Energy requirement for primiparous Holstein × Gyr crossbred dairy cows

Our objective was to estimate the requirements of metabolizable energy (ME) and net energy for the maintenance (NEm) of lactating and dry cows, the efficiency of ME utilization for milk production (kl) and tissue gain (kg), and the use of body energy mobilization for milk production (kt) throughout the lactation of primiparous crossbred Holstein × Gyr cows, using open-circuit respiration chambers. Twenty-nine primiparous Holstein × Gyr crossbred cows with an initial BW averaging 563 ± 40.1 kg and 2.5 ± 0.09 years old were used throughout lactation and dry periods. The cows were kept non-pregnant throughout the study to eliminate possible confounding factors. Apparent digestibility assays, followed by calorimeter measurements, were performed 6 times throughout the lactation period. In the dry-off period, the cows were also evaluated but fed with restricted intake (DMI = 1.1% BW/d) to achieve heat production close to maintenance. After 21 d of diet adaptation, an apparent digestibility assay followed by calorimeter measurements was performed. Parameter estimates for lactation period were obtained by mixed models including lactation stage as repeated measures. For restricted feeding at dry-off and fasting period assays, the requirements were estimated by exponential regression. For whole lactation, the values of MEm and NEm were 0.588 and 0.395 MJ/BW0.75, respectively. The efficiencies klkgkt were 0.672, 0.771, and 0.814, respectively. However, MEm and NEm were higher in early and mid-lactation than late, while kl was higher in early than other lactation stages. Dry and non-pregnant cows had MEm of 0.434 MJ/BW0.75 and NEm of 0.351 MJ/BW0.75 for maintenance level, and MEm of 0.396 MJ/BW0.75 and NEm of 0.345 MJ/BW0.75 for fasting metabolism level and efficiency of ME utilization for maintenance was 0.80. Our findings confirmed that F1 crossbred Holstein × Gyr dairy cows have differences in energy requirement and efficiency throughout the lactation stages, suggesting the use of different values in each stage. The estimated values of energy requirement for maintenance and efficiencies for primiparous lactating crossbred Holstein × Gyr were similar to those reported in the literature in specific studies and requirements systems.

Effects of feeding 25-hydroxyvitamin D3 with an acidogenic diet during the prepartum period in dairy cows: Mineral metabolism, energy balance, and lactation performance of Holstein dairy cows

Our objective was to determine the effects of feeding 25-hydroxyvitamin D₃ [25(OH)D₃], or vitamin D₃ (cholecalciferol) on plasma, mineral, and metabolite concentrations, mineral balance, mineral excretion, rumination, energy balance, and milk production of dairy cows. We hypothesized that supplementing 3 mg/d of 25(OH)D₃ during the prepartum period would be more effective than supplementing vitamin D₃ at the National Research Council (2001) levels to minimize calcium imbalance during the transition period and improve milk production of dairy cows. Forty multiparous, pregnant nonlactating-Holstein cows were enrolled in this study. Body weight, body condition score, parity, and milk yield in the previous lactation (mean ± standard deviation) were 661 ± 59.2, 3.46 ± 0.35, 1.79 ± 0.87, and 33.2 ± 6.43 kg/d, respectively. Cows were enrolled into the blocks (n = 20 for each treatment) at 30 d of the expected day of calving to receive an acidogenic diet (373 g/kg of neutral detergent fiber and 136 g/kg of crude protein, dry matter basis; -110 mEq/kg) associated with the treatments: (1) control (CTRL), vitamin D₃ at 0.625 mg/d (equivalent to 25,000 IU of vitamin D₃/d) or (2) 25(OH)D₃ at 3 mg/d (equivalent to 120,000 IU of vitamin D₃/d). All cows were fed with the base ration for 49 d after calving. Blood samples were taken on d 7, 0, 1, 2, 21, and 42, relative to calving. No effect of treatment was observed for prepartum dry matter intake or body condition score. A trend for increase of ionized Ca was observed for the cows fed 25(OH)D₃, compared with the CTRL, but no effect of treatment was detected for total Ca or total P. Feeding 25(OH)D₃ increased colostrum yield. The plasmatic concentration of 25-hydroxyvitamin D₃ was increased with 25(OH)D₃ supplementation. 25-Hydroxyvitamin D₃ supplementation increased plasma glucose concentration at parturition. The postpartum dry matter intake was not influenced by treatments. Feeding 25(OH)D₃ increases milk yield, 3.5% fat-corrected milk, and energy-corrected milk and improves milk yield components in early lactation. Overall, these findings suggest that 25(OH)D₃ at 3 mg/d can improve the energy metabolism and lactation performance, compared with the current-feeding practice of supplementing vitamin D₃ at 0.625 mg/d.

Differences in methane production, yield and intensity and its effects on metabolism of dairy heifers

The effects of divergent phenotypic classification in crossbreed Holstein × Gyr dairy heifers for methane emissions in relation to performance, digestibility, energy and nitrogen partition, blood metabolites and temperature of body surface were evaluated. Thirty-five heifers were classified as high and low emission for CH₄ production (g/day), yield (g/kg dry matter intake) and intensity (g/kg average daily gain). Digestibility was evaluated by total collection of feces and urine. Gas exchanges were obtained in open-circuit respiratory chambers. A completely randomized design was used and divergent groups were compared by Fisher's test. No differences were found in intake traits between groups of CH₄ production and intensity. The low yield group had higher intake. For digestibility and temperature at different body sites were no differences between variables. High production group had higher energy losses as methane and heat production. Low intensity group had higher digestible energy, energy balance and ratio between metabolizable and digestible energy. Urinary nitrogen was 14.3% lower for low production group. There was a difference between methane yield divergent groups for nitrogen intake, digestible and retained. Energy and nitrogen partitioning traits are correlated to the animals divergent for methane production and yield. The low production group presented lower blood insulin concentration. It was not possible to identify divergent animals for CH₄ emission using the infrared thermography technique.

Performance and methane emissions in dairy cows fed oregano and green tea extracts as feed additives

Plant extracts have been proposed as substitutes for chemical feed additives due to their potential as rumen fermentation modifiers and because of their antimicrobial and antioxidant activities, possibly reducing methane emissions. This study aimed to evaluate the use of oregano (OR), green tea extracts (GT), and their association as feed additives on the performance and methane emissions from dairy between 28 and 87 d of lactation. Thirty-two lactating dairy cows, blocked into 2 genetic groups: 16 Holstein cows and 16 crossbred Holstein-Gir, with 522.6 ± 58.3 kg of body weight, 57.2 ± 20.9 d in lactation, producing 27.5 ± 5.0 kg/cow of milk and with 3.1 ± 1.8 lactations were evaluated (means ± standard error of the means). Cows were allocated into 4 treatments: control (CON), without plant extracts in the diet; oregano extract (OR), with the addition of 0.056% of oregano extract in the dry matter (DM) of the diet; green tea (GT), with the addition of 0.028% of green tea extract in the DM of the diet; and mixture, with the addition of 0.056% oregano extract and 0.028% green tea extract in the DM of the diet. The forage-to-concentrate ratio was 60:40. Forage was composed of corn silage (94%) and Tifton hay (6%); concentrate was based on ground corn and soybean meal. Plant extracts were supplied as powder, which was previously added and homogenized into 1 kg of concentrate in natural matter, top-dressed onto the total mixed diet. No treatment by day interaction was observed for any of the evaluated variables, but some block by treatment interactions were significant. In Holstein cows, the mixture treatment decreased gross energy and tended to decrease the total-tract apparent digestibility coefficient for crude protein and total digestible nutrients when compared with OR. During the gas measurement period, GT and OR increased the digestible fraction of the ingested DM and decreased CH₄ expressed in grams per kilogram of digestible DMI compared with CON. The use of extracts did not change rumen pH, total volatile fatty acid concentration, milk yield, or most milk traits. Compared with CON, oregano addition decreased fat concentration in milk. The use of plant extracts altered some milk fatty acids but did not change milk fatty acids grouped according to chain length (short or long), saturation (unsaturated or saturated), total conjugated linoleic acids, and n-3 and n-6 contents. Green tea and oregano fed separately reduced gas emission in cows during the first third of lactation and have potential to be used as feed additives for dairy cows.

Protein dietary efficiency and methane emission in cattle fed soybean meal treated with tannins

Adding tannins to the dietary protein source will cause complexation between the tannin and protein, which may increase dietary ruminal undegraded protein. Thus, this study aimed to evaluate the effects of replacing soybean meal (SM) with soybean meal treated with tannin (SMT) on the intake, partial and total nutrient digestibility, and protein dietary efficiency of young cattle fed a high-concentrate diet. Five Nellore bulls with bodyweights of 290 ± 11.2 kg were fitted with ruminal and abomasal cannulas and were used in the study. The experimental diets included 7.5% SM, with a proportion of that SM (0%, 33%, 66% or 100%) replaced with SMT. Another treatment (SMT+urea) with only 2.5% SM treated with tannins was tested. The intake of ether extract and the intake of neutral detergent fibre ash and protein were the only parameters related to feed intake that were affected by the replacement of SM with SMT. Ruminal and intestinal digestibility each showed a linear effect on crude protein, which decreased with ruminal digestibility and increased with intestinal digestibility. The intake of ruminal undegraded protein and metabolisable protein showed a positive linear correlation with the amount of SMT in the diet. SMT substitution showed no effect on methane emission. The replacement of traditional SM with SM treated with 2.5% tannins (85% condensed tannins and 15% hydrolysable tannins) for cattle that were fed high-concentrate diets showed increased amounts of metabolisable protein and decreased nitrogen loss per unit of crude protein, without changing the methane emission.

Energy and protein requirements of crossbred (Holstein × Gyr) growing bulls

The objective of this study was to estimate the energy and protein requirements of crossbred (Holstein × Gyr) growing bulls. Twenty-four 10-mo-old bulls [initial body weight (BW) = 184 ± 23.4 kg] were used in a comparative slaughter trial. Six bulls were slaughtered at the beginning of the experiment as the reference group, to estimate initial empty body weight (EBW) and energy and protein contents of the remaining animals. The remaining bulls were assigned to a completely randomized design with 3 levels of dry matter intake and 6 replicates. The levels of dry matter intake were 1.2% of BW, 1.8% of BW, and ad libitum to target orts equal to 5% of the total amount that was fed. The remaining bulls were slaughtered at the end of the experiment. The bulls were fed a diet consisting of 59.6% corn silage and 40.4% concentrate on a dry matter basis. The equation that determined the relationship between EBW and BW was EBW = (0.861 ± 0.0031) × BW. The relationship between empty body gain (EBG) and average daily gain (ADG) was demonstrated by the following equation: EBG = (0.934 ± 0.0111) × ADG. Net energy for maintenance (NE_M) was 74.8 ± 2.89 kcal/kg of EBW^0.75 per day, and metabolizable energy for maintenance (ME_M) was 120.8 kcal/kg of EBW^0.75 per day. The detected efficiency of use of metabolizable energy for maintenance (k_m) was 61.9%. The equation used to estimate net energy for gain (NE_G) was as follows: NE_G = (0.049 ± 0.0011) × EBW^0.75 × EBG^{0.729 ± 0.0532}. The efficiency of use of metabolizable energy for gain (k_g) was 35.7%. The metabolizable protein for maintenance (MP_M) was 3.05 g/kg of BW^0.75. The equation used to estimate net protein requirements for gain (NP_G) = (87.138 ± 65.1378 × EBG) + [(40.436 ± 21.3640) × NE_G]. The efficiency of use of metabolizable protein for gain (k) was 35.7%. We concluded that the estimates of energy and protein requirements presented herein are more appropriate than the National Research Council dairy cattle model and the Brazilian BR-CORTE system to balance the diets of crossbred (Holstein × Gyr) growing bulls.

Effect of sunflower oil supplementation on methane emissions of dairy cows grazing Urochloa brizantha cv. marandu

The objective of the present study was to evaluate the effect of sunflower oil supplementation on methane (CH4) emission of crossbred Holstein × Gyr (Bos indicus) dairy cows grazing tropical pasture. Lactating dairy cows were fed Urochloa brizantha (syn Brachiaria brizantha) pasture managed under rotational grazing. Sunflower oil was supplemented to cows using concentrates with inclusion at 0% or 14.9% (DM basis). Crude fat concentrations in these concentrates were 2.4% and 13.8% respectively (DM basis). Dietary fat concentrations for control and supplemented sunflower oil treatments were 3.2% and 5.2% (DM basis) respectively. Sixteen lactating cows Holstein × Gyr (Bos indicus; 240 ± 10 days in milk, 524 ± 57 kg of bodyweight, 11.2 ± 2.30 kg/day of milk) were used in the study. Methane emissions were estimated by the sulfur hexafluoride tracer technique. The experiment was a randomised-block design with two repetitions of pasture area, with two treatments (0 g or 383 g of sunflower oil supplementation, DM basis) and four replications (cows) per treatment per block. Methane emission and yield expressed as g CH4/day and g CH4/kg of DM intake decreased 21.5% (P = 0.048) and 20.2% (P = 0.032) respectively, in cows supplemented with sunflower oil compared with unsupplemented cows. There was no effect (P = 0.29) of sunflower oil supplementation on CH4 expressed as g CH4/kg of milk. Lactating dairy cows grazing tropical-grass pasture supplemented with sunflower oil (5.3% dietary fat; 383 g oil/day) demonstrated potential for mitigating CH4 emissions without negatively affecting cow milk yield or composition.

Pasture productivity and quality of Urochloa brizantha cultivar Marandu evaluated at two grazing intervals and their impact on milk production

The present study aimed to evaluate two rotational stocking intervals (GI) over three consecutive grazing periods on forage productivity, crude protein and neutral detergent fibre of Urochloa brizantha cv. Marandu pastures, and the subsequent impact on milk production. Grazing treatments were (1) fixed rest period at 30 days (30-FG) and (2) grazing interval when canopy was intercepting 95% photosynthetically active radiation (95-LI). Eighteen multiparous Holstein × Zebu cows (548 ± 61.0 kg bodyweight, BW) and 70 ± 18.1 days in milk were used. Experiment lasted for 99 days (i.e. 33 days per period). Nine cows with similar milk production and BW were randomly allocated to each GI treatment balanced on milk production and BW. The adjustment of carrying capacity per paddock was made aiming to achieve a post-grazing residual height of 20 cm. For this, additional dry Holstein × Zebu cows (averaging 550 kg BW) were added and removed from the paddocks according put-and-take technique. Data were statistically analysed considering field sites as block (n = 2), GI (30-FG vs 95-LI), periods (three consecutive) and interaction GI × periods. Interactions occurred between GI and periods for pre- and post-grazing height (P ≤ 0.05). Greater pre-grazing height was observed for 30-FG (P < 0.01), but post-grazing height was greater (P < 0.01) for 30-FG only in the third period. GI for treatment 30-FG was ~6 days longer (P = 0.01) than that for 95-LIand light interception was greater (2%) for 30-FG. Total forage, stem and dead material mass per area were greater (P < 0.01) for 30-FG than 95-LI. However, stocking rate was 11.3% greater (P = 0.02) for 95-LI than 30-FG. In the pre-grazing period, 95-LI had greater (P < 0.01) proportion of leaves and a greater leaf : stem ratio, whereas neutral detergent fibre concentration tended to be lower (P = 0.08) and crude protein concentration greater (P < 0.01) in 95-LI than in 30-FG. Daily milk productivity per area and its components were 16–28% greater (P < 0.01) for 95-LI than for 30-FD. These results suggest that GI of Marandu grass determined by light interception at 95% (95-LI) enabled the reduction of GI, improved forage nutritive value and increased milk productivity compared with a fixed 30 days (30-FG) of rest.

Greenhouse gases inventory and carbon balance of two dairy systems obtained from two methane-estimation methods

The adoption of carbon inventories for dairy farms in tropical countries based on models developed from animals and diets of temperate climates is questionable. Thus, the objectives of this study were to estimate enteric methane (CH4) emissions through the SF6 tracer gas technique and through equations proposed by the Intergovernmental Panel on Climate Change (IPCC) Tier 2 and to calculate the inventory of greenhouse gas (GHG) emissions from two dairy systems. In addition, the carbon balance of these properties was estimated using enteric CH4 emissions obtained using both methodologies. In trial 1, the CH4 emissions were estimated from seven Holstein dairy cattle categories based on the SF6 tracer gas technique and on IPCC equations. The categories used in the study were prepubertal heifers (n=6); pubertal heifers (n=4); pregnant heifers (n=5); high-producing (n=6); medium-producing (n=5); low-producing (n=4) and dry cows (n=5). Enteric methane emission was higher for the category comprising prepubertal heifers when estimated by the equations proposed by the IPCC Tier 2. However, higher CH4 emissions were estimated by the SF6 technique in the categories including medium- and high-producing cows and dry cows. Pubertal heifers, pregnant heifers, and low-producing cows had equal CH4 emissions as estimated by both methods. In trial 2, two dairy farms were monitored for one year to identify all activities that contributed in any way to GHG emissions. The total emission from Farm 1 was 3.21t CO2e/animal/yr, of which 1.63t corresponded to enteric CH4. Farm 2 emitted 3.18t CO2e/animal/yr, with 1.70t of enteric CH4. IPCC estimations can underestimate CH4 emissions from some categories while overestimate others. However, considering the whole property, these discrepancies are offset and we would submit that the equations suggested by the IPCC properly estimate the total CH4 emission and carbon balance of the properties. Thus, the IPCC equations should be utilized with caution, and the herd composition should be analysed at the property level. When the carbon stock in pasture and other crops was considered, the carbon balance suggested that both farms are sustainable for GHG, by both methods. On the other hand, carbon balance without carbon stock, by both methods, suggests that farms emit more carbon than the system is capable of stock.

Technical note: Assessment of the oxygen pulse and heart rate method using respiration chambers and comparative slaughter for measuring heat production of cattle

The objective of this study was to assess the oxygen pulse and heart rate (O₂P-HR) technique using the respiration chamber (RC) and comparative slaughter (CS) methods for measuring the heat production (HP) of crossbred (Holstein × Gyr) yearling bulls. Twenty-four bulls were used. Six bulls were slaughtered at the beginning of the experiment as a reference group to estimate the initial empty body weight (BW) and energy content of the remaining animals. The remaining bulls were assigned to a completely randomized design with 3 levels of dry matter intake, with 6 replicates. The levels of dry matter intake were 1.2% of BW, 1.8% of BW and ad libitum, with target orts of 5%. The bulls were fed a diet consisting of 59.6% corn silage and 40.4% concentrate on a dry matter basis. The HP (kcal/BW^0.75) was measured using 3 techniques, first using O₂P-HR, followed by the RC and CS methods. The HP did not differ among assessed techniques, averaging 162.7kcal/BW^0.75. The intercepts of the linear regressions (mean ± SE) were 64.82±25.515 (H₀: intercept=0; P=0.024), 33.77±13.418 (H₀: intercept=0), and 50.02±27.495 (H₀: intercept=0) for O₂P-HR versus RC, CS versus RC, and O₂P-HR versus CS, respectively. The slopes of the linear regressions were 0.59±0.153 (H₀: slope=1), 0.88±0.081 (H₀: slope=1), and 0.62±0.155 (H₀: slope=1) for O₂P-HR versus RC, CS versus RC, and O₂P-HR versus CS, respectively. The coefficients of determination were 0.52, 0.90, and 0.52 for O₂P-HR versus RC, CS versus RC, and O₂P-HR versus CS, respectively. The concordance correlation coefficients, 0.70 and 0.68, were moderate for O₂P-HR versus RC and O₂P-HR versus CS, respectively, but high, 0.90, for CS versus RC. The between-animal coefficient of variation was greater for the O₂P-HR method (16.6%) compared with RC (7.7%) or CS (6.7%). We conclude that there was an agreement among the HP measurements detected using the assessed methods and that O₂P-HR is able to predict HP in cattle with great accuracy but only moderate precision. Therefore, the O₂P-HR method may have limitations in terms of assessing HP in low numbers of replications due to greater between-animal coefficient of variation than either the RC or CS methods.

The effects of increasing amounts of milk replacer powder added to whole milk on feed intake and performance in dairy heifers

The aim of this study was to evaluate the effects on feed intake, heifer performance, and health of increasing the total solids (TS) content of liquid feed (whole milk) by adding increasing amounts of milk replacer powder during the pre- and postweaning periods. Crossbred Holstein-Gyr heifers (n=60) were assigned to 1 of 4 treatments (n=15 per group), which consisted of different TS concentrations: 12.5, 15.0, 17.5, and 20.0% of liquid feed. Heifers received 6 L of liquid feed per day, divided into 2 equal meals (0800 and 1600h) and provided in buckets, from 5 to 55d of age. From 56 to 59d of age, the total amount of liquid feed was reduced by half, maintaining only morning feedings. Heifers were weaned at 60d and monitored until 90d of age. Water and starter were provided ad libitum during the entire experiment. Corn silage was included in the diet during the postweaning period (70d of age). Feed intake and health scores were evaluated daily. Body weight and body frame development were recorded weekly. Starting at 14d, ruminal pH was measured every other week. Laboratory analysis determined that the actual TS contents of the liquid feed were 13.5, 16.1, 18.2, and 20.4%, for the proposed 12.5, 15.0, 17.5, and 20.0% TS treatments, respectively. The osmolality of liquid feed treatments was 265 to 533mOsm/L. Intake of liquid feed was similar among treatments from 4wk of age. During the preweaning period, starter intake, fecal score, and days with diarrhea were similar among treatments. Ruminal pH at weaning averaged 6.2 and was similar among treatments. Increasing concentrations of TS in the liquid feed were associated with linear increases in average daily gain, final body weight, and growth performance, but linear decreases in feed efficiency. During the postweaning period, intake of starter, corn silage, and water were similar among treatments, as well as average daily gain and feed efficiency. Final body weight and growth performance during the postweaning period also increased linearly with concentration of TS in liquid feed. Increasing the concentration of TS in liquid feed up to 20.4% increased performance and body frame development in dairy heifers during the pre- and postweaning periods and had no effects on solid feed intake or health.

Effects of Tithonia diversifolia on in vitro methane production and ruminal fermentation characteristics

The present study examined the effects of Tithonia diversifolia on in vitro methane (CH4) production and ruminal fermentation characteristics. The experiment was conducted as a completely randomised design (CRD) using a control (0% T. diversifolia) and three treatment groups with different concentrations (6.9%, 15.2%, 29.2%) of T. diversifolia, which replaced up to 15.2% and 14% dry matter (DM) of fresh sugarcane and concentrates, respectively. Ruminal fluid was obtained from two ruminally cannulated non-lactating Holstein × Zebu heifers maintained on a diet consisting of T. diversifolia, fresh sugarcane and 4 kg of concentrates. The inclusion of T. diversifolia had no effect (P ≥ 0.15) on cumulative gas production (mL, mL/g incubated DM, mL/g digested DM) or in vitro DM disappearance (%). Carbon dioxide (%, mL, mL/g incubated DM) linearly decreased (P ≤ 0.001) and CH4 (%, mL, mL/g incubated DM) quadratically increased (P ≤ 0.01) with increasing concentrations of T. diversifolia replacing fresh sugarcane and concentrates. The total volatile fatty acids (mM) and acetate (A) proportion of total volatile fatty acids (mmol/100 mmol) linearly increased (P < 0.01) with the increasing inclusion of T. diversifolia. Butyrate (mmol/100 mmol) increased quadratically (P ≤ 0.02), while propionate (P; mmol/100 mmol) decreased quadratically (P < 0.02). The A : P ratio increased linearly (P < 0.0001) with increasing amounts of T. diversifolia in the diet. These results indicated that increasing the amount of Tithonia diversifolia in the substrate DM increased the A : P ratio, which resulted in a six-fold increase of CH4 production when fresh sugarcane and concentrates were replaced at up to 15.2% and 14% (DM basis), respectively.

In vitro Fermentation, Digestion Kinetics and Methane Production of Oilseed Press Cakes from Biodiesel Production

Following the extraction of oil for biodiesel production, oilseed press cakes are high in fat. As the dietary supplementation of fat is currently considered the most promising strategy of consistently depressing methanogenesis, it follows that oilseed press cakes may have a similar potential for CH₄ abatement. As such, this study aimed to characterise the nutritive value of several oilseed press cakes, glycerine and soybean meal (SBM) and to examine their effects on in vitro ruminal fermentation, digestion kinetics and CH₄ production. Moringa press oil seeds exhibited the greatest in sacco effective degradability (ED) of DM and CP (p<0.05). In vitro gas production (ml/g digested DM) was not affected (p = 0.70) by supplement at 48 h of incubation. In vitro DMD was increased with the supplementation of glycerine and SBM at all levels of inclusion. Moringa oilseed press cakes produced the lowest CH₄ (mg/g digested DM) at 6 and 12 h of incubation (p<0.05). The findings suggest that moringa oilseed press cake at 400 g/kg DM has the greatest potential of the oilseed press cakes examined in this study, to reduce CH₄ production, without adversely affecting nutrient degradability.

Production, Nutritional Quality and In vitro Methane Production from Andropogon gayanus Grass Harvested at Different Maturities and Preserved as Hay or Silage

Andropogon gayanus is an important grass due to its high biomass production, drought tolerance and favorable growth on low fertility acidic soils. Currently, there is little research on the impact of growth stage on the nutritional quality or the degree of CH4 production that may arise from this forage during ruminal fermentation. The objectives of this study were to determine the effects of regrowth stage of A. gayanus on its chemical composition, in vitro production of gas and CH4, as well as in vitro dry matter (DM) digestibility when grown under tropical Brazilian conditions and conserved as hay or as silage. The nutritional value of A. gayanus grass declined with increasing maturity; however digestible DM yield linearly increased. After 112 d of regrowth, A. gayanus produced higher quality silage (higher lactate and lower pH and butyrate content) and higher DM yield. However, the low levels of crude protein at this time would make protein supplementation a necessity for proper rumen fermentation. No differences in CH4 kinetic parameters were found with advancing maturity or preservation method (hay or silage).