Development of Maize Weevils (Coleoptera: Curculionidae) on Corn Lines Resistant to an Aflatoxin-Producing Fungus

Susceptibility to the maize weevil, Sitophilus zeamais Motschulsky, of corn lines bred for their resistance to the aflatoxin-producing fungus Aspergillus flavus Link ex Fries was determined in the laboratory. Duration of maize weevil development, number of progeny produced, and an index of susceptibility varied with corn line; number of eggs laid and survivorship from egg to adult emergence did not vary with corn line. Soluble carbohydrate, kernel hardness, lipid, soluble nitrogen, free and bound phenolic acids, Kjeldahl protein, and protein/carbohydrate ratio varied with corn line; equilibrium moisture content did not vary with corn line. The only relationship between biological parameters of maize weevils and chemical and physical properties of the stored corn that was predictable was that maize weevil development time increased as lipid content of the corn increased. Susceptibility to A. flavus infection in the field was not correlated with susceptibility to maize weevil population growth or with chemical or physical properties of the stored corn. Predicted weevil population growth over a 180-d period varied 50-fold among the corn lines. Some of the corn lines that are less susceptible to infection by A. flavus in the field were also less susceptible to maize weevils (particularly Mp420 and SC54)

Relationship Between Chemical Percentage Intramuscular Fat and USDA Marbling Score

This paper presents the relationships found and developed into a set of regression formulas for marbling score (MS) and actual percentage intramuscular fat (PIMF) using data from realtime ultrasound (RTU) certification programs. MS was determined to the nearest 10th of a marbling degree by a USDA grader—that is, sm10, sm20, etc. The same USDA grader was used each year. Percentage intramuscular fat was determined by removing a 1/4 in. facing from the 12th rib. This facing was returned to the Iowa State University Meat Laboratory, trimmed so that the sample contained only the longissimus dorsi muscle, freeze-ground, and sub-sampled. Product moment correlations between PIMF and MS were .95, .82, and .89 for 1996, 1997 and combined years, respectively. The results shown in this paper are not characteristic of what is generally observed in the industry. However, it shows that there can be a high correlation between the subjective grading of marbling as compared to actual chemical fat in the longissimus dorsi muscle. The USDA grader that graded these cattle knew he was being compared to an instrument grading system. How much fairer might the current grading system be if this technology were to be embraced and implemented by the beef packing industry

Trends Associated with Marbling Score, Fat Cover, and CAB (Certified Angus BeefTM) Acceptance Rate

The objective of the study was to analyze the Certified Angus Beef (CAB) program carcass database for trends associated with marbling score, fat cover, and CAB acceptance rate in Angus-type cattle. The CAB program carcass database is made up of over 100,000 records collected during 1989 to 1999. Steers make up 90 % of the database, and 89 % of the cattle were finished in the Midwest (NE, CO, KS). The majority of the cattle (62 %) were finished in Nebraska feedyards. The CAB program overall acceptance rate was 23.4 %. Marbling score (84.0 %) is the first limiting factor for CAB acceptance of steers. For steers, a combination of marbling score and yield grade (8.3 %) and yield grade alone (6.1 %) for steers are the second and third limiting factors for CAB acceptance, respectively. The phenotypic correlation between fat cover and marbling score is nearly zero for CAB steers, yet for non-CAB steers the correlation is 0.38 (p \u3c .01). On the average, as yield grade increases from 2.0 to 4.0, by each tenth of a unit, marbling score increases by 0.3 % for every 1 % increase in fat cover for all steers. Comparing CAB steers versus non-CAB steers, marbling score increases by 0.05 % and 0.34 % for every 1 % increase in fat cover, respectively. As fat cover groups increase by 0.1 of an inch, CAB acceptance rate increases up to the 0.6- 0.69 inch group, then starts to decrease for steers. When looking at marbling score by fat cover groups, CAB steers increase 1.0 % for each 0.1 inch increase in fat cover, and for non-CAB steers, there is an increase of 5.0 %. Fat cover increases by 5.6 % and 14.2 % as you go from a USDA marbling score of small to modest and slight to modest, respectively, for all steers. Looking at the slaughter months, there is an increase in marbling score from April to August, although fat cover remains steady. Yet CAB acceptance rate decreases from April to June and then increases from June to November. Producers may be able to improve the CAB acceptance rate of their cattle if there is a clearer understanding of the relationship between traits that are included in the CAB specifications

Predicting Beef Carcass Retail Product Using Real-time Ultrasound and Live Animal Measures: Progress Report

Two-hundred-eighty-two crossbred steers were scanned with real-time ultrasound (RTU), slaughtered, and fabricated into retail cuts to determine the potential for a combination of live animal and ultrasound measures to predict carcass retail yield. Ultrasound measures of fat thickness, ribeye area, rump fat thickness, and body wall thickness, as well as live weight and visual muscle score were recorded three to five days prior to slaughter. Carcass measurements were taken, and one side of each carcass was fabricated into retail cuts with .3 inches fat. Stepwise regression analysis was used to compare possible models for prediction of either pounds or percent retail product from carcass measurements or a combination of live animal traits and ultrasound measures. Results indicate that possible prediction models for percent or pounds of retail product using live animal and RTU measures were similar in their predictive power and accuracy when compared to models derived from carcass measurements