Effects of fat and/or methionine hydroxy analog added to a molasses-urea-based supplement on ruminal and postruminal digestion and duodenal flow of nutrients in beef steers consuming low-quality lovegrass hay.

Five crossbred beef steers (initial BW = 338.6 ± 7.8 kg) fitted with ruminal and duodenal cannulas were used in a 5 × 5 Latin square design experiment to evaluate the effects of methionine hydroxy analog (MHA) and/or yellow grease (fat) added to a molasses-urea-based supplement on intake and characteristics of digestion. Steers were fed low-quality hay (long-stem lovegrass : 3.3% CP, 76.8% NDF; DM basis) ad libitum and supplemented with 0.91 kg/d (as fed) of 1 of 4 supplements in a 2 × 2 + 1 factorial arrangement of treatments. Supplemental treatments were 1) control (no supplement, NC); 2) molasses-urea liquid supplement (U); 3) U containing (as-fed basis) 1.65% MHA (UM); 4) U containing (as-fed basis) 12% fat (UF); and 5) U containing (as-fed basis) 1.65% MHA and 12% fat (UMF). Total and forage OM intake (kg/d and as % of BW) increased ( < 0.01) with molasses-urea, decreased ( ≤ 0.04) with MHA, and were not affected ( = 0.61) with fat supplementation. Total tract NDF digestibility increased ( = 0.01) with molasses-urea supplementation, and was less ( = 0.01) for fat than for nonfat supplementation. Total and microbial N flowing to the duodenum increased ( = 0.01) with molasses-urea supplementation. Although, total N flowing to duodenum was not affected ( = 0.27), microbial N decreased ( = 0.01), and nonammonia nonmicrobial N (NANMN) increased ( = 0.01) with fat supplementation. Extent of in situ OM and NDF digestibility at 96 h increased ( = 0.01) with molasses-urea supplementation, but were not affected ( ≥ 0.14) by either MHA or fat supplementation. Duodenal flow of total AA, essential AA, and nonessential AA increased ( ≤ 0.02) with molasses-urea supplementation. Total and nonessential serum AA concentration decreased ( < 0.01) with molasses-urea supplementation. Total ruminal VFA concentration increased ( = 0.01) with molasses-urea supplementation, and was not affected ( ≥ 0.14) by MHA or fat supplementation. Fat can be used in molasses-urea liquid supplements for cattle consuming low-quality forage to increase energy intake without negatively affecting forage intake or characteristics of digestion. However, adding MHA did not further improve the response to urea supplementation of cattle consuming low-quality forage. Conversely, the inclusion of MHA on urea supplement decreased forage intake.

Influence of forage level and naloxone injection on feed intake, digestion, and plasma hormone and metabolite concentrations in dairy heifers.

Four ruminally cannulated Holstein heifers (287 +/- 26 kg) in a 4 x 4 Latin square were used to evaluate the effects of naloxone injection and forage level on dietary intake, ruminal fermentation characteristics, digestibility, and plasma hormone and metabolite concentrations. Treatments were arranged in a 2 x 2 factorial with naloxone injection (0 vs .3 mg/kg; saline vs naloxone, respectively) and forage level (20 vs 100%; concentrate vs forage) as factors. Stanchioned heifers were allowed 21 d for adaptation before a 5-d collection period. Plasma samples were collected several times on d 1 and daily at 0730. Concentrate-fed heifers consumed more feed (P < .10) than forage-fed heifers. Naloxone injection decreased (P < .10) feed intake (grams/kilogram BW) at 1 and 2 h after feeding on d 1. On d 3 at 24 h after feeding, naloxone-injected heifers had increased DM (P < .10) intakes compared with control (saline-injected) heifers. Concentrate-fed heifers had decreased (P < .10) ruminal pH and increased total ruminal VFA concentration. Acetate proportion was decreased (P < .10) and propionate proportion increased in concentrate-fed heifers. Naloxone-injected heifers had decreased (P < .10) total VFA concentrations and increased propionate proportions. Concentrate-fed heifers had greater (P < .10) DM, OM, and CP digestibilities as well as increased plasma (P < .10) insulin, urea N, and glucose concentrations but decreased (P < .10) GH and NEFA concentrations. Naloxone injection increased (P < .10) plasma insulin concentration. Naloxone injection in dairy heifers reduces intake up to 2 h after injection, alters ruminal fermentation patterns, and increases plasma insulin concentration.

Effects of supplemental soybean oil level on in vitro digestion and performance of prepubertal beef heifers.

In vitro digestion and growth studies were conducted to evaluate the effects of level of soybean oil inclusion in forage-based diets. In Exp. 1, diets were bromegrass hay (H), bromegrass hay and corn-soybean meal supplement (C), C with 3% added soybean oil (O3), and C with 6% added soybean (O6). Diets containing supplements were formulated to be isonitrogenous and isocaloric. Treatment means were compared using a single-degree-of-freedom contrast (H vs C, O3, and O6) and orthogonal polynomial contrasts within diets C, O3, and O6. Diet H had the lowest (P = .0003) IVDMD and a linear decline (P = .0001) in IVDMD was observed from C to O6, but 24-h IVDMD disappearance was greatest (P = .001; quadratic) for O3. Total VFA increased from C to O3 and then decreased from O3 to O6 (quadratic; P = .001), and acetate:propionate ratio decreased linearly (P = .0001) from C to O6. Changes in long-chain fatty acids reflected biohydrogenation by ruminal microbes; however, only 18:3 was hydrogenated to the same extent across all diets. In Exp. 2, 36 Angus x Gelbvieh heifers (260.0 +/- 6.0 kg initial BW) were individually fed C, O3, or O6 as mixed rations for 104 d. Diets were formulated to be isonitrogenous and provide ADG of .91 kg. Feed efficiency and ADG was greatest (P < .02; quadratic) for O3 heifers. Serum NEFA increased linearly (P = .02) and serum glucose (P = .02), cholesterol (P = .002), and GH (P = .04) showed a quadratic response to level of dietary soybean oil. Plasma proportions of 16:0, 16:1, 18:0, and 18:1 increased quadratically (P < .03), and 18:2 increased linearly (P < .001) from C to O6. In Exp. 3, 42 Angus x Gelbvieh heifers (288.7 +/- 6.6 kg initial BW) were divided into six pens (two pens/treatment) in a randomized complete block designed experiment. Rations were delivered as hay plus a top-dressed supplement (C, O3, or O6). Heifers fed O3 conceived 10 d earlier (quadratic; P = .06) than heifers fed C and O6. Other production estimates did not differ (P > or = .10) among dietary treatments. Inclusion of soybean oil at 3% of a forage-based diet increased total VFA, many blood metabolites, ADG, and feed efficiency, and it decreased time to conception. Adding soybean oil as 3% of a forage-based diet is an acceptable feeding strategy for developing beef heifers.

Comparative digestibility by cattle versus sheep: effect of forage quality.

The objective was to determine the effect of forage quality on apparent total tract digestibility and ruminal fermentation in cattle versus sheep. Five yearling English crossbred (Hereford × Angus) steers (440.4 ± 35.6 kg of initial BW) and 5 yearling whiteface (Rambouillet × Columbia × Debouillet) wethers (44.4 ± 4.6 kg of initial BW), each fitted with a ruminal cannula, were randomly assigned to 1 of 3 forage sources within ruminant specie, and the study was conducted over 3 periods. For forage source, both animal and period served as the blocking factor with all forage sources represented once within each animal and all forage sources represented at least once within each period. The treatment structure was arranged in a 2 × 3 factorial with ruminant species (2) and forage source (3) as the factors. Forage sources were 1) alfalfa hay (Medicago sativa; 17.5% CP and 34.1% NDF, DM basis), 2) warm-season grass hay mix (Bothriochloa ischaemum and Cynodon dactylon; 7.3% CP and 74.7% NDF, DM basis), and 3) lovegrass hay (Eragrostis curvula; 2.5% CP and 81.9% NDF, DM basis). As a percent of BW, steers and wethers consumed similar (P ≤ 0.06) amounts of forage, and intake was more influenced by forage quality (P < 0.001) than ruminant species (P = 0.35). When expressed per unit of metabolic BW, cattle consumed more (P < 0.001) DM, NDF, and N than sheep. Apparent total tract digestibility was similar among steers and wethers when alfalfa or grass hay was fed, but decreased to a greater extent in wethers when low-quality lovegrass hay was fed (ruminant species × diet interaction, P ≤ 0.01). Rate (%/h) of ruminal NDF disappearance was greater (P = 0.02) for alfalfa and grass hay than lovegrass, but was not influenced (P = 0.12) by ruminant species. In addition, ruminal DM fill was influenced more (P < 0.01) by forage than by ruminant species (P = 0.07). Steers and wethers had greater (P < 0.01) DM fill from grass hay and lovegrass hay than alfalfa before and 5 h after feeding. Ruminal VFA were generally not influenced (P ≥ 0.06) by ruminant specie. Results suggest that apparent total tract digestibilities are more similar among ruminant species when moderate- to high-quality forages are evaluated. However, sheep are not an adequate model for cattle when low-quality forages are compared because cattle digest low-quality forages to a greater extent than sheep. Expressing digestibility as digestible intake per unit of BW allows for a wider range of forage qualities to be compared when substituting sheep for cattle.