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Intake, digestion and daily gain by cattle consuming bermudagrass (Cynodon dactylon) and supplemented with different combinations of ground corn, vegetable oil, urea, and corn gluten and blood meals
Animal Feed Science and Technology, 25 (1989) 99-110
99
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Intake, Digestion and Daily Gain by Cattle Consuming Bermudagrass (Cynodon dactylon) and Supplemented with Different Combinations of Ground Corn, Vegetable Oil, Urea, and Corn Gluten and Blood Meals* A.C. HARDIN, A.L. GOETSCH, K.M. LANDIS**, G.E. MURPHY, Z.B. JOHNSON and K.L. HALL
Arkansas Agricultural Experiment Station, University of Arkansas, Fayetteville, AR 72701 (U.S.A.) (Received 2 May 1988; accepted for publication 27 October 1988)
ABSTRACT Hardin, A.C., Goetsch, A.L., Landis, K.M., Murphy, G.E., Johnson, Z.B. and Hall, K.L., 1989. Intake, digestion and daily gain by cattle consuming bermudagrass (Cynodon dactylon) and supplemented with different combinations of ground corn, vegetable oil, urea, and corn gluten and blood meals. Anim. Feed Sci. Technol., 25: 99-110. Intake, digestion and daily gain by cattle consuming bermudagrass (Cynodon dactylon; BER) and receiving different concentrate supplements were determined. In one study, 6 tethered Holstein steers (204.5 kg) were fed BER hay ad libitum and in another trial 72 beef cattle (261 kg) grazed BER for 84 days. Animals were not supplemented (control) or received 0.25% body weight of ground corn (LC), 0.75% body weight of corn (HC), 0.25% body weight of corn plus 0.50% body weight of corn mixed with 0.056% body weight of vegetable oil (blend of soybean and coconut oils) and 0.011% body weight of calcium carbonate (HCF), the HCF supplement plus 0.017% body weight of urea (HCFU) or the HCFU supplement plus 0.051% body weight of corn gluten meal and 0.017% body weight of blood meal (HCFUGB; dry matter basis). The low amount of corn appeared to correct a ruminal insufficiency of readily fermentable substrate, presumably increasing nitrogen capture and flow of microbial protein to the small intestine to increase daily gain when nitrogen in BER was not extremely low. In the second 42-day period of the performance trial (Period 2) when forage nitrogen was low, little excess nitrogen from ruminal forage degradation escaping microbial capture probably prevented the low amount of corn from improving gain. The high level of supplemental grain increased performance in Period 2 with low-nitrogen forage but not in Period 1 with forage of higher nitrogen content. Thus, in Period 1 protein status of control and LC calves seemed first-limiting to gain, whereas additional energy was needed for faster gain of control and LC animals in Period 2. Fat mixed with grain may have lessened the *Approved for publication by the Director of the Arkansas Agricultural Experiment Station. **Present address: P.O. Box 55, Happy, TX 79042-0055, U.S.A.
0377-8401/89/$03.50
© 1989 Elsevier Science Publishers B.V.
100 deleterious effects of grain on fiber digestion by protecting concentrate from ruminal degradation, but did not greatly affect performance. Supplementation with urea improved gain with low-nitrogen BER but did not affect digestion or daily gain with BER higher in nitrogen. Supplementation with ruminal escape protein sources improved daily gain in both periods, suggesting that with prior inclusion of other supplement ingredients, intestinal amino acid supply limited performance.
INTRODUCTION
Forage diets provide the basal nutrients for ruminants throughout the world. However, medium- to low-quality forages cannot solely support the maximal performance of many ruminant classes in all instances. Tropical grasses provide nutrients for ruminants in warm weather when temperate grasses grow slowly. Because tropical grasses are generally less digestible than cool-season grasses of similar chemical composition (Akin, 1986 ), the performance of rum inants consuming warm-season grasses without supplementation, is often lower than that with temperate grasses. Adding grain to forage-based diets can impair digestion and/or intake of the basal forage (Hoover, 1986); hence, decreasing ruminal degradation of grain should improve forage utilization. Mixing or coating with fats or oils may impart some resistance of concentrates to ruminal digestion (Glen et al., 1977; Davenport et al., 1987). High affinity of triglycerides and fatty acids for feed particles in ruminal fluid (Harfoot et al., 1974) appears to reduce microbial attachment to concentrate particles and, thus, initiation of digestion (Davenport et al., 1987 ). Adsorption of lipid materials to concentrates before feeding should also minimize attachment of lipids to other feed particles and microbial cells and thereby prevent adverse effects of lipid on digestion (Harfoot et al., 1974) and microbial shifts (Czerkawski et al., 1975 ). Induced deficiences of nutrients, most notably ones containing nitrogen such as ammonia and amino acids, for fiber-degrading microbes contribute to the deleterious effects of high levels of supplemental grain on ruminal fiber digestion (Hoover, 1986; Chase and Hibberd, 1987). Therefore, adding such nutrients to grain supplements could elevate microbial growth and/or digestion and improve forage utilization. In addition, amino acids available in the intestines of grazing ruminants, that have potential to grow rapidly, may be inadequate for maximal growth and/or intake (Kempton, 1982 ). This experiment was conducted to determine the effects of providing cattle consuming bermudagrass with different levels of grain mixed with lipid, nonprotein nitrogen and ruminal escape protein sources on feed intake, digestion and daily gains.
101 M A T E R I A L S AND M E T H O D S
Experiment 1. Intake and digestion Six tethered Holstein steers (169 and 240 kg initial and final body weight, respectively) were used in a 6 × 6 Latin square with 14-day periods. Steer body weight determined on Day 14 at 13.00 along with an estimation of gain in the subsequent period were used to calculate supplement amounts. Control steers were not supplemented while others received supplements at 11.30 daily. Supplements (Table 1) were formulated (dry matter basis) and fed to provide 0.25% body weight of ground corn (low corn; LC ), 0.75% body weight of ground corn (high corn; HC), 0.25% body weight of ground corn plus 0.50% body weight of ground corn mixed with 0.056% body weight of a vegetable oil blend (degummed soybean and coconut oils) and 0.011% body weight of calcium carbonate (high corn and fat; HCF), the HCF supplement plus 0.017% body weight of urea (high corn, fat and urea; HCFU ) or the HCFU supplement plus 0.051% body weight of corn gluten meal and 0.017% body weight of blood meal (high corn, fat, urea and corn gluten and blood meals; HCFUGB). Supplements were constructed through different combinations made at feeding of 4 feeds which were mixed before the trial: ground corn, ground corn mixed with fat and calcium carbonate, ground corn mixed with urea and ground corn mixed with corn gluten and blood meals. Steers were fed bermudagrass (BER) hay (Table 2) at 08.00 and 18.00 at 105-110% of consumption on previous days. Orts were removed before the morning meal. All steers received 25 g (air-dry) of a 1 : 1 mix of dicalcium phosphate and trace mineralized salt (containing 96TABLE1 Composition of supplements fed to Holstein steers (% dry matter) Ingredient
Ground corn Vegetable fat 3 Calcium carbonate ~ Urea Corn gluten meal Blood meal
Supplement 1,z LC
HC
HCF
HCFU
HCFUGB
100.00
100.00
91.80 6.85 1.35
89.93 6.71 1.32 2.04
83.15 6.21 1.22 1.88 5.66 1.88
1LC=low corn; H C = h i g h corn; H C F - - h i g h corn and fat; H C F U = h i g h corn, fat and urea; H C F U G B = high corn, fat, urea and corn gluten and blood meals. eFormulated feeding rates ( % body weight, dry matter basis ): LC = 0.25; HC = 0.75; HCF = 0.817; H C F U = 0.834; H C F U G B = 0.902. 3Mixed with 66.67% of supplemental ground corn.
102 'FABLE 2 Composition of bermudagrass hay fed to Holstein steers in Experiment 1 and clipped forage samples in Experiment 2 (% dry matter) Item
Ash Nitrogen Neutral detergent fiber Acid detergent fiber Acid detergent lignin Cellulose Hemicellulose
Experiment 1
7.8 1.92 71.2 33.4 4.7 27.4 37.7
Experiment 2 (day) 1
42
84
1.88 75.8
1.21 78.7
1.17 77.2
98% NaC1 and more than 0.5% Fe, 0.2% Mn, 0.2% Zn, 0.04% Cu, 0.002% I and 0.007% Co). On Day 9 at the afternoon feeding, 75 g (air-dry) of BER labeled with Yb (Goetsch and Galyean, 1983 ) were fed with a small portion of unlabeled BER. After consumption, the remaining BER of the meal was offered. Rectal grab samples were obtained on Day 11 through 14 at 12-h intervals advancing 3 h daily. Samples were frozen, dried at 55 ° C for 48 h, allowed to equilibrate in air and ground through a l-ram screen. Composite samples were constructed within steer and period on an air-dry basis. Feed composite samples were ground through a 1-mm screen. Feed and feces were analyzed for dry matter (DM), ash, Kjeldahl nitrogen (A.O.A.C., 1984), neutral detergent fiber (NDF; Goering and van Soest, 1970) and acid-insoluble ash (van Keulen and Young, 1977 ). Hay was analyzed for acid detergent fiber and lignin (Goering and van Soest, 1970). Fiber analyses were nonsequential, cellulose was determined as loss in weight upon sulfuric acid treatment and acid detergent fiber subtracted from NDF yielded hemicellulose. Days 1-9 were for adjustment to treatments, and intake was averaged over the last 5 days of each period. Acid-insoluble ash was used as an internal marker for estimation of digestion. Individual fecal samples were ashed and mineral residue was solubilized with acid (Ellis et al., 1982) and analyzed for Yb by atomic absorption spectrophotometry. Regression of the natural logarithm of Yb concentration in fecal samples vs. time post-dosing yielded particulate passage rate (expressed in % h - i ). Data were analyzed by analysis of variance with steer, period and treatment in the statistical model. Individual treatment means were compared by least significant difference when the overall F was significant (P<0.05).
Experiment 2. Performance Thirty-six heifers and 36 steers (Angus, Angus x Hereford and Angus × Angus-Charolais) were used in a grazing experiment at the Beef Sub-
station of the University of Arkansas near Newport. On 15 June 1987, animals were weighed (259 and 263 kg body weight for heifers and steers, respectively) on the morning after being held overnight without water in a small lot with minimal growing herbage. Animals were allotted by body weight, sex and breed to 12 groups (3 heifers and 3 steers per group), dewormed, implanted with Synovex@ (Syntex Agribusiness, Des Moines, IA), given insecticide-impregnated ear tags and placed in twelve 1.62-ha paddocks. Paddocks consisted predominantly of common BER and contained small amounts of tall fescue and weed species. Cattle were weighed 42 and 84 days later, as described earlier. Cattle groups were assigned to treatments used in the first experiment. Average group body weight at the beginning and middle of the trial plus an estimation of body weight gain in the upcoming period were used to calculate supplement amounts. Supplements were fed daily at about 09.00 6 days weekly. Average daily supplement intake in the entire experiment was 0.78,2.31,2.53, 2.56 and 2.80 kg per animal for LC, HC, HCF, HCFU and HCFUGB, respectively. Excess forage was clipped by mowing prior to the start of the trial. The 12 paddocks were divided into 2 sub-groups, with one cattle group of each treatment in each sub-group. Groups were rotated to different paddocks weekly so that each group grazed all paddocks in a sub-group for 7 days in each 42-day period. Trace mineralized salt (same composition as in Experiment 1) blocks were available freely. Clipped forage samples, assumed to be similar to those consumed, were obtained from each paddock at the start, middle and end of the trial and were analyzed for DM, ash and nitrogen. Data were analyzed with a split-split-plot design with treatment being the main plot, and sex and 42-day period serving as sub-plots. Sources of variat,ion considered were treatment, cattle group within treatment (error to test treat ment ) , sex, treatment-sex interaction, group within treatment-sex interaction (error to test preceding two sources of variation), period, treatment-period interaction and treatment-sex-period interaction. Residual variation was used to test for effects of the final three variation sources. Because the 84-day trial length approximates the normal grazing of BER in this region, gain over the 84 days was also analyzed without consideration of period. RESULTS
Experiment 1. Intake and digestion Concentrations of nitrogen, NDF and cate that BER was of fairly high quality. was higher (P < 0.05 ) for control and LC for control than for LC steers (PcO.06). prised 9.3% of the diet, while corn was
acid detergent lignin (Table 2) indiBermudagrass hay intake (Table 3) than for other treatments and higher For the LC treatment, corn com25% of DM intake for HC. Control
104 TABLE 3 Intake, digestion and particulate passage rate for Holstein steers consuming bermudagrass hay and supplemented with concentrates Item
SE 2
Treatment ~ Control
Dry m a t t e r intake (% of body Hay 2.64 bs Supplement 0.00 Total 2.64 ~ Organic m a t t e r Passage (g d a y - 1) Intake 48568 Rectum 1862 Digestion % 61.2 ab g day- ~ 2995 a Neutral detergent fiber Passage (g d a y - ~) Intake 3755 c Rectum 1321 Digestion % 64.3 ¢ g day- ' 2435 c Nitrogen Passage (g d a y - ' ) Intake 100.8 ~ Rectum 44.3 ~ Digestion % 55.8 be g day-~ 56.6" Particulate passage rate (% h - ' ) 3.51
LC
HC
weight) 2.43 b 0.25 2.68 ab
HCF 2.19 a 0.74 2.92 c
2.09 a 0.79 2.88 b~
HCFUGB
HCFU 2.17 a 0.81 2.98 c
2.00 a 0.88 2.88 be
0.074 0.073
4925 a 1961
5432 b 2113
5396 b 1983
5524 b 1886
5381 b 1912
135.4 80.0
59.8 ~ 2964 a
62.1 ab 3319 b
64.1 be 3413 b
66.V 3638 b
64.3 b~ 3470 b
1.20 110.8
3468 bc 1360
3212 ab 1423
3122 a 1279
3198 ab 1255
3032" 1205
108.1 57.6
60.6 b 2109 b
57.1 ~ 17898
60.3 b 1842 ~
61.0 b 1943 ~b
59.9 ab 1827 a
1.05 83.6
100.7 ~ 48.58
108.2 a 55.1 b
104.6 a 52.3 b
120.6 b 49.9 ~b
132.3 ¢ 54.4 b
2.73 2.27
51.6 ~b 52.2 ~
49.9 ~ 53.1 ~
50.2 ~ 52.3 a
58.9 ~ 70.6 b
58.8 ¢ 77.9 b
1.57 2.52
3.80
3.56
3.52
3.54
3.12
0.199
1LC=low corn; H C = h i g h corn; H C F = h i g h corn a n d fat; H C F U = h i g h corn, fat a n d urea; H C F U G B - - high corn, fat, urea a n d corn gluten a n d blood meals. 2Standard error. '~Means in a row without a c o m m o n superscript (a, b, c) differ ( P < 0 . 0 5 ) . steers consumed steers. Organic matter treatments
less (P < 0.05) total DM than HC, HCF, HCFU
intake was lower (P < 0.05) for control and LC than for other
(Table 3), and fecal excretion
(P > 0.05) among
and HCFUGB
treatments.
of organic matter
(OM)
was similar
Total tract digestion of OM for control, LC and
H C w a s s i m i l a r ( P > 0 . 0 5 ), b e i n g l o w e r ( P < 0 . 0 5 ) t h a n f o r H C F U , w h i l e d i g e s tion for HCF and HCFUGB was intermediate. As compared with the control
105
treatment, digestion of OM in g day- 1was not improved by the LC supplement but was increased ( P < 0.05) by all supplements containing the high level of corn as compared with control and LC. Neutral detergent fiber intake was higher (P < 0.05 ) for control than for HC, HCF, HCFU and HCFUGB; intake of NDF by steers receiving LC was greater (P < 0.05) than for HCF and HCFUGB. Rectal passage of NDF was similar among treatments (P>0.05). Total tract digestion of NDF was highest ( P < 0.05 ) for the control treatment and higher for LC, HCF, HCFU ( P < 0.05 ) and HCFUGB (P < 0.08) than for HC. Neutral detergent fiber digested in the total tract (g day -1 ) was highest for control steers and higher for LC than for HC, HCF and HCFUGB (P < 0.05). Nitrogen intake (Table 3) was highest for HCFUGB and higher for HCFU than for control, LC, HC and HCF treatments ( P < 0.05). Fecal nitrogen excretion was lower (P<0.05) for control and LC than for HC, HCF and HCFUGB. Total tract nitrogen disappearance (To) was higher for HCFU and HCFUGB than for LC, HC and HCF and higher for control than for HC and HCF treatments (P < 0.05 ). Total tract nitrogen disappearance (g day-1 ) was higher (P<0.05) for HCFU and HCFUGB than for other treatments and higher (P < 0.06) for HCFUGB than for HCFU. Particulate passage rate (Table 3 ) was similar ( P > 0.05 ) among treatments, but tended to be highest for LC, lowest for HCFUGB and intermediate for other groups.
Experiment 2. Performance Effects of treatment, period and the treatment-period interaction on daily gain were observed (P<0.05). Daily gain (Table 4) for all treatments was greater (P<0.05) in Period 1 (Day 1-42) than in Period 2 (Day 43-84). In Period 1, gain for control cattle was lower (P < 0.05 ) than for cattle given H CF and HCFUGB supplements. Gain values for LC, HC, HCF and HCFU were similar ( P > 0.05) and tended to be higher than gain for the control treatment TABLE4 D a i l y g a i n b y b e e f cattle g r a z i n g b e r m u d a g r a s s p a d d o c k s a n d s u p p l e m e n t e d w i t h c o n c e n t r a t e 1 Days
1-42 43-84
Treatment 2 Control
LC
HC
HCF
HCFU
HCFUGB
1.24 d3 0.01 a
1.40 def - 0.01 a
1.33 de 0.23 b
1.41 ef 0.26 b
1.36 def 0.39 bc
1.51 f 0.46 c
1 S t a n d a r d e r r o r = 0.061. 2 L C = l o w corn; H C = h i g h corn; H C F = h i g h c o r n a n d fat; H C F U = h i g h H C F U G B = h i g h c o r n , fat, u r e a a n d c o r n g l u t e n a n d blood m e a l s . 3 M e a n s w i t h o u t a c o m m o n s u p e r s c r i p t (a, b, c, d, e, f) differ ( P < 0 . 0 5 ) .
corn, f a t a n d urea;
106 and lower than gain with the HCFUGB supplement. In Period 2, no response in daily gain to the LC supplement was observed ( P > 0.05). Gain was, however, improved ( P < 0.05 ) by HC and HCF supplements as compared with control and LC treatments. Gain for HCFU was greater than for HC ( P < 0.05) and HCF (P<0.14), and gain for HCFUGB was greater (P<0.05) than for HC and HCF. Steers tended (P<0.08) to gain faster than heifers (0.82 vs. 0.78 kg day- 1). Interactions involving sex were not significant ( P > 0.15 ). During the entire 84-day trial, daily gain was 0.63, 0.70, 0.78, 0.84, 0.87 and 0.99 kg for control, LC, HC, HCF, HCFU and HCFUGB, respectively (standard error=0.032). Gain was highest for HCFUGB and higher for HCF and HCFU than for control and LC (P<0.05). Also, gain was higher (P<0.11) for HC than for LC and higher ( P < 0.18) for LC than for control. DISCUSSION Depressions in fiber digestion generally worsen as supplemental coacentrate rises, but when mixed diets are fed, effects of low-level concentrate supplementation are minor (Hoover, 1986). Jones et al. (1988) fed grain immediately before BER twice daily, whereas grain was given once daily, 3.5 h after the morning meal of BER, in the present study. Thus, the large amount of concentrate given may have caused substantial changes in ruminal pH, readily fermentable carbohydrate available for preferential usage by fiber-digesting microbes and inhibition of bacterial attachment to fiber (Hoover, 1986) after supplementation as compared with conditions with mixed diets or more frequent supplementation. However, the relative importance of microbial growth and digestion and the degree to which over time such conditions are changed by grain are not well understood. Grain supplementation, once daily, shortly after a period of forage consumption could depress continuing fiber digestion more than grain in mixed diets or grain given right before roughage. The latter might only delay the onset of digestion of newly ingested forage. In the present study, the delay in time after grain was offered before fiber digestion recovered to the rate of digestion before supplementation is unknown. Further, because many starch-fermenting microbes also digest fiber, proliferation after supplementing with a low level of grain before roughage feeding could conceivably enhance forage digestion. The space occupied by grain in the reticulo-rumen is less than that occupied by roughage (Hoover, 1986). Hence, if reticulo-ruminal digesta fill solely controlled intake, the LC supplement altered characteristics of reticulo-ruminal digesta that caused excitation of receptors sensing digesta quantity and/or physical characteristics (Grovum, 1986) at a lower level of digesta fill than in control steers. Thus, factors other than, or in conjunction with, reticulo-ruminal digesta fill seem to have regulated forage intake. To predict the retention of nitrogen by steers fed BER, the digestible energy
107
content of the forage should be considered (Stallcup et al., 1987). It has been suggested that available energy is more limiting to the performance of cattle consuming warm- rather than cool-season grasses {Stobbs et al., 1977; Stallcup et al., 1987). Conversely, increasing the postruminal amino acid supply in cattle consuming tropical forage has elevated performance, suggesting that nitrogen availability in tropical grasses limits performance (Flores et al., 1979; Kempton, 1982). Although these possibilities seem contradictory, both may be partially true. Increasing the readily fermentable substrate for ruminal microbes with tropical forage diets increases the microbial capture of ammonia and the flow of microbial protein to the intestines (Flores et al., 1979; Kellaway and Leibholz, 1983). Supplemental grain increased microbial protein synthesis with BER (Jones et al., 1988), possibly because of the low level and slow and prolonged release of readily fermentable or nonstructural carbohydrate in BER (Mertens and Loften, 1980). Therefore, inefficient utilization of tropical grass nitrogen and inadequate quantities of amino acids reaching the intestines may, in part, be caused by a ruminal imbalance of available nitrogen and energy (perhaps only at certain times after ingestion) leading to substantial nitrogen loss through ruminal ammonia absorption and urinary excretion of urea. Hence, as LC did not increase organic matter digested in Experiment 1, perhaps the trend for increased daily gain in Period 1 was because more microbial protein was synthesized and flowed to the small intestine, increasing the protein: energy ratio of absorbed products of digestion. Consumption of BER in Experiment 1 may have been decreased by LC to minimize deviation of the protein: energy ratio from host needs. The LC supplement did not affect daily gain in Period 2 in contrast to the change in Period 1, perhaps because forage in Period 2 was lower in nitrogen. Supplementation with LC in Period 2 may have accentuated a limitation of nitrogenous compounds for microbial growth and/or digestion. But a ruminal nitrogen deficiency does not always mean that nitrogenous compounds were first-limiting to animal performance and, in fact, low BER intake and digestion would lead to low energy status. Improved daily gain in Period 2 with the HC supplement was probably because of increased microbial production and host absorption and utilization of volatile fatty acids (Hoover, 1986) and ruminal escape of corn protein and starch. Increased host energy status with HC in Period 2, owing to low forage quality, may have minimized the depression in BER intake. Lack of improved performance with HC in Period 1 above LC, suggests that readily fermentable substrate with 0.25% body weight of corn facilitated efficient capture of nitrogen from forage degradation and/or that corn amino acids reaching the intestines did not coincide well with host needs. Increased fiber digestion (%) when fat was mixed with 66.67% of the corn in HC, suggests that fat allowed more grain to escape ruminal digestion (Glen
108 et al., 1977; Davenport et al., 1987) through slowed microbial attachment to fat-coated concentrate (Davenport et al., 1987 ) or altered physical behavior of coated particles. Though high levels of supplemental fat can increase ruminal digesta volume and dilution rate with a set level of feed intake {Czerkawski et al., 1975 ), steady particulate passage rate suggests that the effects of this low level of fat on ruminal digesta kinetics are unlikely. Similar performance for HCF and HC agrees with only a small trend for higher organic-matter digestion (g day -1) with HCF, a portion of which should involve intestinal fat disappearance. The corn-fat mix consisted of about the maximum level of fat (10% of the corn-fat mix) that could be used without experiencing handling or storage difficulties. However, higher levels, as have been used with protein supplements (Glen et al., 1977; Davenport et al., 1987), might increase protection. Calcium carbonate was included in the grain-fat mix to provide calcium for salt formation with fatty acids (Palmquist and Jenkins, 1980) to prevent adsorption to other feed particles or bacteria of fatty acids which might dislocate from grain. However, the level of added fat (about 1.9% of DM intake) should not greatly depress ruminal fiber digestion even if not mixed with grain (Palmquist and Jenkins, 1980). Fecal excretion of Ca soaps can rise when fat is added to ruminant diets also (Palmquist and Jenkins, 1980). Small changes in intake, digestion and performance in Period 1 when urea was supplemented, suggest that organic matter being fermented in the rumen with 0.75% body weight of supplemental corn did not induce an ammonia insufficiency. Conversely, low forage nitrogen in Period 2, leading to low ruminal ammonia levels, could have allowed urea to increase performance, through increased ruminal microbial protein synthesis and outflow and/or increased ruminal forage digestion and intake (Kempton, 1982 ). Higher cereal grain levels increase chances of ruminal ammonia deficiencies that limit fiber degradation (Chase and Hibberd, 1987). The major effect of supplementing with corn gluten and blood meals in the first study was increased uptake of nitrogen. Thus, increased performance with the protein meals in Experiment 2 appears to be a response to greater intestinal amino-acid uptake and not altered forage intake. Increasing amino-acid absorption can increase ruminant performance with or without change in forage intake (Stobbs et al., 1977; Flores et al., 1979; Kellaway and Leibholz, 1983). As compared with Period 2, the large increase in gain in Period 1 when aminoacid absorption was increased by supplementation with protein meals may have been facilitated by high forage quality and host energy status. Effects on performance of corn gluten and blood meals without some of the other supplement ingredients may have differed from those with HCFUGB. Although supplementation with the protein meals should increase amino acids absorbed, as proposed for LC, the extent of increase for one without the other might be less than with both. The protein meals provide less fermentable sub-
109
strate to increase microbial growth than corn. Because the energy demand for gain appeared high in Period 2, supplementation with the protein meals without some of the other feeds to improve host energy status may not have improved gain to the degree noted for HCFUGB. Increased propionate and glucose supplies with supplemental grain might spare amino acids from host degradation to increase amino acids used for tissue accretion and improve efficiency of acetate metabolism (Black et al., 1987a, b). Similarly, urea supplementation in Period 2 could have elevated microbial use of amino acids for net growth as opposed to breakdown for energy and overcome a ruminal deficiency of ammonia, which supplementation with the protein meals might not. Thus, the potential for the efficient use of supplemental ruminal escape protein seems greatest when adequate nutrients are available to ruminal microbes and use of amino acids other than for tissue accretion is minimized (Kempton, 1982; Black et al., 1987a, b). Average daily supplement costs for the 84-day grazing experiment were US$ 0.08, 0.24, 0.40, 0.41 and 0.50 per animal. Using gain for the 84-day experiment, costs of additional gain (kg) above the control treatment were US$1.20, 1.54, 1.90, 1.66 and 1.37 for LC, HC, HCF, HCFU and HCFUGB, respectively. On this basis, therefore, LC was most economical, followed by HCFUGB. Fat inclusion greatly increased supplement cost and did not markedly improve gain; therefore, omission of fat would lessen costs of HCFU and HCFUGB. Low cost makes urea addition a consideration, when nitrogen adequacy of forage is questionable and when a mixed supplement is used. Because of changes in forage intake, grain supplementation should increase animals per unit of land required to achieve similar herbage availability. As gain increases with supplementation, time to reach end-weight declines or weight after a set period of grazing increases. ACKNOWLEDGEMENTS
Appreciationisexpressedtothe Arkansas BeefCouncilforpa~ialfinancial suppo~.
REFERENCES Akin, D.E., 1986. Chemical and biological structure in plants as related to microbial degradation of forage cell walls. In: L.P. Milligan, W.L. Grovum and A. Dobson (Editors), Control of Digestion and Metabolism in Ruminants. Prentice Hall, Englewood Cliffs, NJ, pp. 196-223. A.O.A.C., 1984. Official Methods of Analysis, 14th edn., Association of Official Analytical Chemists, Washington, DC, pp. 152-157. Black, J.L., Gill, M., Beever, D.E., Thornley, J.H.M. and Oldham, J.D., 1987a. Simulation of the metabolism of absorbed energy-yielding nutrients in young sheep: Efficiency of utilization of acetate. J. Nutr., 117: 105-115.
110
Black, J.L., Gill, M., Thornley, J.H.M., Beever, D.E. and Oldham, J.D., 1987b. Simulation of the metabolism of absorbed energy-yielding nutrients in young sheep: Efficiency of utilization of lipid and amino acid. J. Nutr., 117: 116-128. Chase Jr., C.C. and Hibberd, C.A., 1987. Utilization of low-quality native grass hay by beef cows fed increasing quantities of corn grain. J. Anita. Sci., 65: 557-566. Czerkawski, J.W., Christie, W.W., Breckenridge, G. and Hunter, L., 1975. Changes in the rumen metabolism of sheep given increasing amounts of linseed oil in their diet. Br. J. Nutr., 34: 2544. Davenport, G.M., Boling, J.A., Gay, N. and Bunting, L.D., 1987. Effect of soybean lipid on growth and ruminal nitrogen metabolism in cattle fed soybean meal or ground whole soybeans. J. Anita. Sci., 65: 1680-1689. Ellis, W.C., Lascano, C., Teeter, R. and Owens, F.N., 1982. Solute and particle flow marker. In: F.N. Owens (Editor), Protein Requirements for Cattle: Symposium. Okla. Agric. Exp. Stn., Misc. Publ., No. 109, pp. 37-56. Flores, J.F., Stobbs, T.H. and Minson, D.J., 1979. The influence of the legume Leucaena leucocephala and formal-casein on the production and composition of milk from grazing cows. J. Agric. Sci., 92: 351-357. Glen, B.P., Ely, D.G. and Boling, J.A., 1977. Nitrogen metabolism in lambs fed lipid-coated protein. J. Anim. Sci., 46: 871-877. Goering, H.K. and van Soest, P.J., 1970. Forage Fiber Analyses. Apparatus, Reagents, Procedures and Some Applications, A.R.S., U.S.D.A. Agricultural Handbook No. 379, Washington, DC, pp. 1-20. Goetsch, A.L. and Galyean, M.L., 1983. Ruthenium phenanthroline, dysprosium and ytterbium as particulate markers in beef steers fed an all-alfalfa hay diet. Nutr. Rep. Int., 27: 171. Grovum, W.L., 1986. A new look at what is controlling food intake. In: F.N. Owens (Editor), Proceedings: Feed Intake by Beef Cattle. Okla. Agric. Exp. Stn., Misc. Pubi., No. 121, pp. 140. Harfoot, C.G., Crouchman, M.L., Noble, R.C. and Moore, J.H., 1974. Competition between food particles and rumen bacteria in the uptake of long-chain fatty acids and triglycerides. J. Appl. Bact., 37: 633-641. Hoover, W.H., 1986. Chemical factors involved in ruminal fiber digestion. J. Dairy Sci., 69: 27552766. Jones, A.L., Goetsch, A.L., Stokes, S.R. and Colberg, M., 1988. Intake and digestion in cattle fed warm- or cool-season grass hay with or without supplemental grain. J. Anim. Sci., 66: 194-203. Kellaway, R.C. and Leibholz, J., 1983. Effects of nitrogen supplements on intake and utilization of low-quality forages. World Anim. Rev., 48: 33-37. Kempton, T.J., 1982. Role of feed supplements in the utilisation of low protein roughage diets by sheep. World Rev. Anim. Prod., 18: 7-14. Mertens, D.R. and Loften, J.R., 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci., 63: 1437-1466. Palmquist, D.L. and Jenkins, D.L., 1980. Fat in lactation ratios. Rev. J. Dairy Sci., 63: 1-14. Stallcup, O.T., Kreider, D.L., Johnson, Z.B. and Davis, G.V., 1987. Apparent digestibility of nitrogen and nitrogen retention of forages fed to steers in metabolism stalls. J. Anim. Sci., 65: 1690-1699. Stobbs, T.H., Minson, D.J. and McLeod, M.N., 1977. The response of dairy cows grazing a nitrogen fertilized grass pasture to a supplement of protected casein. J. Agric. Sci., 89: 137-141. Van Keulen, J. and Young, B.A., 1977. Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. J. Anim. Sci., 44: 282-287.
99
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Intake, Digestion and Daily Gain by Cattle Consuming Bermudagrass (Cynodon dactylon) and Supplemented with Different Combinations of Ground Corn, Vegetable Oil, Urea, and Corn Gluten and Blood Meals* A.C. HARDIN, A.L. GOETSCH, K.M. LANDIS**, G.E. MURPHY, Z.B. JOHNSON and K.L. HALL
Arkansas Agricultural Experiment Station, University of Arkansas, Fayetteville, AR 72701 (U.S.A.) (Received 2 May 1988; accepted for publication 27 October 1988)
ABSTRACT Hardin, A.C., Goetsch, A.L., Landis, K.M., Murphy, G.E., Johnson, Z.B. and Hall, K.L., 1989. Intake, digestion and daily gain by cattle consuming bermudagrass (Cynodon dactylon) and supplemented with different combinations of ground corn, vegetable oil, urea, and corn gluten and blood meals. Anim. Feed Sci. Technol., 25: 99-110. Intake, digestion and daily gain by cattle consuming bermudagrass (Cynodon dactylon; BER) and receiving different concentrate supplements were determined. In one study, 6 tethered Holstein steers (204.5 kg) were fed BER hay ad libitum and in another trial 72 beef cattle (261 kg) grazed BER for 84 days. Animals were not supplemented (control) or received 0.25% body weight of ground corn (LC), 0.75% body weight of corn (HC), 0.25% body weight of corn plus 0.50% body weight of corn mixed with 0.056% body weight of vegetable oil (blend of soybean and coconut oils) and 0.011% body weight of calcium carbonate (HCF), the HCF supplement plus 0.017% body weight of urea (HCFU) or the HCFU supplement plus 0.051% body weight of corn gluten meal and 0.017% body weight of blood meal (HCFUGB; dry matter basis). The low amount of corn appeared to correct a ruminal insufficiency of readily fermentable substrate, presumably increasing nitrogen capture and flow of microbial protein to the small intestine to increase daily gain when nitrogen in BER was not extremely low. In the second 42-day period of the performance trial (Period 2) when forage nitrogen was low, little excess nitrogen from ruminal forage degradation escaping microbial capture probably prevented the low amount of corn from improving gain. The high level of supplemental grain increased performance in Period 2 with low-nitrogen forage but not in Period 1 with forage of higher nitrogen content. Thus, in Period 1 protein status of control and LC calves seemed first-limiting to gain, whereas additional energy was needed for faster gain of control and LC animals in Period 2. Fat mixed with grain may have lessened the *Approved for publication by the Director of the Arkansas Agricultural Experiment Station. **Present address: P.O. Box 55, Happy, TX 79042-0055, U.S.A.
0377-8401/89/$03.50
© 1989 Elsevier Science Publishers B.V.
100 deleterious effects of grain on fiber digestion by protecting concentrate from ruminal degradation, but did not greatly affect performance. Supplementation with urea improved gain with low-nitrogen BER but did not affect digestion or daily gain with BER higher in nitrogen. Supplementation with ruminal escape protein sources improved daily gain in both periods, suggesting that with prior inclusion of other supplement ingredients, intestinal amino acid supply limited performance.
INTRODUCTION
Forage diets provide the basal nutrients for ruminants throughout the world. However, medium- to low-quality forages cannot solely support the maximal performance of many ruminant classes in all instances. Tropical grasses provide nutrients for ruminants in warm weather when temperate grasses grow slowly. Because tropical grasses are generally less digestible than cool-season grasses of similar chemical composition (Akin, 1986 ), the performance of rum inants consuming warm-season grasses without supplementation, is often lower than that with temperate grasses. Adding grain to forage-based diets can impair digestion and/or intake of the basal forage (Hoover, 1986); hence, decreasing ruminal degradation of grain should improve forage utilization. Mixing or coating with fats or oils may impart some resistance of concentrates to ruminal digestion (Glen et al., 1977; Davenport et al., 1987). High affinity of triglycerides and fatty acids for feed particles in ruminal fluid (Harfoot et al., 1974) appears to reduce microbial attachment to concentrate particles and, thus, initiation of digestion (Davenport et al., 1987 ). Adsorption of lipid materials to concentrates before feeding should also minimize attachment of lipids to other feed particles and microbial cells and thereby prevent adverse effects of lipid on digestion (Harfoot et al., 1974) and microbial shifts (Czerkawski et al., 1975 ). Induced deficiences of nutrients, most notably ones containing nitrogen such as ammonia and amino acids, for fiber-degrading microbes contribute to the deleterious effects of high levels of supplemental grain on ruminal fiber digestion (Hoover, 1986; Chase and Hibberd, 1987). Therefore, adding such nutrients to grain supplements could elevate microbial growth and/or digestion and improve forage utilization. In addition, amino acids available in the intestines of grazing ruminants, that have potential to grow rapidly, may be inadequate for maximal growth and/or intake (Kempton, 1982 ). This experiment was conducted to determine the effects of providing cattle consuming bermudagrass with different levels of grain mixed with lipid, nonprotein nitrogen and ruminal escape protein sources on feed intake, digestion and daily gains.
101 M A T E R I A L S AND M E T H O D S
Experiment 1. Intake and digestion Six tethered Holstein steers (169 and 240 kg initial and final body weight, respectively) were used in a 6 × 6 Latin square with 14-day periods. Steer body weight determined on Day 14 at 13.00 along with an estimation of gain in the subsequent period were used to calculate supplement amounts. Control steers were not supplemented while others received supplements at 11.30 daily. Supplements (Table 1) were formulated (dry matter basis) and fed to provide 0.25% body weight of ground corn (low corn; LC ), 0.75% body weight of ground corn (high corn; HC), 0.25% body weight of ground corn plus 0.50% body weight of ground corn mixed with 0.056% body weight of a vegetable oil blend (degummed soybean and coconut oils) and 0.011% body weight of calcium carbonate (high corn and fat; HCF), the HCF supplement plus 0.017% body weight of urea (high corn, fat and urea; HCFU ) or the HCFU supplement plus 0.051% body weight of corn gluten meal and 0.017% body weight of blood meal (high corn, fat, urea and corn gluten and blood meals; HCFUGB). Supplements were constructed through different combinations made at feeding of 4 feeds which were mixed before the trial: ground corn, ground corn mixed with fat and calcium carbonate, ground corn mixed with urea and ground corn mixed with corn gluten and blood meals. Steers were fed bermudagrass (BER) hay (Table 2) at 08.00 and 18.00 at 105-110% of consumption on previous days. Orts were removed before the morning meal. All steers received 25 g (air-dry) of a 1 : 1 mix of dicalcium phosphate and trace mineralized salt (containing 96TABLE1 Composition of supplements fed to Holstein steers (% dry matter) Ingredient
Ground corn Vegetable fat 3 Calcium carbonate ~ Urea Corn gluten meal Blood meal
Supplement 1,z LC
HC
HCF
HCFU
HCFUGB
100.00
100.00
91.80 6.85 1.35
89.93 6.71 1.32 2.04
83.15 6.21 1.22 1.88 5.66 1.88
1LC=low corn; H C = h i g h corn; H C F - - h i g h corn and fat; H C F U = h i g h corn, fat and urea; H C F U G B = high corn, fat, urea and corn gluten and blood meals. eFormulated feeding rates ( % body weight, dry matter basis ): LC = 0.25; HC = 0.75; HCF = 0.817; H C F U = 0.834; H C F U G B = 0.902. 3Mixed with 66.67% of supplemental ground corn.
102 'FABLE 2 Composition of bermudagrass hay fed to Holstein steers in Experiment 1 and clipped forage samples in Experiment 2 (% dry matter) Item
Ash Nitrogen Neutral detergent fiber Acid detergent fiber Acid detergent lignin Cellulose Hemicellulose
Experiment 1
7.8 1.92 71.2 33.4 4.7 27.4 37.7
Experiment 2 (day) 1
42
84
1.88 75.8
1.21 78.7
1.17 77.2
98% NaC1 and more than 0.5% Fe, 0.2% Mn, 0.2% Zn, 0.04% Cu, 0.002% I and 0.007% Co). On Day 9 at the afternoon feeding, 75 g (air-dry) of BER labeled with Yb (Goetsch and Galyean, 1983 ) were fed with a small portion of unlabeled BER. After consumption, the remaining BER of the meal was offered. Rectal grab samples were obtained on Day 11 through 14 at 12-h intervals advancing 3 h daily. Samples were frozen, dried at 55 ° C for 48 h, allowed to equilibrate in air and ground through a l-ram screen. Composite samples were constructed within steer and period on an air-dry basis. Feed composite samples were ground through a 1-mm screen. Feed and feces were analyzed for dry matter (DM), ash, Kjeldahl nitrogen (A.O.A.C., 1984), neutral detergent fiber (NDF; Goering and van Soest, 1970) and acid-insoluble ash (van Keulen and Young, 1977 ). Hay was analyzed for acid detergent fiber and lignin (Goering and van Soest, 1970). Fiber analyses were nonsequential, cellulose was determined as loss in weight upon sulfuric acid treatment and acid detergent fiber subtracted from NDF yielded hemicellulose. Days 1-9 were for adjustment to treatments, and intake was averaged over the last 5 days of each period. Acid-insoluble ash was used as an internal marker for estimation of digestion. Individual fecal samples were ashed and mineral residue was solubilized with acid (Ellis et al., 1982) and analyzed for Yb by atomic absorption spectrophotometry. Regression of the natural logarithm of Yb concentration in fecal samples vs. time post-dosing yielded particulate passage rate (expressed in % h - i ). Data were analyzed by analysis of variance with steer, period and treatment in the statistical model. Individual treatment means were compared by least significant difference when the overall F was significant (P<0.05).
Experiment 2. Performance Thirty-six heifers and 36 steers (Angus, Angus x Hereford and Angus × Angus-Charolais) were used in a grazing experiment at the Beef Sub-
station of the University of Arkansas near Newport. On 15 June 1987, animals were weighed (259 and 263 kg body weight for heifers and steers, respectively) on the morning after being held overnight without water in a small lot with minimal growing herbage. Animals were allotted by body weight, sex and breed to 12 groups (3 heifers and 3 steers per group), dewormed, implanted with Synovex@ (Syntex Agribusiness, Des Moines, IA), given insecticide-impregnated ear tags and placed in twelve 1.62-ha paddocks. Paddocks consisted predominantly of common BER and contained small amounts of tall fescue and weed species. Cattle were weighed 42 and 84 days later, as described earlier. Cattle groups were assigned to treatments used in the first experiment. Average group body weight at the beginning and middle of the trial plus an estimation of body weight gain in the upcoming period were used to calculate supplement amounts. Supplements were fed daily at about 09.00 6 days weekly. Average daily supplement intake in the entire experiment was 0.78,2.31,2.53, 2.56 and 2.80 kg per animal for LC, HC, HCF, HCFU and HCFUGB, respectively. Excess forage was clipped by mowing prior to the start of the trial. The 12 paddocks were divided into 2 sub-groups, with one cattle group of each treatment in each sub-group. Groups were rotated to different paddocks weekly so that each group grazed all paddocks in a sub-group for 7 days in each 42-day period. Trace mineralized salt (same composition as in Experiment 1) blocks were available freely. Clipped forage samples, assumed to be similar to those consumed, were obtained from each paddock at the start, middle and end of the trial and were analyzed for DM, ash and nitrogen. Data were analyzed with a split-split-plot design with treatment being the main plot, and sex and 42-day period serving as sub-plots. Sources of variat,ion considered were treatment, cattle group within treatment (error to test treat ment ) , sex, treatment-sex interaction, group within treatment-sex interaction (error to test preceding two sources of variation), period, treatment-period interaction and treatment-sex-period interaction. Residual variation was used to test for effects of the final three variation sources. Because the 84-day trial length approximates the normal grazing of BER in this region, gain over the 84 days was also analyzed without consideration of period. RESULTS
Experiment 1. Intake and digestion Concentrations of nitrogen, NDF and cate that BER was of fairly high quality. was higher (P < 0.05 ) for control and LC for control than for LC steers (PcO.06). prised 9.3% of the diet, while corn was
acid detergent lignin (Table 2) indiBermudagrass hay intake (Table 3) than for other treatments and higher For the LC treatment, corn com25% of DM intake for HC. Control
104 TABLE 3 Intake, digestion and particulate passage rate for Holstein steers consuming bermudagrass hay and supplemented with concentrates Item
SE 2
Treatment ~ Control
Dry m a t t e r intake (% of body Hay 2.64 bs Supplement 0.00 Total 2.64 ~ Organic m a t t e r Passage (g d a y - 1) Intake 48568 Rectum 1862 Digestion % 61.2 ab g day- ~ 2995 a Neutral detergent fiber Passage (g d a y - ~) Intake 3755 c Rectum 1321 Digestion % 64.3 ¢ g day- ' 2435 c Nitrogen Passage (g d a y - ' ) Intake 100.8 ~ Rectum 44.3 ~ Digestion % 55.8 be g day-~ 56.6" Particulate passage rate (% h - ' ) 3.51
LC
HC
weight) 2.43 b 0.25 2.68 ab
HCF 2.19 a 0.74 2.92 c
2.09 a 0.79 2.88 b~
HCFUGB
HCFU 2.17 a 0.81 2.98 c
2.00 a 0.88 2.88 be
0.074 0.073
4925 a 1961
5432 b 2113
5396 b 1983
5524 b 1886
5381 b 1912
135.4 80.0
59.8 ~ 2964 a
62.1 ab 3319 b
64.1 be 3413 b
66.V 3638 b
64.3 b~ 3470 b
1.20 110.8
3468 bc 1360
3212 ab 1423
3122 a 1279
3198 ab 1255
3032" 1205
108.1 57.6
60.6 b 2109 b
57.1 ~ 17898
60.3 b 1842 ~
61.0 b 1943 ~b
59.9 ab 1827 a
1.05 83.6
100.7 ~ 48.58
108.2 a 55.1 b
104.6 a 52.3 b
120.6 b 49.9 ~b
132.3 ¢ 54.4 b
2.73 2.27
51.6 ~b 52.2 ~
49.9 ~ 53.1 ~
50.2 ~ 52.3 a
58.9 ~ 70.6 b
58.8 ¢ 77.9 b
1.57 2.52
3.80
3.56
3.52
3.54
3.12
0.199
1LC=low corn; H C = h i g h corn; H C F = h i g h corn a n d fat; H C F U = h i g h corn, fat a n d urea; H C F U G B - - high corn, fat, urea a n d corn gluten a n d blood meals. 2Standard error. '~Means in a row without a c o m m o n superscript (a, b, c) differ ( P < 0 . 0 5 ) . steers consumed steers. Organic matter treatments
less (P < 0.05) total DM than HC, HCF, HCFU
intake was lower (P < 0.05) for control and LC than for other
(Table 3), and fecal excretion
(P > 0.05) among
and HCFUGB
treatments.
of organic matter
(OM)
was similar
Total tract digestion of OM for control, LC and
H C w a s s i m i l a r ( P > 0 . 0 5 ), b e i n g l o w e r ( P < 0 . 0 5 ) t h a n f o r H C F U , w h i l e d i g e s tion for HCF and HCFUGB was intermediate. As compared with the control
105
treatment, digestion of OM in g day- 1was not improved by the LC supplement but was increased ( P < 0.05) by all supplements containing the high level of corn as compared with control and LC. Neutral detergent fiber intake was higher (P < 0.05 ) for control than for HC, HCF, HCFU and HCFUGB; intake of NDF by steers receiving LC was greater (P < 0.05) than for HCF and HCFUGB. Rectal passage of NDF was similar among treatments (P>0.05). Total tract digestion of NDF was highest ( P < 0.05 ) for the control treatment and higher for LC, HCF, HCFU ( P < 0.05 ) and HCFUGB (P < 0.08) than for HC. Neutral detergent fiber digested in the total tract (g day -1 ) was highest for control steers and higher for LC than for HC, HCF and HCFUGB (P < 0.05). Nitrogen intake (Table 3) was highest for HCFUGB and higher for HCFU than for control, LC, HC and HCF treatments ( P < 0.05). Fecal nitrogen excretion was lower (P<0.05) for control and LC than for HC, HCF and HCFUGB. Total tract nitrogen disappearance (To) was higher for HCFU and HCFUGB than for LC, HC and HCF and higher for control than for HC and HCF treatments (P < 0.05 ). Total tract nitrogen disappearance (g day-1 ) was higher (P<0.05) for HCFU and HCFUGB than for other treatments and higher (P < 0.06) for HCFUGB than for HCFU. Particulate passage rate (Table 3 ) was similar ( P > 0.05 ) among treatments, but tended to be highest for LC, lowest for HCFUGB and intermediate for other groups.
Experiment 2. Performance Effects of treatment, period and the treatment-period interaction on daily gain were observed (P<0.05). Daily gain (Table 4) for all treatments was greater (P<0.05) in Period 1 (Day 1-42) than in Period 2 (Day 43-84). In Period 1, gain for control cattle was lower (P < 0.05 ) than for cattle given H CF and HCFUGB supplements. Gain values for LC, HC, HCF and HCFU were similar ( P > 0.05) and tended to be higher than gain for the control treatment TABLE4 D a i l y g a i n b y b e e f cattle g r a z i n g b e r m u d a g r a s s p a d d o c k s a n d s u p p l e m e n t e d w i t h c o n c e n t r a t e 1 Days
1-42 43-84
Treatment 2 Control
LC
HC
HCF
HCFU
HCFUGB
1.24 d3 0.01 a
1.40 def - 0.01 a
1.33 de 0.23 b
1.41 ef 0.26 b
1.36 def 0.39 bc
1.51 f 0.46 c
1 S t a n d a r d e r r o r = 0.061. 2 L C = l o w corn; H C = h i g h corn; H C F = h i g h c o r n a n d fat; H C F U = h i g h H C F U G B = h i g h c o r n , fat, u r e a a n d c o r n g l u t e n a n d blood m e a l s . 3 M e a n s w i t h o u t a c o m m o n s u p e r s c r i p t (a, b, c, d, e, f) differ ( P < 0 . 0 5 ) .
corn, f a t a n d urea;
106 and lower than gain with the HCFUGB supplement. In Period 2, no response in daily gain to the LC supplement was observed ( P > 0.05). Gain was, however, improved ( P < 0.05 ) by HC and HCF supplements as compared with control and LC treatments. Gain for HCFU was greater than for HC ( P < 0.05) and HCF (P<0.14), and gain for HCFUGB was greater (P<0.05) than for HC and HCF. Steers tended (P<0.08) to gain faster than heifers (0.82 vs. 0.78 kg day- 1). Interactions involving sex were not significant ( P > 0.15 ). During the entire 84-day trial, daily gain was 0.63, 0.70, 0.78, 0.84, 0.87 and 0.99 kg for control, LC, HC, HCF, HCFU and HCFUGB, respectively (standard error=0.032). Gain was highest for HCFUGB and higher for HCF and HCFU than for control and LC (P<0.05). Also, gain was higher (P<0.11) for HC than for LC and higher ( P < 0.18) for LC than for control. DISCUSSION Depressions in fiber digestion generally worsen as supplemental coacentrate rises, but when mixed diets are fed, effects of low-level concentrate supplementation are minor (Hoover, 1986). Jones et al. (1988) fed grain immediately before BER twice daily, whereas grain was given once daily, 3.5 h after the morning meal of BER, in the present study. Thus, the large amount of concentrate given may have caused substantial changes in ruminal pH, readily fermentable carbohydrate available for preferential usage by fiber-digesting microbes and inhibition of bacterial attachment to fiber (Hoover, 1986) after supplementation as compared with conditions with mixed diets or more frequent supplementation. However, the relative importance of microbial growth and digestion and the degree to which over time such conditions are changed by grain are not well understood. Grain supplementation, once daily, shortly after a period of forage consumption could depress continuing fiber digestion more than grain in mixed diets or grain given right before roughage. The latter might only delay the onset of digestion of newly ingested forage. In the present study, the delay in time after grain was offered before fiber digestion recovered to the rate of digestion before supplementation is unknown. Further, because many starch-fermenting microbes also digest fiber, proliferation after supplementing with a low level of grain before roughage feeding could conceivably enhance forage digestion. The space occupied by grain in the reticulo-rumen is less than that occupied by roughage (Hoover, 1986). Hence, if reticulo-ruminal digesta fill solely controlled intake, the LC supplement altered characteristics of reticulo-ruminal digesta that caused excitation of receptors sensing digesta quantity and/or physical characteristics (Grovum, 1986) at a lower level of digesta fill than in control steers. Thus, factors other than, or in conjunction with, reticulo-ruminal digesta fill seem to have regulated forage intake. To predict the retention of nitrogen by steers fed BER, the digestible energy
107
content of the forage should be considered (Stallcup et al., 1987). It has been suggested that available energy is more limiting to the performance of cattle consuming warm- rather than cool-season grasses {Stobbs et al., 1977; Stallcup et al., 1987). Conversely, increasing the postruminal amino acid supply in cattle consuming tropical forage has elevated performance, suggesting that nitrogen availability in tropical grasses limits performance (Flores et al., 1979; Kempton, 1982). Although these possibilities seem contradictory, both may be partially true. Increasing the readily fermentable substrate for ruminal microbes with tropical forage diets increases the microbial capture of ammonia and the flow of microbial protein to the intestines (Flores et al., 1979; Kellaway and Leibholz, 1983). Supplemental grain increased microbial protein synthesis with BER (Jones et al., 1988), possibly because of the low level and slow and prolonged release of readily fermentable or nonstructural carbohydrate in BER (Mertens and Loften, 1980). Therefore, inefficient utilization of tropical grass nitrogen and inadequate quantities of amino acids reaching the intestines may, in part, be caused by a ruminal imbalance of available nitrogen and energy (perhaps only at certain times after ingestion) leading to substantial nitrogen loss through ruminal ammonia absorption and urinary excretion of urea. Hence, as LC did not increase organic matter digested in Experiment 1, perhaps the trend for increased daily gain in Period 1 was because more microbial protein was synthesized and flowed to the small intestine, increasing the protein: energy ratio of absorbed products of digestion. Consumption of BER in Experiment 1 may have been decreased by LC to minimize deviation of the protein: energy ratio from host needs. The LC supplement did not affect daily gain in Period 2 in contrast to the change in Period 1, perhaps because forage in Period 2 was lower in nitrogen. Supplementation with LC in Period 2 may have accentuated a limitation of nitrogenous compounds for microbial growth and/or digestion. But a ruminal nitrogen deficiency does not always mean that nitrogenous compounds were first-limiting to animal performance and, in fact, low BER intake and digestion would lead to low energy status. Improved daily gain in Period 2 with the HC supplement was probably because of increased microbial production and host absorption and utilization of volatile fatty acids (Hoover, 1986) and ruminal escape of corn protein and starch. Increased host energy status with HC in Period 2, owing to low forage quality, may have minimized the depression in BER intake. Lack of improved performance with HC in Period 1 above LC, suggests that readily fermentable substrate with 0.25% body weight of corn facilitated efficient capture of nitrogen from forage degradation and/or that corn amino acids reaching the intestines did not coincide well with host needs. Increased fiber digestion (%) when fat was mixed with 66.67% of the corn in HC, suggests that fat allowed more grain to escape ruminal digestion (Glen
108 et al., 1977; Davenport et al., 1987) through slowed microbial attachment to fat-coated concentrate (Davenport et al., 1987 ) or altered physical behavior of coated particles. Though high levels of supplemental fat can increase ruminal digesta volume and dilution rate with a set level of feed intake {Czerkawski et al., 1975 ), steady particulate passage rate suggests that the effects of this low level of fat on ruminal digesta kinetics are unlikely. Similar performance for HCF and HC agrees with only a small trend for higher organic-matter digestion (g day -1) with HCF, a portion of which should involve intestinal fat disappearance. The corn-fat mix consisted of about the maximum level of fat (10% of the corn-fat mix) that could be used without experiencing handling or storage difficulties. However, higher levels, as have been used with protein supplements (Glen et al., 1977; Davenport et al., 1987), might increase protection. Calcium carbonate was included in the grain-fat mix to provide calcium for salt formation with fatty acids (Palmquist and Jenkins, 1980) to prevent adsorption to other feed particles or bacteria of fatty acids which might dislocate from grain. However, the level of added fat (about 1.9% of DM intake) should not greatly depress ruminal fiber digestion even if not mixed with grain (Palmquist and Jenkins, 1980). Fecal excretion of Ca soaps can rise when fat is added to ruminant diets also (Palmquist and Jenkins, 1980). Small changes in intake, digestion and performance in Period 1 when urea was supplemented, suggest that organic matter being fermented in the rumen with 0.75% body weight of supplemental corn did not induce an ammonia insufficiency. Conversely, low forage nitrogen in Period 2, leading to low ruminal ammonia levels, could have allowed urea to increase performance, through increased ruminal microbial protein synthesis and outflow and/or increased ruminal forage digestion and intake (Kempton, 1982 ). Higher cereal grain levels increase chances of ruminal ammonia deficiencies that limit fiber degradation (Chase and Hibberd, 1987). The major effect of supplementing with corn gluten and blood meals in the first study was increased uptake of nitrogen. Thus, increased performance with the protein meals in Experiment 2 appears to be a response to greater intestinal amino-acid uptake and not altered forage intake. Increasing amino-acid absorption can increase ruminant performance with or without change in forage intake (Stobbs et al., 1977; Flores et al., 1979; Kellaway and Leibholz, 1983). As compared with Period 2, the large increase in gain in Period 1 when aminoacid absorption was increased by supplementation with protein meals may have been facilitated by high forage quality and host energy status. Effects on performance of corn gluten and blood meals without some of the other supplement ingredients may have differed from those with HCFUGB. Although supplementation with the protein meals should increase amino acids absorbed, as proposed for LC, the extent of increase for one without the other might be less than with both. The protein meals provide less fermentable sub-
109
strate to increase microbial growth than corn. Because the energy demand for gain appeared high in Period 2, supplementation with the protein meals without some of the other feeds to improve host energy status may not have improved gain to the degree noted for HCFUGB. Increased propionate and glucose supplies with supplemental grain might spare amino acids from host degradation to increase amino acids used for tissue accretion and improve efficiency of acetate metabolism (Black et al., 1987a, b). Similarly, urea supplementation in Period 2 could have elevated microbial use of amino acids for net growth as opposed to breakdown for energy and overcome a ruminal deficiency of ammonia, which supplementation with the protein meals might not. Thus, the potential for the efficient use of supplemental ruminal escape protein seems greatest when adequate nutrients are available to ruminal microbes and use of amino acids other than for tissue accretion is minimized (Kempton, 1982; Black et al., 1987a, b). Average daily supplement costs for the 84-day grazing experiment were US$ 0.08, 0.24, 0.40, 0.41 and 0.50 per animal. Using gain for the 84-day experiment, costs of additional gain (kg) above the control treatment were US$1.20, 1.54, 1.90, 1.66 and 1.37 for LC, HC, HCF, HCFU and HCFUGB, respectively. On this basis, therefore, LC was most economical, followed by HCFUGB. Fat inclusion greatly increased supplement cost and did not markedly improve gain; therefore, omission of fat would lessen costs of HCFU and HCFUGB. Low cost makes urea addition a consideration, when nitrogen adequacy of forage is questionable and when a mixed supplement is used. Because of changes in forage intake, grain supplementation should increase animals per unit of land required to achieve similar herbage availability. As gain increases with supplementation, time to reach end-weight declines or weight after a set period of grazing increases. ACKNOWLEDGEMENTS
Appreciationisexpressedtothe Arkansas BeefCouncilforpa~ialfinancial suppo~.
REFERENCES Akin, D.E., 1986. Chemical and biological structure in plants as related to microbial degradation of forage cell walls. In: L.P. Milligan, W.L. Grovum and A. Dobson (Editors), Control of Digestion and Metabolism in Ruminants. Prentice Hall, Englewood Cliffs, NJ, pp. 196-223. A.O.A.C., 1984. Official Methods of Analysis, 14th edn., Association of Official Analytical Chemists, Washington, DC, pp. 152-157. Black, J.L., Gill, M., Beever, D.E., Thornley, J.H.M. and Oldham, J.D., 1987a. Simulation of the metabolism of absorbed energy-yielding nutrients in young sheep: Efficiency of utilization of acetate. J. Nutr., 117: 105-115.
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Black, J.L., Gill, M., Thornley, J.H.M., Beever, D.E. and Oldham, J.D., 1987b. Simulation of the metabolism of absorbed energy-yielding nutrients in young sheep: Efficiency of utilization of lipid and amino acid. J. Nutr., 117: 116-128. Chase Jr., C.C. and Hibberd, C.A., 1987. Utilization of low-quality native grass hay by beef cows fed increasing quantities of corn grain. J. Anita. Sci., 65: 557-566. Czerkawski, J.W., Christie, W.W., Breckenridge, G. and Hunter, L., 1975. Changes in the rumen metabolism of sheep given increasing amounts of linseed oil in their diet. Br. J. Nutr., 34: 2544. Davenport, G.M., Boling, J.A., Gay, N. and Bunting, L.D., 1987. Effect of soybean lipid on growth and ruminal nitrogen metabolism in cattle fed soybean meal or ground whole soybeans. J. Anita. Sci., 65: 1680-1689. Ellis, W.C., Lascano, C., Teeter, R. and Owens, F.N., 1982. Solute and particle flow marker. In: F.N. Owens (Editor), Protein Requirements for Cattle: Symposium. Okla. Agric. Exp. Stn., Misc. Publ., No. 109, pp. 37-56. Flores, J.F., Stobbs, T.H. and Minson, D.J., 1979. The influence of the legume Leucaena leucocephala and formal-casein on the production and composition of milk from grazing cows. J. Agric. Sci., 92: 351-357. Glen, B.P., Ely, D.G. and Boling, J.A., 1977. Nitrogen metabolism in lambs fed lipid-coated protein. J. Anim. Sci., 46: 871-877. Goering, H.K. and van Soest, P.J., 1970. Forage Fiber Analyses. Apparatus, Reagents, Procedures and Some Applications, A.R.S., U.S.D.A. Agricultural Handbook No. 379, Washington, DC, pp. 1-20. Goetsch, A.L. and Galyean, M.L., 1983. Ruthenium phenanthroline, dysprosium and ytterbium as particulate markers in beef steers fed an all-alfalfa hay diet. Nutr. Rep. Int., 27: 171. Grovum, W.L., 1986. A new look at what is controlling food intake. In: F.N. Owens (Editor), Proceedings: Feed Intake by Beef Cattle. Okla. Agric. Exp. Stn., Misc. Pubi., No. 121, pp. 140. Harfoot, C.G., Crouchman, M.L., Noble, R.C. and Moore, J.H., 1974. Competition between food particles and rumen bacteria in the uptake of long-chain fatty acids and triglycerides. J. Appl. Bact., 37: 633-641. Hoover, W.H., 1986. Chemical factors involved in ruminal fiber digestion. J. Dairy Sci., 69: 27552766. Jones, A.L., Goetsch, A.L., Stokes, S.R. and Colberg, M., 1988. Intake and digestion in cattle fed warm- or cool-season grass hay with or without supplemental grain. J. Anim. Sci., 66: 194-203. Kellaway, R.C. and Leibholz, J., 1983. Effects of nitrogen supplements on intake and utilization of low-quality forages. World Anim. Rev., 48: 33-37. Kempton, T.J., 1982. Role of feed supplements in the utilisation of low protein roughage diets by sheep. World Rev. Anim. Prod., 18: 7-14. Mertens, D.R. and Loften, J.R., 1980. The effect of starch on forage fiber digestion kinetics in vitro. J. Dairy Sci., 63: 1437-1466. Palmquist, D.L. and Jenkins, D.L., 1980. Fat in lactation ratios. Rev. J. Dairy Sci., 63: 1-14. Stallcup, O.T., Kreider, D.L., Johnson, Z.B. and Davis, G.V., 1987. Apparent digestibility of nitrogen and nitrogen retention of forages fed to steers in metabolism stalls. J. Anim. Sci., 65: 1690-1699. Stobbs, T.H., Minson, D.J. and McLeod, M.N., 1977. The response of dairy cows grazing a nitrogen fertilized grass pasture to a supplement of protected casein. J. Agric. Sci., 89: 137-141. Van Keulen, J. and Young, B.A., 1977. Evaluation of acid-insoluble ash as a natural marker in ruminant digestibility studies. J. Anim. Sci., 44: 282-287.