Evaluation of soybean hulls (SBH) as an energy source to improve reproductive performance of replacement beef heifers during the early spring breeding season

Why this research is being done

Heat and humidity during the summer months in the midwestern United States, coupled with challenges created from grazing endophyte-infected fescue (vasoconstriction, elevated body temperature and decreased prolactin) have detrimental effects on reproductive efficiency across much of the U.S. Corn Belt Additionally, heifers are often bred 21-30 days before the cow herd to compensate for a longer post-partum anestrous interval following first calving, and to facilitate calving in synchrony with the mature cow herd during their second and subsequent calving seasons. To mitigate the summer heat stress, many spring-calving cow herds have adopted the development of heifers in a winter drylot to approximately 60% of their mature weight, synchronizing estrus, using fixed-time artificial insemination, and then turning heifers out onto lush, early spring pasture. Early season, lush pasture is characterized as having high water (>85%, which limits dry matter intake) and high soluble nitrogen content, but deficient in energy. Collectively, these factors result in rapid weight loss, which often exceeds 3.0 lb/d, that negatively impacts heifer reproduction. Previous research has shown that weight loss just prior to breeding can cause heifers to stop cycling, and during early pregnancy (d 0 to d 16) can cause early embryo mortality. Our previous collaborative research at Purdue, conducted in drylot with total mixed rations, has shown that continued gain immediately following breeding (vs. either maintenance or weight loss), can significantly reduce these reproductive failures.

Soybean hulls (SBH) are a starch-free, highly digestible fiber energy supplement for cattle consuming a high forage diet that doesn't negatively affect forage digestibility. Development of the SmartFeed™ system (C-Lock, Inc), with on-board computer system, allows individual animal supplementation of predetermined amounts of supplement to precisely measure animal performance.

Results

When replacement beef heifers are developed in drylot (gaining 1.25-1.75 pound/day) to reach 60-65% of their mature weight by start of the breeding season, and then turned out to lush spring pasture when breeding begins, they can crash on energy. Feeding a non-starch, but highly digestible fiber supplement such as soybean hulls during the breeding season appears to have a positive effect on first-service conception and season-long pregnancy rates. Further studies are needed to confirm these results.

Conclusion

While FTAI conception and season-long pregnancy rates were not statistically different (P < 0.05) when SBH was supplemented in the current study, the limited number of heifers on study is likely the reason and the positive effect on conception rate is likely real. A repeat of this study is warranted to increase heifer numbers and confirm reproductive performance. Additionally, follow-up studies designed to evaluate length of supplementation period (45 days used in current study) to something more reasonable, such as 14 or 21 days.

Contact Information

Griffin Nicholls, Ron Lemenager, Nick Minton and Bethany Funnell
rpl@purdue.edu 
765-427-5972