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Reversible addition–fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are the two most common controlled radical polymerization methods. Both methods afford functional polymers with a predefined length, composition, dispersity and end group. Further, RAFT and ATRP tame radicals by reversibly converting active polymeric radicals into dormant chains. However, the mechanisms by which the ATRP and RAFT methods control chain growth are distinct, so each method presents unique opportunities and challenges, depending on the desired application. This Perspective compares RAFT and ATRP by identifying their mechanistic strengths and weaknesses, and their latest synthetic applications. Reversible addition–fragmentation chain-transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) are evaluated in terms of their mechanistic strengths and weaknesses, versatility and latest synthetic advances.

Aromatic foldamer based networks are developed, where the foldamer unit acts as a molecular spring. Energy dissipation increases with the number of turns in the foldamer, consistent with mechanical unfolding of the molecular spring.

Reversible addition-fragmentation chain transfer (RAFT) polymerization is one of the most powerful reversible deactivation radical polymerization (RDRP) processes. Rate retardation is prevalent in RAFT and occurs when polymerization rates deviate from ideal conventional radical polymerization kinetics. Herein, we explore beyond what was initially thought to be the culprit of rate retardation: dithiobenzoate chain transfer agents (CTA) with more active monomers (MAMs). Remarkably, polymerizations showed that rate retardation occurs in systems encompassing the use of trithiocarbonates and xanthates CTAs with varying monomeric activities. Both the simple slow fragmentation and intermediate radical termination models show that retardation of all these systems can be described by using a single relationship for a variety of monomer reactivity and CTAs, suggesting rate retardation is a universal phenomenon of varying severity, independent of CTA composition and monomeric activity level.

We report herein a highly efficient Cu-catalyzed protocol for the conversion of aliphatic carboxylic acids to the corresponding difluoromethylated analogues. This robust, operationally simple and scalable protocol tolerates a variety of functional groups and can convert a diverse array of acid-containing complex molecules to the alkyl-CF2H products. Mechanistic studies support the involvement of alkyl radicals.

This experiment, conducted in the humid lowland tropics of North Sumatra, Indonesia involved 132 young Sumatra (S); Virgin IslandSumatra (HC); and Barbados BlackbellySumatra (BC) ewes. The ewes were mated with rams of their same genotype and monitored until each ewe had weaned two crops of lambs. Data from 230 lambings and 350 lambs were included in the analysis. Mean ages at first and second lambing were 4653 and 6946 days, respectively. Mean interval between first and second lambings was 2315 days. Mean litter size averaged 1.520.04 at birth and 1.230.04 at weaning. There were no significant effects of genotype on age at lambing, lambing interval or litter size. Overall mean weights of lambs at birth and weaning were 1.810.02 and 9.50.1 kg. Genotype, type of birth and rearing, and sex of lamb affected lamb weights at birth and weaning. S lambs were the smallest (1.3 and 6.9 kg at birth and weaning). HC (1.8 and 9.6 kg) and BC (2.0 and 10.3 kg) were significantly heavier (p

A total of 196 young Sumatra (S) ewes and F1 crosses of S with Java Fat-tail (E1), Virgin Island (H1) and Barbados Blackbelly (B1) were mated with rams of their same breed type. The ewes were first exposed to the ram at 10 or 13 months of age, and reproductive performance was monitored until each ewe had reared two litters. Data from a total of 363 lambings and 563 lambs were included in the analysis. Mean ages at first and second lambings were 516 and 733 days. Litter size at birth ranged from 1 to 5 lambs with a mean of 1.55, and pre-weaning mortality (to 3 months) was 11.7%. There were no significant effects of breed type on age at lambing, lambing interval, litter size or mortality. The mean birth weights of lambs born to the S, E1, H1 and B1 ewes were 1.45, 1.62, 2.03 and 2.10 kg, respectively. Weaning weights averaged 8.5, 9.2, 11.7 and 12.1 kg for the four breed types. The differences among breed types were significant (P < 0.001) except for H1 and B1 which were similar. Litter size affected (P < 0.001) birth weights, weaning weights and pre-weaning mortality. A dam productivity index (DPI) for each ewe was calculated from the total weight of lamb weaned at the first two lambings divided by a measure of age. DPI was affected (P < 0.001) by breed type, and averaged 16.0, 18.1, 21.5 and 24.2 kg for the S, E1, H1 and B1 genotypes, respectively. Average weights of ewes at second lambing were 22.0, 24.4, 27.2 and 28.1 kg for the four genotypes, respectively. Thus, productivity expressed in terms of weight of lamb weaned per unit body weight of ewe was 0.73, 0.74, 0.79 and 0.86 for the S, E1, H1 and B1 genotypes, showing that the hair sheep crossbreds were more productive. DPI was slightly higher for ewes mated at 10 months of age than at 13 months, indicating no advantage in delaying first mating.

Sumatra ewes were mated to give Java Fat-tail crossbred (E1), Virgin Island crossbred (H1) and purebred Sumatra (S) lambs, or were inseminated to give Barbados Blackbelly crossbred (B1) lambs. A total of 882 lambs were born to 407 ewes in 568 lambings. Average litter size was 1.55 and lamb mortality to weaning at 3 months was 22.5%. Weights of lambs averaged 1.83 kg at birth and 8.7 kg at weaning. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. At weaning the average increases in weight of the crossbreds above S were E1 10–13%, H1 14–15% and B1 32%. At 3 months of age all breed groups had similar wool scores, but in older animals the ranking was B1 (least wool) < H1 < E1 < S (most wool).

Production performance of Javanese ewes (483 ewes with 1263 records) in West Java, Indonesia, was evaluated. The focus was on the effect of prolificacy and environmental sources of variation on lamb survival (S) as a ewe trait and on lambing and weaning outputs. Non-carriers (FecJ + FecJ + ), carriers (FecJ F FecJ + ) and homozygotes (FecJ F FecJ F ) for a gene affecting prolificacy, averaged 1.24, 1.95 and 2.59 lambs born, respectively. Prolificacy-year (PY) effects were significant, with FecJ F FecJ F animals being more sensitive to fluctuations. Repeatability for litter size was 0.51 and heritability 0.62. PY, gestation ewe weight gain (EGG) and parity significantly affected S. Singles, twins, triplets and quadruplets averaged 87, 69, 47, and 35% S, respectively, with fewer lambs surviving in these litter size categories in poor years. Repeatability of S was 0.19. Litter weaning weights (TWW) were influenced significantly by PY, parity and EGG. EGG contributed less than litter birth weight to the determination of S and TWW in all litters, although its contribution to TWW was proportionally higher than that to S. Repeatability of TWW was 0.20. Higher prolificacy led to a diminution of the ewe's body resources as indicated by EGG, therefore reducing the ewe's ability to support satisfactory birth weights of lambs and lactation, particularly under poor nutrition. With higher EGGs and survival rates under improved nutrition, a single copy of the FecJ F gene increased the productivity of ewes (TWW) by at least 18%; while under suboptimum nutrition, it had a negative effect. There is a need to investigate the nutritional management of animals having the FecJ F gene since the gene is widely distributed in most Indonesian sheep populations.

A 2-yr experiment was conducted to determine whether isolation of ewes from rams is necessary to achieve a high response to the ram effect and whether ewes respond as well in May as in June. The experiment was conducted at two locations, with the same four treatments at each location. The four treatments differed with respect to ewe proximity to rams before mating (isolated vs adjacent) and date of joining with novel breeding rams (May 15 vs June 15). The proximity treatment at one location was changed in the 2nd yr; teaser rams were joined with the ewes instead of being adjacent to them. Overall, 86% of the eligible ewes were judged to have responded to the ram effect. A period of isolation before mating did not increase response compared with ewes that remained adjacent to, or in contact with, rams (86 vs 85%). Response was greater (P less than .05) in June and in the 2nd yr (P = .05). A physiological response, different from that generally described, was identified. Ewes ovulated approximately 8 d (8.0 +/- .19 d) after joining with breeding rams. The subsequent ovulation, accompanied by estrus, occurred approximately 15 d later (15.3 +/- .29 d). Eighty-five percent (87/102) of the ewes sampled responded in this manner. However, 82% (31/38) of a sample of these ewes had at least one morphologically normal corpus luteum when examined by laparoscopy 4 d after joining. It seems that these corpora lutea were not completely functional with respect to progesterone production. The ram effect can be achieved without prior isolation of ewes from rams.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeatability within and between seasons for ovulation rate, and repeatability for litter size and embryo survival of Sardi (S), 3/4S 1/4D (Sardi backcross), F1, F2, 1/4S 3/4D (D'man backcross) and D'man (D) ewes were estimated by the intra-class correlation method. Within-season repeatability estimates for ovulation rate were 0.24, 0.56, 0.24, 0.29, 0.36 and 0.44 for Sardi, Sardi backcross, F1, F2, D'man backcross and D'man ewes, respectively. The pooled between-seasons repeatability estimates for ovulation rate, litter size and embryo survival were 0.26, 0.22 and 0.02, respectively. These repeatability estimates may be useful in a selection program for the improvement of these traits.

Differences in ovulation rate, embryo survival, litter size, and fertility are presented for four lines of mice that have been selected for growth or are homozygous for a recessive gene (hg) imparting rapid postweaning gain. Two of the lines were hg/hg, one in a growth-neutral and one in a growth-selected background. The remaining two were Hg/Hg (the corresponding normal, dominant allele with no effect on postweaning gain) in the same two backgrounds. Average ovulation rates ranged from 10.9 to 17.1 eggs shed, and litter sizes ranged from 8.6 to 14.0. In the growth-selected background, the hg allele reduced the number of ovulations, implantation, and litter size by nearly three compared with the Hg/Hg controls. The impact of the hg allele in the growth-neutral background was not significant. When males of a different line selected for high litter size were mated to females of the four stocks, more than two additional eggs, implants, and pups were recorded, compared with results of mating to males of the same line as the female.

SummaryEffects of a recessive gene causing high growth (hg) were studied on two major components of the growth axis in mice. Plasma and pituitary levels of growth hormone and plasma levels of insulin-like growth factor I (IGF-I) were measured in three lines homozygous forhg, each compared with a control line of alike genetic background but wild type for thehglocus (Hg). Line Gh (hghg) and line GH (HgHg) are from a line which had undergone long-term selection for high postweaning weight gain; line Ch (hghg) and line CH (HgHg) were extracted from the second backcross of Gh to C57BL/6J; line L54 (hghg) was from the sixth backcross to C57BL/6J (B6) (HgHg). Pituitary GH levels and plasma IGF-I levels were measured in both sexes at 3, 4·5, 6 and 9 wk of age. Plasma growth hormone was measured in 8- to 12-wk-old males at hourly intervals from 08.00 to 17.00. Body weight in lines homozygous forhgat 6 and 9 wk of age was 10–30% greater than in control lines. The ontogeny of this increased growth depended on genetic background. Pituitary growth hormone content was 52% lower in the twohghglines measured (lines Ch and Gh) than in control lines at 4·5, 6 and 9 wk. Plasma growth hormone levels were also much lower inhgmice, with values only 20–30% of those in their respective controls,hglines showed consistently low plasma growth hormone levels throughout the 9 hr sampling period, while control lines expressed the characteristic pulsatile hormone secretion. In contrast, plasma IGF-I levels were greater in line Ch (hghg) than in line CH (HgHg) at 3, 4·5 and 9 wk, and were also greater in line Gh (hghg)vs. line GH (HgHg) at 6 wk of age. The results suggest that the growth enhancing effect of thehggene occurs through an IGF-I-mediated process. In addition, the genetic background itself is also a factor in the phenotypic expression of the gene.

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.

Embryos were collected from 4 lines of Targhee sheep between 1986 and 1990. The lines were selected for preweaning growth rate (Lines DH and HW) or for multiple births (Line HT); Line C served as an unselected control group. Estrus was synchronized using fluorogestone acetate-impregnated vaginal pessaries, and ewes were superovulated with FSH. Embryos at the morula or blastocyst stage were surgically recovered from mature ewes at Days 5 to 6 and were frozen following morphological evaluation. The overall average number of freezable embryos per collection was 2.9, and did not differ significantly among years or among lines. Of the embryos collected between 1986 and 1988, 92 were transferred to 53 recipients in 1989, producing 53 lambs. Survival rates were 60.9 and 47.8%, respectively, for embryos evaluated as good and fair after thawing. Good-quality blastocysts yielded the highest survival rate (64.4%). Analyses indicated no significant effects of line, developmental stage or embryo evaluation on the incidence of lambing. It was concluded that embryos of morula or blastocyst stage can be successfully frozen for extended periods. The data on embryo yield and survival following cryopreservation were used to calculate numbers of donors needed to preserve and reconstitute a population of specified size.

Genetic effects were estimated for growth to 1 yr and viability to 90 d of 882 lambs from a diallel cross of Sardi (S), D'man (D), and D'man x Sardi (DS) male and female parents. Sardi direct genetic effects were significantly higher than those of D'man for weights at birth and up to 2 mo, but the difference decreased thereafter and was in favor of D'Man at 6 mo. Sardi maternal ability was better than that of D'man for weights at all ages. Estimates of individual heterosis were small and negative for weight at birth, weight at 1 mo, and lamb viability and positive for other body weights; the estimate was significant for 12-mo weight. Estimates of maternal heterosis were small and did not approach significance for any trait. Epistatic recombination effects were generally small, but negative for all traits and significantly so for viability to 30 d. In general, the results, combined with those on reproduction and total lamb production of ewes of these groups, reported elsewhere, indicate that a population produced by inter se mating of animals 50% D, 50% S breeding is expected to have higher total lamb production than either purebred.

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.

Data from 364 ewes of Sardi (S), D'man (D), S x DS, DS x S, S x D, D x S (F1), F2, D x DS and DS x D breed groups mated to F1 rams were analyzed for fertility, number of lambs born alive, litter size at weaning, litter weight at weaning per ewe joined and mean lamb weight at 60 d. Each ewe was exposed in two seasons and had one or two lambings. Effects of breed group were significant for all traits. The highest number of lambs born alive and litter size at weaning were recorded in D'man (1.84 and 1.45, respectively) and D x DS (1.81 and 1.43, respectively). F1 ewes (S x D and D x S) had the highest fertility (.94) and litter weight at weaning per ewe exposed (13.8 kg). Mean lamb weight at 60 d was highest for S x DS and Sardi ewes (13.4 kg and 13.2 kg). D'man additive effects were positive and significant for number of lambs born alive, litter size at weaning and litter weight at weaning per ewe joined; were significant but negative for mean lamb weight at 60 d; and were not significant, although positive, for fertility. Significant individual heterosis was found for fertility, litter weight weaned and mean lamb weight at 60 d. Maternal heterosis and direct epistatic recombination effects were small for all traits.

Two different open-circuit techniques of measuring metabolic rate were examined in rats at rest and during exercise. With one technique ambient air was drawn through a tightly fitting mask that was secured to the rat's head, whereas with the other technique the rat was placed into and ambient air was drawn through a Plexiglas box. Two series of experiments were performed. In series I, two groups were studied that consisted of rats that had received myocardial infarctions produced by coronary arterial ligations and rats that had received sham operations. In this series of experiments O2 uptake (VO2) and CO2 production (VCO2) were measured at rest, during four levels of submaximal exercise, and during maximal treadmill exercise in the same group of rats by use of both techniques in random order. VO2, VCO2, and the calculated respiratory exchange ratio (R) were similar at rest, during the highest level of submaximal exercise (20% grade, 37 m/min), and during maximal exercise; however, VO2 and VCO2 were significantly lower with the metabolic box technique compared with the mask technique during the three lowest work loads (5% grade, 19 m/min; 10% grade, 24 m/min; and 15% grade, 31 m/min). These differences appeared to be associated with a change in gait produced when the mask was worn. In series II, the arterial blood gas and acid-base responses to both submaximal and maximal exercise were measured using both techniques in a group of instrumented rats that had a catheter placed into the right carotid artery.(ABSTRACT TRUNCATED AT 250 WORDS)

SUMMARYIn an egg-transfer experiment, seven breeds of sheep differing widely in mean mature ewe weight were used: Oxford Down, 96 kg; Borderm Leicester, 77; Finnish Landrace, 55; Southdown, 52; Tasmanian Merino, 42; Welsh Mountain, 34; and Soay, 22. Body weight and gestation length of recipient ewes are briefly examined. Of 60 recipient ewes, 95% became pregnant. Embryo survival averaged 69% and appeared to be independent of breed of embryo. Litter size of Welsh Mountain, Border Leicester and Finnish Landrace ewes each given four eggs averaged 2·6, 2·9 and 2·9 respectively so that most of the normally observed breed differences are mainly due to differences in ovulation rate. Observed birth weights were in general agreement with those predicted from litter size and donor and recipient ewe weights. The maternal capacity of Finnish ewes was close to average. Litter size affected survival mainly through its effect on birth weight. For Oxford lambs in litters of 3 to 5 from Finnish recipients, birth weight was 42% that of normal single-born Oxfords and only 42% survived. For Soays the corresponding values were 59% for birth weight and 85% for survival. Finnish lambs were exceptionally small at birth but had the highest viability of all breeds. Lamb mortality was higher for males (18%) than females (9%) especially in large litters (26 v. 11%) but about the same in both sexes for Finnish lambs.

Ovulation rate was measured in Barbados Blackbelly (United States strain; B), Targhee (T), Barbados X Targhee (B X T) and Barbados X Dorset-Targhee (B X DT) ewes at first and second estrus following synchronization of cycles early in the breeding season. Body weight at sponge removal differed (P less than .001) between B (30.9 kg) and T ewes (54.9 kg) and was intermediate for B X T (44.9 kg) and B X DT (43.5 kg) ewes. Ovulation rate was higher (P less than .01) at first and second estrus for B (1.86, 2.04), B X T (1.93, 2.04) and B X DT (1.72, 1.80) than for T (1.29, 1.40) ewes. Regressions of ovulation rate on body weight within the breed groups did not differ significantly from each other and the average was significant (b = .049 +/- .014 CL/kg at first estrus and b = .046 +/- .011 CL/kg at second estrus, where CL = number of corpora lutea), but differences between the groups in body weight did not explain the differences in ovulation rate. Litter size for B, B X T, B X DT and T groups was 1.71, 1.84, 1.84 and 1.28, respectively. The B X T ewes were superior to the average of the B and T ewes for ovulation rate (P less than .05) and litter size (P less than .01); there was no direct estimate of embryo survival, but the results indirectly indicate superiority of the crossbreds for this component also.(ABSTRACT TRUNCATED AT 250 WORDS)

SUMMARYMice gaining 3 or more standard deviations above the mean were noted beginning in generation 25 in a line selected for high 21–42 day weight gain. The exceptional growth rate appears to be due to an autosomal recessive gene, based on the following: (1) the exceptional individuals appeared suddenly, in only one of 2 closely related sublines; (2) mating high growth individuals to unrelated, normal size strains produces relatively uniform F1's with mean gains below the mid-parent average; (3) F2's have a distribution markedly skewed towards high gain and a coefficient of variation approximately double that of F1's; (4) true breeding high growth strains can be established in one generation by intermating the largest F2's; (5) intermating normal F2's produces progenies with a distribution similar to the F1except for a few large segregates; (6) high growth segregates have been obtained in F2's from each of 4 successive backcrosses to the C57BL/6 inbred line. The symbolhg(high growth) is proposed for the postulated gene, which appears to be completely recessive. Frequency of positively identified segregates in F2's and backcrosses is on average less than 25 and 50%, due probably to some overlap ofHg- andhghgdistributions. Gain ofhghgindividuals from 21–42 days is 30–50% higher than ofHg- contemporaries; mature weight is also much higher, while 21-day weight ofhghgindividuals in segregating litters is slightly lower. Fertility of homozygotes ranges from normal to as much as 40% lower than for comparableHg- mice;hghgmice are not obese. The gene may provide a useful model for study of regulation of mammalian growth.

Data on four lamb crops in 2.5 years from an experimental flock of sheep established to compare prolific (D'Man) and nonprolific (Sardi) Moroccan breeds of sheep and their crosses are presented. Ovulation rate was recorded following matings of three of four seasons. Mean ovulation rates for ewes 30 months and over were 1.32 for Sardi and 3.18 for D'Man, with 99.7% 1's and 2's in Sardi ewes, and a range of one to seven, with 38% ≥ 4, in D'Man ewes. Prenatal survival was high in both breeds. Pregnant Sardi ewes with two corpora lutea (CL) had a survival rate of 89%, and D'Man ewes had survival rates of 90, 82, 69 and 58% for those with 2, 3, 4 and 5 to 7 CL, respectively. Repeatability of ovulation rate averaged 0.18 for Sardi and 0.29 for D'Man, with corresponding values for litter size of 0.18 and 0.27. Young F 1 ewes produced by mating D'Man rams to Sardi ewes were intermediate between the two parent breeds in ovulation rate, and had high prenatal survival.

Data on four lamb crops in 2.5 years from an experimental flock of sheep established to compare prolific (D'Man) and non-prolific (Sardi) Moroccan breeds of sheep and their crosses are presented. Conception rates, litter size, duration of postpartum anoestrus and age at puberty were recorded. Total productivity was consistently higher in the D'Man breed due to generally higher fertility and higher prolificacy. There were large seasonal variations in fertility of Sardi but not of D'Man ewes. Fertility of Sardi ewes was markedly affected by breed of sire used in mating, D'Man rams inducing a higher proportion of ewes to mate than Sardi rams. However, there was only a small effect of the breed of service ram on synchronization of oestrus. The postpartum anoestrus of D'Man ewes was always short (45 to 60 days) while in the Sardi it varied according to season of lambing, suggesting a winter-spring anoestrus. D'Man ewes had good fertility under one year of age and were close to mature litter size at second lambing at two years of age. Sardi ewes reached puberty at a much later age and did not achieve mature levels of reproductive performance before their third lambing. Ten to 11-month-old ewe lambs and 2-year-old F 1 ewes from Sardi dams were equal to D'Man ewes in fertility. The F 1 's reached puberty slightly later than D'Man but much earlier than Sardi and were intermediate between D'Man and Sardi purebreds in litter size.

The nature of genetic variation in litter size and its components was examined using results of long term selection and of crossing selected lines of mice. Selection for small and for large litters produced strains with mean litter size of approximately 6 and 15, respectively. The large litter size line showed a period of renewed response after 45 generations of selection, following a period of 15 generations with no response. The relative contribution of genotype of the dam and of the embryo to prenatal survival was examined using results of selection, crossing and embryo transfer. Genotype of female carrying the litter was responsible for most of the observed differences. Genes for poor survival expressed by the embryo were present in some strains, but accounted for less variation than did maternal genotype. Information from the selected lines and from crosses among them provided evidence for dominance of genes affecting fertility and prenatal survival and additivity of genes affecting ovulation rate and body weight. The information was used to suggest a model for more effective exploitation of heterosis using breeds or strains of animals of known performance for different components. The extent of genetic variation for prenatal survival suggests that natural selection in this species may not always be for maximum survival. It is suggested that the ability to reduce litter size after conception, in response to nutritional or other stress, may at times be of selective advantage, contributing to maintenance of genetic variation in survival rate.

Concentrations of LH, FSH and prolactin (PRL) were measured by radioimmunoassay throughout pregnancy (day of vaginal plug = day 0) in mice exposed to light for 14 hr (on between 0500–1900 hr). During the preimplantation period an increase in LH occurs, with a peak on day 3. Another peak appears during midpregnancy, with the greatest level of LH appearing on day 10 (37 ± 12 ng/ml). A comparable level was found only on the day of parturition. Levels of FSH were greatest on day 0 and on the day of parturition. FSH concentrations were low (

SummaryA short-term selection experiment was undertaken to estimate the realized heritability for birth weight in mice.A cross of two strains was used as a base population, from which heaviest and lightest birth weight individuals were selected to initiate an up (JU) and a down (JD) selected line. Selection was applied on a within-litter basis for six generations. By the end of the experiment, the two lines differed by 0·20 ± 0·01 g. The heritability, estimated from the regression of cumulative response on cumulative selection differentials and adjusted to that of individual values, was 0·14 ± 0·02. Six-week body weight, averaged over both sexes, was higher in line JU than in JD by 1·0 ± 0·3 g at generation 6. Litter size was higher in line JU in every generation, the regression of the divergence between JU and JD on generation number being 0·13 ± 0·03.

The endurance capacities of rats with myocardial infarctions (MI) and of rats having undergone sham operations (SHAM) were tested during a submaximal exercise regimen that consisted of swimming to exhaustion. During this test, a decrement in the endurance capacity of the MI rat was demonstrated as the SHAM rat swam 25% longer than the MI rat (65 ± 4 vs. 52 ± 4 min). Glycogen concentrations were measured in the liver and the white gastrocnemius, plantaris, and soleus muscles of SHAM and MI rats that were randomly divided into four subgroups, which consisted of resting control, swim to exhaustion, swim to exhaustion + 24 h recovery, and swim to exhaustion + 24 h recovery + a second swim to exhaustion. The results demonstrated that the glycogen concentrations found in the liver, white gastrocnemius, plantaris, and soleus muscles of the SHAM and MI rats belonging to the resting control groups were similar. After swimming to exhaustion the glycogen concentrations in these tissues were significantly reduced compared with those found in the resting control groups of rats, and after 24 h of recovery the glycogen concentrations in these tissues were again similar to those found in the resting control groups of rats. Since the magnitude of the glycogen depletion in the liver and the white gastrocnemius, plantaris, and soleus muscles was similar in the SHAM and MI rats and because the SHAM rats consistently swam for longer periods of time in each of the experimental groups, it would be logical to assume that the rates of glycogen utilization for the various tissues may have been greater in the MI rat during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Summary. Selection for litter size (Line SI) and for post-weaning body weight gain (Line G) increased spontaneous ovulation rate in mature females by 69 and 73%, respectively, over that of randomly bred control mice (Line C). Inbreeding from S1 mice with selection for litter size produced highly inbred lines with elevated ovulation rates. Inbreeding from Line C mice produced a 21% divergence among lines, but did not depress the mean ovulation rate. Crosses of these lines revealed little heterosis in ovulation rate. LH receptors were induced by treating females from 22 days of age with diethylstilboestrol for 4 days and FSH for 2 days. The in-vitro binding of 1 25I-labelled hCG per \g=m\gDNA decreased 56% in response to selection for litter size and increased 57% in response to selection for body weight gain, indicating high susceptibility of this trait to genetic change. Inbreeding from Line C mice produced a 135% divergence amongst lines, but did not depress the mean LH receptor induction. Body weight had significant effects on ovulation rate and LH receptor induction. These results show that selection for litter size and for rapid post-weaning body weight gain increases ovulation rate, but we suggest that different mechanisms are involved in these responses.

Pregnant (N = 10) and non-pregnant (N = 10) ewes were bled every 2 h from Days 12 to 17 after oestrus (oestrus = Day 0). Plasma concentrations of progesterone, 15-keto-13,14-dihydro-PGF-2 alpha and 11-ketotetranor-PGF metabolites were determined in all samples. The number of PGF-2 alpha pulses in non-pregnant ewes was 8.2 +/- 0.4 (mean +/- s.e.m.) with an interpulse interval of 10.7 +/- 0.7 h. Two or 3 pulses of low frequency (interpulse interval = 13.4 +/- 1.6 h) occurred in most non-pregnant ewes before the onset of luteolysis; the interpulse interval then decreased to 7.9 +/- 0.4 h for the 6.0 +/- 0.3 pulses temporally associated with luteolysis. In contrast, the number of PGF-2 alpha pulses in pregnant ewes was lower (2.5 +/- 0.7, 0-8) and the interpulse intervals longer (18.9 +/- 6.1 h). Most pulses occurred on Days 14 and 15 in the pregnant and non-pregnant ewes. The mean concentrations of both PGF-2 alpha metabolites in non-pregnant ewes were highest on Day 15 while basal levels of both metabolites remained constant at all times. In pregnant ewes, the mean concentrations of both metabolites were highest on Day 14; basal concentrations of both metabolites were also highest on Day 14. The mean concentrations of 15-keto-13,14-dihydro-PGF-2 alpha were higher in pregnant than in non-pregnant ewes on Days 13 and 14 (P less than 0.05) and higher in non-pregnant than pregnant ewes on Day 15 (P less than 0.05). The basal concentrations of the 15-keto metabolite were higher in pregnant than non-pregnant ewes at Days 13, 14, 15, 16 and 17 (P less than 0.05). Both the mean and the basal concentrations of 11-ketotetranor-PGF metabolites were higher in pregnant than in non-pregnant ewes on Day 14 (P less than 0.05). It is concluded that uterine production of PGF-2 alpha peaks at Days 14-15 after oestrus in pregnant and non-pregnant ewes. Patterns of release differ, however, in that non-pregnant ewes have a pulsatile PGF-2 alpha pattern superimposed on a constant baseline, while pregnant ewes have an increasing basal secretory pattern which is more nearly continuous, i.e. not pulsatile in form. Modification of pulsatile PGF-2 alpha synthesis and release is therefore a key aspect of prolongation of luteal function at the beginning of pregnancy in the ewe.

Mating initiates a pattern of prolactin secretion composed of daily surges which appear with semicircadian rhymicity until Day 8 (Day 0 = Day of plug detection) of mouse gestation. On Day 8, the diurnal (1500-2100 h) prolactin increase diminishes in magnitude in a line selected for high embryo survival (E). By Day 9, the diurnal surge has been terminated. The nocturnal prolactin surge (2400-0900 h) is present in the line E through Day 9 of pregnancy, but on Day 10 it disappears. The temporal pattern of prolactin secretion in a randomly bred control line (C) is similar on Days 2 and 4 of pregnancy to that observed in line E. Collection of head blood and/or trunk blood had no effect on plasma prolactin concentration in either line C or E if no more than 30 seconds elapsed between cage handling and sample collection. In contrast, prolactin levels were dramatically elevated in the blood of animals placed in the same room in which serial exsanguination was performed.

Conception rate, prenatal survival and litter size were recorded for 444 ewes of two age groups from five lines of grade Targhee sheep: two unselected control lines, HC1 and DC(C); two lines selected for 20 yr for increased 120-d weight, HW and DH(W); and a line selected for 18 yr for increased multiple births, T. Line T was equal or superior to the control lines in conception rate, prenatal survival and litter size in both age groups, although most of the differences were not significant. The W selected lines were inferior to the C and T lines in fertility and tended to be lower in prenatal survival, among mature ewes, resulting in a significantly lower number of lambs born per corpus luteum in the W lines than in the other two groups. Among yearlings, C ewes were non-significantly lower in fertility than T and W ewes, while W ewes were significantly lower than C and T ewes in prenatal survival. The T line ewes had higher overall reproductive performance than either of the other two groups. Ewes with two ovulations had a significantly higher conception rate than ewes with single ovulations. Gestation period was exceptionally uniform with a coefficient of variation of 1.3% and little difference due either to line or litter size. It was concluded that selection for multiple births improved overall reproductive performance, whereas selection for increased growth rate had an adverse effect on several components of reproduction, leading to a net decline in fitness.

Three breeds of Javanese sheep are described briefly and data suggesting the segregation of a gene with large effect on ovulation rate and litter size are presented. The three breeds are Javanese Thin Tail (JTT), Javanese Fat Tail (JFT) and Semarang (SEM), the last possibly a substrain of JTT. All three breeds have mean mature ewe weights under 30 kg. Ovulation rate and litter size did not differ significantly among the three; all had litter sizes of up to 4 or 5 with a mean for mature ewes of approximately 2. Ovulation rate ranged from 1 to 5 and had an average within-breed repeatability of .8 within season and .65 between seasons. Within-breed repeatability of litter size was .35 +/- .06. Prenatal survival in pregnant ewes with two, three and four or more ovulations averaged 93, 88 and 86% over two seasons. Dams that had at least one ovulation rate or litter size record greater than or equal to 3 produced two groups of daughters in approximately equal numbers: one group with many records greater than or equal to 3 and mean ovulation rate and litter size of 2.73 and 2.31, respectively, and one group with ovulation rates and litter sizes of 1 or 2 and corresponding means of 1.39 and 1.38. Dams with ovulation rate or litter size records of only 1 or 2 produced daughters in which over 90% had records of only 1 or 2. Estimated heritabilities for the mean of approximately three ovulation rate or litter size records from these daughter-dam comparisons exceeded .7. These results suggest segregation of a Booroola-type gene, one copy of which increases ovulation rate by about 1.3 and litter size by .9 to 1.0. Relationships between duration of estrus and ovulation rate, and between timing of release of luteinizing hormone and number of eggs shed, resemble the pattern in Booroola Merino more closely than that in Finnish Landrace or Romanov, supporting the hypothesis of a major gene.

The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.

SUMMARYA theoretical equation is proposed which describes the dynamics of foetal growth in mice. The equation is basically of exponential form and takes into account the effects of stage of gestation (T) and number of foetuses (N) on the instantaneous relative growth rate. The model was tested against experimental data by using a stepwise regression technique. Both stage of gestation and number of foetuses had significant effects (P< 0·01) on the instantaneous growth rate. When the model was tested against another set of data 44 out of a total of 52 comparisons had a prediction error less than 15 %. As a result, the following equation is proposed to describe the foetal growth of miceW = e-14·34Ne(1·302–0·0276T–0·00059)TAn equation of this form could be useful in interpreting prenatal growth data for other species. Other factors which may influence the dynamics of foetal growth, such as maternal age or weight, could also be incorporated into the equation.

Mortality and growth rates of D'Man (D), Sardi (S) and F 1 (D X S) lambs from four lamb crops from an accelerated lambing program are reported. Excluding the first season, when an outbreak of white muscle disease resulted in considerable death loss, mortality to 60 days was less than 10% for single and twin lambs from D'Man or Sardi dams, and less than 5% for single lambs from Sardi dams. There were triplets and higher multiples only in the D'Man breed. Mortality was 14% higher for triplets, and 38% higher for litters ≥ 4, than for twins. D'Man lambs weighed less than Sardi lambs at all ages, though less so than expected on the basis of the 50% higher mature weight of Sardi (48 kg) than of D'Man ewes (32 kg). Although F 1 lambs from Sardi dams were significantly lighter than Sardi lambs at birth, the difference was less apparent at 30 days and had disappeared by 60 days. Total weight of lamb weaned per ewe in the flock was highest for D'Man ewes in spite of their smaller size. Sardi ewes with F 1 (D X S) lambs had significantly higher productivity than Sardi ewes with S X S lambs. The results, along with those on reproduction, indicate that the D'Man breed has excellent potential for increasing total lamb production when crossed with less prolific breeds.

The effect of fetal and maternal genotype on embryo survival was studied in two lines of mice from the same base population: line E, selected for high embryo survival, and line CN-, selected for small litter size. Embryos were collected at 3.5 days postcoitus from normally mated donors of both lines and were transferred to the uteri of 2.5-day pseudopregnant recipients from each line. The number of embryos recovered and the proportion of those recovered that had been fertilized were greater in line E donors than in line CN- donors (P < .05). Development into blastocysts was slower for CN- embryos. The proportion of recipient females that were pregnant was higher for line E than for line CN- after transfer of line E embryos (P < .005). The same trend was observed following transfer of line CN- embryos (P < .10). Embryos of both lines showed greater survival when transferred to line E recipients than when transferred to line CN- recipients (P < .005), and, within line E recipients, E embryos tended to survive better than did CN- embryos (P < .10). The results suggest that although the genotype of the embryo may play a role, the maternal genotype has greater influence on embryo survival in the two lines of mice.

Ovulation rate was measured by laparoscopy at two consecutive cycles on 366 ewes 2 yr old and over and 85 yearling ewes of five lines of Targhees from the base base population; 53 yearling linecross ewes were also included. The lines were two unselected controls (HCl and DC), two selected for 21 yr for increased 120-d weight (HW and DH) and one selected for 19 yr for multiple births (T). Ewes were synchronized in late July or early August at the start of the normal breeding season with intravaginal pessaries impregnated with 60 mg methylacetoxyprogesterone and examined at first and second estrus. Ovulation had occurred in both cycles in 327 (89%) and 177 (85%) of the mature and yearling ewes, respectively. Overall mean numbers of corpora lutea at first and second estrus were 1.42 and 1.63, respectively for ewes 2 yr and over and 1.20 and 1.44 for yearlings, indicating an effect of synchronizing treatment, season, flushing, or a combination of these. Among mature ewes, ovulation rate was higher (P less than .05) in DH (+.20), HW (+.19) and T (+.16) than in controls at first estrus, and in HW (+.29) and T (+.21) but not DH (-.04) at second estrus. Among yearlings, differences were significant only at second estrus (HW, +.40; T, +.35) and again not for DH (+.08). The failure of line DH to increase in ovulation rate from first to second estrus as did other lines was transmitted to linecross progeny. Body weight within line affected ovulation rate significantly, with a greater effect at second estrus, in both age groups. Adjustment for body weight removed the difference between HW and controls but not between T and controls. Repeatability of corpora lutea count was .27 and .25 for mature and yearling ewes, respectively.