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M K Nielsen

Publications and source records attributed to M K Nielsen.

At least 37 records · Page 2Linked to original sources
PubMed1999

Responses in ovulation rate, embryonal survival, and litter traits in swine to 14 generations of selection to increase litter size.

Eleven generations of selection for increased index of ovulation rate and embryonal survival rate, followed by three generations of selection for litter size, were practiced. Laparotomy was used to count corpora lutea and fetuses at 50 d of gestation. High-indexing gilts, approximately 30%, were farrowed. Sons of dams in the upper 10% of the distribution were selected. Selection from Generations 12 to 14 was for increased number of fully formed pigs; replacements were from the largest 25% of the litters. A randomly selected control line was maintained. Responses at Generation 11 were approximately 7.4 ova and 3.8 fetuses at 50 d of gestation (P < .01) and 2.3 fully formed pigs (P < .01) and 1.1 live pigs at birth (P < .05). Responses at Generation 14 were three fully formed pigs (P < .01) and 1.4 live pigs (P < .05) per litter. Number of pigs weaned declined (P < .05) in the index line. Total litter weight weaned did not change significantly. Ovulation rate and number of fetuses had positive genetic correlations with number of stillborn pigs per litter. Significantly greater rate of inbreeding and increased litter size at 50 d of gestation in the select line may have contributed to greater fetal losses in late gestation, greater number of stillborn pigs, and lighter pigs at birth, leading to lower preweaning viability. Heritabilities of traits were between 8 and 25%. Genetic improvement programs should emphasize live-born pigs and perhaps weight of live-born pigs because of undesirable genetic relationships of ovulation rate and number of fetuses with numbers of stillborn and mummified pigs and because birth weight decreased as litter size increased.

Animal Husbandry↗
PubMed1999

Evaluation of the ovine callipyge locus: III. genotypic effects on meat quality traits.

A resource flock of 362 F2 lambs provided phenotypic and genotypic data to estimate effects of callipyge (CLPG) genotypes (NN, NC, CN, and CC) on meat quality traits. The mutant allele is represented as C, the normal allele(s) as N, and the paternal allele of a genotype is given first. Lambs of each genotype born in 1994 and 1995 were serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age. Warner-Bratzler shear force and subjective evaluation of marbling were collected during both years from longissimus. Calpastatin activity was measured on longissimus from the 1994 group, and ELISA quantification of calpastatin protein was obtained from the 1995 group. Significant additive and paternal polar overdominance effects on meat quality traits were detected. This is in contrast to previous research that detected only polar overdominance effects on slaughter and carcass traits in this population. The magnitude of genotypic effects on shear force differed significantly between years; however, additive (P < .01), paternal polar overdominance (P < .001), and maternal dominance (P < .01) effects adjusted for variation in carcass weight were detected within each year. Shear force data adjusted to the mean slaughter age or carcass weight indicated that the means and variances of CN and CC genotypes were greater than values of NC and NN. Shear force values were greatest for CN and were intermediate for CC. The difference in shear force (adjusted for variation in slaughter age) between homozygous genotypes (additive effect) was supported by calpastatin activity data with 2-df F-tests of 3.66 (P < .05) and 11.84 (P < .001) at d 0 and 7 postmortem, respectively. Corresponding values for the paternal polar overdominance effects on calpastatin activity were 53.80 (P < .001) and 87.43 (P < .001). Calpastatin ELISA data (d 0, adjusted for slaughter age) exhibited a paternal polar overdominance effect exclusively with a 2-df F-test of 57.63 (P < .001). Additive and paternal polar overdominance effects on marbling adjusted for slaughter age had F-tests of 6.41 (P < .01) and 93.29 (P < .001), respectively. Consequences of increased longissimus shear force must be addressed if the advantages of CN lambs for dressing percentage and carcass composition are to be realized. Further research is needed to establish whether selection targeted at changing the background genome can mitigate the negative effects of the C allele on meat tenderness.

Animals↗
PubMed1998

Evaluation of the ovine callipyge locus: II. Genotypic effects on growth, slaughter, and carcass traits.

A resource flock of 362 F2 lambs provided phenotypic and genotypic data to estimate effects of callipyge (CLPG) genotypes on growth, slaughter, and carcass traits. Lambs were serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age to allow comparisons at different end points. Probabilities of CLPG genotypes were calculated at a position 86 cM from the most centromeric marker of chromosome 18. A contrast of CLPG genotypic effects, based on the paternal polar overdominance model, was used to evaluate callipyge and normal phenotypes. Relationships of traits with slaughter age, carcass weight, or 12th-rib fat depth for callipyge and normal phenotypic groups were estimated by regression. Callipyge and normal lambs did not differ for growth traits measured from birth to slaughter. Callipyge lambs produced 55.9% of live weight as chilled carcass weight compared with 51.7% for normal lambs at the same mean live weight of 48.32 kg. Lighter pelt, kidney-pelvic fat, and liver weights contributed to this advantage of callipyge lambs for dressing percentage (P < .001). Estimated accretion rates of carcass protein at the mean slaughter age were 12.5 and 10.2 g/d for callipyge and normal carcasses, respectively. Corresponding values for carcass fat were 35.2 and 42.1 g/d. Compositional differences in favor of callipyge carcasses were detected at constant values of slaughter age, carcass weight, and 12th-rib fat depth. Callipyge carcasses had 2.56 kg greater fat-free lean and 1.39 kg less fat than normal carcasses at the same mean age of 214.9 d (P < .001). The majority of these differences were established before the initial group was slaughtered and were maintained as age increased. Callipyge carcasses consisted of 24.3% fat and 71.3% fat-free lean, compared with 31.5 and 64.0% for normal carcasses at 25.6 kg of carcass weight. When evaluated at .49 cm of 12th-rib fat depth, callipyge lambs were 15.4 d older and produced 4.1 kg heavier carcasses with 4.3% less fat (P < .001). Effects of CLPG genotypic groups on carcass composition were greater than virtually all reported breed substitution effects. Use of the CLPG mutant allele in structured mating systems can dramatically increase production of lean lamb.

Age Factors↗
PubMed1998

Evaluation of the ovine callipyge locus: I. Relative chromosomal position and gene action.

Genotypic and phenotypic data were collected to estimate chromosomal position of the callipyge (CLPG) gene and to test gene action. Nine Dorset rams of extreme muscling phenotype and 114 Romanov ewes composed the grandparent generation of a resource flock of 362 F2 lambs segregating at the CLPG locus. The parent generation consisted of eight F1 sires and 138 F1 dams. The F2 lambs were serially slaughtered in six groups at 3-wk intervals starting at 23 wk of age to allow comparisons at different end points. A linkage group of 25 marker loci (mean of 708 informative meioses per marker) spanning 87.2 cM was developed and improved the previous known coverage and precision of marker order and interval distance from available maps of ovine chromosome 18. Probabilities of each CLPG genotype were calculated at 1-cM intervals (0 to 107 cM). Statistical models included effects of year, sex, sire, regressions on genotypic probabilities, and genotype-specific linear and quadratic regressions on appropriate covariates. Orthogonal contrasts of CLPG genotypic effects evaluated additive, maternal dominance, and paternally derived polar overdominance models of gene action. The most parsimonious model did not include the additive and maternal dominance genetic contrasts. From analyses of four key traits, a consensus for position of CLPG was obtained at 86 cM relative to the most centromeric marker. An F-test with 3 df representing polar overdominance was maximum at position 86 cM (F = 407.4; P < .00001) with leg score as the dependent variable. These results are consistent with assignment of the CLPG locus to the telomeric region of chromosome 18 and support the polar overdominance model of gene action proposed by Cockett et al. (1996). Furthermore, recombinant individuals with definitive phenotypes confined the position of CLPG to a 3.9-cM interval, facilitating positional cloning experiments.

Animals↗
PubMed1997

Variability in metabolic rate, feed intake and fatness among selection and inbred lines of mice.

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss (HLOSS), along with randomly selected controls (MC). Objectives of this study were to (a) compare MH, ML and MC lines for HLOSS and correlated traits of feed intake, body composition and organ weights; (b) compare three widely used inbred mouse lines with MH, ML and MC for the same traits; and (c) investigate potential genotype by diet interaction resulting from feeding diets differing in fat percentage. Heat loss (kcal/day) of MH and ML mice differed by 37% of the mean and remained significant (33%) when HLOSS was expressed on a fat-free mass basis. MH mice consumed more energy than ML with a greater difference in mice fed high-fat compared with standard diets (27% vs 13.9%). Despite greater energy consumption, MH mice were leaner than ML with a difference in total body fat percentage of 40%. The greatest difference in HLOSS between selection and inbred lines was between MH and C57BL/6J (BL), which differed by 26.3%. MH and BL mice also differed in energy intake (15.5%). Body composition of BL mice was similar to MH when fed a standard diet, but similar to ML when fed a high-fat diet. Crosses between MH and ML or between MH and BL would be useful to investigate the genetic regulation of, and identify quantitative trait loci influencing HLOSS, energy intake and body composition. Feeding of a high-fat diet may allow diet-specific loci influencing body composition to be identified in MH and BL lines.

Adipose Tissue, Brown↗
PubMed1997

A simulation model including ovulation rate, potential embryonic viability, and uterine capacity to explain litter size in mice: I. Model development and implementation.

Litter size in mice was studied using a model including ovulation rate, potential embryonic viability, and uterine capacity. Simulated results were compared with experimental results from a selection experiment with mice. The four criteria of selection were selection on number born (LS), selection on an index of ovulation rate and ova success (IX), selection on number born to unilaterally ovariectomized females (UT), and unselected control (LC). Comparisons were made to statistics of the base generation and to responses after 13 generations of selection. Phenotypic and genetic statistics for uterine capacity were generated so that simulations produced the experimental means, standard deviations, and correlations between left and right litter size, as well as responses in number born using the LS, IX, and UT criteria. Statistics for the simulated data generally agreed with observed values. Simulated heritability in the base generation for uterine capacity was .065. Experimental and simulated responses per generation in litter size through 13 generations of selection were .15 and .16, .17 and .18, and .10 and .11 for LS, IX, and UT, respectively. Simulated responses in uterine capacity after 13 generations were 2.19, 1.60, and 3.40 for LS, IX, and UT, respectively. Simulated means for the base generation were 13.22 and 16.30 for ovulation rate and uterine capacity, respectively. Uterine capacity was an important component of the variability in litter size; however, ovulation rate was the more limiting component.

Algorithms↗
PubMed1997

A simulation model including ovulation rate, potential embryonic viability, and uterine capacity to explain litter size in mice: II. Responses to alternative criteria of selection.

Direct selection for litter size was compared with selection for ovulation rate, ova success, or uterine capacity and for indexes of ovulation rate with ova success or uterine capacity. Selection was simulated for 10 generations in a mouse population based on a model integrating ovulation rate, potential embryonic viability, and uterine capacity. Two indexes including ovulation rate (OR) and ova success (OS) were I = .291 x OR + 2.19 x OS and I = .165 x OR + .736 x OS. Heritabilities for ovulation rate and ova success, assumed in the simulation and to derive the indexes, were .25 and .06, respectively. Both indexes resulted in the same response in litter size, 12.9% greater than response to direct selection for litter size. Two indexes including OR and uterine capacity (TUC = true total uterine capacity; UC = uterine capacity measured as number born for a female with right ovary excised) were I = .881 x OR + .223 x TUC and I = .876 x OR + .568 x UC. Heritabilities assumed for uterine capacity were .09 (TUC) and .065 (UC). The first index assumed true parameters for uterine capacity (TUC) and resulted in a response in litter size that was 23.9% greater than direct selection. The second index was calculated using parameters estimated under a unilateral-ovariectomy model and resulted in response that was 14.7% greater than direct selection. Selection for OR, TUC, UC, or OS resulted in responses that were 4.5, 48.5, 38.7, or 74.8%, respectively, less than that from direct selection for litter size.

Animals↗
PubMed1997

Effects of sire, dam traits, calf traits, and environment on dystocia and subsequent reproduction of two-year-old heifers.

A study was conducted over 3 yr to evaluate effects of sire birth weight EPD, calf birth weight and shape, and heifer pelvic area and weight, individually and in combination, on dystocia and subsequent rebreeding of 2-yr-old heifers. Heifers (n = 550), MARC II yearlings, were assigned for breeding to one of four Angus sires with birth weight EPD of -.95, -82, +2.9, and +2.7 kg. At calving, heifers were assisted as needed. A gauge attached to the cal puller recorded applied traction pressure. Analysis of traction pressure detected only slightly larger amounts of variation (2 to 3%) affecting dystocia than the standard five-point scoring system. Dam weight did not affect calving difficulty score (CDS), except dam birth weights were heavier (P < .05) for CDS 5 (Caesarean section) than CDS 1 (unassisted). Dams requiring Caesarean section had smaller pelvic areas (P < .05), with no other differences among CDS. The CDS increased as calf birth weight and cal external measurements increased. Low EPD sires produced calves with smaller (P < .05) birth weights and smaller calf head and food circumferences and caused less dystocia than high EPD sires. The CDS did not affect subsequent pregnancy rates but did affect conception date of the second calf. Calves delivered by Caesarean section were lighter (P < .05) at weaning than other calves but had similar slaughter weights. As mean winter temperature increased (6.1 degrees C) from yr 1 to 3, calf birth weight decreased (4.6 kg) and calving difficulty decreased 23%. Results indicate sire birth weight EPD, calf birth weight and shape, dam pelvic area, and climate affected CDS, and CDS affected subsequent conception date.

Aging↗
PubMed1997

Divergent selection for heat loss in mice: I. Selection applied and direct response through fifteen generations.

Divergent selection for heat production/loss (kcal.kg-.75.d-1), measured in 9- to 11-wk-old male mice, was conducted for 15 generations. Heat loss was measured for 15 h on individual animals placed overnight in direct, gradient-layer calorimeters. Selection for high (MH) and low (ML) heat loss and unselected control (MC) occurred in each of three replicates for a total of nine unique lines. Repeatability of the heat loss measurement was .45 and the CV was 10.5%. Cumulative realized selection differentials, averaged for the three replicates, were 145.1 and -105.0 (kcal.kg-.75.d-1) and ranged from 136.9 to 149.2 and -17.1 to -101.3 for MH and ML selection, respectively. Cumulative standardized realized selection differentials, averaged for the three replicates, were 10.06 and -9.51 for MH and ML selection, respectively. Direct responses (kcal.kg-.75.d-1) in heat loss after 15 generations were 44.2 for MH and -27.4 for ML as deviations from MC. Asymmetry of response was evident (P = .03) by Generation 10. Realized heritability was .28 +/- .01 based on divergence of MH and ML selection. For selection for higher and lower heat loss, realized heritabilities were .31 +/- .01 and .26 +/- .01, respectively.

Animals↗
PubMed1997

Divergent selection for heat loss in mice: II. Correlated responses in feed intake, body mass, body composition, and number born through fifteen generations.

Divergent selection for heat loss (kcal.kg-.75.d-1), measured in 9- to 11-wk-old male mice, was conducted for 15 generations. Selection for high (MH) and low (ML) heat loss and unselected control (MC) occurred in each of three replicates for a total of nine unique lines. Feed intake in males was measured during Generations 9 through 15. Body mass at commencement of mating in females and at time of measurement of heat loss in males was recorded. Body fat percentage at 12 wk for animals of Generations 6, 10, and 14 was predicted as a function of electrical conductivity and body mass. Litter size was recorded for all generations, and components of litter size were evaluated at Generation 11 in one replicate and Generation 12 in the other two replicates. Feed intake changed in the same direction as heat loss for the MH and ML selections; at Generation 15, the difference between MH and ML (P < .002) was 20.6% of the MC mean. Body mass did not change with selection for heat loss. Differences in body fat percentage were not significant in earlier generations, but at Generation 14, MH and ML were significantly (P < .01) different with MH mice having the lowest fat percentage; MC was intermediate. Selection had a significant (MH vs ML; P < .01) effect on litter size, causing an increase in MH and a decrease in ML. This difference was explained by a difference (P < .01) in ovulation rate. There was no asymmetry of response in feed intake, fatness, litter size, or number of ovulations.

Animals↗
PubMed1996

Estimates of heritabilities and genetic and environmental correlations for left- and right-side uterine capacity and ovulation rate in mice.

Heritabilities for and genetic and environmental correlations between uterine capacity, ovulation rate, and body mass (BM) were estimated in mice. Uterine capacity was defined as the number of fetuses (LUC or RUC for left or right side) in one uterine horn for unilaterally ovariectomized females. Ovulation rate (corpora lutea, LCL or RCL for left or right ovary) was measured on the remaining single ovary in these same females. Data on 1,931 mice from four selection populations were used. Left ovulation rate and LUC were measured on 958 animals, and RCL and RUC of another 972 animals were recorded. Genetic and environmental variances and covariances were estimated simultaneously using an animal model with a multiple-trait, derivative-free, restricted maximum-likelihood procedure. Averages for heritability and correlation estimates derived from separate analyses of the selection populations are presented below. Heritability of LUC was higher (.33 +/- .06) than that of RUC (.19 +/- .02). Heritability of LCL and RCL ranged from .17 +/- .03 to .27 +/- .06, and heritability for BM was .65 +/- .05. The genetic correlation between LUC or RUC and LCL or RCL ranged between .43 +/- .29 and .68 +/- .05, and between LUC and RUC was .92 +/- .05. Body mass had a higher genetic correlation with LCL and RCL (.70 +/- .12 and .93 +/- .02) than with LUC and RUC (.37 +/- .05 and .47 +/- .12). Environmental correlations between LCL and LUC and RCL and RUC were .32 +/- .09 and .36 +/- .05, respectively.

Analysis of Variance↗
PubMed1996

Embryonal survival to 6 days in mice selected on different criteria for litter size.

Embryonal survival was compared in mice resulting from four criteria of selection: LS = selection on number born; IX = selection on an index of ovulation rate and ova success; UT = selection on number born to unilaterally ovariectomized females; and LC = unselected control. Selection occurred for 21 generations with three replicates of the four criteria; thereafter, relaxed selection was practiced. The evaluation was performed using mice of two replicates at Generation 35 and one replicate at Generation 36. Data on a total of 289 female mice were recorded. Females, at an average age of 9 wk, were mated to males of the same line. Six days after mating, each female was killed, ovaries were excised, corpora lutea were counted and equated to number of ova shed, and the numbers of implantation sites in each uterine horn were recorded. Least squares means were .84, .91, .85, and .82 for left embryonal survival (left implantations/left ova) and .91, .90, .86, and .87 for right embryonal survival for LS, IX, UT, and LC, respectively. The right side had greater ovulation rate (P < .001) and number of implantations (P < .001). For embryonal survival, the criterion x side interaction was possibly important (P < .09). Selection for litter size by different criteria increased ovulation rate (P < .003) and embryonal survival (P < .05) to 6 d. However, responses in embryonal survival were not greater after UT selection compared with LS or IX selection.

Animals↗
PubMed1995

Differences in pup birth weight, pup variability within litters, and dam weight of mice selected for alternative criteria to increase litter size.

Selection for litter size had been practiced for 21 generations and relaxed selection for 13 generations in mice. Three replicates were used with four selection criteria: index of components (ovulation rate and ova success), uterine capacity, litter size, and an unselected control. Especially with selection for litter size and the index relative to the control, number of pups born had increased, and differences also occurred in mating weight. Dams of the three replicates and their litters were used to evaluate the effects of accumulated selection on pup birth weight, variability in weight of littermates, and dam's weight at mating and after littering. Total number born, number born alive, number of males, and number of females were also recorded and studied. Mean pup birth weight did not differ among the criteria; however, variability among littermates in pup weight tended to differ among criteria of selection. Regressions for pup weight and within-litter standard deviation of pup weight on number born were small and negative but significant (P < .001). The distribution of pup weight within litter was normal for 77.2% of the litters, with no differences among the criteria. The difference between weight of male and weight of female pups was significant (P < .001); overall males were 2.5% heavier than females. There was a difference (P < .02) among criteria in mating weight and littering weight; however, the maternal weight gain between mating and littering was not different among criteria. Number born differed (P < .003) among the criteria, but there was no significant difference among criteria in numbers of males and females.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Uterine mass and uterine blood volume in mice selected 21 generations for alternative criteria to increase litter size.

Lines of mice, selected for 21 generations using alternative criteria to increase litter size, were evaluated for uterine mass and uterine blood volume to help explain differences in uterine capacity. For this study, mice were sampled from Generation 27, the sixth generation after relaxation of selection. Mice came from all four criteria of selection (LS = selection on number born to unaltered females; IX = selection on index of ovulation rate and ova success; UT = selection on uterine capacity; and LC = unselected control) in each of three replicates (a total of 12 lines). Measurement was at one of two stages, either 3 d or 6 d of gestation. Matings were at 10 wk of age, and a total of 508 mice (17 to 26 per line-day of pregnancy subclass) were measured. The mean of the three selected groups exceeded the control in uterine mass (P < .001), uterine blood volume (P < .002), uterine mass/body mass (P < .03), and uterine blood volume/body mass (P < .04) but not in uterine blood volume/uterine mass. Greater uterine mass and concomitantly greater uterine blood volume may have been partly responsible for greater uterine capacity resulting from LS, IX, and UT selections.

Animals↗
PubMed1994

Serum cholesterol concentration of mice selected for litter size and its relationship to litter size and testis mass.

This study assessed the genetic relationship between litter size and serum cholesterol concentration and between litter size and testis mass in mice. Mice were from a long-term experiment in which selection had occurred for 21 generations in three replicated lines per criterion of selection (LS = selection to increase litter size based on number born; LC = unselected control). Thereafter, random mating within lines was practiced. Serum cholesterol concentrations were evaluated in female and male mice from two replicates at Generation 29 and one replicate at Generation 30. Body weights and blood samples were collected from primiparous females 8 d after weaning their pups. Data from males were collected as they came out of breeding cages. In addition, the testes were excised, stripped clean of connective tissue and the epididymides, and weighed. Means for body mass of females and males, serum cholesterol, number born, and testis mass were as follows: 35.2 vs 32.5 g (P < .09), 33.9 vs 30.7 g (P < .08), 117.5 vs 110.5 mg/dL (P < .08), 14.0 vs 10.3 pups (P < .04), and 126 vs 122 mg, respectively, for LS and LC. Serum cholesterol was greater in males than in females (133.3 vs 95.1 mg/dL; P < .001), but there was no interaction between sex and selection criterion. Serum cholesterol concentration was not correlated phenotypically to number born or body mass, but it had a small negative relationship with testis mass. Therefore, we concluded that selection for litter size tended to increase serum cholesterol in addition to the increase in number born but did not change testis mass.

Animals↗
PubMed1994

Effects of Synovex C implants on growth rate, pelvic area, reproduction, and calving performance of replacement heifers.

Two trials were conducted to evaluate effects of Synovex C implants on replacement heifers, given at two different ages. Crossbred heifer calves (n = 370) were allotted to four treatments: 1) nonimplanted controls, 2) implanted at 2 mo, 3) implanted at 6 mo, and 4) implanted at both 2 and 6 mo of age. Heifers implanted at 2 mo gained 7 kg more (P = .01) by 6 mo than those not implanted at 2 mo. No differences were found in 22-mo weights. All implanted heifers had larger (P = .01) yearling pelvic area than controls. All heifers implanted at 6 mo continued to have larger (P = .01) pelvic area at 22 mo. All implanted heifers had higher (P = .05) occurrence of non-ovulatory estrus. No differences were found among treatments in percentage of heifers puberal before breeding, in estrus first 21 d of breeding, or in first-service conception rate. In only one trial, pregnancy first 21 d and total pregnancy in 63-d breeding season were decreased (P = .05) by implanting at 6 mo. At subsequent calving, an interaction existed between the effects of the 2- and the 6-mo implant for calf birth weight and pelvic area:birth weight ratio. A single implant at either 2 or 6 mo decreased (P = .01) calving difficulty score; and implanting at both 2 and 6 mo showed the greatest reduction in calving difficulty. Implants had no significant long-term effects on reproduction or calf production of 2-yr-old cows.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗