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1.
Jackass penguins Spheniscus demersus hatch two different-sized eggs asynchronously: the second-hatched chick, being, on average, 59% of the weight of the first-hatched chick on hatching. We examined the effect of hatching order on growth rates of mass, culmen length and culmen depth by comparing: (i) growth rates of first-and second-hatched chicks, and (ii) chicks from experimentally synchronized broods to chicks from normal asynchronous broods. Only growth rates in mass showed significant variation. Within a brood, B chicks grew more slowly than A chicks. The effect of synchronizing a brood was to lower the growth rate of both chicks to that of a B chick, suggesting that equal-sized siblings feed less efficiently. Chicks hatching from larger A eggs, that had been synchronized for age and size with chiçks from B eggs, did not grow faster, indicating that chicks hatching from A and B eggs do not have intrinsically different growth rates. Single-chick nests result usually from egg infertility. Singletons showed only a non-significant trend towards faster growth in mass than offspring in two-chick broods, even though food availability in one-chick nests should be better than in two-chick nests. Overall, hatching order had more impact on growth rates of mass than did brood size or egg dimensions.  相似文献   

2.
Breeding success (fledglings pair?1 y?1) of the Red-listed African Black Oystercatcher (Haematopus moquini) is highly variable, both spatially and temporally. Despite a diversity of natural factors causing this variability, there is evidence that two anthropogenic factors, i.e. disturbance and an introduced mussel (Mytilus galloprovincialis), are having an impact on the local breeding success of this species. Using a data set comprising 87 site-years of nest-monitoring data across most of the species’ breeding range, we analysed the extent and causes of variability in breeding success. Breeding success differed across three population categories defined by varying levels of human disturbance: island populations, protected mainland populations, and unprotected mainland populations. Differences in breeding success between island populations and protected mainland populations were likely due to differing exposure to predators; however, differences between protected and unprotected mainland populations were unlikely caused by this as both experience equivalent predation levels (although from different predators). Protection only improved the breeding success of oystercatchers in very high-quality habitats (with a high biomass of alien mussels), and where populations were ‘released’ from high levels of human disturbance. In unprotected mainland areas, human activity impacted on the breeding success of local populations primarily through predation of small chicks by uncontrolled dogs, and by rising tides drowning chicks that were hiding from human disturbance. The findings of this study note the potential conservation dilemma resulting from an invasive species improving the conservation status of a Red-listed species, and encourage the implementation of restricted sites in high-quality habitats with high breeding pair densities.  相似文献   

3.
Abstract

Reproductive and aerial tillering dynamics in Lolium perenne L. (perennial ryegrass) was monitored for two years under grazing. Reproductive tillers were observed from winter (June) to midsummer (February) with the main period of initiation occurring in spring to early summer (August to October). For infrequent lenient grazing, reproductive tiller densities ranged from 102 (July 1993) to 1 900 (September 1993) tillers m?2, and from 29 (June 1994) to 980 (September 1994) tillers m?2. By contrast, simulated continuous grazing (CG) resulted in reproductive tiller densities ranging from 13 (August 1993) to 100 (October 1993) tillers m?2, and from 25 (July 1994) to 46 (September 1994) tillers m?2. Aerial tillers were initiated mainly during spring, and to a lesser extent autumn and winter, with no appreciable number being recorded during summer. For infrequent lenient grazing, aerial tiller densities ranged from 25 (February 1993) to 1 620 (September 1993) tillers m?2, and from 362 (August 1994) to 1 524 (September 1994) tillers m?2. By contrast, CG resulted in aerial tiller densities ranging from 123 (May 1993) to 14 (June 1993) tillers m?2, and from 5 (July 1994) to 29 (May 1994) tillers m?2. There was no indication that reproductive or aerial tillers contribute to the persistence of perennial ryegrass under the grazing frequencies and intensities tested.  相似文献   

4.
The redclaw crayfish Cherax quadricarinatus is a recent introduction into Lake Kariba, Zimbabwe where it is rapidly spreading. There are, however, no studies that have investigated the population dynamics and possible ecological impacts of the crayfish in the lake. This study investigated aspects of the population biology of C. quadricarinatus in the lake. These included sex distribution, population growth and mortality parameters, probability of capture, recruitment and length at age of ge at maturity. Crayfish were captured monthly between January and December 2013 from 13 sites using opera house bait traps. Aspects of the species population biology were estimated using a fish stock assessment tool, FISAT II. A total of 3 205 crayfish were captured, of which 44% were male, 49% female and 7% intersex individuals. The asymptotic length (L∞ = 112.88 mm), curvature parameter (k = 0.72), longevity (tmax = 4.17 years), growth performance index (? = 3.96), total mortality (Z = 2.06 y?1), fishing mortality (F = 1.07 y?1), natural mortality (M = 0.99 y?1), rate of exploitation (E = 0.52) and length-at-first capture (Lc = 44.48 mm) were estimated. Fecundity averaged 503 ± 229 eggs female?1 and increased with size (weight and carapace length). Gravid females were found throughout the year but the highest proportion of females with eggs (4–10%) were found in the first quarter, whereas recruitment peaked in May and June. The smallest crayfish with eggs (48.75 mm CL) was estimated to be 1.02 years and the largest (94.82 mm CL) 2.85 years. Cherax quadricarinatus exhibited an r strategy life-history pattern due to continuous reproduction and high fecundity. In Lake Kariba, C. quadricarinatus is now well into the establishment stage of the Introduction–naturalisation–invasion continuum and spreading in the lake. Management options should thus aim at preventing further spread and reducing the population size and the potential negative impacts of this species.  相似文献   

5.
The energy values and ash contents of 15 species of macrolauna found on three exposed sandy beaches on the west coast of South Africa were examined over an 18-monlh period. The values obtained ranged from a mean of 26,65 kJ.g?1 ash-free dry weight (AFDW) in the haustoriid amphipod Urothoe grimaldii to 19,83 kJ.g?1 for the bivalve Donax serra and the values obtained are applied to biomass data for the three beaches. A pattern of decreasing energy content with increasing mean body weight was observed. No patterns of seasonal or regional variation were detected in either energy values or ash contents. Ash contents depended on taxonomic group (owing to morphological effects) and the mean size of the species; in the case of the Crustacea increasing with size within a given taxonomic grouping. The mean energy value for the 15 species was 23,81 kJ.g?1, higher than the 23,09 kJ.g?1 conversion factor obtained by Brey, Rumohr & Ankar (1988) for aquatic macrobenthic invertebrates in general, and in accordance with the suggestion by Slobodkin & Richman (1961) that energy contents are affected by the extent of storage for adverse conditions.  相似文献   

6.
The breeding habits of the bushveld gerbil Tatera leucogaster were examined in relation to rainfall and diet. Breeding is seasonal and associated with regular summer rainfall. The duration of the breeding season is variable, which is indicative of a temporally dynamic reproductive strategy. Litter size is large, and the punctuated iteroparity of T. leucogaster is associated with a xeric environment. The reproductive tactics of T. leucogaster are discussed in relation to other gerbils and rodents exhibiting similar reproductive strategies. Tatera leucogaster is a selective feeder on transient but seasonally available insects and seeds, but feeds on herbage when preferred foods are unavailable.  相似文献   

7.
《African Zoology》2013,48(4):299-305
The status of waterbirds breeding in protected areas in North Africa needs constant monitoring because of a naturally fluctuating environment and permissive attitudes towards illegal activities likely to negatively affect population dynamics of threatened species. We present the results of a study conducted at a protected site, Lake Tonga, north-eastern Algeria, on a breeding population of Ferruginous Duck Aythya nyroca, a Near-Threatened duck subjected to considerable pressure from egg-pilfering and illegal hunting. Two distinct habitats within the lake were used by Ferruginous Duck: an Alder carr (Alnus glutinosa) and floating islets across the lake. The mean clutch size was 9.51±1.84 eggs (N = 51 clutches) with hatching rate of 80.7% for successful clutches. Breeding success was low (37%) with predation (33%) and clutch desertion (17%) accounting for the majority of failed nests. The probabilities of nest failure and nest desertion increased with a delayed onset of egg laying. Predation was not significantly associated with egg laying date and vegetation cover, but late breeders nesting in dense vegetation seemed to suffer less predation. Conspecific brood parasitism was positively associated with nest size, whereas interspecific brood parasitism was marginally associated with water depth. We discuss different hypotheses concerning nest desertion, and argue that illegal hunting and disturbance may best explain why birds desert their nests.  相似文献   

8.
Seasonal variation in forage quality and mimosine contents of two varieties (cultivars Cunningham and Spectra) of Leucaena leucocepha/a were evaluated. Cultivar (cv.) Cunningham was available throughout summer, autumn, winter and spring seasons while cv. Spectra was available during summer, winter and spring seasons. Differences in crude protein (CP) and mimosine contents of young Cunningham and Spectra leaves were not significant. Also, difference in mimosine contents of mature leaves of both cultivars were not significantly different. But mean CP content of mature Spectra leaves was significantly higher (24.9 vs 18.7%, p = 0.023) than that of leaves of mature Cunningham. Mean P content of young Spectra leaves was significantly higher (1.6 vs 2.10gkg?1, p = 0.046) than that of young Cunningham leaves but mean Cu content of young Cunningham leaves was higher (10.5 vs 9.0mgkg?1, p = 0.06) than that of young Spectra leaves. Mature leaves of cv. Spectra also had higher P content (2.3 vs 1.6gkg?1, p = 0.06), but lower Ca (20.8 vs 30.5gkg?1, p = 0.06) and Mg (5.6 vs 7.6gkg?1, p = 0.06) contents than those of mature Cunningham leaves, Apart from CP, fat and mimosine, other analysed constituents increased with plant maturity.  相似文献   

9.
1. Oxygen permeabilities (KO2 ) of the shell and shell membranes of fertile and infertile chicken eggs were measured at 37.5 °C and a relative humidity of 0.60 throughout 14 d incubation, with turning. The KO2 of the shell and membranes of infertile eggs was around 1.0 × 10?7 cm3 O2STP sec?1 cm?2 Torr?1 (1 Torr = 133.322 Pa) throughout incubation. With fertile eggs, from which there was a linear loss of water during incubation, the KO2 of the shell and shell membranes was about 1.0 × 10?7 cm3 O2STP sec?1 cm?2 Torr?1 for the first four days of incubation. Thereafter the majority of shells and membranes had a Ko2 of about 1.0 × 10?6 cm3 O2STP sec?1 cm?2 Torr?1.

2. A diminution of the Na+ and K+ content of the shell membranes of fertile eggs was not associated with changes in the dimensions of the glyco‐protein mantle on the cores of the individual fibres of the membranes. There was, however, a progressive deterioration in the limiting membrane of fertile but not of infertile eggs.

3. It was concluded that changes in the O2 resistance of the integument of fertile eggs were not a product of change in either of the shell membranes but of damage caused to the limiting membrane by the chorioallantois.  相似文献   


10.
The modification of natural habitats requires behavioural plasticity, which may be challenging for ‘specialist’ species. Quantifying habitat requirements and behavioural responses of specialists to landscape transformation is thus a priority for baseline data to inform conservation practices. Using camera-trap surveys of the forest-dependent Lemon Dove Aplopelia larvata in conjunction with detailed microhabitat-scale covariates, we assessed habitat use during two periods in the year: autumn–winter and spring–summer (which largely encompassed peak breeding). We used occupancy modelling of forest-structural covariates to produce models of the probability of occupancy and detection of Lemon Doves in patches of the Indian Ocean Coastal Belt Forest of South Africa. The average occupancy and detection probability as indicated by the top-performing models was 0.39 ± 0.08 and 0.26 ± 0.05, respectively, during autumn–winter, and 0.37 ± 0.08 and 0.25 ± 0.04, respectively, during spring–summer. Although occupancy and probability of detection remained relatively constant between seasons, there was seasonal variation in the influence of individual covariates for both measures. The overall trend of positive influences on Lemon Dove occupancy was that of complex and diverse habitat structures and high plant species richness. The specific covariates that influenced occupancy positively during spring–summer may reflect the ecological requirements for nestling provisioning for both dietary needs and an avoidance of potential disturbance. Thus, while Lemon Doves may be less habitat-specific during autumn–winter, conservation management plans for safeguarding the breeding success of the species are advised to ensure adequate protection of large forest patches with complex and diverse interior structures and minimal disturbance.  相似文献   

11.
Botanical and chemical compositions of Boer goat diets, determined with repeated collection of forage samples taken from the goat’s mouth, were studied in a gypsophilous grassland during four seasons of the year. Ten pluriparous goats were used to collect selected forage species. Shrubs were a minor dietary component throughout the year (<7.5%). Goats selected more (p?<?0.01) grass during autumn and winter (34.2–37.8%) than during spring (21.2%) and summer (29.0%). During all seasons goat diets were dominated by forbs (>59%). Diets were lowest (p?<?0.05) in percentage of crude protein during spring, summer and autumn (13.2?±?3.5, 13.2?±?2.4 and 14.2?±?3.9, respectively) than winter (17.5?±?2.9) with levels above the recommended quantities for goats throughout the year. In vitro dry matter digestibility of forages selected by goats did not differ between seasons (range 47.4–53.3%). It was concluded that in this particular ecosystem goats preferred forb species over grasses across all seasons. In addition, goats maintained relatively stable diet quality by forage-class mixing of diets.  相似文献   

12.
The seasonality of growth and low nutritional value of kikuyu (Pennisetum clandestinum) pasture restrict milk production. The aim of the study was to determine the dry matter yield, botanical composition and nutritional value of irrigated kikuyu over-sown with annual ryegrass (Lolium multiflorum var. westerwoldicum), white clover (Trifolium repens) and red clover (T. pratense) or a mixture of perennial ryegrass (Lolium perenne) with white and red clovers under intensive grazing conditions with dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture changed the seasonal fodder flow and increased the spring dry matter (DM) production. The over-sowing of kikuyu with annual ryegrass had no effect on the DM production of kikuyu during the summer and autumn. Kikuyu and kikuyu–ryegrass, fertilised with nitrogen fertiliser, had a higher DM production rate than kikuyu–clover pastures. Kikuyu–ryegrass pasture transformed from ryegrass-dominant in spring to kikuyu-dominant in summer and only kikuyu in autumn. This led to a decrease in metabolisable energy (ME) and increase in neutral detergent fibre (NDF) content of the pasture during spring, summer and autumn as kikuyu became more dominant. The clover content of kikuyu over-sown with clover decreased annually but was still higher than 30% at the end of two years after establishment. As the kikuyu content of the kikuyu–clover pastures increased, the seasonal growth rate changed from a low autumn growth (37.9 kg DM ha?1 d?1) in the first year to a higher autumn growth (48.5 kg DM ha?1 d?1) in the second year. The over-sowing of kikuyu with clover resulted in lower DM production and NDF values and higher crude protein (CP), ME and calcium (Ca) values. The lowest CP content in kikuyu–ryegrass pasture was during summer and autumn when kikuyu was dominant. The Ca content of the grass pastures (kikuyu and kikuyu–ryegrass) was low. The phosphorus (P) content of both the kikuyu–clover and grass pastures exceeded the requirement needed for dairy production (0.38%). The mean Ca:P ratio of the kikuyu–clover pasture meets the 1.6:1 ratio needed by dairy cows. The kikuyu and kikuyu–ryegrass pasture had a Ca:P ratio lower than 1:1 and Ca supplementation would be needed for dairy cows. The incorporation of annual ryegrass, perennial clover or perennial ryegrass–clover into kikuyu pasture improved the seasonal DM production and nutritional value of the pasture.  相似文献   

13.
Objective To compare the fresh gas flow requirements of the ‘Maxima’ and Jackson‐Rees modified Ayre's T‐piece (JRMATP) in spontaneously breathing anaesthetized in cats. Study design Prospective randomized clinical study. Animals or sample population Fifteen adult cats (6 male, 9 female, 3.1 ± 0.4 kg [x? ± SD]). Materials & methods After pre‐anaesthetic medication with acepromazine and pethidine, anaesthesia was induced using thiopentone and the trachea was intubated with a cuffed endotracheal tube. This was attached to either a ‘Maxima’ or a JRMATP breathing system; allocation was randomized. Anaesthesia was maintained with halothane delivered in a 1 : 1 oxygen : nitrous oxide mixture. Initial total fresh gas flow (FGF) was set at 600 mL kg?1 min?1. After 20 minutes, FGF was reduced in increments of 200 mL min?1 until rebreathing (inspired CO2 concentration >0.2%) occurred. At this point, FGF was increased to 600 mL kg?1 and the process was repeated with the other breathing system. The respiratory rate and airway pressure at the endotracheal tube connector were monitored throughout anaesthesia. Results The mean fresh gas flow that prevented rebreathing with the Maxima system (164 ± 39 mL kg?1) was significantly less (p < 0.0001) than that required in the modified T‐piece (455 ± 0.77 mL kg?1). Respiratory rates and airway pressures at the endotracheal tube connector were not significantly affected by breathing system employed. Conclusions In terms of the gas flow requirements that prevent rebreathing, the ‘Maxima’ breathing system is more efficient than the modified Ayre's T‐piece in spontaneously breathing cats anaesthetised with halothane.  相似文献   

14.
2008和2009年,我们采取漂流调查和行走调查相结合的方式,对长白山脉(中国境内区域)的中华秋沙鸭(Mergus squamatus)繁殖种群分布状况进行了连续和重复调查.每年的调查都包括春季对中华秋沙鸭繁殖对和夏季繁殖家族的调查.两年期间,共调查了鸭绿江、松花江、图们江、牡丹江4个水系的17个河段,调查距离总计1553 km,共记录到中华秋沙鸭个体1354只.全部调查河段的中华秋沙鸭繁殖密度为每公里河段0.26±0.30个中华秋沙鸭繁殖对;春季中华秋沙鸭种群个体密度为平均每公里河段0.75±0.88只中华秋沙鸭个体.根据调查结果,我们初步估计在长白山脉我国境内区域分布的中华秋沙鸭繁殖种群数量大约为170对.在该项调查过程中,我们还探明了在长白山脉3个最主要的中华秋沙鸭繁殖栖息地.  相似文献   

15.
Abstract

A study was performed to investigate the effect of environmental temperature (18°C or 28°C) and increasing levels of pea fibre in the diet on digestive tract, visceral organ size, digestibility and energy metabolism in rats. Thirty-six male Wistar rats, initial liveweight (LW) 77-79 g, were allocated to six groups and housed at either 18°C (three groups) or 28°C (three groups). Three wheat starch, fish meal and pea fibre-based diets were prepared to contain 100, 200 and 300 g pea fibre kg?1 (68, 110 and 157 g dietary fibre kg?1 DM) and 160 g protein (N × 6.25) kg?1. One group of rats at each temperature was fed one of the diets for four balance periods. Gas-exchange measurements were made and urine and faeces were quantitatively collected. Food to gain ratio was higher (P <.05) at 18°C than at 28°C and increased (P <.05) as the level of fibre was increased. The weight of the visceral organs from rats housed at 18°C was higher (P<.05) than at 28°C. The empty weight of the small intestine, caecum and colon increased (P <.05) as the level of pea fibre was increased. The digestibility of DM, protein and dietary fibre (DF) was lower (P <.05) at 18°C than at 28°C. As the level of pea fibre was increased, the digestibilities of nutrients and energy decreased (P <.05). However, the digestibility of DF increased (P <.05) as the level of pea fibre was increased. The partial digested energy value for pea fibre was 11.9 kJ g?1. The metabolizable energy (ME) intake and heat production at 18°C (1128 and 974 kJ (W0.75 day)?1 respectively) were higher (P<.05) than at 28°C (831 and 674 kJ (W0.75 day)?1 respectively). As the level of pea fibre was increased, ME intake (W0.75 day)?1 and heat production (W0.75 day)?1 decreased (P <.05). Heat production as a percentage of ME was higher (P <.05) at 18°C than at 28°C: 86.6% and 81.2%, respectively. Heat production as a percentage of ME was higher (P <.05) for rats fed the 100 g pea fibre kg?1 diet than the 200 or 300 g pea fibre kg?1 diet. In conclusion, environmental temperature as well as DF influenced digestive tract and visceral organ size, digestion and protein and energy metabolism.  相似文献   

16.
1. The responses to genetic selection on yolk proportion as a technique for increasing egg dry matter content, an important criterion for the egg-product industry, was investigated in a pedigree flock of White Leghorn hens.

2. Parents were preselected on high and low yolk proportion from a base population. The absolute estimated breeding value for yolk proportion of both groups differed by 3%. The realised selection difference in dry matter content of eggs between groups was more than 1% in the analysed offspring population.

3. Heritability estimates were moderate and dry matter had a lower heritability (h2 = 0.39) than yolk proportion (h2 = 0.44).

4. The genetic correlation between yolk proportion and dry matter content was highly positive (rg = 0.91). Genetic correlations with egg weight were negative and would have to be compensated for in a breeding programme (rg = ?0.76 with yolk proportion and rg = ?0.64 with dry matter content). The genetic correlation between the laying performance and yolk proportion was rg = 0.28 and close to zero (rg = ?0.05) for dry matter content.

5. Easy recording and lower undesirable correlations make yolk proportion more suitable for commercial selection compared with egg dry matter content in layer breeding.  相似文献   

17.
The aim of this study was to determine the influence of the season of birth on the body weight, testicular size, testosterone concentrations, semen output and sexual behaviour in Saint Croix male lambs. Thirty‐three lambs were born in spring (n = 10), summer (Sum; n = 12) or autumn (n = 11). Body weight and the scrotal circumference were weekly recorded; semen was also weekly collected by electroejaculation; and sexual behaviour towards oestrous ewes was weekly evaluated. Data were recorded from 15 to 33 weeks of age. The reproductive development of Saint Croix male lambs differed according to the period in which they were born. More lambs born in spring than in summer and autumn achieved puberty during this study and were also more precocious in semen production and displayed sexual behaviour earlier. Lambs born in summer delayed their semen production; however, season‐related negative effects were less pronounced at the end of the study than in autumn born lambs born. In conclusion, despite the apparently low seasonality of the breed, Saint Croix male lambs showed in this study a seasonal pattern in their reproductive development at least until they achieve the puberty.  相似文献   

18.
Seasonal morphometric and physiological changes associated with vltellogenesis in the female agamid lizard, Agama atra are described. Vitellogenic activity during August - September marked the onset of the breeding season. It is suggested that at least two clutches were ovulated during the breeding season. Large abdominal fatbodles deposited prior to the winter months were possibly utilized to meet metabolic demands during winter and the onset of vitellogenesis during early spring (August - September). Follicular growth and fatbody deposition coincided with low plasma cholesterol levels. The liver index and total plasma proteins did not show a clear seasonal pattern. Of the seven plasma protein fractions, Fraction 2 (‘human beta-globulin’ mobility) increased during vltellogenesis while the foremost migrating proteins (‘human albumin’ mobility) showed a compensatory decrease. Total plasma calcium levels increased during vitellogenesis. The oviducts remained hypertrophied throughout the breeding season, while progesterone levels increased following each ovulation cycle in the presence of corpora lutea and remained elevated until oviposition. The onset of the second vitellogenic cycle (December) coincided with high progesterone levels.  相似文献   

19.
Complete rest or grazing deferment is a general recommendation to encourage vegetative recovery following fire in the western United States. However, effects of grazing deferments on animal performance have not been determined. Prescribed fires were individually applied to nine separate, 1.5-ha pastures each year (2006 and 2007) for a total of 18 pastures. Grazing was deferred until spring (16 May), early summer (19 June), or late summer (1 August) the growing season after fire. At the end of each deferment, a 70-d (2007) or 41-d (2008) grazing period was initiated. Stocking rates were consistent between treatments within year, but were adjusted between years to achieve the targeted residual biomass of approximately 300 kg · ha?1. Diet quality was assessed approximately every 15 d throughout each grazing period (three pastures · period?1) via collection of rumen extrusa throughout the 2-yr study. Ewe body weight was measured on and off-test for each grazing period. Diet extrusa samples for in vitro organic matter disappearance was less (P = 0.03) for late summer than early summer grazing periods and equal to the spring period (62.9, 64.6, and 61.0 ± 0.90%, respectively for spring, early summer, and late summer grazing periods). In vitro neutral detergent fiber disappearance decreased (P = 0.01) by 10.6 percentage units from early grazing to late grazing period in 2007, whereas no differences were observed in 2008. Ewe average daily gain did not differ between spring and early summer grazing periods and were greater (P = 0.03) than the negligible body weight gains of the late summer grazing period. Total gain was 10.9 kg · ha?1 greater in 2008, and a quadratic response was measured for grazing period in 2007. Results indicate that deferment until early summer may be preferable so that stocking rates can be more accurately determined and animal performance is not diminished.  相似文献   

20.
This study aims to characterize the reproductive patterns in Asinina de Miranda jennies during the non‐breeding season. Reproductive activity was surveyed in 12 females, aged between 3 and 18 years old, using ultrasound and teasing with a jack. The animals were monitored from September to April, six in each consecutive year. Of these 12 females, nine showed disruption to the normal pattern of ovarian activity during the non‐breeding season. Loss of normal cyclicity included anoestrus (41.7%), silent ovulatory oestrus (25%), and persistence of corpus luteum (8.3%). Only three females maintained a regular cyclic pattern with oestrous behaviour during the non‐breeding season. Anoestrus began in early November and lasted for an average of 147 ± 28 days (113–191 days), ending near to the spring equinox. Onset of silent oestrous cycles began more erratically, between October and February. In both groups the first behavioural ovulation of the year occurred around the time of the spring equinox. Disrupted reproductive activity was preceded by a shorter oestrous cycle only in females entering anoestrus. The mean follicle size in the first ovulation of the year was larger than in the reproductive season (44.7 ± 2.45 mm vs 39.2 ± 3.60 mm) in anoestrous jennies with protracted oestrus. Though age and body condition score (BCS) were associated, changes in BCS below a threshold of four points (for anoestrus) and five points (for silent oestrus) contributed greatly to disruption of reproductive cycles. BCS in females with regular oestrous cycles during the winter season remained unchanged or exceeded five points prior to the winter solstice.  相似文献   

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