STUDIES IN THE DIGESTIBILITY OF HERBAGE

Results are reported from six digestibility experiments in which frozen herbage was fed to groups of sheep at HIGH and Low levels of intake. The sheep on the HIGH level of intake digested the dry matter, organic matter, nitrogen and normal-acid fibre in the herbage less efficiently than those on the LOW level, confirming earlier results reported in Part VI of this series. Evidence suggests that this difference results from the higher rate of passage of food through the digestive tract at the HIGH level of intake.
These results are discussed with reference to the errors introduced into the faecal-index method for estimating the digestibility of grazed herbage.     

Susceptibility of potato (Solanum tuberosum L.) foliage and tubers to the US8 genotype ofPhytophthora infestans

Late blight is an important disease of potato(Solanum tuberosum L.) worldwide, and therefore, many potato-breeding programs have prioritized the development of late blight-resistant potato cultivars. Although the emphasis has been to enhance foliar resistance, it is also necessary to evaluate tuber late blight resistance in new breeding lines and new sources of late blight resistance. We report here on the assessment of foliar and tuber resistance and the correlation between these aspects of resistance in a sample of Michigan State University potato breeding lines. Two MSU breeding lines had significantly less infected foliage than the susceptible check cultivars. Tuber susceptibility was significantly different (P < 0.05) only between the most susceptible and the least susceptible breeding lines/cultivars. Foliar and tuber susceptibility to potato late blight were not correlated as low tuber susceptibility was associated both with extremely low (e.g., MSG274-3) and high (e.g., MSE202-3Rus) foliar susceptibility.     

Tibial tuberosity advancement for treatment of CrCL injury: complications and owner satisfaction

The purpose of this retrospective study of 171 dogs that underwent 193 tibial tuberosity advancement (TTA) surgeries was to describe complications and owner satisfaction associated with the procedure. Complications occurred in 21 cases (11%). Subsequent meniscal tear was the most common complication (10/193, 5.2%). Increasing body weight (P=0.02-0.04) and small cage size (P=0.06) were significantly associated with postsurgical complications. Ninety-two percent of owners were satisfied with the outcome of the TTA procedure, but only 84% stated that they would be willing to have the procedure performed again. The authors concluded that TTA had a complication rate and owner satisfaction similar to other tibial osteotomies for the surgical correction of cranial cruciate ligament disease.     

Influence of tillage and method of metam sodium application on distribution and survival ofVerticillium dahliae in the soil and the development of verticillium wilt of potato

The effect of plowing and deep-rip tillage, in combination with chemigation or shank injection of metam sodium, onVerticillium dahliae populations and disease development was assessed in two fields with differing soil types and potato rotations. Soil samples were collected on a geo-referenced basis at depths of 0 to 10 cm and 10 to 20 cm before tillage, after tillage, after chemical application, and before planting and assayed for the presence of the pathogen. Propagules ofV. dahliae were detected at 140 of 141 sites sampled prior to tillage. Most (74.4% in heavy, sandy loam; 63.1% in light, loamy sand) were concentrated in upper 10 cm of the soil profile. Plowing redistributed inoculum vertically while deep-rip tillage did not. In the non-chemical treated areas of both fields, theVerticillium population reached a maximum between 25 July and 8 August before declining to near pre-tillage levels. Overall, the population generally was lower in the field with heavy soil, higher organic matter content, and a 3-year crop rotation. Metam sodium appeared to be most effective when shank injected, as the levels of inoculum in both fields declined by 60% to 80% following this application method. Chemigation was ineffective in the lighter soil, but the inoculum density in the deep-rip tillage area of the field with the heavier soil declined by nearly 20% in the upper and 60% in the lower strata following this treatment. The number ofV. dahliae propagules at the 10- to 20-cm depth in the plowed area of the same field was reduced by 25% following chemigation, but remained unchanged in the upper strata. Wilt was reduced in both fields by as much as 50% with shank injection of metam sodium with concomitant increases in total yield, marketable yield and gross income. Increases in total yield were significant (P<0.05) for the main effect of chemical, in the plowed area of the field with the heavier soil type following shank injection. These data suggest that growers might benefit from altering their tillage and chemical application practices as part of an integrated approach to managing Verticillium wilt.     

Economic implications of a virus prevention program in deciduous tree fruits in the US

Viral diseases in fruit trees present a potential danger that could injure the fruit industry, the planting stock industry (nurseries), and consumers in the United States and abroad. Currently, the US has a virus protection program (VPP) that serves to minimize the spread of viral diseases. This paper reports research estimating the economic consequences of the loss of the program on nurseries, growers and consumers. The potential economic losses are a measure of the value of the existing program. The paper focuses on apples, sweet cherries, and Clingstone peaches.

The effects of a loss of a VPP on nurseries would include direct and indirect losses from viral diseases in the form of lower quantity and quality of planting stocks. Fruit growers would be affected by reduced plant growth and fruit yield. Consumers would be affected by higher prices and reduced quantity of fruit.

We measured benefits of the virus prevention program as changes in consumer and producer surpluses. Empirical estimates were made using the method of avoided losses. Benefit estimates to three economic sectors—nurseries (avoided change in producer surplus), producers (avoided change in consumer and producer surpluses), and consumers (avoided change in consumer surplus)—were calculated. Total benefits for all three sectors were approximately $227.4 million a year, or more than 420 times the cost of the program. Our analysis utilizes a method that might be used to evaluate other programs that prevent the introduction of plant diseases.