Lean Line Research Articles

Selection for lean growth in pigs with a restricted feeding regime

Divergent selection lines for lean growth on a restricted feeding regime, in Large White and Landrace pigs, were established to complement the lean growth selection lines on ad-libitum feeding. This study estimated the direct and correlated responses after four generations of selection and the corresponding genetic and phenotypic parameters.The selection objective for lean growth on restricted or scale (LGS) feeding was to obtain equal correlated responses in growth rate and carcass lean content, measured in phenotypic s.d. The selection criterion included measurements of growth rate and ultrasonic backfat depth.Large White (LW) and Landrace (LR) boars and gilts were purchased from eight British nucleus herds and boars from national artificial insemination centres in 1982. Homozygous or heterozygous halothane positive pigs were not included in the experiment. The base populations consisted of 31 LW and 19 LR sires and 57 LW and 67 LR dams. Within each population, there were high and low selection lines with a control line, each consisting of 10 boars and 20 gilts, with a generation interval of 13.5 and 12 months for LW and LR pigs. Animals were performance tested in individual pens from 30±3 kg for a period of 84 days and fed a high energy (13.8 MJ DE/kg DM) and high protein (210 g/kg DM crude protein) pelleted ration. Daily food intake was equal to 0.75 g/g of the daily food intake for ad-libitum fed pigs and the total food intake was 134 kg for LW pigs and 150 kg for LR pigs. On average, 3 boars and 3 gilts were tested per litter. The total number of pigs tested per line and average inbreeding coefficients at generation four, by population are given below.

Inadvertent Support of Traditional Employment Practices: Impediments to the Internationalization of Japanese Employment Law

INADVERTENT SUPPORT OF TRADITIONAL EMPLOYMENT PRACTICES: IMPEDIMENTS TO THE INTERNATIONALIZATION OF JAPANESE EMPLOYMENT LAW Yoichiro Hamabet INTRODUCTION The at-will employment system of the United States, which permits employers to hire employees during times of business ex- pansion and lay them off during recessions, arguably promotes fair and free competition for workers and jobs, resulting in an efficient labor market. American companies generally seek to keep lean manufacturing lines and efficient distribution systems, goals that do not permit paying salaries to unnecessary workers. In Japan, on the other hand, business enterprises, in accordance with social norms, assume responsibility for lifetime employ- ment-that is, long-term employment by a single firm, from hir- ing fresh out of college until retirement. This responsibility to provide long-term job security tempers cost-cutting measures for Japanese enterprises and has a number of side effects, both good and bad. First, preserving the numer- ous job positions in established industries can preclude effective enforcement of antimonopoly policy in Japan. Second, regard- less of changing economic conditions, Japanese companies feel compelled to retain male workers because typically they support their households; accordingly, a recession disproportionately harms the employment prospects of women. Furthermore, in or- der to benefit existing providers of employment, the Japanese government extends protection-such as exemptions from the t Visiting attorney, Masuda, Funai, Eifert & Mitchell, Ltd. (Chicago); mem- ber, Daini-Tokyo Bar Association; LL.B., Keio University, Tokyo (1985); LL.M., Indiana University School of Law (1992). The author would like to express his ap- preciation to Carol H. Morita of Masuda, Funai, Eifert & Mitchell, Ltd., for her useful comments. All unattributed translations from the Japanese are by the author.

Ontogeny of growth hormone (GH), insulin-like growth factors (IGF-I and IGF-II) and IGF binding protein-2 (IGFBP-2) in genetically lean and obese swine

Serum GH, IGF-I, IGF-II and IGFBP-2 concentrations were determined by radioimmunoassay in swine of genetic lines which were selected for high (obese) and low (lean) backfat. Blood samples were collected at birth, before and after nursing, at 1 and 3 days of age and at weekly or fortnightly intervals until 30 weeks of age. Overall, GH, IGF-I, IGF-II and IGFBP-2 were highest at birth and declined during the first week of postnatal life. An age-by-line interaction was apparent for GH and IGF-I during the early neonatal period with levels being higher in the lean line than the obese line at 1 day of age and similar at 1 week of age. At 3 to 5 weeks of age there was an elevation in GH which was greater in lean than obese pigs. IGFBP-2 concentration patterns were characterized by a nadir at 5 to 7 weeks of age and a decline from an apex at 8 weeks of age in both lines. IGF-II declined steadily from birth until about 10 weeks of age. A subsequent increase in IGF-II was then observed between 12 and 22 weeks, which was greater in the obese line and in male pigs but not apparent in lean females. At birth, pigs which had not nursed had higher GH and IGFBP-2 and lower IGF-I and IGF-II concentrations. The effect of nursing on IGF-I was significantly influenced by line. These data indicate that the endocrine milieu and developmental changes in the endocrine milieu of pigs with differing propensities for obesity differs, suggesting that there is an association between growth factors and physiological traits such as the development of obesity.

Thermoregulation at high ambient temperature in genetically fat and lean broiler hens fedad libitumor on a controlled‐feeding regime

Abstract 1. Hens of lines divergently selected for fatness and leanness, fed either ad libitum or on a controlled regimen, were compared for susceptibility to heat stress. 2. The rate of increase in deep‐body (rectal) temperature during exposure to 32°C was used as the index of thermoregulatory ability. Comb and foot surface temperatures were measured as indicators of peripheral vasomotor tone. 3. Because body temperature control depends on the balance between heat production and heat loss, heat production was measured to determine whether fat line hens had a higher heat production, which they would then have to dissipate. 4. During the first hour of heat exposure, rectal temperature in the ad libitum‐fed birds increased twice as rapidly as in the corresponding lean line sample and 6 times more rapidly than in the control‐fed fat‐line group. 5. Surface temperatures of comb and foot increased from 27°C to 37°C within the first hour at 32°C, with no effect of either genotype or feeding regimen on rate of in...

Plasma oestrogen and triglyceride concentrations and reproductive characteristics of broiler chickens after ten generations of selection at seven weeks of age for high or low plasma very low density lipoprotein concentration.

1. Day old female chicks from two lines of broilers, selected for high or low plasma concentrations of very low density lipoproteins, were fed ad libitum or restricted until point of lay. All birds were fed ad libitum after laying an egg, and aspects of growth and reproduction were measured to 40 weeks of age. 2. Compared with lean line birds the growth rate of fat line females fed ad libitum declined from 16 weeks of age. 3. Mortality from apparently stress-related causes in ad libitum fed fat line females increased from 16 weeks of age and was 71% overall, compared with 26% in ad libitum fed lean line females. Mortality in the corresponding restricted birds was 20% and 7%, respectively. 4. Few fat line females fed ad libitum commenced lay and those which were restricted during rearing stopped laying after the initiation of ad libitum feeding. Egg productions in lean line birds fed ad libitum or restricted were similar. 5. Fat line females fed ad libitum had few yellow follicles and a high rate of atresia at first egg and between 37 and 39 weeks, as did restricted fat line birds between 37 and 39 weeks of age after being fed ad libitum. 6. Plasma concentrations of oestradiol-17 beta were 5-fold higher in fat compared with lean line females at 35 weeks of age. There was a similar large difference in concentrations of plasma triglyceride which reached 59 mg/ml in fat line females fed ad libitum.

Effect of porcine somatotropin on number of granulosa cell luteinizing hormone/human chorionic gonadotropin receptors, oocyte viability, and concentrations of steroids and insulin-like growth factors I and II in follicular fluid of lean and obese gilts.

Prepubertal gilts of obese (n = 24) or lean (n = 24) genetic lines were injected (s.c.) daily with 0, 2, or 4 mg of porcine somatotropin (pST) for 6 wk starting at 160 d of age to determine whether pST affects follicular function. Blood and ovaries were collected at slaughter 24 h after the last injection. Surface follicles greater than or equal to 1.0 mm in diameter were counted, and pools of follicular fluid (FFL) and granulosa cells were collected from 1.0- to 3.9-mm (small) and 4.0- to 6.9-mm (medium) follicles. Oocytes were collected from small and medium follicles and evaluated for maturational stage and viability. Porcine somatotropin increased (P less than .08) the numbers of small but not the numbers of medium follicles per gilt (P greater than .10). Oocyte maturation and viability were not affected by pST or genetic line. Porcine somatotropin increased (P less than .05) concentrations of insulin-like growth factor I (IGF-I) in serum and FFL of both obese and lean gilts; IGF-I was lower (P less than .01) in lean gilts. Treatment with pST decreased (P less than .05) IGF-II in FFL of lean but not in that of obese gilts. Dose of pST and line had no effect on concentrations of progesterone in FFL of small or medium follicles or on concentrations of estradiol in FFL of small follicles.(ABSTRACT TRUNCATED AT 250 WORDS)

Stearyl-CoA desaturase activity and triglyceride secretion in isolated and cultured hepatocytes from genetically lean and fat chickens

1. 1. A new culture system (adapted from the procedure of Seglen, 1975) of 9-week-old chicken hepatocytes is presented, validated by a hepatic enzyme activity time-course (stearyl-CoA desaturase) during a 6-day period. 2. 2. Stearyl-CoA desaturase activity was measured in isolated and cultured hepatocytes from genetically lean or fat chickens. A significantly higher activity was shown in the isolated hepatocytes from the fat line as compared to the cells of the lean line. This difference disappeared after 24 hr of culture. 3. 3. The triglyceride secretion by cultured hepatocytes was determined and a correlation with the animal adiposity was shown. 4. 4. These results obtained on a hepatocyte culture system directly confirm previous observations showing that adiposity would be related to VLDL processing and secretion, and monoene availability in the chicken hepatocytes.

Correlated physiological responses to selection forcarcass lean content in sheep

Correlated responses in physiological traits in lines of Texel-Oxford sheep selected for high or lowcarcass lean content were examined. Serum samples were taken at the end of performance test, 20 weeks of age, from 66 rams when fed ad libitum and every 24 h when fasted for 56 h. The lean line had higher serum concentrations of β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA) and insulin-like growth factor- 1 (IGF-1) with lower concentrations of triglyceride (TRIG), creatinine (CREA) and UREA, but only the differences in UREA were statistically significant. There were substantial changes in serum concentrations of physiological traits in response to fasting as glucose and IGF-1 decreased while BHB, NEFA, TRIG, CREA and UREA increased. The correlated responses suggested that the lean line preferentially synthesises protein rather than deposits fat during normal feeding. When the animals are fasted, there may be relatively greater use of fat as an energy source in the lean line, rather than using products from protein catabolism as glucose precursors. The accuracy of selection was examined when physiological traits were incorporated into a selectionindex, which included the performance test traits: liveweight, ultrasonic backfat and muscle depths, to predict genetic merit for carcass lean content. UREA may be a useful predictor of genetic merit for lean meat production as it was correlated with estimated carcass lean content and there were substantial differences between the selection lines.

Growth hormone response to TRH in male broiler chickens selected for body weight gain or food conversion and reared at either a moderate or a high ambient temperature.

The aim of the present experiment was to study the growth hormone (GH) response upon thyrotropin releasing hormone (TRH) challenge (2 micrograms/kg body weight) in broiler chickens selected for body weight gain (GL line: fat line) or for feed efficiency (FC line: lean line) reared at either a moderate (33-23 degrees C) or high (33 degrees C) ambient temperature. A higher plasma GH level at 5 min after TRH administration was observed in the high temperature conditioned chickens of both lines. Also at high ambient temperature, an enhanced GH decrease between 15 min and 30 min post-injection and a higher acute elimination rate was calculated compared to moderate ambient temperature. A significantly higher GH secretory response was observed in the leaner FC line chickens, which was probably related to the more pronounced pulsatory GH secretion rate in these chickens. There was no difference in GH acute elimination rate between both lines in both environments. No interactions between line and rearing temperature for these parameters of GH dynamics were observed.

Analysis of lines of mice selected for fat content: 3. Flux through thede novolipid synthesis pathway

The flux through the de novo fatty acid synthesis pathway was estimated in lines of mice which differed substantially in fat content following 26 generations of selection at 10 weeks of age. Previous estimates of lipogenic enzyme activities had indicated an increase in the capacity for lipogenesis in the Fat compared to the Lean line. Therefore the in vivo flux in lipogenesis was measured in both liver and gonadal fat pad (GFP) tissues of males at 5 and 10 weeks of age, using the rate of incorporation of 3H from 3H2O and 14C from acetate and citrate into total lipids. At both ages and in both tissues the Fat line had a higher flux, about 20% increase in the liver and up to three-fold increase (range 1.2- to 3.4-fold) in the GFP. We conclude that direct selection for fatness in mice has resulted in metabolic changes in the rate of de novo fatty acid synthesis, and that the changes are largely detectable before 10 weeks, the age of selection.

Energy exchanges of broilers, selected for fatness and leanness, on diets with and without a repartitioning agent

1. Two experiments were undertaken for 3 or 5 d in respiration chambers, on two experimental lines of broiler chickens (aged 25-38 d) selected for leanness and fatness. Diets were without or with 0.4 mg cimaterol per kg. 2. The lean line with sexes combined (experiment 1), or with females only, had a significantly greater heat production than the fat line. Net availability of metabolisable energy for gain (kg) was 0.54 for the lean birds and and 0.84 for the fat birds. 3. Cimaterol did not have an effect on any of the variables examined.

Nitrogen Metabolism in Genetically Fat and Lean Chickens

Two experiments were conducted to investigate the effect of dietary protein content (170 to 230 g/kg in Experiment 1 and 131 to 251 g/kg in Experiment 2) and initial growth rate, estimated from live body weight at 4 wk of age, on growth rate from 4 to 7 wk of age, nitrogen retention, energy metabolism, and amino acid catabolism in genetically fat (FL) and lean (LL) lines of chickens. There was no difference between lines in energy utilization either in metabolizability or in expenditure (basal metabolic rate, maintenance, or diet-induced thermogenesis). The only divergence between lines was in the partition of a similar amount of retained energy between lipid and protein deposition. In both experiments, LL chickens showed greater protein retention efficiency than FL birds; moreover, the LL line did not appear more sensitive to low dietary protein contents than the FL line. Selecting birds on their growth rate or live body weight at 4 wk of age resulted in the selection of different rates of fattening. Indeed, the slow-growing FL and LL chickens differed less in their nitrogen metabolism than did fast-growing birds, which were also fatter. The lower protein retention efficiency observed in FL chickens was related to an increase of dietary amino acid degradation as revealed by a greater rate of uric acid excretion in the fed state.

Changes in the Glycosylated and Nonglycosylated Forms of Prolactin and Growth Hormone in Lean and Obese Pigs during Pregnancy*

The concentrations of glycosylated (G-PRL) and nonglycosylated (non-G-PRL) forms of PRL and GH were measured during pregnancy in pigs of lean and obese (high backfat thickness) lines. Pregnant sows of the two genetic lines were killed, in groups of five to eight, at 60, 75, 90, and 105 days of gestation, and their pituitary glands and plasma were analyzed for the two hormones by immunoblotting, lectin-binding, and RIA techniques. In both lean and obese pigs, pituitary concentrations of G-PRL and non-G-PRL increased with advance in pregnancy, but there were no significant changes in either form of pituitary GH. Plasma concentrations of radioimmunoassayable PRL also increased with advance in pregnancy, with no consistent changes in serum GH concentrations. The dominant PRL constituent in plasma during the second half of pregnancy was G-PRL, and its concentration either increased or remained constant with advance in pregnancy. In contrast, plasma non-G-PRL concentrations decreased with advance in pregnancy in both lines of pigs, resulting in a steady rise in the plasma G-PRL/PRL ratio toward term. Compared to lean pigs, obese pigs had less radioimmunoassayable PRL and GH in their plasma and less GH (glycosylated as well as nonglycosylated) in their pituitary glands, but obese pigs had more G-PRL in their pituitary glands than lean pigs, and their plasma G-PRL levels tended to be higher and non-G-PRL levels lower than those of lean pigs. Pituitary concentrations of non-G-PRL in the two lines of pigs were similar. Overall, the results show a preponderance of G-PRL over non-G-PRL in the plasma of pregnant sows, with a preferential secretion of the glycosylated form during the latter half of pregnancy. Furthermore, they indicate a prevalence of higher G-PRL/PRL ratios in the pituitary glands of obese than lean pigs. These findings raise the possibility of a functional role for the glycosylated variant of PRL in the initiation and/or maintenance of events associated with pregnancy and obesity in the pig.

Relationship between body fatness, ovarian structure and reproduction in mature females from lines of genetically lean or fat broilers given different food allowances

Abstract 1. Reproductive and other characteristics were measured at 34 and 60 weeks of age in broiler breeder hens on 6 different feeding regimes. The hens came from genetically lean and fat lines selected on the basis of low or high 7‐week plasma very low density lipoprotein (VLDL) concentration. 2. Plasma VLDL concentrations were consistently higher at all ages in fat line hens but were not affected by dietary treatment. 3. Mature body weight did not differ between the lines in birds fed ad libitum but with food restriction throughout life, fat line birds were lighter at 34 weeks. 4. There was little difference between the lines in abdominal fatness of birds fed ad libitum up to 60 weeks. Fat line birds were always fatter than lean line counterparts under food restriction. 5. Egg production was higher in lean line birds fed ad libitum but food restriction improved egg production in both lines. Peak egg productions were similar in both lines but there was evidence that the optimal food allowances for egg production was higher in the lean compared with the fat line. 6. Ovarian yellow follicle numbers were highest at 34 weeks in ad libitum fed lean line birds and declined linearly with decreasing body weight caused by food restriction but there was no such relationship in fat line birds. 7. White follicle numbers were higher and follicular atresia was lower in the lean line. 8. It is concluded that poor reproduction in fat line birds was associated with inhibition of follicular development and atresia rather than by high plasma VLDL concentrations promoting excessive yolk formation.

Divergent selection of lean and fat lines of broilers over eight generations using plasma very low density lipoprotein as selection criterion

Abstract 1. Male and female broilers from a male grandparent line have been selected over 8 generations on the basis of low or high plasma very low density lipoprotein (VLDL) concentration. This has given lines of lean and fat broilers. 2. Plasma VLDL concentration in the two lines has diverged steadily and showed a 7‐fold difference in the 8th generation. 3. Divergence of other traits, including abdominal and total body fat, body protein and conversion efficiencies of food and dietary protein has continued but body weight has not changed with selection. 4. Divergence of body composition and nutrient conversion relative to a commercially selected control line derived from the same origin as the experimental lines has been slightly greater for the fat line. 5. In the lean line, females have been more responsive to selection with the result that body compositions of lean line males and females at 7 weeks have become quite similar. 6. Plasma VLDL concentration decreased little in the lean line over the later...

Responses of body composition, growth and food efficiency to dietary protein in genetically lean and fat broilers up to seven weeks of age

1. Growth, food intake and abdominal fatness were measured at 7 weeks of age in male and female broilers from genetically lean and fat lines fed on isoenergetic diets containing 160, 190, 210, 230 and 260 g crude protein/kg from hatching. 2. The mean proportions of abdominal fat decreased from 39 to 20 g/kg body weight in the fat line and from 26 to 11 g/kg in the lean line over this range of protein concentrations. 3. Protein requirements, for optimum growth as a proportion of the diet did not differ between the lines but the lean line was less tolerant of inadequate dietary protein. 4. In birds fed on the same diet, conversion efficiencies of food (FCE) and dietary protein (PCE) were always superior in the lean line but energetic efficiency (EE) was similar in good growing birds of both lines. 5. When dietary protein was adequate for growth and body compositions were equalised in the two lines (by feeding higher protein diets to the fat line), lean line birds had 10% better FCE, 6% better EE and 33% better PCE. 6. It is concluded that genetic selection is a more effective and economic means of producing leaner broilers than dietary manipulation.

Analysis of lines of mice selected for fat content. 2. Correlated responses in the activities of enzymes involved in lipogenesis

Estimates of the activities (Vmax) of six enzymes involved in de novo fat synthesis were made in replicated lines of mice differing in fat content. These lines had been selected high and low for 20 generations with three replicates each of Fat, Control and Lean lines and for a further eight generations high and low as an unreplicated line. The activities of ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACC), fatty acid synthetase (FAS), cytoplasmic malate dehydrogenase (MDH), malic enzyme (ME) and pyruvate kinase (PK) were determined in vitro in both liver and gonadal fatpad tissues taken at ages five and ten weeks. The activities of ACL, ACC, FAS and ME were significantly higher in the Fat than the Lean lines, and the differences were more pronounced at the earlier age and in the gonadal fatpad where activities in the Fat lines were higher by factors of 3.5, 2.4, 2.5 and 3.5 respectively. The activity of PK was unchanged in each tissue. MDH activity was significantly lower in adipose tissue in the Fat lines than the Lean lines at age ten weeks but not at age five weeks or in liver tissue. Results from replicates indicated that random genetic drift affected enzyme activities but nevertheless significant changes in activity were associated with the direction of selection. The changes in enzyme activity reported here are similar to those known to be associated with major mutations causing obesity in mice.

The growth to maturity of lean and fat lines of broiler chickens given diets of different protein content: body composition, plasma lipoprotein concentration and initial egg production

ABSTRACTThe proportions of abdominal fat and total body lipid and protein were measured up to 30 weeks in males and 21 weeks in females from lines of lean and fat broiler chickens given diets of different protein content. There was a constant relationship between the proportions of abdominal fat and body lipid independent of line, diet or age. Data on males showed effects of line and diet on body fatness at all ages up to 30 weeks. In females, line and diet had effects on body fatness during early growth but little effect on composition at 21 weeks. Plasma very low density lipoprotein concentration was higher in the fat line in both sexes at all ages. Egg production over the first few weeks of the laying period was much higher in lean line hens.

Metabolism of very low density lipoproteins in genetically lean or fat lines of chicken

Metabolism of very low density lipoproteins (VLDL) has been compared in fat (FL) and lean (LL) lines of chicken. When refed after fasting, plasma triglyceride concentration reached a significantly higher plateau in FL, although their feed consumption was lower than in LL. Newly synthesized VLDL were studied using anti-lipoprotein lipase antibodies. VLDL triglyceride (TG) concentrations were increased by antibody injection and reached a higher concentration in FL plasma than in LL. Newly synthesized VLDL exhibited a similar lipid composition. Fatty acid profiles were also similar when birds ingested a very low fat diet. Comparison of in vitro affinity of lipoprotein lipase and VLDL from both genotypes did not reveal any difference in Km and Vmax. [14C]labelled VLDL from fat or lean donors were prepared and were injected into chickens from both genotypes. Fractional rate constants did not differ between lines. However, as plasma VLDL-TG pools were very different, plasma turnover was higher in FL than in LL. About 3-fold more VLDL-TG were incorporated in abdominal fat of FL than in LL. Difference in fattening between both genotypes seem to be due to both increased VLDL secretion and VLDL removal from plasma without difference in VLDL characteristics.

SHHF/Mcc-cp Rat: Model of Obesity, Non-insulin-dependent Diabetes, and Congestive Heart Failure

It is well established that obesity and diabetes contribute to increased cardiovascular complications in humans. Many feel that the increased prevalence of heart disease in obese or diabetic patients can be attributed to increased atherosclerotic lesions caused by hyperglycemia, hyperlipoproteinemia, hypertension, obesity, and hyperinsulinemia. However, more recent data indicate there may be a specific diabetic cardiomyopathy not associated with coronary artery disease that may explain some of the increased mortality and morbidity seen in diabetics (Crepaldi and Nosandini, 1988; Fein and Sonnenblick, 1985). Knowledge of the heart and cardiovascular system in genetic animal models of obesity and diabetes is limited (Chobanian et al., 1982; McCune, 1989). Various combinations of risk factors may cause different heart problems, with obesity and non-insulin-dependent diabetes mellitus (NIDDM) combined with hypertension probably causing the most deleterious effects on the heart. The use of animal models with obesity, diabetes, or both conditions, combined with other risk factors, may clarify what each component contributes to the cardiovascular disease. This report summarizes some of the current information on the cardiovascular and diabetic complications found in the SHHF/Mcc-cp rat model, which exhibits obesity, NIDDM, and congestive heart failure (CHF). rats heterozygous for the cp gene) (Koletsky, 1975) to SHR/N (spontaneously hypertensive) rats. We obtained the rats after the seventh backcross. The only other SHR/ N-cp rats currently available are from the fourteenth backcross (Michaelis et al., 1986) and may have divergence in as many as 20 percent of their genes from our substrain, now designated SHHF/Mcc-cp. This colony exhibits the following traits: hypertension (100 percent), obesity (25 percent), and CHF (100 percent in recent sibships). Obesity is expressed as an autosomal recessive (cp/cp) trait, and hypertension is multifactorial (Yen et al., 1974). The CHF trait has been maintained through at least 15 generations. The colony is closed, but it has not been completely brother x sister mated. The incidence of CHF has increased with inbreeding, and the onset of CHF seems to be occurring at an earlier age. The mode of inheritance of the CHF is probably multifactorial, much like hypertension. The majority of the lean animals that died of CHF were heterozygous for the obesity trait (+/cp). It is possible that the presence of the cp gene on this genetic background is required for the expression of the CHF or at least for the earlier age of onset of CHF. We have been successful in getting our obese male rats to breed (McCune et al., 1989); therefore, all of their lean offspring will carry the cp gene. A homozygote lean (+/+) line is also being bred, and their offspring will be compared for incidence of CHF with the heterozygote lean parents.