Effect of semen thaw method on conception rate in four large commercial dairy heifer herds.

Semen processed with procedures intended to permit a flexible thaw method is used to breed millions of cows yearly. One method of thawing straws, the "pocket thaw" is used extensively with semen prepared with these procedures. Published field data is lacking for thaw method comparisons with semen processed to permit flexible-thawing. The objective of the present study was to measure the effect of semen thaw method (warm-water or pocket thaw) over all seasons and its interaction with herds, inseminators, straw package size, and sperm number on conception rate in commercial dairy heifer herds using semen processed with procedures historically optimized for success with flexible-thawing. Professional inseminators performed 11,215 services over a 16-month period in four large herds, achieving a 67.6% conception rate. Thaw method was alternated weekly. Thaw effect on conception status, determined by 70 days non-return rate, was estimated by a generalized linear mixed model. Neither thaw method nor number of sperm per straw significantly affected probability of conception (P=0.658 and 0.769, respectively). No interactions of thaw method with herd, sperm number, season, straw size, and straw size by season were detected (P=0.297, 0.526, 0.365, 0.723, and 0.824, respectively). Bull, herd, inseminator within herd, year, season, and straw size affected conception rate (P=0.002, 0.000, 0.000, 0.000, 0.000, and 0.014, respectively). In conclusion, for semen processed with procedures that permit flexible-thawing, thaw method (pocket thaw versus warm-water thaw) did not affect conception rate under commercial conditions and with routine semen handling methods.

Resonant and localized breathing modes in terminal regions of the DNA double helix.

A Green's function approach is used in constructing a dynamic model of a semi-infinite length of the DNA homopolymer B poly(d) . poly(d). Considerable attention is focused on the hydrogen bond stretching close to the terminus. A melting (or breathing) coordinate (M) is defined as an average over the three linking hydrogen bond stretches in a unit cell. The thermal mean squared amplitude of (M) is enhanced at the chain end compared with the interior. Spectral branches at 69, 80 and 105 cm-1, as well as a local mode at 75 cm-1, are primary contributors to the enhancement. We suggest that this fact can affect the thermal melting of a DNA double helical homopolymer, enhancing the tendency to start from an end (if one is available). We show how certain infinite chain modes with small (M) amplitude can turn into breathing modes near the terminus, and suggest that the same phenomenon may occur near other specific base-pair sequences. There is also considerable attention paid to the low microwave region from approximately 0 to 1.75 cm-1. The thermally activated modes in this frequency region contribute approximately (0.02 A)2 to [M2(0)] at 40 K, approximately two orders of magnitude greater than for [M2(infinity)]. Most important however, is the existence of narrow resonant modes in this frequency region. Particularly pronounced resonances near 0.03 cm-1 and 0.08 cm-1 (approximately 0.9 and 2.4 GHz) amplify M2(0) at the terminus by about for orders of magnitude over the infinite chain value M2(infinity).