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A quantitative trait locus (QTL) analysis of female reproductive data from a three-generation experimental cross between Meishan (MS) and Large White (LW) pig breeds is presented. Six F1 boars and 23 F1 sows, progeny of six LW boars and six MS sows, produced 573 F2 females and 530 F2 males. Six traits, i.e. teat number (TN), age at puberty (AP), ovulation rate (OR), weight at mating (WTM), number of viable embryos (NVE) and embryo survival (ES) at 30 days of gestation were analysed. Animals were genotyped for a total of 137 markers covering the entire porcine genome. Analyses were carried out based on interval mapping methods, using a line-cross (LC) regression and a half-full sib (HFS) maximum likelihood test. Genome-wide (GW) highly significant (P < 0.001) QTL were detected for WTM on SSC 7 and for AP on SSC 13. They explained, respectively, 14.5% and 8.9% of the trait phenotypic variance. Other GW significant (P < 0.05) QTL were detected for TN on SSC 3, 7, 8, 16 and 17, for OR on SSC 4 and 5, and for ES on SSC 9. Two additional chromosome-wide significant (P < 0.05) QTL were detected for TN, three for WTM, four for AP, three for OR, three for NVE and two for ES. With the exception of the two above-mentioned loci, the QTL explained from 1.2% to 4.6% of trait phenotypic variance. QTL alleles were in most cases not fixed in the grand-parental populations and Meishan alleles were not systematically associated with higher reproductive performance.

Six-wk-old piglets of both sexes from European Large White (LW, n = 36) and Chinese Meishan (MS, n = 24) breeds were individually exposed to a novel environment, a stressful stimulation. Behavioral and pituitary-adrenal reactivity were investigated. When compared with LW, MS pigs displayed low locomotion (18.5 +/- 2.2 vs. 41.0 +/- 3.8 squares crossed/10 min; P < 0.0001), and defecation scores (0.58 +/- 0.15 vs. 4.86 +/- 0.37 fecal boli; P < 0.0001). Basal concentrations of cortisol were higher in MS (96.1 +/- 1.1 vs. 44.9 +/- 1.1 ng/ml; P < 0.0001), although no differences between breeds were found in basal concentrations of adrenocorticotropic hormone (ACTH). In response to novel environment exposure, the ACTH increase was greater in LW than in MS, but the cortisol response was not different on a log scale. To further investigate the pituitary-adrenal differences between the two breeds, the 24-hr profile of ACTH and cortisol plasma concentrations, a corticotropin-releasing factor (CRF) and a coupled dexamethasone-ACTH test were studied. Five castrated male 9-wk-old piglets from each breed were fitted surgically with a jugular vein catheter. A classic marked circadian rhythm of cortisol and a weak nycthemeral variation of ACTH were found. Cortisol concentrations were approximately twice higher in MS exclusively during the early light phase (from 0800-1200 hr) of the cycle, but no significant interbreed difference was found in the circadian rhythm of ACTH. Administration of CRF (1 microgram/kg iv) induced the same significant increase in plasma ACTH and cortisol concentrations in both breeds. Administration of ACTH (10 micrograms/kg i.v.) increased significantly cortisol concentrations and revealed no difference in plasma cortisol response to ACTH. These data suggest that the hypercortisolism of MS pigs is of adrenal origin, and related to extrapituitary factors that control the adrenal sensitivity during the light phase of the diurnal cycle.

The purpose of this study was to estimate the effect of the proportion of Meishan (MS) genes upon the lipid composition of longissimus dorsi and trapezius muscles and perirenal and s.c. dorsal adipose tissues. Five groups of 11-15 pigs with 0, 12·5, 25, 37·5 and 50% MS genes were made up from a large herd of crossbred animals (0-100% MS dams × Piétrain sires). Results showed that: (1) the i.m. lipid content was higher in 1 2 MS than in controls and 1 4 MS pigs. Differences in the fatty acid composition of i.m. lipids, as related to genotype, depended more particularly on muscle fatness as the fatty acid compositions of triglycerides and phospholipids were little affected by the genotype. (2) The weight of perirenal and s.c. dorsal adipose tissues increased with the proportion of MS genes. Differences in the chemical composition of the adipose tissues were not related to the proportion of MS genes. The fatty acid composition was little affected by the genotype. Although the levels of polyunsaturated fatty acids decreased with increasing proportion of MS genes, these small variations had no marked influence on adipose tissue quality., (Copyright © 1992. Published by Elsevier Ltd.)