Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Heifer calves developed for herd replacements are often developed one of two ways. Heifers may be developed in a feedlot where feed is provided daily or on range where they graze for feed. Heifers are often bred by artificial insemination (AI) to ensure calving ease. Breeding season usually begins during late spring when nutrients and/or forage may be limited. Heifers developed on range can receive poor nutrition before and after AI when range conditions are poor. Heifers developed in a feedlot can have poor nutrition after AI when taken to pasture. Egg development and fertility could be decreased by poor nutrition before AI. Embryo development could be decreased by poor nutrition after AI. Effects of energy restriction before and after AI were studied here. Poor nutrition before AI decreased key mineral levels in the uterus. When an embryo was recovered, uterine levels of sulfur, calcium, potassium, and aluminum were reduced. This is likely due to use of these minerals by the growing embryo. In a second study conducted, uterine magnesium and sulfur levels were reduced. In summary, the embryo appears to use sulfur, calcium, and magnesium for development, and energy restrictions after AI can potentially reduce embryo growth.

Technical Abstract: Crossbred heifers (n = 129) were assigned to one of two dietary treatments (Low or High). In year 1, heifers (n = 79) were offered 90% and 81% (Low) and 162% and 148% (High) of maintenance energy requirements, Pre-and Post-AI, respectively. At AI half were reassigned to the other treatment. Uteri were flushed for embryo recovery on d 7 or 8. In year 2, heifers (n = 50) were only treated after AI (with 77.5% or 161.5% of maintenance energy requirements) until uteri were flushed on d 14. In study 1, Low post-AI diet resulted in reduced uterine sulfur and calcium concentrations. When an embryo was recovered, uterine sulfur, calcium, potassium, and aluminum were reduced, and uterine magnesium tended to be reduced. In study 2, Low heifers tended to have elevated plasma cobalt concentrations and reduced uterine iron concentrations. When an embryo was recovered uterine magnesium and sulfur concentrations were reduced, and uterine calcium and manganese concentrations tended to be impacted. In summary, the embryo appears to use sulfur, calcium, and magnesium for development, and energy restrictions after AI can negatively influence the uterine histotroph, potentially impacting embryo growth.