Annual Reproductive Rate Research Articles

Reproductive performance and productivity of Menz sheep in the Ethiopian highlands

Ewe lambs attain puberty at 10 months and 16.9 ± 0.1 kg (56% of mature weight) and first lamb at 15 months. Postpartum anoestrus is 76 days, lambing interval is 8.4 months and 65% of ewes lamb three times in 2 years with a gestation period of 149 days. Ewes cycle year-round but oestrus activity declines from June to September due to increased silent ovulations. Fertilisation rates are high (⩾90%) but lambing rate is 72%, suggesting moderate embryonic mortality. Conception rates to first, second and third oestrus postpartum are 78%, 18% and 4%, respectively. Litter size (prolificacy) is 1.12 but can be increased by 10–40% through premating ewe nutrition management or treatment with gonadotropins. Ewe oestrus activity can be synchronised by ram introduction after a period of isolation and with progesterone sponges or prostaglandin F 2α therapy. Lambs average 2.0 ± 0.1 kg at birth but preweaning mortality (15%) and slow growth, resulting in 8.6 kg weaning weight, still limit overall productivity index to 11.0 ± 0.87 kg per ewe per year, and the annual reproductive rate to 1.4 lambs per ewe. In the traditional management system, where most animals are raised, further studies are required into better nutrition and control of diseases (endoparasitism) in young animals to increase reproductive efficiency, flock productivity and number of animals for finishing and slaughter. This could serve as a model for interventions in other ruminants in the agroecological zone.

Reproduction in North Atlantic right whales (Eubalaena glacialis)

The reproductive biology of the western North Atlantic right whale population was assessed using photoidentification techniques. From 1980 to 1992, 145 calves were born to 65 identified cows. There was no detectable trend in the number of calves produced per year. Mean age at first parturition was 7.57 years. The reproductively active female pool was static at approximately 51 animals from 1987 to 1992. Gross annual reproductive rate, population growth rate, and mortality rate were estimated to be 4.5, 2.5, and 2.0%, respectively. The population size was estimated to be 295 individuals in 1992. Mean calving interval, based on 86 records, was 3.67 years, significantly longer than the South African right whale population but not different from the Argentine population. There was an indication that calving intervals may be increasing over time, though the trend was not quite statistically significant (P = 0.083). Potential causes for the reduced growth rate of this population are unknown but include anthropogenic mortality, inbreeding depression resulting in reduced fecundity, competition for food from other species, climatic changes affecting food availability, and sublethal effects of toxic contaminants.

Age-specific reproduction in female sea otters (Enhydra lutris) from south-central Alaska: analysis of reproductive tracts

We estimated age at sexual maturity and age-specific reproductive rates by examining carcasses and reproductive tracts from 177 female sea otters (Enhydra lutris). Carcasses were recovered from south-central Alaska, primarily from western Prince William Sound, as a result of the T/V Exxon Valdez oil spill in 1989. We found 65% of our sample to be sexually mature. Sexual maturity was first attained at age 2. The proportion of sexually mature animals increased from 30% at age 2 to 100% at age 5. Annual reproductive rates increased from 22% at age 2 to 78% at age 5 and remained relatively stable (75–88%) through to age 15. The sex ratio (♀:♂) of 49 fetal sea otters was 18:37 and differed significantly from parity. Females younger than 8 tended to produce more female fetuses, while older mothers did not. Our estimates of the reproductive characteristics of female sea otters obtained by examination of reproductive tracts were similar to those reported in the literature based on in situ observations of marked individuals.

Coexistence ofTetranychus urticae with different diapause capacities: a mathematical model

JapaneseTetranychus urticae is highly variable in diapause traits both among populations from different localities and host plants, as well as within populations. Many southern populations have almost lost their diapause capacity, and those from central Japan (34–37°N) are a mixture of diapausing (DP) and non-diapausing (ND) individuals. A simple mathematical model was constructed for analyzing the conditions under which the ND is more favourable than the DP in a system consisting of two different microhabitats: L, in which winter is lethal for the ND, and O, in which some of the ND can overwinter successfully. The model suggests that if winter mortality is not very high for the ND, and the annual reproductive rate of the ND is higher than that of the DP in microhabitat L, then a higher dispersal rate of the mites from L to O, and an equal number of patches of the two microhabitats will favour the ND more than the DP.

Effect of nutrition and endoparasitic treatment on growth, onset of puberty and reproductive activity in Menz ewe lambs

Ewe lambs of the Ethiopian Menz breed were assigned at weaning (90±3 days) to four levels of nutrition (poor, low, medium and high) to achieve different premating growth rates with or without treatment for endoparasites. A concentrate mixture providing 2.5 Mcal/kg dry matter (DM) metabolizable energy and 15.2 g/kg DM digestible protein was used. Improved nutrition increased lamb postweaning average daily weight gain up to puberty by 6 to 26 g/day and the conception rate to first estrus by 9 to 16% while it reduced the mortality rate by 24 to 31% and age at first lambing by 2 to 5 months. Lambs reached puberty (age at first estrus) at 16.9±0.1 kg (±SEM) or 60% of mature body weight and 350±12 days of age. The onset of puberty was advanced by weaning weight (P<0.05), itself being well correlated with birth weight (r = 0.51, P<0.001), and by level of nutrition (high=299±19, medium=301±18, low=383±23 and poor=454±31 days, P<0.001) through enhanced growth rate (r = −0.82, P<0.001). No independent effect of drenching for endoparasites on pubertal development was observed (P>0.05), but its interaction with season-of-birth improved the growth of lambs born during the period of short rains (P<0.05). Overall mean litter size at first lambing was 1.07; the twinning rate was 6.5% and the birth weight was 1.9±0.1 kg. Up to 13.4% of newborn lambs, averaging 1.3±0.6 kg, died on the day of parturition. The results indicate that improved growth rate and body weight, resulting from better postweaning nutrition, affects the attainment of puberty in Menz ewe lambs. Mitigation of nutrition stress and endoparasitic infection depending on season-of-birth would thus increase the annual reproductive rate of breeding ewes and flock productivity.

REPRODUCTION, SURVIVAL AND TAG LOSS IN CALIFORNIA SEA OTTERS

AbstractWe observed 40 California sea otters, Enhydra lutris, that were instrumented with implanted radio transmitters and flipper‐tagged, and obtained additional data on the reproduction of tagged female otters from the California Department of Fish and Game.The proportion of instrumented females accompanied by a pup peaked in the spring, with a secondary peak in the fall. Two methods of estimating the annual reproductive rate gave comparable values of 0.90 and 0.94. The average inter‐birth interval was 389 d. Two methods of estimating pup survival to weaning gave values of 0.46 and 0.58. Pups either remained with a female less than 80 or more than 120 d. Early mortality of dependent pups appears to be more frequent in California than in Prince William Sound, Alaska.Two methods of estimation indicated that adult females had the highest survival rates and adult males the lowest. Juvenile females had lower survival rates than adult females but juvenile males had higher survival rates than adult males. The survival rate of juvenile females was lower than that of juvenile males.The estimated annual loss rate for flipper‐tags, based on the instrumented individuals, was 0.26. More individuals lost two tags than would be expected by chance. It is unlikely that accurate estimates of sea otter survival rates can be derived from observations of tagged individuals.

Resumption of post-partum oestrous behaviour and associated plasma progesterone profiles in Menz ewes

ABSTRACTFifty Ethiopian Menz ewes maintained on pasture grazing with uncontrolled mating showed ovarian cyclicity at all times of the year. Conception rates to first, second and third service were 78, 18 and 4%, respectively. Mean post-partum anoestrous interval was 76·1 (s.e. 4·6) days. Two-thirds of ewes conceived before lamb weaning at 90 days and had 8 month lambing intervals. Twice weekly progesterone determinations showed that 67% of ewes exhibited a silent ovulation 66·4 (s.e. 10·5) days post partum, 12% of oestrous cycles were longer than 20 days and 8% of heats were false or anovulatory. It was concluded that Menz ewes have the natural potential for three lambings in 2 years, under adequate nutrition. Their better management and genetic improvement should further reduce current lambing intervals and increase annual reproductive rates.

Dynamics of a grizzly bear population during a period of industrial resource extraction. III. Natality and rate of increase

Reproductive parameters and rate of increase were estimated for a grizzly bear (Ursus arctos) population in southeastern British Columbia during a period of timber harvest and gas exploration, 1979–1987.I hypothesized that these activities would be detrimental to the population and predicted a negative rate of increase. There was an average of 2.26 cubs in 31 litters. The average of nine interbirth intervals was 2.67 years, and the average age at which five females produced their first litter was 6 years. The population's annual reproductive rate calculated by three methods averaged 0.86 cubs per adult female. By iteration of the Lotka equation, the best estimate of the exponential rate of increase was 0.081. Industrial activities did not appear to have a significant detrimental effect on the grizzly bear population in the Flathead Valley during the period of study but the roads built provided easy access for hunters and poachers.

Livestock production in central Mali: Reproductive components in traditionally-managed sheep and goats

Results of a 6 1 2 - year study into the main reproductive parameters of traditionally-managed sheep and goats in agro-pastoral rainfed millet and irrigated rice systems in a semi-arid area are presented. Least-squares mean litter sizes for sheep were 1.04 young per birth with a parturition interval of 256 days and an annual reproductive rate of 1.60. For goats, the figures were 1.16, 296 and 1.55, respectively. The annual reproductive rate could be improved by attempting to increase litter size, either through selection or by crossing to more prolific tropical breeds, rather than by reducing the parturition interval.

Effective period for control ofBandicota bengalensisin paddy fields

Abstract The reproductive biology and the population structure of Bandicota bengalensis was studied from a regular monthly collection, made in the Paddy fields around Bangalore, Karnataka from 1982 to 1984. The bandicoot exhibits a seasonal reproductive activity lasting from early August till the end of April with an anoestrous period between March and July. Correlatively, the reproductive glands and the sex accessories show seasonal changes in their weights. The peak reproductive activity was seen during September, October and November, when the prevalence of pregnancy was 0.81 with a mean litter size of 7.1. Analysis of data compared with temperature and rainfall showed that variation in breeding activity could be due to rainfall and the availability of food in the environment. The annual reproductive rate is calculated to be 67 young per female per breeding season. The bandicoots exhibit lesser body weights during summer months, and greater body weight coincides with the peak breeding season when the p...

Long-term reproductive patterns and sighting bias in Weddell seals (Leptonychotes weddelli)

The reproductive performance of tagged Weddell seals (Leptonychotes weddelli) was monitored at McMurdo Sound, Antarctica, from 1970 to 1984. An age-specific reproductive schedule revealed the major onset of pupping at age 6 years, and a mean age of first birth of 7.1 years. The average asymptotic pupping rate of 0.61 is reached by age 10. The cost of pupping in a given year is reflected in a 0.05 drop in the probability of pupping the following year. This cost is not evident in females over 7 years old, suggesting that postweaning condition affects newly mature females more than those that are fully mature. Annual adult reproductive rates ranged from 0.46 to 0.79, with a possible periodicity of 5 to 6 years. Simulations were conducted to determine the impact on reproductive estimates of sighting biases associated with seals having had at least one pup (Parous) or having pupped that season (With-Pup). Age at first reproduction as deduced from an age-specific pupping schedule is strongly affected by both forms of sighting bias, but bias in sighting Parous females was the more important. Estimates of adult reproduction were affected minimally. Comparisons of reproductive estimates with those of Weddell seals at Signy Island are discussed with regard to the effects of sighting biases.

Energy Use, Life Histories, and the Evaluation of Potential Competition in Two Species of Garter Snake

The energy flow in syntopic populations of the greater snakes Thamnophis radix and T. sirtalis in Ohio ranged from 74,676 to 144,041/kJ/ha/yr. Important factors affecting this quantity were the high densities of the snakes (114 to 212 snakes/ha), the high annual reproductive rate (approximately 15 to 19 young/female), and the high growth rates of the newborn snakes prior to their first hibernation period. This large intake of energy was channeled primarily into secondary productivity, with calculated tissue production/assimilation ratios (P/A) averaging 74% for new- born snakes prior to their first hibernation period and then dropping to a yearly average of 14% for the adults of both species. The factors that allow for high P/A values were the low metabolic rates, the circadian oscillations in metabolic rates, the winter period of low temperatures, voluntary hypothermia during the day, and generally low activity levels. The garter snakes' impact upon the food resources at the study site appeared to be minimal during the three years of this study. A 1 to 4 predator/prey biomass ratio was estimated to be sufficient for maintenance, growth, and reproduction. Since the calculated predator/prey ratios were much smaller than this value, interspecific exploitative competition for food resources is unlikely to be a major factor in the population dynamics of either species of garter snake at the site studied.

Life history of the bowhead whale, Balaena mysticetus (Mammalia: Cetacea)

This paper synthesizes data collected from bowhead whales (Balaena mysticetus) landed by Alaskan Eskimos between 1973 and 1982. From these data, and from the literature, length at birth has been estimated to be 4‐4.5 m, length at one year to be 8‐2 m, length at sexual maturity to be 14 m in females, and maximum length to be 20 m. Sexual activity, possibly mating, has been observed in March through May and the length of gestation is estimated to be 13 months. The calving period appears to extend from March through August, with the peak in births occurring in May. Lactation may extend for one year. Evidence has been provided for a pregnancy rate (percentage pregnant in mature female catch) of 015 and it has been suggested that calving occurs every three to six years. Gross annual reproductive rate (based on calf sightings) is estimated to be at least 3–6%. Sources of mortality are discussed. The sex ratio of animals taken by Eskimos is 0.83: 1.00 (females to males) and is not significantly different from unity.SummaryThe conclusions drawn in each of the preceding sections are likely to be re‐evaluated as more information becomes available. Still, it is suggested that the length at birth is 4–4.5 m, length at one year is 8.2 m, length at sexual maturity is 14 m in females, and the maximum attainable length is 20 m. Conception is most likely to occur in late winter while the whales congregate in Bering Sea polynyas, whereas the peak in calving appears to occur in May. Consequently, it has been hypothesized that the gestation time is greater than one year, but less than two. By analogy with other right whales and sparse data collected, the duration of lactation is assumed to be one year, although this is arguable. The pregnancy rate of mature females, calculated from ovarian data, is 0.15, projecting a calving interval of approximately seven years. The gross annual reproductive rate generated from field data is 3.6–12.4%. The sex ratio of the harvested animals is 0.83: 1.0, and it is assumed that this does not reflect the whole population. Whatever changes are yet to be made in the understanding of the bow‐head life history, all of the traits delineated are consistent with those predicted for slowly reproducing animals, the quintessential K‐strategist.We are most grateful to the scores of field biologists who have helped us count whales and sample those landed by the Eskimos, and who have contributed ideas and enthusiasm. In addition, we thank R. Tarpley for information on ovaries collected in 1982, J. Breiwick for running several sex ratio estimates, and H. Marsh for her generous assistance with the ovarian histology. Under contract to us R. Davis and W. Koski of L.G.L., environmental research associates, provided the photogrammetric measurements. An earlier, less complete version of our paper was submitted in 1982 as an unpublished report (document SC/34/PS1) to the International Whaling Commission, resulting in many valuable comments from members of the Scientific Committee. P. Best, D. Chapman, and an anonymous reviewer substantially improved the manuscript. Finally, we thank the people of Barrow, Point Hope, Wainwright, Gambell, Savoonga, and Kaktovik for their patience and assistance. Without their support this research would not have been possible.

Aspects of reproduction in goats and sheep in south-central Kenya

ABSTRACTAge at first parturition in this environment occurs at approximately 18 months. The biggest cause of variation is flock with neither species nor any other source being significant. Parturition intervals for both species are approximatley 10·5 months: flock and season are significant on this variable and there is a decreasing, although non-significant, interval with advancing age. Litter size in goats is 1·25 and in sheep is 1·04, with parity and flock having significant effects for both species, while season also has an effect on goats. Annual reproduction rate is 1·42 kids and 1·19 lambs per breeding female per year.

Breeding by Peromyscus in seasonal environments

Reproductive characteristics of Peromyscus maniculatus in Manitoba and Peromyscus leucopus in Ontario were compared in order to determine the extent to which breeding compensates for relatively short breeding seasons. Peromyscus maniculatus had a shorter breeding season than P. leucopus, but frequency of litters, litter size, and age of females at sexual maturity were the same for both species. A comparison of breeding characteristics among Peromyscus from different geographic areas indicated that basic reproductive characteristics do not vary in relation to length of the breeding season.In general, we have no evidence that the basic reproductive characteristics of Peromyscus vary in relation to length of the breeding season. Peromyscus with short breeding seasons, on average, must have a lower annual reproductive rate than Peromyscus with long breeding seasons.

Snowshoe hare populations in woodlot habitat

Snowshoe hare (Lepus americanus) population dynamics were monitored on six woodlots totaling 33 ha in an agricultural area near Westlock, Alberta, from May 1970 to May 1974. Numerical trends in woodlot and nearby forest hare populations at Rochester were similar, but densities were consistently lower in woodlot habitat until the final stages of a general population decline. Annual reproductive rates were greater in woodlot populations in 1971 (11.2 vs. 9.1 young per adult female) and 1973(11.1 vs. 7.4); and similar to forest populations in 1970 and 1972. Consistently low rates of 1st-year survival (4 to 7%) in woodlot hare populations resulted in lower annual population growth rates and hence lower population densities. Browsing-intensity surveys indicated that both forest and woodlot hare populations encountered overwinter food shortages. In addition, woodlot hare populations may have suffered higher rates of predation.

Annual reproductive rhythm and ovulation rate in four fat-tailed sheep breeds

ABSTRACTKarakul, Mehraban, Naeini and Bakhtiari sheep were checked twice a day for oestrus using aproned rams and were laparotomized within 5 to 16 h of the end of every second oestrous period. Oestrus was observed for 12 monthly periods commencing on 21 April.The Mehraban breed with 1 -6 oestrous periods per month was less seasonal in its breeding activity (P&lt;0·01) than the other breeds. Four-year-old ewes were more sexually active (P&lt;0·01) than 3-year-old ewes (1·48 v. 1·28 oestrous periods per month). Seasonal variation in the sexual activity of the ewes was observed (P&lt;001); the peak of activity in July to January was followed by a steady decline in February and March to a low in April and May, and then a steep recovery phase in June. There was only limited sexual activity for at least 4 months (March to June).The overall mean cycle length was 17·8 days (14 to 23 days), and the means for the four breeds were 17·6, 17·8, 17·8 and 17·9. The oestrous cycle was longer (P&lt;0·05) during the period from December t o February than during that from June to August.The overall mean duration of the oestrous period was 36·9 h and the means for the four breeds were 35·2, 38·0, 37·4 and 37·1 h, respectively (P&lt;0·05). The duration showed some monthly variation (P&lt;0·01) but did not follow a special seasonal pattern. The ovulation rates for the four breeds were 1·07, 1·13,0·94 and 0·95 respectively, (P&lt;0·01). There was a non-significant decline in the mean ovulation rate from March to June. Right ovaries were more active than left ovaries as judged by the observation of a higher average number of corpora lutea per ewe per laparotomy (0·58 v. 0·43, P&lt;001).

Population Ecology of Alberta Red Squirrels

Temporal changes and spatial differences in population structure and density of red squirrels (Tamiasciurus hudsonicus) were investigated in 3 habitats near Rochester, Alberta. Between 1966 and 1969, red squirrels were more abundant in spruce (Picea mariana and Picea alba) stands (161—684/100 ha), less abundant in jack pine (Pinus banksiana) stands (86—264/100 ha), and least abundant in aspen (Populus tremuloides) woods (0—99/100 ha). Summer populations fluctuated between 67 (1966) and 151 (1968) per 100 ha of mixed habitat, but spring populations were more stationary (32—49/100 ha of mixed habitat). Ovulation rates of adult and yearling squirrels and the percentage of yearling ♀ ♀ which bred varied annually. Variation in annual reproductive rate (2.4—4.4 young/♀) was correlated with the date of onset of breeding, and the number of days of snow cover subsequent to 1 January. Juvenile sex ratios were 1:1 but there was a trend toward preponderance of ♂ ♂ in older age classes. Although sex ratios on the study areas were close to 1:1 during early summer, late—summer mortality of adult ♀ ♀ resulted in a preponderance of ♂ ♂ (60%) during the remainder of the year. Equality of sex ratio was restored during the breeding season when ♂ ♂ experienced high mortality rates. After fall dispersal, the percentage of adults was higher in the spruce (78—85%) than in pine (30—50%) but virtually 100% of the squirrels occupying aspen habitat were juveniles. Changes in age ratios suggested that juveniles suffered higher overwinter losses than did adults. Spring age ratios were not related to fall age ratios because of differential annual survival of juvenile squirrels. Dispersal movements occurred in spring and fall; squirrels were relatively sedentary the remainder of the year. The spring shuffle involved breeding ♂ ♂ visiting territories of ♀ ♀ and redistribution of squirrels from deciduous and pine forest into spruce forest. Almost all fall dispersants were young of the year. High adult densities in spruce stands prompted emigration of most juveniles from these areas. Fewer juveniles emigrated from jack pine where adult densities were lower and territories were available. Juveniles apparently dispersed into the large tracts of aspen—dominated deciduous forest. Survival of squirrels varied seasonally and annually, among habitats and between sex and age cohorts. Heavy mortality of adult ♀ ♀ and nestlings occurred between parturition and weaning (July—September). The overwinter period (October—February) was one of high juvenile losses. During the 3—mo breeding season (March—May), ♂ ♂ experienced higher mortality rates than ♀ ♀. Annual survival was highest in the spruce and lowest in the aspen. Survival rates were highest during 1966—1967, °30% lower in 1967—1968, and °44% lower in 1968—1969. Survival of juveniles was lower in all years than survival of adults. In the wild an average of 639 meristematic buds, and the seeds from 35 pine cones were consumed by a single squirrel each day. Captive feeding trials indicated that an average of 176 black spruce cones or 123 white spruce cones per day were necessary to sustain 1 squirrel when offered no supplementary foods. Territorial boundaries in spruce and pine did not change detectably between 1966 and 1969. Within monotypic habitats, territories were similar in size. Territories in white spruce were smallest (x = 0.24 ha), those in mixed spruce larger (x = 0.35 ha), and those in jack pine much larger (x = 0.66 ha). Territory size may be related to cone supply in poor mast years. In 1967, a year of poor cone mast, sufficient numbers of cones were produced per territory to provide one—half of the annual energy requirement of 1 squirrel. The stability of spring populations, despite the change in mast crop from very poor (1966 and 1967) to medium—heavy (1968), implies regulation of squirrel densities at levels which preclude critical food shortage. We hypothesize that territorial behavior is the mechanism which regulates densities about a mean determined by food supply in years of poor cone mast, and that it operates through density—dependent mortality by excluding nonterritorial squirrels from winter cone supplies. Similarities in red squirrel densities (or territory sizes) in similar forest types recorded by numerous authors in different areas and different years imply consistency of territory size within particular habitats. We believe that variation in numbers of squirrels harvested primarily reflects variation in annual production.

Reproduction, Growth and Development, and Juvenile Mortality in the Hawaiian Monk Seal

Data on reproduction were collected during a tagging and census-ing study at Kure Atoll in the Leeward Hawaiians. Fifty-three known-age seals were tagged in 1964 and 1965, and observations on growth and development were made on 47 individuals. The annual reproductive rate at Kure was 15 live pups per 100 adults. About 19% of the adult females bred in successive years, and only 56% of the adult females had pups in either of the two seasons. Pups are usually born in March, April, or May. Pups spend about 5 weeks ashore before disappearing from the island. This period is devoted to slight growth in total length and deposition of large amounts of fat. Females remain with the pups during this 5-week period, and nursing is believed to end with departure of the pup. Sharks and adult seals contribute to juvenile mortality.

OBSERVATIONS ON SOME KENYA EAGLES

OBSERVATIONS ON SOME KENYA EAGLES