Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7

Structural analysis from powder neutron and single-crystal x-ray diffraction data for a sample of the Tl2Mn2O7 pyrochlore, which exhibits colossal magnetoresistance (CMR), shows no deviations from ideal stoichiometry. This analysis gives an Mn-O distance of 1.90 angstroms, which is significantly shorter than the Mn-O distances (1.94 to 2.00 angstroms) observed in phases based on LaMnO3 perovskites that exhibit CMR. Both results in Tl2Mn2O7 indicate oxidation states very close to Tl23+Mn24+O7. Thus, Tl2Mn2O7 has neither mixed valence for a double-exchange magnetic interaction nor a Jahn-Teller cation such as Mn3+, both of which were thought to have an important function in CMR materials. An alternate mechanism for CMR in Tl2Mn2O7 based on magnetic ordering driven by superexchange and strong spin-fluctuation scattering above the Curie temperature is proposed here.     

Genetic and phenotypic parameter estimates for feed intake and other traits in growing beef cattle, and opportunities for selection

Growth, feed intake, and temperament indicator data, collected over 5 yr on a total of 1,141 to 1,183 mixed-breed steers, were used to estimate genetic and phenotypic parameters. All steers had a portion of Hereford, Angus, or both as well as varying percentages of Simmental, Charolais, Limousin, Gelbvieh, Red Angus, and MARC III composite. Because the steers were slaughtered on various dates each year and the animals thus varied in days on feed, BW and feed data were adjusted to a 140-d feeding period basis. Adjustment of measures of feed efficiency [G:F or residual feed intake (RFI), intake adjusted for metabolic body size, and BW gain] for body fatness recorded at slaughter had little effect on the results of analyses. Average daily gain was less heritable (0.26) than was midtest BW (MBW; 0.35). Measures of feed intake had greater estimates of heritability, with 140-d DMI at 0.40 and RFI at 0.52; the heritability estimate for G:F was 0.27. Flight speed (FS), as an indicator of temperament, had an estimated heritability of 0.34 and a repeatability of 0.63. As expected, a strong genetic (0.86) correlation was estimated between ADG and MBW; genetic correlations were less strong between DMI and ADG or MBW (0.56 and 0.71). Residual feed intake and DMI had a genetic correlation of 0.66. Indexes for phenotypic RFI and genotypically restricted RFI (no correlation with BW gain) were compared with simple economic indexes incorporating feed intake and growth to elucidate expected selection responses under different criteria. In general, few breed differences were detected across the various measurements. Heterosis contributed to greater DMI, RFI, and MBW, but it did not significantly affect ADG, G:F, or FS. Balancing output (growth) with input costs (feed) is needed in practicing selection, and FS would not be recommended as an indicator trait for selection to change feed efficiency. An index including BW gain and RFI produced the best economic outcome.     

A lupinosis-associated myopathy in sheep and the effectiveness of treatments to prevent it

A lupinosis-associated myopathy occurred in 26 of 48 sheep given a crude toxic extract of Phomopsis leptostromiformis, and in 18 of 34 sheep that grazed a toxic lupin stubble. Treatment with selenium or alpha-tocopherol alone neither prevented nor cured the myopathy, but selenium and alpha-tocopherol together may have been partially effective. Among the group of 48 intoxicated sheep, those with myopathy had a significantly lower mean terminal concentration of alpha-tocopherol in their livers than those with no myopathy. There was no relationship between the severity of liver injury and the occurrence of the myopathy. It was considered that this lupinosis-associated myopathy may have a similar pathogenesis to nutritional myopathy. Data on plasma creatine phosphokinase and erythrocyte glutathione peroxidase activities, plasma alpha-tocopherol concentrations and terminal tissue concentrations of selenium and alpha-tocopherol are presented.     

Y are you not pregnant: identification of Y chromosome segments in female cattle with decreased reproductive efficiency

Reproductive efficiency is of economic importance in commercial beef cattle production, since failure to achieve pregnancy reduces the number of calves marketed. Identification of genetic markers with predictive merit for reproductive success would facilitate early selection of females and avoid inefficiencies associated with sub-fertile cows. To identify regions of the genome harboring variation affecting reproductive success, we applied a genome-wide association approach based on the >700,000 SNP marker assay. To include the largest number of individuals possible under the available budget, cows from several populations were assigned to extremes for reproductive efficiency, and DNA was pooled within population and phenotype before genotyping. Surprisingly, pools prepared from DNA of low reproductive cattle returned fluorescence intensity data intermediate between fertile females and males for SNP mapped to the Y chromosome (i.e., male sex chromosome). The presence of Y-associated material in low reproductive heifers or cows was confirmed by Y-directed PCR, which revealed that 21 to 29% of females in the low reproductive category were positive by a Y chromosome PCR test normally used to sex embryos. The presence of the Y chromosome anomaly was further confirmed with application of additional Y-specific PCR amplicons, indicating the likelihood of the presence of some portion of male sex chromosome in female cattle in various beef cattle herds across the U.S. Discovery of this Y anomaly in low reproductive females may make an important contribution to management of reproductive failures in beef cattle operations.     

Farm management factors associated with bulk tank somatic cell count in Irish dairy herds

The relationship between bulk tank somatic cell count (SCC) and farm management and infrastructure was examined using data from 398 randomly selected, yet representative, Irish dairy farms where the basal diet is grazed grass. Median bulk tank SCC for the farms was 282,887 cells/ml ranging from 82,209 to 773,028 cells/ml. Two questionnaires were administered through face-to-face contact with each farmer. Herd-level factors associated with bulk tank SCC were determined using linear models with annual somatic cell score (i.e., arithmetic mean of the natural logarithm of bulk tank SCC) included as the dependent variable. All herd level factors were analysed individually in separate regression models, which included an adjustment for geographical location of the farm; a multiple regression model was subsequently developed. Management practices associated with low SCC included the use of dry cow therapy, participation in a milk recording scheme and the use of teat disinfection post-milking. There was an association between low SCC and an increased level of hygiene and frequency of cleaning of the holding yard, passageways and cubicles. Herd management factors associated with bulk tank SCC in Irish grazing herds are generally in agreement with most previous studies from confinement systems of milk production.     

Assessment of positional candidate genes myf5 and igf1 for growth on bovine chromosome 5 in commercial lines of Bos taurus

Quantitative trait loci for growth traits in beef cattle have been previously reported and fine-mapped in three chromosomal regions of 0 to 30 cM, 55 to 70 cM, and 70 to 80 cM of bovine chromosome 5. In this study, we further examined the association between gene-specific single nucleotide polymorphisms (SNP) of two positional candidate genes, bovine myogenic factor 5 (myf5) and insulin-like growth factor-1 (igf1), in the QTL regions and the birth weight (BWT), preweaning average daily gain (PWADG), and average daily gain on feed (ADGF) in commercial lines of Bos taurus. The QTL regions for the growth traits identified using a haplotype association analysis, which included the gene-specific SNP markers for both genes in this study, were in agreement with previous studies. The gene-specific SNP marker association analysis indicated that the SNP in myf5 had a significant additive effect on PWADG in the M1 line of Beefbooster Inc. (P < 0.10), and a significant additive effect (P < 0.05) and a significant dominance effect (P < 0.10) on ADGF in the M3 line of Beefbooster Inc. When the data from the two commercial lines were pooled, the SNP in myf5 showed a significant association with PWADG (P < 0.10) and with ADGF (P < 0.05). The association between the SNP and BWT, however, did not reach a significance level in the M1 line, the M3 line, or across the lines. For igf1, no significant association between the SNP and the growth traits was detected in either the M1 line or the M3 line, whereas there was only a significant dominance effect (P < 0.10) on BWT detected for the SNP in igfl when the data from the two commercial lines were pooled. These results suggest that myf5 is a strong candidate gene that influences PWADG and ADGF in beef cattle. The SNP of igf1 may not be a causative or close to the causative mutation that affects the three growth traits in the populations of beef cattle examined in this study. Other SNP of igf1 and myf5 or other genes in their respective chromosomal regions, however, should also be studied.