J. Anim. Sci. 2004. 82:3560-3566
© 2004 American Society of Animal Science
Effect of fiber-based creep feed on intake, digestion, ruminal fermentation, and microbial efficiency in nursing calves1
S. A. Soto-Navarro,
M. H. Knight2,
G. P. Lardy,
M. L. Bauer and
J. S. Caton3
Department of Animal and Range Sciences, North Dakota State University, Fargo 58105
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Abstract
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Six Angus crossbred cow-calf pairs (653 ± 35 kg and 157 ± 10 kg initial BW for cows and calves, respectively) were used to evaluate the influence of a fiber-based creep feed on intake, ruminal fermentation, digestion characteristics, and microbial efficiency in nursing beef calves. Cow-calf pairs were stratified by calf age and assigned randomly to one of two treatments: control (no supplement) or supplemented. Supplemented calves received 0.9 kg of a 49% soy hulls, 44% wheat middlings, 6% molasses, and 1% limestone supplement (DM basis) daily. All calves were cannulated in the rumen and duodenum and given ad libitum access to chopped brome hay (Bromus inermus L; 7.43% CP, 40.96% ADF, and 63.99% NDF; DM basis). Supplementation was initiated on May 1 (88 ± 10.3 d calf age). Three sampling periods were conducted throughout the study (June 14 to 25, July 5 to 16, and August 9 to 20). Supplement and forage were offered at 0800 daily. Total, hay, and milk OM intakes of nursing calves were not affected by supplementation (2,014 vs. 2,328 ± 288.8, 1,486 vs. 1,029 ± 3,06.9, and 528 vs. 575 ± 87.0 g/d, respectively). Milk OM intake was less (P < 0.09) in August than in June and July (635, 691, and 345 ± 110.6 g/d for June, July, and August, respectively). A supplementation x month interaction occurred (P < 0.10) for total-tract OM digestion. Supplementation did not affect (P > 0.40) total-tract OM digestibility during June and August; however, during July, total-tract OM digestibility was lower (P = 0.03) for the control calves. Ruminal ammonia concentration, total VFA, and butyrate molar proportion increased (P < 0.05), whereas acetate proportion decreased (P = 0.01) in supplemented calves. Microbial efficiency was not influenced by supplementation (11.8 vs. 12.0 g/kg of OM truly fermented for control and supplemented calves, respectively). These data indicate that fiber-based supplements can be used as creep feed without negative effects on OM intake, total-tract OM digestibility, and ruminal fermentation characteristics in nursing beef calves.
Key Words: Digestibility • Forage • Intake • Nursing Calves • Ruminal Fermentation • Supplement
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Introduction
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Gross income of many cow-calf production systems is highly dependent on calf weaning weights (Martin et al., 1981
). Providing supplements to nursing calves has been used to increase preweaning weight gains (Tarr et al., 1994; Loy et al., 2002). Supplementation of nursing beef calves is commonly referred to as creep feeding, and traditionally consists of allowing calves access to grain- or grain by-product-based mixes.
Feeding grain-based creep feed decreases forage intake and fiber digestibility (Cremin et al., 1991; Tarr et al., 1994). Other studies have reported no negative effects on forage intake with a limited amount of creep feed based on corn or soyhulls (Faulkner et al., 1994; Loy et al., 2002). Recently, Gelvin et al. (2004) reported that a field pea creep feed increased total intake and decreased ruminal pH. Creep feeds based on highly digestible fiber would not be expected to have negative effects on ruminal fermentation. Lardy et al. (2001) reported that nursing calves responded to undegraded intake protein supplementation, whereas Loy et al. (2002) indicated that energy was the first-limiting nutrient to nursing calves grazing native range. However, because direct measurements of intestinal nutrient flow in nursing calves are not currently available in the literature, it is difficult to evaluate animal responses and to assess first-limiting nutrients. We hypothesized that digestible fiber-based creep feed will increase digestible OM intake, with little or no adverse effects on ruminal fermentation and digestive characteristics in nursing beef calves. In addition, we hypothesized that fiber-based creep feeds increase microbial protein flow and metabolizable protein supply. Therefore, the objectives of this study were to evaluate the influence of a fiber-based supplement on intake, ruminal fermentation, digestion characteristics, and microbial efficiency in nursing beef calves.
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Materials and Methods
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Animals and Diets
All surgical and animal care procedures throughout the study followed protocols approved by the North Dakota State University Institutional Animal Care and Use Committee guidelines. Six Angus crossbred cow-calf pairs (653 ± 35 and 157 ± 10 kg initial BW for cows and calves, respectively) were use to evaluate the influence of a fiber-based supplement on intake, ruminal fermentation, digestion characteristics, and microbial efficiency in nursing beef calves. At approximately 100 d of age, calves were fitted with ruminal and duodenal cannulas using procedures similar to those of Streeter et al. (1990, 1991). Cow-calf pairs were stratified by calf age and assigned randomly to one of two treatments: a control (unsupplemented) and supplemented (0.9 kg/d); the supplement composition is shown in Table 1. The supplement was pelleted (0.64 cm diameter) and formulated (Loy et al., 2002) to meet or exceed projected degradable intake protein requirements. All calves were given ad libitum access to brome hay (Bro-mus inermus L; 7.4% CP, 41.0% ADF, and 64.0% NDF, DM basis; chopped to pass through a 7.62-cm screen). Supplementation was initiated on May 1 (88 ± 10.3 d calf age). Cow-calf pairs were housed individually in 4 m x 5 m pens adapted with a restricted creep feeding area to feed the calves, and Calan gates to individually feed the cows. Calves in both treatments were fed individually (hay for control calves and hay and supplement for the treatment calves) at 0800 daily. Refusals were collected and weighed following each feeding. Because of problems related to intestinal cannulation, one calf (supplemented treatment group) was removed from the study.
Milk Intake
Milk intake was measured at the end of each collection period using a 12-h weigh-suckle-weigh technique according to the methods described by Boggs et al. (1980). Briefly, the evening before measurement, calves were separated from their dams for 3 h, allowed to nurse, and then separated for the remainder of the night. The following morning (12 h later), all calves were weighed. Nursing times were recorded so 24-h milk intake could be calculated. Calves were then allowed to nurse the appropriate dams and weighed immediately once suckling had ceased. Milk intake was calculated as the difference between the two weights.
Sampling Protocol
Data collection periods were 12 d long and occurred June 14 to 25, July 5 to 16, and August 9 to 20. Chromic oxide was used as an indigestible flow marker. Eight grams of Cr2O3 was weighed into gelatin capsules and dosed through the rumen at 0800 and 2000 daily. Dosing began on d 1 and continued throughout the collection period. During collections, fecal output was collected into fecal bags from d 6 to 10. Fecal bags were emptied, and the feces were weighed twice daily at 12-h intervals. A 10% (wet basis) subsample of feces was collected from each calf at each collection time. Duodenal samples were taken four times daily during the collection period from all calves as follows: d 6, 0800, 1400, and 2000; d 7, 0200, 0930, 1530, and 2130; d 8, 0330, 1100, 1700, and 2300; d 9, 0500, 0630, 1230, 1830; and 0030 on d 10. Individual duodenal samples consisted of approximately 200 mL of duodenal chyme. Duodenal and fecal samples from each calf and within each collection period were composited for analysis. On d 11 of the collection period, calves were dosed intraruminally with 200 mL of Co-EDTA 2 h before the morning feeding to determine fluid dilution rate. The Co-EDTA was prepared as described by Uden et al. (1980). Ruminal fluid samples were taken via the ruminal cannula at –2, 0, 2, 4, 6, 8, 10, 12, and 24 h after feeding using a suction strainer. Ruminal pH was recorded and a 4-mL sample of fluid was retained, and 1 mL of 25% HPO3 was added to the fluid. Samples were frozen (–20°C) for later analysis of NH3-N and VFA. In addition, a 10-mL sample of ruminal fluid was retained and frozen (–20°C) for later analysis of Co. On d 12 of the collection period a 4-kg sample of ruminal contents was taken and 2 L of formaline/saline solution (3.7% formeldahyde/0.9% NaCl) were added for isolation of bacterial cells, which were later analyzed for DM, ash, N, and purines (Zinn and Owens, 1986).
Laboratory Analyses
Samples were stored frozen (–20°C) until analysis. Hay, dietary ort, and fecal samples were dried at 50°C in a forced-air oven for 48 h. Dried samples were ground with a Wiley mill (2-mm screen; Arthur H. Thomas, Philadelphia, PA). Duodenal samples were lyophilized (Virtis Genesis 25LL; The Virtis Co., Inc., Gardiner, NY) and ground with a coffee grinder (KSM2 Braun, The Gillette Co., Boston, MA). Samples were subjected to all or part of the following analysis: DM (oven drying at 105°C until no further weight loss, AOAC, 1997); ash, Kjeldahl N, ammonia N (AOAC, 1997); ADF and NDF (Robertson and Van Soest, 1991); purines (Zinn and Owens, 1986); VFA concentration in ruminal fluid (Goetsch and Galyean, 1983); and chromic oxide (Fenton and Fenton, 1979).
Calculations
The amount of microbial OM and N (MN) leaving the abomasum was calculated using purines as a microbial marker (Zinn and Owens, 1986). Assuming that all milk bypassed the rumen, OM fermented in the rumen (OMF) was considered equal to OM intake minus the difference between the amount of total OM reaching the duodenum and the sum of microbial OM reaching the duodenum and milk OM. Feed N escape to the small intestine was considered equal to total N leaving the abomasum minus MN plus milk N and would therefore include any endogenous and ammonia N contribution. Dilution rate for Co was calculated by regressing the natural log of marker concentration on sampling time.
Statistical Analyses
Data were analyzed as a repeated measures design using Mixed procedures of SAS (SAS Inst., Inc., Cary, NC). The model included terms for calf within treatment, month, and the interaction treatment x month. Measures were repeated across months, and an unstructured covariance structure was specified. When significant (P < 0.10) F-statistics were noted, means were separated using the method of least significant difference. Tendencies are discussed when 0.10 < P < 0.15.
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Results and Discussion
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Organic Matter Intake
Effects of supplementation on OM intake and digestion in nursing beef calves are shown in Table 2. Main effects of treatment and month are presented in the table, whereas means of simple effects for the variables that had interactions are shown in the text. Total, hay, or milk OM intakes by nursing calves were not affected (P > 0.32) by supplementation. Others have reported substitution effects of supplementation for nursing calves, with decreased forage intake as supplement intake increased (Cremin et al., 1991; Tarr et al., 1994). Both of these previous studies used supplements that were based on corn. Because the supplement used in the present study was based on digestible fiber sources and low in starch, negative effects on forage intake were not expected (Caton and Dhuyvetter, 1997). Energy supplementation of forage-fed cattle often decreases forage intake (Lake et al., 1974; Chase and Hibberd, 1987). Soluble carbohydrates, such as starch or sugar, may impede cellulose digestion due to factors such as lowered pH, competition between cellulolytic and noncellulolytic bacteria for essential nutrients other than energy, or use of alternative energy sources by certain cellulolytic bacteria (Bryant, 1973). These effects seem to be overcome when the degraded intake protein requirement is met (Olson et al., 1999). Total OM intake was not affected by supplementation (P = 0.57). Others have reported greater total OM intake for supplemented nursing calves (Faulkner et al., 1994; Loy et al., 2002; and Gelvin et al., 2004).
Milk OM intake was lower (P < 0.09) in August than in June and July. When milk intake was measured, calves were approximately 125, 149, and 182 d old for the June, July, and August collections, respectively. The decrease in milk intake is likely because cows were more advanced in lactation at the August collection period. Clutter and Nielsen (1987) reported that low-, medium-, and high-milk-producing beef cows demonstrated peak lactation between d 50 and 60 following parturition, and then declined throughout the remainder of lactation. Previous research has reported that milk intake (kg/d) was not affected by advancing season, but that it decreased linearly when expressed as grams per kilogram of BW (Lardy et al., 2001; Loy et al., 2002; Gelvin et al., 2004).
Total and microbial OM flows to the duodenum were not affected (P > 0.40) by either supplementation or period. Because milk was assumed to bypass the rumen, milk OM flowing to duodenum was similar to milk OM intake and was not affected (P = 0.70) by supplementation of nursing calves, but decreased (P = 0.09) during the August collection period. Apparent feed OM flowing to the small intestine was lower (P = 0.02) for the July collection than for the June and August collections. Biological reasons for the lower apparent feed OM flowing to duodenum during July are unclear. Perhaps by July, ruminal development and hence OM fermentation was increased, which resulted in lower duodenal OM flow. Increasing apparent feed OM flow at the duodenum during August likely reflected numerically greater forage intake and lower ruminal OM digestion. A supplementation x month interaction occurred (P < 0.07) for fecal OM flow. Fecal OM output of supplemented calves was not affected (P > 0.38) by month of supplementation (720, 587, and 716 ± 160.2 g/d for June, July, and August, respectively). However, fecal OM flow of control calves increased (P = 0.01) during the August collection compared with June and July (520, 737, and 757 ± 176.7 g/d for June, July, and August, respectively). Apparent ruminal, true ruminal, and postruminal OM digestibilities were not affected (P > 0.38) by supplementation of nursing calves; however, true ruminal OM digestibility tended to be greater (P = 0.11) during the July collection, which coincided with the lower apparent feed OM flow to the small intestine. In addition, postruminal OM digestibility was affected (P = 0.09) by period, being greater for the June collection than for the July and August collections. Most likely, the June postruminal OM digestibility was greater because of a compensation for the lower true ruminal digestibility observed during the June compared with July collection. Supplemented calves had greater (P = 0.09) total-tract OM digestibility than controls. A supplementation x month interaction occurred (P = 0.09) for total-tract OM digestion. Supplementation did not affect (P > 0.39) total-tract OM digestibility during June and August (72.5 vs. 73.4 ± 0.67% and 63.8 vs. 68.7 ± 5.31% for control and supplemented calves during June and August, respectively). However, for the July measurements, total-tract OM digestibility was lower (P = 0.03) for the control calves (57.4 vs. 74.4 ± 3.31% for control and supplemented calves, respectively). The greater digestibility of the supplement compared with that of the hay fed most likely was the reason for the greater total tract digestibility observed for the supplemented calves during the July collection. It seems that the ruminal digestibility of nursing calves has high variability, which likely reflects adaptation or transition of milk to solid diets, ruminal development, and/ or microbial adaptation to solid diets. Supplementation of nursing calves with highly digestible fiber seems to improve the conditions for such transition by preventing the decrease in digestibility. Another possible explanation for the decrease in digestibility might be a decrease in chewing activity by unsupplemented calves as they get older. If hay is chewed less, larger particles are exposed to the digestive tract, and a decrease in digestibility is expected. It has been reported with sheep that younger animals chew roughage to a greater degree than older animals (Egan and Doyle, 1982; Weston et al., 1989). Our results for the months of June and July might be explained by this theory; however, those for August would not. Digestibility of ADF and NDF were not affected by supplementation (P > 0.17; data not shown). Total-tract NDF and ADF digestibilities averaged 55.8 ± 0.50 and 46.3 ± 1.03 across treatments, respectively.
Nitrogen Digestion and Microbial Efficiency
Effects of energy supplementation on N digestion in nursing beef calves are presented in Table 3. Main effects of treatment and month are presented in the table, whereas means of simple effects for the variables that had interactions are shown in the text. Total N intake tended (P = 0.11) to increase with supplementation. Milk N followed the same patterns as milk OM. A supplementation x month interaction occurred (P < 0.03) for fecal N flow. Fecal N flow of supplemented calves was not affected (P > 0.19) by month of supplementation (16.2, 14.4, and 18.5 ± 3.5 g/d for June, July, and August, respectively). However, fecal N flow of control calves increased (P < 0.06) for the July and August collections compared with June (10.0, 16.0, and 16.4 ± 3.08 g/d for June, July, and August, respectively). Postruminal N digestibility decreased (P = 0.08) with energy supplementation. The lower postruminal N digestibility by supplemented calves seems to have resulted from a tendency toward greater N intake observed for the supplemented group compared with controls because N disappearing postruminally was similar between treatments. Total-tract N digestibility was not affected (P = 0.58) by treatment, but it was lower (P = 0.01) during August than that of June and July. Apparently, younger calves that depend more on milk have greater N digestibility than older calves that consume greater proportions of forage. Microbial efficiency was not affected (P = 0.86) by treatment. Microbial efficiency values were similar to those of steers after weaning (Caton et al., 1994); however, the current report is one of the first in the literature to provide microbial efficiency values for nursing calves.
Ruminal Fermentation Characteristics
The effects of energy supplementation on ruminal fermentation characteristics are shown in Table 4. No supplement treatment x sampling period interactions were observed; therefore, main effects of treatment and month are presented. Supplementation tended (P = 0.15) to decrease ruminal pH (6.6 vs. 6.4 for control and supplemented calves, respectively). Others have observed decreased ruminal pH with creep feed based on corn or corn gluten feed (Cremin et al., 1991), corn and corncobs (Tarr et al., 1994), or field peas (Gelvin et al., 2004). The decrease in ruminal pH reported by these studies is likely a result of dietary additions of fermentable carbohydrates, which could potentially decrease forage digestibility (Caton and Dhuyvetter, 1997). In our study, ruminal pH was not affected by supplementation, most likely because the supplement was based on soybean hulls and wheat middlings, which are relatively low in starch and high in potentially fermented fiber components. Ruminal ammonia concentration increased (P = 0.02) in the supplemented calves compared with controls. Reasons for greater ruminal ammonia concentrations seem to be the numerically greater N intake observed for the supplemented calves than for the control group. Ruminal ammonia concentrations observed were greater than 3.57 mM, which has been suggested as necessary for optimal fermentation and growth (Miller, 1973; Satter and Slyter, 1974). In addition, the ruminal ammonia concentration was lower (P = 0.08) during August than in June and July, which coincided with numerically lower N intake during August compared with June and July.
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Table 4. Effect of calf supplementation on ruminal pH, ammonia concentration, and VFA molar proportion in nursing beef calves
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Total VFA concentration increased (P = 0.05) with supplementation, which was expected due to the greater potential digestibility of the supplement as compared with the hay (NRC, 1996). Acetate molar proportion decreased (P = 0.01) and butyrate molar proportion increased (P = 0.01) with supplementation. Decreases in acetate likely reflect numerically lower hay intakes and supplementation of a more fermentable nutrient source. Increases in butyrate may be explained by fermentation of AA originating from the supplements. Other work (Caton et al., 1988) with protein supplementation of low-quality forages has shown increased ruminal butyrate proportions with supplementation.
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Implications
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These data indicate that potentially digested fiber sources, such as soybean hulls and wheat middlings, can successfully be used as creep feed ingredients. In the nursing beef calves used in this study, fiber-based supplements increased total-tract organic digestibility and ruminal fermentation, and had no effect on intake and microbial efficiency.
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Footnotes
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1 This research partially supported by Regional Research Funds NC-189. Gratitude is expressed to the employees of Nutrition Research Laboratory for analytical assistance. 
2 Current address: Food and Livestock Planning, Inc., 1600 Genessee Ste. 533, Kansas City, MO 64102.
3 Correspondence: 185 Hultz Hall (phone: 701-231-7653; fax: 701-231-7590; e-mail: Joel.Caton{at}ndsu.nodak.edu).
Received for publication March 22, 2004.
Accepted for publication September 13, 2004.
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Abstract
Introduction
