Effects of energy, mineral supplementation, or both, in combination with monensin on performance of steers grazing winter wheat pasture.

A 2-yr study was conducted during the 2004 to 2005 (YR1) and 2005 to 2006 (YR2) winter wheat grazing seasons to determine the effects of supplementation strategies and delivery methods on supplement intake and growth performance of grazing steers (YR1, n = 253, initial BW 255 +/- 25 kg; YR2, n = 116, initial BW 287 +/- 14 kg). The 5 treatments were as follows: 1) negative control (NC), no supplemental nutrients; 2) free-choice, nonmedicated mineral (MIN); 3) free-choice, medicated mineral with 1,785 mg of monensin/kg of mineral mixture (RMIN); 4) RMIN and soybean hulls (SH-RMIN); and 5) a soybean hull-based energy supplement containing 165 mg of monensin/kg (GRNGOLD). Energy supplements were hand-fed on alternate days (average daily intake = 0.91 kg/steer). Inclusion of monensin in the free-choice mineral mixture decreased intake of the mineral mixture by 63% in YR1 and 55% in YR2 when no other supplement was offered. Consumption of RMIN provided from 129 to 161 mg of monensin/steer on average, whereas GRNGOLD provided 150 mg of monensin/d. Compared with NC, MIN did not affect ADG in YR1 (P = 0.38) but increased (P = 0.01) ADG by 0.22 kg/steer in YR2. Conversely, ADG of RMIN steers was greater (P = 0.03) than that of MIN steers during YR1 (0.72 vs. 0.55 kg/steer) but not different (P = 0.35) in YR2. Providing supplemental energy increased ADG by 0.13 kg/steer (0.85 vs. 0.72 +/- 0.053) in YR1 compared with RMIN, but no increase in ADG was observed in YR2. No difference (P > 0.24) was observed in ADG between SH-RMIN and GRNGOLD in either year. Conversion of the energy supplements (kg of as-fed supplement divided by kg of additional ADG) was excellent in YR1, resulting in 1 kg of BW gain for each 3.1 kg of supplement consumed. However, due to smaller increases in ADG with the energy and monensin supplements in YR2, supplement conversion for YR2 averaged 17.6. The absence of a difference (P > 0.24) in ADG between steers that received SH-RMIN and GRNGOLD suggests that the method of delivery (separate packages vs. a single package) for energy, monensin, and mineral supplementation is not important.

Interactions between supplement energy source and tall fescue hay maturity on forage utilization by beef steers.

This experiment was conducted to determine the effects of tall fescue hay maturity on intake, digestion, and ruminal fermentation responses to different supplemental energy sources fed to beef steers. Twelve ruminally cannulated, crossbred steers (initial BW = 228 +/- 21 kg) were used in a split-plot experiment with a 3 x 4 factorial treatment arrangement. Steers were assigned randomly to three supplement treatments: 1) no supplement, 2) pelleted soybean hulls, or 3) coarse cracked corn. The second treatment factor was fescue hay maturity: 1) vegetative (VEG), 2) boot-stage (BOOT), 3) heading-stage (HEAD), and 4) mature (MAT). Supplements were fed once daily at 0.67% of BW (OM basis) and tall fescue hay was offered once daily at 150% of average intake. Supplement type x forage maturity interactions were not detected (P > or = 0.25) for forage, total, or digestible OM intake, which generally decreased (P < 0.01) with advancing forage maturity. Supplementation decreased (P < 0.01) forage and increased (P < 0.01) total OM intake. Supplement type had no effect (P = 0.56) on substitution ratio (unit change in forage intake per unit of supplement intake). Digestible OM intake was increased (P < 0.01) by supplementation and was greater (P = 0.05) with soybean hulls than with corn. Supplement type x forage maturity interactions (P < or = 0.10) were observed for OM and NDF digestibilities and N retention. Increases in digestibility with soybean hulls relative to corn were greater and supplementation elicited greater increases in N retention with more mature forages. Compared with soybean hulls, corn supplementation resulted in greater (P < 0.01) negative associative effects on OM digestibility. Supplementation did not affect (P > or = 0.10) ruminal pH, total VFA concentrations, or acetate:propionate ratio. Corn supplementation decreased (P < or = 0.07) ruminal NH3-N concentrations compared with control and soybean hulls; however, decreases in ruminal NH3-N concentrations were not consistent with the presence of negative associative effects. Thus, mechanisms not involving ruminal pH or NH3-N concentration seem responsible for negative associative effects observed with corn supplementation. Within the range of forage quality in this study, increases in digestible OM intake from starch- or fiber-based supplements were independent of forage maturity. When fed at similar levels of OM, soybean hull supplementation provided an average of 6% greater digestible OM intake than corn supplementation.

Effect of supplemental nutrient source on heifer growth and reproductive performance, and on utilization of corn silage-based diets by beef steers.

Two experiments were conducted to determine effects of oilseeds or soybean hulls on growth and reproductive performance of heifers and utilization of corn silage diets by growing beef cattle. In Exp. 1, 96 beef heifers (249 kg of BW) were used in a randomized complete block design. Treatments were as follows: 1) corn and soybean meal (CON) at 56% of the DMI; 2) whole linted cottonseed at 15% of the DMI (COT); 3) whole raw soybeans at 15% of the DMI (SB); or 4) pelleted soyhulls at 30% of the DMI (SH). Diets were formulated to be isonitrogenous (13.8% CP) and fed to achieve target weights equal to 65% of expected mature BW at the time of AI. Estrus was synchronized and heifers were inseminated by AI in response to detected estrus. Because the energy value for SH was underestimated, cumulative ADG for SH (1.03 kg/d) was greater (P < or = 0.03) than for CON (0.89 kg/d), COT (0.87 kg/d), or SB (0.86 kg/d). Treatment did not affect (P > 0.10) the proportion of pubertal heifers at the beginning of the breeding season: CON (60%), COT (53%), SB (69%), SH (71%), or first-service conception rates: CON (37%); COT (38%); SB (57%); SH (42%). In Exp. 2, crossbred steers (387 kg) were used in a 6 x 6 Latin square design to evaluate the effects of supplemental nutrient source on utilization of corn silage diets. Treatments included diets used in Exp. 1, plus a negative control (soybean meal at 10% of the DMI; SIL) and whole raw soybeans at 25% of the DMI (SB25). Diets were formulated to be isonitrogenous (13.8% CP) except SB25 (17% CP), and were fed twice daily at 1.8 x NEm. Oilseed inclusion decreased (P < 0.10) acetate:propionate ratios and (P < 0.10) apparent ruminal OM and ruminal and total tract NDF digestibilities. The CON and SH diets had the greatest (P < 0.10) total-tract OM digestibilities. Microbial efficiencies were greatest (P < 0.10), and long chain fatty acid flow to the duodenum increased (P < 0.10) with oilseeds. Biohydrogenation averaged 90.4% and increased slightly (P < 0.10) when oilseeds were added to the diet. Adding oilseeds or soybean hulls to corn silage-based diets did not affect reproductive performance of heifers. Although oilseed additions increased total fatty acid flow to the duodenum, a high degree of biohydrogenation occurred, greatly increasing C18:0, with only marginal increases in unsaturated fatty acid flow. Depending on diet and feeding conditions, inclusion of whole oilseeds may not be an effective means of increasing linoleic acid supply for ruminant animals.

Characterization of season and sampling method effects on measurement of forage quality in fescue-based pastures.

Information on seasonal changes and effects of sampling methods on the measurement of forage quality is limited for fescue-based pastures. Eight continuously grazed, 0.76-ha, fescue-based pastures were used to compare forage type, method of collection, and seasonal effects on forage quality in a repeated-measures, split-plot design. Four pastures were interseeded with red clover in March 2000. Masticate (M; from four ruminally cannulated steers) and hand--clipped (C) samples were collected every 28 d from April to October 2000. Interseeding red clover did not affect (P > 0.10) OM, CP, NDF, and ADF concentrations or CP degradability. Sampling method and season interacted (P < 0.03) for OM, CP, NDF, and ADF concentrations. Concentrations of OM averaged 5 percentage units more (P < 0.01) in C than in M in all months and were more variable with M than with C. Samples clipped between April and September averaged 5.5 percentage units greater NDF (P < 0.01), 3.0 percentage units greater ADF (P < 0.01), and 4.5 percentage units less CP (P < 0.01) than masticate samples obtained during the same time period. Fiber and CP concentrations did not differ (P > 0.10) between C and M samples obtained in October. Differences in CP degradability estimates (using Streptomyces griseus protease) between the two sample types were greater in late-season samples than in samples obtained from April to June. When S. griseus protein degradability estimates were compared with in situ estimates for masticate samples, no differences (P > 0.10) were detected early in the season (April to June). However, the S. griseus procedure overestimated in situ values (P < 0.01) by an average of 3 percentage units in samples obtained between July and October. Differences in composition of C and M samples were substantial until late season, when opportunities for selective grazing were minimal. Small differences between S. griseus and in situ estimates of CP degradability indicate that the S. griseus procedure can yield useful CP degradability estimates for fescue-based pasture samples. Although it might be possible to apply correction values to clipped samples to estimate CP and fiber concentrations of diets selected by grazing cattle, inconsistent relationships preclude this approach for estimates of CP degradability.