Sierra Foothill Research and Extension Center

There are 10 publications in this collection, published between 1997 and 2004.

Estimating Environmental Loading Rates of the Waterborne Pathogenic Protozoa, Cryptosporidium Parvum, in Certain Domestic and Wildlife Species in California

Cryptosporidium parvum (C. parvum) is a protozoal parasite that can cause gastrointestinal illness in a wide variety of mammals, including humans, livestock, companion animals, and wildlife. New species of Cryptosporidium are constantly being discovered, such as C. canis and C. felis, but their significance relative to the large role that C. parvum plays in livestock and human cryptosporidiosis is still unclear. In the majority of livestock species, clinical disease and shedding of C. parvum typically occurs in youngstock under a few months of age, but fecal shedding of oocysts can also occur in healthy older animals which can then serve as a source of infection for these younger animals. In humans, clinical disease and shedding can appear at all ages, but is typically more common among children. The predominant clinical sign is profuse, watery diarrhea lasting from a few days to several weeks in normal (immunocompetent) individuals, but can be prolonged and life threatening among immunocompromised hosts such as AIDS patients. Modes of transmission range from direct fecal-oral transmission, as might occur between infected and susceptible calves during lay behavior, or ingestion of food or water inadvertently contaminated with oocysts from the feces of an infected host.

Waterborne transmission of the pathogenic protozoa, Cryptosporidium parvum, has emerged as an important public health concern. Because the infectious stage of C. parvum (oocysts) is resistant to conventional water treatment processes, public health agencies and water districts are actively seeking methods of reducing surface water contamination with this parasite. Protection of source water such as rivers and lakes has the potential to reduce the risk of transmission to humans and animals through drinking water, as well as through human recreational contact with untreated water. Given that the parasite readily infects a large number of mammalian hosts (Fayer et al. 1997), there are a number of possible contributing sources of oocysts present for any given watershed. Unfortunately, the primary quantitative sources of waterborne C. parvum oocysts are not well defined, and our methods of prioritizing point and non-point vertebrate sources of this zoonotic parasite are lacking.

Our objective is to develop a standardized methodology for comparing environmental loading rates for different populations of vertebrate hosts for C. parvum. Such a comparison would help form the basis of a rational decision making process for evaluating land use practices and vertebrate populations with respect to their relative environmental loading rates for important waterborne microbial pathogens. Both domestic and wild animal populations are infected by and can shed in their feces the infectious stage of this parasite. Attempting to characterize or assess the risk of point and non-point source protozoal contamination requires numerous parameters to be estimated, the most important being a valid and precise estimate of the oocyst loading rate per animal unit (Atwill et al. 2001; Hoar et al. 2000). The oocyst loading rate, which can be defined as the total number of oocysts excreted by a defined cohort of animals for a specific period of time, can be calculated directly by measuring the kinetics of total oocyst shedding, that is, duration and intensity per Kg feces, multiplied by fecal production. This direct measurement method is very difficult for free-ranging wildlife and some species of livestock. An alternative approximation for determining the oocyst loading rate for cohorts of mammals is to measure the prevalence of infection and the intensity of shedding using cross-sectional surveys of the mammalian population, and then relying on experimental or laboratory estimates of fecal production (Hoar et al. 2000). We applied these concepts to a variety of domestic and wild animal species to generate a set of comparative loading rates for the waterborne pathogen, C. parvum.

Heparin-Binding Proteins as an Indicator of Bull Potency

INTRODUCTION

Over 20 years ago, research was underway to develop methods for in vitro fertilization utilizing bovine sperm and eggs. Freshly ejaculated sperm cannot fertilize an egg. Those sperm must reside in the female reproductive tract for 6-8 h and become diluted from seminal fluid. That process is called capacitation because it allows sperm to acquire the “capacity” to fertilize an egg. The final change sperm cells undergo after capacitation involves a morphological remodeling with release of enzymes packaged in the tip of the sperm head’s acrosome. This irreversible remodeling is known as the acrosome reaction. All of these events had to be controlled in the lab to successfully fertilize eggs from cows.

Proteins produced in the seminal vesicles, prostate, and Cowper’s glands convey the capacitating effects of heparin, a carbohydrate, to bull sperm. Those proteins are collectively referred to a heparin-binding proteins because they function as “docking’ molecules to allow heparin to physically attach to the sperm, causing capacitation. Heparin per se is not found in the female reproductive tract. However, several other heparin-like carbohydrates do exist, and heparin mimics their normal biological action.

One specific heparin binding protein has been named fertility-associated antigen (FAA). For the past 13 years, research has focused specifically on FAA, its identity, the ability to detect it in semen, and field trials comparing fertility of bulls classified as FAA-positive or FAA-negative. Trials included multiple-sire pastures with or without parentage of calves being confirmed by DNA testing. Herds have utilized A.I. in some instances, and serving capacity was also evaluated one year before bulls were allocated to pastures.

Field Trials Comparing Bulls Categorized as FAA-Positive or FAA-Negative

Since 1992, field trials have been conducted in Texas, Nebraska and California to compare prolificacy of bulls that produced semen classified as FAA-positive or FAA-negative. Multiple-sire pastures: Table 1 contains data from 7 consecutive years of field trials at King Ranch. When bulls were 14-19 mo. of age, FAA status was determined after they passed a breeding soundness exam. All pastures contained 8-16 bulls for 60d at a constant ratio of 1 bull per 25 cows. Overall, FAA-positive bulls were 19 percentage points more fertile than their FAA-negative herdmates. FAA was quantified in the Ax lab at the University of Arizona.

Serving capacity and FAA: The ability of a bull to breed cows can be estimated as “serving capacity.” This is ordinarily evaluated by placing a group of virgin bulls with heifers that were synchronized to be in heat. Mounts with penetration are scored for each bull over a period of 20 min. Bulls are then ranked as “high” or “low” in that social setting.

FAA-positive bulls with high serving capacity impregnated 87% of cows exposed to them for a 60d breeding season. FAA positive bulls with low serving capacity only impregnated 69% of the exposed cows. Bulls with semen lacking FAA but with high serving capacity impregnated 78% of the cows pastured with them. Therefore, their libido was able to compensate for the absence of FAA, but they were inferior to herdmates with high serving capacity possessing seminal FAA (Table 2). FAA was measured in the University of Arizona Lab. A.I. outcomes: With A.I., serving capacity is not an issue because cows are inseminated when they are in estrus. Holstein heifers and range beef cows were inseminated once with semen from mixed breeds of beef bulls designated as FAA-positive (n=18) or FAA-negative (n=7). Overall, there was a 16% higher fertility in females inseminated with FAA-positive semen (66% pregnancy rate) compared to FAA-negative semen (50% pregnancy rate, Table 3). The University of Arizona Lab analyzed semen for FAA content.

Efficiency of the cow herd: What does selection for FAA-positive bulls do for the cow herd? Research obtained from 1992 through 1998 at King Ranch indicated that the distribution of calves born during the calving season shifted to births occurring earlier (Table 4). In the nucleus herd, cows were initially bred only to FAA-positive bulls. Their replacement daughters were also only bred to FAA-positive bulls in subsequent generations. By 1998, 22% more calves were born in the first 20 days of the calving season from this FAA selection management practice (Table 4). Clearly, efficiency in the cow herd had improved.

DNA parentage of calves: In a collaboration with Drs. Dave and Cindy Daley and Harris Ranches, FAA status of bulls was determined using a newly developed chute-side cassette. Those bulls were in multiple-sire pastures with cows for a 60-day breeding season in 3 consecutive breeding years (2000, 2001, 2002). The trial was conducted to relate parentage of calves by DNA fingerprinting to growth and carcass traits of individual sires. Analysis of FAA status became a retrospective comparison to evaluate utility of the cassettes to analyze semen for FAA within 20 minutes.

Results from this study are being analyzed. Overall, 12 out of 62 total bulls were found to be FAA-negative. This was close to the incidence found in a population of 914 bulls screened in 6 states in April, 2003. In those bulls, 26% were FAA-negative using the same test cassette to quantify FAA in semen.

With the Harris Ranch bulls, complete DNA profiles were achieved with 47 of the 62 bulls. Overall, as bulls got older, they sired more calves per bull (1.1 as yearlings to 22.2 as 5-year old breeding bulls). Irrespective of age, FAA-positive bulls produced 5.9 more calves in the 3 years (1.9 calves/year) compared to FAA-negative herdmates. That translated into a 19% higher calf production for FAA-positive bulls for the 3-year duration of the trial (Table 5). There was clearly an age influence in terms of calf production in relation to FAA status of bulls. As yearlings and 5-year olds, FAA status did not factor into calf yield. However, between the ages of 2 and 4, each FAA-positive bull averaged 35.4 total calves, whereas his FAA-negative herdmates produced 27.3 total calves in that period of time. Therefore, the FAA-negative bulls were 77% as prolific as their FAA-positive contemporaries based upon those numbers.

From ages 1 through 3 years, a higher proportion of FAA-negative bulls were more likely to not sire any calves compared to FAA-positive bulls. In other words, sterility of a bull in a given year corresponded to FAA status of bulls 3 years old or younger.

CONCLUSION

FAA is a good thing! Fertility data support that regardless of years, pasture, or breed, the FAA positive bulls resulted in a higher percentage of cows pregnant compared to FAA negative herdmates. A conservative estimate places pregnancy rates 15% higher in heifers or cows bred to FAA positive bulls.

The calving season should also tighten up if daughters are retained from FAA positive bulls and are bred to known FAA positive bulls. In tern, daughters in subsequent generations need to be bred to FAA positive bulls, and that practice should continue.

FAA testing only takes 20 minutes and is based upon visible detection of a reddish-purple line on a plastic cassette that contains all the necessary chemicals to detect FAA if it is in a semen sample. The projected payback per cow in a herd from testing for FAA in bulls will be 16 to -25 fold if net profit per calf is $50.00. Obviously, if profit per cow exceeds $50.00, then the value of testing for FAA increases substantially.

For more information, pricing, and to order testing kits, contact:

ReproTec, Inc. (520) 888-0401 (520)888-0297 (FAX) www.reprotec.us

Cows in Space

George, Mel

A great deal has been learned about foraging behavior and livestock distribution in the last several decades. We hope to apply and fine tune this knowledge to reduce the impacts of beef cattle on riparian areas, surface water and wildlife habitat. Likewise, to use cattle as a tool to manage weeds we need to be able to attract cattle into patches of undesirable species.

Beef cattle and other grazers focus on water sites and sites that provide thermal comfort, foraging away from these focal points to meet their nutritional needs. Most ungulates first harvest food, then move either to loafing and bedding sites to ruminate and digest the food ingested in a previous grazing bout (meal), and/or to areas for predator avoidance. The distance covered by the animal during foraging depends on digestive capacity, rate of passage, forage harvest rate, grazing velocity and level of hunger. Once satisfied the animal returns to a thermal, water or bedding site depending on their needs and priorities.

Time spent grazing depends on forage availability, forage quality, and thermal balance. Animals reduce daily grazing time as digestibility of available forage declines and retention time of ingesta increases. When daytime temperatures are within the thermal comfort zone of cattle, most grazing takes place during daylight hours. During hot weather cattle reduce afternoon grazing and increase night-time grazing. Most researchers report little grazing and traveling after darkness. However, recent nighttime observations at San Joaquin Experimental Range in Madera County indicate that grazing and change of bedding sites do occur during darkness on some nights. The objective of this study at UC SFREC is to understand where beef cattle distribute themselves in a typical foothill oak woodland or annual grassland during a 24 hour period and how this may change seasonally. Studies on private ranches are underway to document the effectiveness of protein supplement sites as attractants for beef cattle at different distances from stock water and riparian areas.

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Sierra Foothill Research and Extension Center

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