Charles Michaux

Genetic analysis of some maternal reproductive traits in the Belgian Blue cattle breed

Abstract A genetic analysis of some reproductive traits was made on the female progeny of artificial insemination (A.I.) sires of the Belgian Blue cattle breed. As the sires were used in commercial herds, the progenies are of two biological types: beefy (double-muscled) and conventional. The traits considered were body measurements (chest girth and height at withers) at 1, 2, 3 and 4 years of age, percent culled for infertility, non-return rates (proportion of calvings resulting from one single insemination) after the first insemination, number of inseminations per gestation, ages at first and second calving, calving interval and milk yield score. For these traits, the differences between the two biological types were estimated. From the comparison of the two biological types for production and reproductive traits, it is shown that the beneficial effects of the beefy condition to the carcass composition and to the commercial value represent several phenotypic standard deviations, while the detrimental effects on the fertility traits are only a fraction of the phenotypic standard deviations of these traits. The estimates of the coefficients of heritability were chest girth (1 year=0.04, 2 years=0.11, 3 years=0.13, 4 years=0.18); height at withers (1 year=0.07, 2 years=0.12, 3 years=0.24, 4 years=0.21); age at first calving=0.03; age at second calving=0.04; calving interval=0.03; milk yield score (first lactation=0.08, second lactation=0.10). The genetic correlations between successive measurements were large and positive, but the genetic correlations between the ages at calving on the one hand and body measurements and milk yield score on the other hand were systematically negative and thus favourable.

Selection in action: dissecting the molecular underpinnings of the increasing muscle mass of Belgian Blue Cattle

BackgroundBelgian Blue cattle are famous for their exceptional muscular development or “double-muscling”. This defining feature emerged following the fixation of a loss-of-function variant in the myostatin gene in the eighties. Since then, sustained selection has further increased muscle mass of Belgian Blue animals to a comparable extent. In the present paper, we study the genetic determinants of this second wave of muscle growth.ResultsA scan for selective sweeps did not reveal the recent fixation of another allele with major effect on muscularity. However, a genome-wide association study identified two genome-wide significant and three suggestive quantitative trait loci (QTL) affecting specific muscle groups and jointly explaining 8-21% of the heritability. The top two QTL are caused by presumably recent mutations on unique haplotypes that have rapidly risen in frequency in the population. While one appears on its way to fixation, the ascent of the other is compromised as the likely underlying MRC2 mutation causes crooked tail syndrome in homozygotes. Genomic prediction models indicate that the residual additive variance is largely polygenic.ConclusionsContrary to complex traits in humans which have a near-exclusive polygenic architecture, muscle mass in beef cattle (as other production traits under directional selection), appears to be controlled by (i) a handful of recent mutations with large effect that rapidly sweep through the population, and (ii) a large number of presumably older variants with very small effects that rise slowly in the population (polygenic adaptation).

Effects of dobutamine on isovolumic and ejection phase indices of cardiac contractility in conscious healthy dogs.

The aim of this study was to determine cardiac contractility using indices derived from cardiac catheterisation in conscious healthy dogs during dobutamine infusion. Eight dogs were studied. An ECG was recorded together with left ventricular pressure and volume which were measured using a conductance catheter with an integrated microtip pressure sensor. Eight indices of left ventricular systolic performance were derived from these records. Measurements were realised under basal conditions and during an incremental dobutamine challenge. The maximal rate of rise in ventricular pressure (max dP/dt), max dP/dt divided by the developed pressure and the mean systolic ejection rate were the most sensitive indices to detect dobutamine induced changes in contractility with maximal percentage changes of 122+/-11 per cent, 130+/-7 per cent and 102+/-24 per cent respectively. Ejection fraction increased significantly during dobutamine infusion (maximal percentage change of 43+/-9 per cent) whereas the pre-ejection period (PEP) and the left ventricular ejection time (LVET) decreased significantly (maximal percentage change of -41+/-2 per cent and -28+/-3 per cent respectively). All these six indices were significantly correlated with each other. Conversely, the ratio PEP/LVET and the LVET corrected for heart rate dependency showed a maximal percentage change of only -10+/-1 per cent and -16+/-7 per cent, respectively, during the dobutamine infusion and were not significantly correlated with the other contractility indices. This study demonstrated the feasibility of the conductance method to determine cardiac contractility in conscious healthy dogs submitted to a pharmacological stress testing and provides control values for eight indices of left ventricular contractility during dobutamine infusion at increasing dosages.

Pulmonary vasoreactivity in spontaneously hypertensive rats - Effects of endothelin-1 and leptin

BackgroundSystemic hypertension may be associated with an increased pulmonary vascular resistance, which we hypothesized could be, at least in part, mediated by increased leptin.MethodsVascular reactivity to phenylephrine (1xa0μmol/L), endothelin-1 (10xa0nmol/L) and leptin (0.001–100xa0nmol/L) was evaluated in endothelium-intact and -denuded isolated thoracic aorta and pulmonary arteries from spontaneously hypertensive versus control Wistar rats. Arteries were sampled for pathobiological evaluation and lung tissue for morphometric evaluation.ResultsIn control rats, endothelin-1 induced a higher level of contraction in the pulmonary artery than in the aorta. After phenylephrine or endothelin-1 precontraction, leptin relaxed intact pulmonary artery and aortic rings, while no response was observed in denuded arteries. Spontaneously hypertensive rats presented with increased reactivity to phenylephrine and endothelin-1 in endothelium-intact pulmonary arteries. After endothelin-1 precontraction, endothelium-dependent relaxation to leptin was impaired in pulmonary arteries from hypertensive rats. In both strains of rats, aortic segments were more responsive to leptin than pulmonary artery. In hypertensive rats, pulmonary arteries exhibited increased pulmonary artery medial thickness, associated with increased expressions of preproendothelin-1, endothelin-1 receptors type A and B, inducible nitric oxide synthase and decreased endothelial nitric oxide synthase, together with decreased leptin receptor and increased suppressor of cytokine signaling 3 expressions.ConclusionsAltered pulmonary vascular reactivity in hypertension may be related to a loss of endothelial buffering of vasoconstriction and decreased leptin-induced vasodilation in conditions of increased endothelin-1.