Growing consumer interest in grass-fed beef products has raised a number of questions with regard to the perceived differences in nutritional quality between grass-fed and grain-fed cattle. Research spanning three decades suggests that grass-based diets can significantly improve the fatty acid (FA) composition and antioxidant content of beef, albeit with variable impacts on overall palatability. Grass-based diets have been shown to enhance total conjugated linoleic acid (CLA) (C18:2) isomers, trans vaccenic acid (TVA) (C18:1 t11), a precursor to CLA, and omega-3 (n-3) FAs on a g/g fat basis. While the overall concentration of total SFAs is not different between feeding regimens, grass-finished beef tends toward a higher proportion of cholesterol neutral stearic FA (C18:0), and less cholesterol-elevating SFAs such as myristic (C14:0) and palmitic (C16:0) FAs. Several studies suggest that grass-based diets elevate precursors for Vitamin A and E, as well as cancer fighting antioxidants such as glutathione (GT) and superoxide dismutase (SOD) activity as compared to grain-fed contemporaries. Fat conscious consumers will also prefer the overall lower fat content of a grass-fed beef product. However, consumers should be aware that the differences in FA content will also give grass-fed beef a distinct grass flavor and unique cooking qualities that should be considered when making the transition from grain-fed beef. In addition, the fat from grass-finished beef may have a yellowish appearance from the elevated carotenoid content (precursor to Vitamin A). It is also noted that grain-fed beef consumers may achieve similar intakes of both n-3 and CLA through the consumption of higher fat grain-fed portions.

A study was conducted to estimate the retention efficiency of vegetative buffers for Escherichia coli deposited on grasslands in cattle fecal deposits and subject to natural rainfall-runoff conditions. The study was conducted on annual grasslands in California's northern Sierra Nevada foothills, a region with a distinct wet-dry season Mediterranean climate. We used 48, 2.0- by 3.0-m runoff plots to examine the efficacy of 0.1-, 1.1-, and 2.1-m buffers at three land slopes (5, 20, and 35%) and four dry vegetation matter levels (225, 560, 900, and 4500 kg/ha) across 27 rainfall-runoff events during two rainfall seasons. Buffer width treatments were implemented by placement of cattle fecal material containing known loads of E. coli 0.1, 1.1, or 2.1 m upslope of the plot runoff collector. Mean total runoff to total rainfall ratio per plot ranged from 0.014:1 to 0.019:1 and reflected the high infiltration capacity of these soils. Approximately 94.8 to 99.995% of total E. coli load applied to each plot appears to be either retained in the fecal pat and/or attenuated within 0.1 m downslope of the fecal pat, irrespective of the presence of a wider vegetated buffer. Relative to a 0.1-m buffer, we found 0.3 to 3.1 log10 reduction in E. coli discharge per additional meter of vegetative buffer across the range of residual dry vegetation matter levels, land slope, and rainfall and runoff conditions experienced during this project. Buffer efficiency was significantly reduced as runoff increased. These results support the assertion that grassland buffers are an effective method for reducing animal agricultural inputs of waterborne E. coli into surface waters.

Our primary goal was to generate an accurate estimate of the daily environmental loading rate of Cryptosporidium parvum oocysts for adult beef cattle, using immunomagnetic separation coupled with direct immunofluorescence microscopy for a highly sensitive diagnostic assay. An additional goal was to measure the prevalence and intensity of fecal shedding of C. parvum oocysts in pre-and postparturient cows as an indicator of their potential to infect young calves. This diagnostic method could detect with a >90% probability oocyst concentrations as low as 3.2 oocysts g of feces ؊1 , with a 54% probability of detecting just one oocyst g of feces ؊1 . Using this diagnostic method, the overall apparent prevalence of adult beef cattle testing positive for C. parvum was 7.1% (17 of 240), with 8.3 and 5.8% of cattle shedding oocysts during the pre-and postcalving periods, respectively. The mean intensity of oocyst shedding for test-positive cattle was 3.38 oocysts g of feces ؊1 . The estimated environmental loading rate of C. parvum ranged from 3,900 to 9,200 oocysts cow ؊1 day ؊1 , which is substantially less than a previous estimate of 1. . Use of this highly sensitive assay functioned to detect a greater proportion of low-intensity shedders in our population of cattle, which reduced the estimated mean intensity of shedding and thereby reduced the associated environmental loading rate compared to those of previous studies.Cryptosporidium parvum has emerged as a ubiquitous waterborne microbial pathogen, with specific genotypes readily transmitted ambidirectionally between livestock and humans (7,9,12,25,28,36). One of the first steps in designing watershed management programs for minimizing the occurrence of C. parvum in drinking water supplies is to identify significant quantitative sources of this parasite. Adult cattle are often considered potential nonpoint sources of environmental contamination for C. parvum, but there is some disagreement over the relative importance that adult cattle have in loading watersheds with significant amounts of C. parvum oocysts. In particular, there is a wide range of reported prevalences of fecal shedding of C. parvum for adult beef and dairy cattle. Numerous investigators have reported mean prevalences of fecal shedding from ϳ20 to ϳ70% in groups of clinically healthy adult cattle (23,31,34), yet several large cross-sectional epidemiologic surveys have observed prevalences of only 2% or less in asymptomatic adult cattle populations (4, 20, 41). Some of this variation in the observed prevalence of fecal shedding can be explained by different investigators using diagnostic assays of differing sensitivity and specificity (11,13,15), but much of the variation is the result of studying different populations of cattle (e.g., beef versus dairy), different age distributions within those populations, and groups of cattle under different management practices, especially when only a single farm or a small sample is examined. For example, we found in two different studies that calving duration fo...

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