Offering maternal composite ewes higher levels of nutrition from mid-pregnancy to lambing results in predictable increases in birthweight, survival and weaning weight of their lambs

Management of nutrition during pregnancy for maternal composite ewes has the potential to improve lamb production and survival in prime lamb production systems but existing condition score (CS) guidelines developed for Merinos may not be appropriate for the optimum production of maternal ewes. To address this, three replicated experiments were conducted at two research sites in Victoria and one in Western Australia. Ewes (781–800 per site) were allocated to four CS treatments following pregnancy scanning (~Day 50) and differentially fed to reach approximate targets of CS 2.4, 2.8, 3.2 and 3.6 by lambing. Single and multiple bearing ewes grazed together, and nutritional treatments were applied until the end of lambing after which ewes and lambs were aggregated into management groups containing all treatments. At lambing, maternal ewe liveweight had a range between treatments of 13.7–19.1 kg (average 16.4 kg) and CS varied by 1.1–1.5 of a CS (average 1.24). Across site analysis indicated that lamb birthweight and weaning weight increased with application of higher CS treatments (P < 0.001). There was also an improvement in survival of multiple born lambs with increasing CS at lambing (P < 0.001). Birthweight was significantly related to survival (P < 0.001) at all sites with no significant effect of birth type on lamb survival. Changes in birthweight and weaning weight could be predicted from ewe joining liveweight, ewe liveweight change to Day 90 and ewe liveweight change Day 90 to lambing. The coefficients derived for each of these effects were similar to those found in previous experiments examining Merino and crossbred Border Leicester Merino ewes. The optimum CS targets for multiple bearing maternal composite ewes may be higher than the industry recommended target for Merino ewes based on advantages in lamb survival and weaning weight.

Meta-analysis of lamb birth weight as influenced by pregnancy nutrition of multiparous ewes

Across the literature, there is large variation in lamb birth weight responses to changes in the ewe pregnancy nutrition. Much of this heterogeneity has been attributed to several factors inherent to each experiment; however, the relative contribution of these experimental factors has not yet been quantified. This meta-analysis aimed to systematically review the variation in lamb birth weight responses across nutritional studies involving adult multiparous ewes. Effect-sizes for individual studies were estimated using the unbiased estimator Hedges' g, whereby positive and negative values indicate heavier and lighter treatment lambs vs. controls, respectively. Heterogeneity varied between early-, mid- and late-pregnancy undernutrition studies (I2total [early pregnancy] = 19.90%, I2total [midpregnancy] = 52.10%, I2total [late pregnancy] = 68.70%). The small average effects for early- (0.04, highest posterior density [HPD] interval = -0.22, 0.28) and mid-pregnancy undernutrition (-0.15, HPD interval = -0.35, 0.05) suggest that if farmers anticipate a potential feed shortage, ewes can be allowed to lose weight providing nutrition is resumed to adequate levels later in pregnancy. On the contrary, late-pregnancy undernutrition was associated with a significant decrease in lamb birth weight (-0.72, HPD interval = -0.86, -0.55). Thus, management practices should focus on ensuring adequate nutrition in late pregnancy. Increasing lamb birth weight could be possible by feeding ewes above their pregnancy maintenance requirement (0.23, HPD interval = 0.002, 0.48), though the number of studies is limited and further research is needed.

Using transrectal ultrasound to examine the effect of exogenous progesterone on early embryonic loss in sheep

The financial impact of early embryonic loss in Australia may be as high as $137 million AUD/year. Embryos may be lost due to environmental conditions, or maternal factors such as nutrition or progesterone (P4) profiles. However, studies on the supplementation of P4 during early pregnancy have returned contradictory results, partly as a reliable method of detecting embryos in the early stages of gestation (<day 20) has yet be established. As such, Merino ewes (n = 62) were either not supplemented (control) or were given exogenous P4 at the time of insemination (day 0) or 3 days later (day 3). Transrectal ultrasound (TRUS) was performed on day 10, 12, 14, 17, 19 and 29 following laparoscopic artificial insemination. Transcutaneous ultrasound (TCUS) was performed on day 54 to confirm pregnancy and peripheral blood was collected for hormone analysis on day 19 to compare the accuracy of all three pregnancy diagnosis methods. Data were then analysed in developmental periods. The percentage of ewes detected as pregnant by TRUS during pre-, peri- and post implantation was 66% (41/62; day 12 and 14), 61% (38/62; day 17 and 19) and 58% (36/62; day 29), respectively. TCUS during established gestation recorded a pregnancy rate of 60% (37/62). The sensitivity of TRUS to correctly diagnose ewes as pregnant during pre-, peri- and post implantation was 68% (25/37), 89% (33/37) and 100% (36/36), respectively, while the sensitivity to correctly identify multiples was 49% (16/33), 60% (21/35) and 97% (34/35), respectively (P<0.05). The majority of embryonic loss occurred between pre- and peri- implantation (0.9±0.15 per ewe; P<0.001). No further loss was recorded after this point. Ewes that were given P4 at day 0 had significantly higher embryonic loss (77%) compared to the control (52%) and day 3-ewes (56%; P<0.05). These results show TRUS is a viable tool for investigating early embryonic loss and that the variability noted in previous P4 supplementation studies may be due to variation in time and length of treatment.

Relationships among Puberty, Muscle and Fat, and Liveweight Gain during Mating in Young Female Sheep

Greater depths of muscle are associated with better reproductive performance in ewe lambs, but, in adult ewes, reproductive performance also seems to vary with liveweight gain during the mating period. Therefore, in a large field study with Merino ewe lambs, we tested whether the relationships among eye muscle depth (EMD), fat depth (FAT) and reproductive performance depend on liveweight gain during the mating period. We selected lambs with a wide range in phenotypic values for depths of eye muscle (EMD) and fat (FAT) and assigned them to dietary treatments designed to achieve low (LOW, n = 244) or high (HIGH, n = 237) rates of liveweight gain during a 28-day mating period. The LOW treatment maintained live weight, whereas the HIGH treatment gained 179 ± 3.8 g/day (p < 0.001). From those ewe lambs that attained puberty, first oestrus was detected at live weight 37.8 ± 0.2 kg and age 232 days. The proportion of ewes that attained puberty increased with EMD (p < 0.01). Ewes from the HIGH treatment were more fertile (pregnant ewes per 100 ewes exposed to rams) and had a higher reproductive rate (foetuses in utero per 100 ewes exposed to rams; p < 0.001) than those from the LOW treatment. Fertility and reproductive rate were positively correlated with weight gain during mating as well as live weight at the start of mating, FAT and EMD (p < 0.05 to <0.001). We conclude that faster growth, due to either extra nutrition during mating or higher phenotypic potential for fat and muscle, will increase reproductive performance in ewe lambs mated at 8 months of age.

Monitoring liveweight in sheep is a valuable management strategy: a review of available technologies

Liveweight is a widely accepted proxy for the energy status of sheep at a particular point in time. Fleece- and conceptus-free ewe liveweight and liveweight change influence the productivity of the ewe and optimisation may increase whole-farm profitability. Despite this, it is uncommon for producers to monitor ewe liveweight regularly and objectively. The current review discusses why ewe liveweight is important, identifies and assesses available technologies for monitoring sheep liveweight, and highlights future research priorities. The common theme in the literature is that while there are options that could possibly be used to monitor the liveweight of sheep in extensive grazing systems, few of them offer realistic solutions, especially in regard to timeliness of data collection. Thermal and stereo imaging, body measurements and plasma hormonal assays are unlikely to be commercially viable, while visual assessment, although widely practised, offers a surprisingly poor indication of sheep liveweight. Alternatively, assessment of body condition (condition scoring) or fat (fat scoring) offers viable methods of assessing sheep energy status; however, like conventional static weighing, they are performed infrequently and therefore contribute little to the day-to-day tactical management of sheep flocks. Walk-over weighing systems offer a feasible alternative for regular monitoring of sheep liveweight. Such systems are fully automated, and may be operated remotely. Currently, there are challenges associated with monitoring the liveweight of individual animals using such systems and hence there is little commercial opportunity for individual animal management. Mob-based walk-over weighing, which generates flock average liveweight estimates, offers greater potential in the short term, although the technology would benefit from further research and development, primarily to increase the frequency and repeatability of liveweight capture.

The relationship between phenotypic variation among offspring and mother body mass in wild boar: evidence of coin-flipping?

1. In highly variable environments, the optimal reproductive tactics of iteroparous organisms should minimize variance in yearly reproductive success to maximize the long-term average reproductive success. To minimize among-year variation in reproductive success, individuals can either minimize the variance in the number of offspring produced at each reproductive attempt (classical bet-hedging) or maximize the phenotypic diversity of offspring produced within or among reproductive attempts (coin-flipping). 2. From a long-term detailed study of an intensively exploited population facing a highly unpredictable environment, we identify a continuum of reproductive tactics in wild boar females depending on their body mass. 3. At one end, light females adjusted litter size to their body mass and produced highly similar-sized offspring within a litter. These females fitted the hypothesis of individual optimization commonly reported in warm-blooded species, which involves both an optimal mass and an optimal number of offspring for a given mother. At the other end of the continuum, heavy females produced litters of variable size including a mixture of heavy and light offspring within litters. 4. Prolific heavy wild boar females diversify the phenotype of their offspring, providing a first evidence for coin-flipping in a warm-blooded species.

Housing conditions and management practices associated with neonatal lamb mortality in sheep flocks in Norway

A study was conducted in order to obtain information about sheep farms in Norway and to identify housing and management characteristics that were risk factors for neonatal mortality of lambs 0-5 days of age. A questionnaire was submitted to sheep farmers, who provided demographic data and information on sheep housing conditions and feeding and management practices. Our description of farms is based on the questionnaire responses received from 2260 farmers. Data on lamb mortality during the preceding lambing season were available for those flocks that were enrolled in the Norwegian Sheep Recording System. Some flocks where the number of lambing ewes was less than 20 or greater than 400 were excluded. The total number of flocks included in the analysis of neonatal mortality was 1125. An increase in the mean number of live-born lambs per ewe per flock was associated with increasing neonatal mortality. Factors independently associated with increased neonatal survival were continuous monitoring of the ewes during the lambing season, active support to ensure sufficient colostrum intake of the lambs, feeding a combination of grass silage and hay compared with grass silage alone, and supplying roughage at least twice per day versus only once. Increased survival was also observed in flocks where the farmer had at least 15 years of experience in sheep farming. Flocks in which the Spæl breed predominated had lower odds for neonatal deaths compared to flocks in which the Norwegian White breed predominated. In conclusion, measures in sheep flocks targeted at feeding practices during the indoor feeding period and management practice during lambing season would be expected to reduce neonatal lamb mortality.

The birthweight and survival of Merino lambs can be predicted from the profile of liveweight change of their mothers during pregnancy

The single largest influence on the survival of lambs in the first few days of life is their birthweight. Fetal growth and birthweight are regulated by genotype of the fetus, maternal genotype, maternal nutrition and the external environment. In this paper we report the extent to which the changes in maternal liveweight during pregnancy and lactation (liveweight profile) of Merino ewes can be used to predict the birthweight and survival of their progeny to weaning. At two sites [Victoria (Vic.) ~700 ewes and Western Australia (WA) ~300 ewes] in each of 2 years, a similar experiment used adult Merino ewes to explore effects of nutrition from joining to Day 100 of pregnancy and from Day 100 of pregnancy to weaning. The average difference between extreme treatments at Day 100 of pregnancy were 7 kg in ewe liveweight and 0.7 of a condition score (CS) and at lambing 11.9 kg and 1.3 of a CS. This resulted in average birthweights of progeny from different treatments ranging from 4.0 to 5.4 kg and survival to weaning ranging from 68 to 92%. Across the four experiments between 68 and 85% of all lamb deaths to weaning occurred within 48 h of birth. Lambs born to ewes in CS 2 at Day 100 of pregnancy were lighter (P < 0.05) in both years at the Vic. site than those from ewes in CS 3 at Day 100 of pregnancy. Lambs born to the ewes grazing a feed on offer of 800 kg DM/ha during late pregnancy were also lighter than those from other levels of feed on offer between 1100 and 3000 kg DM/ha at the Vic. site in both years and at the WA site in 1 year (P < 0.001). Lambs from the 800 kg DM/ha treatment during late pregnancy at the Vic. site had a lower survival than other treatments, especially in the second year. There were no significant effects of treatments on lamb survival at the WA site; however, the results were in the same direction. The birthweight of individual lambs was significantly related to the liveweight profile of their mothers. Their liveweight at joining, change in liveweight to Day 100 of pregnancy and change in liveweight from Day 100 to lambing all contributed (P < 0.05) to the prediction of the birthweight of their lambs. The responses were consistent across experimental sites and years, lamb birth rank and sex, and confirmed that the effects of poor nutrition up until Day 100 of pregnancy could be completely overcome by improving nutrition during late pregnancy. At the Vic. site, survival to 48 h was most influenced by the birthweight of the lamb and survival was significantly higher in single- than twin-born lambs and female than male lambs after adjusting for differences in birthweight. A higher chill index during the 48 h after birth reduced survival of both single and twin lambs to a similar extent, but reduced survival of male lambs more than female lambs. There were no effects of birthweight or chill index on lamb survival at the WA site where most lambs weighed more than 4 kg at birth and climatic conditions during lambing were less extreme. Overall, these results supported our hypothesis that improving the nutrition of Merino ewes during pregnancy increases birthweight and this leads to improved survival of their progeny.

Introduction of meat sheep breeds in extensive systems of Patagonia: lamb growth and survival

Genotype effects on lamb growth, survival, and commercial finishing were estimated in a 5-yr study aimed at assessing potential benefits from introducing meat breeds into extensive sheep systems of northeastern Patagonia. Five ram [Corriedale: CO; Border Leicester: BL; Ile de France: IF; Texel: TX; and synthetic CRIII (25% Merino, 37.5% IF, 37.5% TX)] and 5 dam (CO; synthetic CRIII; BLCO: BL x CO; IFCO: IF x CO; and TXCO: TX x CO) genotypes were represented in the study. Data were collected from 1,426 born and 1,258 weaned lambs of 9 resulting genotypes (CO x CO, BL x CO, IF x CO, TX x CO, CRIII x CO, CRIII x BLCO, CRIII x IFCO, CRIII x TXCO, and CRIII x CRIII). Birth weight was recorded on all lambs; subsequently, BW and BCS (scale 1 to 5) were recorded at regular intervals until weaning. Body weights were adjusted to 60 and 90 (weaning) d of age, and ADG were calculated from the adjusted BW for the periods 0 to 60 d and 60 to 90 d; BCS was adjusted to 90 d. Survival to weaning and percentage of lambs reaching commercial finishing (BW >or= 23 kg and BCS >or= 2.5 points) were also recorded. Significant (P < 0.05) genotype x litter size interactions were detected for birth weight and ADG 60 to 90 d. With the exception of CRIII x CO, crossbred and synthetic genotypes presented greater (P < 0.05) ADG 0 to 60 d and BW at 60 and 90 d than CO x CO lambs. Second cross lambs reared as singles presented greater ADG 60 to 90 d (P < 0.05) than BL x CO, TX x CO, and CRIII x CO, but less (P < 0.05) ADG 60 to 90 d, and no differences were observed for twins. The IF x CO, CRIII x BLCO, CRIII x IFCO, and CRIII x CRIII genotypes showed greater BCS at 90 d (P < 0.05) than CO x CO. The probability of greater commercial finishing for crossbred and synthetic genotypes relative to CO x CO was at least 79%. Probabilities of greater survival to weaning in CO x CO and CRIII x BLCO lambs relative to IF x CO, TX x CO, CRIII x CO, and CRIII x CRIII lambs were greater than 81%. Results indicate significant improvements in lamb BW and saleable lambs from the introduction of meat genotypes. Among the terminal sire breeds evaluated, BL and IF would produce the greatest impact. Differential nutritional management of pregnant ewes carrying twins and of twin lambs beyond 60 d should be implemented to mitigate litter size x genotype interactions constraining growth potential benefits, which may be critical for northeastern Patagonia conditions.

Nutritional paradigms of ovine fetal growth restriction: Implications for human pregnancy

Low birth weight and prematurity are associated with short inter-pregnancy intervals, low pre-pregnancy weights, insufficient maternal weight gains during pregnancy, multifetal pregnancies and a young maternal age. Improvements in maternal nutritional status are arguably imperative for ensuring an appropriate pregnancy outcome in these vulnerable groups, but ethical boundaries limit these investigations. Experimental paradigms using the pregnant sheep have been widely used to identify the nutritionally sensitive periods of conceptus development. In adult sheep, severe undernutrition during the periconceptual period accelerates maturation of the fetal hypothalamic-pituitary adrenal axis and results in pre-term delivery. Low pre-pregnancy weight, followed by undernutrition during mid-pregnancy, results in reduced placental growth and lower birth weights at term. Studies that have restricted nutrients during mid-gestation only reveal variable effects on the placental and fetal growth trajectory, however if undernutrition is prolonged during late-pregnancy, fetal growth is compromised, particularly in twin pregnancies. In contrast, overnourishing the adolescent sheep to promote rapid maternal growth, results in the premature delivery of low birth weight lambs. These effects are mediated by impaired placental growth, uteroplacental blood flows and fetal nutrient uptakes. At the other end of the nutritional spectrum, undernourishing the adolescent sheep to gradually deplete nutrient reserves, results in fetal growth restriction which is independent of alterations in placental mass.

Effect of concentrate supplement and sward height on twin-bearing ewe body condition and the performance of their offspring

These studies investigated the effects of offering concentrate supplement, from day 102 of pregnancy, to twin-bearing ewes grazing a 2- or 6-cm sward, on the condition of the ewe and the performance of their offspring in 2005 and 2006. In both years, 80 twin-bearing ewes were randomly assigned to either the 2- or 6-cm sward height pasture treatment from day 70 of pregnancy until parturition. From pregnancy day 102, half of the ewes within each sward height were offered 400 g/ewe.day of concentrate supplement. From day 102 until day 140 of pregnancy, ewes offered the concentrate supplement gained more liveweight then ewes offered pasture only. While supplementation affected ewe liveweight, its effects on lamb birthweight and growth were variable. In 2006, concentrate supplementation within the 6-cm sward height treatment increased (P < 0.05) lamb birthweight from an average of 4.8 to 5.3 kg. In 2005, concentrate supplementation increased (P < 0.05) lamb growth by 20 g/day. These inconsistent and minor production gains are unlikely to be cost effective because of the satisfactory performance of lambs from all other nutritional treatments and the extensive feeding of concentrate supplement. Therefore, feeding 400 g/ewe.day of concentrate supplement from day 102 of pregnancy to twin-bearing ewes on a 2- or 6-cm sward height pasture appears not to be a viable management strategy for commercial sheep farmers.

Effects of plane of nutrition during the first month of pregnancy on conception rate, foetal development and lamb output of mature and adolescent ewes

Embryo transfer studies have demonstrated that high plane feeding in early pregnancy is detrimental to the successful establishment of pregnancy in adolescent but not mature ewes. To further examine this relationship with ewes that conceive naturally and to investigate its effects on foetal development, 102 Greyface and Texel×Greyface ewes (body condition score (BCS) 3·8) and 114 Texel×Greyface adolescent ewes (BCS 3·3) were allocated to one of three treatments following a synchronized mating. From day 1 to 31 of pregnancy, animals were offered grass nuts (10·2 MJ metabolizable energy (ME) per kg dry matter (DM); 163 g crude protein per kg DM) at one of three levels to supply approximately 2·0 (H); 1·0 (M) and 0·6 (L) of their predicted ME requirements for maintenance. Increasing the post-mating plane of nutrition resulted in significant increases in ewe live weight (P<0·001) and BCS (P<0·001) during the treatment period. When diets were standardized for all animals during mid pregnancy (days 31 to 105), L ewes gained more live weight (P<0·05) and BCS (P<0·001) than H ewes. Early pregnancy nutrition had no effect on the conception rate of mature ewes; however adolescent ewes on the H and M treatments had lower conception rates (P<0·05) than those offered the L diet (0·59, 0·61 and 0·82 respectively). As a result, L adolescent ewes tended to have a higher mean total lamb birth weight per ewe mated (P=0·09) although lamb output at weaning was not influenced by plane of nutrition. Lambs born from adolescent mothers had lower lamb birth weights (P<0·001) and a shorter mean head length, crown-rump length and thoracic girth (P<0·001). Foetuses from H ewes had longer hind legs than those from L ewes on day 83 of gestation (P<0·05) and at term (P<0·05). The results of this study suggest that allowing adolescent but not mature ewes to lose live weight and body condition can increase the proportion of productive ewes following a natural service.

Lifetime changes in wool production of Merino sheep following differential feeding in fetal and early life

In commercial Merino farming, a major determinant of profitability is quantity and quality of wool production. We tested the hypothesis that the level of feed restriction commonly encountered by autumn/early winter lambing Merino ewes in southern Australia was sufficient to have a detrimental effect on their progeny’s lifetime wool production. Two periods of feed restriction of the dams were tested, viz. from day 50 to 140 of gestation (Expt 1), and from day 50 of pregnancy to weaning at 12 weeks of age (Expt 2). In order to reduce the numbers of experimental animals required, identical twin lambs were produced by cloning embryos. There was a total of 35 and 22 pairs of clones in Expts 1 and 2 that were recorded to 6.4 and 4.4 years of age, respectively. In Expt 1 it was estimated (i.e. conceptus-free weight) that the submaintenance (Sub-M) ewes lost 18 kg in weight compared with 9 kg by the Control (C) ewes over the period of differential feeding. In Expt 2 the Sub-M ewes lost 10 kg during pregnancy and 10 kg during lactation, compared with a loss of 3 kg and a gain of 4 kg over the same period in the C ewes. Gestation length was 1.3 days shorter (P < 0.01) in the Sub-M than C ewes in Expt 1. Birthweights of the Sub-M lambs were 0.5 kg lighter than the C lambs in Expts 1 (P < 0.01) and 2 (P < 0.05). At 12 weeks of age, liveweights of the lambs in the Sub-M and C treatments were 24.2 and 25.9 kg in Expt 1 (P < 0.01) and 14.0 and 25.0 kg in Expt 2 (P < 0.001). Corresponding liveweights at 4 months of age were 30.9 and 32.5 kg (P < 0.01) and 19.9 and 29.7 kg (P < 0.001), the Sub-M animals producing less clean wool (0.1 and 0.4 kg, P < 0.01 and < 0.001, Expts 1 and 2, respectively), that was finer in Expt 2 (2.7 μm, P < 0.001) than their C counterparts. Throughout the rest of the study the Sub-M animals in Expt 2 (but not Expt 1) were on average 3.2 kg lighter (P ranging from < 0.05 to < 0.001) than C animals. In both experiments the ratio of secondary to primary wool-producing follicles was lower (1.1–2.6 units, P < 0.001) in the Sub-M than C animals. These differences led to (P < 0.05) lower significantly adult clean wool production of 0.17 kg (Expt 1) and 0.24 kg (Expt 2) per annum. There was no significant interaction between nutritional treatment and age of the animal for clean wool production. Within experiments there were no significant differences between nutritional treatments in any of the wool quality measurements. However, when fibre diameter data for both experiments were combined for 3.4 and 4.4 years of age, the Sub-M animals were significantly broader (0.3 μm, P < 0.01) when compared with the C animals. We conclude that Sub-M feeding of the pregnant ewe will permanently affect liveweight, the wool follicle population, and wool production and quality, in Merino sheep. Extension of the period of under feeding into lactation (Expt 2) appears to increase the amplitude of the differences in young animals, which is largely overcome by the time the animal reaches 2.4 years of age.

Effect of nutrient intake during pregnancy on fetal and placental growth and vascular development

Remarkable diversity of size and health of offspring exists after normal pregnancies. When pregnancies are complicated by an extrinsic variable such as inappropriate maternal nutrition, birth weight and health of the neonate are substantially affected. The placenta is the organ through which respiratory gases, nutrients, and wastes are exchanged between the maternal and fetal systems. Thus, transplacental exchange provides for all the metabolic demands of fetal growth. Transplacental exchange is dependent upon uterine and umbilical blood flow, and blood flow rates are in turn dependent in large part upon vascularization of the placenta. Therefore, factors that influence placental vascular development will have a dramatic impact on fetal growth and development, and thereby on neonatal mortality and morbidity. Recent work from our laboratories has focused on the effects of nutrient intake during pregnancy on placental growth and vascular development. Both nutrient restriction of the adult dam and overnourishment of the adolescent dam during pregnancy suppress placental cell proliferation and vascularity. Furthermore, placental expression of angiogenic factors and their receptors, factors that are known to affect vascular growth, are perturbed by level of nutrition. Studies in this area will lead to improved methods to manage nutritionally-compromised pregnancies.

Comparison of hay and silage for pregnant and lactating Finnish Landrace ewes

A comparison of conserving timothy/meadow fescue/meadow grass as silage or hay was conducted with Finnish Landrace ewes. Intake of hay (H), silage (S) and hay/silage (HS), and the performance of 30 Finnish Landrace ewes carrying twins, triplets and quadruplets and suckling either twin or triplet lambs was measured during the last 8 weeks of pregnancy and during the first 6 weeks of lactation. The dry matter (DM) intake of HS was lower (p<0.03) than H during lactation, whereas there was no difference in DM intake between pregnant and lactating ewes fed either H or S. The intake of metabolisable energy was on an average 12.8, 14.3 and 13.4MJperday in pregnancy, and 17.7, 20.2 and 18.1MJ in lactation for H, S and HS, respectively. Daily intakes of protein assessed in terms of amino acids absorbed in the small intestine (AAT) were on an average 92, 110 and 102g for H, S and HS during pregnancy and 157, 184 and 165g during lactation, respectively. Ewes in all treatments were, relative to calculated requirements, deficient in energy and protein during the last month of pregnancy and early lactation. Ewes performed consistently better when fed silage than hay. Lamb mortality was low for all treatments. The number of artificially reared lambs tended to be highest when ewes were fed both hay and silage ad libitum. Lamb growth was higher on S than H based diet (p<0.005). With respect to winter feeding of ewes, grass silage compared favourably with hay and indicated that hay could be replaced by well preserved grass silage. During late pregnancy and early lactation, there was no advantage of supplementing silage with hay, relative to entirely silage based diets.

Maternal undernutrition during late pregnancy in sheep. Its relationship to maternal condition, gestation length, hepatic physiology and glucose metabolism

There is a paucity of information on the metabolic effects of undernutrition of the ewe carrying multiple fetuses in late pregnancy. In the present study the effects of induction of ketosis from 132 d gestation in ewes carrying twin fetuses were compared with a control group. The ewes were well fed up to 132 d. Ketotic ewes showed a loss of condition score from 3.7 (SE 0.11) at 130 d gestation to 3.0 (SE 0.15) 10 d later after clinical recovery, compared with control twin-pregnant ewes (P < 0.01). The weight loss during the same time period was from 70.6 (SE 2.7) kg at 130 d to 64.2 (SE 2.7) kg at 140.d gestation. As expected, both groups lost weight and condition score in the first 28 d of lactation. Induction of ketosis caused a significant shortening of the gestation period to 142.8 (SE 0.7) d compared with 150 (SE 0.4) d in normal twin-pregnant ewes (P < 0.001). Ewes with induced ketosis recovered clinically and showed a normal feed intake by 3.4 (SE 0.07) d; three required treatment. Induction of ketosis resulted in reduction of hepatic uptake of bromosulphthalein (P < 0.01) and its biliary excretion (P < 0.05), metabolic clearance rate (P < 0.001), fractional clearance (P < 0.001) and 15 and 30 min retention compared with control twin-pregnant ewes. Most values had returned to normal by the first week of lactation. It is thought that in human pregnancy similar changes in bromosulphthalein clearance may be related to reduced binding sites for bromosulphthalein in the liver caused by increased circulating oestrogens. Induction of ketosis resulted in a significant hypoglycaemic (P < 0.01), ketotic (P < 0.001) state compared with well-fed twin-pregnant ewes. These changes could be correlated with the severity of the clinical signs, together with a significant rise in plasma urea (P < 0.001) and NH3 (P < 0.05) concentrations. Again, the return of most of these values to normal by the first week of lactation lends support to the reversibility of hepatic lesions caused by fatty infiltration of the liver. The severity of this condition in naturally occurring cases suggests that factors other than undernutrition may be contributory, such as the general body condition of the ewe and glucose metabolism by the liver, including the conversion of propionate to glucose.

Maternal undernutrition during mid-pregnancy in sheep. Placental size and its relationship to calcium transfer during late pregnancy

The aim of the present experiment was to determine the relationship between placental and fetal weight after placental growth had been retarded by maternal undernutrition. Placental weight and fetal weight were measured in single-lamb-bearing ewes which were well-fed throughout pregnancy, or severely undernourished between the 30th and 96th day of pregnancy. Placental transfer of calcium and whole-body metabolism of both glucose and Ca were measured during late pregnancy. The change in fleece-adjusted live weight between the 30th and 96th day of pregnancy was 99 (SE 9.8) and -146 (SE 9.6) g/d for the well-fed and undernourished ewes respectively. The condition score of well-fed ewes did not significantly change between the 96th (2.9 (SE 0.08)) and 140th (3.0(SE 0.13)) day of pregnancy, while it increased from 1.6 (SE 0.15) to 2.3 (SE 0.11) for the previously undernourished group. Undernutrition caused an increase (P less than 0.01) in placental weight measured on the 96th (21%) and 140th (30%) day of pregnancy. In contrast fetal growth was not significantly affected by maternal undernutrition. While the voluntary dry matter intakes (g/d) of previously undernourished ewes after the 97th day of pregnancy were higher than for their well-fed counterparts, there was no significant difference between whole-body glucose or Ca metabolism, or the placental transfer of Ca measured during late pregnancy. This experiment confirms earlier reports of an increase in placental weight as a result of maternal undernutrition during mid-pregnancy; but the factors causing and the functional significance of this response have not been identified. Contrary to earlier proposals, placental weight per se did not limit fetal growth during late pregnancy. It is hypothesized that a combination of factors originating from maternal, placental and fetal sources act together to regulate growth of the fetus.