Effects of restricted feeding of prepubertal ewe lambs on reproduction and lactation performances over two breeding seasons

The aim of this study was to determine the effects of restricted feeding before puberty on reproduction, lactation and offspring growth performance in replacement ewe lambs over two breeding seasons. At weaning, 41 Dorset ewe lambs were assigned to one of three diets: an ad libitum control diet with medium-quality forage (MQF; 13.3% crude protein (CP), 1.81 Mcal metabolizable energy per kg, 42.8% ADF; diet A-MQF); a restricted diet with the same forage as A but less feed concentrate (diet R-MQF); or a high-quality forage (HQF) diet (14.8% CP, 2.15 Mcal ME/kg, 34.7% ADF; diet F-HQF). The quantity of concentrate offered to the group R-MQF and F-HQF ewe lambs was adjusted to obtain 70% of the control ewe lambs' growth rate. The diets were offered for 75 days following weaning to cover the allometric phase of mammary gland development. Prepubertal restriction did not affect (P > 0.10) the gestation rate, number of lambs born or the body weight and body condition score of ewes at lambing or at the end of lactation. Ewes from groups R-MQF and F-HQF tended to produce more milk during their first lactation compared to those from group A-MQF (P = 0.07). During the second lactation, groups R-MQF and F-HQF had better standardized milk production than group A-MQF (P < 0.05), and group R-MQF produced more milk than group F-HQF (P < 0.05). Milk fat and protein content were not affected by treatments (P > 0.10) Fat and protein yield were affected by treatments only at the second lactation (P < 0.10 and P < 0.05, respectively). Lamb birth and weaning weights were not affected by prepubertal restriction of feeding in their mother (P > 0.10). However, the average daily gain of second breeding season lambs was higher for the R-MQF group than the F-HQF group (P < 0.05), and a similar trend was observed for total gain (P < 0.10). Restricted feeding before puberty does not impair future reproductive performance; however, it has a positive impact on lactation and on lambs' growth performance.     

Effects of rapid weight gain to puberty on reproduction, mammary development and lactation in ewe lambs

The effects of rapid weight gain to puberty on reproduction, mammary development and milk production in ewes lambing at 13 mo of age were investigated on three trials. A total of 64 Dorset and 93 Suffolk ewe lambs were weaned at 42 d of age and their mean weight was 16 kg. These ewes were assigned, within breed groups, to either a finishing diet or a growing diet. Onset of puberty was determined by daily checks for estrus and ewes were bred beginning at 7 mo of age. In Trial 2, mammary gland development was determined in eight Suffolk ewes from each diet. Ewes on the finishing diet were younger at puberty than those on the growing diet (199 vs 206 d, P<0.05) but required more services per conception (1.3 vs 1.1, P<0.05). Dietary conception rate and lambing rate means were similar. Mean 4-h milk yield was lower (P<0.10) for ewes on the finishing diet (283 g) than for those on the growing diet (310 g). Mammary gland fat pad area was higher (P<0.05) for ewes on the finishing diet compared with those fed for growth. Gross and adjusted duct areas were higher in ewes on the growing diet, but differences were not significant. At puberty, negative correlation coefficients for milk yield with performance traits were as follows: daily weight gain, -0.184 (P<0.08); weight-to-height ratio -0.262 (P<0.01); body condition score, -0.189 (P<0.07); and body weight, -0.212 (P<0.05). Results of this study indicate that rapid weight gain to puberty impairs mammary gland development and milk production in ewe lambs.     

Dietary protein or energy restriction influences age and weight at puberty in ewe lambs

The working hypothesis was that restricted protein content in diets of prepubertal ewe lambs would delay time of onset of puberty to a greater extent than restricted energy content. Restriction of dietary protein (metabolizable protein, MP) or energy (ME) intake on age and weight at puberty was studied in ewe lambs in two experiments. In Experiment 1, 85 crossbred ewe lambs were assigned by weight to one of five dietary treatment groups: control (CTL; 18 mg ME day⁻¹ and 173 g MP day⁻¹); energy restricted (ER; 10.2 mg ME day⁻¹ and 96 g MP day⁻¹); protein restricted (PR; 11 mg ME day⁻¹ and 66 g MP day⁻¹); ER for 9 weeks then switched to CTL (ER/CTL); PR for 9 weeks then switched to CTL (PR/CTL). Ewe lambs were weighed biweekly, bled weekly, and serum was assayed for progesterone to determine time of puberty. Average age at puberty differed among lambs fed the various diets (P < 0.01). Ewe lambs in the CTL group were younger and weighed more at puberty. Lambs fed diets restricted in protein or energy content were similar in age at puberty. Dietary switching, ER/CTL and PR/CTL, affected body weight and gain (P < 0.05), but did not result in changed age at puberty compared with lambs fed ER or PR diets. In Experiment 2, two breed types (maternal type and meat type) were used to compare responses of dietary protein restriction to dietary energy restriction. In Experiment 2, lambs (n = 60) were assigned to either the CTL, PR or ER diets. Lambs in the CTL group gained more weight than lambs fed the PR diet and lambs fed the PR diet gained more weight than lambs fed the ER diet (P < 0.05). Diet affected age (P < 0.001), but not weight at puberty (P = 0.13). Dietary energy and protein restriction influenced age at puberty in ewe lambs with energy restriction having a greater influence on delaying onset of puberty than protein restriction. Realimentation did not overcome effects of previous feed restriction by inducing an earlier age at puberty than ewe lambs fed the ER or PR diet throughout the experimental period. Body weight gain prepuberty is more important than type of dietary restriction (protein or energy) with regard to impacting age at puberty. We, therefore, reject the working hypothesis that dietary protein restriction prepuberty would have a greater impact in delaying onset of puberty than dietary energy restriction.     

Gastro-intestinal nematode parasite populations in ewes and lambs and the origin and time course of infective larval availability in pastures

Changes in the numbers of infective larvae available on pasture and the development of helminth infection in spring-born lambs were studied in an environment with a mild winter and where pastures are grazed throughout the year. Prior contamination of pastures in autumn and early winter was compared with egg deposition by lambing ewes as sources of infection. Larvae derived from eggs deposited by lambing ewes did not appear on pasture until 8 weeks after the beginning of lambing but were present in increasing numbers for the last 7 weeks before weaning at 11–15 weeks of age. Lambs exposed to prior contamination became infected earlier than those exposed only to ewe contamination, but lamb egg output made no contribution to larval numbers on pasture before weaning. Lamb growth rates to weaning did not differ between groups exposed either to prior contamination alone, to ewe egg output alone or to both, but all groups carried appreciable infections at weaning. After weaning, lambs remained on the same pastures, and those exposed to ewe contamination suffered severe trichostrongylosis 5 weeks after weaning. Lambs exposed only to over-wintered contamination also developed severe trichostrongylosis 9 weeks after weaning. The results are compared with those of similar recent studies in Britain and their implications for control of infection are discussed.     

Pinealectomy delays puberty in ewe lambs

Fifteen pinealectomized and 15 unoperated ewes were exposed to constant light for 3 weeks before and 10 weeks after lambing. Fourteen pinealectomized and 15 unoperated ewes were allowed to lamb outdoors. Five ewe lambs born in constant light to the 2 groups of dams were pinealectomized at 10 weeks of age. Ewes and lambs were then returned to the field. Puberty (determined by weekly progesterone analysis) was significantly delayed (P less than 0.05) in the pinealectomized ewe lambs. Median pubertal age in pineal-intact ewe lambs was 37 weeks compared to 49 weeks in pinealectomized lambs. Constant light during the first 10 weeks of life had no effect upon puberty onset nor did the pineal status of the dam. Control lambs entered seasonal anoestrus at the time pinealectomized ewe lambs were entering puberty. Pinealectomized lambs entered anoestrus at the same time as control lambs were beginning their second breeding season. These results confirm a key role of pineal-mediated hormonal signals in the control of puberty in the sheep.     

Serum luteinizing hormone, growth hormone and insulin-like growth factor-I after releasing hormone challenge in prepubertal ewe lambs selected for twinning

Two studies evaluated hormonal markers as indicators of the onset of puberty in Debouillet sheep selected for twinning. In Trial 1, 29 ewe lambs (50 +/- 0.5 kg, 159 to 187 d of age) were given 10 microg GnRH (i.v.) on September 15 and blood was collected at 30 min intervals after the injection for 2 h. Additional samples were taken twice weekly and progesterone (P4) was measured. The day that serum P4 was greater than 1 ng/mL for 2 consecutive sampling days was classified as the day of puberty. Average day of puberty was October 12 (average age at puberty was 199 d) and ewes with values less or greater than the average were classified as early or late, respectively. Average weight at GnRH challenge was 50 kg and ewes weighing less or more were classified as light or heavy, respectively. Early ewes weighed more (P = 0.01) and reached puberty sooner (P = 0.01) than late ewes. Heavy lambs reached puberty earlier, weighed more at GnRH challenge, and had more LH area under the curve (AUC, P < 0.05) than light ewes. In Trial 2, we gave 27 ewe lambs (54 +/- 0.9 kg, 173 to 189 d of age) a single i.v. injection of 10 microg GnRH and 10 microg GHRH on September 17. Average day of puberty was October 13, average weight was 54 kg, and average age at puberty was 208 d. Categories were designated as described for Trial 1. Early lambs reached puberty sooner (P = 0.01) and weighed more (P = 0.01) than late lambs, but the puberty groups had similar LH AUC (P = 0.64) and GH AUC (P = 0.75), whereas IGF-I was greater (P = 0.01) in early puberty ewes than in late puberty ewes. Heavy lambs reached puberty earlier (P = 0.06), weighed more (P = 0.01), and tended (P = 0.11) to have more GH AUC than light ewes. No difference was observed in LH AUC or IGF-I between weight groups (P > 0.15). Results suggest that serum LH after GnRH is not a reliable indicator of the onset of puberty in ewe lambs selected for twinning, but heavier ewes tended to produce more GH after a GHRH challenge and reach puberty earlier than lighter ewe lambs.     

Growth response, reproductive activity, and serum growth hormone in fine-wool ewe lambs treated with triiodothyronine

Forty-four 6-mo-old, fine-wool ewe lambs were randomly allotted to one of three triiodothyronine (T(3)) treatment groups (14 or 15 ewe lambs/group). Treatments (0, 200, and 400 mug T(3)) were administered daily by subcutaneous injection during a 30-d treatment period in September. Following the treatments, ewe lambs were allowed to mate with Debouillet rams during a 34-d breeding season. Animal weights did not differ (P > 0.10) among treatment groups throughout the study. However, ewe lambs receiving 400 mug T(3)/d gained less (P < 0.05) during the treatment period than did those receiving 200 mug T(3)/d or controls. Grease fleece weights (6-mo clip) were similar (P > 0.10) among treatment groups. Serum growth hormone (GH) values in blood samples collected on Days 7 and 28 of the 30-d treatment were similar (P > 0.10) before treatments were administered and on Day 7 after treatments were administered. However, on Day 28 after treatments were administered, serum GH was lower (P < 0.01) in ewe lambs receiving 400 mug T(3)/d (1.5 ng/ml) than in those receiving 200 mug/d (2.1 ng/ml) or controls (2.2 ng/ml). Ovarian cyclicity was determined by monitoring serum progesterone. Forty percent of control ewe lambs were determined to have cycled during treatment compared with 20% of those receiving 200 mug T(3)/day and none of those receiving 400 mug T(3)/d (P < 0.10). Pregnancy rates were lower (P < 0.10) in ewe lambs receiving 400 mug T(3)/d (29%) compared with those receiving 200 mug T(3)/d (60%) or controls (66.7%). Day of conception, lambs born/ewe exposed, lambs born/ewe lambing, and lambs weaned/ewe lambing did not differ (P > 0.10) among treatments. Preweaning performance of offspring was not altered by maternal treatment with 200 or 400 mug T(3)/d (P > 0.10). These data indicate that 200 and 400 mug T(3)/d will not enhance GH production or improve reproductive performance of ewe lambs.     

Effects of dietary sewage solids on second-generation ewes fed an experimental diet from weaning through two reproductive cycles

Eighteen fine-wool ewe lambs produced by mature, conventionally fed dams and 21 similar offspring from sewage-fed ewes were randomly allotted at weaning to one of two groups. Half of the lambs from each maternal diet group received a conventional (18% protein) diet during the growing phase while the remainder was fed the conventional diet plus 7% undigested, irradiated sewage solids (18% protein). At the end of the 147-day growing period and just before a fall breeding season, conventionally fed ewe lambs were switched to a control diet (12% protein) suitable for mature ewes and sewage-fed ewe lambs began receiving the control diet plus 7% sewage solids. Animals received these diets for two years. Maternal sewage consumption did not influence performance of F₁ ewe lambs. By the beginning of the first breeding season, controls were heavier (P<0.01) than were animals receiving sewage solids (51.7 and 44.5 kg, respectively). Similarly, only 75% of sewage-fed ewe lambs exhibited estrus during their first breeding season compared with 94.7% of controls (P<0.10). Conception rate (40.0 and 84.2%, respectively) and lambs born per ewe exposed (0.4 and 0.89, respectively) were also lower (P<0.05) in animals receiving sewage solids than in controls. During the second reproductive cycle, conception rate as well as lambs born per ewe exposed was comparable (P>0.10) between the two groups. Offspring from the sewage-fed ewe lambs, however, weighed less (P<0.05) at weaning than did lambs produced by control animals. Results indicate that a diet containing 7% sewage solids may not be suitable for preparing ewe lambs to go into the breeding flock; once mature size is attained, however, reproductive performance is not hampered by sewage feeding.     

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.     

Sexual maturation of ewes raised without ram exposure in a controlled lighting environment

Finn x Dorset ewe lambs (n = 70) born in the spring (March 28 to April 6) from two successive lambing seasons were evaluated for age at first ovulation in the absence of mature rams. Ewe lambs were born in a controlled, short light (8L:16D) photoperiod or in ambient light (13L:11D). At about 10 to 11 wk of age, ewe lambs were allocated to a short (8L:16D) or long (16L:8D) light environment. Plasma progesterone (P(4)) concentrations were measured as an index of first ovulation. First exposure of ewes to sexually mature rams was in November. Most ewe lambs (77%) ovulated before ram exposure. More lambs (P < 0.025) born in ambient light and raised in short light reached puberty with typical cycles of plasma progesterone compared to other treatments. Long days tended to retard the onset of puberty. Although pregnancy rate did not differ across light treatments, more ewes became pregnant from the ambient-light born and short-light raised treatment. Photoperiod is an important factor affecting the onset of sexual maturation and genesis of normal luteal progesterone secretion in the ewe lamb.     

Low pasture allowance until late gestation in ewes: behavioural and physiological changes in ewes and lambs from lambing to weaning

Low pasture allowance during gestation affects ewes’ BW at parturition, the bond with their lamb, lamb development, and thus also may affect their responses to weaning. The objectives were to determine if native pasture allowance from before conception until late pregnancy affects ewe–lamb behaviours at lambing, ewes’ milk yield, lambs’ BW, and the behavioural and physiological changes of ewes and lambs at weaning. From 23 days before conception until 122 days of pregnancy, 24 ewes grazed on two different native pasture allowances: high (10 to 12 kg of dry matter (DM)/100 kg of BW per day; HPA treatment; n=12) or low (5 to 8 kg of DM/100 kg of BW per day; LPA treatment; n=12). Thereafter, all ewes grazed on Festuca arundinacea and received rice bran and crude glycerine. Ewes’ body condition score (BCS) and BW were recorded during pregnancy and postpartum periods. Milk yield was determined on days 32, 41 and 54 after lambing. Lambs’ BW was recorded from birth until 72 days after lambing. Latency from parturition until the ewe licked her lamb, maternal behaviour score (a test that evaluates maternal attachment to the lamb) and latency for lamb to stand up and suckle were determined. The behaviour of the lambs and ewes was recorded before and after weaning (at 65 days). The ewes’ serum total protein, albumin and globulin concentrations were measured before and after weaning. The HPA ewes presented greater BW (P<0.005) and BCS (P<0.005) than the LPA ewes during pregnancy and postpartum (P<0.04), and had a greater milk yield than the LPA ewes (P<0.03). Treatments did not influence any behaviour at lambing, lambs’ BW, neither the ewes’ behavioural and physiological changes at weaning. HPA lambs paced and vocalized more than LPA lambs (P<0.0001). The variation of albumin concentration before and after weaning was greater in the HPA lambs than in the LPA lambs (P<0.0001). In conclusion, although ewes’ BW, BCS and milk production were affected by pasture allowance until late pregnancy, this did not affect the behaviours that lead to the establishment of the mother–young bond, nor the ewes’ behavioural responses at weaning. Lambs reared by ewes that grazed on low pasture allowance during pregnancy presented fewer behavioural changes and a lower decrease of albumin concentration after weaning. Lambs’ BW was not affected by the feeding received by their mothers.     

Growth response, endocrine profiles and reproductive performance of fine-wool ewe lambs treated with ovine prolactin before breeding

Twenty-four 6-mo-old ewe lambs received one of two ovine prolactin (oPRL) treatments 28 d before fall breeding. Beginning on the first day of treatment (Day 0), 12 lambs received a subcutaneous injection (12 ml) of a carrier vehicle (0 mg oPRL) on alternate days for 28 d while 12 lambs received injections containing 5 mg oPRL. On Days 0 and 28, jugular blood was collected from six lambs in each group before treatment and at 30-min intervals for 6 h thereafter. Neither feed intake, efficiency of gain nor animal weights differed (P > 0.20) between groups. One hour after treatment on Day 0, ewe lambs receiving 5 mg oPRL had greater (P < 0.10) serum PRL levels than did controls (121.9 and 61.5 +/- 24.7 ng/ml, respectively). Differences in serum PRL persisted throughout remaining sampling intervals on both Days 0 and 28. Serum samples obtained on alternate days during the 28-d treatment period revealed no differences (P > 0.20) in PRL concentrations between control (48.3 +/- 5.3 ng/ml) and oPRL-treated (55.7 +/- 5.3 ng/ml) ewes. Neither serum insulin nor growth hormone responded (P > 0.05) to exogenous oPRL on either Day 0 or 28. No difference (P > 0.30) in percentage of ewe lambs cycling during treatment or breeding was detected between groups. Subsequent lambing percentages were similar (P > 0.30), with 36.4% of control and 25.0% of oPRL-treated ewes producing offspring. Administering 5 mg oPRL on alternate days for 28 d before breeding did not enhance growth and(or) reproductive performance in virgin ewe lambs.     

Birthdate and survival in bighorn lambs (Ovis canadensis)

The relationship between parturition date and lamb survival was investigated among individually marked bighorn ewes in south-western Alberta, Canada. Lambs were born from 17 May to 21 July. Most births occurred in the first two weeks of the lambing period. Lambs born in May enjoyed greater survival than lambs born in June and July. The viability of lambs born after 10 June was extremely low. Inadequate nutrition is suggested as the cause of greater mortality of lateborn lambs. Ewes that give birth late are at an earlier stage of lactation when forage quality declines and may not produce sufficient milk to ensure lamb survival. Their lambs have access to high-quality forage for a shortened period. The proportion of late lambs appeared to be correlated with ewe density in the winter range.     

Risk factors associated with lambing traits

The objective of this study was to establish the risk factors associated with both lambing difficulty and lamb mortality in the Irish sheep multibreed population. A total of 135 470 lambing events from 42 675 ewes in 839 Irish crossbred and purebred flocks were available. Risk factors associated with producer-scored ewe lambing difficulty score (scale of one (no difficulty) to four (severe difficulty)) were determined using linear mixed models. Risk factors associated with the logit of the probability of lamb mortality at birth (i.e. binary trait) were determined using generalised estimating equations. For each dependent variable, a series of simple regression models were developed as well as a multiple regression model. In the simple regression models, greater lambing difficulty was associated with quadruplet bearing, younger ewes, of terminal breed origin, lambing in February; for example, first parity ewes experienced greater (P<0.001) lambing difficulty (1.56±0.02) than older ewes. The association between lambing difficulty and all factors persisted in the multiple regression model, and the trend in fixed effects level solutions did not differ from the trend observed in the simple regression models. In the simple regression analyses, a greater odds of lamb mortality was associated with male lambs (1.31 times more likely of death than females), lambs of very light (2 to 3 kg) and very heavy (>7.0 kg) birth weights, quadruplet born lambs and lambs that experienced a more difficult lambing (predicted probability of death for lambs that required severe and veterinary assistance of 0.15 and 0.32, respectively); lambs from dual-purpose breeds and born to younger ewes were also at greater risk of mortality. In the multiple regression model, the association between ewe parity, age at first lambing, year of lambing and lamb mortality no longer persisted. The trend in solutions of the levels of each fixed effect that remained associated with lamb mortality in the multiple regression model, did not differ from the trends observed in the simple regression models although the differential in relative risk between the different lambing difficulty scores was greater in the multiple regression model. Results from this study show that many common flock- and animal-level factors are associated with both lambing difficulty and lamb mortality and management of different risk category groups (e.g. scanned litter sizes, ewe age groups) can be used to appropriately manage the flock at lambing to reduce their incidence.     

Effects of lambing season,sex and birth type on growth performance in Norduz lambs

The aim of this study was to evaluate effects of two production systems (spring and winter), sex and birth type on growth performance in Norduz lambs. Data were collected using 103 and 140 lambs born during the winter and spring, respectively. Lambs born in the winter were heavier (P < 0.01) than those born in the spring at birth, 90 and 180 days of age by 0.5, 1.6 and 1.7 kg, respectively. Ram lambs were heavier (P < 0.01) than ewe lambs at birth, 90 and 180 days of age by 0.5, 1.0 and 2.3 kg, respectively, while lambs born as singles were heavier (P < 0.01) than lambs born as twins at birth, 90 and 180 days of age by 0.9, 1.6 and 2.3 kg, respectively. Lambs born in the winter recorded a higher (P < 0.01) pre-weaning ADG (15 g/day) than spring-born lambs, while ram lambs recorded a higher (P < 0.01) pre-weaning ADG (11 g/day) than ewe lambs. The effect of birth type was not significant on pre-weaning ADG. The influence of lambing season and sex were also not significant on post-weaning ADG. Lambs born as singles recorded a higher (P < 0.01) post-weaning ADG (16 g/day) than lambs born as twins. Results suggest the winter season to give rise to heavier lambs at weaning and post-weaning and suggest lambs born in different seasons to have distinctly different growth patterns. The data also confirm that the influence of sex and type of birth on growth to be very important and to be take into account sheep production.     

Control of oestrus in ewe lambs and yearling ewes with medroxyprogesterone acetate and fluorogestone acetate

Two experiments were conducted in a large flock of Berrichon purebred and Romanov × Berrichon F₁ crossbred ewes. In experiment 1, 157 ewe lambs were placed in six groups according to season of mating and maternal breed. Within each group equal numbers of females were treated with either medroxyprogesterone acetate (MAP) or fluorogestone acetate (FGA)-impregnated sponges for 14 days; dosage of PMSG at the time of sponge removal was 500 and 300 I.U. respectively for pure and crossbred. In experiment 2, 111 dry yearling ewes of the Berrichon breed were involved, of which 35, 51 and 25 had either a short lambing to treatment interval (approximately 3 months), a long lambing to treatment interval (approximately 6 months), or were primiparous or nulliparous. They were also treated either with MAP or FGA.The conception rates were extremely high (overall near 86%) in ewe lambs and not significantly affected by seasons or breeds or treatments. Prolificacy and number of lambs per ewe mated were higher in the F₁ crossbred group than in pure Berrichon females (respectively 1.91 vs. 1.34 lambs/mated ewe). No significant difference between the two progestagens could be observed for any of the productivity criteria. Fertility was equally satisfactory in yearlings (overall near 85%) irrespective of the interval between lambing and mating. However, the fertility of the nulliparous ewes (those that failed to conceive as ewe lambs) was significantly lower (72%). The number of lambs per ewe mated was 1.78 in yearlings with a 6-month interval from lambing to mating but was not significantly different from the numbers recorded in the other two groups (1.37 and 1.36). As in experiment 1, there was no difference in the results obtained after either of the two progestagen treatments.In conclusion, progestagen treatment has been shown in both ewe lambs and yearlings to be a very effective means of increasing lamb production in large flocks. This was achieved in ewe lambs regardless of the season and, in dry yearling ewes, regardless of the interval from lambing to mating in the anoestrous season.     

Plane of nutrition during the rearing phase for replacement ewes of four genotypes: II - effects on performance during first pregnancy and to weaning,and of their progeny

Plane of nutrition (PN) offered to ewe replacements during the rearing phase (8 to 17 months) and first pregnancy may affect reproductive and progeny performance when replacements are joined at ~19 months. The effects of PN offered to spring-born ewe replacements during their first winter (winter_1), second summer (summer_2) and subsequent winter (mid and late pregnancy; winter_2) were evaluated, over 3 consecutive years, using 287 ewe lambs of four genotypes: Charmoise×Scottish Blackface (C×SBF), Belclare×SBF (Bel×SBF), Belclare (Bel) and Belclare×SBF (heterozygous for a gene, either FecG^H or FecX^G mutations, that increases ovulation rate: BelMG×SBF). Ewe lambs were offered, daily, a deferred-grazed herbage allowance (HA) of either 0.75 or 1.75 kg dry matter during winter_1. During summer_2 the replacements were set-stocked to maintain sward heights of 4 or 6 cm. Ewes were housed during mid and late pregnancy (winter_2) and offered either medium or high-feed-value grass silage, thus yielding a 2×2×2 factorial design. Increasing HA during winter_1 and residual sward height during summer_2 increased ewe BW post joining (P<0.001) and at lambing (P<0.01), but had no effect (P>0.05) on number of lambs reared. Increasing HA during winter_1 increased lamb BW at birth (P<0.05) and reduced carcass fat score (P<0.05). There was a significant interaction between PN offered during winter_1 and summer_2 for average daily gain (ADG) from birth to 5 weeks (P<0.01) and from 5 to 10 weeks (P<0.05): progeny of replacements that experienced either a high or low PN throughout the rearing phase had lower ADG than lambs born to the replacements that experienced a low PN only during winter_1 or summer_2. Increasing PN during winter_2 increased ewe BW (P<0.001), lamb BW at birth (P<0.001) and weaning (P<0.05) and reduced the proportion of ewes that failed to lamb (P<0.01). Ewe genotype had a significant (P<0.001) effect on litter size (1.48 to 2.45), number of lambs reared, lamb BW at birth and weaning, lamb ADG and age at slaughter. It is concluded that, among the nutrition treatments examined, increasing PN during mid and late pregnancy had the greatest effect on ewe and progeny performance. Although increasing PN offered during winter_1 increased lamb birth BW, PN offered during summer_2 had no effect on lamb performance. There were no significant interactions between PN and ewe genotype.     

Economic weights of production and functional traits for Merinolandschaf, Romney, Romanov and Sumavska sheep in the Czech Republic

Economic weights of production and functional traits were estimated for the dual-purpose sheep breeds Romney (RY), Merinolandschaf (ML), Romanov (RV) and Sumavska (SA). A bio-economic computer model simulating the profit function for production systems with one lambing per year was used for the calculations. First, marginal economic values were calculated which were defined as partial derivatives of the profit function with respect to the average level for each trait. Applying gene-flow methodology, absolute and relative economic weights for direct and maternal components of the traits were then estimated for pure-bred production systems and systems which included partial terminal cross-breeding. The following traits were evaluated: birth weight, daily gain till weaning and during rearing, mature weight, dressing percentage, fleece weight, conception rate of ewe lambs and ewes, litter size at lambing (total number of lambs born per ewe lambing), survival rate of lambs at birth and till weaning and productive lifetime of ewes. Standardized economic weights were calculated as the product of the economic weight and the genetic standard deviation of each trait or trait component. The total economic importance was defined as the sum of the absolute (not taking into account the sign) standardized economic weights over all traits and trait components, and relative economic weights were then computed as the standardized economic weights expressed as percentages of total economic importance. The direct components of survival rate at birth and till weaning, the direct component of daily gain till weaning and litter size had the highest relative economic weights (greater than 10%) in pure-bred systems in all four breeds. In ML and RV, the maternal component of lamb survival rate till weaning also had a relative economic weight exceeding 10%. In systems with partial terminal cross-breeding for all four breeds, relative economic weights of maternal traits and trait components were slightly larger than in pure-bred production systems, particularly for litter size. Based upon comparison of relative economic weights of traits among breeds, separate breeding goals for RY and RV are recommended, whereas a common breeding goal is deemed appropriate for ML and SA.     

Effects of joining at 7 months,and ewe genotype,on the performance of ewes to 19 months of age and that of their progeny to slaughter

Two ways of reducing the cost of replacements are increasing litter size and number of litters produced; thus, the total weight of lamb carcass output per ewe lifetime. The effects of ewe genotype on the performance of ewes lambing at 1 year and of their progeny to slaughter, and the effect of age at first joining (7 or 19 months) on BW at ~19 months and survival to joining at 19 months were evaluated over two consecutive years, using 460 ewe lambs from three genotypes: Belclare (Bel), Suffolk × Belclare (Suf × Bel) and ≥ 75% Suffolk ancestry (Suf75). Lambs from the three genotypes were at a similar proportion of mature BW and half of the lambs, within genotype, were allocated to be joined for the first time at 7 or 19 months. The ewe lambs were managed in a grass-based rotational-grazing system, except when housed from December to March on a grass silage-based diet. Belclare ewes had larger litters (P < 0.001), reared more lambs per ewe joined (P < 0.01), were lighter at lambing and at 19 months (P < 0.01), were of smaller body size at 19 months (P < 0.001) and their progeny were lighter at weaning (P < 0.05) relative to Suf75 genotype; the Suf × Bel ewes were intermediate for most traits but had a significantly lower litter size (P < 0.05) than Bel ewes. Progeny from Suf × Bel ewes were 17 days younger at slaughter (P < 0.01) relative to those from Bel ewes. Ewe genotype had no effect (P > 0.05) on lamb mortality (born dead, total mortality to weaning), lambing assistance, number of ewes that failed to lamb, or on ewe survival to 19 months of age. Increasing ewe BW at joining increased the probability (P < 0.001) of rearing at least one lamb and this effect was consistent across genotypes. There were significant relationships (P < 0.001) between ewe BW at lambing and lamb BW at birth and at weaning of 0.053 (SE 0.0089) kg and 0.29 (SE 0.049) kg, respectively. Ewes that lambed at 1 year were 2 kg lighter (P < 0.001) at 19 months of age and had a smaller body size (P < 0.01) relative to those not joined. It is concluded that ewe genotype had a significant effect on number of lambs reared, and thus lamb carcass output. Whilst lambing at 1 year reduced BW by 2 kg when joined at 19 months, it did not affect ewe survival to that stage.     

Effect of maternal exposure to the environmental estrogen,octylphenol, during fetal and/or postnatal life on onset of puberty,endocrine status,and ovarian follicular dynamics in ewe lambs

Octylphenol (OP) is one of a number of compounds found in the environment that has estrogen-mimicking actions in vivo. Our objective was to determine if maternal exposure to octylphenol during fetal and/or postnatal life would affect the onset of puberty, endocrine status, and subsequent ovarian follicular dynamics of ewe lambs. Lambs were born in March to ewes that received twice weekly s.c. injections of octylphenol (1000 micro g/kg/day) from Day 70 of gestation to weaning (n = 6); Day 70 of gestation to birth (n = 3); birth to weaning (n = 5; gestation = 145 days); or corn oil from Day 70 of gestation to weaning (control; n = 5). Blood samples were collected twice weekly to determine progesterone and FSH concentrations from 20 wk of age throughout the first breeding season. Onset of puberty and interestrous intervals were determined from 20 wk of age by twice daily observation for estrus in the presence of a vasectomized ram. During January the ovaries of each lamb were examined using transrectal ultrasonography from the day of estrus for 15 days. Blood samples were collected every 8 h to examine FSH concentrations and every 2 h to detect the preovulatory gonadotropin surge throughout this estrous cycle. The onset of puberty and first progesterone rise was advanced and the FSH preovulatory surge was elevated for longer in the OP-treated lambs compared with the control lambs (P < 0.05). Interestrous intervals, FSH profiles, and ovarian follicular dynamics were not affected (P > 0.05) by exposure to octylphenol. In conclusion, octylphenol exposure advanced the onset of puberty but it did not disrupt FSH concentrations or the dynamics of ovarian follicular growth.