Growth Rate In Sheep Research Articles

Growth and development of young sheep of Edilbaev breed under the conditions of farm in the Republic of Kazakhstan

The features of growth and development of young animals of Edilbaev breed obtained from sheep bred under the production conditions of the farm “Birzhanov” in the Auliekolsky area in the Kostanay region of the Republic of Kazakhstan have been studied in the paper. In a comparative aspect the live weight was studied, the conformation features of the young sheep of Kazakh fat-tailed rough-haired and Edilbaev breeds were determined. Two groups of sheep were formed for the research: a control group (Kazakh fat-tailed rough-haired breed) and an experimental (Edilbaev breed) with 15 heads in each group. Studies have shown that with the same housing and feeding of animals of diff erent breeds, the gain in live weight was diff erent. The largest absolute gain in live weight was shown by young rams and young ewes of Edilbaev breed 11,3 and 10,0 kg, while young rams and young ewes of Kazakh fat-tailed rough-haired breed only 10,3 and 8,8 kg. The highest growth rate in sheep of the experimental groups was observed until the age of one month. In other age periods the growth rate was signifi cantly infl uenced by feeding conditions, however, in general, the growth rate of young animals was high. When studying the conformation features of the experimental young sheep, it was found that with age the conformation of the lambs of the experimental group changed in the same way as in the control group, however, high indices of blockness and massiveness allow us to state that the lambs of the experimental group have well-developed meat forms. Studies have shown that there is a significant difference in the experimental young animals of the compared groups in terms of live weight, body measurements and conformation indices in favor of sheep of Edilbaev breed.

Effects of the Seleno-Chitosan on Daily Gain, Wool Yield, and Blood Parameter in the Chinese Merino Sheep.

To study the effects of the seleno-chitosan on daily gain, wool yield, and blood parameters in the Chinese merino sheep in the selenium (Se)-deficient pastures. The samples of soils, forages, and tissues had been collected in the Southern Xinjiang of Northwest China. Our findings indicated that the Se contents in soils and forages from affected pastures were remarkably lower than those unaffected by the pastures (P < 0.01). The Se contents in the blood and the wool from affected Chinese merino sheep were extremely lower than those from healthy sheep. Meanwhile, the values of Hb, PCV, and PLT in affected sheep were significantly decreased (P < 0.01). The yield of wool and the growth rate in affected sheep were also remarkably reduced (P < 0.01). The affected Chinese merino sheep were orally treated by seleno-chitosan for 150days; the Se contents in blood were remarkably increased and reached the healthy range on day 5. The blood parameters soon recovered to a healthy range on day 10. The growth rate of sheep in the treated group was remarkably higher than that in the control animals. The yield of the wool was also significantly increased in the treated group. Consequently, the Se-deprived environment caused a threat to daily gain, wool yield, and blood parameters in the Chinese merino sheep. The seleno-chitosan could not only markedly increase the Se contents blood contents, but also significantly increase the production performance (daily gain and wool yield), and release the symptoms of anemia in the Se-deprived animal.

Interrelationships Between Morphometric, Densitometric, and Mechanical Properties of Teeth in 5-Month-Old Polish Merino Sheep.

Interrelationships between morphological, densitometric, and mechanical properties of deciduous mandibular teeth (incisors, canine, second premolar) were investigated. To perform morphometric, densitometric, and mechanical analyses, teeth were obtained from 5-month-old sheep. Measurements of mean volumetric tooth mineral density and total tooth volume were performed using quantitative computed tomography. Microcomputed tomography was used to measure total enamel volume, volumetric enamel mineral density, total dentin volume, and volumetric dentin mineral density. Maximum elastic strength and ultimate force of teeth were determined using 3-point bending and compression tests. Pearson correlation coefficients were determined between all investigated variables. Mutual dependence was observed between morphological and mechanical properties of the investigated teeth. The highest number of positive correlations of the investigated parameters was stated in first incisor indicating its superior predictive value of tooth quality and masticatory organ function in sheep. Positive correlations of the volumetric dentin mineral density in second premolar with final body weight may indicate predictive value of this parameter in relation with growth rate in sheep. Evaluation of deciduous tooth properties may prove helpful for breeding selection and further reproduction of sheep possessing favorable traits of teeth and better masticatory organ function, leading to improved performance and economic efficiency of the flock.

Assessment of Growth Rate of UDA Sheep Fed Diets Containting Varying Energy Levels Using Live Morphometry

A study was conducted to evaluate varying energy levels on growth rate of sheep using live morphometric measurements. Twenty growing Uda lambs were randomly allocated into four dietary treatments (five animals per treatment) with varying energy levels in a completely randomized experimental design (CRD). The animals were fed diets containing 1800, 2000, 2200 and 2400 kcals ME/kg. Data were collected on feed intake, live weight gain and body morphometric indices. The findings of the study revealed that dry matter intake, live weight gain and growth rate increased with increasing energy level (P 0.05). Relationship between the body measurements and initial live weight of the animals was not significant (P> 0.05). Except for knee to floor and hock to floor heights, live weight and body measurements of the animals were highly significant with the final live weight (P<0.01). It was concluded that the optimum energy level for body gain and growth rate of sheep is 2200kcals ME/ kg.

Measurement and error of hoof horn growth rate in sheep

SUMMARYDetermining the rate of hoof horn growth in sheep is important for understanding the physiology and pathology of the foot and the impact of the environment and the treatment of diseased feet on foot health. It could lead to improved understanding of the interaction between hoof horn and pasture/barn floor characteristics and in methods for prevention and treatment of ovine foot diseases. In the current study, the hoof horn was measured using a previously tested protocol on all eight digits of 21 healthy yearling mule ewes on a farm in North Wales on four occasions over a period of 53 days. The mean hoof horn growth rate was 0·11 mm (s.e.m. 0·02) per day; the residual error variance was 0·024 and the R2 was 0·245. There were no significant differences between hoof horn growth rates in front and hind feet or between medial and lateral claws or over time.

Transient high glycaemic intake in the last trimester of pregnancy increases offspring birthweight and postnatal growth rate in sheep: a randomised control trial.

ObjectiveInvestigate the effect of transient hyperglycemic intake (analogous to snacking on high glycaemic foods) in the third trimester of pregnancy on offspring birthweight and subsequent growth in sheep.DesignRandomised trial.SettingUniversity research farm.SampleThird trimester pregnant ewes.MethodsEwes were blocked on weight, age and litter size and were randomly assigned to receive oral administration of 100 ml of propylene glycol (PG; n = 51) or 100 ml of water (control, C; n = 53) twice/day. Twice during treatment, 12 ewes from each group were selected and blood samples collected to determine the glucose and insulin response to treatment.Main outcome measuresAt birth, blood was collected from the lambs, their body dimensions measured and body weights recorded at 0, 6 and 12 weeks of age after which lambs were slaughtered when they reached 40 kg live weight.ResultsAdministration of PG elevated (P < 0.05) plasma glucose and insulin concentrations for 2 hours post administration compared with control ewes. Lambs (C: n = 80; PG: n = 70) born to ewes fed high glycaemic meals had higher birthweights (C: 5.01 ± 0.18 kg; PG: 5.27 ± 0.22 kg, P = 0.032), plasma glucose concentrations (P = 0.001) and ponderal index (weight/height3, P = 0.043) and reached a similar (P > 0.05) slaughter carcass weight (C: 20.0 ± 0.51 kg; PG: 20.6 ± 0.55 kg) at an earlier age (PG: 166.0 ± 13.2; C: 183.4 ± 13.8 days, P = 0.039) compared with control lambs.ConclusionsTransient high glycaemic intakes in the third trimester of pregnancy resulted in heavier offspring at birth that had faster growth rates in early postnatal life. This animal model is relevant for studying the relationship between maternal diet, fetal size and the risk of childhood obesity.

A model to account for the consequences of host nutrition on the outcome of gastrointestinal parasitism in sheep: model evaluation

This paper describes sensitivity analyses and expectations obtained from a mathematical model developed to account for the effects of host nutrition on the consequences of gastrointestinal parasitism in sheep. The scenarios explored included different levels of parasitic challenge at different planes of nutrition, for hosts differing only in their characteristics for growth. The model was able to predict the consequences of host nutrition on the outcome of parasitism, in terms of worm burden, number of eggs excreted per gram faeces and animal performance. The model outputs predict that conclusions on the ability of hosts of different characteristics for growth to cope with parasitism (i.e. resistance) depend on the plane of nutrition. Furthermore, differences in the growth rate of sheep, on their own, are not sufficient to account for differences in the observed resistance of animals. The model forms the basis for evaluating the consequences of differing management strategies and environments, such as breeding for certain traits associated with resistance and nutritional strategies, on the consequences of gastrointestinal parasitism on sheep.

Genetic Parameters of Growth Traits in Crossbred Sheep

Data spread over 11 years (1986-1996) pertaining to a synthetic population developed by inter se mating of half-breds of Corriedale and Russian Merino with Nali maintained at CCS Haryana Agricultural University, Hisar were utilized for the estimation of genetic parameters for growth traits. The means for birth weight (BWT), weaning weight (WWT), six month body weight (SWT), yearling weight (YWT), preweaning daily gain (PRW) and post weaning daily gain (POW) were 3.35 kg, 10.79 kg, 13.28 kg, 18.96 kg, 82.6 gm and 27.6 gm, respectively. The effects of year and season of birth and sex of lamb were significant for all the traits under study except the effect of season of birth for WWT, SWT and PRW. No definite trend was observed over the years for the averages of body weight and gain. Lambs born during the spring season performed better for BWT, WWT and PRW while the performance of lambs born during autumn was better for the other traits included in the study. The male lambs were heavier than the females for body weight at all stages and gain in weight. The heritability estimates for WWT and PRW were low; for BWT and SWT were moderate and for YWT and POW were high. Birth weight had high heritability and high genetic correlations with subsequent body weights and gains but due to the presence of a maternal effect on BWT and WWT, a sequential selection procedure is recommended for the improvement of growth rate in sheep.

Strip grazing to control wool growth rate of sheep grazing green annual pastures

We compared strip grazing (SG) as a means of controlling wool growth rate, reducing variation in fibre diameter along the staple, and of carrying more Merino sheep through winter on green annual pastures, with set stocking (SS) in 3 experiments. In experiments 1 and 2, SG involved grazing to a residual feed on offer (FOO) of 400 kg DM/ha with an estimated intake of about 0.8 kg DM/day for each sheep. Treatments commenced after pasture establishment in autumn–winter, with both treatments stocked at 20 wethers/ha until late spring. During spring, average liveweight changes were lower (P&lt;0.01) under SG than SS (55 v. 153 g/day experiment 1; –16 v. 217 g/day experiment 2). Strip grazing, compared with SS, reduced (P&lt;0.01) the variation in wool growth rate and fibre diameter along the staple leading to lower (P&lt;0.01) clean wool weights (3.54 v. 3.94 and 2.97 v. 4.12 kg), but finer (P&lt;0.01) (20.9 v. 22.0 and 19.5 v. 21.5 mm), stronger (P&lt;0.01) (28.6 v. 25.3 and 39.9 v. 35.5 N/ktex) wool. However, there was also an increase in vegetable matter content of the wool. The effects on annual pastures were to increase grass (79 v. 48 and 59 v. 25%) and reduce legume (12 v. 36 and 22 v. 54%) content at the end of spring. In experiment 3, two strip grazing treatments were used: SGl with a residual FOO of about 400 kg DM/ha and a stocking rate of 28 wethers/ha; and SGh with a residual FOO of about 800 kg DM/ha and stocking rate of 14 wethers/ha. The stocking rate for SS was 12 wethers/ha. SGl, following an autumn deferment, enabled a stocking rate of 28 wethers/ha to be sustained through winter without supplementary feeding. This is substantially higher than the district average stocking rate of about 7 sheep/ha. Strip grazing reduced (P&lt;0.01) liveweights at the completion of treatments (SGl 41.9 v. SGh 47.9 v. SS 60.3 kg), reduced (P&lt;0.01) clean wool weights (3.40 v. 3.72 v. 4.54 kg) and mean fibre diameter (19.1 v. 19.0 v. 20.9 m), but increased staple strength (21.3 v. 19.0 v. 16.9 N/ktex). These results are discussed in relation to opportunities to utilise strip grazing in sheep production systems on annual pastures in south-western Australia.

Straw degradability as a predictor of intake and growth rate in sheep

AbstractThe dry-matter (DM) intake and growth rate in male lambs were predicted from rumen degradability characteristics, rumen DM losses at different times, neutral- or acid-detergent fibre (NDF or ADF) contents and DM apparent digestibility of roughages. Four different straws consisting of wheat, barley, oat and rice were each offered ad libitum to 24 Merino male lambs with 200 glday concentrate for 4 weeks to determine DM intake and growth rate. Apparent digestibilities of the straws were measured with three Merino male sheep. Measurements were made during the last 10 days of each 20-day period. The degradation characteristics of the straws were measured by incubating samples in nylon bags for 8, 16, 24, 48, 72 and 96 h in the rumens of three Merino male sheep fitted with rumen cannulae. The exponential model p = a + b(l - er^) was fitted to the data. Potential degradabilities of DM (defined as a + b) and apparent digestibilities of DM ranged from 530 to 679 and 440 to 560 g/kg, respectively. The mean DM intake of the straws varied from 543 to 745 glday, the digestible DM intake from 236 to 417 glday and growth rate from 17 to 95 glday. Using the degradation characteristics A, B and c in a multiple regression analysis, the correlation coefficients with DM intake and growth rate were 0·79 and 0·70, respectively. NDF and ADF were related to DM intake (i = 0·65; r = 0·64) and growth rate (r = 0·55; r = 0·56). The correlation coefficient between DM apparent digestibility and DM intake was 0·76. It is concluded that the rumen degradation characteristics have potential for predicting intake of straws and growth rate in sheep.

The production of transgenic domestic livestock: successes, failures and the need for nuclear transfer

The direct transfer of recombinant DNA to embryos is conceptually a powerful method for the manipulation of the genetic potential of domestic animals, but in practice the technology has yet to fulfil its promise. In this paper, two examples are given of research utilising direct genetic manipulation, both of which are aimed at increasing aspects of productivity in sheep. The first of these involves the modification of the growth hormone status of sheep by the use of the ovine growth hormone gene, the regulation of which has been altered by the use of an ovine metallothionein promoter. While there has been a large amount of research already conducted in this area by many groups, our recent results provide one of the first demonstrations that this approach can increase the growth rates of sheep while maintaining the animals in good health. The second project involves the modification of intermediary metabolism in sheep by the introduction of the cysteine biosynthetic pathway. The results to date demonstrate that it is possible to change intermediary metabolism in animals using our approach but that there are species-specific requirements that must be satisfied in order to make the approach a practical method for improving animal productivity.

Sesbania and lablab supplementation of oat hay basal diet fed to sheep with or without maize grain

This study investigated the effects of supplementing oat hay (OH; milk stage at harvest) with 250 g (as-fed) of either lablab ( Dolichos lablab, 50% flowering at harvest) hay or sun dried leaves of sesbania ( Sesbania sesban) with or without 91 g dry matter (DM) of crushed maize grain on rumen pH and ammonia concentration (RAC), intake, degradability, rumen particle passage rate ( k1) (in Experiment 1), digestibility, microbial N synthesis and live weight gain (LWG) (in Experiment 2). A randomized complete block design with a 2 × 2 factorial structure was used in both experiments. In sacco DM and N degradabilities of the feeds were also determined in three sheep. Sesbania degraded faster and to a greater extent than lablab DM. Lablab N was more soluble than sesbania N. Maize-free diets of sesbania and lablab had similar k1 but k1 was lower ( P < 0.05) for lablab than for sesbania in the presence of maize. No other effect of forage legume by maize grain interaction was significant. Crushed maize grain induced lower ( P < 0.05) pH, tended to depress the rate of OH degradation by 23%, depressed ( P < 0.05) hay intake, increased the intake of DM ( P < 0.05) and N ( P < 0.001) and the growth rate of sheep ( P < 0.05) but had no effect on the digestibility (DM, OM, neutral detergent fibre (NDF) or N) and microbial N synthesis. Multiple regression analysis indicated pH ( P < 0.03) but not RAC ( P > 0.05) affected the rate of OH degradation. Sesbania sustained higher ( P < 0.001) RAC, lower ( P < 0.05) potential degradability of OH and higher intakes ( P < 0.01; OH, DM and N), N digestibility ( P < 0.05), N retention ( P < 0.01) and microbial N synthesis ( P < 0.07) than lablab. Sesbania and lablab diets had similar rates of OH degradation, digestibility (DM, OM or NDF) and LWG. It was concluded that sesbania promoted higher OH intake and tended to increase ( P < 0.08) microbial N supply but had no effect on LWG. Maize grain tended to depress OH degradation rate but promoted faster LWG.

Growth performance and plasma insulin-like growth factor I concentrations in sheep selected for high weaning weight1

A study was undertaken to determine the effect of selection for high weaning weight on concentrations of plasma insulin-like growth factor I (IGF-I) in sheep and to evaluate the usefulness of measuring IGF-I as an aid in identification of genotypes with a higher growth potential. Lambs from two lines selected for high 120-d weight (HW and DH) and an unselected control (C) were weighed and blood samples collected monthly from birth to weaning (4 mo. of age). A clear differentiation in size occurred after 1 mo of age between lines, between sexes, and between singles and twins. At weaning, selected lines were 3.8 and 5.0 kg heavier than controls. Plasma IGF-I concentrations were 1.5 to 2 times higher (P less than .001) in males than in females after 1 mo of age. There were no significant differences in IGF-I concentration between lines or types of birth. However, line DH and single lambs on average had higher concentrations of IGF-I. Within sex and type of birth correlations between IGF-I concentrations at 0, 1, 2, 3, and 4 mo and 4-mo BW ranged from -.16 to .49 in the three lines, and most were not significant. Coefficients of variation for IGF-I concentrations (36 to 50%) were two to three times higher than those for BW (11 to 15%). Due to the high variability of IGF-I measurements, the low correlations between IGF-I concentration and BW, and the small differences in IGF-I between control and selected lines, measurement of plasma IGF-I is unlikely to be an effective aid to selection for growth rate in sheep.

Measurement of plasma osteocalcin in sheep: assessment of circadian variation, the effects of age and nutritional status and the response to perturbation of the adrenocortical axis

An assay for plasma osteocalcin (BGP) in ruminants is described. Satisfactory cross-reaction was obtained for bovine BGP in several species, namely ovine, cervine, caprine and human. Sample stability at room temperature, after freezing and thawing and after lyophilization and reconstitution is described. Sheep of both sexes have been used throughout and no significant sex effect has been noted. A series of experiments showed a lack of circadian rhythm of plasma BGP concentration in sheep. Plasma BGP values from sheep ranging in age from 0.25 to 7 years fell exponentially from 300 ng/ml at 0.25 years to approximately 50 ng/ml at 1.25 years of age where it remained until the end of the study at 7 years. Long-term administration of adrenocorticotrophic hormone (ACTH) depressed plasma BGP concentrations, although plasma BGP levels were not affected sufficiently by short-term administration of ACTH to increase plasma cortisol concentrations 10-fold during a period of 4 h. It was confirmed that dietary phosphate deficiency depressed plasma BPG concentrations. It is concluded that neither circadian variation nor the short-term stress of handling and bleeding untrained animals need be considered in sampling sheep for measurement of plasma BGP concentration and that the change with age reflected the pattern of development of skeletal maturity in sheep. Values in both growing and mature sheep were at least 6 times higher than in human subjects, which may reflect the 10-fold higher skeletal growth rate in sheep than in humans. This high skeletal activity in sheep may have been selected for in the development of highly productive breeds.

A note on the effects of health environment on heterosis for growth rate in pigs

Heterosis for growth rate in pigs is usually expressed, and reviews of European and North American studies have been given by Sellier (1976) and Johnson (1981). Kennedy and Moxley (1980) observed heterosis of 0·044 to 0·067 for weight at 154 days and attributed some of the crossbred advantage to heterosis for resistance to atrophic rhinitis. Similarly, McGuirk, Bourke and Manwaring (1978) attributed some of the heterosis for growth rate in sheep to heterosis for resistance to pneumonia. Although little attention has been paid to interactions between heterosis and health environment, Barlow (1981) concluded from an extensive review of studies involving farm and laboratory animals that heterosis is environment dependent and is enhanced by increased stress. Sellier (1976) commented that it would be useful to examine the degree of heterosis with ‘specific pathogen free’ pigs raised in a healthy environment, and this study examined heterosis for days to 90 kg in Yorkshire × Landrace pigs under three different environments with respect to health conditions.

Growth Hormone-Releasing Factor Effects on Pituitary Function, Growth, and Lactation

Growth and lactation are complex processes controlled by several metabolic hormones such as insulin, glucagon, and thyroid hormones but most notably growth hormone. Growth hormone secretion is regulated by two hypothalamic hormones, somatostatin, an inhibitory regulatory factor, and growth hormone-releasing factor. The quantity and pattern of growth hormone secretion is ultimately regulated in concert by the secretion of both regulatory factors from the hypothalamus through the hypothalamo-hypophyseal portal system, where they exert their actions at unique pituitary receptors. Because the potential use of exogenous growth hormone administration for the stimulation of growth efficiency and lactation has been demonstrated, recent efforts have been directed toward the enhancement of production through manipulation of endogenous growth hormone secretion via its releasing factor. Thus far, releasing factor-stimulated growth and lactation has not been achieved to the same extent as that of exogenous growth hormone. Growth hormone-releasing factor has stimulated growth in two growth hormone-deficient children, as well as female, but not male, rats. Although all food-producing species tested to date respond to growth hormone-releasing factor with the appropriate growth hormone response, continuous or pulsatile administration of releasing factor has not resulted in increased growth rate in sheep, chicks, or hogs. Despite levels of circulating growth hormone that would be expected to produce a 30% increase in milk production if given exogenously to dairy cows, releasing factor-stimulated growth hormone secretion has resulted in only a 3 to 9% increase. It is clear from these studies that further developments are necessary to demonstrate the practical application of growth hormone-releasing factor.

Rumen fermentation pattern, postruminal protein flow and wool growth rate of sheep on a high-barley diet

Variations in the wool growth rate of sheep fed diets containing cereal grains were investigated. In experiment 1, eight sheep consuming similar quantities of a pelleted diet of barley grain and lucerne chaff (60:40 by weight) were selected for high (n = 4) or low (n = 4) wool growth rate. These wool growth differences were eliminated by feeding a high-protein, predominantly roughage diet. Subsequent reintroduction of the high-grain diet regenerated wide between-sheep variance, but there was little evidence of repeatability of performance on this ration. These variations in wool growth were examined in experiment 2 in terms of rumen fermentation pattern and postruminal protein flow. Ten sheep with simple cannulae in the rumen and abomasum were given a pelleted lucerne chaff diet for 14 weeks and the high-grain diet of experiment 1 for a further 16 weeks. The variance of all measured characters was low on the lucerne diet, but the high-barley diet generated wide variance in rumen fermentation pattern, protein flow from the rumen and wool growth rate. Fermentations characterized by high ammonia level, high minimum fluid pH and high butyrate molar proportion were associated with high urinary nitrogen output, high diet digestibility and low postruminal protein flow. Wool growth rate was closely related to protein flow on the high-grain diet alone (r2 = 0.77, P &lt; 0.01) and for the high-grain and lucerne diets considered together (r2= 0.86, P &lt; 0.001).

Effects of pasture type on the growth and wool production of weaner sheep during summer and autumn

The productivity of weaner sheep grazing lucerne, white clover, red clover or Persian clover and pastures sown with subterranean clover and perennial ryegrass, cocksfoot or tall fescue, was measured in summer-autumn trials incorporating four soil types in each of three years. During summer and autumn, the mean growth rate of sheep grazing lucerne, white clover or Persian clover pastures was 50 g/d compared with 1 g/d for sheep grazing perennial grass-subterranean clover pastures. Sheep grazing strawberry clover on reclaimed swampland, and sheep in a feedlot (fed hay and lupin grain) averaged 100 and 75 g/d, respectively. Sheep grazing red clover averaged 45 g/d over years 1 and 2. In year 2, a subterranean clover-dominant pasture was included in the study. Its feeding value was similar to that of the perennial grass-subterranean clover pastures. Sheep grazing legume pastures, and sheep in the feedlot, consistently produced more wool (up to 700 g/head) than sheep grazing the perennial grass-subterranean clover pastures. The concentration of neutral detergent fibre in herbage from legume pastures was frequently lower (P&lt; 0.05) and the concentration of crude protein was frequently higher (P&lt; 0.05) than in herbage from grass pastures. The dry matter digestibility of legume herbage was higher (P&lt;0. 05) than that of grass herbage on only one occasion. Measurements of crude protein and neutral detergent fibre of pasture in December accounted for 67% of the variation in liveweight gain (P&lt;0.01). Ewe weaners grazing red clover pasture exhibited an increase (P&lt; 0.05) in teat length of 3.9 mm in 21d of grazing. Oestrous activity of ewe weaners was related to liveweight gain (r = 0.77). The implications of the results for agricultural systems are discussed.

The growth of weaner sheep on clover or grass pastures during summer in Western Victoria

Three pasture types were grazed by weaner sheep during two summers in the Western District of Victoria: (1) dried off grass-subterranean clover pasture (DP); (2) dried off pasture with a higher subterranean clover content (SUB); and (3) pasture with a high proportion of green strawberry clover. Additional treatments during the first summer included sheep grazing DP and fed a supplement of subterranean clover hay (80% clover) or grass hay (77% grass). Further information was obtained by feeding both hays to penned sheep. The digestibility of the SUB pasture declined between early and mid-summer, crude protein content remained constant and neutral detergent fibre content increased markedly. During both summers, the average growth rates of sheep grazing strawberry clover, SUB or DP were 106, 12 and -2 g/d, respectively. In the first summer, supplements of clover hay and grass hay significantly increased the growth rates of weaners on DP by 39 and 44 g/d, respectively. Sheep supplemented with clover hay or grass hay during the first summer grew 0.44 and 0.28 kg more wool, respectively, than unsupplemented sheep grazing DP. In the winter and spring following both summers, poorly grown sheep showed compensatory growth sufficient to make up for lack of growth during summer. Conservation of subterranean clover dominant pasture as hay, and feeding it as a supplement in summer, appears a more effective means of improving the growth and wool production of weaner sheep than simply grazing the mature plant in situ. However, there would be a much greater potential for improvement if a legume that remained green throughout the summer could be found to substitute for subterranean clover.

Nutritional and Placental Determinants of Foetal Growth Rate in Sheep and Consequences for the Newborn Lamb

New techniques now permit the growth rates of individual foetal sheep to be monitored throughout the last half of pregnancy. Changes in foetal growth rate in ewes given a variety of nutritional treatments indicate a far greater foetal sensitivity to maternal underfeeding than had been suspected previously. Placental weight varies widely in uniformly treated ewes and much of this variation remains unexplained. It is shown that the importance of the placenta as a determinant of foetal growth rate has been greatly underestimated and that the survival of the foetus is jeopardized more by a small placenta than by maternal underfeeding. The implications for the newborn of the biochemical and physiological changes which accompany foetal growth retardation caused by different types of maternal underfeeding and by the presence of a small placenta are described and some practical measures which may improve the survival and growth of lambs are outlined.