Large N_c, Constituent Quarks, and N, Delta Charge Radii

We show how one may define baryon constituent quarks in a rigorous manner, given physical assumptions that hold in the large-N_c limit of QCD. This constituent picture gives rise to an operator expansion that has been used to study large-N_c baryon observables; here we apply it to the case of charge radii of the N and Delta states, using minimal dynamical assumptions. For example, one finds the relation r_p^2 - r_{Delta^+}^2 = r_n^2 - r_{Delta^0}^2 to be broken only by three-body, O(1/N_c^2) effects for any N_c.Comment: 15 pages, 1 eps figure. Version to appear in Phys. Rev.

Symmetries and asymmetries associated with non-random segregation of sister DNA strands in Escherichia coli

AbstractThe successful inheritance of genetic information across generations is a complex process requiring replication of the genome and its faithful segregation into two daughter cells. At each replication cycle there is a risk that new DNA strands incorporate genetic changes caused by miscopying of parental information. By contrast the parental strands retain the original information. This raises the intriguing possibility that specific cell lineages might inherit “immortal” parental DNA strands via non-random segregation. If so, this requires an understanding of the mechanisms of non-random segregation. Here, we review several aspects of asymmetry in the very symmetrical cell, Escherichia coli, in the interest of exploring the potential basis for non-random segregation of leading- and lagging-strand replicated chromosome arms. These considerations lead us to propose a model for DNA replication that integrates chromosome segregation and genomic localisation with non-random strand segregation

Phenotypic profiles for body weight, body condition score, energy intake, and energy balance across different parities and concentrate feeding levels

The objective of this study was to investigate potential differences in lactation profiles for body weight (BW), body condition score (BCS), net energy intake (NEI) and energy balance (EB) across different parities and concentrate feeding levels. Records collected from the research farm in southern Ireland from 1995 to 2002 were analysed using random regression methodology. A total of 27,126 and 8212 records were available for BW and BCS, respectively; 1861 and 1835 records were available for NEI and EB, respectively. Significantly different lactation profiles existed for BW, BCS, NEI and EB across parities one to three. First parity cows were lighter, lost more BCS in early lactation, had lower NEI and were in negative energy balance for longer compared to later parity cows. Average NEI across the first 225 days of lactation was 15.4, 19.5 and 21.0 UFLs/day for first, second and third parity cows, respectively. Energy balance turned positive at days 71, 60 and 73 of lactation for first, second and third parity cows, respectively. Cows on the higher feeding levels were heavier, mobilised less body condition in early lactation and had higher NEI than cows on the lower feeding level. No significant difference in height of the EB profile existed between the cows on the low and high feeding level indicating that the duration and extent of NEB was not influenced by the concentrate feeding levels adopted in this study

The relationship between genetic merit for yield and live weight, condition score, and energy balance of spring calving Holstein Friesian dairy cows on grass based systems of milk production

The objectives of this study were to estimate the effects of genetic merit for milk yield on energy balance, DM intake (DMI), and fertility for cows managed on three different grass-based feeding systems and to estimate possible interactions between genetic merit and feeding system. Individual animal intake estimates were obtained at pasture on 11 occasions across three grazing seasons. The data set contained 96 first lactation, 96 second lactation, and 72 third lactation cows in 1995, 1996, and 1997, respectively. Half of these cows were of high genetic merit, and half were of medium genetic merit for milk solids production. Genetic effects for the traits of interest were estimated as the contrast between the two genetic groups and by the genetic regression of phenotypic performance on the estimated breeding value for fat and protein yield, based on pedigree index. Significant effects of feeding system were observed on yields, DMI, and energy balance, with no effect on live weight, condition score, or reproductive performance. The interaction between genetic merit and feeding system was not significantly different from zero for any of the traits. Yields, grass DMI, and total DMI were all higher for cows of high genetic merit than for those of medium genetic merit and were positively correlated (P < 0.001) with pedigree index. Furthermore, condition score, conception to first and second services, and pregnancy rate were significantly negatively correlated with pedigree index. While at pasture, energy balance was positively (P < 0.01) correlated with pedigree index, although the contrast between high genetic merit and medium genetic merit was not significantly different from zero. This positive energy balance was unexpected and was probably due to the lactation stage that intake was measured. Condition score changes and energy balance measures on a small subgroup of the animals, while indoors offered a diet of silage and concentrates (n = 33), demonstrated that high genetic merit had a more negative energy balance than did medium genetic merit. The results clearly illustrate the production potential of high genetic merit cows on grass-based systems. The reduced reproductive performance questions the suitability of high yield for seasonal calving systems

Genetic parameters for production and fertility in spring-calving Irish dairy cattle

The objective of this study was to estimate genetic parameters for milk production and selected fertility traits in Irish dairy cattle. Data were derived from 74 seasonal spring-calving dairy herds with a potential cow population of 6,783 in the 1999 calving season. The average 305-day yields (kg) of milk, fat, and protein, the concentrations (g/kg) of fat and protein were 6572, 245, 222, 37.6 and 33.9, respectively. Calving to first service interval (CFS), calving to conception interval (DO) and first service to conception interval (FSCO) averaged 72, 90, and 17 days, respectively, while pregnancy rate to first service (PRFS) and number of services/cow were 0.48 and 1.78, respectively. The proportion of cows conceiving within the first 21, 42, and 63 days after start of breeding (PR21, PR42, and PR63) were 0.36, 0.57 and 0.72, respectively. (Co)variance components were estimated for the complete data set as well as a separate analysis for pedigree and non-pedigree herds within the data set. Heritability estimates, using the complete data set, for milk production traits ranged from 0.22 (±0.042) for milk yield to 0.70 (±0.049) for milk fat concentration while heritability estimates for fertility traits ranged from zero for PR21 to 0.03 (±0.017) for CFS and SBFS (start of breeding to first service interval). Heritability estimates were numerically greater than zero for all fertility traits in the pedigree herd data set with the exception of PR21. Only two fertility traits had heritability estimates for the non-pedigree herds, namely, CFS (0.03 ± 0.030), SBFS (0.03 ± 0.030); analyses for the other fertility traits failed to converge. Genetic correlations between production and fertility traits were mostly antagonistic, for example, correlations between milk yield and number of services (0.98 ± 0.35) and PRFS (-0.51 ± 0.61). Results indicate that selection for yield alone may lead to a deterioration in fertility and that future selection programmes should include some measures of reproductive performance