Nitrate supplementation has marginal effects on enteric methane production from Bos indicus steers fed Flinders grass (Iseilema spp.) hay, but elevates blood methaemoglobin concentrations

This experiment has quantified the methane abatement potential of nitrate in the context of extensively managed cattle. The experimental protocol consisted of two, 4 × 4 Latin square design using eight rumen fistulated Bos indicus steers fed Flinders grass (Iseilema spp.) hay ad libitum. The treatments were Control (nil nitrogen supplement), urea (32.5 g/day urea) and two levels of calcium nitrate: CaN1 and CaN2 (to provide 4.6 g and 7.9 g NO3/kg DM equivalent to ~0.46% and 0.80% of DM, respectively). Complete supplement intake was ensured by dosing any supplement that had not been voluntarily consumed, through the rumen fistula, 1 h after feeding. Enteric methane production was measured using open circuit respiration chambers. Methane yield (g/kg DM intake) from the CaN2 treatment tended to be lower (P < 0.07) than either the Control or urea treatments. There were no significant differences in methane yield between Control, urea or CaN1 treatments. Mean blood methaemoglobin concentrations were significantly (P < 0.001) higher for CaN2 animals compared with the Control, urea or CaN1 treatments. In addition, a significant time effect after dosing (P < 0.001) and a significant interaction between treatment and time after dosing (P < 0.001) was apparent. Overall mean total volatile fatty acid concentration was 74.0 ± 1.53 mM with no significant treatment effect, but a significant effect for both time of sampling (3 h vs 6 h) within days and among 7 sampling days. The inclusion of calcium nitrate as a non-protein-N source significantly reduced the molar proportions of butyrate (P < 0.001), iso-butyrate (P < 0.05) and iso-valerate (P < 0.001) compared with the Control. The provision of nitrate supplements, providing both a NPN and an alternative sink for H that would otherwise support enteric methanogenesis, has some potential. In extensive grazing systems effective methane abatement strategies are required. The elevated concentration of MetHb using CaN2 suggests that the strategy of replacing urea with nitrate in supplements fed to extensively managed cattle in the northern rangelands may be inappropriate where supplement intake cannot be controlled on an individual animal basis and forage quality is seasonally variable.

Nutrition of beef breeder cows in the dry tropics. 1. Effects of nitrogen supplementation and weaning on breeder performance

The effects of two dry season management strategies consisting of timing of weaning and/or nitrogen (N) supplementation on the body reserves, nutritional status and reproductive performance were, commencing in the early dry season, examined in Bos indicus × Bos taurus breeder cows (n = 122) grazing native pasture in the seasonally dry tropics. Cows were early-weaned in April in the early dry season or late-weaned in September in the late dry season. The supplement consisted of loose mineral mix which provided on average 14 g N/day, principally as non-protein N. In the early dry season in April 1997 all of the cows had been lactating for 3–5 months, averaged 363 kg (s.d. = 28) conceptus-free liveweight (CF.LW) and 4.7 (s.d. = 0.6) body condition score (9-point scale), and 53% were pregnant. In addition, from April to June 1997 10/26 non-pregnant lactating cows, and 24/31 non-pregnant non-lactating (i.e. early-weaned) cows became pregnant so that 81% of cows were pregnant by June. Predictions of diet from near-infrared spectroscopy of faeces indicated that the forage diet selected during the dry season (April–November) by the cows contained on average 9% (s.d. = 2) non-grass dicotyledonous plants and 4.4% (s.d. = 0.38) crude protein (CP), while DM digestibility was 51.1% (s.d. = 1.3). The diet CP concentration, the ratio of CP to metabolisable energy (ME) in the diet (mean 5.7, s.d. = 0.53, g CP/MJ ME) and faecal N concentration (mean 1.05, s.d. = 0.097, % N) all indicated that unsupplemented cows were deficient in dietary N during the dry season. Microbial CP synthesis in unsupplemented non-lactating cows decreased from 360 to 107 g microbial CP/day, or from 6.5 to 2.4 g microbial CP/MJ ME intake, as the dry season progressed from May to September 1997. Net endogenous N transfer to the rumen of up to 2 g CP/MJ ME apparently occurred from May to August. Microbial CP synthesis was 25% higher (P < 0.001) in lactating than in non-lactating cows. From April to September cow CF.LW was improved by 0.35 kg/day (P < 0.001) by early weaning, and by 0.11 kg/day (P < 0.10) by N supplementation, but there was no interaction (P > 0.10) between these treatments. From April to June 1997 calf LW gain averaged 0.79 kg/day, but from June to September was only 0.10 kg/day in unsupplemented paddocks and 0.13 kg/day in N-supplemented paddocks. Pregnant cows calved from November 1997 to March 1998. During subsequent mating 96% of non-lactating cows, but only 17% of lactating cows became pregnant. During the 1997–98 wet season there was compensatory LW gain of lower CF.LW non-lactating cows but not of lactating cows. In conclusion, weaning early in the dry season had a much greater effect than a non-protein N-based supplement to conserve breeder cow body reserves, and the effects of the two management strategies were additive.

Daily and alternate day supplementation of urea or biuret to ruminants consuming low-quality forage: I. Effects on cow performance and the efficiency of nitrogen use in wethers

Two experiments were conducted to determine the influence of supplemental nonprotein N (NPN) provided daily (D) or every other day (2D) on ruminant performance and N efficiency. Treatments included an unsupplemented control (CON) and a urea (28.7% CP) or biuret (28.6% CP) supplement provided D or 2D at 0700. In Exp. 1, five wethers (39 +/- 1 kg BW) were used in an incomplete 5 x 4 Latin square with four 24-d periods to determine the influence of supplemental NPN source and supplementation frequency (SF) on the efficiency of N use in lambs consuming low-quality grass straw (4% CP). The amount of CP supplied by each supplement was approximately 0.10% of BW/d (averaged over a 2-d period). In Exp. 2, 80 Angus x Hereford cows (540 +/- 8 kg BW) in the last third of gestation were used to determine the effect of NPN source and SF on cow performance. The NPN treatments were formulated to provide 90% of the estimated degradable intake protein requirement. The supplemented treatments received the same amount of supplemental N over a 2-d period; therefore, the 2D treatments received double the quantity of supplemental N on their respective supplementation day than the D treatments. In Exp. 1, total DM, OM, and N intake; DM, OM, and N digestibility; N balance; and digested N retained were greater (P < 0.03) for supplemented than for CON wethers, with no difference (P > 0.05) between NPN sources or SF. Plasma urea-N (PUN) was increased with N supplementation compared with CON (P < 0.01), and urea treatments had greater PUN than biuret (P < 0.01). In addition, PUN was greater (P = 0.02) for D than for 2D treatments. In Exp. 2, pre- and postcalving (within 14 d and 24 h after calving, respectively) cow weight and body condition score change were more positive (P < 0.05) for supplemented groups than for CON. These results suggest that supplements containing urea or biuret as the primary source of supplemental N can be effectively used by lambs and cows consuming low-quality forage, even when provided every other day.

Effect of supplementation frequency and supplemental urea level on dormant tallgrass-prairie hay intake and digestion by beef steers and prepartum performance of beef cows grazing dormant tallgrass-prairie

Effect of supplementation frequency and supplemental urea level on forage use (Exp. 1) and performance (Exp. 2 and 3) of beef cattle consuming low-quality tallgrass-prairie were evaluated. For Exp. 1 and 2, a 2 x 2 factorial treatment structure was used, such that two supplements (30% CP) containing 0 or 30% of supplemental degradable intake protein (DIP) from urea were fed daily or on alternate days. In Exp. 1 and 2, supplement was fed at 0.41% BW daily or at 0.83% BW (DM basis) on alternate days. For Exp. 3, a 2 x 4 factorial treatment structure was used, such that four supplements (40% CP) containing 0, 15, 30, or 45% of supplemental DIP from urea were fed daily or 3 d/wk. Supplements were group-fed at 0.32% BW daily or at 0.73% BW (DM basis) 3 d/wk. In Exp. 1, 16 Angus x Hereford steers (initial BW = 252 kg) were blocked by BW and assigned to treatment. Urea level x supplementation frequency interactions were not evident for forage intake, digestion, or rate of passage. Forage OM intake (OMI) and total digestible OMI (TDOMI) were not significantly affected by treatment. Total-tract digestion of OM (P = 0.03) and NDF (P = 0.06) were greater for steers supplemented daily. In Exp. 2, 48 Angus x Hereford cows (initial BW = 490 kg) grazing winter tallgrass prairie were used. Significant frequency x urea interactions were not evident for BW and body condition (BC) change; similarly, the main effects were not substantive for these variables. In Exp. 3, 160 Angus x Hereford cows (initial BW = 525 kg) grazing dormant, tallgrass prairie were used. Supplement refusal occurred for cows fed the highest urea levels, particularly for cows fed the supplement with 45% of the DIP from urea 3 d/wk, and supplement refusal increased closer to calving. A frequency x urea interaction (P = 0.02) was observed for prepartum BW changes. As supplemental urea level increased, prepartum BW loss increased quadratically (P = 0.02); however, a greater magnitude of loss occurred when feeding supplements containing > or = 30% of DIP from urea 3 d/ wk. Cumulative BC change followed a similar trend. In conclusion, moderate protein (< or = 30% CP) supplements with < or = 30% of supplemental DIP from urea can be fed on alternate days without a substantive performance penalty. However, infrequent feeding of higher protein (> 30% CP) supplements with significant urea levels (> 15% of DIP from urea) may result in decreased performance compared with lower urea levels.

Daily and alternate-day supplementation of urea or biuret to ruminants consuming low-quality forage: II. Effects on site of digestion and microbial efficiency in steers1,2

Five steers (491 +/- 21 kg BW) were used in an incomplete 5 x 4 Latin square with four 24-d periods to determine the influence of supplemental non-protein N (NPN) source and supplementation frequency (SF) on nutrient intake and site of digestion in steers consuming low-quality grass straw (4% CP). Treatments (TRT) included an unsupplemented control and a urea- or biuret-containing supplement placed directly into the rumen daily (D) or every other day (2D) at 0700. The NPN treatments were formulated to provide 90% of the estimated degradable intake protein requirement. Daily TRT were supplemented CP at 0.04% of BW/d, whereas the 2D TRT were supplemented at 0.08% of BW every other day. Therefore, all supplemented TRT received the same quantity of supplemental CP over a 2-d period. Forage OM intake was not affected (P > 0.05) by NPN supplementation, NPN source, or SF; however, total OM and N intake were increased (P < 0.01) with CP supplementation. Duodenal flow of N was greater (P = 0.04) with CP supplementation compared with the control. In addition, duodenal bacterial N flow was increased with CP supplementation (P = 0.04) and for biuret compared with urea (P < 0.01). Bacterial efficiency (g bacterial N/kg OM truly digested in the rumen) was greater (P = 0.05) for biuret than for urea. Apparent total-tract N digestibility was increased with NPN supplementation (P < 0.01) but not affected by NPN source or SF. These results suggest that urea or biuret can be used effectively as a supplemental N source by steers consuming low-quality forage.

Influence of supplemental protein source and feeding frequency on rumen fermentation and performance in dairy cows

Multiparous Holstein cows in early lactation were fed a basal mixed ration of 47% (DM) alfalfa and timothy silage and 53% barley and corn concentrate twice daily for ad libitum intake at 1630 and 0600 h. Two supplemental protein sources that differed in their resistance to rumen proteolysis were fed at 9% of total DMI in either two meals per day at 1730 and 0700 h or five meals per day at 1730, 2130, 0200, 0700, and 1200 h. The study was a 4 x 4 Latin square design with six blocks of 4 cows in which one block of cows was fitted with rumen cannulas. Intakes of DM, OM, NDF, and CP were not influenced by treatments. However, cows supplemented with five meals a day tended to consume the mixed ration more rapidly after both the p.m. and a.m. feedings. Milk yield and its content of protein, fat, and lactose also were not influenced by treatments. Average rumen pH was higher, and propionate concentrations were lower, for cows supplemented with five meals, but diurnal patterns were not influenced. Propionate and rumen ammonia N concentrations were lower for cows supplemented with the more resistant protein source; however, rumen VFA, as well as soluble and peptide N concentrations, were not influenced by the type of supplemental protein. Results do not support benefits of synchronized rumen release of energy and N to overall cow production, but rather support previous research that soluble protein or peptide N, or both, may act as a pool to provide N for microbial growth at times of the day when ammonia N concentrations are very low.