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ANIMAL PRODUCTION |
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
Abstract
Objectives of this research were to compare animal performance with or without supplementation, compare effectiveness of three intake limiters, and to examine seasonal changes in nutritive value of native range in south-central North Dakota. Treatments included 1) control (CONT; no supplement); 2) hand-fed (HF) supplement, with no chemical limiter; 3) 16% salt (NACL); 4) 5.25% ammonium chloride and ammonium sulfate (AS); and 5) 7% calcium hydroxide (CAOH). Supplements were based on wheat middlings, barley malt sprouts, and soybean hulls and were formulated to provide 40% of the CP intake and 32% of the NEm intake of 350-kg steers. Trials 1 and 2 each used 70 yearling steers (370.8 ± 0.04 and 327.9 ± 0.76 kg initial BW for Trials 1 and 2, respectively). In each year, four 28-d periods from the latter half of June through mid-October were used. Steers were stratified by weight and allotted randomly to treatments in 1 of 10 16-ha pastures (two pastures per treatment for each trial). In Trial 1, diet sampling began in the first 28-d period, but supplementation did not begin until the second 28-d period. In Trial 2, supplementation and diet collection began in the first 28-d period. Cation-anion differences (DCAD; Na + K - Cl - S) for NACL, AS, CAOH, and HF supplements were 151, -735, 160, and 166 mEq/kg, respectively. In Trial 1, no treatment, period, or treatment x period effects for supplement intake were detected (P 
0.29). In Trial 2, a treatment x period interaction for supplement intake occurred (P = 0.005) because HF steers were offered a constant amount of supplement daily, whereas steers fed AS, CAOH, and NACL were allowed to consume ad libitum quantities of supplement. Average daily gain in Trial 1 was not affected (P = 0.21) by supplementation. In Trial 2, NACL, AS, and HF treatments had higher (P 
0.07) ADG than CONT. In Trial 1, final weights were not affected by supplementation (P = 0.23). In Trial 2, final weights of NACL- and HF-fed steers were greater than for CONT and CAOH steers (P < 0.10). In Trial 2, CONT steer final weights were lower than all supplemented treatments (P < 0.10). For yearling steers grazing native range, use of NACL as a limiter resulted in increased weight gains compared with using either CAOH or AS; however, no limiter that was tested restricted supplement intake as effectively as HF. More research is necessary to determine the optimum limiter level and the effect of forage quality on supplement intake.
Key Words: Cattle • Intake • Limiter • Salt • Steers • Supplement
Introduction
Grasslands in the northern Great Plains provide the primary forage for ruminants, particularly cattle, throughout much of the year. However, forage nutritive value begins to decline as early as July (Hirschfeld et al., 1996
), indicating that supplementation may be necessary to maintain production. Supplementation programs need to accurately and effectively provide limiting nutrients for growth, lactation, and/or reproduction in an economical manner (Bowman and Sowell, 1997).
A primary concern when administering self-limiting supplements is ensuring that animal intake is maintained at the desired level to provide supplemental nutrients to meet nutrient requirements (Bowman and Sowell, 1997). Including salt in supplements can effectively limit feed intake (Riggs et al., 1953; Cardon et al., 1951; Beeson et al., 1977). However, some research indicates that salt-limited supplements can result in high intake variation among animals (Bowman and Sowell, 1997).
Salt can also negatively affect forage digestibility when fed at high levels (Moseley and Jones, 1974). Thacker (1959) demonstrated that the inappetence of rabbits and calves consuming a heavily fertilized timothy hay could be corrected by changing the dietary cation-anion difference (DCAD). A low DCAD (Na + K - Cl - S) also limits feed intake in lactating dairy cattle (Block, 1984; Oetzel et al., 1988; Oetzel and Barmore, 1993). Calcium hydroxide has also been used as an intake limiter (U.S. Patent & Trademark Office, 1990), but its practical application requires further investigation. Limited data are available evaluating intake limiters other than sodium chloride. The objectives of this research were to compare animal performance with or without supplementation, evaluate the effectiveness of three intake limiters fed to yearling steers grazing native range, and to examine seasonal changes in nutritive value of native range in south-central North Dakota.
Materials and Methods
Study Location
Research was conducted at North Dakota State University’s Central Grasslands Research Center, located in south-central North Dakota, approximately 14 km northwest of Streeter. The research center is located near the eastern edge of the Missouri Coteau, an area of young morainic hills formed from recent glaciation (Lura, 1985). Climate at the study area is characterized by marked seasonal variations in both temperature and precipitation. With approximately 120 frost-free days, monthly temperature means range from -13.7 in January to 20.0°C in July. The mean annual precipitation of 44.7 cm is seasonal, with over 68% occurring between May and September (NDAWN, 2001).
The study site, for both the intake limiter research and characterization of nutritive quality, was located in the Wheatgrass-Needlegrass vegetation association of the northern Great Plains (Barker and Whitman, 1988). Sedivec (1989) characterized the range sites as 48% overflow and 46% silty, with the remaining land either wetland or wet meadow. Lura (1985) characterized the graminoid species in these sites as 35% warm- and 65% cool-season species. Communities most prevalent on the site were blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths), needle and thread (Stipa comata Trin. + Rupr.), and sun sedge (Carex heliophila Mack.) communities and western snowberry (Symphoricarpos occidentalis Hook.) and Kentucky bluegrass (Poa pratensis L.) communities (Hirschfeld et al., 1996).
Sampling Periods
Trial 1 was conducted in 1998. In Trial 1, four 28-d sampling periods were conducted from June 22 to July 19 (JUN–JUL), July 20 to August 16 (JUL–AUG), August 17 to September 13 (AUG–SEP), and September 14 to October 11 (SEP–OCT). Diet samples were collected over these four sampling periods. Supplementation began July 20 (JUL–AUG period).
Trial 2 was conducted in 1999. In Trial 2, four 28-d sampling periods were conducted from June 22 to July 19 (JUN–JUL), July 20 to August 16 (JUL–AUG), August 17 to September 13 (AUG–SEP), and September 14 to October 11 (SEP–OCT). Supplementation and diet collection began June 22 (JUN–JUL period).
Supplementation
In Trial 1, 70 yearling steers (370.8 ± 0.04 kg initial BW) were used. In Trial 2, 70 yearling steers (327.9 ± 0.76 kg initial BW) were used. All cattle finished both trials. Before the initiation of each trial, all steers were vaccinated with a four-way viral and a seven-way clostridial vaccine and implanted with 20 mg of estradiol benzoate and 200 mg of progesterone (Synovex-S, Fort Dodge Animal Health, Fort Dodge, IA). Steers were stratified by weight and allotted randomly to one of five treatments. Water was provided from a water tank located in the center of the pastures. The pastures were arranged in a wheel-spoke design. Treatments were allotted randomly to 1 of 10 16-ha pastures (two replications per treatment for each trial) at the beginning of each period to eliminate any confounding effect of pasture on response to supplement. Stocking density was 0.57 ha/animal unit•month, which was similar to Hirschfeld et al. (1996), who used a stocking rate of 0.54 ha/animal unit•month. Initial and final weights were 2-d weights, taken without withholding steers from feed and water. On d 28 of each period, steers were weighed at 0800. Steers were not withheld from water and feed for interim weights.
Treatments were as follows: control (CONT; no supplement); 16% salt (NACL; DM basis); 5.25% anionic salts (ammonium chloride and ammonium sulfate; AS; DM basis); 7% calcium hydroxide (CAOH; DM basis); and hand-fed control, which included no limiter (HF). The HF supplement was fed at 0.50% of initial BW (2.24 kg daily in Trial 1 and 1.6 kg daily in Trial 2; DM basis) in bunks (87.2 cm of trough space per animal) at 0800 daily. Free choice salt blocks were provided in all pastures.
Supplements were based on wheat middlings, barley malt sprouts, and soybean hulls (Table 1). In order to balance for the nonprotein nitrogen supplied by the ammonium salts used in AS, urea was added to the NACL, CAOH, and HF treatments. The CAOH supplement was fed in meal form due to difficulty in achieving suitable pellet quality; all other supplements were pelleted (4.4 mm diameter). Calculated cation-anion differences (Na + K - Cl - S) for NACL, AS, CAOH, and HF supplements were 151, -735, 160, and 166 mEq/kg, respectively. Supplements containing limiters were offered in a self-feeder (43.5 cm of linear trough space per animal) and the cattle consumed the supplements ad libitum. Supplement remaining in feeders was emptied weekly, weighed, subsampled, and discarded. Supplement samples for laboratory analysis were taken weekly when feeders were filled.
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). Grass, forb, and shrubs were clipped within a 0.25-m2 frame in the following range sites in each pasture: shallow, silty, and overflow. Ten quadrats (two locations of five quadrats each) were clipped in each range site in each pasture.
Diet Collections
In Trial 1, 12 ruminally cannulated crossbred yearling beef heifers (400.0 ± 38.7 kg BW) grazed similar range on one 32-ha (0.44 ha/animal unit•month) pasture immediately adjoining the study site to monitor forage nutritive value. In Trial 2, six ruminally cannulated crossbred 2-yr-old beef heifers (533.6 ± 31.3 kg BW) and five ruminally cannulated mature crossbred beef steers (580.5 ± 15.1 kg BW) grazed on the same 32-ha pasture as Trial 1. All pastures used in the study, including the pastures grazed by the cannulated cattle, were previously managed in a 6-mo season-long grazing treatment for 5 yr before the initiation of our research. The plant species composition and range sites in the pasture provided for the cannulated cattle were the same as described previously for the intake limiter study (Lura, 1985).
Ruminal fistulation procedures were conducted in a one-step standing technique similar to those outlined by Streeter et al. (1990). These procedures were approved by the Institutional Animal Care and Use Committee at North Dakota State University. Postoperative care, outlined by Caton et al. (1987), involved i.m. penicillin (BP-48; Pfizer, Inc.; Lee’s Summit, MO) at 17.6 kIU/kg on d 0 and 8.8 kIU/kg on d 2 and 4.
Masticate samples were collected weekly throughout the trial. Cattle were gathered at sunrise, and the rumens were evacuated and rinsed with water. The cattle were allowed to graze freely for 60 to 90 min before ruminal ingesta samples were collected. Ingesta samples were kept separate by animal and a subsample from each animal was frozen (-20°C) immediately.
Laboratory Analysis
Supplement samples and refusals were dried at 50°C for 72 h to determine DM and ground to pass a 2-mm screen. Ash was determined in a muffle furnace at 470°C for 12 h (AOAC, 1990). Crude protein was determined using a Kjeldahl procedure (AOAC, 1990; Kjeltec 1030, Herndon, VA). Samples of ingested forage were lyophilized and ground to pass a 2-mm screen. Ash and CP were determined as previously described (AOAC, 1990). Neutral detergent fiber analysis was conducted using the method of Robertson and Van Soest (1982). Acid detergent fiber was determined using the AOAC (1997) methodology. In vitro OM digestibility (IVOMD) of diet samples was determined using the procedure of Tilley and Terry (1963) with the following modification: 1 g urea/L of McDougall’s artificial saliva (McDougall, 1948) was added. Samples were centrifuged for 15 min at 1,000 x g and the supernatant was discarded before adding HCl and pepsin. Inoculum used for the in vitro procedure was collected from two ruminally cannulated steers fed long-stem grass hay. Clipped forage samples were dried at 50°C for 72 h to determine DM. Clipped forage samples collected in Trial 2 were ground to pass through a 2-mm screen for analysis of Cl (Skoog and West, 1976) and Na, K, and S (Hunt and Shuler, 1989).
Statistical Analysis
Data were analyzed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) using a split-plot design for the JUN-JUL, JUL-AUG, AUG-SEP, and SEP-OCT periods in both years (Cochran and Cox, 1957). Because supplementation in Trial 1 did not begin until the JUL-AUG period, data were not combined across trials, and trials were analyzed separately. The model contained effects for treatment, period, and treatment x period interactions. Pasture was the experimental unit and pasture within treatment served as the main-plot error term for treatment. Period (subplot) and interactions were analyzed using the residual error term. Data analyzed included supplement intake, ADG, final weights, and supplement efficiency (G:F). When a significant (P < 0.10) F-test for treatment was observed, means were separated using the least significant difference method. When significant (P < 0.10), F-test for period was observed, means were compared using linear, quadratic, and cubic contrasts.
Forage nutritive value in Trial 1 was analyzed in a randomized complete design, with period and heifer identification number included in the model. Because both steers and heifers were used to collect diet samples in Trial 2, forage nutritive value was analyzed in a randomized complete block design with sex serving as block and period and animal(sex) also included in the model. Means were compared using linear, quadratic, and cubic contrasts.
Results and Discussion
Climatic Conditions
June through October precipitation at the study site was 36.4 cm and 37.4 cm in Trial 1 and Trial 2, respectively; which was 33 and 37% greater than the long-term (30 yr) average precipitation, respectively (NDAWN, 2001). Average temperatures for the same time periods were 16.4 and 15.1°C, respectively, which were equal to and 1.3°C below the long-term average (30 yr) average temperature, respectively (NDAWN, 2001).
Herbage Availability
Herbage production peaked in late July in both trials (data not shown). This is similar to findings reported by Whitman et al. (1951). Peak herbage production in Trial 1 for grasses, forbs, and shrubs was 2869, 526, and 1180 kg DM/ha, respectively. In Trial 2, peak herbage production for grasses, forbs, and shrubs was 2366, 495, and 909 kg DM/ha, respectively. Dietary cation-anion differences (DCAD) were not evaluated in Trial 1; however, in Trial 2, DCAD averaged 1334, 2404, and 2190 mEq/kg for grasses, forbs, and shrubs, respectively.
Dietary Composition
In Trial 1, crude protein exhibited a cubic response (P = 0.04) with advancing season; however, the magnitude of the changes was small (11.4 to 12.8% CP; Table 2). Neutral detergent fiber responded quadratically (P = 0.09) with advancing season; NDF increased from JUN–JUL through JUL–AUG and then declined through AUG–SEP and SEP–OCT. Acid detergent fiber responded cubically (P = 0.03) with advancing season. Acid detergent fiber increased from JUN–JUL to JUL–AUG and then decreased in AUG–SEP, before increasing again in SEP–OCT. In vitro organic matter digestibility decreased quadratically (P = 0.01) as season progressed. In Trial 2, crude protein exhibited a cubic response (P = 0.01). Crude protein increased from JUN–JUL to JUL–AUG, then decreased in AUG–SEP, and then increased again in SEP–OCT. Neutral detergent fiber and ADF exhibited a quadratic response (P = 0.01 and 0.01, respectively) to advancing season. Neutral detergent fiber increased from JUN–JUL to JUL–AUG and then decreased through SEP–OCT. Acid detergent fiber increased from JUN–JUL through AUG–SEP and then declined. In vitro organic matter digestibility exhibited a quadratic response (P = 0.01) with advancing season; IVOMD decreased from JUN–JUL through AUG–SEP and then increased in SEP–OCT. Cubic and quadratic effects present in both years are likely the result of seasonal precipitation events and resulting late-season growth of cool-season forages. The cubic effects we observed may be not be biologically significant because only four sampling periods were used. Decreasing forage quality with advancing season has been observed with other research conducted on the Great Plains (McCollum et al., 1985; Kirby and Parman, 1986). Crude protein in our studies was similar to that in Hirschfeld et al. (1996); however, NDF, ADF, and IVOMD were lower than those reported by Hirschfeld et al. (1996) on the same study site.
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). However, in Trial 2, a treatment x period interaction was detected for supplement intake expressed either as kilograms DM/d or % BW (P = 0.005 and 0.004, respectively; Table 4). Steers fed CAOH consumed less supplement (P 0.02) than AS fed steers in JUN–JUL and JUL–AUG. Steers fed NACL consumed less supplement (P = 0.01) than AS-limited steers in JUL–AUG. Steers fed NACL, AS, and CAOH consumed more (P 0.02) supplement (kg DM/d) than steers fed HF in AUG–SEP and SEP–OCT, and steers fed AS also had greater intake (P = 0.02) than HF in JUL–AUG. Intake responses expressed as a percentage of BW did not differ dramatically, with the exception that, in JUL–AUG, the CAOH fed steers consumed less supplement (P 0.09) than HF steers (Table 4). It is not surprising that a treatment x period interaction occurred given the design of this study. Supplement intake for HF was held constant, whereas intake of the self-limited treatments increased over time, which caused the interaction to occur.
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). Totusek et al. (1971) and Rush et al. (1972) reported that salt levels between 20 and 29.5% limited protein supplement intake to approximately 1.25 kg DM/d for steers grazing Oklahoma winter range. Additionally, Riggs et al. (1953) demonstrated that when 25% salt was included in free choice cottonseed meal, supplement intake of pregnant beef cows consuming dry winter range was limited to 2.0 kg/d. Therefore, we expected NACL to limit supplement intake by steers to approximately 2.0 kg DM/d. In Trial 1, NACL intakes averaged 2.69 kg DM/d; however, in Trial 2, intake for steers fed NACL ranged from 1.40 to 4.11 kg DM/d. Increases in supplement intake as season progressed, especially in Trial 2, may be due to decreased sensitivity of steers to palatability effects of salt. Beeson et al. (1957) recommended salt inclusion level in supplements be adjusted to compensate for palatability of the basal ration to ensure that the targeted intake is realized.
Intake of AS (kg DM/d and % of BW) was similar to HF and NACL in Trial 1. However, in Trial 2, intake of AS (% of BW) was greater than HF in AUG-SEP and SEP-OCT (Table 4). When expressed in kilograms of DM per day, AS did not limit intake similar to HF in three of the four periods (Table 4). Anionic salts have decreased ration consumption by dairy cows. Oetzel and Barmore (1993) reported an intake reduction of 34.0 and 28.6% when ammonium sulfate and ammonium chloride, respectively, were fed to lactating dairy cows (DCAD = 110.4 and 109.0 mEq/kg, respectively). Differences in effectiveness of anionic salts between trials may be attributed to a higher estimated dietary DCAD level in our trial. In our study, assuming a forage DCAD of 1,500 mEq/kg (10 kg/d estimated forage intake), calculated dietary DCAD was 1,213, 990, 1,247, and 1,302 mEq/kg for NACL, AS, CAOH, and HF, respectively. Therefore, even though AS supplement was -735 mEq/kg, it may not have effectively altered intake of the total diet due to elevated dietary concentrations of Na and K.
Intake of supplements containing calcium hydroxide (kg DM/d and % BW) by steers was similar to research reported by Cooperative Research Farms (U.S. Patent & Trademark Office, 1990). They reported that intake of a supplement containing 7% CAOH fed to steers was not different (P > 0.05) than an 18% salt-limited treatment, which supports results found in this trial (Tables 3 and 4). In Trial 1, CAOH-limited supplement intake was similar to HF. As the season progressed in Trial 2, the effectiveness of CAOH declined. The decreased ability of CAOH to limit intake as the trial progressed may be due to decreased sensitivity of steers to palatability effects of CAOH.
Average Daily Gain
In Trial 1, there were no treatment or treatment x period interactions (P = 0.21 and 0.71, respectively) for ADG. However, a period effect (P = 0.01) was observed. Average daily gain averaged 0.63 kg/d. In Trial 1, ADG exhibited a quadratic decrease (P = 0.02) with advancing period (Table 5). Steers lost weight during the SEP–OCT period in Trial 1, and supplementation did not enhance weight gain regardless of the limiter used. Forage quality measurements do not fully explain the decrease in weight gain as season progressed. In vitro organic matter digestibility did not decrease substantially between AUG–SEP and SEP–OCT, but averaged 49.0%. Crude protein decreased from 12.6 to 11.4% (Table 2) over the same time period.
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0.07) ADG than CONT. Average daily gain for steers fed CAOH was not different (P 0.19) than other treatments, including CONT. The inability of CAOH to increase ADG over CONT in Trial 2 indicates that CAOH possibly had a negative affect on livestock performance. In Trial 2, ADG decreased quadratically (P = 0.04) as season progressed. Average daily gain reached a plateau between JUL–AUG and AUG–SEP and then decreased in SEP–OCT. Regardless of the intake limiter, steers tended to gain slowly during SEP–OCT in Trial 2. Decreases in ADG as season progressed may be partially explained by diet quality data. In vitro organic matter digestibility exhibited a quadratic decrease as the season advanced. In vitro organic matter digestibility decreased from JUN–JUL through AUG–SEP and then increased slightly (51.7 to 52.4%) from AUG–SEP to SEP–OCT. However, these small changes from AUG–SEP to SEP–OCT do not fully explain the decreases in performance, especially when one considers the fact that the CP of diet samples collected during Trial 2 averaged 13.8%.
Our results with HF support results reported by Karn (2000), who fed barley-based supplements (454 g/d) to grazing yearling steers in the northern Great Plains and increased gains 0.13 kg/d for supplemented steers compared to unsupplemented steers.
Final Weight
In Trial 1, no significant effect of treatment on final weights was detected (P = 0.23; Table 6). In Trial 2, final weight for NACL and HF was greater than either CAOH or CONT (P < 0.10). Final weights for steers fed CAOH and AS were also greater than CONT (P < 0.10). Additionally, CONT steer final weights were lower than all supplemented treatments (P < 0.10). These results were similar to other work reporting that supplementation increases weight gain in yearling steers grazing native range. Vadiveloo and Holmes (1979) fed energy and protein supplements to grazing steers. When herbage supply was limiting, energy supplementation increased weight gains, whereas protein supplementation exhibited no benefit. During periods of herbage adequacy, energy or protein provided no benefit in steer weight gains.
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A period effect (P = 0.02) was observed for G:F in Trial 2, but no treatment or treatment x period effects were detected (P = 0.11 and 0.62, respectively). Gain:feed exhibited a cubic response (P = 0.09) as season progressed (Table 7), and AUG-SEP had the lowest G:F. In SEP-OCT, G:F increased, which is difficult to explain as ADG decreased and intake increased across treatments. However, because G:F is expressed as added gain above the CONT, a negative ADG (data not shown) by the CONT treatment actually increased the G:F ratio for supplemented treatments in SEP-OCT, even as supplemented treatments increased intake and decreased ADG. Whereas Moseley and Jones (1974) demonstrated that high levels of salt used to control supplement intake may affect fiber and protein digestion, these differences were not seen in this study, as evidenced by the lack of difference in G:F between HF and NACL. Although the NACL-fed cattle consumed more supplement than HF in two periods, G:F was not different, indicating that if fiber and protein digestion were affected, the additional supplement compensated for these differences. Although NACL did not always limit intake similar to HF, NACL-limited supplements improved livestock performance, as indicated by increased final weights.
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Mid-June to mid-September supplementation increased weight gain in yearling steers consuming native range in the Missouri Coteau. However, supplementation did not consistently improve performance after September 15. Regardless of supplementation, grazing yearling steers from late September through October may result in low weight gains or weight loss. The ability of intake limiters to limit supplement intake was not consistent between years. Self-feeding sodium chloride- or calcium hydroxide-containing supplements often resulted in similar supplement intake compared to hand feeding. However, calcium hydroxide, used as an intake limiter, may result in decreased livestock performance compared with hand-feeding or self-feeding sodium chloride-limited supplements. Anionic salts limited supplement intake less effectively than sodium chloride or calcium hydroxide. Further research is needed to evaluate self-limiting supplements for yearling steers grazing native range.
Footnotes
1 The authors are grateful to Cooperative Research Farms and Harvest States Cooperatives, Sioux Falls, SD, for partially funding this project. 
2 Present address: Eastern Oregon Agric. Res. Center, Oregon State Univ., Burns 97720.
3 Correspondence: 177 Hultz Hall (fax: 701- 231-7590; e-mail: glardy{at}ndsuext.nodak.edu).
Received for publication December 10, 2002. Accepted for publication September 15, 2003.
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