Substitution of neutral detergent fiber from forage with neutral detergent fiber from by-products in the diets of lactating cows.

Four lactating dairy cows that were ruminally and duodenally cannulated were used in an experiment with a 4 x 4 Latin square design to determine the effects of the substitution of neutral detergent fiber (NDF) from forage with NDF from wheat middlings, corn gluten feed, or a blend of distillers dried grains and hominy. Dietary crude protein and NDF averaged 18 and 31%, respectively, for the diet with 71.2% of the NDF from forage (control diet) and for diets with 55% of the NDF from forage (by-product diets). The substitution of NDF from these by-products for forage NDF did not affect dry matter intake (20.1 kg/d) or digestibility of organic matter. Total tract digestibility of acid detergent fiber was lower for cows fed the diet containing a blend of distillers dried grains and hominy than for cows fed the diet containing corn gluten feed. Microbial crude protein synthesis, milk production (23.9 kg/d), and milk fat percentage were similar for all cows, regardless of diet. Cows fed the diets containing wheat middlings or a blend of distillers dried grains and hominy had reduced ruminal pH compared with that of cows fed the diet containing corn gluten feed or the control diet. Diets containing 55% of total NDF from forage with 31% of total NDF from corn gluten feed, wheat middlings, or a blend of distillers dried grains and hominy can supply sufficient effective fiber to maintain normal ruminal function.

Balancing carbohydrates and proteins for optimum rumen microbial yield.

Establishing conditions under which rumen fermentation will be optimized requires an understanding of the nutrient requirements of the mixed microbial population. The major nutrients required by rumen microbes are carbohydrates and proteins, but the most suitable sources and quantities needed to support maximum growth have not been determined. Digestion of proteins results in the production of peptides, which can accumulate in the rumen. Peptides are further hydrolyzed to amino acids, some of which are deaminated, producing ammonia. Although peptides, amino acids, and ammonia all may individually serve as sources of N for various microbes, the total population achieves the highest growth rate on mixtures of all three sources. In a somewhat analogous manner, carbohydrates are digested by exoenzymes to oligosaccharides that are available for crossfeeding by the mixed microbial population. Based on data from both in vitro and in vivo studies, there is general agreement that rate of digestion of carbohydrates is the major factor controlling the energy available for microbial growth; in addition, rate of digestion of total carbohydrate is directly related to proportion of starches, pectins, and sugars. Proteins affect both total fermentation and production of microbial DM per unit of carbohydrate fermented. It appears that the quantity of ruminally available protein needed to optimize microbial growth may, under some conditions, be as high as 14 to 15% of diet DM.

Ruminal digestion and microbial utilization of diets varying in type of carbohydrate and protein.

Three ruminally and duodenally cannulated, lactating Holstein cows were used in a 3 x 3 Latin square experiment to study the effects of differing levels of nonstructural carbohydrate and degradable intake protein on ruminal digestibility and microbial protein production. Three diets were formulated to contain 1) 38 and 13.2%, 2) 31 and 11.8%, and 3) 24 and 9% nonstructural carbohydrate and degradable intake protein as percentages of the DM, respectively. Dry matter intakes were similar for all diets (21.9, 21.1, and 18.3 kg/d for diets 1, 2, and 3, respectively). Likewise, microbial efficiency, as estimated from purine analysis, was unaffected by diet and averaged 24 g of microbial N/kg of OM digested for all treatments. Ruminal digestion of OM averaged 66.6, 65.1, and 55.7% for diets 1, 2, and 3, respectively, resulting in lower microbial N flow per day for diet 3 (317, 333, and 202 g, respectively). Digestion of nonstructural carbohydrate and CP followed similar trends as did OM digestion, whereas NDF digestion remained similar across all diets. These results indicate that nonstructural carbohydrate greater than 24% and ruminally degradable protein greater than 9% of DM will enhance microbial protein flow from the rumen.

Impact of carbohydrate and protein levels on bacterial metabolism in continuous culture.

Diets formulated with three levels of nonstructural carbohydrate (54, 37, and 25% of DM), with various concentrations of degradable intake protein ranging from 19 to 4% of DM, were fermented in continuous cultures to ascertain the effects of ratio of nonstructural carbohydrate to degradable intake protein on bacterial metabolism. Fermenters were maintained at a dilution rate of 12%/h with a solids retention time of 24 h. Regardless of degradable intake protein level, bacterial efficiency (g of bacterial N/kg of DM digested) and VFA production (mM/d) were lower for diets with 25% nonstructural carbohydrate compared with the 37 and 54% nonstructural carbohydrate diets. In response to widening nonstructural carbohydrate:degradable intake protein ratios, bacterial efficiencies at all nonstructural carbohydrate levels declined quadratically from 34.2 to 10.3 with the lowest efficiencies on the 25% nonstructural carbohydrate diets. Bacterial protein production, DM digestion, NDF digestion, and VFA production (mM/d) increased linearly in response to dietary protein. The enhanced NDF and DM digestion, VFA production, and bacterial efficiencies observed with the narrower ratios of nonstructural carbohydrate:degradable intake protein support the theory that level of both degradable intake protein and nonstructural carbohydrate should be considered in order to enhance ruminal digestion and bacterial N production.

Effects of fish meals on rumen bacterial fermentation in continuous culture.

Effects of various forms of fish meal on microbial metabolism were investigated in continuous cultures of rumen contents. Five diets were formulated to contain 12% ruminally degradable protein and 47 to 48% nonstructural carbohydrate. Soybean meal was the major protein source in the control diet, whereas in the other four diets, various fish meals were substituted for 6% of total diet DM. Fish meals were: fish meal containing 34.4% FFA, fish meal containing 34.4% FFA with CaCl2 added, fish meal containing 65.6% FFA, and fish meal defatted using 1:1 ethanol:ether extraction. The five treatments were fermented with pH either held constant at 6.2 or not controlled. When pH was maintained at 6.2, the inclusion of any fish meal except defatted fish meal reduced the acetate:propionate ratio, decreased protein digestion, and reduced microbial N produced/per kilogram DM digested when compared with the soybean control. When not controlled, pH decreased after feeding to 6.0 or lower. Under these conditions, the soybean control had a lower acetate:propionate ratio and lower NDF digestion than all diets containing fish meal. In this study, oil-containing fish meal affected microbial metabolism more negatively when the fermentation pH was held at 6.2 than when the pH was 6.0 or lower.

Feed intake and digestion by beef cows fed prairie hay with different levels of soybean meal and receiving post-ruminal administration of antibiotics.

Six cannulated beef cows (one Angus, two Hereford and three Angus x Hereford; 405 kg) were used in a 6 x 6 latin square experiment with a 2 x 3 factorial arrangement of treatments. Prairie hay (.77% N, 73% neutral detergent fiber [NDF] and 7% acid detergent lignin) was fed ad libitum from d 1 through 14 and at 90% of ad libitum intake from d 15 through 21 during digesta collection. Periods lasted 21 d. Soybean meal (SBM) was offered at 0 (control, C), .12 (low, L) or .24% of body weight (high, H; dry matter basis). Cows received daily doses of an antibiotic mixture (1 g neomycin and .125 g bacitracin) or saline in the duodenum. Prairie hay dry matter (DM) intake increased (P less than .05) linearly with SBM supplementation, being 25 and 40% greater for L and H than for C, respectively. Ruminal fluid concentrations of NH3-N and total volatile fatty acids increased (P less than .05) linearly as SBM was added to the diet. Ruminal fluid dilution rate increased linearly and particulate passage rate increased (P less than .05) quadratically with increasing SBM. True ruminal digestibilities of organic matter, NDF and N increased (P less than .10) quadratically with increasing SBM (organic matter; 50.3, 57.9 and 58.3%; NDF: 54.7, 60.4 and 59.8%; N: 17.5, 45.1 and 51.4% for C, L and H, respectively). Main effects of antibiotic administration were not significant. Increases in DM intake when SBM was given were large compared with the small elevations in ruminal digestion, implying that metabolic regulation was modifying intake of low-quality forage.

Feed intake and digestion by beef steers consuming and receiving ruminal insertions of prairie hay differing in level and particle size.

A 5 X 5 Latin square design involving five cannulated beef steers (342 and 358 kg avg initial and final body weights, respectively) fed prairie hay (76.7% neutral detergent fiber, 5.7% acid detergent lignin and .85% N) was conducted to evaluate effects on feed intake and nutrient digestion of variations in physical characteristics of ruminal digesta achieved by ruminal insertion of different amounts of prairie hay differing in particle size. Steers were fed hay ad libitum in two equal meals (0800 and 2000). At 1200, four of the steers received manual, ruminal insertions of ground hay. Fine hay (F) was ground through a screen with 2-mm openings (.39 mm mean particle size), whereas coarse hay (C) was ground through a screen with 2.54-cm openings (4.46 mm mean particle size). Amounts of hay inserted were .2 (low, L) or .4% (high, H of initial body weight of individual steers. Ruminal hay insertions comprised 18% of total dry matter (DM) intake for L and 34 and 37% for HF and HC, respectively. Fed hay consumption decreased (P less than .05) with hay insertion and was lower for H than L; total DM intake was not influenced by treatment (P greater than .10). Ruminal NH3-N concentrations and ruminal organic matter digestion was greater (P less than .05) with ruminal hay insertion than without and with H than with L (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Intake and digestion in cattle fed warm- or cool-season grass hay with or without supplemental grain.

Intake and digestion in cattle fed warm- or cool-season grass hay with or without low-level grain supplementation were studied with a 2 x 2 factorial arrangement of treatments in two 4 x 4 Latin square experiments. In Exp. 1, four cannulated beef cows (396 kg) were given Bermuda grass (B) or orchard grass (OG) hay at 1.5% body weight (BW) with 0 or .3% BW of ground corn (C; dry matter). Bermuda grass contained 12.1% crude protein, 79.3% neutral detergent fiber (NDF) and 5.5% acid detergent lignin (ADL); OG contained 10.6% crude protein, 82.4% NDF and 8.1% ADL. An interaction (P less than .07) between forage type and C supplementation was noted for microbial N entering the duodenum; C supplementation had a positive effect with B (30% increase) and little effect with OG. Corn supplementation did not affect ruminal NDF digestion with B, but it elicited an increase with OG (interaction, P less than .05; means were 60.7, 60.1, 61.5 and 66.3%). In the second experiment, growing dairy steers (196 kg) were given ad libitum access to similar B or OG hays and were fed 0 or .5% BW of C. Dry matter (DM) intake was lower for OG than for B (P less than .05) and was lower with than without C (P less than .06; means were 2.76, 2.56, 2.53 and 2.30% BW for B, BC, OG and OGC, respectively). Total tract organic matter digestion (%) was higher for OG than for B (P less than .10) and was higher with than without C (means were 54.7, 61.5, 60.4 and 65.3%). In conclusion, chemical constituents such as NDF may govern differences in intake between warm- and cool-season grasses, but physical attributes of the forages appear more important to digestion.

Effects of supplemental Bermuda grass hay or corn on intake, digestion and performance of cattle consuming endophyte-infected fescue.

Effects of supplemental Bermuda grass hay (BG) or ground corn on intake, digestion and performance of cattle consuming endophyte-infected fescue (I) were studied. In Exp. 1, a Latin square study, five growing Holstein steers (158.1 kg) consumed I ad libitum and were offered 0, .3, .6, .9 or 1.2% body weight (BW) of BG daily. Total dry matter (DM) intake rose linearly (P less than .05) with increasing BG, although intake was numerically similar with .6, .9 and 1.2% BW of BG. Digestibility was constant with diet (P greater than .10). Six growing Holstein steers used in Exp. 2, a Latin square with a 2 x 3 factorial arrangement of treatments, ingested I or noninfected (NI) fescue hay ad libitum with 0, .5 or 1.0% BW of ground corn. Total DM intake increased linearly as the level of corn rose (P less than .05). Total intake with I increased more with the first than with the second addition of corn, and the opposite occurred with NI (interaction between fescue infection and the quadratic effect of corn level, P less than .10). Organic matter digested (g/d) was greater for NI than for I and rose linearly with increasing corn ingestion (P less than .05). Ninety-six crossbred beef heifers and steers (184.2 kg avg initial live weight) were used in a 77-d fall grazing experiment (Exp. 3) with a 2 x 3 factorial treatment arrangement. Cattle grazed I or NI paddocks and were given no supplement or .34% BW of BG or .65% BW of ground corn on a daily basis (DM).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of frequency of offering and type of supplemental forage on intake and digestion in calves consuming endophyte-infected fescue hay.

Two experiments were conducted to determine the effects of frequency of offering and type of supplemental forage on intake and digestion in calves consuming endophyte-infected fescue hay (I). In Exp. 1, five Holstein steers, averaging 128 kg body weight (BW), were used in a 5 X 5 Latin square experiment. All steers were given free access to I in the afternoon. Morning meals consisted of 1) ad libitum access to I daily (control), 2) .5% BW of Bermuda-grass hay (BG) daily, 3) 1.0% BW of BG every 2nd d, 4) 1.5% BW of BG every 3rd d and 5) 2.0% BW of BG every 4th d. Steers receiving BG consumed less (P less than .01) I and more (P less than .01) total dry matter (DM) than did steers given I alone. Within treatment, I intake was similar (P greater than .10) among days of the feeding cycle without BG. Organic matter (OM) digestion was lower (P less than .05) with than without BG. In Exp. 2, 12 beef calves (Angus and Hereford X Angus; 6 mo of age, 155 kg initial BW) were used in a completely randomized-design experiment. Calves were given ad libitum access to I daily (control) or to BG or wheat hay (WH) on d 1 and I the following 3 d. Hay (I, BG or WH) intake d 1 of the feeding cycle was higher for BG and WH than for the control treatment (16 and 45%, respectively) and higher for WH than BG (25%; P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary forage proportion on digestive function in maintenance-fed beef cows. 3. Bermudagrass and clover hays.

Five crossbred beef cows (Hereford X Angus, 438 kg), cannulated in the rumen and duodenum, were used in a Latin square experiment to determine the effects of dietary proportions of bermudagrass (B) and clover (C) hays (0: 1, .25: .75, .5: .5, .75: .25 and 1: 0) on digestive function. Feed intake was 85% of ad libitum intake of B alone (1.35% of body weight). Bermudagrass contained 1.88% nitrogen (N), 79.6% neutral detergent fibre (NDF) and 5.2% acid detergent lignin (ADL), and C contained 2.30% N, 55.3% NDF and 6.3% ADL. Molar proportion of acetic increased linearly while propionic acid moved in the opposite direction as B replaced C (P less than .05). Mean particle size of duodenal digesta increased linearly (P less than .05) as B increased, but specific gravity of particles was constant (P greater than .10). Fluid passage rate decreased while volume increased linearly with increasing B (P less than .05) so that ruminal fluid outflow rate increased quadratically (P less than .10). Particulate passage rate ranged from 3.0 to 3.4% h. Apparent ruminal organic matter (OM) digestion was 69.0, 54.0, 53.0, 49.1 and 49.7% for 0, 25, 50, 75 and 100% B, respectively, decreasing quadratically as B rose (P less than .05). Postruminal OM digestibilities as percentages of intake and available OM changed quadratically (P less than .05) as dietary B increased, causing total tract OM digestion to decrease linearly (P less than .05; 73.8, 66.4, 63.1, 60.3 and 58.2% for 0, 25, 50, 75 and 100% B diets, respectively). Duodenal microbial-N flow increased quadratically with increasing B (P less than .05), being 45, 108, 103, 105 and 101 g/d, and microbial growth efficiency increased quadratically as well (P less than .05). True ruminal N disappearance ranged from 69.0 to 79.4% and was not affected by diet (P greater than .10). Ruminal digestibilities of fibre fractions were similar to OM. Little digestive function benefit was achieved by mixing warm season grass and legume hays in diets of maintenance-fed beef cows.

Effects of dietary forage proportion on digestive function in maintenance-fed beef cows. Fescue and bermudagrass hays.

Five crossbred beef cows (Hereford x Angus, 428 kg), cannulated in the rumen and duodenum, were used in a Latin square experiment to determine the effects of dietary proportions of fescue (F) and bermudagrass (B) hays (0:1, .25: .75, .5:.5, .75: .25 and 1:0) on digestive function. Feed intake was 85% of ad libitum intake of F alone (1.04% of body weight). Fescue contained 1.19% nitrogen (N), 74.8% neutral detergent fibre (NDF) and 6.3% acid detergent lignin (ADL), and B contained 1.99% N, 84.5% NDF and 6.1% ADL. Ruminal ammonia-N decreased and four- and five-carbon fatty acid concentrations increased linearly (P less than .05) with increasing F. Mean particle size of duodenal digesta was not affected by F level, but specific gravity of duodenal particles changed quadratically (P less than .05) as F rose, being greatest with 25 and 50% F. Ruminal fluid volume was constant, but dilution rate increased linearly (P less than .05) as F increased. Passage rate of B was faster than that of F in mixed diets. Organic matter (OM) flow and digestibilities, true ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance and microbial efficiency were not affected (P greater than .10) by F. True ruminal N disappearance ranged from 73 to 78%, and microbial growth efficiency was between 18 and 22 g microbial N/kg OM fermented. Ruminal digestibilities of NDF, acid detergent fibre (ADF), cellulose and hemicellulose decreased linearly (P less than .05) as F increased, being 68.2, 64.9, 65.6, 61.2 and 61.6% for NDF, 58.9, 54.7, 56.2, 53.3 and 53.2% for ADF, 64.7, 61.3, 62.1, 59.0 and 59.1% for cellulose, and 76.1, 74.4, 75.4, 70.1 and 72.2% for hemicellulose for 0, 25, 50, 75 and 100% F, respectively. Digestive function in beef cows fed mixed F-B diets at a low level of intake related directly to dietary forage proportions and digestive characteristics when forages were fed alone.

Intake, digestion, passage rate and serum prolactin in growing dairy steers fed endophyte-infected fescue with noninfected fescue, clover or wheat straw.

Growing Holstein steers were used in two Latin-square experiments to determine the effects of supplementation of endophyte-infected fescue hay diets with other forages on intake, digestion, passage rate and serum prolactin concentration. In Exp. 1, five steers (average weight of 186 kg) were fed ad libitum amounts of endophyte-infected and noninfected fescue hays (I and NI, respectively) of similar quality in 0:1, 1:3, 1:1, 3:1 and 1:0 proportions. Total dry matter (DM) intake as a percentage of body weight (BW) linearly decreased .0055% for each 1% increase in dietary I (P less than .05). Dry matter intakes with 100% I and 100% NI diets were 2.13 and 2.72% of BW, respectively. Total tract digestion of neutral detergent fiber (NDF) increased linearly (P less than .05) with increasing I (66.0, 65.9, 66.3, 68.1 and 69.6%). Ruminal passage rate of particulates changed linearly (P less than .05) and quadratically (P less than .10) as I in the diet increased (3.5, 3.4, 2.6, 2.8 and 2.8%/h), while serum prolactin concentration and rectal temperature decreased linearly (P less than .05). In Exp. 2, four steers (average weight of 137 kg) were given ad libitum amounts of wheat straw (WS) or .73% of BW of clover hay (C) at 0800 and free access to either I or NI at 1600. Total intake as a percentage of BW was greatest for C with NI (3.04), intermediate for WS with NI (2.70) and lowest for C with I (2.30) and WS with I (2.23; P less than .05). Fescue intake (percentage of BW) was lowest (P less than .05) for C with I (1.56) and higher (P less than .05) for WS with NI (2.63) than WS with I (2.12); fescue intake for C with NI (2.33) was intermediate (P greater than .10) to WS with NI and WS with I. The results are interpreted to indicate that increasing the dietary level of I depressed intake linearly and markedly. Intake of diets high in I appears to be lower than can be explained only by ruminal-fill factors. When animals that are consuming basal I diets are provided access to nontoxic, high-quality forage, changes in intake may differ from those with basal diets of nontoxic forage.

Effects of offering different amounts and types of supplemental feeds to growing dairy steers fed endophyte-infected fescue hay ad libitum on intake, digestion, passage rate and serum prolactin concentration.

Ten Holstein steers (141 kg) were used in two 5 X 5 Latin-square experiments conducted simultaneously to determine the effects of offering different levels and types of feeds with endophyte-infected fescue given ad libitum. In Exp. 1, steers were given ad libitum access to infected fescue hay in the afternoon; in the morning fescue was given ad libitum (basal) or bermudagrass or clover hays were fed at .5 or 1.0% of body weight (BW). Supplementation did not affect total dry matter intake (P greater than .10), but supplementation at 1.0% of BW yielded total intake greater than supplementation at .5% of BW (P less than .05). Supplementation did not change digestibilities of dry or organic matter (P greater than .10). Particulate passage rate was greater (P less than .10) with supplementation at 1.0 than at .5% of BW, and increasing the level of supplementation from .5 to 1.0% of BW affected fluid passage rate positively with clover but negatively with bermudagrass (interaction, P less than .05). Serum prolactin increased (P less than .05) with all supplementation treatments, although no differences were observed between supplement type-supplementation level combinations (P greater than .10). Ground corn and wheat hay were supplements in Exp. 2. Total intake of dry matter was greater with supplements provided at 1.0 rather than at .5% of BW and for corn rather than wheat hay (P less than .05). Neutral detergent fiber digestion (percent of intake and grams per day) rose when wheat hay was offered at 1.0 vs .5% of BW but declined when the level of supplemental corn increased from .5 to 1.0% of BW (interaction, P less than .05). There were no differences among diets in particulate and fluid passage rates and serum prolactin concentration. Supplementation with nontoxic forage of a basal diet of infected fescue yielded intake substitution when forage was offered at .5% of BW, although incomplete substitution occurred with 1.0% of BW of supplemental forage such that total intake increased as compared to the lower level of supplementation.