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1 Department of Animal Science, Iowa State University, Ames 50011
2 American Protein Corporation, Ankeny, IA 50021
3 Northeast Iowa Community-Based Dairy Foundation, Calmar, IA 52132
Corresponding author: J. A. Coverdale; e-mail: jcover{at}uga.edu.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Key Words: calf • forage • particle size • rumen development
Abbreviation key: ADG = average daily gain, C = commercial coarse starter, G = ground starter, G/F = gain to feed ratio, H1 = coarse starter with additional 7.5% bromegrass hay of consistent particle size, H2 = coarse starter with additional 15% bromegrass hay of consistent particle size
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The amount of roughage necessary in the diet of young calves is unclear (Klein et al., 1987). Trials investigating the use of forage in starter rations have yielded inconsistent results. Several investigators concluded that forage addition to the diet increases starter intake (Kincaid, 1980; Thomas and Hinks, 1982; Stobo et al., 1985). However, others have seen a negative impact of forage addition on the consumption of starter rations (Hibbs et al., 1956; Whitaker et al., 1957; Leibholz, 1975).
Ration particle size influences the ruminal environment, volatile fatty acid production, and papillae structure and function. Diets that are chopped or ground to fine particle sizes decrease rumen pH and cellulolytic bacteria populations (Beharka et al., 1998). This decrease in pH is caused by a lack of rumination and saliva flow into the rumen in calves and mature cows (Kellaway et al., 1977; Santini et al., 1983). Ruminal papillae of animals receiving small forage particles have increased keratinization (McGavin and Morrill, 1976a). This decrease in active tissue results in decreased VFA absorption (Hinders and Owen, 1965; Nocek et al., 1980; Greenwood et al., 1997b). Papillae begin to branch to compensate for the loss in metabolically active tissue (McGavin and Morrill, 1976b; Greenwood et al., 1997b; Beharka et al., 1998).
Determining the proper level of forage, if any, to include in starter diets for optimal rumen development will benefit the producer greatly by shortening the length of time the calf requires milk replacer and allow early weaning of a mature ruminant calf. There are several advantages of early weaning when compared to the prolonged feeding of milk replacer. Labor is greatly reduced when calves are fed starter rations when compared to feeding milk replacer. Calves that are weaned earlier have fewer digestive problems (Klein et al., 1987). Determining the optimal level of forage necessary to develop the rumen properly will allow producers to wean younger calves that have more mature digestive systems. This should prevent the decline in intake and growth seen immediately after weaning. The objective of these studies was to determine the effect of form of diet and the inclusion of various levels of controlled particle size of hay on rumen development, growth, and health parameters in restricted-fed and ad libitum-fed calves.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Experiment 1
Calves and treatments.
Holstein bull calves (n = 60) obtained from sale barns were utilized. The calves were approximately 2 to 5 d of age at arrival and BW averaged 44.2 ± 5.0 kg. Upon arrival (prior to initiation of the study), calves were randomly assigned to one of 4 treatment groups. On the day of arrival, calves received one dose of a colostrum supplement (APC Lifeline Calf, Inc., Ames, IA). Calves were housed in individual hutches with wood shavings for bedding. Water was offered ad libitum. Eight calves died during the investigation, and 2 more were removed due to failure to consume adequate amounts of starter. Death losses did not differ according to treatment. Calves were vaccinated based on the protocol of the research facility.
Diets consisted of commercial coarse starter (C; Land O’Lakes, Ft. Dodge, IA), a ground starter (G) with grain processed with a hammer mill and intact pellets, coarse starter with 7.5% bromegrass hay of consistent particle size (H1), and coarse starter with 15% grass hay of consistent particle size (H2). All diets were formulated to be isocaloric and isonitrogenous. The pellets in diets H1 and H2 were modified to account for the addition of hay (Table 1
). Bromegrass hay used for the H1 and H2 diets was chopped and sorted by particle size using a Penn State Forage Separator as described by Lammers et al. (1996). Hay particles were approximately 8 to 19 mm in length. Samples of diets were collected weekly and stored (–20°C) prior to analysis by a commercial laboratory (Iowa Testing Laboratory, Eagle Grove, IA) (Table 2).
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Collection of jugular blood samples and BHBA analysis.
Blood samples were obtained approximately 3 h after the a.m. meal. Blood was collected by jugular venipuncture in tubes containing EDTA (K3) as an anticoagulant. After collection, plasma was harvested by centrifugation (3000 x g for 15 min), placed in storage tubes and frozen (–20°C) until further analysis. Samples were then transported to the Iowa State University College of Veterinary Medicine Clinical Pathology Laboratory. Plasma samples were allowed to thaw, and then concentrations of BHBA were determined spectrophotometrically at 340 nm using a commercial reagent kit (Sigma Diagnostics, St. Louis, MO).
Collection of rumen fluid and VFA analysis.
Rumen samples were obtained via a stomach tube approximately 3 to 4 h after the a.m. meal. Fluid was immediately frozen using dry ice and stored (–20°C) until later analysis. Samples were first prepared for VFA analysis by allowing them to thaw at room temperature. The sample tubes were then centrifuged at 3500 x g for 10 min. Samples containing large amounts of particulate matter were strained through 2 layers of cheesecloth. After centrifugation, samples were treated with 25% meta-phosphoric acid at a ratio of 5 parts rumen fluid to 1 part acid. Tubes were then covered, mixed, and allowed to stand for 30 min. Fluid was then centrifuged at 3500 x g for 10 h. The clear supernatant was removed and placed in 15-mL tubes and frozen (–20°C).
Samples were than transported to North Carolina State University for VFA analysis, where the frozen supernatant thawed and centrifuged at 3500 x g for 10 min. A 1-mL aliquot of supernatant was added to 100 µL of internal standard in a gas chromatogram vial. The mixture was placed in the autoanalyzer. Rumen fluid VFA concentrations were determined by a Varion 3800 gas chromatograph (Varian Chromatography Systems, Walnut Creek, CA) using a Nikol fused silica capillary column (15 m; 0.53 mm i.d.; 0.5-µm film thickness; Supleco, Bellefonete, PA). Samples were run with a run time of 6 min. Peaks from samples were then compared to 4 standard solutions.
Statistical analysis.
All data were analyzed using the mixed linear model (PROC MIXED) of SAS (1989). The covariance structure was modeled using an autoregression structure within animals and a random effect between animals (Littell et al., 1998). The model uses both RANDOM and REPEATED statements. This covariance structure specifies a random effect of differences between animals and creates a correlation structure within animals that decreases with increasing amount of time between measurements (Littell et al., 1998). Least square means and standard errors were obtained according to treatment and week/day x treatment. The data were analyzed for 4 treatments (coarse = C, ground = G, coarse with 7.5% hay = H1, and coarse with 15% hay = H2). Main treatment effects were analyzed using calf within treatment as the error term. Orthogonal contrasts were made: G vs. C, C vs. H1 + H2, and H1 vs. H2. Data were analyzed for the entire trial as well as preweaning and postweaning time periods to account for different methods of feeding. Insufficient rumen fluid for VFA analysis was obtained from calves on d 8 and 15; therefore, these data were omitted. Statistical significance was declared at probabilities < 0.05. Probability values between 0.05 and 0.15 were considered to be trends towards significance.
Experiment 2
Calves and treatments.
Holstein (n = 48), Jersey (n = 3), Ayrshire (n = 2), and Brown Swiss (n = 3) calves (total n = 56) were obtained from the Northeast Iowa Community College herd. At birth all calves received colostrum and injections of 5 cc penicillin G procaine and 4 cc Bo-Se vitamin E and selenium (Schering-Plough Animal Health, Union, NJ). Calves were alternately assigned to one of 4 treatment groups according to order of birth and averaged 39.2 ± 6.4 kg. Calves were housed in individual pens with wood shavings or straw for bedding. Water was offered on an ad libitum basis.
Diet composition (Table 1
) and analysis (Table 2) was the same as used in experiment 1. A commercial milk replacer (12.5% DM, 22% CP, 20% fat, Land O’Lakes) was offered at 10% of initial BW daily via buckets until the calf was weaned. Weaning occurred when calves consumed 1.5% of initial BW as calf starter for 3 consecutive days (Greenwood et al., 1997a). All diets were offered from d 1 of age on an ad libitum basis.
Refusals of starter and milk replacer were recorded daily. In addition, daily fecal scores and administration of antibiotics and electrolytes were also recorded. Jugular blood was obtained and BW was measured weekly. Calves were removed from the trial approximately 2 wk after weaning.
Collection of jugular blood samples and BHBA analysis.
Blood samples were obtained and analyzed as in experiment 1.
Statistical analysis.
All data were analyzed as in experiment 1.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Body weight gain and feed efficiency.
Throughout the course of the trial, there was a tendency for BW to differ with treatment (P < 0.15) and age (P < 0.01) (Table 3). Mean BW of the treatment groups did not differ on d 0 of the trial (P > 0.15). Average daily gain (ADG) was affected by treatment (P < 0.02) and increased with the use of the coarse diet and the addition of hay (Table 3).
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).
Differences were observed in BW, ADG, and G/F with treatment (P < 0.01, P < 0.01, and P < 0.01, respectively) after weaning (Table 3). Calves fed diet C were heavier (P < 0.03), had greater ADG (P < 0.01), and had greater feed efficiency (P < 0.01) than calves fed G. Calves fed diet H1 and H2 were heavier (P < 0.01), had greater ADG (P < 0.04), and greater G/F (P < 0.03) than calves fed diet C. Calves fed diet H1 tended to have higher ADG (P < 0.07) and greater feed efficiency (P < 0.12) than calves fed diet H2 (Table 3).
These results conflict with those observed by Beharka et al. (1998) who observed greater BW in calves fed a ground diet offered in restricted amounts versus an unground diet of identical composition. However, all diets in their study included 25% alfalfa hay. Others have shown no difference in BW gain with respect to form of diet (fine, intermediate, and coarse). All diets used in their study included a source of bromegrass hay added at 15% of the diet (Greenwood et al., 1997b). Due to differences in both form of diet and forage inclusion in the current trial, gut fill may have influenced BW measurements.
Calf health.
Daily fecal scores and days of electrolyte and antibiotic administration did not differ with treatment. Fecal scores were not different throughout the trial (P = 0.64), preweaning (P = 0.66), or postweaning (P = 0.81). Mean fecal scores were 1.38, 1.39, 1.39, and 1.41 (SE = 0.02) for calves fed C, G, H1, and H2, respectively. There was no administration of antibiotics or electrolytes after weaning. Prior to weaning there was no difference in antibiotic treatments (P = 0.68) or electrolyte administration (P = 0.59) with respect to treatment. Mean days given electrolytes were 0.003, 0.005, 0.008, and 0.009 (SE = 0.003) for calves fed C, G, H1, and H2, respectively. Mean days treated with antibiotics were 0.03, 0.03, 0.02, and 0.04 (SE = 0.01) for calves fed C, G, H1, and H2, respectively.
Volatile fatty acid concentrations.
Total VFA concentrations (sum of acetate, propionate, isobutyrate, butyrate, isovalerate, and valerate) differed by treatment (P < 0.01) and age (P < 0.01) (Figure 1). Total VFA concentrations increased with increasing age of calves. Others have also observed this increase in total VFA concentrations with age (Greenwood et al., 1997b; Beharka et al., 1998). Total ruminal VFA concentrations observed in this investigation are higher than those previously recorded from rumen fluid sampled via stomach tube (Greenwood et al., 1997b). This most likely reflects the time of sampling and difference in feeding methods between the preweaning and postweaning periods. Samples of rumen fluid were obtained approximately 3 h after the offering of starter when VFA concentrations typically peak (Stobo et al., 1966).
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Total ruminal VFA concentrations were higher in calves fed G diet vs. C (P < 0.01) and tended to be higher for calves fed H1 vs. H2 (P < 0.10) (Figure 1). Beharka et al. (1998) also observed an increase in total VFA concentrations with ground diets versus unground.
Molar concentrations of acetate also were greater in calves fed diet G than in calves fed C (P < 0.01) (Table 4). Concentration of propionate also was greater in calves fed diet G vs. C (P < 0.01) and diet H1 vs. H2 (P < 0.03) (Table 4). Butyrate concentrations were greater in calves fed diet G than in those fed C (P < 0.01) (Table 4). Concentrations of isovalerate were unaffected by treatment (P = 0.50). Calves fed diet G had higher concentration of valerate and isobutyrate than calves fed C (P < 0.01 and P < 0.02, respectively). Ratio of acetate to propionate tended to change with treatment (P < 0.12). Calves fed diet H2 had a higher ratio of acetate to propionate than calves fed H1 (P < 0.03). Beharka et al. (1998) also reported no difference in acetate-to-propionate ratio between calves fed different forms of diet (ground vs. unground). Others have also observed an increase in acetate-to-propionate ratio in the rumen of calves fed diets with increasing levels of hay (Thomas and Hinks, 1982; Kerley et al., 1985).
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). Calves fed diet G tended to have a greater proportion of isobutyrate (P < 0.09), greater proportions of valerate (P < 0.01), and lower proportions of acetate (P < 0.06) than calves fed C. Calves fed diet C tended to have greater proportions of butyrate than calves fed H1 and H2 (P < 0.10). Quigley et al. (1992) reported similar results with the inclusion of hay in the diet. Calves fed H1 had greater proportions of propionate (P < 0.01) and lower proportions of isovalerate (P < 0.05) than calves fed H2 (Table 4).
ß-Hydroxybutyrate concentrations.
Plasma concentrations of BHBA did not differ with treatment prior to or after weaning or during the entire trial (Table 5). This is in contrast to Quigley et al. (1992), who observed a decrease in plasma BHBA as hay intake increased. However, this trial used restricted amounts of grain and ad libitum access to long hay postweaning. Therefore, calves did not consume consistent amounts of hay. Plasma BHBA concentrations did increase with age of the calf regardless of treatment (P < 0.01). Others have observed this increase in BHBA with age and increased consumption of fermentable carbohydrates (Quigley et al., 1992; Greenwood et al., 1997b). There were no significant differences throughout the entire trial (P = 0.46), as well as the preweaning (P = 0.62) or postweaning periods (P = 0.36). Others have also observed little influence of form of diet on plasma BHBA concentrations (Greenwood et al., 1997b). Plasma BHBA concentrations were similar to those observed by Greenwood et al. (1997b), who also utilized 15% bromegrass hay in the diets.
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). However, there was a tendency for starter intake to be greater for calves offered H1 and H2 vs. C (P < 0.11) after weaning (Table 6). Intake of starter and DM increased with age (P < 0.01). Total DMI also did not differ by treatment over the entire trial (P = 0.25). Dry matter intake of calves fed both C and G tended to be lower than H1 and H2 (P < 0.15) (Table 6). This is similar to data from experiment 1.
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There was no difference in DMI prior to weaning (P = 0.84) (Table 6). However, after weaning there was an effect of treatment on total intake (P < 0.15). Calves receiving diet C tended to consume more total DM than calves fed diet G (P < 0.15), indicating that form of diet impacts the intake of solid feed. Franklin et al. (2003) also observed an effect of form of diet on starter intake in calves. Their trial evaluated textured, ground, and pelleted starters. The authors observed that calves fed textured starter had greater intake and were weaned sooner than calves fed pelleted starter. However, this trial did not include forage in the dietary treatments.
Calves fed diets H1 and H2 tended to consume more total DM than those fed C (P < 0.11) postweaning (Table 6). This is similar to other investigations that have shown an increase in starter consumption with the addition of forage to the diet (Kincaid, 1980; Thomas and Hinks, 1982; Stobo et al., 1985). However, others have seen a negative impact of forage addition on the consumption of starter rations (Hibbs et al., 1956; Whitaker et al., 1957; Leibholz, 1975). In experiment 1 there was no difference in starter or total DM consumption postweaning. However, the calves in that trial had restricted intake of solid feed prior to weaning; this may have altered the consumption of feed postweaning.
Body weight gain and feed efficiency.
Body weight gain increased with age of the calves (P < 0.01). However, there were no differences in BW gain with respect to treatment throughout the entire trial (P = 0.72), preweaning (P = 0.75), or postweaning (P = 0.68) (Table 6). This is similar to the results observed by Greenwood et al. (1997b). In contrast, Beharka et al. (1998) observed that calves fed ground diets had higher BW than those fed unground rations. However, in that study the ground diet did contain 25% alfalfa hay. In experiment 1 we observed that calves fed diet C were heavier than those fed G, and calves receiving diet H1 and H2 were heavier than those receiving diet C postweaning.
Average daily gain also did not differ by treatment over the entire trial (P = 0.76), preweaning (P = 0.73), or postweaning (P = 0.53) (Table 6). Feed efficiency, expressed as a ratio of kilograms of gain per kilogram of feed, also was unaffected by treatment. Gain-to-feed ratios were not different for the entire trial (P = 0.85), for the period prior to weaning (P = 0.91), or for the period after weaning (P = 0.69) (Table 6). Experiment 1 resulted in higher ADG and G/F in calves fed diet C vs. diet G. In our previous trial, calves fed diets H1 and H2 had higher ADG and G/F than those consuming C when intake was restricted, suggesting that the restricted intake may have promoted increased efficiency of feed utilization in calves fed those diets.
Calf health.
Daily scour scores and electrolyte and antibiotic administration did not differ with treatment. Scour scores were not different throughout the trial (P = 0.62). Mean fecal scores were 1.39, 1.50, 1.42, and 1.43 (SE = 0.06) for calves fed C, G, H1, and H2, respectively. The administration of antibiotics or electrolytes was also unaffected by treatment (P = 0.70). Mean days given electrolytes or antibiotics were 0.06, 0.08, 0.06, and 0.05 (SE = 0.02) for calves fed C, G, H1, and H2, respectively.
Age at weaning.
Weaning occurred according to starter intake by individual calves. Mean age at weaning was 32.5, 30.7, 31.6, and 30.9 d for calves fed C, G, H1, and H2, respectively. Weaning age did not differ with treatment (P = 0.72). This indicates that there was little difference in DM consumption and minimal variation in intake among the treatments.
ß-Hydroxybutyrate concentrations.
Plasma concentrations of BHBA did not differ with respect to treatment (Table 7). However, the plasma concentrations did increase with age of the calf regardless of treatment (P < 0.01). Others have observed this increase in BHBA with age (Quigley et al., 1992; Greenwood et al., 1997b). There were no significant differences throughout the entire trial (P = 0.91), as well as the preweaning (P = 0.83) or postweaning periods (P = 0.97). This indicates that there was little difference in the rumen metabolism of butyrate by diet.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Received for publication July 16, 2003. Accepted for publication March 5, 2004.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
; G 
) and inclusions of forage (H1 
; H2 X), experiment 1.