Intensive Grazing/Seasonal Dairying: The Mahoning County Dairy Program

1987-1991

OARDC Research Bulletin 1190

Chapter 4: Herd Health

Two major areas of herd health, i.e., udder health and the reproductive program, are covered in Chapters 5 and 6 of this Bulletin. This chapter will describe the remainder of the Herd Health program for the Mahoning County Project.

Early concerns at the Mahoning Project were those health problems, e.g., internal parasites, bloat, grass tetany, or infectious foot rot, that might be expected in cattle that are grazing pasture. In a seasonal dairying program, breeding and calving seasons would be expected to resemble somewhat those of a well-managed beef herd. That is, breeding of the entire herd occurred within a short period of time and subsequently all cows in the herd would be at a similar stage of pregnancy. Finally, all calves would be born in a short period of time. Thus, a scenario for introduction of an infectious disease resulting in either an abortion storm or an epidemic of calf disease seemed a real possibility. See Table 4.1 for an overview of the health maintenance program.

Metabolic Diseases

In general, the occurrences of metabolic diseases such as milk fever, ketosis, and retained placenta were at or below the rates expected in well-managed herds. Bloat and grass tetany were not detected during the study.

Infectious Diseases

After site-reared replacements became available in 1989, the herd was maintained as a closed-herd. We believe this was especially important given the nature of the breeding program required in seasonal dairying. Several abortions were detected during the project. As is often the case, although diagnostic efforts were made, a conclusive diagnosis was not achieved. While serologic titers suggested a possibility of leptospirosis in 1988 and IBR-induced abortion in 1990, results were not definitive. The herd vaccination program consisted of modified-live virus vaccines given to heifers at four to six months of age and repeated one month later. Replacement heifers were also calfhood vaccinated against brucellosis. Older animals received inactivated (killed) virus vaccines (IBR-PI3, BVD, bovine respiratory syncytial virus (BSVD)) and pentavalent leptospirosis bacteria every six months. Given present technology, it is probably not realistic to expect complete prevention of losses resulting from the common infectious diseases. However, preventing the entry of new disease agents (CLOSED-HERD) and developing and maintaining herd immunity (PROPER VACCINATION PROGRAM) should allow producers to keep losses at a low level.

Calf Health

Because of the high intensity of calving in the seasonal dairying project, a monoclonal antibody product given orally to calves to prevent Escherichia coliinduced diarrhea was used initially. In later years, this was replaced with a maternal vaccination given to cows during the dry period. Colostrum was fed to all calves. Prior to feeding, the specific gravity of colostrum was measured with a colostrometer. Specific gravity is associated with antibody level in colostrum. An injectable selenium product (Bo-Se)¹ was given to all heifer calves shortly after birth.

Occasional diarrhea was noted in calves and treatment consisted primarily of supportive therapy such as oral electrolyte fluids. During one spring calving season, scours were noted in virtually every calf. A viral cause such as rotavirus or coronavirus was suspected but not conclusively demonstrated. Prompt electrolyte therapy resulted in reversal of clinical signs, and no death losses were noted as a result of diarrhea. One six-day-old bull calf died suddenly during feeding. Laboratory tests indicated the cause to be acute white muscle disease which led to heart failure. This bull calf had not received a Bo-Se injection.

Internal Parasites

During their first summer, calves were raised in a small permanent pasture and were dewormed in the autumn. Yearling heifers were grazed behind cows in the intensive system. Yearlings were dewormed in June and July of each season approximating the third and sixth week (eight weeks if Ivermectin² is used) after turnout as recommended by OSU parasitologists. Fecal samples checked at various times had low worm egg counts indicating success in keeping pasture larval counts low. Grazing yearlings behind cows in the intensive grazing system at Mahoning did nct appear to result in heavy worm exposure. Controlling internal parasite loads in heifers has been proven to be very beneficial economically in previous research conducted at OSU (Herd, 1983). In addition to adopting OSU research-generated deworming recommendtions (Herd and Heider, 1980; Herd et al., 1987), producers should be cautioned to work closely with their veterinarians to monitor worm burdens in heifers. Fecal egg counts in heifers of greater than 100 eggs per gram are generally considered significant.

Johne's Disease

In 1990, one cow with diarrhea was subsequently found positive by fecal culture for the bacterium which causes Johne's disease. A considerable risk of introducing Johne's disease is assumed when establishing a herd or adding purchased replacements. The diagnosis in the Mahoning herd emphasizes the following:

(1) If purchases are necessary, determine, if at all possible, the Johne's disease status of the herd of origin; and

(2) Practice good hygiene in raising replacements, including separation of the calf from its dam at birth.

Subsequently, fecal samples from the entire herd were cultured an additional three times at sixmonthintervals, and to date, no more positives have been detected.

Note: For further information regarding prevention and control of Johne's disease, the reader is referred to the Ohio State University Extension bulletin by Hoblet and Shulaw (1988).

Summary

In general, herd health during the Mahoning project was very good. In fact, it was better than might have been expected when a herd is assembled from multiple sources. The experience with the Mahoning herd indicates that disease occurs periodically even in well-managed herds. However as was demonstrated in the Mahoning project, an excellent on-going working arrangement between the dairy producer and the veterinarian can be expected to greatly minimize herd health problems.

¹ Source: Schering Plough Animal Health Corp., Kenilworth, NJ 07033.

² Source: Merck and Co., P.O. Box 2000, Rahway, NJ 07065.