Heifer development using stockpiled, dormant native forages delays gain without altering reproductive performance

Abstract Text:

Winter grazing utilizing stockpiled forages is an economical alternative to feeding harvested feedstuffs during heifer development. However, development on stockpiled forages may have a negative impact on productivity due to restricted growth during a key physiological period. Therefore, our objective was to determine growth rate, nutritional status and reproductive performance of yearling heifers grazing differing stockpiled forages.  Spring-born, crossbred heifers (n = 155) were stratified by BW at weaning to 1 of 3 stockpiled forage types: (1) endophyte-infected tall fescue (TF; 7.51% CP and 65.82% NDF, DM basis) (2) big bluestem and indiangrass combination (BI; 4.54% CP and 69.74% NDF, DM basis), or (3) switchgrass (SG; 4.23% CP and 75.77% NDF, DM basis).  Each year, grazing began in January and was terminated in April at the onset of a 60-d breeding season. Heifers were fed twice per week at a rate of 0.18 kg·heifer^-1·d^-1 of CP and were managed together before and after the grazing period.  Heifer BW was obtained monthly from initiation of grazing until breeding and again at overall pregnancy diagnosis in September.  Blood samples were collected 10 d prior and the day of timed-AI for serum metabolite analysis. Initial BW was not different (P = 0.72) among forage types.  However, ADG from January to March was lower (P < 0.01) in heifers grazing BI and SG pastures.  From March to April, ADG was not different (P = 0.56) among forage types.  However, from April until September, heifers grazing both BI and SG pastures compensated and outgained (P < 0.01) heifers developed on stockpiled tall fescue pastures. Overall, heifers developed on TF pastures did have greater (P < 0.01) BW at final pregnancy detection. Circulating serum glucose concentration did not differ (P = 0.19) irrespective of forage type. Forage type x year interactions (P < 0.05) were exhibited for circulating NEFA and serum urea N concentrations. Serum β-hydroxybutyrate concentrations did not differ (P = 0.15) among forage types. Although BI and SG heifers exhibited restricted growth early in development, timed-AI pregnancy rates were 66, 51, and 59% for TF, BI, and SG heifers (P = 0.40), respectively.  In addition, final pregnancy rates were 93, 92, and 87% for TF, BI, and SG heifers (P = 0.56), respectively.  These results indicate that stockpiling native warm-season forages for winter grazing during heifer development delayed gain without reducing reproductive competence.  

Keywords:  beef heifers, heifer development, stockpiled forages