- Animals: bovine
- Animal Production: housing, grazing management, livestock breeding
The cost of developing replacement heifers has a tremendous impact on the profitability of cow-calf operations, and the economic value of reproduction for commercial beef producers has been reported to be five times greater than calf growth. Therefore, methods of heifer development that decrease costs but maintain high reproductive performance can have a tremendous impact on profitability. The first objective of this project compared two methods of heifer development (wintered in a feedlot or on grass) and three diets initiating after artificial insemination (maintain weight, gain weight on a diet high in metabolizable protein or low in metabolizable protein). Although there were no differences between heifer development methods, diet impacted both uterine pH and blood urea nitrogen concentrations. Both uterine pH and blood urea nitrogen can influence pregnancy success, and therefore have a tremendous impact on the economics of heifer development and ranch profitability. The second objective determined the influence of post-AI change in nutrition on pregnancy success and embryonic loss. The percentage of heifers that had reached puberty prior to the start of the breeding season tended to be more in the feedlot developed heifers compared to the range developed heifers. However, heifers developed on range tended to have greater pregnancy success compared to heifers developed in the feedlot. The third objective was to demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers. For this objective we worked with 7 producers and over 1300 heifers. Weight change data from AI to pregnancy determination was collected on over 800 heifers, and pregnancy success was decreased when heifers lost weight from AI to pregnancy determination (30 to 65 days). However, when heifers were developed on grass, there was no effect on pregnancy success weather they were returned to grass and supplemented or not or even kept in the feed lot.
The cost of developing replacement heifers has a tremendous impact on the profitability of cow-calf operations. Cow-calf production systems that rely heavily on harvested and purchased feeds have less potential to be profitable (Adams et al., 1994), and an important part of any production system is reproductive performance and costs associated with developing heifers. The economic value of reproduction for commercial beef producers was reported to be five times greater than calf growth (Trenkle and Willham, 1977).
Heifer development throughout the North Central Region of the U.S. usually involves placing heifers into a confined feeding situation from weaning until the following breeding season. Development of heifers in a confined environment can create several management problems; the greatest of which are the labor and cost involved with daily feeding. Developing heifers on range is not a common practice in the North Central Region of the U.S. due to the perception that adequate reproduction cannot be maintained in such a system. It is hypothesized that a range supplementation management system could be used to develop replacement heifer calves.
Following insemination, heifers are usually turned to grass and are often not supplemented. Spring grass can vary tremendously in nutrient content, and producers often ask if the change in diet following insemination will reduce pregnancy rates. It is possible that energy and protein requirements may be undersupplied or oversupplied and therefore increases embryonic mortality. Supplementation following insemination to balance nutrients may therefore increase pregnancy rates.
Development and utilization of forage-based heifer development and post-insemination supplementation will reduce the number of animals fed in confinement situations, decrease cost and improve the reproductive efficiency of heifer development. This will allow ranchers to be more profitable by decreasing the labor involved with heifer development and allowing them more time to devote to other obligations.
Overall Objective: Evaluate the benefits of forage-based heifer development and determine appropriate post-insemination supplementation to maximize heifer performance.
Objective 1: To determine the influence of post-AI change in nutrition on uterine environment and circulating concentrations of plasma urea nitrogen.
Objective 2: To determine the influence of post-AI change in nutrition on pregnancy success and embryonic loss.
Objective 3: To demonstrate the benefit of forage-based heifer development compared to traditional feedlot developed heifers.