Genetic selection foror against resistance to the mycotoxicosis, facial eczema (FE), was begun in a Romney flock in 1975. Randomly selected ewes were mated with rams which had been previously identified by progeny testing as resistant (R) or susceptible (S) to FE. In subsequent years (until 1982), the same ewes and their daughters were again mated within flock to progeny-tested rams. From 1983 until 1987 , performance testing was substituted for progeny testing. The most resistant R rams and most susceptible S rams by performance test were then used for mating in their respective flocks. Over these 5 years, young rams bred in the trial were performance-tested using a challenge with sporidesmin, the mycotoxin which causes FE. The severity of the liver damage induced was assessed by measuring plasma gamma-glutamyltransferase (GGT) activity. In 1982, two further flocks were established from a common Romney source as demonstration flocks; they were managed together with the R and S flocks. Six years of matings were carried out with selected performance-tested rams in one flock (P) and with randomly sampled rams in a second flock as a control (C). A best linear unbiased prediction (BLUP) analysis of GGT data from all four flocks over the 1982-87 lamb crops was used to determine the effects of selection. This showed that, in 1982, the R flock had 16% more animals resistant to FE than the P flock. From estimates of subsequent rates of genetic change in the R and P flocks, performance testing achieved 0.9 and 2.4% more animals resistant per year respectively. The different rates of change from performance testing in the R and P flocks partly resulted from different flock sizes, but there was also considerable between-year variation in response. By 1987, 21 and 15% more R and P animals respectively, were resistant than before selection began. There were 27 ± 13% more animals from the S flock susceptible in 1987 than in the C flock. Comparisons of weaning weight, autumn weight (4-6 months of age), yearling weight, fleece weight, litter size, and lamb survival from up to 2426 lamb records and 2065 ewe lambing records showed few significant differences between R and S flocks, or between P and C flocks.
Two concurrent trials were conducted to examine the effects of gender, time of castration, genotype and feeding regimen on lamb growth rate and carcass fatness. Trial 1 compared Polypay and Coopworth x Polypay male lambs either left intact or castrated early, mid or late in growth. Trial 2 compared Hampshire-sired lambs (females, early castrate wethers and late castrate wethers) from Suffolk x Coopworth dams and whiteface x Coopworth dams. Gender and time of castration significantly affected growth rate in Trial 1 but not in Trial 2. Rams were more efficient than wethers, but no other gender or time of castration effects on feed efficiency were observed. Delaying castration and pasture grazing both reduced fatness. Lambs grazed on irrigated pastures until they weighed 41 kg then finished in drylot had a lower dressing percentage than lambs fed in the drylot throughout, but USDA quality grades were similar. Substitution of Polypay genes by Coopworth genes in crossbred lambs did not significantly alter any of the fatness traits measured but increased ribeye area. Hampshire-sired lambs grew faster than whiteface lambs, particularly in drylot. They had a higher dressing percentage without increased fatness, apparently because of greater muscling in ribeye and leg.
Blood flow to the pancreatic islets of the anesthetized rat has been measured by application of microspheres, intravital staining of the endocrine tissue by Dithizon, and induction of organ transparency by incubation in glycerol. Thus the microspheres could be counted separately in the islet tissue and in the remaining organ. The total pancreatic blood flow in the rat amounted to 0.48 +/- 0.04 ml.min-1.g-1 and the flow fraction of the islet tissue to 1.22 +/- 0.09%, corresponding to a flow rate through the pancreatic islets of 5.42 +/- 0.63 microliters/min. When isoproterenol was applied (0.1 and 1.0 micrograms.kg-1.min-1 iv for 15 min), total pancreatic blood flow rose to 0.60 +/- 0.08 and 0.98 +/- 0.10 (P less than 0.01) ml.min-1.g-1, whereas the flow fraction to the islets decreased to 0.82 +/- 0.08 (P less than 0.01) and 0.61 +/- 0.07% (P less than 0.01). The absolute islet perfusion remained nearly unchanged. Norepinephrine (2.0 and 5.0 micrograms.kg-1.min-1 for 15 min) similarly increased total blood flow to 0.78 +/- 0.08 (P less than 0.01) and 0.64 +/- 0.08 ml.min-1.g-1) while reducing the islet flow fraction to 1.15 +/- 0.13 and 0.83 +/- 0.05% (P less than 0.01). The absolute flow rate through the islet tissue did not change significantly. The conclusion may be drawn from these experiments that changes in total pancreatic blood flow are not necessarily accompanied by corresponding changes in the perfusion rate of the endocrine islet tissue.
A multistate cooperative study was conducted to study the current issue of tail length in docked lambs and its relationship to incidence of rectal prolapse. A total of 1,227 lambs at six locations were randomly allocated to two or three tail dock treatments: 1) short--tail was removed as close to the body as possible, 2) medium--tail was removed at a location midway between the attachment of the tail to the body and the attachment of the caudal folds to the tail, and 3) long--tail was removed at the attachment of the caudal folds to the tail. Short-docked lambs had a greater (P < 0.05) incidence of rectal prolapse (7.8%) than lambs with a medium (4.0%) or a long (1.8%) dock. Female lambs had a higher (P < 0.05) incidence of rectal prolapse than male lambs. At two stations, lambs were finished either in a feedlot on a high-concentrate diet or on pasture with no grain supplementation. At one station, with a very low incidence of rectal prolapse, there was no difference in incidence between lambs finished in the feedlot or on pasture; however, at the station with a relatively high incidence of rectal prolapse, lambs in the feedlot had a higher (P < 0.05) incidence than lambs on pasture. The half-sib estimate of heritability for the incidence of rectal prolapse was low (0.14). The results of this study strongly implicate short dock length as a cause of rectal prolapse in lambs finished on high-concentrate diets. Furthermore, the results of this study and the only other study known conducted on this issue strongly suggest that docking lambs at the site of the attachment of the caudal folds to the tail will result in a negligible incidence of rectal prolapse.
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