Accounting for lactation length and weaning-to-conception interval in genetic evaluations for litter size in swine.

Effects of lactation length and weaning-to-conception interval on the subsequent litter size of purebred sows were estimated using an animal model. Data on 2,847 Landrace sows with 7,125 litters born between January 1989 and May 1997 and on 1,234 Yorkshire sows with 2,999 litters born between January 1990 and May 1997 were obtained from two Canadian selection herds. Sows having a lactation of less than 14 d (MMEW) were usually not mated until their second estrus, whereas sows weaned after at least 14 d of lactation (later weaning) were usually mated on their first estrus. Litter size included both number of pigs born alive and those stillborn. Linear, quadratic, and logarithmic effects of lactation length were tested. The effect of weaning-to-conception interval on litter size was modeled using an approach based on threshold variables and an approach using segmented polynomials. Results indicated linear and logarithmic effects of lactation length on subsequent litter size for Yorkshire and Landrace breeds, respectively. Litter size decreased as weaning-to-conception interval increased up to 7 and 10 d for Yorkshire and Landrace, respectively, then increased with further increases in weaning-to-conception interval up to 35 and 30 d for the two breeds, and then remained constant. The MMEW sows did not have lower subsequent litter sizes than later-weaned sows because the negative effect of a shorter lactation was offset by the positive effect of a longer weaning-to-conception interval. However, average time spent open per parity was longer for MMEW sows than for later-weaned sows. Both lactation length and weaning-to-conception interval should be considered in models for the genetic evaluation of litter size in purebred swine. Segmented polynomials can be used to predict litter size as a continuous function of weaning-to-conception interval or to derive weaning-to-conception interval adjustment factors for litter size.

The virgin, modified, human, umbilical vein graft: morphologic characteristics and mechanical properties.

The authors used macrophotography, endoscopy, roentgenography, light microscopy, and transmission and scanning electron microscopy to assess the morphologic characteristics of 37 virgin, human, umbilical vein grafts. The specimens showed deep longitudinal folds (22%) and multiple transverse folds of the intimal surface (27%), irregularity of wall thickness (41%) and intimal breakdown exposing thrombogenic layers of the vein wall to blood (19%). The mechanical properties also studied were dynamic compliance, Young's modulus, breaking strength and breaking strain. The mean dynamic compliance was 6.44 X 10(-4) mm Hg-1 (SD = 2.02 X 10(-4) mm Hg-1, i.e., 31%), which is in agreement with results of others. The specimens showed great variability in Young's modulus, breaking strength and breaking strain. The structural deficiencies and variable mechanical properties of human umbilical vein grafts require investigation to determine their effect on patency rates due to increased thrombogenicity and thus to establish whether there are potential hazards associated with their use.

[Progressive complications associated with the use of a bovine heterograft for vascular access]. / Complications évolutives associées à l'utilisation d'une hétérogreffe bovine comme abord vasculaire.

Three bovine carotid heterografts, used for vascular access, were analysed after removal following the development of aneurysms in two cases and thrombosis in one. The first prosthesis was implanted in a 17-year-old man who suffered from myasthenia gravis and was undergoing plasmapheresis. It became notably dilated several months after implantation, and resection was necessary 14 months after insertion. The second graft was placed in a 31-year-old woman being treated for a severe chronic potassium insufficiency. It was removed 16 months after insertion because of thrombosis. The third bovine carotid heterograft was inserted in a 48-year-old patient on long-term hemodialysis and was removed 3.5 months later because of aneurysmal dilatation adjacent to the arterial anastomosis. These evolutionary and degenerative changes associated with the bovine carotid heterograft illustrate the limitations of this material as an interpositional limb for arteriovenous fistulas in angioaccess therapy. Small weaknesses have sometimes been noted in the microstructure of the graft material studied before implantation.

Congenital absence of the portal vein.

A 4 1/2-year-old girl is described in whom the portal vein is absent and the venous return from the gastrointestinal tract, spleen, and pancreas is through the left renal vein into the inferior vena cava. She had a hepatoblastoma, which was treated surgically by right hepatic lobectomy. Regeneration occurred in the remaining left lobe within 3 months after surgery. This is the second such case documented in the literature.