months. iv. 90 mg thyroxine implanted at the optimum time gives on average a fleece weight increase of 0.6 lb (or 6%) the increase being mainly due to additional staple length. Fleece grade is not significantly improved, but the percentage of cotted fleeces is reduced. v. Late-summer implantations made before mating for maximum wool response have caused a sl...

Influence of stocking rate and mixed grazing of Angora goats and Merino sheep on animal and pasture production in southern Australia. 3. Mohair and wool production and quality

The effects of animal species (AS; Angora goats, Merino sheep, mixed-grazed goats and sheep at the ratio of 1 : 1) and stocking rate (SR; 7.5, 10 and 12.5 animals/ha) on fibre production and quality were determined in a replicated experiment on improved annual temperate pastures in southern Australia from 1981 to 1984. Separately grazed sheep produced the most total clean fibre/ha at each SR. Mixed-grazed treatments produced amounts of clean fibre/ha similar to the arithmetic mean of sheep and goat treatments at 7.5/ha (21.9 versus 21.3 kg/ha), 10% more at 10/ha (28.3 versus 25.3 kg/ha, P &lt; 0.05) and 7% more at 12.5/ha (31.6 versus 29.6 kg/ha, P &lt; 0.10). Clean wool production/head was affected by AS and SR but not year. Clean mohair production was affected by SR and year but not AS. Variation in mean fibre diameter (MFD) accounted for 67 and 71%, respectively, of the variation in clean wool and clean mohair production/head. There was an AS × SR interaction for clean fibre production/t pasture. Growth rate of mohair was highest in autumn and least in summer. In each season, an increase in the SR reduced the clean mohair growth rate. Growth rate of wool was highest in spring and least in summer. Wool and mohair MFD were affected by an AS × SR interaction. Mohair MFD was also affected by year and season. At 10/ha, wool from mixed-grazed sheep had a greater MFD than wool from separately grazed sheep (20.2 versus 18.9 μm) and mixed-grazed goats grew mohair 1 μm coarser than separately grazed goats. At 12.5/ha mixed-grazed goats grew mohair 1.9 μm finer than separately grazed goats. Mohair MFD was predicted by a multiple regression that included average liveweight for the period of fleece growth, season of growth (summer 1 µm finer than winter) and year (range 1.27 µm). Mohair MFD increased 4.7 µm/10 kg increase in average fleece-free liveweight (P = 6.4 × 10–14). Fleece-free liveweight alone accounted for 76.4% of the variation in mohair MFD. There was an AS × SR interaction for the incidence of kemp and medullated fibres; under severe grazing pressure their incidence was suppressed. This experiment indicated that the principles associated with the effects of SR on wool production on annual temperate pastures apply to mohair production. Mixed grazing of Merino sheep and Angora goats produced complementary and competitive effects depending on the SR. Angora goats should not be grazed alone or mixed-grazed with sheep on annual temperate pastures at SR greater than that recommended for Merino sheep.

Effects of the absence of protozoa from birth or from weaning on the growth and methane production of lambs

Merino ewes (n 108) joined to a single sire were allocated into three flocks, with ewes in one flock being chemically defaunated in the second month of gestation. Single lambs born to defaunated ewes (BF lambs) were heavier at birth and at weaning than lambs born to faunated ewes (F lambs). After weaning, all BF and F lambs were individually housed then half of the F lambs were chemically defaunated (DF lambs). In trial 1, BF, DF and F lambs were offered a concentrate-based diet containing either 14 or 19 % protein for a 10-week period. Wool growth rate of BF lambs was 10 % higher than that of DF or F lambs and was increased 9 % by the high-protein diet. While there was no main effect of protozoa treatment on enteric methane production, there was an interaction between protozoa treatment and diet for methane production. BF and DF lambs produced more methane than F lambs when fed the low-protein diet but when fed the high-protein diet, emissions were less than (BF lambs) or not different from (DF lambs) emissions from F lambs. In trial 2, lambs were offered 800 g roughage per d and, again, methane production was not affected by the presence of protozoa in the rumen. The data indicate that while lambs without rumen protozoa have greater protein availability than do faunated ruminants, there is no main effect of rumen protozoa on enteric methane production by lambs fed either a concentrate or roughage diet.

Relationships between plasma methylmalonic acid and ruminal succinate in cobalt-deficient and -repleted sheep

We measured methylmalonic acid (MMA) in plasma and succinate in the rumen during the depletion of sheep to a state of severe cobalt deficiency and repletion by various forms of supplementation. Groups of 10, cobalt-deficient weaners were allocated to one of 4 treatments: no supplement, 0.1 or 4.0 mg/day of cobalt as a solution of CoSO4.7H2O per os, or intramuscular vitamin B12. Plasma concentrations of MMA were elevated above the normal range (5 µmol/L) after 35 days on the cobalt-deficient diet, before a reduction in feed intake and while liveweights were still increasing. In all 3 supplemented groups of sheep, plasma vitamin B12 concentrations increased to normal levels within 10 days of supplementation (P &lt; 0.001). Plasma MMA concentrations were reduced to normal levels within 10 days with vitamin B12 supplementation but took 31 days with oral cobalt supplementation (P &lt; 0.001). Plasma MMA concentration in the unsupplemented group continued to rise and remain high for the duration of the experiment and did not show the peak and decline to levels indistinguishable from cobalt adequate levels as observed by others. Rumen succinate concentrations were elevated within 6 days of sheep being introduced to a cobalt-deficient diet and in the unsupplemented sheep remained elevated for the duration of measurement. This rise in rumen succinate was seen at a wider range of cobalt intakes than previously reported. In both oral cobalt treatments, vitamin B12 concentrations increased (P &lt; 0.001) and succinate concentrations decreased (P &lt; 0.001) in the rumen to normal levels within 6 days of supplementation. However, the vitamin B12 provided to the sheep by injection was not recycled to the rumen to any effective degree, as demonstrated by the persistence of high rumen succinate concentrations. The ability of the vitamin B12-supplemented sheep to maintain higher rates of wool growth than deficient sheep, while still exhibiting elevated succinate concentrations in the rumen, demonstrates that overcoming the blockage of the methylmalonyl CoA mutase pathway in the rumen is not essential for restoring metabolic pathways such as those responsible for wool growth. This work contributes to the knowledge of plasma MMA and rumen succinate as useful indicators of functional cobalt status and cobalt intake in sheep.

Responses of wool growth rate and body reserves to nutrition in Merino ewes: a potential biological link between production and fitness

This study examined whether the low body-fat reserves in sheep with high estimated breeding values (EBVs) for clean fleece weight (CFW) reported previously are affected by nutritional history, and second whether the effect may be related to differences in the variation in fibre diameter (CVfd). Groups of 11 20-month-old Merino ewes with high and low EBVs for CFW and for CVfd were compared in a 2 × 2 design at low bodyweight, then fed ad libitum for 100 days and re-measured. The response of wool growth rate to feed supply (WRF) was estimated as the slope of the regression against time of clean wool mass collected from mid-side patches at intervals of 30–40 days throughout the experiment. High CFW sheep had greater feed intake relative to liveweight and liveweight gain (P = 0.02), but did not differ significantly in other characteristics from low CFW sheep. High CVfd sheep had lower plasma concentrations of insulin (P = 0.02), IGF-1 (P = 0.03), and albumin (P = 0.02) throughout the study, and had less fat when in poor body condition (P = 0.02). The WRF was greater in both the high CFW (P = 0.003) and the high CVfd (P = 0.004) genotypes. When studied in poor body condition, sheep with a high WRF had lower liveweight (P &lt; 0.001), lower body condition score (P &lt; 0.001), lower plasma albumin (P &lt; 0.001), and higher plasma growth hormone (P = 0.02), but these relationships weakened or disappeared after ad libitum feeding. Sheep with high WRF also had lower plasma concentrations of insulin (P = 0.002) and IGF-1 (P = 0.008) throughout the study, which may have brought about the increased responsiveness of protein and energy metabolism to nutrition. The results indicate that genetic selection for wool characteristics can affect the responsiveness of wool growth rate to nutrient supply. Sheep that are highly responsive grow more wool when offered abundant feed, but may have lower body nutrient reserves when on limited feed.

Skin characteristics and skin protein composition of Merinos differing in estimated breeding values for wool growth and fed at above and below maintenance

Twenty castrated male sheep were selected from a commercial flock, 10 with high estimated breeding values (EBVs) (F+) and 10 with low EBVs for wool production (F–). Five of each EBV treatment were offered feed at 0.8M [0.8 times their metabolisable energy (ME) requirement for maintenance] and the other 5 were offered feed at 1.8M for 6 weeks. On the midside area of skin, the F+ group had a greater rate of clean wool growth (g/100cm2.day) and daily growth in fibre length (mm/day) than the F– group at both feeding levels (P&lt;0.05). Fibre diameter (FD) was finer for F+ than F– sheep at both feeding levels (P&lt;0.001). As the feeding level increased, FD increased (P&lt;0.001), but the ratio of fibre length growth to mean FD remained constant. The secondary follicle density in F+ sheep decreased with an increase in the feeding level (P&lt;0.01), whereas the secondary follicle density of F– sheep remained unchanged (P&gt;0.05). The ratio of secondary to primary follicles (S/P) was 21% higher (P&lt;0.01) in skin from F+ sheep than in skin from F– sheep, but this difference was not related to the feeding level. Skin thickness at the midside was thinner (P&lt;0.05) when sheep were underfed, but F+ sheep had a thicker (P&lt;0.05) skin than F– sheep. The trephine (diameter: 1.5 cm; area: 1.766 cm2)-sampled skin weight was heavier for F+ than for F– (0.339 v. 0.294 g, P&lt;0.05) but did not differ (P&gt;0.05) with the level of intake. The weight of the dermis layer was greater in F+ than F– sheep (0.231 v. 0.190 g per trephine, P&lt;0.05) and F+ sheep also tended to be more responsive to feeding level than F– sheep (interaction: P = 0.06). True protein content per 100 g wet skin did not differ between F+ and F– sheep or between feeding levels, whereas the protein content per 100 cm2 skin was significantly (P&lt;0.05) higher in F+ sheep. The concentration of collagen in skin protein (g/100 g) was lower in F+ sheep than F– sheep at both feeding levels (P&lt;0.05). Of the amino acids evaluated, significant differences occurred between F+ and F– sheep for the methionine (Met) concentration in plasma (P&lt;0.05) and in the free amino acid pool in the skin (P = 0.06). The distribution ratio of skin Met concentration to plasma Met concentration was significantly lower in the F+ sheep than F– sheep (0.77 v.1.18 kg skin/ L plasma). Results presented here indicate that skin characteristics such as skin thickness, follicle density, S/P ratio, skin weight, dermis weight, true protein or collagen content were a consequence of genetics and nutritional variation in wool growth rate, fibre length and fibre diameter. Selection for high EBVs for wool growth has resulted in animals which grow more wool at the 2 levels of feed intake provided, supported by their higher S/P ratios, higher skin and protein masses, more responsive dermides and higher efficiency of Met usage in skin tissue.

The costs for protein and energy requirements by nematode infection and resistance in Merino sheep

The requirements of metabolizable energy (ME) and metabolizable crude protein (MCP) of Merino sheep in response to infection with Trichostrongylus colubriformis and Ostertagia circumcincta were measured in an animal house environment. Two genotypes of growing sheep, parasite-resistant line and unselected control, were fed at maintenance, 1.5× maintenance, or ad libitum for 24 or 18 weeks in two experiments, and the body weight, weight change, and wool growth rate of the sheep were measured at six weekly intervals. Extra protein required for infected sheep was 6.5 g/day for sheep at maintenance and about 9 g/day for sheep gaining 100 g/day weight, and was consistent across the body weight range. The extra energy requirement by the infection ranged from 0.71 to 1.76 MJ/day, depending on the body weight and weight gain, and declined with increasing body weight. The costs of MCP and ME by the infection in relation to total nutrient requirements declined with increasing body weight, indicating that the infection had more severe detrimental effects on young sheep. Compared with the control line, the parasite-resistant sheep at 10 months of age required an additional 0.02 MJ ME/kg of metabolic live weight (W 0.75) and 0.19 g/W 0.75 MCP. These extra requirements by the resistant sheep were approximately 4% of the daily ME and 5% MCP requirements in young sheep. At an older age (18 months), the additional nutrient requirement by resistant sheep was no longer evident.

Relationship between MT1 melatonin receptor gene polymorphism and seasonal physiological responses in Île-de-France ewes

The gene encoding the MT1 melatonin receptor in sheep has a restriction fragment length polymorphism (RFLP) site to the MnlI enzyme whose incidence is associated to the expression of seasonality in several breeds. The aim of this study was to examine the relationship between this genetic marker and the physiological effects of MT1 receptor gene polymorphism on several seasonal functions in Ile-de-France ewes. The study was performed using 12 pairs of half-sib adult Ile-de-France ewes. Within each pair, ewes were selected on the basis of their genotype at the MnlI RFLP site: group +/+ and -/- (presence and absence of MnlI restriction site, respectively). No difference in the dates of the beginning, the end or the length of the breeding season was observed between groups during the two-year study. The seasonal changes in prolactin secretion were not different between groups. Similarly, wool growth rate and primary follicle activity, measured for one year, varied with the time of the year in the same way in the two groups. Our study therefore failed to show any relationship between MT1 polymorphism and reproductive seasonality in Ile-de-France ewes. This suggests that the influence of this polymorphism on the regulation of seasonal function is dependent upon the breed and/or environmental conditions. The MT1 polymorphism can explain only a small part of the genetic variability of seasonal functions and the implication of other genes must be investigated.