Monte Carlo computer simulation of a closed strain herd of swine was used to investigate the accuracy of genetic parameter estimates for litter size at birth by REML. A breeding herd of 10 sires and 50 dams in a base population was assumed; one male was randomly mated to five females. From each litter, one boar and one, two, or three gilts as three schemes were reared and one boar per five gilts was randomly selected and mated. Eleven generations including the base population, without overlapping, was simulated. The heritability of litter size at birth was assumed to be 0.1. Generation constants were generated as a fixed effect. A hundred replications were simulated for each scheme. For each generation of each replicate, means of the genetic parameter estimates and the square roots of their mean square errors (SMSE) were calculated. When the number of animals with a record of litter size at birth was less than 500, additive genetic variance and heritability for litter size at birth were overestimated and the environmental variance was underestimated. SMSE of each genetic parameter decreased rapidly with increase in population size, but it declined slightly when the number of animals with a record was more than 500. When the number of growing females per litter was one, heritability estimates of about 30% were less than 0.1% even if records of over five generations were used for genetic parameter estimates.

View full abstract

Two experiments were conducted to assess effects of outdoor fattening on pigs' behavior, growth performance, and carcass traits. For each experiment, 8 pigs (WL×D) were separated equally into a control group (CG) and an outdoor fattening group (OFG). For Experiment 1, CG pigs were fattened entirely indoors (slatted floors, 1.8m²/pig). The OFG pigs were fattened outdoors (bamboo thicket, 60m²/pig) during 10 : 00-17 : 00, and indoors during 17 : 00-10 : 00 (1.8m²/pig). The CG pigs were fed a commercial diet ad libitum. The OFG pigs were fed a commercial diet restrictively (750g /pig/day) when pigs were outdoors ; they were fed ad libitum other times. For Experiment 2, CG pigs were fattened entirely indoors (1.8m²/pig) ; OFG pigs were fattened outdoors (30m²/pig). Both groups were fed a commercial diet ad libitum. Experiments ceased when the pig weight reached 105kg. Based on results of Exp. 1 OFG pigs had significantly lower feeding, drinking, and resting, and a higher behavior ratio of exercise than CG pigs had (P<0.05). Their feed intake was lower than that of CG pigs. The OFG pigs had significantly lower average daily gain than CG pigs had (P<0.05). The OFG pigs had longer carcass length, back loin length I, back loin length II, and loin length than CG pigs had (P<0.05). The backfat depth (shoulder, back, loin, and three-point average) of OFG pigs was less than that of CG pigs. Based on Exp. 2, no significant differences in feeding, drinking, or behavior ratios of eliminating between were found between the two groups. However, OFG pigs displayed significantly less resting and a higher ratio of exercise behavior than CG pigs did (P<0.05). The OFG pigs showed less feed intake than the CG pigs did. Consequently, the average daily gain of OFG pigs was lower than that of CG pigs (P<0.05). The OFG pigs showed lower growth performance attributable to more exercise, less rest, and less intake, but carcass traits included longer loin length and thinner back fat, suggesting that outdoor fattening for pork production gives a high red-meat yield.

View full abstract

The effects of selection and population size on estimates of variance components and breeding values using REML estimation were assessed by stochastic computer simulation. One hundred closed breeding herds of one through 100 sires per generation were simulated, assuming six generations including a base population without overlap. A boar was mated to 10 gilts randomly and each mating produced two males and two females as candidates for selection. Two different heritabilities of 0.25 and 0.50 per trait were used. Selection was either at random or based on the phenotypic performance of the individual. Generation constants were generated as a fixed effect. One hundred replicates were simulated for each combination of heritability, population size, and selection scheme. For each replicate, variance component estimates and their square roots of mean square errors (SMSE) were calculated, and breeding values and generation effects were estimated using the estimates of additive genetic and error variances. SMSE of additive genetic and error variance estimates were slightly smaller from randomly selected populations than from phenotypically selected populations. SMSE of additive genetic and error variance estimates decreased with the increase in population size. SMSE of estimates of fixed generation effect from randomly selected populations were smaller than from phenotypically selected populations. For randomly selected populations, correlations between true and estimated breeding values were higher and their SMSE were slightly smaller than phenotypically selected populations.

View full abstract