Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science

First Advisor

R. J. Pruitt


A 3 yr. 22 factorial study was conducted with 133 mature Simmental X Angus cows calving for 81 d beginning in mid-March to determine minimum cow body condition required for adequate reproductive performance of range beef cows. Two levels of early (early December to mid-February) and late (from calving date to early May) winter nutrition were imposed. Nutritional treatments produced total winter (December-May) weight changes ranging from -188 to -5 kg and wide cow body condition differences at calving and breeding. The breeding season lasted 60-70 d beginning June 5 each yr. Visual condition scores (CS 1-9, l=thin), weight to height ratios (WHR, kg/cm), and backfat measurements (mm) were determined monthly from December to July. Blood samples were collected 7-10 d apart in May, June and July for progesterone and in March and May for serum d-B-hydroxybutyrate (BHB) and urea nitrogen (SUN) determinations. Percentage of cows on low early and late winter nutrition that were cycling at the start of the breeding season was depressed (P< .05} and calving interval for those cows was extended (P< .05). Calf weight gains (calving to May) and 205 d adjusted weights were higher (P< .05) as level of winter nutrition increased during the last 2 yr. of the study. Cows on early winter low energy treatment had higher (P< .05) SUN levels in March. Within late winter treatments BHB levels were higher (P<.05) and SUN levels were lower (P< .05) for those cows on high vs low early winter nutrition. Pregnancy rates were similar and ≥90% for all treatments. As cow body condition increased in March and May percentage of cows cycling in June increased (P< .05). As level of CS in June increased thin cows (CS≤4) in March had a more positive (P< .05) response in percentage of cows cycling in June than cows in average or good condition (CS=5 and ≥6 in March, respectively). For cows >60 d postpartum at the start of the breeding season calving interval was decreased (P<.05) as June WHR increased from 2.6 to 3·.3 kg/cm. For cows ≤60 d postpartum calving interval was decreased (P<.05) as March, May and June WHR increased. Interactions between cow body condition in March and May or June did not affect calving interval.

Library of Congress Subject Headings

beef cow

bosy condition



Animal Sciences



Number of Pages



South Dakota State University