Merino Weaners Research Articles

Protective efficacy of Barbervax® in Merino weaner sheep trickle infected with five doses of Haemonchus contortus infective larvae

Barbervax® protects sheep against H. contortus infection; however, the level of protection afforded by the vaccine at different levels of larval challenge under field conditions has not been reported. Therefore, this study was designed to investigate the protective efficacy of Barbervax® at increasing doses of trickle infection with H. contortus third stage larvae (L3). Merino lambs (220) were randomly allocated to challenge treatment groups and received Barbervax® vaccinations at approximately 8, 11, 15 and 22 weeks of age or not vaccinated (control group). Animals within each treatment group were subjected to one of five levels of H. contortus L3 trickle infection (0, 300, 600, 1200 and 2400 L3/week in two split doses). Trickle infections started two weeks after the third vaccination (week 0). Worm egg count (WEC), packed cell volume (PCV), antibody titre and bodyweight were measured at week 2 (start of trickle infection), week 5 and then every two weeks for 11 weeks. Vaccinated weaners had a significantly (P < 0.0001) lower faecal WEC than unvaccinated control animals. Vaccination induced significant specific antibody responses that were not influenced by level of trickle infection. Vaccination significantly reduced the number of weaners requiring salvage anthelmintic treatment (9.4% vaccinated weaners versus 33.6% unvaccinated). Vaccine protective index based on WEC was similar at all challenge levels (overall mean> 60%) and at the higher challenge levels did not reduce H. contortus infection to levels that would not require anthelmintic treatment. Therefore, it is suggested that under conditions of high larval challenge the use of Barbervax® should be integrated with other control methods.

Arena behaviour of Merino weaners is heritable and affected by divergent selection for number of lambs weaned per ewe mated

Data of 3375 6.5-month-old Merino weaners from two divergently selected lines at Elsenburg were used to evaluate the genetics of the response of weaner lambs to flock isolation and a stationary human in an arena test. The High (H) line was selected upwards and the Low (L) line was selected downwards for number of lambs weaned per ewe mated (NLW) from 1986 to the present. Selection resulted in divergent lines for NLW, live weight up to yearling age, wrinkle scores as well as other breech strike indicator traits such as breech and crutch cover scores. Weaners from the H line (selected for NLW) travelled longer distances in the arena, based on the number of squares crossed. They also bleated at a lower frequency and urinated and defecated at a lower frequency than their L line contemporaries (all P < 0.05). The average distance the weaners maintained from the stationary human (0.10 ± 0.03), urinating events (0.15 ± 0.03), and defecating events (0.07 ± 0.02) were all lowly heritable. In contrast, the number of lines crossed (0.30 ± 0.04) and the number of bleats (0.38 ± 0.04) were moderately to highly heritable. Genetic correlations suggested that the weaners maintaining a larger distance from the stationary human covered a greater distance in the arena and were more likely to urinate during the test. Animals with a high urinating frequency were also likely to defecate more often. Genetic trends indicated that, over time, L line animals increased their distance from the human operator while they also bleated, urinated and defecated at a higher frequency. H line animals, in turn, exhibited fewer urination and defecation events over time. It was concluded that selection for NLW in the H line resulted in a range of behaviours that would indicate lower levels of stress when interacting with a stationary human in the arena. Animal welfare is facilitated by lower levels of stress as well as good animal-stockperson relations during unfamiliar procedures.

10.4314/sajas.v40i5.65268

Sheep fat contains relatively high levels of saturated fatty acids while poly-unsaturated fatty acids (PUFA) are toxic to cellulolytic bacteria and are also saturated in the rumen. Stabilization of residual oil in sunflower oilcake by conversion into calcium salts would be advantageous. Alpha lipoic acid acts as an antioxidant to ameliorate the effects of oxidative stress caused by high dietary levels of PUFA. Residual oil (14%) in mechanically extracted (expeller) sunflower oilcake (SFOC) was saponified in situ and compared in a complete feedlot diet (100 g crude protein and 31 g extractable fat/kg feed) with commercially extracted oilcake containing 2.4% residual oil (control diet with 29 g fat and 123 g crude protein kg feed) fed to four groups of 10 SA Mutton Merino weaner lambs (ca. 23 kg) for nine weeks. Both diets were fed either with, or without a weekly oral dosing of 500 mg α-lipoic acid. Fatty acid composition was determined on back fat samples while thiobarbituric acid-reactive substances (TBARS) were determined on samples of m. longissimus dorsi stored for zero and six months and displayed for six days. The back fat of the lambs on the saponified expeller SFOC diets contained significantly higher levels of saturated fatty acids and lower levels of mono-unsaturated fatty acids. PUFA were unaffected. High TBARS levels (>1.0) were found after six months storage. Non significant increases in TBARS were observed in the groups that received lipoic acid.

Genetic parameters involving subjective FAMACHA© scores and faecal worm egg counts on two farms in the Mediterranean region of South Africa

Data from two research farms, Elsenburg and Tygerhoek, were used to study genetic parameters for traits measured as part of the FAMACHA© system, as well as for the natural logarithm of faecal worm egg count+100 (LFEC). The traits assessed subjectively as part of the FAMACHA© system were eye score (ES), rib fat score (FSR), loin fat score (FSL) and dag score (DS). The study used between 1701 and 1815 records of Dormer and SA Mutton Merino weaner lambs at Elsenburg and between 1531 and 2219 Merino hoggets at Tygerhoek. Direct heritability estimates at respectively Elsenburg and Tygerhoek amounted to 0.13 and 0.12 for ES, 0.12 and 0.38 for FSR, 0.17 and 0.30 for FSL, 0.31 and 0.31 for DS as well as 0.12 and 0.14 for LFEC. The genetic correlation between ES and LFEC was significant at 0.66 at Elsenburg. This correlation suggest that animals with anaemic eye scores would also have higher values for LFEC. Negative genetic correlations (ranging from −0.45 to −0.82) among traits indicated that animals with a higher ES (i.e. higher levels of anaemia) would have lower fat scores (i.e. they were leaner) both at Elsenburg and Tygerhoek. Fat scores (FSR and FSL) were genetically highly correlated at both localities (0.92 at Elsenburg and 0.80 at Tygerhoek), suggesting that they were genetically very similar traits. Genetic correlations involving DS and LFEC were mostly low, variable in sign and magnitude and not significant. The practical implications of these results were discussed.

Differential response to an algae supplement high in DHA mediated by maternal periconceptional diet: intergenerational effects of n-6 fatty acids.

Algae high in docosahexaenoic acid (DHA) may provide a source of long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFA) for inclusion in the diet of lambs to improve the LCn-3PUFA status of meat. The effect of background LCn-3PUFA status on the metabolism of high DHA algae is, however, unknown. The aim of the current study was to determine whether the response to a high in DHA algae supplement fed to lambs for sixweeks prior to slaughter was mediated by a maternal periconceptional diet. Forty Poll Dorset×Border Leicester×Merino weaner lambs were allocated to receive either a ration based on oat grain, lupin grain, and chopped lucerne (control) or the control ration with DHA-Gold™ algae included at 1.92% DM (Algae) based on whether the dams of lambs had previously been fed a diet high in n-3 or n-6 around conception. LCn-3PUFA concentration was determined in plasma and red blood cells (RBC) prior to and following feeding. The concentrations of EPA and DHA in the plasma and RBC of lambs receiving the control ration were significantly (p<0.001) lower when lambs received the ration for 14days compared with pre-feeding concentrations. The concentrations of EPA and DHA were also significantly (p<0.001) higher when lambs consumed the Algae ration compared with the control ration for 42days. The increase in EPA and DHA was, however, significantly (p<0.05) lower if lamb dams had previously been fed a diet high in n-6 at conception. Assessing the previous nutrition and n-3 status of lambs may allow producers to more accurately predict the likely response to supplements high in LCn-3PUFA, particularly, DHA.

Nutrient partitioning of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent genetic selection for resistance to Haemonchus contortus had produced correlated changes in the metabolism of amino-nitrogen in the absence or presence of H. contortus infection. Partitioning of amino acid-nitrogen between tissues was determined in 42 Merino weaner wethers from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner wethers were fed a restricted diet (9.8MJME/kgDM, 86gMP/kgDM) calculated to allow a gain of 125g/d bodyweight throughout the experimental period and were either worm-free or trickle infected with H. contortus. At 8 weeks post-infection animals were injected with 15N-labelled duckweed directly into the abomasums. Animals were euthanased at either 6 or 24h after the injection to collect tissue samples for calculation of percentage recovery of 15N in tissue and to determine abomasal worm counts. Worm egg count and worm counts at week 8 of infection were lower in animals from the IRH line. IRH animals had a lower N digestibility, increased oxidation of amino acids and lower N balance but whole-body protein flux was unaffected. Amino acid metabolism, as assessed from 15N uptake and excretion in response to H. contortus infection, differed between IRH and DRH animals. In IRH animals a greater recovery of 15N in the thymus and abomasal smooth muscle indicated greater partitioning of amino acids towards the immune response. In DRH animals an increased recovery of 15N in the spleen, in response to infection, may be a possible adaptation. It appears that divergent selection for worm egg count has not been associated with symmetrical changes in amino acid metabolism, but rather the partitioning of amino acid resources reflects each selection line's independent response to infection.

Growth and Body Conformation Responses of Genetically Divergent Australian Sheep to Spirulina (Arthrospira platensis) Supplementation

The hypothesis that supplementation with Spirulina will increase liveweight, growth and body conformation with significant interactions between sire breed and sex was tested using purebred Merino weaners and first-cross weaners from Merino dams sired by Dorset, Black Suffolk and White Suffolk rams under the same pasture-based management system. Our experimental objective was to evaluate the effects of varying levels of Spirulina supplementation, sire breed and gender on liveweight and body conformation traits. We utilized a complete randomized block experimental design balanced by 4 sire breeds, 3 supplementation levels and 2 sexes in which weaned prime lambs with an average liveweight of 37.6 ± 5.2 kg and body condition score of 3.1 ± 0.4 at 6 months of age were balanced by sire breed and gender and randomly allocated into 3 treatments (8 lambs per treatment) – the control group grazing without Spirulina (0%), low (10%wt/vol) and high (20%wt/vol) Spirulina. Lambs in the low and high Spirulina treatment groups were drenched daily with Spirulina prior to being released for grazing with the control group of lambs over a 6-week trial period, following a 3-week adjustment phase. Weekly measurements of chest girth, withers height, body length, body condition score and liveweight were taken. Mixed linear model procedures in SAS with sire breed, sex, Spirulina level and their second order interactions as fixed effects and sire as a random variable, were used for statistical analysis. Spirulina level significantly influenced lamb liveweight (P<0.018), body condition score (P<0.001) and body length (P<0.015). Lambs on Spirulina levels of 10% recorded the highest mean liveweight of 41.9 ± 0.7 kg. Spirulina levels of 20% did not significantly improve liveweight compared to the control group (0%). Highly significant sire breed interactions with Spirulina level (P<0.001) resulted in the heaviest (47.08 kg) and lightest (35.14 kg) average liveweights in Black Suffolk-sired crossbreds and purebred Merino lambs respectively, supplemented at the 20% Spirulina level. Body conformation (P<0.001) and liveweight (P<0.014) responses to Spirulina supplementation significantly varied between ewe and wether lambs. It was evident that a cost-effective supplementation strategy with Spirulina for optimal liveweight gains in weaner lambs was achieved at the 10% level. These findings will aid sheep farmers in making informed choices about appropriate sire breed and gender combinations in their enterprises when supplementing with Spirulina for growth improvement as a strategic pathway for the early attainment of market weights in prime lambs. We concluded that based on the empirical experimental evidence within the scope of this study, the tested hypothesis is acceptable.

Rumen function and digestion of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

The aim of this experiment was to investigate the effect of Haemonchus contortus infection on rumen function and digestion of Merino sheep from lines divergently selected for genetic resistance to H. contortus. Rumen function and whole-tract digestibility were determined in 29 Merino weaner wethers from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Wethers were fed a restricted low quality roughage diet (5.9 MJ ME/kg DM, 29 g MP/kg DM) to maintain weight and were either uninfected (NIL) or infected with H. contortus (INF). Measurements were taken at week 7 of infection, while animals were housed in metabolic crates. Animals were then euthanased to determine abomasal worm counts. IRH had significantly lower worm egg count than DRH and C lines however, adult worm and larval counts, though lower in IRH animals, did not differ significantly. DM and OM digestibility and in sacco degradability of IRH and DRH selection lines were greater than C animals. Rumen function of animals from the IRH line was altered in response to H. contortus infection with an increase in fluid outflow and turnover rate and a decrease in propionic acid concentration. These changes may be a component of a greater host resistance and begin to explain the failure of IRH animals to translate lower worm egg count into greater bodyweight gain.

Voluntary feed intake and diet selection of Merino sheep divergently selected for genetic difference in resistance to Haemonchus contortus

This research was designed to determine if divergent selection for resistance to Haemonchus contortus had produced correlated changes in voluntary feed intake and diet selection. Voluntary feed intake, diet selection and production were determined in 54 Merino weaner rams from the CSIRO Haemonchus selection flock, increased resistance to Haemonchus (IRH), decreased resistance to Haemonchus (DRH) and random bred control (C) selection lines. Weaner rams were fed ad libitum either a high (9.2 MJ ME/kg DM, 90 g MP/kg DM) or moderate (6.3 MJ ME/kg DM, 30 g MP/kg DM) quality diet and given the choice between the two diets, when uninfected (NIL) or infected with H. contortus (INF). Symmetrical response to divergent selection for worm egg count (WEC) was not matched by a symmetrical change in feed intake and there was no difference in diet selection between selection lines. Feed intake, growth and wool production of DRH animals remained the same as that of IRH, yet DRH animals had five times greater WEC than IRH. This study begins to explain the mechanisms that allow resistant animals to effectively prevent establishment and/or development of H. contortus, by maintaining a greater immune response to infection through higher circulating eosinophils, plasma globulin and IgG 1 antibody titres. Susceptible animals have displayed resilience by improving feed conversion efficiency and increasing protein synthesis.

Effect of saponified high fat sunflower oilcake and lipoic acid

Sheep fat contains relatively high levels of saturated fatty acids while poly-unsaturated fatty acids (PUFA) are toxic to cellulolytic bacteria and are also saturated in the rumen. Stabilization of residual oil in sunflower oilcake by conversion into calcium salts would be advantageous. Alpha lipoic acid acts as an anti-oxidant to ameliorate the effects of oxidative stress caused by high dietary levels of PUFA. Residual oil (14%) in mechanically extracted (expeller) sunflower oilcake (SFOC) was saponifiedin situ and compared in a complete feedlot diet (100 g crude protein and 31 g extractable fat/kg feed) with commercially extracted oilcake containing 2.4% residual oil (control diet with 29 g fat and 123 g crude protein kg feed) fed to four groups of 10 SA Mutton Merino weaner lambs (ca. 23 kg) for nine weeks. Both diets were fed either with, or without a weekly oral dosing of 500 mg &alpha;-lipoic acid. Fatty acid composition was determined on back fat samples while thiobarbituric acid-reactive substances (TBARS) were determined on samples of m. longissimus dorsi stored for zero and six months and displayed for six days. The back fat of the lambs on the saponified expeller SFOC diets contained significantly higher levels of saturated fatty acids and lower levels of mono-unsaturated fatty acids. PUFA were unaffected. High TBARS levels (>1.0) were found after six months storage. Non significant increases in TBARS were observed in the groups that received lipoic acid.

High Merino weaner survival rates are a function of weaning weight and positive post-weaning growth rates

Survival and subsequent productivity of Merino ewe weaners (weaned in 2006 and 2007, respectively) on commercial properties in the New South Wales Central Tablelands were monitored through routine liveweight measurement until weaning of their own progeny from their maiden joining. Growth rates were calculated from the regular liveweight measurements with survival determined by the continuing presence of an individual animal at subsequent measurements. This study demonstrates that high weaner survival rates are a function of both weaning weight and post-weaning growth rates. Importantly, it indicates that low post-weaning growth rates can negate the survival benefit conferred by a high weaning weight such that weaners who were unable to sustain positive post-weaning growth rates were at high risk of death. Furthermore, classification of weaners into liveweight profile groups based on their weaning weight and post-weaning growth rates identified another group of weaners that are also at high risk of death. These weaners (14% of the mob) had above average weaning weights but low post-weaning growth rates and a mortality rate nearly 1.5 times that of the lightest cohort of weaners. High weaner survival rates about the 95% industry benchmark are possible if weaners show positive growth rates post weaning. Weaning weight continues to have a residual influence on the subsequent productivity of ewe weaners until they wean their first lambs. Maiden ewes that were heavier at weaning tend to have higher scanning percentages and are more likely to successfully rear their progeny to marking than their lighter weight counterparts. This finding should be taken into account when economic analyses of the benefits of alternative management strategies to promote weaner survival are undertaken.

Selenium supplementation increases wool growth and reduces faecal egg counts of Merino weaners in a selenium-deficient area

This paper reports on the effects of selenium supplementation on liveweight (LW), greasy fleece weight (GFW), fibre diameter (FD), impact of parasite infection and plasma glutathione peroxidase (GSH-Px) activity in weaned Merino sheep reared in a selenium-deficient area (blood GSH-Px &lt;40 U/g Hb). At weaning, 208 Merino wethers were assigned to two groups: control (CTRL) and treatment (SEL). The SEL group was injected with 0.5 mL of Deposel, a slow release selenium injection. LW, blood and faecal samples were taken at 6-week intervals over a 24-week period. At the end of the trial the animals were shorn and GFW and FD measurements were taken. The SEL group had significantly higher (P &lt; 0.01) LW compared with the CTRL group at Weeks 6, 12, 18 and 24. There was a significant difference (P &lt; 0.05) in GFW between the SEL and CTRL group, 2.93 and 2.75 kg, respectively. There was no difference in FD between the two groups. A trend (P &lt; 0.06) towards lower faecal egg counts in the SEL group was seen but the difference between the two groups was not significant. As expected, the SEL group had significantly (P &lt; 0.001) higher plasma GSH-Px activity compared with the CTRL group. In conclusion, selenium supplementation in weaned Merino sheep reared in a selenium-deficient area could increase the LW and GFW of the young sheep while perhaps reducing the level of parasitic infection.

Risk factors for post‐weaning mortality of Merino sheep in south‐eastern Australia

To measure associations between body weight, growth rate, sex, time of shearing and post-weaning mortality of Merino sheep. Uni- and multivariable survival analyses of sheep mortality during the first year after weaning, using records (n = 3657) from two field experiments conducted in Western Victoria from 1996 to 2003. Overall mortality was 14.3% (range 4.5-26.8%) and mean maximum mortality rate was 29 deaths/1000 weaners/month. Increased mortality risk was associated with decreases in fleece-free body weight and mean weaner growth rate, particularly at low weights and growth rates. Weaners in the lightest weaning weight quintile had a hazard ratio of 3.5, compared with the middle quintile. The hazard ratio for a 2-kg decrease in weaning weight was 1.2 to 1.7 for weaners lighter than 22 kg. The hazard ratio for a reduction in mean weaner growth rate in the first 5 months after weaning of 0.25 kg/month was 1.1 to 6.8 if mean growth rate was less than 1 kg/month, but did not differ significantly from 1 at greater growth rates. The hazard ratio for wether weaners was approximately 1.5 compared with ewe weaners. The hazard ratio for weaners shorn between December and May, compared with unshorn weaners, was 1.2 to 3.5, with the greatest risk difference associated with shearing in March (45 deaths/1000 weaners/month). Improving the body weight and mean growth rate of weaner sheep is likely to reduce post-weaning mortality. Lightweight weaners in a flock should be managed separately from the main portion after weaning. In southern Australia, not shearing spring-born Merino weaners between December and May may assist in reducing overall post-weaning mortality.

Effectiveness of a non‐surgical alternative to the Mules operation in sheep

To measure changes to the perineal bare area, local tissue reaction and healing responses of young sheep, following intradermal administration of cetrimide and polyvinylpyrrolidone (PVP), with and without ethanol, to the breech and tail. A needle-less injector was used to deposit formulations containing 40 g/L cetrimide and 30 g/L PVP (group 2) or 20 g/L cetrimide, 30 g/L PVP and 15 g/L ethanol (group 3), within the dermis of the tail and the region surrounding the perineal bare breech area of groups (N = 8) of Merino weaner sheep. The dimensions of the perineal bare area (length, width and diagonal distances left and right) and tail width were recorded before and at intervals after treatment for 60 days. Observations of swelling and bruising and scab formation at the treatment sites were recorded for up to 35 days after treatment. Rectal temperatures were monitored for up to 35 days after treatment and bodyweight for up to 60 days after treatment. An untreated control group (group 1) was included. Comparison of day -3 and day 35 measurement data showed that both treated groups had significantly (P < 0.05) wider breech bare areas compared to the untreated controls and that group 2 sheep had significantly (P < 0.05) longer breech bare areas compared to group 3 sheep or to the untreated controls, which were not significantly different. At this time scabs were still firmly in place on many treated sheep. At day 35 there was no increase in tail bare area caused by either treatment. By day 60 there was no significant difference between the treated and control groups in either the breech or tail regions indicating that the changes present at day 35, were not permanent. Mean weight gain in the groups throughout the 60-day interval was unaffected by treatment. Intradermal treatment was associated with a significant elevation in body temperature. This effect lasted for 3 days and was associated with signs of discomfort and depressed appearance in at least some of the treated sheep. Bruising was mild to severe in all treated sheep within two days of treatment but was not evident in any sheep by day 21. Mild to moderate swelling was also associated with treatment but was not uniform across sheep in the groups. The tail of one sheep was severely swollen for several days. Swelling remained obvious in most treated sheep until day 14 but was not present at day 21. Under the conditions of this study intradermal injection of cetrimide had no permanent effect on bare area measurements on the breech or the amount of wool-bearing skin on the tail. It also caused signs of discomfort and pain that raise welfare concerns.

Strategic use of crutching and dicyclanil to protect unmulesed sheep against breech strike

To test strategies for the application of dicyclanil and mid-season crutching to maximise protection of unmulesed sheep against breech strike. Three hundred and eighty unmulesed Merino weaners were randomly allocated to four groups either left untreated or treated by different strategies with 50 g/L dicyclanil. Treatments included breech treatment alone and breech plus body treatment, with two application times, immediately after shearing and 6 weeks after crutching or shearing. To assess protection, larval implants with newly hatched Lucilia cuprina larvae were applied to 10 different sheep from each group at 3, 4, 5 and 6 months after crutching and shearing and assessed for the development of strike at 48 hours. The concentration of dicyclanil was measured in wool samples clipped from the breeches of the test sheep. All dicyclanil treatments gave significant reduction in strike in comparison to controls up until 4 months after crutching but protection in the sheep treated immediately after shearing had waned at 5 months. Treating at 6 weeks after crutching provided significant reduction (P < 0.05) in strike for 6 months. Results for strike incidence immediately after shearing and concentration of dicyclanil in the breech wool also suggested improvements in protection by delaying treatment for 6 weeks. In most environments it should be possible to protect unmulesed sheep against breech strike with a carefully planned integrated control program incorporating strategically timed crutching, shearing and dicyclanil application. Delaying treatment with dicyclanil to at least 6 weeks after shearing or crutching increased the protection provided in comparison to treatment immediately after shearing.

Stress-strain properties of individual Merino wool fibres are minor contributors to variations in staple strength induced by genetic selection and nutritional manipulation

This paper investigates the contribution of single fibre stress-strain properties to variations in staple strength induced by both selective breeding for staple strength and nutritional manipulation. Merino weaners (n = 40), selected from ‘sound’ and ‘tender’ lines of staple strength selection flocks, were allocated to feeding regimes designed to induce liveweight changes simulating typical Mediterranean seasonal changes. Average staple strength differed by 5 N/ktex between ‘sound’ and ‘tender’ selection flocks and 18 N/ktex between extreme nutritional treatments. The force-extension properties of individual wool fibres (n = 100 per sheep) were measured using a single fibre strength meter. After normalising for differences in fibre cross-sectional area at the point of break, the key parameters used to describe the stress-strain curve for each fibre were: Young’s modulus (GPa), yield stress (MPa), stress at 15% strain (MPa), stress at break (MPa), strain at break (%) and work to break (MPa). The average stress-strain properties of single fibres differed widely between individual sheep. Stress at break ranged from 163 to 235 MPa (44% range), strain at break ranged from 21 to 44% (103% range) and work to break from 43 to 71 MPa (65% range). There were no significant differences in any of the single fibre properties between the staple strength selection flocks, nor was there any significant interaction (P &gt; 0.05) between staple strength selection flock and nutritional regimes. Nutritional regime had a significant effect on stress at break, strain at break and work to break, but none of the single fibre stress-strain properties removed any appreciable variance in staple strength over and above that accounted for by differences in along- and between-fibre diameter variation. There appears to be little scope for improvement of single fibre stress-strain properties as a means of increasing staple strength in normal production environments. Selection directly for staple strength or indirectly using the fibre diameter variability traits is an effective method to improve staple strength.

Putting Merino weaner management recommendations to the test

Merino weaner survival is poor under normal traditional management practices. Data from four trials conducted between 2001 and 2005 were used to assess the effectiveness of current industry recommendations to achieve 95% survival rates of Merino weaners. There was very little difference between 2001 and 2003 in survival of Merino weaners despite average weaning weight ranging from 20 to 24 kg between years. The recommended target weaning weight of 23 kg does not always appear to be a good predictor of survival. However, a target of 45% mature liveweight at pasture senescence achieved the industry recommendation of 95% weaner survival. Merino weaners were fed over the summer–autumn period to reach 40 kg liveweight by the time green feed became available. Weaner survival reached 93% compared with 89% survival to hogget shearing in weaners managed under normal growth paths. Furthermore, twice as many ewe weaners died in the traditional feeding program compared with the well fed ewe weaners. Differences in mortality between feeding levels in the wether weaners was less than that observed in the ewe weaners. Flock average growth rates were not useful indicators of weaner survival and there was no relationship between Merino ram estimated breeding values for weaning weight and the survival of the progeny.

Sheep select combinations of high and low sodium chloride, energy and crude protein feed that improve their diet

A major limitation of saltland pasture systems is the high sodium chloride content of the forage and the physiological implications of this for the grazing animal. Incorporating low salt alternatives has been found to improve livestock performance from high salt feeds. The aim of this study was to investigate how sheep offered high salt diets (such as saltbush pastures) select low salt alternatives to improve their diet. Five groups of six Merino weaner wethers were individually penned and offered a choice of two feeds. Sheep were offered a high salt feed containing 18.5% added NaCl and one of five alternative feeds. The alternatives were high–high, high–low, low–high, low–low energy and crude protein feed that contained no added salt or the high salt feed. Diet selection, liveweight gain and wool growth were determined in the sheep over 4 weeks. Additionally, water intake, pattern of feed intake and digestibility were measured. This study shows that sheep actively select combinations of high salt and alternative feeds that improve the overall feeding value of their diet. Sheep offered a low energy alternative feed had a higher intake of the high salt feed compared with those offered high energy alternatives (788 g/day versus 183 g/day). However, intake of the high salt feed did not differ significantly in sheep offered a low crude protein alternative compared with sheep offered a high crude protein alternative feed (422 g/day versus 550 g/day). Sheep selected an initial combination of high and low salt feeds that did not change as they became familiar with the feeds. The total organic matter intake of the sheep offered any of the four low salt alternatives was about 50% higher and their liveweight gain was at least double that of sheep offered only the high salt feed.

Characteristics of fleeces of fine-wool Merino weaners shorn at either 9- or 12-months of age

The wool of high producing, fine-wool sheep can be discounted for over-length staple length if shorn on an annual cycle. This paper contains data on fleece characteristics (including length, strength and position of break) from the initial shearing in a project investigating different shearing intervals. Increases in both clean fleece weight and staple length indicate that wool growth between 9 and 12 months of age was proportionately greater than during the first 9 months. The mean fibre diameter of the 2 groups of fleeces (15.9 and 16.7 µm for fleeces shorn at 9- and 12-month, respectively) reflected the higher wool growth rates. However, staple strength of the 12-month shorn group was lower than that of the 9-month group (30.5 v. 36.5 N/ktex) and the mean relative position of the break moved closer to the tip (28.5 v. 33.9 %).

Effects of protein supplementation of young sheep on resistance development and resilience to parasitic nematodes

The influence of dietary protein content, particularly the supply of metabolisable protein, on immunocompetence and on resilience to pathogenic effects during continuous exposure of young sheep to infective larvae is reviewed for the most important abomasal and small intestinal nematodes infecting young sheep in Australian grazing systems. In lambs infected with Haemonchus contortus supplementary protein improves both development of immunity and resilience in breeds of sheep that are susceptible to haemonchosis, but in relatively resistant breeds dietary supplementation appears unnecessary. Recent studies indicate that the increased protein requirements of Merino weaners parasitised by H. contortus would be met by diets containing about 190 g crude protein/kg dry matter, depending on the rumen degradability of the dietary protein source and level of feed intake. Some evidence exists for an enhanced immune response to Teladorsagia circumcincta in lambs receiving an increased supply of protein at the intestines.Response to protein supplementation of lambs infected with Trichostrongylus colubriformis depends on the metabolisable protein content of the basal diet and on the period of exposure to incoming larvae. Where the basal diet only meets requirements for maintenance or low growth rates, increased supply of rumen undegradable protein enhances immune expression in terms of reducing faecal egg count and expelling adult worms, but does not appear to limit the initial establishment of incoming larvae. Effects on growth rate and wool production are most pronounced during the period of worm expulsion, indicating that this phase of the immune response competes with production when nutrient resources, and particularly protein, are limited.Field trials in the Armidale region have shown that supplementation with protein meals of Merino weaners, exposed to natural infection from pasture, can reduce faecal egg count and improve resilience in terms of both growth rate and wool production. These effects may persist for some time after supplementation ceases. Further work is needed to determine the generality of these responses in other sheep-producing regions and genotypes and to establish cost-effective supplementation strategies.