Biomedical subjects

K A Leymaster

Publications and source records attributed to K A Leymaster.

45 records · Page 3Linked to original sources

PubMed1990

Genetic implications of a simulation model of litter size in swine based on ovulation rate, potential embryonic viability and uterine capacity: I. Genetic theory.

A simulation model of litter size in swine based on ovulation rate, uterine capacity and potential embryo viability was compared to three genetic models to clarify its genetic characteristics. The simulation model is equivalent to independent culling based on fixed levels of potentially viable embryos and uterine capacity. Litter size also can be described by a combination of additive, additive x additive, mean environment x additive, random environment and additive x random environment effects. A third genetic model that can describe the simulation model is the associative effects model, in which litter size is the result of grouping two genotypes. The fixed independent culling levels model predicts that genetic parameters will change as the component means change. This genetic model also predicts that selection on an index of ovulation rate and uterine capacity would improve selection response for litter size. This genetic model predicts asymmetry of correlated responses in ovulation rate and uterine capacity when selecting for high and low litter size. The nonadditive genetic model predicts covariances among relatives that are different from their additive relationships; however, simulated results did not detect any differences. The nonadditive genetic model also predicts that heterosis for litter size will differ among crosses based on the mean environment and on additive x additive genetic interaction. The associative effects model predicts that selection for litter size will always lead to a positive response in litter size.

Animals↗

PubMed1990

Genetic implications of a simulation model of litter size in swine based on ovulation rate, potential embryonic viability and uterine capacity: II. Simulated selection.

Direct selection for ovulation rate, uterine capacity, litter size and embryo survival and selection for indexes of ovulation rate with each of the remaining traits were simulated for a swine population. The relationships among these traits were determined from a simulation model that assumed that litter size was always less than or equal to both ovulation rate and uterine capacity. Heritabilities of ovulation rate and uterine capacity were assumed to be .25 and .20, respectively, and uncorrelated genetically and phenotypically. No additional genetic variation was assumed. Responses to weak selection pressure were simulated by recurrent updating of phenotypic variances and covariances combined with the heritabilities of ovulation rate and uterine capacity. Two indexes of ovulation rate and uterine capacity each resulted in 37% greater increase in litter size than direct selection for litter size. Indexes of ovulation rate and either litter size or embryo survival increased litter size by 21% more than direct selection for litter size. Selection for ovulation rate, uterine capacity or embryo survival was 6, 35 and 79%, respectively, less effective than direct selection for litter size. Responses to intense selection pressure were determined by direct simulation of genotypes and phenotypes of individuals. The two indexes of ovulation rate and uterine capacity exceeded direct selection for litter size by 39 and 27%. The indexes of ovulation rate and either litter size or embryo survival exceeded direct selection for litter size by 19 and 13%, respectively. Intense selection for ovulation rate or uterine capacity decreased selection response by 26 and 67%, respectively, relative to direct selection for litter size. Intense selection for embryo survival decreased litter size slightly.

Animals↗

PubMed1989

Integration of ovulation rate, potential embryonic viability and uterine capacity into a model of litter size in swine.

A mathematical model of litter size in swine was developed from ovulation rate, potential embryonic viability and uterine capacity. The model assumed that ovulation rate was reduced to potentially viable embryos by factors innate to the ovum and embryo. Potentially viable embryos then could be further reduced to uterine capacity, the maximum number of fetuses that a female can carry to term. Consequently, litter size can be no greater than either ovulation rate or uterine capacity. Means and variances of ovulation rate and potential embryonic viability used in the model were based on experimental results. The mean and variance of uterine capacity were varied until the simulated mean and variance of litter size were equal to experimental results. Simulated results of relationships among ovulation rate, embryo survival and litter size were similar to observed experimental relationships. Heritabilities of simulated litter size and embryo survival were similar to literature values when the heritability of ovulation rate was set at .25 and the heritability of uterine capacity was set at either .15 or .20. Litter size was simulated for 25 combinations of average ovulation rate and uterine capacity to develop equations relating mean ovulation rate and uterine capacity to litter size, embryo survival and correlations among them. Results suggest that changing either ovulation rate or uterine capacity independently will not result in large changes in litter size. Consequently, the model suggests that a single gene, hormonal manipulation or nutritional change will not result in large increases in litter size and that combinations of factors will be needed to increase litter size.

Algorithms↗

PubMed1987

The crossbred sire: experimental results for sheep.

Crossbreeding of sheep is practiced to exploit simultaneously the use of additive and nonadditive genetic effects. The goal is to achieve optimal levels of performance appropriate for defined systems of sheep production and marketing. Although the beneficial effects of individual and maternal heterosis on sheep production have been well documented and widely implemented, considerably less is known about the effects of paternal heterosis. Limited evidence suggests that crossbred rams are more sexually aggressive and exhibit greater testicular growth than do purebred rams. Average estimates of paternal heterosis effects were 1.4, -.7 and 2.3% for seasonal fertility, prolificacy and preweaning survival, respectively. The average effect of paternal heterosis on fertility during spring breeding was 29.5%. Progeny of crossbred and purebred sires were similar in birth weight, weaning weight and postweaning growth rate and in phenotypic variation for these growth traits. However, favorable paternal heterosis effects need not exist to warrant the use of crossbred sires. Composite or F1 sires can be used as an effective method to manage the composition of additive breed effects. For example, varying proportions of germ plasm from highly prolific breeds such as the Finnsheep and Romanov can be realized through the use of crossbred sires to set reproductive rates at desired levels. Crossbred sires may be used to a greater extent to optimize additive breed effects than to exploit effects of paternal heterosis. The role of composite breeds in managing both additive and nonadditive effects is discussed.

Animals↗

PubMed1987

Feeding behavior characteristics of intact male lambs as affected by number of lambs in a pen with restricted access to the feed stall.

To investigate the effect of number of animals housed in a pen upon feed intake, 72 intact male lambs were randomly assigned to treatments consisting of 3, 7, 11 or 15 animals/pen in each of two trials. For each animal's feeding event, length of feeding (s) and feed consumption (g) were recorded through use of an automatic feeding system. This system allows one animal to feed at a time. Pens were treated as experimental units with observations repeated daily for 21 d. Response variables were feed consumption (g), time (s) and rate of feed consumed (g/s) per visit and feed consumption (g), average time (s) and number of visits per animal daily. Number of animals/pen was significant for most feeding behavior characteristics. As number of lambs within a pen increased, feed consumption/visit increased linearly in both trials. For Exp. 1, rate of feed consumption/visit increased at a decreasing rate, while in Exp. 2 only the linear effect of lamb numbers on this trait was significant. Daily feed consumption/lamb was greatest for intermediate lamb numbers, and the number of visits and time spent feeding/lamb decreased as the number of lambs within a pen increased. Results suggest that the feeding behavior of ram lambs with restricted access to a feeding stall can be modified by the number of lambs housed in a pen.

Animals↗

PubMed1987

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine.

Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Genetic variation in testicular development and its relationship to female reproductive traits in swine.

In situ length and width of both testes and body weight were recorded on 40 Chester White, 60 Landrace, 60 Large White and 62 Yorkshire boars born in the spring and on 57 Duroc, 54 Hampshire, 57 Pietrain and 50 Spot boars born in the fall. Testicular biopsies on one-half of the boars in each breed group were evaluated for percentage of tubules with complete spermatogenesis and for diameter of tubules. Testicular volume of both testes was estimated at 98 and 154 d of age and 36 and 81 kg. Breed effects were significant for all testicular traits except testicular volume at 36 kg in the spring farrowing and testicular volume at 98 d of age in the fall farrowing. The estimate of heritability for testicular volume was low at 98 d of age (.12 +/- .14) but large at 154 d of age (.55 +/- .12). Heritability estimates for testicular volume were lower at constant weights (.11 +/- .14 and .14 +/- .12) than at constant ages (.12 and .55). Heritability estimates for traits measured by biopsy were moderate to large (.22 +/- .22 to .78 +/- .18). Phenotypic correlations of in situ testicular volume with traits measured by biopsy were moderate and positive when estimated within a breed (.16 to .52). Genetic correlations of testicular volume at constant ages and weights with traits measured by biopsy were moderate to large and positive (.58 to greater than 1.0); similar correlations among bred means were quite variable (-.35 to .91). Selection for increased testicular volume would not be antagonistic to selection goals for growth and backfat. However, selection for improvement in traits measured by biopsy may result in undesirable changes in growth rate and backfat probe. Genetic correlations of testicular traits with age at puberty and litter size of females were not consistent in magnitude or sign between the two estimation procedures.

Animals↗

PubMed1985

Relationships of birth weight and pre-nursing concentrations of serum albumin to survival and growth rate in swine.

Data from 29 litters of swine were analyzed to estimate the relationships of birth weight and pre-nursing concentrations of serum albumin to survival and daily gain from birth to 14 d and from 14 to 28 d. Means and standard deviations of birth weight and serum albumin were calculated within each litter and used as analytical units. Positive linear partial regression coefficients were detected for effects of serum albumin on birth weight (P less than .01) and daily gains (P less than .05). As both serum albumin and birth weight increased, survival also increased but at a decreasing rate (P less than .05). Survival decreased as the standard deviations of serum albumin (P less than .05) and the birth weight (P less than .10) increased. Daily gain from 14 to 28 d of age increased (P less than .10) as the standard deviation of serum albumin varied above or below about .5 mg/ml. The linear effect of birth weight on daily gain from birth to 14 d of age was positive (P less than .01), whereas daily gain from 14 to 28 d of age increased as birth weight varied above or below about 1.3 kg (P less than .01). Daily gains during the first and second periods also increased as the standard deviation of birth weight varied above or below .3 kg (P less than .05) and .25 kg (P less than .001), respectively. Fitting birth weight and serum albumin simultaneously into the statistical model accounted for 57% of the variation in survival, a level at least twice as great as previously reported. It is speculated that use of a marker of physiological maturity, such as pre-nursing concentrations of serum albumin, might facilitate selection for survival.

Aging↗

PubMed1984

Differential deposition and utilization of backfat layers in swine.

Growing pigs were nutritionally manipulated to study depletion, depletion followed by repletion or deposition of the individual backfat layers. Obese and lean pigs were used to gain insight into the possible role of genetic selection for backfat depth on each backfat layer. Backfat depth, including individual layers was measured in live pigs at sequential times by ultrasonic methods. At a variety of anatomical locations, change in backfat expressed as a rate or as percentage change during both depletion and deposition was greater in layer 2 than layer 1 (outermost). Genetically obese pigs increased backfat depth by accretion of layer 2 to a greater extent than layer 1. Genetically lean pigs had more equal accretion of the two layers with a preference toward layer 1 in some cases. Selection for total backfat depth appears to have selected layer 2 in preference to layer 1. Backfat layer 1 changed to a small extent compared to layer 2 during depletion, deposition or genetic selection possibly indicating a greater metabolic role in vivo for layer 2.

Adipose Tissue↗