No abstract

ExtractFive hundred low birth weight children and 492 full-term infants were seen when approximately 40 weeks of age for a pediatric-neurologic examination. Of these, 822 provided the data upon which this report is based. To each child, when eight to ten years of age, there was administered ten subtests of the Wechsler Intelligence Test for Children (WISG), the Bender Gestalt Test and the Wide Range Reading and Spelling Achievement Test. In addition, observations were recorded regarding speech articulation and complexity of grammar. The number of perseveration instances and indications of possible comprehension aphasia observed during the examinations were recorded. The Verbal IQ_, Performance IO_ and Full Scale IO_ scores, as well as the independently obtained Bender Gestalt score, showed increasing impairment with decreasing birth weight. Approximately twice as large a proportion of low birth weight children as of control children fell into the IO_ category (50-79) which is associated with special medical or educational needs. At the ages of six to seven years the results of the Stanford-Binet Test showed an IQ, difference between the low birth weight and full-sized groups of 3.4 points (F = 7.77, 3 and 810 df, p < 0.001), whereas the WISG given at the ages of eight to ten years indicated an IO_ difference of 4.9 points (F = 10.87, 3 and 810 df, p < 0.001) for the same samples of children. Of the twenty psychological measures used to assess development of those who had been premature, relative impairment on 16 were significantly associated with birth weight and one was nearly so at the 0.05 level of significance. When the effect of the presence of indicators of possible neurologic abnormality was removed by analysis of covariance, the statistical significance of the association with birth weight was reduced for each of the variables measured, and only six of the twenty remained with significant assocation. SpeculationFuture research might profitably consider whether performance by adolescents of low birth weight is relatively impaired in scholastic situations. Also, recent research suggests that a low birth weight occurring in conjunction with long gestational periods, may significantly prejudice intellectual capacity. However, there are little longitudinal data regarding this.

The incidence of lamb mortality from birth to 8 months of age has been studied over a 6-year period in an upland, grassland flock of sheep comprising the Scottish Blackface, Cheviot and Welsh Mountain breeds and the crosses among these breeds. Each breed and cross-bred type was maintained at varying levels of inbreeding. Approximately half the lambs which died were stillborn or dead on the day of birth, nearly 40 % died thereafter but before weaning and about 10% after weaning.Post-mortem examinations on 586 of the 632 lambs which died from among the 2453 born attributed death on average to two causes per lamb. Approximately 11 % of the causes were stillbirths or delayed births; 11 % were cases of dystokia; congenital defects of various types accounted for about 10% of the causes; 25% made reference to weakly lamb, exposure or starvation; 14% to infectious diseases and 16% to noninfectious diseases. The extent to which causes of death occur together is examined.Breeds differed in mortality rate with the Welsh the lowest and Cheviot the highest. Cross-breds were better than the average of the pure breeds but this advantage emerged only in the period between 3 days and. 6 weeks of age. Inbreeding, both of dam and of lamb, increased mortality. Lambs from dams which were crosses of inbred lines had the best survival. Litter size, type of rearing, parity of dam, sex of lamb and birth weight also had significant effects on mortality rate. INTRODUCTION describe breed differences in relation to specific causes of death. Many studies of sheep flock performance provideThe present study was initiated primarily with information on the incidence of lamb mortality in the latter end in view: to document the lamb different countries and farming circumstances and mortality rate in relation to three breeds and their at different periods between birth and weaning, crosses kept together as a single flock and also subSome describe the effect of factors such as number jected to intense inbreeding. The effects of breed, of lambs born, parity, management, nutrition and cross-breeding and inbreeding were further studied other environmental variables and a smaller number m relation to the causes of death as identified at of papers present information on causes of death, post-mortem examination. Other factors affecting Although these reports encompass many breeds and variation in overall mortality and the incidence of crosses of sheep, only a few can be interpreted as different causes are also examined, showing whether genetic variation contributes sigAn early finding in this flock was that both breed nificantly to lamb survival and even fewer papers a n d breeding system affected overall lamb mortality

Changes in Cu concentration in the livers of adult Scottish Blackface (B), Welsh Mountain (W) and B x W ewes fed diets containing 4, 9, 17 and 29 mg Cu/kg D.M. were measured over a 28-week period. Measurement continued during two further periods of 18 weeks when first all sheep were fed the diet containing 4 mg Cu/kg D.M. and finally, when 4 mg Mo/kg D.M. was added to this diet.During the first period the increase on all diets was least in B ewes and, apart from the 4 mg Cu/kg D.M. diet, greatest in W ewes; this difference increased as the Cu in the diet increased. The rate of increase for all ewes diminished towards the end of the period. All breed types retained proportionately less Cu in their livers as the Cu in the diet increased; at one extreme B ewes fed 17 or 29 mg Cu/kg D.M. retained equal amounts.When during the second period all sheep were fed the 4 mg Cu/kg D.M. diet the Cu concentration in their livers decreased, the rate of decrease being greatest for ewes whose mean concentration in the liver was highest, but at similar concentrations the decrease was greater in B than W ewes. During the final period the decrease was faster and was again associated with the mean Cu concentration, but the decrease was not significantly affected by breed.Throughout the trial, W ewes had the highest concentration of Cu in their plasma, whilst B ewes and ewes fed the 4 mg Cu/kg D.M. diet throughout had the lowest concentrations both in plasma and in their kidneys at slaughter.The results show that breeds differ in their ability to retain Cu from the diet in their livers. The magnitude of these differences depends on the intake of Cu and Mo from the diet and is affected by the concentration of Cu in the liver. Breed differences in the absorption and endogenous loss of Cu are suggested.

Sheep of three hill breeds, Scottish Blackface, Cheviot and Welsh Mountain and the reciprocal crosses among these breeds were inbred (mostly by parent × offspring mating) for four generations to five levels with inbreeding coefficients ofO, 0·25 (I1), 0·38 (I2), 0·50 (I3) and 0·59 (I4). Inbred females were also mated to unrelated inbred males of the same breed type to produce line crosses (LC). Each type of dam (except LC and I4) was mated to produce lambs of up to three different inbreeding levels thus allowing the effects of the individual's own inbreeding to be separately assessed from the effects of maternal inbreeding. This study examined body weight at a sequence of ages from birth to 4 years of age with 2369 animals (ages up to 78 weeks old) or 1062 animals (2 to 4 years old) contributing to the analyses.Inbreeding of the individual had a highly significant retarding effect on body weight and growth rate up to the I2 level for weights of lambs up to 24 weeks old, with a slight recovery in performance thereafter. For the later ages examined, the maximum depression was reached at the I3 stage. The partial recovery in performance at the higher levels of inbreeding for lambs less than 24 weeks of age was also noted within lines and did not therefore appear to arise only from a loss of lines as inbreeding proceeded. The effect of dam's inbreeding was to depress growth up to the I3 level and at most ages up to I4. Line-cross lambs were generally heavier (but not significantly so) than non-inbred (F2 and the pure equivalent, O2) and progeny of line-cross dams were similar in weight to those from other non-inbred (F1, or F2 and O1, or O2 dams) or slightly better. The more highly inbred the individuals the more, in general, they fell behind the weights of the corresponding non-inbreds as they grew older. Inbreeding may thus have permanently stunted the sheep.There were no significant differences between purebred and crossbred sheep in the rate of inbreeding depression. Only at the ages of 3 and 6 weeks was there a significant difference between the three pure breeds in the changes in weight attributable to inbreeding. Up to the age of weaning (15 weeks) the changes with inbreeding of individuals could not be explained statistically in terms of dominance effects alone and non-allelic interactions may therefore also be involved. At all ages the effect of inbreeding of the dam was consistent with dominance effects alone.

The influence of maternal and genetic factors on the size of lambs at birth and on their gestation length has been studied from the results of two experiments involving the transfer of fertilised eggs from one breed of sheep to another. In the first experiment, eggs were transferred reciprocally between old ewes of the large Lincoln breed and of the small Welsh Mountain breed. Results are based on 20 transfer lambs and 14 normally born singles. In the second experiment, 35 pure Lincoln and 28 pure Welsh lambs were born as a result of transferring eggs into 18-month-old nulliparous Scottish Blackface sheep.The breed type of the lamb was found to be the most important factor influencing weight and cannon length at birth, although maternal-foetal interactions were present. As the maternal environment became poorer, genotypic differences remained distinct but decreased in magnitude. The maternal environment provided by 4th parity Lincoln ewes, if judged by lamb's size at birth, was better than that provided by 4th parity Welsh ewes, and this in turn was better than that provided by 1st parity Blackfaces. Lincoln and Welsh lambs in the same maternal environment differed in average birth weight by 5·7, 3·8 and 3·0 1b. respectively in the Lincoln, Welsh and 1st parity Blackface maternal environments. Lincoln and Welsh lambs, each in their own normal maternal environment, differed by 6·5 lb. The maternal influence on cannon length was similar but small. Gestation length of Lincoln lambs in Welsh recipients was almost 4 days shorter than that of Welsh lambs in Lincoln recipients. In the Blackface maternal environment, Lincoln and Welsh lambs differed little in gestation length but males were, on average, carried about a day longer than were females.At the individual level, weight of (Blackface) recipient ewe had a somewhat greater effect on lamb's size than had weight of (Lincoln or Welsh) donor ewe. The magnitudes of these ‘genetic’ and ‘maternal’ effects were comparable with those found at the level of group means; even so, donor's and recipient's weight together accounted for only a small part of the individual variation in lamb's size about the group means.It was concluded that a ewe was able to respond to progressively greater demands made by a lamb or lambs of progressively larger (combined) potential size—but in accordance with the law of diminishing returns—and that the upper limit of maternal accommodation must be considerable. By contrast, the upper limit of mean genetic size at birth appears to be not far above the mean size of single lambs born to their natural mothers in good condition. A model has been constructed from which mean birth weight of lambs can be predicted.

1. Data are presented on variation in age at eruption of permanent incisor teeth in one-egg (MZ) and two-egg (DZ) twins and in pairs of half sisters (HZ). The 1st pair of incisors erupted when animals were on average 100 weeks old and the other three pairs came at roughly 26-week intervals thereafter. Variation in age at eruption increased from 1st to 4th incisors, but the coefficient of variation remained constant at about 8%. The mean interval between eruption and complete emergence was about 5 weeks for the first three pairs of teeth and nearly 10 weeks for the 4th pair.2. Variation in age at eruption within MZ pairs was no greater than that between left and right sides of the same animal. DZ displayed greater within-pair variances than MZ twins, and HZ pairs greater than DZ.3. Correlations of age at eruption of teeth with body weight and with gain in weight were negative but non-significant. Age at eruption of 1st and of 3rd teeth was positively correlated with age at 1st and 2nd calving, but eruption of 2nd and of 4th teeth was not.4. For 2nd, 3rd and 4th incisors, the intra-pair variance of the HZ group was in excess of that expected. This can be interpreted to mean that the estimates of environmental and genetic variation derivable from MZ and DZ pairs are not adequate to account for all the variation within HZ pairs.

THE purpose of this paper is to compare female sheep of five breeds (Scottish Blackface, Cheviot, Welsh Mountain, Lincoln Longwool and Southdown) which were maintained together as a single grassland flock. Particular interest in this situation is derived from the fact that breed differences are not confounded with differences of farm environment, at least from the age of six months when the sheep were brought together. In Great Britain, different breeds-and especially hill breeds-are, as a rule, kept in separate regions not merely on separate farms.Female sheep were purchased as lambs in September 1955. At that time the Welsh Mountain sheep were five months old. Birth dates were not known for the Scottish Blackface and the Cheviot lambs but they were born during the lambing period normal for the district, which would make them the same age as the Welsh, viz. five months old. The Southdowns were, on average, about three weeks older and the Lincolns five weeks older.In order to make the sheep as representative as possible of their respective breeds and to obtain, as far as possible, unrelated sheep for the experimental flock, the lambs of each breed were chosen from flocks which were large, using many rams and were 'typical' of their breeds. The Blackfaces and Cheviots were bought in open market and each breed was drawn from four sources, the Welsh were obtained from two flocks in Merionethshire (one belonging to the Animal Breeding Research Organisation), the Lincolns came from two flocks in Lincolnshire and the Southdowns from two flocks in Sussex. The Blackfaces represented an admixture of the Lanark and Newton Stewart strains. The Cheviots were the South Country type.The sheep were brought together to Blythbank, Peeblesshire, a grassland farm at an elevation of around 800-1000 feet. They were run and managed as a single flock throughout their life. They grazed fenced fields and were moved between fields as management required. Supplementary feed (hay and concentrates) was offered only during periods of prolonged snow and for about six weeks prior to lambing. It was observed that all the breeds availed themselves of these supplements. Hardly any segregation of the 177