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Estrus Synchronization with CIDR

Estrus synchronization with CIDR may be less sensitive to plane of nutrition than more traditional systems. Scientists at the Agriculture Canada Crops and Livestock Research Centre and Atlantic Veterinary College fed grass-legume silage to 57 winter-calving beef cows at three different levels of intake (1.5%, 1.7%, and 2.0% of body weight) until pasture turn-out. Equal numbers of cows on each plane

Estrus synchronization with CIDR may be less sensitive to plane of nutrition than more traditional systems. Scientists at the Agriculture Canada Crops and Livestock Research Centre and Atlantic Veterinary College fed grass-legume silage to 57 winter-calving beef cows at three different levels of intake (1.5%, 1.7%, and 2.0% of body weight) until pasture turn-out.

Equal numbers of cows on each plane of nutrition were assigned to one of two estrus synchronization systems:

  • Ovsynch (gonadotropin-releasing hormone, or GnRH, injection followed seven days later by prostaglandin and a second GnRH 48 hours after that; and insemination 16 hours after second GnRH);

  • CIDR (CIDR inserted for seven days; 1 mg estradiol benzoate and 100 mg progesterone injected at time of CIDR insertion; second injection of 1 mg estradiol benzoate 24 hours after CIDR removal; and insemination 28 hours after second injection).

Interestingly, plane of nutrition had no effect on cow weight gain, condition score or backfat. However, there was a significant linear response to plane of nutrition in calf weight gain and calf weight at pasture turnout. This was attributed to increases in milk fat and milk protein percentages as plane of nutrition increased.

First-service pregnancy rates were 61% and 83% for Ovsynch and CIDR, respectively. Pregnancy rates for Ovsynch cows on the low, medium and high planes of nutrition were 29%, 57% and 89%, respectively. For the CIDR cows, pregnancy rates were 80%, 80% and 89%, respectively.

The authors concluded that CIDR synchronization may be less sensitive to plane of nutrition than more traditional methods of estrus synchronization.

Journal of Animal Science Charmley et al. 2002, 80 [Suppl. 1]: 206. Reprinted from the Michigan State University March issue of “Beef Cattle Research Update.”

Vaccinating young calves with modified-live vaccine (MLV) for bovine virus diarrhea virus (BVDV) while maternal antibody is present generates T-cell mediated immunity to BVDV.

Interference by maternal antibodies prevents the development of an antibody response following vaccination with either a killed or attenuated BVDV vaccine. However, T-cell mediated immune response to BVDV may be generated in the absence of a detectable serum neutralizing antibody response.

Two trials were conducted to evaluate the potential to elicit T-cell mediated immune responses to BVDV in calves with circulating maternal antibody to BVDV. USDA scientists in Ames, IA, conducted the trials.

In the first trial, calves with high levels of circulating maternal antibody to BVDV1 and BVDV2 were experimentally challenged with BVDV2 at 25 weeks old. The T-cell mediated immune responses of the experimentally infected calves and non-infected calves were monitored.

Calves experimentally challenged with BVDV developed BVDV-specific T-cell responses while high levels of maternal antibody were circulating. A second challenge with BVDV2 was performed once maternal antibody could no longer be detected. Previous exposure to BVDV in the presence of maternal antibody protected calves from the clinical signs of acute BVDV infection compared to the control calves.

In the second trial, three groups of calves with circulating maternal antibody to BVDV were given either a modified-live vaccine (MLV) containing BVDV1 and BVDV2, a killed vaccine containing BVDV1 and BVDV2, or no vaccine, at 7 weeks of age.

Calves vaccinated with MLV BVDV developed BVDV1- and BVDV2-specific T-cell responses in the presence of maternal antibody. Vaccination with killed BVDV did not result in the generation of measurable antigen specific T-cell immune responses. Calves vaccinated with either an MLV or killed BVDV vaccine while maternal antibody circulated developed a memory antibody response to BVDV2 upon subsequent vaccinations.

USDA/Agricultural Research Service technical abstract, “BVDV Immunity And Maternal Antibody (Detecting And Controlling BVDV Infections, 4/4-5/02, Ames, IA.)”.

A perennial cereal rye cultivar shows great promise as an alternative to barley silage.

“ACE-1 rye is a silage crop that is superior to barley in yield and other agronomic characteristics and has similar feed quality,” says Canadian forage breeder Surya Acharya. “Another advantage is that perennial cereal rye (PC rye) can be used in long-term hay and pasture rotations.”

Originating from a cross between an annual rye and a perennial grass, the new forage captures the best of both worlds. It easily can be integrated in most crop rotations, as it doesn't require special equipment or significant changes in cultural practices. Commercial seed is expected to be available this fall.

“Due to its perennial characteristics, PC rye can take advantage of early spring moisture and is ready for silage harvesting three to four weeks earlier than barley,” says Acharya. The crop regrows vigorously and under favorable conditions will sustain a second cut of silage.

The regrowth can be used to extend fall grazing, he says. The savings in over-wintering costs for 30 days can reduce feed costs $7(Can.)/calf, plus $4.50(Can.)/calf savings in feedlot labor and feed.

A serious limitation of PC rye is that it has a tendency for floret sterility, he says. This relates to its origin as an interspecific cross. The floret sterility results in reduced seed set and affected seed heads are susceptible to infection with ergot, a fungal disease that is toxic to livestock.

“PC rye must be harvested before the ergot balls are formed to avoid the risk of poisoning,” cautions Acharya. “The silage-making process reduces the toxic effects, but to avoid poisoning when used as pasture, the crop must be intensively grazed before seed heads appear. Fortunately, the regrowth after silage harvest produces very few seed heads and they do not reach maturity so ergot is not a problem in fall grazing.”

Researchers are currently investigating several strategies to improve the fertility of PC rye.

Research is also focused on increasing the crop's grazing tolerance.

“Trials indicate PC rye can't withstand prolonged grazing pressure,” says Acharya. “Significant variability in tolerance within the PC rye population has, however, been observed and we have started a selection program for grazing tolerant plants that will continue for the next two years.”

Ultimately, he wants to generate a PC rye cultivar that can grow with forage legumes to produce high-quality pasture and hay.

For further information, contact: Surya Acharya, 403/ 317-2277, Agriculture and Agri-Food Canada, Lethbridge Research Centre.

Preschool children generally took bigger bites and consumed more food when served super-sized portions of their normal entrees, according to a research study at the Children's Nutrition Research Center in Houston, TX. But when these same children were offered smaller portions, they ate less than when served the super-sized portions.

Jennifer Fisher, assistant professor of pediatrics at Baylor's College of Medicine, led the six-month nutrition study.

In the study, two series of lunches were served to 30 preschool children, ages 3 to 5. One series offered an age-appropriate portion of a macaroni-and-cheese entree, while the other was a portion twice as large. Researchers found that the children ate about 25% more of the entree when served the larger portion, and their overall calorie intake at lunch was 15% higher.

Fisher and her Penn State researchers Barbara Rolls and Leann Birch say the findings imply that minimizing children's exposure to excessive portions may reduce overeating.

This study was published in the May 2003 issue of the American Journal of Clinical Nutrition.

More targeted control of cattle warble grubs may soon benefit cow-calf and feedlot production, thanks to a new breakthrough diagnostic test.

Scientists at the Lethbridge Research Centre in Alberta, Canada, have collaborated with Spanish scientists to develop at test that is 95% accurate in diagnosing active grubs.

Unlike the previous test - which isn't very accurate and is only reliable on calves after their first pasture season - the new test can be used on all age classes of animals and is very sensitive, researchers say.

The test is able to detect very small traces of a protein secreted by the parasite as it migrates through the animal.

Researchers explain that adult flies lay eggs on the legs and underside of cattle, and when the eggs hatch, tiny maggots burrow into the animal's skin. They migrate through the connective tissue of the animal by excreting enzymes that break down tissue for the developing maggot to ingest.

Feedlots typically treat cattle for grubs as part of broad-spectrum internal parasite treatments. Researchers say not only will this new test help monitor the effectiveness of such treatments, but it also will help reduce the amount of treatment and prevent the potential build-up of resistance.

What's more, the new test serves as a tool to help researchers learn more about grub interactions with cattle.

For more information, contact Doug Colwell at 403/317-2254.

To submit items for “Research Roundup,” e-mail [email protected] or fax to 952/851-4601.