Effects of cloned-cattle meat on reproductive physiology in rats

The influence of the cloned-cattle meat diets upon reproduction in mammals was rarely studied. This study was performed to analyze the effects of the diets containing cloned-cattle (Korean native beef, Hanwoo) meat on the reproductive physiology in rats. The male and female rats were fed with the diets containing 5% or 10% of normal- (N-5 or N-10) or cloned- (C-5 or C-10) cattle meat during test periods. The rats fed with commercial pellets were used as control. Lower food consumption in normal- and cloned-cattle meat diet groups is detected in both male and female rats compared with that of control (P < 0.05, 0.01 and 0.001). No signs of cloned-cattle meat diets on male reproductive parameters are found in all groups, except for lower sperm deformity in C-5 group (P < 0.05) and higher testosterone concentration in C-10 group (P < 0.05), respectively. There are no significant test substance-related differences of Caesarean section and delivery in dams and external examination and physiological development test in neonate compared with control and normal meat groups. Based on these results, it can be postulated that there are no obvious negative effects on the reproductive physiology in rats fed with cloned-cattle meat diets compared to their comparators.     

Fourteen-week feeding test of meat and milk derived from cloned cattle in the rat

Agricultural application of cloned livestock produced by nuclear transfer requires public and governmental understanding of food-safety issues. To determine whether physiological effects occurred in animals fed products derived from cloned cattle, we conducted long-term (14 week) trials feeding Crj:CD(SD)IGS rats meat and milk from cloned cattle. Diets containing meat and milk were equal in nutritional value to the basal diet (AIN93G). Urinalysis was performed at Weeks 4, 8 and 12; at the end of the feeding period, blood sampling and autopsies were conducted. During the feeding periods, there were no significant differences in general condition, death loss, growth, battery of functional observational tests and estrous cycles among groups given diets containing meat and milk powder from non-clone, embryonic clone and somatic clone cattle. Furthermore, no significant changes attributed to consumption of clone meat or milk were detected in urinalysis, hematological and blood chemical, gross pathological or histological examinations. Therefore, we concluded that the physiologic conditions of the rats were not affected by consumption of meat and milk from bovine clones.     

Adult Female Rats Defend “Appropriate” Energy Intake after Adaptation to Dietary Energy

Objective: To determine if adult female rats adapt to lower and higher dietary energy density. Research Methods and Procedures: Study 1 compared high‐fat (56%), high‐energy density (HD) (21.6 kJ/g) and high‐fat (56%), low‐energy density (LD) (16.0 kJ/g) diets before surgery (two groups, 2 weeks, n = 16) and after surgery [ovariectomy (O) Sham (S); 2 × 2 factorial, n = 8; 6 weeks]. The second study (no surgery) compared high‐fat (60.0%), high‐energy (22.0 kJ/g) and low‐fat (10.0%), low‐energy (15.1 kJ/g) diets (n = 8). Results: In study 1, food intake was similar for the first 2 weeks, but rats on the LD diet consumed less energy, gained less weight, and had lower nonfasted serum leptin (all p < 0.0001) than rats on the HD diet. After surgery, rats on the LD and HD diets had similar weight gain, but rats on the LD diet consumed more food (p < 0.0001) and less energy (p < 0.009). O rats consumed more food and gained more weight (p < 0.0001) than S rats. Results from study 2 were similar to those from study 1. Discussion: The results demonstrated that O and S surgery rats and rats with no surgery adjust their food intake to defend a level of energy intake. This defense only occurred after a 2‐week adaptation period. The major differences in final body weights and abdominal fat resulted from the initial 2 weeks before adaptation to energy density. Rats fed higher‐energy diets seemed to “settle” at a higher level of adiposity, and rats fed lower‐energy diets consumed more food to increase energy consumption.     

Meal pattern of male rats maintained on histidine-, leucine-, or tyrosine-supplemented diet

Objective: Food intake is known to be affected by macronutrient composition of the diet, and protein manipulation has been reported to alter food intake, but the effect of individual amino acids on eating behavior has not been fully studied. This study investigated the effect of diet supplementation with three individual amino acids on meal pattern in male rats. Research Methods and Procedures: Thirty‐two Sprague‐Dawley rats were randomly divided into four equal groups and fed control diet or histidine (5%)‐, leucine (5%)‐, or tyrosine (5%)‐supplemented diet for 2 weeks and were monitored for their meal pattern. Results: Total food intake and feeding rate of the different groups were not affected, although other components of meal pattern were altered. Histidine supplementation reduced diurnal meal size by 42% (p < 0.05), whereas that of leucine increased nocturnal meal size by ～35% (p < 0.05). Tyrosine supplementation increased food intake of the nocturnal period and decreased that of the diurnal period. Both histidine and tyrosine supplementation elevated fasting plasma insulin levels and suppressed fasting glucose significantly. Discussion: Individual amino acids were found to alter meal pattern differently. Further investigations are required to dissect the involvement of central and peripheral factors in these alterations.     

Does Perinatal ω‐3 Polyunsaturated Fatty Acid Deficiency Increase Appetite Signaling?

Objective: To investigate the effect of maternal dietary ω‐3 polyunsaturated fatty acid (PUFA) deficiency and repletion on food appetite signaling. Research Methods and Procedures: Sprague‐Dawley rat dams were maintained on diets either supplemented with (CON) or deficient in (DEF) ω‐3 PUFA. All offspring were raised on the maternal diet until weaning. After weaning, two groups remained on the respective maternal diet (CON and DEF groups), whereas a third group, born of dams fed the DEF diet, were switched to the CON diet (REC). Experiments on food intake began when the male rats reached 16 weeks of age. Food intake was stimulated either by a period of food restriction, by blocking glucose utilization (by 2‐deoxyglucose injection), or by blocking β‐oxidation of fatty acids (by β‐mercaptoacetate injection). Results: DEF animals consumed more than CON animals in response to all stimuli, with the greatest difference (1.9‐fold) demonstrated following administration of 2‐deoxyglucose. REC animals also consumed more than CON animals in response to food restriction and 2‐deoxyglucose but not to β‐mercaptoacetate. Discussion: These findings indicate that supply of ω‐3 PUFA, particularly during the perinatal period, plays a role in the normal development of mechanisms controlling food intake, especially glucoprivic (i.e. reduced glucose availability) appetite signaling. Dietary repletion of ω‐3 PUFA from 3 weeks of age restored intake responses to fatty acid metabolite signaling but did not reverse those in response to food restriction or glucoprivic stimuli.     

Defective Dietary Induction of Uncoupling Protein 3 in Skeletal Muscle of Obesity‐Prone Rats

Objective: The goal of this study was to determine whether differential induction of skeletal muscle uncoupling protein 3 (UCP3) contributes to the development of diet‐induced obesity (DIO) or resistance to the development of obesity (DR) when rats are placed on a moderate fat (31%) high energy (HE) diet. Research Methods and Procedures: Gastrocnemius muscle was obtained from Sprague‐Dawley rats that were identified as DIO‐prone (n = 5) or DR (n = 5) on the basis of urinary norepinephrine excretion while consuming a chow diet. Muscle was also obtained from animals in the top tertile of weight gain (DIO_HE, n = 5) and the bottom tertile of weight gain (DR_HE, n = 5) after 2 weeks on the HE diet. UCP3 and actin mRNA levels were measured in all muscle samples by Northern analysis. To distinguish the effect of dietary energy content from the effect of obesity itself, we studied additional DIO and DR animals that had been returned to a chow diet for 10 weeks after consuming a HE diet for 10 weeks. Results: The muscle UCP3/actin mRNA ratio in animals that resisted the development of obesity during 2 weeks on the HE diet was 3‐fold higher than in the other groups (DR_HE = 3.24 ± 0.83, DIO_HE = 0.91 ± 0.20, DIO‐prone = 0.72 ± 0.15, DR = 0.63 ± 0.15; p = 0.002). However, there was no difference in muscle UCP3/actin mRNA ratios between DIO animals and DR animals that had been fed the HE diet for 10 weeks and then returned to either an ad libitum chow diet for 10 weeks (DIO = 13.8 ± 3.53, DR = 11.1 ± 3.43, p = NS) or to a restricted chow diet for 10 weeks (DIO = 11.0 ± 2.85, DR = 10.6 ± 2.20, p = NS) despite significantly greater body weight of the DIO animals. Discussion: DR animals may initially resist weight gain when placed on a HE diet through a greater induction of muscle UCP3. This induction is transient and is related more closely to dietary fat content than to body fat stores. DIO animals show no initial induction of muscle UCP3, which may contribute to their increased metabolic efficiency soon after exposure to a HE diet.     

Effect of meta-chlorophenylpiperazine and cholecystokinin on food intake of Osborne-Mendel and S5B/P1 rats

Objective: To investigate whether there is a difference in sensitivity to a serotonin agonist, meta‐chlorophenylpiperazine (mCPP), or cholecystokinin (CCK‐8), an intestinal hormone that inhibits food intake, between the Osborne‐Mendel (OM) rat, which becomes obese eating a high‐fat diet, and the S5B/Pl (S5B) rat, which is resistant to dietary‐induced obesity. Research Methods and Procedures: OM and S5B rats were adapted to either a high‐saturated‐fat diet (56% energy as fat) or a low‐fat diet (10% energy as fat) or to both for 14 days and then treated with several doses of mCPP or CCK‐8. Results: Treatment with mCPP reduced food intake in both strains of rats. The dose‐response curve showed that the OM rats had an increased sensitivity to the serotonergic agonist. Animals eating the high‐fat diet had less response to mCPP; and in the S5B rats, the response was significantly reduced. After treatment with CCK‐8, there was a similar dose‐related suppression of food intake in both the OM and S5B rats. Discussion: These data are consistent with the hypothesis that the serotonin system in the S5B rat has a greater activity that could act to inhibit fat intake. The response to CCK was not significantly affected by strain or diet.     

Multigenerations Assessment of Dietary Nucleotides Consumption in Weaned Rats

With the multifaceted activities of nucleotides, there is a history of safe consumption of dietary nucleotides (NTs) in the human diet. This study investigated the multigenerations cumulative toxicity on rats’ development after weaning. Weaning rats (F0) were fed with NTs at the dosage of 0.01, 0.04, 0.16, 0.64, and 1.28% (wt/wt) for 90 days and then mated for 1:1 pattern. The offspring was F1. F1 rats were fed with NTs for 90 days after weaning. Afterwards, F1 go on to the second reproductive part. We repeated the above process, until F3 rats were born. We observed the weight, food consumption in the whole experiment, and detected the blood indicators and organ pathology at the terminal. No abnormal reaction, behavior disorder, and organ pathology related to toxic symptom were observed in NTs‐treated groups. Weight gain and diet utilization ratio of males in each NTs group had significant increase after weaning (p < 0.05). With the exception of decrease in uric acid (p < 0.05) of NTs male, there were no differences between the control and NTs groups in blood indicators. NTs could promote early growth and development of rats after weaning, especially in males.     

Intentional Weight Loss Reduces Mortality Rate in a Rodent Model of Dietary Obesity

Objective: We used a rodent model of dietary obesity to evaluate effects of caloric restriction‐induced weight loss on mortality rate. Research Measures and Procedures: In a randomized parallel‐groups design, 312 outbred Sprague‐Dawley rats (one‐half males) were assigned at age 10 weeks to one of three diets: low fat (LF; 18.7% calories as fat) with caloric intake adjusted to maintain body weight 10% below that for ad libitum (AL)‐fed rat food, high fat (HF; 45% calories as fat) fed at the same level, or HF fed AL. At age 46 weeks, the lightest one‐third of the AL group was discarded to ensure a more obese group; the remaining animals were randomly assigned to one of three diets: HF‐AL, HF with energy restricted to produce body weights of animals restricted on the HF diet throughout life, or LF with energy restricted to produce the body weights of animals restricted on the LF diet throughout life. Life span, body weight, and leptin levels were measured. Results: Animals restricted throughout life lived the longest (p < 0.001). Life span was not different among animals that had been obese and then lost weight and animals that had been nonobese throughout life (p = 0.18). Animals that were obese and lost weight lived substantially longer than animals that remained obese throughout life (p = 0.002). Diet composition had no effect on life span (p = 0.52). Discussion: Weight loss after the onset of obesity during adulthood leads to a substantial increase in longevity in rats.     

Evaluation of meat products from cloned cattle: biological and biochemical properties

Agricultural utilization of cloned livestock produced by nuclear transfer and their products for food will require public and governmental acceptance. A series of studies of properties of meat derived from cloned cattle was carried out to collect data for the safety assessment of cloned cattle products. Meat samples obtained from embryonic cloned, somatic cloned and non-cloned cattle were analyzed for chemical composition, as well as amino acids and fatty acids. Digestibility, allergenicity, and mutagenicity of meat were also examined. There were no significant differences in these properties among embryonic cloned, somatic cloned and non-cloned cattle. The analyses and tests revealed that there were no significant biological differences in meat from a non-cloned, an embryonic cloned, or a somatic cloned animal. A 14-week feeding trial in rats showed there were no abnormalities in body growth, general condition, locomotor activity, reflexes, sexual cycle, urinalysis, hematology, blood biochemistry, and histology. This study showed for the first time that the biological/biochemical properties of meat of cloned cattle are similar to those of non-cloned cattle.     

Effects of dietary amylose and amylopectin ratio on growth performance,meat quality,postmortem glycolysis and muscle fibre type transformation of finishing pigs

The present study was conducted to investigate the effects of dietary amylose and amylopectin ratio on growth performance, meat quality, postmortem glycolysis and muscle fibre type transformation of finishing pigs. Twenty-four barrows (Duroc × Landrace × Yorkshire) with an average initial body weight of 61.7 ± 2.01 kg were randomly assigned to four dietary treatments with amylose: amylopectin ratios of 1:1 (HD), 1:2 (MD), 1:3 (CD) and 1:4 (LD). The results showed that the average daily weight gain of finishing pigs tended to reduce with the ratio of amylose and amylopectin decreased (p = 0.09). Diet LD increased the pH_24h value and decreased the shear force in longissimus dorsi (LM) compared with diet HD (p < 0.05). Diet LD decreased the lactate content and the HK-2 mRNA abundance and increased the mRNA abundance of ATP5B in LM compared with diet HD (p < 0.05). Higher mRNA abundance of MyHC I and lesser abundance of MyHC IIb in LM were found in pigs fed diet CD and LD than those fed diet HD (p < 0.05). Furthermore, pigs fed diet LD had higher mRNA abundances of PGC-1α and PPAR δ in LM than other groups (p < 0.05). These results suggested that diet with low amylose and amylopectin ratio could improve meat quality of finishing pigs via delaying muscle glycolysis capacity and shifting muscle fibre types.     

Energy intake and milk production in mink (MUSTELA vison)‐effect of litter size

Energy intake and milk production were measured in 12 mink dams raising litters of 3, 6 and 9 kits one to four weeks post partum by means of balance experiments and measurements of milk intake of the kits by the water isotope dilution technique. The dams were fed ad libitum on a conventional wet mink diet (DM: 323 g/kg; CP: 173 g/kg; ME: 4.4 MJ/kg). Milk samples collected from dams with corresponding litter sizes and lactation weeks, and body composition of kits nursed by these dams, were analysed for content of DM, ash, N and fat. The ME and drinking water consumption were higher in dams nursing 9 kits than in dams nursing 3 kits. The N and water balances as well as the live weight of dams were not affected by litter size. Daily milk production was higher in dams nursing 9 kits than in dams nursing 3 kits. The DM, N and fat content of the milk increased during lactation, but were not affected by litter size. Individual kit live weight was higher in litters of 3 than in litters of 6 and 9 kits four weeks post partum. The DM and fat content of the kits were lowest in kits from litters of 9 kits, whereas these kits had the highest protein content. Daily ME for maintenance of kits and the efficiency of utilisation of ME in milk for body gain were estimated to 356 kJ/kg^0.75, k_p ≈0.53 and k_f ≈0.71, respectively. In conclusion, daily milk production increased with increasing litter size, but not in proportion to the number of kits, indicating that milk production limits the growth rate of the young. In the fourth week of lactation, milk production was not different between dams nursing 6 or 9 kits, indicating a maximum capacity.     

Altered Hypothalamic Signaling and Responses to Food Deprivation in Rats Fed a Low‐Carbohydrate Diet

Objective: To model how consuming a low‐carbohydrate (LC) diet influences food intake and body weight. Research Methods and Procedures: Food intake and body weight were monitored in rats with access to chow (CH), LC‐high‐fat (HF), or HF diets. After 8 weeks, rats received intracerebroventricular injections of a melanocortin agonist (melanotan‐II) and antagonist (SHU9119), and feeding responses were measured. At sacrifice, plasma hormones and hypothalamic expression of mRNA for proopiomelanocortin (POMC), melanocortin‐4 receptor, neuropeptide Y (NPY), and agouti related protein (AgRP) were assessed. A second set of rats had access to diet (chow or LC‐HF) for 4 weeks followed by 24 h food deprivation on two occasions, after which food intake and hypothalamic POMC, NPY, and AgRP mRNA expression were measured. Results: HF rats consumed more food and gained more weight than rats on CH or LC‐HF diets. Despite similar intakes and weight gains, LC‐HF rats had increased adiposity relative to CH rats. LC‐HF rats were more sensitive to melanotan‐II and less sensitive to SHU9119. LC‐HF rats had increased plasma leptin and ghrelin levels and decreased insulin levels, and patterns of NPY and POMC mRNA expression were consistent with those of food‐deprived rats. LC‐HF rats did not show rebound hyperphagia after food deprivation, and levels NPY, POMC, and AgRP mRNA expression were not affected by deprivation. Discussion: Our results demonstrate that an LC diet influences multiple systems involved in the controls of food intake and body weight. These data also suggest that maintenance on an LC‐HF diet affects food intake by reducing compensatory responses to food deprivation.     

Effect of Dietary Carbohydrate Source on the Development of Obesity in Agouti Transgenic Mice**

Objectives: Our objective was to evaluate the effects of a qualitative change in dietary carbohydrate source on body weight and adiposity in a rodent model of diet‐induced obesity. Research Methods and Procedures: We evaluated the effects of high‐fat diets (basal) varying in carbohydrate source in aP2‐agouti transgenic mice. In the ad libitum study, animals were given free access to the basal diet or one of four test diets for 6 weeks. In two of the diets, dietary carbohydrate was derived from a single source: mung bean noodles (MUNG) or rolled oats (ROLL). The remaining diets were designed to mimic commercially available instant oatmeal with added sugar (IO‐S) or flavored instant oatmeal (IO‐F). In the energy‐restricted study, animals were given ad libitum access to the basal diet for 6 weeks. Subsequently, animals were assigned to one of six treatment groups for 6 weeks. One group was continued on the basal diet ad libitum. The remaining groups were maintained with energy restriction (70% ad libitum) on either the basal, MUNG, ROLL, IO‐S, or IO‐F diet. Results: Subcutaneous fat pad mass was significantly higher (p < 0.05) in the energy‐restricted basal and IO‐S groups compared with the energy‐restricted ROLL diet. Similarly, visceral fat pad mass was significantly lower with ROLL and MUNG diets (p < 0.05 for both) compared with basal and IO‐S diets, and the insulin:glucose ratio was reduced (by 23% to 34%, p < 0.05) in these two diets compared with all others. In ad libitum‐fed animals, liver fatty acid synthase expression was 43% to 62% lower (p < 0.05) with ROLL and MUNG diets compared with all others. Discussion: These data suggest that a qualitative change in dietary carbohydrate source modulates body weight and adiposity.     

Genetic mapping of quantitative trait loci for meat quality and muscle metabolic traits in cattle

A whole‐genome scan was carried out in New Zealand and Australia to detect quantitative trait loci (QTL) for live animal and carcass composition traits and meat quality attributes in cattle. Backcross calves (385 heifers and 398 steers) were generated, with Jersey and Limousin backgrounds. The New Zealand cattle were reared and finished on pasture, whilst Australian cattle were reared on grass and finished on grain for at least 180 days. This paper reports on meat quality traits (tenderness measured as shear force at 4–5 ages on two muscles as well as associated traits of meat colour, pH and cooking loss) and a number of metabolic traits. For meat quality traits, 18 significant QTL (P < 0.05), located in nine linkage groups, were detected on a genome‐wise basis, in combined‐sire (seven QTL) or within‐sire analyses (11 QTL). For metabolic traits, 11 significant QTL (P < 0.05), located in eight linkage groups, were detected on a genome‐wise basis, in combined‐sire (five QTL) or within‐sire analyses (six QTL). BTA2 and BTA3 had QTL for both metabolic traits and meat quality traits. Six significant QTL for meat quality and metabolic traits were found at the proximal end of chromosome 2. BTA2 and BTA29 were the most common chromosomes harbouring QTL for meat quality traits; QTL for improved tenderness were associated with Limousin‐derived and Jersey‐derived alleles on these two chromosomes, respectively.     

Efficiency of intermittent exercise on adiposity and fatty liver in rats fed with high-fat diet

Objective: This study aimed to examine and compare the effects of continuous or intermittent exercises on adiposity and fatty liver in rats fed with high‐fat diet. Methods and Procedures: Wistar rats were divided according to diet composition—chow diet (C) or high‐fat diet (H)—and kinds of exercise—sedentary (S), continuous (CE), or intermittent (IE) exercises. The CE group swam 90 min/day, and the IE group swam 3 × 30 min/day (at 4‐h intervals between sessions); both groups exercised 5 days/week during 8 weeks. Body weight and food intake were recorded daily. Lipogenesis rate in vivo was determined by the incorporation of ³H₂O into saponified lipids in retroperitoneal (RET), epididymal (EPI), and visceral (VIS) white adipose tissues, brown adipose tissue (BAT), liver (L), and gastrocnemius muscle (GAST) using the gravimetric method. Total cholesterol, high‐density lipoprotein (HDL)‐cholesterol, and triacylglycerol (TG) were analyzed. Results: The major finding of this study is that IE was more efficient than CE in reducing the adverse effects of high‐fat diet and sedentarism. There was an improvement in the lipid profile and a reduction in food intake, body weight gain, visceral and central adiposity, and fatty liver, contributing to the control of obesity and other comorbidities, including nonalcoholic fat liver diseases. Discussion: Earlier studies have discussed the effects of diet consumption on adiposity and their relation to chronic diseases and obesity. This study discusses the effects of high‐fat diet consumption and the different kinds of exercise on weight gain, adiposity, fatty liver, and lipid profile in rats. The results may depend on the exercise, time of each session, age, gender, and experimental period.     

Interactive effects of prenatal cocaine and nicotine exposure on maternal toxicity,postnatal development,and behavior in the rat

Two experiments were performed to investigate the interactive effects of prenatal coadministration of cocaine hydrochloride (C) and nicotine tartrate (N). Experiment I was designed to determine doses of C and N that could be coadministered without altering maternal gestational parameters and/or fetal viability. Exposure of Sprague-Dawley rats to combined high-dose C (20 mg/kg) and high-dose N (5.0 mg/kg) on gestation days 8–21 was not more toxic to dam or fetus than that of exposure to C alone. Experiment II investigated pregnancy outcome, postnatal development, and behavior of the offspring following drug exposure to either high-dose cocaine (20 mg/kg: CS), high-dose nicotine (5.0 mg/kg: NS), or both (NC) on gestation days 8–21. N was administered by osmotic minipump and C by sc injection. Saline-injected dams, fitted with saline-filled pumps (SS), and untreated dams, pair-fed (PF) to NC females, served as controls. Alterations in maternal variables were limited to a 10–15% decrease in food consumption in NC and CS groups. Pregnancy outcome and birth statistics were unaffected by prenatal treatment, as was offspring body weight during the first four postnatal weeks. However, the development of surface righting was delayed in CS pups, and only CS offspring were underresponsive to the stimulatory effects of dopamine agonists on activity and stereotypy. Behavioral responses to N challenge were similar in all groups. In addition, only CS offspring showed altered behavioral responses in a spontaneous alternation task. Treatment effects on dopamine D₁ and D₂ binding in the caudate nucleus were not observed. The combination of N and C did not exacerbate any of the behavioral changes seen in CS offspring. These results support the hypothesis that C is a behavioral teratogen in rodents, and suggest that in the present model, nicotine can mitigate some of the consequences ofin utero exposure to cocaine.     

Diet,Obesity, and Hyperglycemia in LG/J and SM/J Mice

Objective: To examine the differential response of obesity‐ and diabetes‐related traits to a high‐ or low‐fat diet in LG/J and SM/J mice. We also examined food consumption in these strains. Research Methods and Procedures: Mice were placed on a high‐ or low‐fat diet after weaning. Animals were weighed once per week and subjected to glucose tolerance tests at 20 weeks. At sacrifice, fat pads and internal organs were removed along with serum samples. For food consumption, LG/J and SM/J mice of each sex were assigned to a high‐fat or low‐fat diet after reaching maturity. Mice were weighed three times per week, and food consumed was determined by subtraction. Results: LG/J animals consume more total food, but SM/J animals consume more food per gram of body weight. LG/J mice grow faster to 10 weeks but slower from 10 to 20 weeks, have higher cholesterol and free fatty acid levels, and have lower basal glucose levels and better response to a glucose challenge than SM/J mice. For most traits, SM/J mice respond more strongly to a high‐fat diet than LG/J mice, including body weight and growth, basal glucose levels, organ weights, fat distribution, and circulating triglycerides and cholesterol levels. Discussion: Obesity‐related phenotypes, as well as response to increased dietary fat, differ genetically between LG/J and SM/J and can, therefore, be mapped. This study indicates that the cross of SM/J and LG/J mice would be an excellent model system for the study of gene‐by‐diet interaction in obesity.