Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science

First Advisor

R. J. Pruitt


beef cow, body condition, reproduction, nutrition


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 (P60 d postpartum at the start of the breeding season calving interval was decreased (P

Library of Congress Subject Headings

Beef cattle -- Reproduction.
Beef cattle -- Weight.



Number of Pages



South Dakota State University