ABSTRACT
The objective of this study was to determine the effect of stockpiled forage type and protein supplementation on VFA production, serum metabolites, and BW in yearling beef heifers. Over 2 yr, spring-born, Angus crossbred yearling beef heifers ( = 42; 305 ± 2.9 kg initial BW) were randomly assigned to 1 of 3 forage pasture types: 1) endophyte-infected tall fescue [TF; (Schreb.) Dumort], 2) a big bluestem ( Vitman) and indiangrass ( L.) combination (BI), or 3) switchgrass (SG; L.). Each pasture was then randomly assigned to receive either 1 of 2 isonitrogenous CP treatments: 1) 0.68 kg·heifer·d of dried distiller's grains with solubles (DDGS; 28% CP and 88% TDN) or 2) 0.22 kg·heifer·d of blood meal and fish meal (BF; 72.5% CP and 69.5% TDN), resulting in a 3 × 2 factorial arrangement of treatments. Treatments were initiated in January and terminated in April in both years of the study. Body weights and blood samples were collected approximately every 28 d from initiation of grazing until the end of the trial. Heifer BW change from January to February and overall BW change were greater ( < 0.01) for TF heifers. However, BW change from March to April was not different ( = 0.84) among forage types. Supplement type did not influence ( ≥ 0.13) BW or BW change from January to February and from January to April; however, heifers fed DDGS had greater ( = 0.03) BW gain from March to April. Heifer BW change from February to March exhibited ( < 0.05) a forage type × supplement interaction, with BF-fed heifers gaining more BW on BI pastures than DDGS-fed heifers. Serum glucose concentrations, ruminal acetate, and the acetate:propionate ratio were greater ( ≤ 0.04) for SG heifers. However, circulating serum NEFA and urea N (SUN) concentrations were not different ( ≥ 0.85) among forage types. Serum glucose and NEFA concentrations were not influenced ( ≥ 0.61) by supplement type. Circulating SUN concentrations were greater ( < 0.01) in BF-supplemented heifers. Ruminal acetate tended to be greater ( = 0.09) and butyrate concentrations were greater ( < 0.01) for BF-supplemented heifers. The acetate:propionate ratio was not influenced ( = 0.15) by supplement type. These results suggest that a compensatory gain period prior to breeding would be needed for these native warm-season species to be a viable opportunity for growing and developing replacement heifers in the southeastern United States.
