A total of 383 barrows and gilts from a French Large White experimental herd were slaughtered at 100 kg BW. Samples of longissimus muscle were taken to categorize myofibers according to their contractile (I, IIA, and IIB) and metabolic (oxidative and nonoxidative) properties. Myofiber percentages, cross-sectional areas (CSA), and relative areas were measured. Growth rate, carcass composition, muscle chemical composition, metabolic enzyme activities, and meat quality traits were also measured to estimate phenotypic and genetic correlations between these traits and myofiber characteristics. Genetic parameters were estimated using a REML procedure applied to an individual animal model. Heritabilities of fiber traits were moderate to high (h2 = .20 to .59). Highest heritabilities were found for type I fiber percentage (h2 = .46 +/- .11), type IIBw fiber percentage (h2 = .58 +/- .11), and type I fiber cross-sectional area (h2 = .59 +/- .10). For a given fiber type, the relative area was phenotypically and genetically more closely related to the percentage than to the CSA. Phenotypic correlations between fiber type composition and other traits were low. Genetically, growth rate, carcass leanness, and loin eye area were positively related to fiber CSA. Intramuscular fat content was not related to fiber type composition (r(g) = -.05 to .06), whereas it was positively related to fiber CSA (r(g) = .68). Type IIBw fiber percentage was related to pH at 30 min (r(g) = -.46), pH at 24 h (r(g) = -.62), glycolytic potential (r(g) = .31), and lightness of color (r(g) = .55) of longissimus muscle.

Effect of halothane genotype (NN, Nn, nn) on growth, carcass and meat quality traits of pigs slaughtered at 95 kg or 125 kg live weight By C. LARZUL', P. LE ROY', R. GUEBLEZ', A. TALMANT3, J. GOGUE4, P. SELLIER' and G. MONIN3three halothane genotypes (NN, Nn, and nn). In recent studies using DNA-based genotyping, but involving only N N and Nn pigs, GARC~A-MAC~AS et al. (1996) andLEACH et al. (1996) found no significant halothane genotype by slaughter weight interaction.This work aimed to compare the NN, Nn, and nn halothane genotypes, as determined by a DNA-based test, among pigs sharing the same polygenic background (Pietrain x Large White F2 cross) and slaughtered at either of two live weights (around 95 kg or 125 kg), thus bracketing the current average slaughter weight of French market pigs (105-110 kg), to study slaughter weight x HAL genotype interaction. Materials and methods An i m a 1 sThis study involved a total of 446 F2 Pietrain x Large White pigs from two contemporary experiments. Though these experiments were not carried out at the same place, important similarities in their designs (genetic type, slaughtering conditions, traits measured) enabled the data, after separate analyses gave similar results for common traits (GU~BLEZ et al. 1995;LARZUL et al. 1996), to be pooled for a global analysis. Experiment 1In this experiment, carried out on the INRA Farm in Bourges (Cher), 22 Large White sows were inseminated by seven Pietrain boars. The expected N n halothane genotype of the resulting F1 pigs was verified, using a DNA-based test (DALENS and RUNAVOT 1993). U.S.Eight F1 boars were mated to F1 gilts to produce 57 F2 litters, in which the same DNAbased test was used to determine the halothane genotype of the piglets. In four fattening batches, females and castrated males were reared in pens homogeneous for sex and halothane genotype (around nine animals per pen), and they were given ad libitum access to feed (crude protein: 17.0 %; ME 3091 kcal/kg) until their live weight reached 100 kg ('light') or 125 kg ('heavy'). The experiment was designed so that about two-thirds and one-third of the pigs were allocated to the 'light' and 'heavy' slaughter weight treatments, respectively.During fattening, the mortality rates were 1.1%, 0.6%, and 15% for the NN, Nn, and nn genotypes, respectively, and, within one slaughtering series, the three nn pigs died during transport to the abattoir. Experiment 2This experiment was carried out on three commercial farms, where Pietrain x Large White sows were inseminated by 18 Pietrain x Large White boars, in order to obtain F2 piglets from the three halothane genotypes, as determined by the same DNA-based test described in experiment 1. Castrated males from 42 F2 litters were reared in two fattening batches on a single commercial farm. They were penned by halothane genotype (around 11 animals per pen) and fed ad libitum, with a commercial diet of similar energy and crude protein content to that used in experiment 1, until their live weight reached 90 kg ('light') or 125 kg ...

The aim of this work was to estimate whether genetic dissection of QTL on chromosomes 1, 2, 4, and 7, detected in an F2 Meishan x Large White population, can be achieved with a recombinant back-cross progeny test approach. For this purpose, a first generation of backcross (BC1) was produced by using frozen semen of F1 Large White x Meishan boars with Large White females. Four BC1 boars were selected because of their heterozygosity for at least 1 of the 4 regions. The BC1 boars were crossed with Large White sows, and the resulting BC2 offspring were measured for several growth and body composition traits. Contrary to the F2 animals, BC2 animals were also measured for meat quality traits in adductor, gluteus superficialis (GS), longissimus dorsi, and biceps femoris (BF) muscles. Each BC1 boar was tested for a total of 39 traits and for the 4 regions with statistical interval mapping analyses. The QTL effects obtained in BC1 families showed some differences compared with those described in F1 families. However, we confirmed QTL effects for growth in the SW1301-SW2512 markers interval on chromosome 1 and also for body composition in the SW1828-SW2512 markers interval on chromosome 1, in the SW2443-SWR783 markers interval on chromosome 2, and in the SW1369-SW632 markers interval on chromosome 7. In addition, we detected new QTL for growth traits on chromosome 2 and for meat quality traits on chromosomes 1 and 2. Growth of animals from weaning to the end of the test was influenced by the IGF2 gene region on chromosome 2. Concerning meat quality, ultimate pH of adductor, longissimus dorsi, and BF were affected by the interval delimited by UMNP3000 and SW2512 markers on chromosome 1, and a* of GS, L* of BF, and water-holding capacity of GS were affected by QTL located between marker loci SW2443 and SWR783 on chromosome 2. Recombinant progeny testing appeared to be a suitable strategy for the genetic dissection of the QTL investigated.

Genetic trends for body composition and blood plasma parameters of newborn piglets were estimated through the comparison of two groups of pigs (G77 and G98, respectively) produced by inseminating Large White (LW) sows with semen from LW boars born either in 1977 or in 1998. Random samples of 18 G77 and 19 G98 newborn piglets were used for whole carcass and tissue sampling. Plasma concentrations of glucose, albumin and IGF-1 were determined on 75 G77 and 90 G98 piglets from 18 litters. The G98 piglets had less carcass dry matter, protein and energy (P , 0.01) than their G77 counterparts. When expressed in g/kg birth weight, livers were lighter (P , 0.001) and contained less glycogen (P , 0.01) in G98 piglets, with no difference in the activity of the hepatic glucose-6-phosphatase between G98 and G77 piglets. Concentrations of protein, DNA, RNA in longissimus dorsi muscle were unaffected by selection. Plasma concentrations of glucose (P , 0.05) and IGF-1 (P , 0.01) were lower in G98 than in G77 piglets. On the whole, the results suggest that the improvement in lean growth rate and in sow prolificacy from 1977 to 1998 has resulted in a lower maturity of piglets at birth.

Effects of selection for ovulation rate or prenatal survival were examined using data from 3 pigs lines derived from the same base Large White population. Two lines were selected for 6 generations on high ovulation rate at puberty (OR line) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS line). The third line was an unselected control line. Genetic parameters for ovulation rate on the left, right, and both ovaries at puberty (ORPL, ORPR, and ORP, respectively) and at fertilization (ORFL, ORFR, and ORF, respectively), total number of piglets born (TNB) per litter, prenatal survival (PS = TNB/ORF), and PS corrected for ovulation rate (CPS = PS + 0.018ORF) were estimated using REML methodology. Responses to selection were estimated by computing differences between OR or PS and control lines at each generation using least squares and mixed models methodology. Average genetic trends were computed by regressing line differences on generation number. Realized heritabilities were estimated using standard procedures. Heritability estimates were 0.17, 0.11, 0.34, 0.13, 0.09, 0.33, 0.14, 0.11, and 0.17 (SE = 0.01 to 0.03) for ORPL, ORPR, ORP, ORFL, ORFR, ORF, PS, CPS, and TNB, respectively. Realized heritabilities were 0.37 +/- 0.08 and 0.10 +/- 0.09 for ORP and CPS, respectively. The different measures of ovulation rate had strong genetic correlations (r(g) > 0.7). The ORF had midrange negative genetic correlations with PS and CPS (-0.45 +/- 0.07 and -0.42 +/- 0.08, respectively). The ORP also had an antagonistic genetic relationship with PS (-0.26 +/- 0.07) but was almost independent from CPS (-0.02 +/- 0.11). The TNB was moderately correlated with ORP and ORF (r(g) = 0.41 +/- 0.09 for both traits). Average genetic trends in OR and PS lines were, respectively, 0.49 +/- 0.10 and 0.11 +/- 0.10 for ORP, and 0.43 +/- 0.11 and 0.11 +/- 0.11 for ORF. Responses to selection were slightly superior in the left than in the right ovary. No significant difference was found for PS or CPS in any of the lines. The TNB did not change in the OR line but significantly improved in the PS line (0.24 +/- 0.11 piglets/generation).