Autumn Lambing Research Articles

Milk and meat exploitation, autumn lambing and use of forest resources in Neolithic Corsican sheep farming systems (fifth to third millennia cal BC)

Corsica has been inhabited since the ninth millennium BC, but it is only from the sixth millennium BC onwards, that Neolithic societies originating from Italy settled mostly along coastal areas but also inland, in high mountainous areas. By then, Corsica was already experiencing some Mediterranean climate trends and was covered with dense forests. In order to assess how these Neolithic societies sustainably occupied this new insular territory, we need to understand how the local environment and resources were incorporated in the pastoral system. Osteological and isotopic analyses on remains from the sites of Araguina Sennola (late fifth – early third millennia cal BC) and Montlaur (4100–3600 cal BC) investigated the key parameters of these husbandry systems. Sheep mortality profiles from dental remains suggest mixed meat and milk exploitation. Modelled intra-tooth variations of oxygen isotope ratios (δ18O) revealed extended birth season, including autumnal lambing. Carbon isotope ratios (δ13C) showed high seasonal variation, involving forest resources in winter, as well as high-δ13C summer plant resources, possibly C4 plants from coastal salt marshes. This raises the question of the seasonal mobility of herds. Great inter-individual variability in δ13C values reflects variable degrees and patterns of mobility, suggesting that herders adapted to the conditions of the contrasted Mediterranean landscape.

Effects of the breeding season, birth type and sex on growth and reproductive performances of sheep breeds.

The study aimed at determining the effects of breed type, breeding season, sex and type of birth on the growth and reproductive traits of lambs. Two ewe breed types (Gellaper and Swakara) and four ram breed types (Damara, Dorper, GeDo and Swakara) were used. Two lambing seasons, spring (March-May) and autumn (September-November), were considered. Gellaper-based lambs born in autumn had higher (P < 0.05) mean birth weight (4.58 kg) compared to spring-born lambs (3.43 kg). Ram lambs were heavier (P < 0.05) than ewe lambs at weaning and post-weaning age. Singletons were heavier than twins (P < 0.05) at birth, weaning and breeding. Single and autumn-born lambs had a higher average daily gain (ADG) than spring-born lambs (P < 0.05). Ram lambs had a higher pre-weaning and overall ADG (P < 0.05) compared with ewe lambs. Swakara-based lambs gained more from weaning to mating compared to Gellaper-based lambs (P < 0.05). The conception, lambing and annual reproductive rate were all influenced by breed type and season (P < 0.05). Swakara-based lambs had higher reproductive capabilities, while Gellaper-based lambs grew faster but take longer to breed type; autumn lambing gave rise to low birth weights but heavier lambs at weaning and post-weaning, hence suitable for mutton production.

Effect of climatic factors on urinary cortisol and peripheral blood leukocytes in lambs grazing on a semi-natural grassland in the Hokuriku District of Japan.

The effects of climatic factors on stress and immune functions of grazing lambs in summer and autumn in the Hokuriku District of Japan were evaluated by determining urinary cortisol (U-COR) levels and peripheral blood leukocyte populations and comparing those with lambs kept indoors. Two groups of five lambs, consisting of those grazed on a semi-natural grassland (GRL) and those housed indoors in a domestic animal shelter (INL), were maintained at from July to October. The temperature-humidity index at each location was indicative of heat stress during summer; however, the U-COR elevation was not observed in both groups. The elevation was observed in GRL in autumn and was higher than INL in October. Climatic conditions in autumn were characterized by high humidity and a sudden drop in temperature. U-COR was positively correlated with the relative humidity. The GRL was exposed to low-nutrient conditions for a relatively long time. The CD4+ /CD8+ T cell ratio in GRL decreased in October. Subsequently, the total leucocyte, including granulocytes, monocytes, and lymphocytes, sharply increased. The responses indicated an immune deficiency caused by immunosuppression because of a low nutrition caused by grazing and high-stress conditions in autumn.

Direct and correlated responses to selection for autumn lambing in sheep

BackgroundSeasonal reproduction limits productivity, flexibility, and profitability in commercial sheep production. Hormonal and (or) photoperiodic manipulation can be used to control estrous cycles in sheep and reduce limitations that are imposed by the seasonal anestrous but are often impractical or incompatible with the extensive management systems preferred for ruminant livestock. Thus, the current study investigated the use of selection to improve realized fertility (i.e., the proportion of ewes that lambed) following an out-of-season spring joining period (May and June) in a crossbred sheep population.ResultsOver 17 years, estimated breeding values (EBV) for fertility in selected (S) ewes increased by 0.175 (0.01 per year). The mean EBV for fertility of S ewes was greater than that of control ewes by year 10 (P = 0.02), and the fertility of adult (≥ 3 years old) ewes reached 0.88 ± 0.05 by year 17. Lambing began approximately 140 days after the introduction of rams, and 64% of the S ewes that lambed did so in the first 17 days of the potential lambing season, which indicated that most of the S ewes were cycling at the time of ram introduction and were not induced to cycle by the introduction of breeding males (i.e., the so-called “ram effect”). Animals in the S line had modest increases in body weight and scrotal circumference. A modest negative trend in the additive maternal effect on birth weight was observed but was reversed by additional selection on EBV for maternal birth weight. The heritability of litter size in autumn lambing was low (0.04) and could potentially limit the response to selection for this trait.ConclusionsSelection improved realized ewe fertility in out-of-season mating, with absolute increases of approximately 1% per year in the percentage of joined ewes that lambed in the autumn. Genetic antagonisms with other performance traits were generally small. A modest antagonism with maternal breeding values for birth weight was observed but it could be accommodated by selection on EBV for maternal birth weight. Our results support results of previous studies that indicate that these selected ewes had one of the shortest seasonal anestrous periods reported for temperate sheep breeds and that spring-lambing lactating ewes from the selection line were capable of relatively rapid rebreeding in the spring.

Effect of grazing different forage systems prior to and during mating on the liveweight, condition score, conception and reproductive rate of maternal-composite ewe lambs

Context Economic modelling identified that mating of ewe lambs for lambing at 1 year of age has the potential to increase the profitability of sheep-production systems in south-western Victoria. In order to optimise reproductive rates, ewe lambs should weigh at least 35–40 kg, have a condition score (CS) of 3.0 at mating, and be gaining weight (100–150 g/day) during mating. However, typical perennial ryegrass (Lolium perenne L.) pastures in south-west Victoria do not support the attainment of these targets without additional supplementation. Aim Our research aimed to determine how grazing summer-active pastures or brassica (Brassica napus L.) forages affects the liveweight, CS, conception and reproductive rate of ewe lambs when offered before and during mating compared with a system using perennial ryegrass plus supplement. Methods A field experiment was conducted at Hamilton, Victoria, Australia, in 2014 and 2016 testing seven forage treatments replicated four times in a complete block design. The treatments were: canola (B. napus, two treatments of different cultivars), forage brassica, lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), plantain (Plantago lanceolata L.) and perennial ryegrass. Key results Ewe lambs grazing canola or forage brassica had higher (P &lt; 0.05) liveweight gains during the pre-mating and mating periods than those grazing the perennial ryegrass treatment (148 vs 75 g/day in 2014, s.e.m. 17; 139 vs 54 g/day in 2016, s.e.m. 17). In 2014, spring-sown dual-purpose canola, lucerne and chicory resulted in higher (P &lt; 0.05) reproductive rates (144–151%) than the perennial ryegrass treatment (103%); forage brassica and plantain gave intermediate results (128% and 129%). Conclusion Brassica forages (including spring-sown canola), lucerne and chicory can support the attainment of key liveweight and CS targets for successful mating of ewe lambs in autumn. Implications Spring-sown canola is therefore a viable alternative forage for use by livestock producers in southern Australia and presents an opportunity to incorporate an alternative income stream in mixed-farming systems.

Evaluation of perennial lupin/cocksfoot pasture relative to lucerne pasture under summer dry conditions

The productivity of a perennial lupin/cocksfoot mix was compared to that of lucerne in summer dry conditions at Lincoln University, Canterbury, New Zealand. The pastures were planted in December 2013 and rotationally grazed by ewe lambs in autumn 2014 (Year 1), and by ewe hoggets in spring-summer and ewe lambs in autumn of 2014/2015 (Year 2) and 2015/2016 (Year 3). For lupin/cocksfoot relative to lucerne in Years 1 to 3, sheep liveweight gains were 54% of 107 kg/ha, 68% of 1134 kg/ha and 50% of 1347 kg/ha; herbage dry matter yields were 122% of 3520 kg/ha, 64% of 10 230 kg/ha and 59% of 9680 kg/ha; and in Years 2 and 3, the water use efficiency of sheep liveweight gain was 76% of 2.0 kg/ha/mm and 49% of 2.7 kg/ha/mm, respectively. The lupin content in the pre-grazing herbage in Years 1 to 3 averaged 42, 22 and 12%, whereas the lucerne content averaged 78, 95 and 98%, respectively. This showed that perennial lupin was not persistent at this lowland site. Keywords: Lupinus polyphyllus, Dactylis glomerata, Medicago sativa, dryland, sheep liveweight gain, water use

Grazing crops: implications for reproducing sheep

Integration of crops and livestock has been revitalised in Australia, initially as an opportunity to increase cropping within the high-rainfall grazing zones, and more recently, to improve enterprise diversification and profitability across the low-, medium- and high-rainfall, and mixed-farming zones. Young crops are highly digestible (&gt;80% dry matter digestibility, DMD) with a high energy density (&gt;12 MJ/kg DM) and, in much of southern Australia, fill a winter feed gap. The quality and time of feed availability also coincide with the high nutrient requirements of ewes in late pregnancy and lactation. In Western Australia and South Australia, young crops are available for lactating ewes and young growing lambs (autumn lambing). For the smaller proportion of growers who lamb later in winter, young crops are available for the last 1–2 months of pregnancy. In the later-lambing states of New South Wales and Victoria, crops may be grazed by ewes at any stage of pregnancy and lactation and/or by young lambs. In Tasmania, crops are more likely to be available during early–mid-gestation. Limited studies on feed budgeting with grazing crops have indicated that ewes can maintain or even increase liveweight, with a much lower level of feed on offer than would be required with traditional pastures (&lt;500 kg DM/ha). This has the potential to increase whole-farm stocking rates and/or reduce fetal mortality, increase lamb birthweight and survival and improve lifetime production. Maintaining or increasing ewe liveweight during pregnancy and lactation may also result in heavier ewes the following year and higher ovulation rates. Pregnancy and lactation are also periods of increased susceptibility to metabolic disturbances. The composition of young crops increases this susceptibility. Pregnancy toxaemia, hypocalcaemia and hypomagnesaemia can influence ewe health and fetal survival. Chronic acidosis and excessive ammonia absorption from rapid introduction of pregnant ewes onto young crops may risk appetite loss and increase susceptibility to pregnancy toxaemia. Low magnesium and sodium combined with high potassium increases the risk of grass tetany. Most young crops (except canola) also have a tetany index &gt;2.2, indicating a high risk of grass tetany. The elevated potassium also contributes to a high dietary cation–anion difference of approximately +49 mEq/100 g DM and this may cause metabolic alkalosis and hypocalcaemia. Pregnancy toxaemia, hypocalcaemia and grass tetany are all potential causes of increased ewe mortality. Pregnancy and/or lactation outcomes will also be influenced by a deficiency of trace elements. Grazing young crops in areas with a history of selenium, copper, iodine and cobalt deficiency will increase susceptibility to deficiency by increasing growth and feed intake. In conclusion, the grazing of young growing crops presents new opportunities for increased production and stocking rates in the mixed-farming zones. The value of this feed source is well recognised by some producers. While growing crops have a highly productive potential, they also come with an increased risk of a range metabolic disturbances and nutritional imbalances. These risks can be minimised by regular monitoring of livestock and crop biomass and the provision of mineral supplements.

Patterns of estrous cycles, estrous behavior, and circulating prolactin in spring and summer in ewes selected for autumn lambing and exposed to ambient or long-day photoperiods

Estrous behavior in response to ambient and long-day photoperiods was evaluated in ewes developed by 10 years of selection for ability to lamb in autumn. Following October lambing, 67 ewes were moved indoors and exposed to long-day (16L:8D) or ambient photoperiods from February 2 until July 6. Two vasectomized rams with marking harnesses were housed with each group. Estrous behavior was monitored twice weekly. Ewes from the selection line were unresponsive to long days, with no effects on estrous behavior, frequency of ovulation, or circulating prolactin. Adult ewes were anestrus for only 34 ± 3 d, but 2- and 3-years-old ewes were anestrus for 72 ± 7 and 57 ± 10 d, respectively. Frequencies of ovulation based on circulating progesterone concentrations in March, May, and June were 97%, 95% and 52%, respectively, indicating that many ewes that did not exhibit estrus still ovulated. Prolactin concentrations increased from 10 ng/ml in February to 27 ng/ml in March and 173 ng/ml in June but were not affected by light treatment. Ten ewes that failed to exhibit estrus behavior for at most 24 d during the main study were then monitored for 74 additional long days. Nine of 10 ewes did not exhibit estrus for periods similar to 1 or 2 estrus cycles during this period, but eight ewes re-initiated cycles by the end of the study on September 18. Selection for ability to lamb in autumn thus resulted in ewes with an abbreviated seasonal anestrus and reduced sensitivity to long days.

Lambing season and fertility of fat-tailed ewes under an extensive production system are associated with liveweight and body condition around mating

The objective of this study was to investigate to what extent fertility and lambing season of fat-tailed ewes raised under an extensive production system are related to liveweight, body condition and changes around mating. Ewe liveweight and body condition score (BSC) were recorded in June, July and August over a period of 3 years (1999–2001) in 11 flocks (eight flocks of Kurdi breed and three flocks of Kurdi × Sanjabi crossbred). Both Kurdi and Sanjabi are native fat-tailed breeds in western Iran. In total, 3278 lambing records relating to 1592 ewes and data on mating date, liveweight and BCS of 1930 ewes (3975 records) were used for statistical analyses. The statistical model for bodyweight and body condition data included fixed effects of breed group, flock nested within breed group, year, the future lambing status following summer breeding (barren, autumn lambing and winter lambing), ewe age and all two-way interactions. Breed group had a significant effect on ewe liveweight (P &lt; 0.01). However, there was no significant difference between BCS of the two breed groups around mating. Ewe liveweights measured in June, July and August had significant effects on fertility and lambing season (P &lt; 0.01). Ewes that produced lambs were generally heavier at mating than barren ewes (P &lt; 0.01). Autumn-lambing ewes were heavier than winter-lambing ewes in June and July (P &lt; 0.01). Effects of changes in liveweight on fertility and lambing season were significant (P &lt; 0.01). The effects of BCS in June, July and August (P &lt; 0.01) and changes in BCS during the mating period (P &lt; 0.05) on fertility and lambing season were also significant. The mean BCS (in June and July) of autumn-lambing ewes was greater than that of the winter-lambing and barren ewes (P &lt; 0.05). The proportion of autumn-lambing ewes significantly increased as BCS in July increased, whereas the proportion of barren ewes decreased (P &lt; 0.01). Fertility was associated with age so that as the age of the ewes increased from 2 to 7 years, the proportion of barren ewes significantly decreased from 29 to 5% (P &lt; 0.01). There was a relatively high proportion of very thin ewes of 2 and 3 years of age. These findings imply that low body condition is a particular problem in younger ewes suggesting the importance of giving special nutritional treatment to younger ewes to reduce the proportion of barren ewes.

Field evaluation of juvenile in vitro embryo transfer (JIVET) in sheep

The practicality of using juvenile in vitro embryo transfer (JIVET) on a field scale in China was evaluated in each of three seasons (summer, autumn and winter) from 2006 to 2007. A total of 102 donor Merino lambs (18 summer, 69 autumn and 15 winter) aged 4–8 weeks were stimulated with 4 × 40 mg FSH administered at 12 h intervals plus 400 IU PMSG given at the time of the first FSH treatment. Overall, 89.2% (91/102) of the lambs exhibited follicle development and 79.1 ± 65.5 (mean ± S.D.) cumulus–oocyte complexes were recovered per donor lamb. Compared with the groups of summer (84.9 ± 55.3) and autumn (83.6 ± 70.8) lambs, the number of recovered cumulus–oocyte complexes was significantly decreased in winter (51.4 ± 43.7; p < 0.05). After recovery, the cumulus–oocyte complexes were matured and fertilized in vitro using frozen–thawed semen and culture in synthetic oviduct fluid medium to the 2–4-c stage of development, when they were transferred surgically in groups of 3–8 (5.33 ± 1.47) to the ipsilateral uterine horn of a total of 603 synchronized recipients. The overall mean proportion of cumulus–oocyte complexes developing to 2-c embryos was 61.4% (4308/7013) and differed significantly between seasons (summer 38.5%, autumn 66.1%, winter 74.6%; p < 0.01). Pregnancy rate assessed by ultrasound examination approximately 60 days after embryo transfer was 54.4% (328/603) overall, and 36.7% (221/603) of the recipients maintained their pregnancy to full-term, producing an average 1.49 (330/221) offspring, of which 1.21 (267/221) were viable and healthy lambs, per pregnant recipient. Pregnancy rate at day 60 was affected by season (summer 40.5%, autumn 56.7%, winter 55.7%; p < 0.05), but did not differ significantly between seasons at full-term (summer 34.2%, autumn 38.9%, winter 30.4%; p > 0.05). Based on the number of donors stimulated, the total number of offspring and viable progeny produced per donor lamb in autumn (5.81 and 4.87) was significantly ( p < 0.01) higher than that of summer (2.79 and 1.94) and winter (4.24 and 3.31). This study showed that each donor lamb after stimulation produced an average of 48.6 transferable embryos that resulted in 4.04 viable and healthy progeny. These results indicate that JIVET is a cost-effective method of multiplying desirable sheep genotypes in China.

Effect of high nitrogen fertiliser applications on profitability within a lamb trading operation

This study aimed to examine the economic response to high rates of N in a winter lamb trading operation and was an "add on" to a commercial lamb trading operation in Hawkes Bay. The general policy of the lamb trading operation was to purchase store lambs in autumn at 35 kg liveweight, rotationally graze through winter and early spring and draft for slaughter at 45 kg liveweight. Keywords: nitrogen fertiliser, lamb performance, farmlet trials, lamb finishing, cost effectiveness

Evaluation of Ewe Performance in 795 Selected Sheep Flocks in South-Eastern Norway

A study of ewe performance was undertaken in 795 sheep flocks based on data from the Norwegian Sheep Recording System. Herd level data included in the annual report for 1998 were used as the basis for the study. Average flock size was 75.3 ewes. The material was considered as representative of the better and more motivated sheep farmers in the mountain valley regions in south-eastern Norway. The average number of lambs born per ewe, inclusive (and exclusive) of barren ewes, was 1.89 (2.02), and of autumn lambs (those surviving from birth in the spring to autumn) 1.60 (1.66). The average autumn weight of the lambs corrected to 145 days of age was 42.4 kg, giving an overall performance of 67.9 kg lambs live weight per ewe. When including artificially reared lambs, overall performance was 70.4 kg per ewe.Artificial rearing of lambs, mostly triplets which had been removed from the ewe, was practised on 395 of the farms. In the 74 flocks with a rate of artificial rearing of more than 10% of all lambs, overall performance per ewe was 13.3 kg higher than in flocks with no artificial rearing. Total lamb mortality from birth to autumn recording, including stillborn lambs, was 12.44%. Mortality had a skewed distribution, some flocks having very high mortality figures. The arithmetic means (and medians) for mortality were as follows: 2.75 (2.29)% stillbirths, 2.93 (2.30)% died during the indoor feeding period, 0.88 (0.00)% at spring pasture, and 6.16 (4.40)% at summer pasture. In regression models using Proc Genmod in SAS®, it was found that average number of autumn lambs per ewe was negatively associated with the rate of barren ewes, late lambing date (flock average day in year when lambing took place), and total lamb mortality. The corrected autumn weight of the lambs was positively associated with the average number of lambs born per ewe and non-fertility rate, and negatively associated with flock size and total lamb mortality. The Dala breed had a positive effect on number of autumn lambs per ewe, and Spæl breed a negative effect on corrected autumn live weight of the lambs.

Effects of lambing season and stage of lactation on ewe milk quality

A total of 240 bulk milk samples were collected and examined from January to July of 2000. The milk samples were obtained from 5 intensively managed flocks of Comisana ewes located in southern Italy. Milk sampling was performed separately on the ewes which had lambed in the autumn (October and November) of 1999 (ALB, autumn lambing) and in the winter (January and February) of 2000 (WLB, winter lambing). For each lambing season, 6 sampling cycles were carried out during early-, mid- and late-lactation (less than 60 days from 100 to 130 days and from 150 to 180 days in lactation, respectively), using the bulk milk of four consecutive milkings. In all the farms, the ewes received hay and concentrates during the winter season, while during the spring and summer season ewes grazed and were supplemented with hay and concentrates. The milk yielded by the WLB ewes recorded lower fat and protein contents compared to that of the ALB ewes (6.71 vs. 6.93% and 5.15 vs. 5.39%, respectively), as well as deteriorating renneting and hygienic characteristics. Irrespective of the lambing season, a higher SCC was recorded in late, compared to early- and mid-lactation milk (6.16 vs. 5.93 and 5.87log10somatic cells/ml) as well as a marked worsening in coagulating behavior. Reduced cheese-making efficiency was associated with a reduction in the casein and fat content of milk from the ALB ewes, and decreased calcium and phosphorus content in the WLB ewe milk. For both lambing seasons increased plasmin activity was recorded in the milk. Results suggest that ovine milk quality is strongly affected by the combined effects of seasonal changes in climate and herbage availability and variations in ewe metabolic status with the advancement of lactation. Proper housing sanitation, flock management and milking procedures play a major role in optimizing the quality of ewe milk during the late-lactation when several factors concur to increase the risk for mastitis, such as the involution of the mammary epithelium, rises in ambient temperatures, and worsening in air and surface hygiene. During the summer season, strategies to reduce the impact of high temperatures on lactating ewes and an appropriate administration of mineral elements with the feed diets are necessary to sustain the yield and quality of milk and cheese in ewes.

Evaluation of melatonin receptor 1a as a candidate gene influencing reproduction in an autumn-lambing sheep flock.

The effect of the melatonin receptor 1a (MTNR1A) gene on fertility and litter size in autumn lambing was studied with 373 ewes from a population of sheep selected for 10 yr for fertility in May and June matings. Animals were from a composite line of 50% Dorset, 25% Rambouillet, and 25% Finnsheep. Two restriction fragment length polymorphisms were present in the population, with allelic frequencies of 0.42 and 0.58 for an MnII polymorphism (alleles M and m, respectively) and of 0.34 and 0.66 for an RsaI polymorphism (alleles R and r, respectively). Genotypic frequencies for the polymorphisms were not independent, suggesting an association between them in foundation animals. Effects of MTNR1A genotype on fertility and litter size were evaluated using mixed linear model or REML procedures, but were not significant for matings involving ewes of all ages. However, in adult ewes (3 yr old and older), fertility of ewes of genotype mm was 10.0 (mixed model; P < 0.09) to 11.2% (REML; P = 0.03) less than that of other ewes. Genotypic effects associated with MTNR1A in adult ewes accounted for 23.8% of the estimated total additive genetic variance in fertility. Litter size was not significantly associated with MTNR1A genotype; adult ewes of genotype mm had approximately 0.11 fewer lambs per ewe lambing than ewes of other genotypes. Fertility in autumn lambing is lowly heritable, expressed only in females, and manifested relatively late in life and only in some management systems. Access to genetic markers would thus be advantageous in selection programs.

Nocturnal melatonin and prolactin plasma concentrations in sheep selected for fertility in autumn lambing'.

Ewes selected for fertility in autumn lambing were used to evaluate correlated responses in nocturnal hormone levels. Four jugular blood samples were obtained during nighttime in August from each of 113 selected and 69 control ewes. Melatonin levels were lower for selected ewes (143 +/- 14 pg/mL) than for control ewes (184 +/- 13 pg/mL), and melatonin levels decreased with increases in estimated breeding values (EBV) for fertility (-2.23 +/- 0.79 pg mL(-1) x %(-1)). Prolactin levels were higher for selected ewes (90 +/- 7 ng/mL) than for control ewes (52 +/- 7 ng/mL), but significant line x ewe age interaction was also observed, with smaller differences in prolactin levels in 2-yr-old and older ewes (74 +/- 7 vs. 56 +/- 9 ng/mL for select and control ewes, respectively; P < 0.20 before and P = 0.05 after logarithmic transformation). Prolactin levels increased with both fertility EBV (1.23 +/- 0.53 ng mL(-1) x %(-1)) and maternal birth weight EBV (9.0 +/- 4.0 ng x ml(-1) kg(-1)). Heritability estimates were 0.43 (P < 0.02) for melatonin levels and 0.11 (P > 0.25) for prolactin levels. Thus, we conclude that selection for fertility in autumn lambing has affected patterns of melatonin and prolactin secretion during the dark phase.

Evaluation of the feeding value of Aries HD perennial ryegrass (Lolium perenne). II. Performance of weaned lambs in summer and autumn

The feeding value of Aries HD perennial ryegrass (Lolium perenne) was evaluated over summer (2 Dec 1996 to 12 March 1997) using Romney weaned lambs, with Yatsyn 1 perennial ryegrass as the control cultivar. There were three replicate plots of each cultivar of 0.33 ha continuously stocked with 8 lambs per plot to maintain a mean sward surface height of 6 cm. There was no significant difference in lamb liveweight gain (116 versus 111 ± 5.1 g day−1, P > 0.6) or herbage intake (0.7 versus 0.6 ± 0.10 kg OM day−1, P > 0.5) between Aries HD and Yatsyn 1 lambs. Liveweight gain of lambs (mean of two treatments) decreased as the experiment progressed from 174 g day−1 in December, to 102 g day−1 in January/February, to 76 g day−1 in February/March. Incidence of ryegrass staggers was low with 9% of Yatsyn 1 lambs being affected over late February/early March, which coincided with a peak lolitrem B concentration of 1.37 ppm in Yatsyn 1 pasture, which was similar between cultivars. There was no significant difference in final carcass weight of lambs grazing Aries HD and Yatsyn 1 (14.9 versus 14.6 ± 0.24 kg, P > 0.5), reflecting the similar nutritive value and alkaloid concentrations of the two cultivars over this summer/autumn period.

Genetic parameters for lamb birth weight in spring and autumn lambing

AbstractGenetic parameters for birth weight were estimated for two sets of spring-born and one set of autumn-born lambs of the same breed composition and genetic origin using a model that included random additive, additive maternal, permanent environmental maternal, litter and residual effects. Litter effects were significant for all data sets, indicating that within-year effects of common environment and (or) non-additive genotype were important for birth weight and should be included in genetic evaluation programmes. Estimates of variance components for autumn-born lambs differed significantly from those obtained from spring-born lambs or from the combined data. In contrast, estimates obtained for the two sets of spring-born lambs did not differ from those obtained when data on all spring-born lambs were pooled. The estimate of h2 for birth weight in spring-born lambs was over twice as large as that obtained for autumn-born lambs (0·26 v. 0·22).In contrast, the across-year repeatability of ewe effects was much larger in autumn lambs (0·41 v. 0·26) as was the full-sib littermate correlation (0·73 v. 0·49). Mean birth weights were also 0·4 to 0·6 kg less in autumn lambs. These results suggest that negative effects on birth weight that have been reported for lambs gestated during summer in equatorial and subtropical regions are also manifested (albeit at reduced levels) in less extreme climates (in this case, 37°, 15' N latitude and 654 m elevation) and that maternal variation exists in the ability of the ewe to maintain adequate lamb birth weights in autumn lambing systems.

Managing sheep grazing systems in southern Australia to minimise greenhouse gas emissions: adaptation of an existing simulation model

This study summarises the development of a framework in which changes in the management strategies of sheep grazing systems in temperate Australia can be evaluated in terms of their impact on greenhouse gas emissions and financial viability. An exploratory study of a sheep grazing system at Hamilton, in western Victoria, indicates that reducing emissions from some sheep grazing systems in temperate Australia by 20% over the next 15 years will require a similar (i.e. 18%) reduction in stock numbers providing that no other management or technology is used to reduce emissions. This reduction in stock numbers will reduce both farm operating surplus and net cash income by about 15.5 to 17%. The reduction in net cash income represents a direct reduction in the general welfare of the farmer. However, economically viable reductions in emissions may be able to be achieved through changing the time of lambing. Spring lambing resulted in returns per unit emissions which were 15 to 20% greater than those for autumn lambing. Surveys suggest that about two-thirds of all flocks in the area lamb in autumn. Therefore, there exists an opportunity to reduce emissions by the order of 15 to 20% from the region without substantial economic penalties. Overstocking resulted in both increased net methane and nitrous oxide emissions and reduced profitability. The relatively small reductions in stocking rate needed in such situations will reduce greenhouse emissions significantly and also may have the effect of reducing soil and vegetation degradation, thereby improving the sustainability of these enterprises. Implementation of these stocking rate recommendations to reduce greenhouse gas emissions could thus be achieved as part of overall sustainable farming.

A putative role for larval nematode infection in diarrhoeas of lambs which did not respond to anthelmintic drenches.

Attempts to control a summer diarrhoea in grazing Finnish landrace lambs which had been unresponsive to anthelmintics and coccidiostats were made by supplementing them with cupric oxide particles and withdrawing a magnesium-rich mineral, while maintaining parasite control measures. The diarrhoea persisted from July to September and plasma pepsinogen activities were raised, suggesting that the anthelmintic did not prevent abomasal damage; the jejunum of an affected lamb showed lesions of parasitic gastroenteritis. Small responses to cupric oxide particles and larger responses to the withdrawal of magnesium were deceptive, possibly being confounded by differences in parasite challenge. In another experiment Finnish landrace lambs were more susceptible to diarrhoea than Suffolk cross lambs in autumn. The susceptibility was then linked to a strong inhibition of worm egg output and may have been caused by a hypersensitive mucosal response to the larval challenge. Plasma pepsinogen concentrations were again raised in the Finnish landrace lambs and did not decline after treatment with anthelmintic, whereas the concentrations increased later in the Suffolk cross lambs, and were apparently responsive to anthelmintic. The cases of diarrhoea were similar to 'July disease' and may have been caused by continuous nematode infections which were only briefly controlled by drenches. Anthelmintic-unresponsive diarrhoea is the term proposed for the disorder, which may be controllable by devices releasing anthelmintic continuously or by a move to less infected pasture. Faecal egg counts remained low in the condition and were diagnostically misleading.

The effect of exogenous melatonin and the plane of nutrition after weaning on ovulation rate in salz ewes lambing in the seasonal anoestrus

Induction of oestrus and pregnancy in the seasonal anoestrus permits lambing during the breeding season and mating in a short period of time after weaning, but after spring lambing postpartum anoestrus is longer than it is in autumn lambing, and no breeds are able to resume cyclic activity two months after lambing. Nutrient status has been shown to be a major factor affecting the onset of ovarian cyclicity in postpartum ewes. On the other hand, melatonin implants were demonstrated to be efficient in advancing the annual breeding season, but the efficiency of this treatment could be modified by the nutritional status of the animals. The aim of this experiment was to determine the effect of exogenous melatonin, connected with the plane of nutrition after weaning, on the resumption of sexual activity and ovulation rate (OR) in a synthetic Spanish sheep breed lambing in spring.