Benefits of forage-based heifer development and post-AI supplementation.

Benefits of forage-based heifer development and post-AI supplementation.

Summary

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.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Objective 1 has been completed and data has been submitted to the Midwest section of the American Society of Animal Science.

Results: Weaned heifers were developed to gain 0.454 kg/d for 6 mo either in the feedlot (LOT) or on grass (GRASS). All heifers were synchronized with a controlled internal drug release (CIDR) protocol and artificial insemination (AI) was performed following detection in estrus. Following AI all heifers were moved to a feedlot and each development group, LOT and GRASS, was divided into 3 groups. The groups were fed to maintain weight (MAIN; 6.4 kg hay and 0.01 kg urea/hd) or to gain weight on a diet high (HMP; 6.2 kg hay, 2.9 kg DDGS and 0.03 kg urea/hd)] or low (LMP; 8.0 kg hay and 0.8 kg DDGS/hd) in metabolizable protein. Uterine pH and blood samples were collected from a subset of each group (n=3 LOT and 3 GRASS per post-AI group) on d 0, 7, and 11 after estrus. There was no difference (P>0.20) in Body Weight between MAIN, HMP, or LMP heifers on the day of AI (311±3.6 kg), but heifers in the HMP and LMP group weighed more (P≤0.01) than heifers in the MAIN group on d 11 (344±5.5, 338±5.5 kg, and 315±7; respectively). Uterine pH did not differ (P>0.14) between LOT and GRASS heifers; however, uterine pH decreased (P0.18) between lot and grass developed heifers for blood urea nitrogen (BUN); however, there was a post-AI treatment by time interaction (P0.14) BUN concentrations on d 0. BUN concentrations in LMP heifers did not change from d 0 to d 7 or 11. BUN increased from d 0 to d 7 and 11 in both MAIN (P≤0.04) and HMP (P<0.01). In summary, method of heifer development (LOT or GRASS) did not influence uterine pH or BUN when heifers were fed in a feedlot following AI; however, post-AI diet had an impact on both uterine pH and BUN.

Objective 2: Still needs to be completed

Objective 3: Still needs to be completed

Impacts and Contributions/Outcomes

Recent data from our laboratory has indicated that heifers can be developed on native range, and reproductive performance can be maintained. Therefore this proposal will evaluate the cost and reproductive performance differences between heifers developed in a conventional system and ones developed on forage. Results from the first objective demonstrated that method of heifer development had no impact on uterine pH or blood urea nitrogen, but the diet that heifers were moved to following AI did impact both uterine pH and blood urea nitrogen. Therefore, method of heifer development during the winter should be decided by cost of development and how heifers will be managed after insemination. Objective 2 will further add to this by determining how post-AI diet change can impact pregnancy success and embryonic loss.

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