Early Lambing Research Articles

Evaluation of the influence of melatonin implants during the gestation period in sheep from a selenium-deficient region

To evaluate the possible effect of melatonin implants on blood glutathione peroxidase (GSHPx) activity and in the prevention of selenium (Se)-responsive disorders in sheep from an Se-deficient region. Randomized controlled clinical trial. 100 Merino ewes. Ewes of the same age, parity, body weight, body condition, and reproductive and health history were randomly allotted to 1 of 2 groups (control and implanted) of 50 sheep each. Treatment consisted of implants of melatonin (18 g) administered SC in the pinna of the right ear 6 weeks prior to introduction of rams. The control group did not receive implants. Hematologic and serum biochemical analyses were performed at various points before and after treatment, in addition to determinations of erythrocyte mean corpuscular fragility (MCF) and blood GSHPx activity. The incidence of Se-responsive disorders in lambs was recorded in both groups. Hematologic and serum biochemical analyses yielded values within respective reference ranges for both groups. Significant differences between groups were evident in MCF at early mating (lower in the implanted group vs the control group) and in blood GSHPx activity at early mating, gestation, and early lambing (higher in the implanted group vs the control group). There were significantly fewer lambs with nutritional myodystrophy in the implanted versus the control group. Use of melatonin implants in sheep may improve reproductive performance and yield an earlier start of breeding season. The stimulating effect of melatonin on GSHPx activity may protect against oxidative damage during the first stage of gestation.

Genetische Parameter für Fruchtbarkeitsmerkmale bei Landschafrassen

Abstract. Title of the paper: Genetic parameters for reproduction traits in land sheep breeds The objective of the study was a genetic statistical analysis of reproduction traits from 13164 lambings in German Grey Heath, 2260 in German White Heath, 12961 in German Polled Heath, 11258 in Bentheim and 3088 in Coburg. Reproduction traits included early lambing (≤ 550 days), late lambing (>550 days), first lambing interval, second lambing interval and total number of lambs born. Three different linear animal models were used for analysing of these traits. The heritabilities ranged from h² = 0.43 to 0.45 for the trait early lambing, between h2 = 0.11 and 0.40 for the trait late lambing, between h2 = 0.05 and 0.24 for the first lambing interval, between h2 = 0.02 and 0.20 for the second lambing interval and between h2 = 0.06 and 0.07 for the total number of lambs born. There were high additive genetic correlations between the first three parity numbers. Because of this, the parity numbers were analysed together using a repeatability model. Additive genetic correlations between early or late lambing and first lambing interval, early lambing and late lambing interval as well as between first and second lambing interval were moderate and negative.

Analysis of associations between the prion protein genotype and reproduction traits in meat sheep breeds

AbstractThe objective of this study was to analyse the associations between ovine prion protein (PrP) genotypes and reproduction traits in three German meat sheep breeds. Reproduction traits were age at first early lambing, age at first late lambing, first lambing interval, second lambing interval and total number of lambs born. The data set included 595 genotyped German Texel sheep among 5225 recorded sheep, 351 genotyped German Black-Headed Mutton among 10 177 sheep and 282 genotyped Suffolk sheep among 2849 sheep. Linear animal models were employed for the analysis of the PrP-genotype effect. The PrP-genotype effect was analysed by comparing the most frequent PrP genotypes ARR/ARR, ARR/ARQ, and ARQ/ARQ. In a more general analysis three PrP genotype classes of animals with two, one or no copy of the ARR allele were compared.In most cases, no significant associations were found between the PrP genotypes and the reproduction traits investigated. Only for the traits age at first early lambing in German Texel and second lambing interval in German Black-Headed Mutton and Suffolk could a significant association with the PrP genotype be observed.

Relationship between ewe body condition at mating and reproductive performance in the fat-tailed Barbarine breed

The relationship between reproduction performance in early May and ewe body weight (BW), body (or tail) condition score, the week before the rams were introduced into the flock, are presented for the Tunisian fat-tailed Barbarine breed grazing natural ranges in central Tunisia. Dur- ing 2 contrasting years, 2 flocks (130 to 170 mature ewes each) differing by prolificacy (120%: Control and 160%: Prolific) and mature size (50 and 45 kg) were weighed and scored (according to 2 methods based on back fat thickness, BCS and on tail size, TCS), just before the introduction of rams. Rainfall during the pre-mating periods induced highly significant differences ( P < 0.01) in animal body condition. In both flocks, fertility was equal to 75% and 92-96% for groups of ewes whose pre- mating BW was respectively lower or higher than 35 kg. Similarly, the group composed by the 123 leanest ewes (less than 1.5 BCS) was significantly less fertile than the remainder of the flocks: 86% versus 91-95%. In both flocks, the higher the ewe BW, BCS or TCS at the beginning of the mat- ing period, the earlier the lambing date and the higher the litter size. The first and the last lambing ewes (first 2 weeks and third month) weighed over 50 kg and only 35-40 kg, respectively, when rams were introduced into the flock. According to BW, BCS or TCS classes, litter size varied from 1.0 to 1.3 and from 1.2 to 1.8, respectively, in the C and P flocks. Target BW, BCS and TCS at mating to obtain early lambing and adequate litter size in Barbarine flocks can be proposed. According to ewe size, the following values: 39 or 50 kg for BW, 2.1 or 3.0 for BCS and TCS, mean values of the group of ewes lambing during the second month, can be considered as minimal for the whole flock. A second method, taking into account the within-flock animal variability can be used. The percent- age of too emaciated ewes (less than 35 kg BW and back and/or tail condition score < 1.5) must be lower than 4 to 10% for BW, 6 to 8% for BCS and 10 to 15% for TCS. fat-tailed sheep / mating period / body condition / reproduction performances

Risk factors associated with postpartum deaths in early born, housed lambs in southwest England

The mortality of lambs was recorded in three early lambing, housed flocks in southwest England. Total mortality in the 2 year period ranged from 7.7 to 11.7%. The greatest risk of death occured during parturition and in the first week after birth (4.2–9.7%). Factors associated with death in this period have been described elsewhere. In lambs over 1 week old there were flock differences in the proportion of deaths and the diseases observed. The most frequent causes of death included focal abscessation (liver, lung, umbilicus, joint, spine), enteric and neural infections, anaemia and cerebrocortical necrosis (CCN). Diseases were observed to follow specific age patterns. Multiple logistic regression indicated that there was an increased odds of death postpartum as birth weight decreased, in male lambs compared with females, as litter size increased (with the exception of triplets) and as preweaning daily live weight gain decreased. The odds of dying were also associated with the flock of origin.

Problems and some solutions in the collection of data when investigating diseases of lambs in early lambing (housed) flocks

The problems encountered and some solutions found when collecting data for a survey of morbidity, mortality and finishing quality of early-born lambs are presented. Major problems included farm selection, farmer compliance, number of farms, accurate identification and detection of lambs, collection of morbidity data and handling of data prior to analysis. Farms were ascertained from a list of those contracted to provide lambs to a large abattoir in Devon. Farmer compliance was assisted by selecting farms where farmers appeared to be genuinely interested in the research. It was maintained by personal contact during farm visits and by holding meetings where preliminary results were presented. The number of farms used in the study (three) was decided upon from a combination of the number of suitable farms and the frequency and duration of each farm visit. Three designs of ear tag were used to identify lambs. The RD2000 was considered the most succesful in this project. Morbidity data were collected using two techniques; in the first year a randomly selected cohort of lambs in each flock was given a clinical examination every 7 or 14 days from birth to slaughter. In the second year lambs which farmers considered sick were presented for treatment. The former approach provided detailed information on approximately 12% of lambs in each flock and led primarily to the observation of sub-clinical diseases. There were five out of 72 (6.9%), six out of 73 (8.2%) and one out of 80 (1.3%) deaths postpartum in Cohorts A, B and C. The latter approach was less objective but monitored acute, severe disease; 15% (Flock A) and 29% (Flock B) of sick lambs died. A data capture device was used to record observations. It reduced the time required to load data onto microcomputer but was unreliable and was abandoned.

Descriptive epidemiology of listerial meningoencephalitis in housed lambs

During a prospective study of diseases of 4413 lambs in three housed early lambing (December and January) flocks, listerial meningoencephalitis was observed in dead lambs from two flocks (A and C) and was suspected in 1.1–1.3% (exact 95% confidence intervals (ECI), 0.3–6.7%) of live lambs from flock A. Listerial meningoencephalitis was confirmed at post-mortem in 0.5–1.6% of housed lambs which either died or were euthanased. Lambs were affected during a 2–4 week calendar period during February or March when 6–12 weeks of age. There was no age, breed or sex association with the condition. All lambs in the study were exposed to several possible risk factors but only a small proportion of lambs developed clinical signs of the disease. Previous reports of listerial meningoencephalitis in young lambs come from individual flock outbreaks or retrospective analysis of Veterinary Investigation Centre data, whereas these findings come from lambs under individual surveillance from birth to slaughter.

Effects of body size, population density, and maternal characteristics on age at first reproduction in bighorn ewes

The factors affecting variation in age at first reproduction of bighorn ewes (Ovis canadensis) were investigated in two marked populations in Alberta. One population was studied for 20 years, the other for 11 years. As yearlings, females that lactated at 2 years of age were on average heavier and larger, and had longer horns than females that did not lactate at 2 years. However, there was wide overlap in body mass between early and late producers, and increases in body mass over the threshold for reproduction had little effect on the probability of early lambing. The body mass of females at 4 months of age explained less than half of the variance in female body mass at 1 year or at 15 months. In one population, the proportion of 2-year-old ewes lactating was not correlated with density and declined after a pneumonia epizootic. In the other population, the proportion of 2-year-old ewes lactating was higher during an experimental reduction of density, and dropped to near zero as density increased. There was a significant interaction effect of body mass and population density upon the probability that a ewe would lactate at 2 years of age. Independently of body mass, yearlings were less likely to lactate at 2 years of age at high population density than at low density. The number and age distribution of rams did not affect the proportion of 2-year-old ewes lactating. The mothers of lactating 2-year-olds were not older or heavier than the mothers of ewes that did not lactate at 2 years. Although some of the variation in age at first reproduction was due to differences in mass and population density, much of it remained unexplained and could be due to genetic factors.

Mortality in early born, housed lambs in south-west England

During a 2 year study of diseases in lambs in three early lambing (housed) flocks a total of 428 of 4413 (9.7%) lambs died. All these lambs were examined at post mortem by one investigator who used a routine procedure. Results were stored on a database (dBase III Plus) and analysed using Epiinfo. The peak rate of death occured in lambs less than 1 week old. Over 50% of deaths took place in this period. A small proportion of lambs (approximately 10 out of 1000) died during the prenatal period. Fatalities included chlamydial and mycotic abortions, but in the majority of cases there was no specific abortive agent, lambs were either freshly dead or mummified. Partum deaths (23.3–45.1 per 1000) were categorised into those due to the lambing process, lambs born dead and congenital defects. The most frequent abnormality observed was subcapsular liver rupture (9.3–20.9 per 1000) with up to 60% of affected lambs also having signs of malpresentation (subcutaneous oedema of the neck). Early postpartum deaths (12.9–31.5 per 1000) were primarily associated with starvation.

Average Milk Yields and Environmental Effects on Latxa Sheep

Average quantitative milk yield and environmental effects have been estimated in 214 flocks of the Latxa breed of sheep under milk recording during 1988, 1989, and 1990. For this study, 57,725 lactations of the Black-Faced Latxa strain and 9564 of the Blond-Faced Latxa strain were used. Average yield per lactation (from d 31 after lambing to the end of lactation) was 93.9L for Black-Faced Latxa and 93.2L for Blond-Faced Latxa with lactation lengths of 114.3 and 126.7 d, respectively.Yields by age of ewes at lambing follows a quadratic curve; minimum yields occur at 1 yr of age, and maximum yields occur between 4 and 7 yr of age. Persistency between the first 2 test days decreases with age in Black-Faced Latxa. Within age at lambing, increase in the total number of lambings by ewes affects yield favorably. Lactations after early lambing (November and December) yield most. Yield estimated per lactation, as well as milk yielded at the first 2 test days, increases as the number of live lambs at lambing increases.The more relevant correlations between yield variables are those between the milk yield on a specific test day and the persistency between that test day and next. These correlations are always negative (between –.31 and –.37).

A comparison of the frequency of lambing on the reproductive performance of finn dorset ewes

One of the major factors affecting the efficiency and profitability of sheep production is the number of lambs reared per ewe. In 1991 lambs reared per ewe accounted for 14% of the difference in gross margin per hectare between top third and average lowland spring lambing flocks (MLC, 1992). The hypothesis was developed that in managing the prolific ewe three possible management systems could be employed; frequent lambing (FL), early annual lambing (EAL), or late annual lambing (LAL). The choice of these lambing systems was based on minimising the problems of the prolific ewe. Of these systems FL (lambing on an eight month cycle), provided the best opportuity for achieving high numbers of lambs sold per ewe.

Nitrogen fertiliser use in early lambing systems

Nitrogen fertiliser was applied in June 1990 to early-August lambing systems and production was compared with traditional September lambing. Nitrogen (30 kg N/ha) increased pasture growth rates by 3-4 kg DM/ha/day and increased production by 210 kg DM/ha during July-September inclusive, Nitrogen responses were greatest in southfacing paddocks; least on easy contoured paddocks; and did not differ between "resident" pastures and "improved" pastures that had been oversown with new pasture cultivars 5 years before. Compared with traditional September lambing, early-August lambing (plus N) resulted in20% fewer lambs at weaning; 2.4 kg heavier lamb weaning weights; similar ewe weaning weights; and similar bull live weights in January. While N applications to earlier lambing systems reduced the differences in ewe and bull weights previously recorded between the lambing date treatments, it was not a profitable strategy. Assessment of pasture response to N (30 kg N/ha) was repeated in 1991. Nitrogen increased production by 260 kg DM/ha and responses were similar for all paddock and pasture types. Keywords nitrogen fertiliser, early lambing, hill country

Seasonal cycles in testicular activity in Mouflon, Soay sheep and domesticated breeds of sheep: breeding seasons modified by domestication

The seasonal reproductive cycle in rams was monitored in Mouflon (wild-type), Soay (feral type) and a variety of domesticated breeds of sheep (Shetland, Blackface, Herdwick, Norfolk, Wiltshire, Portland and Merino) by measuring the changes in the diameter of the testes (first three years of life in all breeds) and the blood plasma concentrations of FSH and testosterone (first four to six years of life in Mouflon and Soay rams). In the Mouflon rams there was a pronounced seasonal cycle in all the reproductive parameters from one to six years of age. The plasma concentrations of FSH increased from June to September associated with redevelopment of the testes; maximum testicular size and plasma concentrations of testosterone occurred in October at the onset of the rut. In the Soay and domesticated breeds the seasonal maximum in testicular size occurred in late September or October except in two of the southern breeds (Portland and Merino) which showed an earlier peak to the sexual cycle in August. The change in size of the testes from the minimum to the maximum was less in the domesticated breeds (135–157%) compared to the Soay (171%) and Mouflon (160%). Crossbred rams produced by mating Soay ewes (highly seasonal breed) with Portland or Merino rams (less seasonal breed) had a seasonal testicular cycle intermediate in timing compared to the pattern characteristics of the parent breeds; this is consistent with the involvement of multiple genes in the mechanism controlling the sexual cycle in the ram. The earlier seasonal onset of full testicular activity in the southern breeds is assumed to be the result of selection for a prolongation of the breeding season for early lambing.

Use of an intraruminal soluble glass bolus containing melatonin for early lamb production.

The use of melatonin to advance the onset of seasonal oestrus is potentially useful for early lamb production. A number of delivery systems for melatonin have been developed and this study evaluates an intraruminal soluble glass bolus under field conditions. Anoestrous, non-lactating mule and Dorset cross mule ewes were treated in late June with two types of bolus of different solubilities (melatonin 1, 'slow release' and melatonin 2, 'extra slow release'). Rams were introduced in mid-August for a target lambing pattern in mid-January. The percentage pregnancy/lambing rates were 80/78, 97/92 and 100/100 in the control, melatonin 1 and melatonin 2 groups, respectively. The number of lambs born per ewe put to the ram was significantly increased by treatment with melatonin 2 (P less than 0.05) from 1.17 to 1.64 in the mule ewes and 1.64 to 1.72 in the Dorset cross mule ewes. The melatonin containing soluble glass bolus is a novel and convenient method of reducing the number of barren ewes in an early lambing flock.

Further report on hormonal inducing fertility in the anoestrous ewes

Further experiment of out-season of lamb production by PMS pretreated with progesterone was carried out with 23 ewes (two of them was lost by accidents) at the University Farm. Two groups of experimental consisted of PMS (Exp. I) and PMS followed with LH-rich gonadotrophin treatment (Exp. II). Four ewes with the same condition as to age and previous lambing results were allotted to one of the non-treated control (Cont. I). The other control (Cont. II) with another eight ewes untreated was also employed to refer the result obtained from the treatment. The reason of setting the non-treated control was due to the fact of a tendency of early lambing within the year. The mode and the name of hormones used were progesterone, Luteogen-Tomoda 12.5mg twice-daily for three days, followed 2 days intermission, and then PMS, Peamex-Tomoda 1, 000 i u. Exp. II was further administered with LH, rich gonadotrophin Synahorin-Teizo 200 Rb. u. on the next morning of PMS injection. During oestrus last from 2 to 4 days after about 48 hrs. of PMS treatment, ewes were properly served with two rams once a day. Before and after the treatment the ewes were put on the pasture. Taking pregancy period for 145±5 days, lambing date between 18 th and 28th November, was accounted for a positive. Results in lambing were as followed: Exp. I, 3/5, Exp. II, 2/4, Cont. I, 0/3, Cont. II, 0/5. Assuming no differences existed between I and II, experimental and control sum up to 5/9 and 0/8, respectively. So that it was again demonstrated the successive percentage of nearly a half. Negative cases proved fertility of ewes and some of them showed early lambing. As was reported in the previous report, oestrus was not so prominent that holding ewes by head for mating was needed, and was variable in its length. Since the authors had obtained some cases of failure in inducing ovulation (unpublished data, '59) LH-rich gonadotrophin was introduced to test the effectiveness in the lambing result, however, no advantage seemed to be expected so far as in the final result.Further studies aiming improvement in the result and producing Autmn lambs are on progress.