Performance of mouse lines divergently selected for heat loss when exposed to different environmental temperatures. II. Feed intake, growth, fatness, and body organs

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for feed intake, growth, body fatness, and organ weights when reared at 12, 22, and 31 degrees C, and investigate potential line x environment interactions. Feed intake was recorded weekly from 3 to 9 wk of age, and BW at 3, 6, and 9 wk of age. Body fat percent and organ weights were measured at 9 wk of age. No line x environment interactions were detected for any of the traits measured. The MH mice consumed more feed than ML mice from 5 to 9 wk of age. Between 8 and 9 wk of age, MH mice consumed 13% more feed than the ML mice, but they were relatively leaner (14.45 vs. 16.32% body fat); MC mice were intermediate for both traits. Mice in the cold environment consumed the greatest amount of feed, and those in the hot environment consumed the least. Males consumed more feed than females, and the difference was greater in the cold than in the hot environment. No differences in BW were found between the lines. Mice in the 22 degrees C environment were heavier than their age-matched counterparts in the other two environments, and males were heavier than females at all ages. Relative to BW, the three lines had similar tail length, body length, and liver weight. Mice in the cold environment had heavier spleens and livers than those in the hot environment but relatively shorter bodies and tails; the normal environment was intermediate for these traits. Results from this study indicate that selection to decrease maintenance requirements did not produce mice with any less ability to grow and perform under an array of environmental temperatures.     

Correlated responses in maternal performance following divergent selection for heat loss in mice

Divergent selection in mice was applied in 3 independent replicates for high (maintenance high; MH) and low (maintenance low; ML) heat loss for 16 generations. An unselected control (maintenance control; MC) was also maintained in all replicates. Selection ceased for 26 generations; heat-loss measurement and selection resumed at generation 42. Lactation performance, dam weight, dam feed intake, and efficiency of production of pup weight were recorded or calculated for MH and ML dams in all 3 replicates at generation 46 or 47 with the objective of determining whether selection for heat loss has created correlated responses in maternal performance. One-half of the dams reared their own litters, and one-half reared cross-fostered (across lines) litters. Between 10 and 12 litters were used from each replicate-line-rearing class. Litter size was recorded, and litters were standardized to 8 pups within 24 h of birth. For cross fostering, MH litters were matched to ML litters born within 24 h of each other, and MH-ML litter pairs were cross-fostered at 3 d of age. A weigh-suckle-weigh protocol was used to obtain milk production estimates over a 2-h suckling period at 6, 9, 12, and 15 d. Dam (plus litter) feed intake was also recorded at these times and was calculated as the disappearance of feed over 3-d intervals. Dams of the MH selection tended (P < 0.11) to have greater litter size than those of the ML selection; litter size of MC dams was intermediate. Line of dam affected milk production (P = 0.04) and dam feed intake (P < 0.03) as MH dams produced more milk and consumed more feed than ML dams. Average milk production for the 2-h measurement period was 1.70 +/- 0.07 and 1.41 +/- 0.07 g, and average 3-d feed consumption was 50.8 +/- 1.2 and 45.2 +/- 1.2 g for MH and ML dams, respectively. Cross-fostering had no effect (P > 0.86) on milk production. Line of dam tended to affect 21-d litter weight (P = 0.15) with litters reared by MH dams weighing more than those reared by ML dams, but there was no difference (P > 0.86) in 21-d dam weights. Efficiency of producing litter weight (litter 15-d weight: dam plus litter feed intake from d 6 to 15) was greater (0.49 vs. 0.46, SE = 0.009; P = 0.03) for ML than for MH dams. Selection for reduced heat loss (lower maintenance feed intake in the ML line) resulted in reduced milk production and feed intake in dams and greater efficiency of litter weight production.     

Renewed selection for heat loss in mice: direct responses and correlated responses in feed intake, body weight, litter size, and conception rate

Divergent selection in mice was renewed in 3 independent replicates for high (MH) and low (ML) heat loss. An unselected control (MC) was maintained in all replicates. Heat loss was measured for individual male mice for 15 h, overnight in direct calorimeters. After 16 initial generations of selection followed by 26 generations of relaxed selection, divergent selection resumed for 9 generations. The realized selection applied was very close to the maximum possible selection according to the criteria and protocol. Selection differentials were greater for high than for low selection due to greater variation in the MH line. When corrected for SD, standardized selection differentials were similar for MH and ML selection. Unintended selection in MC was negligible. Realized heritability for divergence was 0.14 +/- 0.01, which was considerably less than that realized during the initial generations of selection (0.28 +/- 0.03). Realized heritabilities for MH selection (0.16 +/- 0.05) and for ML selection (0.07 +/- 0.06) were less, especially for ML selection, than were observed in the earlier generations. The difference in heat loss between MH and ML males was 55.7% of the MC mean at generation 51, compared with a difference of 53.6% in generation 15; this difference had decreased to 34.4% at the end of the relaxed selection (generation 42). For feed intake between 8 and 11 wk, MH and ML males differed by 34.0% of the MC mean by the end of the selection process. Body weight at 12 wk for MH and ML males was less than for MC males. Litter size response was positively related to the heat loss response. Conception rate was poorer in MH matings than in MC and ML matings.     

Effects of concurrent lactation and postpartum mating on reproductive performance in mice selected for large litter size

Reproductive and maternal performance of a line of mice selected for large first parity litter size (L+) and a control line (K) were compared under two mating systems: (1) postpartum mating (PP), in which females undergo concurrent gestation and lactation, and (2) postweaning mating (PW), in which females wean their litter before being remated. Females were evaluated in their first two parities. Litters in each line were standardized at birth to 4, 8, 12 or 16 pups in parity 1, and to 10 pups in parity 2. Concurrent gestation had no adverse effect on postnatal maternal performance in parity 1 of either line. In parity 2, both L+ and K declined in reproductive and postnatal maternal performance in PP compared with PW. The pattern of delayed implantation as number of pups nursed increased was similar in both lines under the PP regimen. Several interactions indicated that reproductive performance of L+ was more adversely affected than in K under postpartum mating. Pup mortality was greater in L+ than K under PP but not under PW. In the PP regimen, L+ dams nursing 12 and 16 pups had a lower mating success rate and dams nursing 16 pups had a smaller litter size and higher pup mortality than did K dams. Thus, when L+ dams nurse their natural litter, frequently exceeding 16 pups, their reproductive advantage over K dams observed in PW would be eliminated in PP. If the differences in the first two litters reflect subsequent parities, lifetime reproductive performance in the PP environment would be reduced in the high fecundity line. High fecundity appears to depend upon the environment of selection.     

Impacts of an endophyte-infected fescue seed diet on traits of mouse lines divergently selected for response to that same diet

In previous work, mouse lines were selected for eight generations for resistance (R) or susceptibility (S) to endophyte-infected fescue toxicosis using depression in postweaning gain caused by a toxin-containing diet as the selection criterion. Characterizing biological changes associated with resistance or susceptibility in those mice might suggest genetic or therapeutic approaches to alleviate fescue toxicosis in cattle. The first objective of the current experiment was to determine whether the toxin-containing diet depressed reproduction and mature size more severely in S than in R mice. The second was to investigate line and diet effects on hepatic glutathione-S-epoxytransferase (GST) and uridine diphosphate glucuronosyl-transferase (UDPGT) activities and to relate enzyme activities to reproduction within line by diet groups. Twenty-eight pairs per line (S or R) x diet (toxin-containing [+] or toxin-absent [-]) group cohabitated for 36 wk. The + diet depressed the number of pups born and weaned and litter weight weaned (P < .01) within the first two litters produced. Diet effects were greatest early in the experiment. Percentage changes in reproduction caused by the + diet for R and S pairs, respectively, were -13 and -28 for total pups born, -10 and -25 for total pups weaned, -13 and -14 for total litters produced, and -30 and -42 for total litter weight weaned. The S line mice were heavier than R line mice on both diets, but the + diet had a larger depressing effect on mature size of S line than of R line males (line x diet interaction, P = .09) and females (interaction not significant). Averaged across diets, GST activity was higher in R than in S dams (P = .05) at 44 wk of age but was not affected by diet or line x diet. Activity of GST was correlated with number of pups born (-.50), number of litters produced (-.44), and survival percentage (.40) within the R- group; in the R+ group, GST activity was correlated only with survival percentage (.37). In the S- and S+ groups, GST activity was not correlated with any reproductive trait. Line, diet, and their interaction did not affect UDPGT activity, and UDPGT activity was not correlated with any reproductive trait in any line x diet group. Selected lines differed in response to a toxin-containing diet as measured by its effect on reproduction and mature size. The R and S mice also differed in GST activity, but GST activity was correlated with reproductive traits only in R-line mice.     

Reallocation of body resources in lactating mice highly selected for litter size

The present study investigated differences in the allocation patterns of body stores in lactating female mice from a line selected for high litter size at birth (S-line, average litter size of 20) and dams from a nonselected control line (C-line, average litter size of 10). Body weight, litter size, litter weight, and absolute and relative lipid and protein mass were measured at peak lactation (2 wk in lactation) and at weaning (3 wk in lactation). Body size in S-line females has been increased as a correlated effect of selection for high litter size at birth, allowing for larger litters and higher absolute milk production. However, these dams produce larger litters relative to their own body weight. At peak lactation, lipid and protein percentage did not differ between lines. At weaning, S-line females had a higher protein percentage (P < 0.001) and lower lipid percentage (P < 0.05) than C-line females. Apparently, S-line females produce more offspring but at a greater cost to their own metabolism. This process was insufficient to supply the offspring with adequate resources, resulting in reduced (P < 0.0001) pup development and increased (P < 0.0001) preweaning mortality rates.     

Locomotor activity, core body temperature, and circadian rhythms in mice selected for high or low heat loss

Daily locomotor activity, core body temperature, and their circadian rhythms were measured in lines of mice selected for high (MH) or low (ML) heat loss and unselected controls (MC). Lines were created by selecting for 16 generations in each of three replicates. Collection of locomotor activity and core temperature data spanned Generations 20 and 21 for a total of 352 mice. Physical activity and core body temperature data were accumulated using implanted transmitters and continuous automated collection. Measurement for each animal was for 3 d. Activity was recorded for each half hour and then averaged for the day; temperature was averaged daily; circadian rhythm was expressed in 12-h (light vs dark) or 6-h periods as well as by fitting cyclic models. Activity means were transformed to log base 2 to lessen heterogeneity of variance within lines. Heat loss for a 15-h period beginning at 1630 and feed intake for 7 d were measured on 74 additional mice in order to estimate the relationship between locomotor activity and heat loss or feed intake. Selection lines were different (P < 0.01) for both locomotor activity and core body temperature. Differences were due to selection (MH-ML, P < 0.01), and there was no evidence of asymmetry of response (P > 0.38). Retransformed from log base 2 to the scale of measurement, mean activity counts were 308, 210, and 150 for MH, MC, and ML, respectively. Mean core temperatures were 37.2, 36.9, and 36.7 degrees C for MH, MC, and ML (P < 0.01), respectively. Females had greater physical activity (P < 0.01) and body temperature (P < 0.01) than males. There was no evidence of a sex x selection criterion interaction for either activity or temperature (P > 0.20). Overall phenotypic correlation between body temperature and log base 2 activity was 0.43 (P < 0.01). Periods during the day were different for both 12- and 6-h analyses (P < 0.01), but there were no period x selection criterion interactions (P > 0.1) for physical activity or body temperature. More sensitive cyclic models revealed significant (P < 0.01) 24-, 12-, 8-, and 6-h cycles that differed (P < 0.01) among lines. Estimated differences between MH and ML mice in feed intake and heat loss due to locomotor activity were 36 and 11.5%, respectively. Variation in activity thus contributed to variation in feed intake.     

Cytoplasmic effects on selection response for increased growth rate in mice

To determine if cytoplasmic effects have contributed to long-term selection response for increased growth rate in mice, reciprocal cross matings were made between an unselected control line (ICR) and a line (M16) derived from ICR by long-term selection for high postweaning weight gain from 3 to 6 wk of age. Embryos were recovered 2 to 4 d following mating and transferred to pseudopregnant F1 (DBA/2NCrlBR X C57BL/6NCrlBR) females. Thus, all embryos developed in similar uterine and postnatal maternal environments. A total of 122 M16 X ICR and 123 ICR X M16 mice was produced, representing 19 litters from each cross. Litters were standardized at birth to five to seven pups. Litter weights at birth and 1 wk were recorded. Body weights at 2, 3, 4, 5 and 6 wk and weight gain from 3 to 6 wk were obtained. Weights of liver, kidneys, and sc and epididymal fat pads of males were obtained at 6 wk. Females were mated at 8 wk, and litter size at birth was recorded. Least-squares procedures were used to test for differences between reciprocal crosses for all traits. Body weight at 4 wk was higher (P less than .05) for mice with ICR cytoplasm. No other significant differences were detected. There was no evidence that cytoplasmic effects influenced direct or correlated responses to long-term selection for increased postweaning weight gain.     

Ovulation rate and pre- and postimplantation survival in mice with a major gene for rapid postweaning gain

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.     

Babesiosis in a litter of pups

Babesia canis infection was diagnosed in a litter of seven 3-week-old Mastiff pups kept in a north Florida kennel. The pups were evaluated because of poor weight gain; the smallest pup also was markedly lethargic. Six of the pups were anemic and thrombocytopenic. A positive linear correlation between PCV and absolute reticulocyte count suggested that the variation in PCV may have been related more to the ability of a pup to increase erythrocyte production than to a difference in magnitude of erythrocyte destruction. All pups recovered from clinical signs and hematologic abnormalities attributable to babesiosis within 2.5 weeks after treatment with diminazene aceturate. Transient neurologic signs observed in 1 pup 3 days after treatment were believed to represent an adverse drug reaction. The dam of the litter had a serum titer of 1:640 for B canis, but appeared healthy, as did approximately 30 other adult dog in the kennel. The strain of B canis infecting dogs in the kennel caused severe illness and death in some pups, but clinically inapparent disease in adult dogs.     

Comparison of feed energy costs of maintenance, lean deposition, and fat deposition in three lines of mice selected for heat loss

Three replications of mouse selection populations for high heat loss (MH), low heat loss (ML), and a nonselected control (MC) were used to estimate the feed energy costs of maintenance and gain and to test whether selection had changed these costs. At 21 and 49 d of age, mice were weighed and subjected to dual x-ray densitometry measurement for prediction of body composition. At 21 d, mice were randomly assigned to an ad libitum, an 80% of ad libitum, or a 60% of ad libitum feeding group for 28-d collection of individual feed intake. Data were analyzed using 3 approaches. The first approach was an attempt to partition energy intake between costs for maintenance, fat deposition, and lean deposition for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight (kg(0.75)), fat gain, and lean gain. Approach II was a less restrictive attempt to partition energy intake between costs for maintenance and total gain for each replicate, sex, and line by multiple regression of feed intake on the sum of daily metabolic weight and total gain. Approach III used multiple regression on the entire data set with pooled regressions on fat and lean gains, and subclass regressions for maintenance. Contrasts were conducted to test the effect of selection (MH - ML) and asymmetry of selection [(MH + ML)/2 - MC] for the various energy costs. In approach I, there were no differences between lines for costs of maintenance, fat deposition, or protein deposition, but we question our ability to estimate these accurately. In approach II, selection changed both cost of maintenance (P = 0.03) and gain (P = 0.05); MH mice had greater per unit costs than ML mice for both. Asymmetry of the selection response was found in approach II for the cost of maintenance (P = 0.06). In approach III, the effect of selection (P < 0.01) contributed to differences in the maintenance cost, but asymmetry of selection (P > 0.17) was not evident. Sex effects were found for the cost of fat deposition (P = 0.02) in approach I and the cost of gain (P = 0.001) in approach II; females had a greater cost per unit than males. When costs per unit of fat and per unit of lean gain were assumed to be the same for both sexes (approach III), females had a somewhat greater estimate for maintenance cost (P = 0.10). We conclude that selection for heat loss has changed the costs for maintenance per unit size but probably not the costs for gain.     

Uncoupling proteins and energy expenditure in mice divergently selected for heat loss

The objective of this study was to determine whether variation in energy expenditure created by selection on heat loss is mediated by uncoupling protein-1 (UCP1) in brown adipose tissue. Divergent selection for heat loss developed lines of mice with high (MH) and low (ML) maintenance energy expenditure. Concentration of UCP1 mRNA in brown adipose tissue (BAT) was 93% greater in ML than in MH mice (P < 0.02). Two new lines of mice, KH and KL, were bred by backcrossing a UCP1 knockout gene into the MH and ML lines, respectively; KH and KL with both knock-out (-/-) and wild type (+/+) UCP1 genotypes were generated. At 13 wk of age, KH mice exhibited greater heat loss (166 kcal x kg(0.75) x d(-1)) than KL mice (126.4 kcalkg(0.75) x d(-1)) regardless of the UCP1 knockout (P < 0.0001). Concentration of UCP2 mRNA in BAT was 74% greater in UCP1 knockout mice (-/-) than in wild type (+/+; P = 0.0001). We conclude that response to selection for increased energy expenditure was not mediated by increased expression or function of UCP1.     

Cytoplasmic genetic effects and growth of hybrid mice

Variation in cellular biochemical functions controlled by cytoplasmic genes was studied in relation to phenotypic differences between progeny of reciprocal hybrid female mice. Least squares procedures were used to test for differences in mitochondrial respiratory metabolism and in capacity for ATP synthesis, and differences in growth of progeny of hybrid dams. Under identical nuclear influences, mitochondria of A/J and C57BL/6J cytoplasms differed (P less than .10 to P less than .01) from those of BALB/cJ cytoplasm in energy conservation. No differences were detected in mitochondrial efficiency between BALB/cJ cytoplasm evaluated in different nuclear environments. Three-way cross progeny of C57BL/6J x BALB/cJ reciprocal hybrid females mated to DBA/2J males differed (P less than .05) in litter weight at weaning and 1 wk and 2 wk postweaning. The F2 progeny of reciprocal C57BL/6J x BALB/cJ dams and F2 and three-way cross progeny of reciprocal A/J x BALB/cJ dams did not differ in weight at any age measured. Across all genotypes of dam, rank correlations of mitochondrial traits with F2 litter weights were nonsignificant. Observed variation in mitochondrial functions partially controlled by cytoplasmic genes did not limit mouse growth under these experimental conditions.     

Genetic variation in reproductive responses to a high-energy diet in mice

Effects of a high-energy diet on reproduction were studied in 300 mice from lines selected for litter size and(or) 6-wk BW (L+, increased litter size; W+, increased body weight; L+W-, increased litter size and decreased body weight; L-W+, decreased litter size and increased body weight; and K, randomly selected control). Mice received a high-energy diet (HED; 3.8 kcal/g of ME) or a standard diet (STD; 3.3 kcal/g of ME) from 8 to 11 wk of age and were then mated and evaluated for ovulation rate and embryo survival through 17 d of gestation. The HED increased ovulation rate in all lines (P less than .05). The line x diet interaction was significant, with increased ovulation rate due to HED ranging from 9.9% in W+ to 24.2% in L-W+. Within-line regression coefficients of ovulation rate on ME intake (kilocalories from 10 to 11 wk) varied from .08 +/- .04 (P less than .05) in L+W- to .177 +/- .05 (P less than .01) in L+. In contrast, nonsignificant increases were observed in litter size (live fetuses at 17 d of gestation) due to HED. Effects of HED on embryo survival rate were significantly negative in L+ and L+W-; the decrease in L+ was a result of preimplantation losses, and the decrease in L+W- was due to postimplantation losses. The line x diet interaction was significant for postimplantation embryo survival. The results indicate significant genetic variation in reproductive responses to a high-energy diet in mice.     

Traits affecting postweaning weight gain and feed intake of primiparous sows

Seventy-six primiparous Duroc and Landrace sows from two genetic lines with or without selection for improved sow productivity were used to identify sow traits that affect postweaning gain (positive or negative) and feed intake. Sows lost weight (P less than .01) and consumed less feed (P less than .01) during wk 1 postweaning (37 d) compared with wk 2, 3, and 4. Sows gained more weight during wk 2 and 3 (P less than .01) than during wk 4. Weekly feed consumption was similar during wk 2 and 4 and highest during wk 3 (P less than .05). Sow weight gain postweaning was predicted by sow weaning weight (P less than .01) and adjusted 21-d litter weight (P less than .05) during wk 1, wk 1 to 2, and wk 1 to 4 feeding periods. Feed consumption was best predicted by adjusted litter weaning weight (P less than .01), sow weaning weight (P less than .01), average backfat at farrowing (P less than .01), average backfat change (P less than .05), and adjusted 21-d litter weight (P less than .05). Feed intake was positively correlated (P less than .01; r = .77) and sow weight at breeding, farrowing, and weaning was negatively correlated (P less than .05; r = -.23, -.21, and -.26, respectively) with sow weight gain. Average backfat at weaning was negatively correlated (P less than .05) with gain and feed intake during each period. Adjusted 21-d litter weight and adjusted litter weaning weight were positively correlated with postweaning feed intake (P less than .05; r = .22 and .23, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

The ontogeny of serum insulin-like growth factor-I concentration in foals: Effects of dam parity,diet, and age at weaning

The effects of dam parity, age at weaning, and preweaning diet were examined in the ontogeny of serum insulin-like growth factor-I (IGF-I) concentrations in foals. Foals born to 13 primiparous and 19 multiparous draft-cross mares were weighed and bled near birth. About one-half of the foals in each group were weaned early (about 13 wk old); the remaining foals were weaned late (about 16 wk of age). Pooled values for serum IGF-I concentrations between birth and 17 wk of age were higher (P < 0.065) for foals born to multiparous (386 ng/ml) than to primiparous mares (237.5 ng/ml). Colts (378 ng/ml) had higher (P < 0.05) serum IGF-I concentrations than fillies (254.5 ng/ml), regardless of dam parity. Colts (173.5 kg) also tended (P = 0.12) to be heavier than fillies (159.2 kg). Weaning, whether at 13 or 16 wk of age, reduced (P < 0.05) growth rates and serum IGF-I concentrations. Serum IGF-I values recovered to preweaning values within 1–3 wk postweaning concurrent to an improved weight gain. Fifteen 1-d-old foals in a second study were fed milk replacer for 7 wk and were compared with five foals that nursed their mares for 8 wk. During the first 2 wk, replacer-fed foals (0.46 kg/d) did not gain as rapidly (P < 0.03) as mare-nursed foals (1.73 kg/d). The associated serum IGF-I values for replacer foals (139.4 ng/ml) were lower (P < 0.0001) than values for mare-nursed foals (317.4 ng/ml). Despite similarity in gains for both groups thereafter, serum IGF-I concentrations of replacer-fed foals were only 36 and 60% of values obtained for mare-nursed foals at 8 (weaning) and 18 wk of age, respectively. The intrinsic differences between mare-nursed and milk-replacer foals in serum IGF-I concentrations persisted to 1 yr of age despite similarities in dietary management and body weight of the foals. At 1 yr of age, the serum IGF-I concentration of mare-nursed foals (1,203 ng/ml) was 48% higher than that of replacer-fed foals (815 ng/ml). These data indicate that dam parity, sex of foal, and preweaning nutrition affect the ontogeny of serum IGF-I concentration in the foal. The chronic, persistent difference in serum IGF-I values created by the early nutritional management of growing animals has implications in the interpretation of longitudinal serum IGF-I studies in all species.     

Long-term responses, changes in genetic variances and inbreeding depression from 122 generations of selection on increased litter size in mice

Data on mice selected for litter size over 122 generations have been analysed in order to reveal the effect of long‐term selection on responses and changes in variances over a long selection period. Originally, three lines were established from the same base population, namely an H line selected for large litter size, an L line selected for small litter size and a K line without selection. In generation 122, the mean number of pups born alive (NBA) was 22 for the H line and 11 for the K line. Phenotypic response to selection is reduced over generations, but crossing of plateaued lines increased responses and realized heritabilities. Both realized heritabilities and heritabilities from residual maximal likelihood (REML) analyses were, in general, calculated from generation (?1)–44 (period 1), 45–70 (period 2) and 71–122 (period 3) separately. Realized heritabilities were in general smaller than heritabilities estimated from mixed model analysis. An overall estimate of heritability for NBA was found to be 0.19 (±0.01) by REML analysis. Additive variance is constant over all periods in the high line and the control line, but is reduced over periods in the low line. The reduction of additive variance in the low line could probably be explained by changes in gene frequencies. In all lines, environmental variances increased over periods. Inbreeding reduced the mean litter size by 0.72 (±0.10) pups per 10% increase in inbreeding, with substantial variance between periods and lines.     

Stearoyl-coenzyme A desaturase gene expression during growth in adipose tissue from obese and crossbred pigs.

This investigation addressed the hypothesis that, as a marker of adipocyte differentiation, stearoyl-coenzyme A desaturase (SCD) gene expression would be greater during growth in obese pigs than in crossbred, contemporary pigs. Suckled pigs from a single litter were removed from the sow for sampling at 0, 3, 10, and 17 d. The number of litters at 0, 3, 10, and 17 d of age was zero, two, three, and three (obese sows) and four, two, three, and three (crossbred sows), respectively. Postweaning pigs were removed from the sow at 14 d of age. One set of postweaning pigs was fed a high-fat, milk-based diet from d 28 to 49; pigs were killed on d 28 and 49 for sampling. The grain-fed pigs were switched to a pelleted, grain-based grower diet at d 28, and samples were obtained at 31, 35, or 49 d of age. Adipose tissue from all pigs in a litter for preweaning and postweaning pigs was pooled for the measurement of cellularity and SCD mRNA. There were significant genetic and age effects for adipocyte diameter and volume; overall, adipocytes from obese pigs were larger than those from crossbred pigs. Stearoyl-coenzyme A desaturase mRNA was barely detectable at 0 d of age and increased (P < .01) by 20-fold by 49 d of age. There was a significant genetic x age interaction (P = .026); there was more SCD mRNA in adipose tissue from obese pigs than in that from crossbred pigs during the suckling period, whereas crossbred pigs exhibited greater SCD gene expression than obese pigs during the postweaning period. The lesser SCD gene expression in postweaning obese pigs was caused by a strong depression in SCD gene expression in the grain-fed obese pigs. The data indicate that SCD gene expression provides a marker for terminal differentiation, especially in preweaning pigs. Furthermore, these results provide additional evidence that SCD gene expression is up-regulated by diets high in saturated fatty acids.     

A Review of Genotype x Environment Interaction Studies Conducted in the U.S. Involving Cattle Varying in Percentage Bos indicus Inheritance

A summary of genotype x environment interaction studies involving cattle varying in percentage Bos indicus inheritance indicates that the interactions are important for most measures of preweaning productivity and, to a lesser extent, for postweaning and carcass traits. For most of these studies, the genotype x environment interactions were represented by a change in magnitude rather than a change in rank of the Bos indicus genetic types when evaluated under different environment scenarios. To date, most genotype x environment interaction studies have been conducted to assess the importance of the interactions. Since the evidence is substantial that the interactions are important, it is suggested that any future studies be directed not at assessing if the interactions are important, but in terms of elucidating why the interactions occur.     

Neosporosis in Beagle dogs: clinical signs, diagnosis, treatment, isolation and genetic characterization of Neospora caninum

Clinical neosporosis was diagnosed in a litter of five pups born to a Beagle bitch from Virginia, USA. Four of the pups developed limb weakness starting at 4 weeks of age. The dogs were suspected to have neosporosis based on clinical signs and empirically treated with Clindamycin (75 mg, oral, twice daily, total 150 mg) starting at 9 weeks of age and the dosage was doubled at 13 weeks of age. Antibodies to Neospora caninum were detected in sera of the dam and pups when first tested serologically at the age of 4 months. The owner donated the pup with the worst clinical signs and the dam for research; both dogs were euthanized. Viable N. caninum was isolated in gamma interferon gene knock out (KO) mice and in cell culture from the pup killed at 137 days of age. Tissue cysts, but no tachyzoites, were found in histological sections of brain and muscles. The isolate was also identified as N. caninum by PCR and sequence analysis and designated NC-9. N. caninum was neither isolated by bioassay in KO mice nor found in histological sections of tissues of the bitch. Clinical signs in the remaining three pups improved considerably after a 6-month treatment with Clindamycin; N. caninum antibody titers were still persistent in these pups at 23 months of age. Results indicate that medication with Clindamycin can improve clinical condition but not eliminate N. caninum infection.