By Christina Mogck
Nutritional stress following artificial insemination (AI) has been reported to have negative effects on conception rates. This decrease in conception rates could be from an increase in embryonic mortality due to nutritional stress following breeding. When considering heifer development strategies, it may be important for a producer to consider nutritional stress from changes in the diet following breeding, and this nutritional stress could be initiated by how you manage heifers between weaning and breeding?
Heifer Development Methods: Drylot vs. Range
Research from Perry et al. looked at two different heifer development methods; drylot and range. All heifers were developed to reach 65% of mature body weight prior to breeding in both development methods. Prior to breeding there was no difference between treatments for puberty status. However, moving drylot developed heifers to pasture immediately following breeding had a significant negative impact on conception rates (around 10%) compared to heifers that were developed on range. Considering that this abrupt change in nutrition may have impacted conception rates, average daily gain (ADG) was recorded on heifers throughout the grazing season following breeding. Within that first week on range, drylot developed heifers had negative ADG (-3.4 lbs/d). After a month out on pasture there was still a tendency for drylot heifers to have lower ADG (-0.5 lbs/d) compared to heifers that had previous grazing experience. This negative ADG can be correlated to drylot heifers having to relearn grazing behaviors.
Impact on Pregnancy
What effect could negative ADG or negative energy balance have on heifer pregnancy success? It is known that estrus cycles and pregnancy initiation are one of the last priorities for energy uses in the body by cattle. Thus, experiencing a negative balance following insemination there was a negative effect on embryo stage, embryo quality, total cells in the embryo and percentage of cells alive in the embryo (Perry et al, 2016). This could result in higher embryonic loss among the drylot developed heifers. Since some drylot developed heifers did conceive to AI, what effect did this nutritional stress have on the calve in utero?
Research Findings
For five years, data was recorded on 105 heifers for longevity and calving date. Heifers were divided into two development system; drylot or range. Culling decisions were kept consistent over those five years. Calving data included birth weight, weaning weight, and ADG. All AI bred calves were bred to a single sire so there was no difference in sire performance among AI calves. Heifers were divided into four groups following pregnancy diagnoses. The groups were divided based on development method either range or drylot and AI bred or bull bred. Longevity among these heifers did not change between drylot and range nor did the heifer calves in utero the treatment year have any change in longevity. Calves sired by AI and born to range heifers had heavier birth weight (81.9 ±1.5 lbs) and heavier weaning weights (456.2 ±10.2 lbs) compared to AI sired calves born to drylot heifers (75.2 ±1.4 lbs and 422.9 ±9.6 lbs, respectively). Both AI calves and bull bred calves born to range heifers had better ADG (1.8 ±0.04 lbs) compared to AI and bull bred calves born to drylot heifers (1.7 ±0.04 lbs) (Mogck, 2017). Since there was no difference in sire among AI bred calves the difference in birth weight, weaning weight and ADG is likely from the nutritional changes in utero post insemination.
The Bottom Line
Overall, developing replacement heifers in drylot following weaning can have an impact on their grazing behavior which can affect their ability to ingest forages efficiently during the following grazing season. This abrupt change in nutrition following breeding has negative effects on pregnancy success, embryo quality, and performance of the calves in utero. Producers should consider heifer development strategies prior to and post insemination to achieve maximum conception rates.