Effects of supplementation on intake and growth of nursing calves grazing native range in southeastern North Dakota T. W. Loy 1 , G. P. Lardy 2 , M. L. Bauer, W. D. Slanger, and J. S. Caton Department of Animal and Range Sciences, North Dakota State University, Fargo 58105-5727 ABSTRACT: A 2-yr study was conducted to deter- mine the first limiting nutrient for gain in nursing calves grazing native range in southeastern North Da- kota. Thirty-two calves (20 steers, 12 heifers) in Trial 1 (169 ± 5 kg initial BW) and 31 (16 steers, 15 heifers) in Trial 2 (214 ± 5 kg initial BW) grazed common pastures. Calves were blocked by sex and stratified by weight. Calves were stratified by age of dam in Trial 1 and by pretrial milk intake (MI) in Trial 2. Treatments were nonsupplemented control (CON); energy supplement (ENERGY; 100% soyhulls); degradable intake protein supplement (DIP; 68% soyhulls, 32% SBM); and de- gradable with undegradable intake protein supplement (DIP+UIP; 80% sulfite-liquor treated SBM, 16% feather meal, 4% blood meal). In Trial 2, 5% molasses was added to all supplements with the ratios of other ingre- dients held constant. Supplements were formulated to be similar in NE. The DIP and DIP+UIP supplements supplied equal amounts of degradable protein. Supple- mented calves were fed individually, with similar sup- plement DMI. Weight and MI were measured in July, August, and September. Forage intake (FI) was mea- Key Words: Calves, Growth, Intake, Nursing, Protein, Supplements 2002 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2002. 80:2717–2725 Introduction Relative to most classes of livestock, the nutritional requirements of nursing calves have not been well defined. Research that has been conducted has focused on milk consumption and its correlation to weaning weight (Neville, 1962; Clutter and Nielsen, 1987) and its interaction with forage intake (FI) (Boggs et al., 1980; Ansotegui et al., 1991); diet selectivity and FI of suckling calves (Boggs et al., 1980; Grings et al., 1995); and ruminal parameters (Ansotegui, 1986; 1 Current address: University of Nebraska-Lincoln, Department of Animal Science, C220 Animal Science, Lincoln, NE 68583. 2 Correspondence: 177 Hultz Hall (phone: 701-231-7660; fax: 701- 231-7590; E-mail: glardy@ndsuext.nodak.edu). Received August 21, 2001. Accepted May 10, 2002. 2717 sured in July, August, and September of Trial 1 and July and August of Trial 2. Gain data were analyzed as a randomized complete block and MI and FI as a split-plot in time. Orthogonal contrasts were used to separate means and included CON vs supplemented, ENERGY vs protein, and DIP vs DIP+UIP. No trial effect or trial × treatment interactions (minimum P- value = 0.30) were detected for ADG. Supplemented calves gained faster than CON (P = 0.06). No other contrast differences were observed (minimum P-value = 0.50). Treatment did not affect FI (P ≥ 0.55). Forage intake was lower (P < 0.001) in Trial 1 than in Trial 2. A linear increase (P = 0.0001) in FI (kg OM/d and percentage BW) occurred over time. Calves in Trial 2 consumed more (P = 0.004) fluid milk than calves in Trial 1, though no difference (P = 0.28) was observed relative to BW. No treatment or period differences were detected for fluid MI (minimum P-value = 0.23). Rela- tive to BW, MI declined linearly (P = 0.0001) with suc- cessive periods. Energy may be limiting weight gain of nursing calves grazing native range in southeastern North Dakota. Cremin et al., 1991). The first limiting nutrient of nursing calves has not been established. Energy and protein supplementations are used to maintain a targeted production level or to minimize weight losses of grazing livestock (Clanton, 1982; Ca- ton and Dhuyvetter, 1997). Gross income of many cow- calf production systems is highly dependent on calf weaning weights (Martin et al., 1981). Providing creep feed to nursing calves has been used to increase pre- weaning weight gain (Scarth et al., 1968; Stricker et al., 1979; Prichard et al., 1989). To improve supple- ment efficiency, limiting creep intake (Lusby and Wet- temann 1986; Cremin et al., 1991; Faulkner et al., 1994) and increasing protein concentration (Cremin et al., 1991; Hollingsworth-Jenkins, 1994; Lardy et al., 2001) have been investigated. An understanding of what is first limiting weight gain of nursing calves may help in the formulation of more efficient supplementation programs. Faulkner et