Effects of nitrogen fertilisation rate and maturity of grass silage on methane emission by lactating dairy cows

Grass silage is typically fed to dairy cows in temperate regions. However, in vivo information on methane (CH₄) emission from grass silage of varying quality is limited. We evaluated the effect of two rates of nitrogen (N) fertilisation of grassland (low fertilisation (LF), 65 kg of N/ha; and high fertilisation (HF), 150 kg of N/ha) and of three stages of maturity of grass at cutting: early maturity (EM; 28 days of regrowth), mid maturity (MM; 41 days of regrowth) and late maturity (LM; 62 days of regrowth) on CH₄ production by lactating dairy cows. In a randomised block design, 54 lactating Holstein–Friesian dairy cows (168±11 days in milk; mean±standard error of mean) received grass silage (mainly ryegrass) and compound feed at 80 : 20 on dry matter basis. Cows were adapted to the diet for 12 days and CH₄ production was measured in climate respiration chambers for 5 days. Dry matter intake (DMI; 14.9±0.56 kg/day) decreased with increasing N fertilisation and grass maturity. Production of fat- and protein-corrected milk (FPCM; 24.0±1.57 kg/day) decreased with advancing grass maturity but was not affected by N fertilisation. Apparent total-tract feed digestibility decreased with advancing grass maturity but was unaffected by N fertilisation except for an increase and decrease in N and fat digestibility with increasing N fertilisation, respectively. Total CH₄ production per cow (347±13.6 g/day) decreased with increasing N fertilisation by 4% and grass maturity by 6%. The smaller CH₄ production with advancing grass maturity was offset by a smaller FPCM and lower feed digestibility. As a result, with advancing grass maturity CH₄ emission intensity increased per units of FPCM (15.0±1.00 g CH₄/kg) by 31% and digestible organic matter intake (33.1±0.78 g CH₄/kg) by 15%. In addition, emission intensity increased per units of DMI (23.5±0.43 g CH₄/kg) by 7% and gross energy intake (7.0±0.14% CH₄) by 9%, implying an increased loss of dietary energy with advancing grass maturity. Rate of N fertilisation had no effect on CH₄ emissions per units of FPCM, DMI and gross energy intake. These results suggest that despite a lower absolute daily CH₄ production with a higher N fertilisation rate, CH₄ emission intensity remains unchanged. A significant reduction of CH₄ emission intensity can be achieved by feeding dairy cows silage of grass harvested at an earlier stage of maturity.     

Ruminal large and small particle kinetics in dairy cows fed red clover and grass silages harvested at two stages of growth

Passage, comminution and digestion rates of large and small particles were estimated using a rumen evacuation technique and total faecal collection with five lactating dairy cows in a 5 × 5 Latin square experiment. Two grass and two red clover silages harvested at early and late primary growth stages and a 1:1 mixture of late harvest grass and early harvest red clover were the dietary treatments. Cows received 9.0 kg supplementary concentrate per day. Ruminal contents and faeces were divided into large (>1.25 mm) and small (1.25–0.038 mm) particles by wet sieving. Indigestible neutral detergent fibre (iNDF) was determined by 12 days ruminal in situ incubation followed by neutral detergent extraction. Plant species did not affect ruminal particle size distribution, whereas advancing forage maturity decreased the proportion of large particles for both grass and red clover silage diets. Ruminal pool size of iNDF was higher (P<0.001) with red clover compared to grass silage diets. Ruminal passage rates of iNDF and potentially digestible NDF (pdNDF) increased with decreasing particle size (P<0.01). Passage rate of iNDF for small particles was slower (P<0.01) when red clover compared to grass silage diets were fed. Particle comminution rate in the rumen was slower (P<0.001) with red clover compared to grass silage diets and it increased (P<0.01) with advancing forage maturity. The contribution of particle comminution to ruminal mean retention time of iNDF in the ruminal large particle pool was smaller (P<0.01) in red clover compared to grass silage diets and it increased (P<0.05) with the mixed silage compared to the separate silages. Passage rate of pdNDF for both large and small particles was not affected by dietary treatments. Digestion rate of pdNDF for large particles was faster (P<0.001) with red clover compared to grass silage diets. Differences in ruminal passage and digestion rates of the large and small particles, in addition to differences in the passage and digestion rates of red clover compared to grass silage diets, emphasize the need to consider particle size and forage type in metabolic models predicting feed intake and fibre digestibility in ruminants.     

Nitrogen and energy losses and methane emissions from beef cattle fed diets with gradual replacement of maize silage and concentrate with grass silage and corn-cob mix

Diets based on large proportions of grassland-based feed are uncommon in forage-based intensive beef production, thus contradicting governmental or commercial strategies to promote the use of grassland-based feed in ruminant production systems. Compared with typical maize silage/concentrate diets, grassland-based diets are associated with impaired nitrogen (N) and energy utilisation because of the comparably lower energy and higher CP content of these feeds. However, quantitative studies concerning the effects of increased dietary proportions of grassland-derived feeds on N and energy losses and utilisation and on methane emissions are missing and the compensation potential of using a limited proportion of an energy-rich forage is unknown. Therefore, we tested five diets with varying types and proportions of forage and concentrate. Three diets consisted of grass silage, maize silage, and concentrate in ratios of, g/kg DM, 100:600:300 (G100; control), 300:500:200 (G300), and 500:300:200 (G500), respectively. Two diets were composed of grass silage, corn-cob mix (CCM), and concentrate in ratios of, g/kg DM, 500:300:200 (G500_CCM), and 750:150:100 (G750_CCM), respectively. A high-protein concentrate (270 g CP/kg DM) was fed to G100, whereas a low-protein concentrate (140 g CP/kg DM) was used in the remaining diets. Diets were fed throughout the entire fattening period to groups of six Limousin-crossbred bulls each. When weighing 246 ± 18 kg, each animal underwent a 7-day total daily faeces and urine collection, which was followed by measuring methane emissions in respiration chambers for 48 h. Total DM intake was similar across all diets, whereas the N intake varied (P < 0.05). Urinary N loss (g/day) was the highest for G750_CCM (28.2) and G100 (26.6) and lowest for G500_CCM (15.2) and G300 (16.9) (P < 0.001). Energy utilisation was comparable among all groups. Metabolisable energy intake decreased numerically only with increasing proportions of grass silage in the diet. Substituting maize silage with CCM counteracted the loss in metabolisable energy intake. Absolute methane emissions were not different across the groups, but methane emission intensity (mg/g body protein retention) varied (P < 0.05), being numerically lower for G100 (349) and G500_CCM (401) compared with the other groups (488 on average). In conclusion, the results show that the grass silage proportion in beef cattle diets can be substantially increased when strategically combined with energy-dense forages, such as CCM. This also limits the need for concentrate and additional protein sources; in addition, the associated urinary N emissions, which are potentially noxious to the environment, are avoided.     

Effects of hydrolysable tannin-treated grass silage on milk yield and composition,nitrogen partitioning and nitrogen isotopic discrimination in lactating dairy cows

The objective of this study was to evaluate the effects of oak tannin extract (OTE) added in forage before ensiling on dairy cows fed at 92% of their digestible protein requirements. Six multiparous lactating Holstein cows were used in a crossover design (two treatments × two periods). The control treatment (CON) was based on a diet including 50% of grass silage, whereas the experimental treatment (TAN) included grass silage sprayed with OTE (26 g/kg DM) just before baling. Milk yield (on average 24 kg fat protein corrected milk per day) was not affected, but both milk and rumen fatty acids profiles were impacted by OTE. Nitrogen intake (415 g N per cow per day) and nitrogen use efficiency (NUE; 0.25 on average) were not affected, but a shift from urine (−8% of N intake relatively to control, P = 0.06) to faecal N (+5%; P = 0.004) was observed with the TAN diet (P ≤ 0.05). Nitrogen apparent digestibility was thus reduced for TAN (−3%; P ≤ 0.05). The effect of OTE on ruminal and milk FA profiles suggests an impact on rumen microbiota. Nitrogen isotopic discrimination between animal proteins and diet (Δ¹⁵N) was evaluated as a proxy for NUE. While no differences in NUE were observed across diets, a lower Δ¹⁵N of plasma proteins was found when comparing TAN v. CON diets. This finding supports the concept that Δ¹⁵N would mainly sign the N partitioning at the metabolic level rather than the overall NUE, with the latter also being impacted by digestive processes. Our results agree with a N shift from urine to faeces, and this strategy can thus be adopted to decrease the environmental impact of ruminant protein feeding.     

Nitrogen utilisation,energy utilisation and methane emissions of sheep grazing in two types of pasture

Livestock grazing plays a significant role in maintaining grasslands and promoting animal production globally. To understand the livestock performance in sown pasture (SP) vs native pasture (NP) is important to ensure more effective grassland-livestock interactions with minimal environmental impact. A 2 (treatment) * 2 (period) Latin Square design experiment was conducted with 10 growing Hu sheep ♂ × thin-tailed Han sheep ♀ rams grazed perennially SP vs NP in an inland arid region of China. The objectives were to evaluate the effects of grazing management on nutrient digestibility, nitrogen (N) and energy utilisation and methane (CH₄) emission. The N intake, N retained and energy intake (gross energy (GE), and digestible and metabolisable energy) of sheep grazing in SP were significantly increased compared with those grazing in NP. There were significant linear relationships between DM intake (DMI) (g/kg BW or g/kg BW^0.75) or CH₄ (g/kg BW or g/kg BW^0.75) emissions and forage nutrient and GE concentrations within each grassland type. The linear regression analysis indicated that forage CP or ether extract concentration was a good predictor for DMI (g/kg BW or g/kg BW^0.75) (R² = 0.756 or 0.752), and CH₄ emission could be predicted using forage nutrient and GE concentrations (R² = 0.381–0.503). These results suggest that DMI and CH₄ emissions per unit metabolic BW were accurately predicted by multiple-factor combinations of forage nutrients, including ether extract and CP paired with GE. The present output could provide useful information for the development of sustainable sheep grazing systems in the inland arid regions of the world.     

Methane emissions from two breeds of beef cows offered diets containing barley straw with either grass silage or brewers’ grains

Increasing the concentration of dietary lipid is a promising strategy for reducing methane (CH₄) emissions from ruminants. This study investigated the effect of replacing grass silage with brewers’ grains on CH₄ emissions of pregnant, non-lactating beef cows of two breeds. The experiment was a two×two factorial design comprising two breeds (LIMx, crossbred Limousin; and LUI, purebred Luing) and two diets consisting of (g/kg diet dry matter (DM)) barley straw (687) and grass silage (301, GS), or barley straw (763) and brewers’ grains (226, BG), which were offered ad libitum. Replacing GS with BG increased the acid-hydrolysed ether extract concentration from 21 to 37 g/kg diet DM. Cows (n=48) were group-housed in equal numbers of each breed across two pens and each diet was allocated to one pen. Before measurements of CH₄, individual dry matter intake (DMI), weekly BW and weekly body condition score were measured for a minimum of 3 weeks, following a 4-week period to acclimatise to the diets. CH₄ emissions were subsequently measured on one occasion from each cow using individual respiration chambers. Due to occasional equipment failures, CH₄ measurements were run over 9 weeks giving 10 observations for each breed×treatment combination (total n=40). There were no differences between diets for daily DMI measured in the chambers (9.92 v. 9.86 kg/day for BG and GS, respectively; P>0.05). Cows offered the BG diet produced less daily CH₄ than GS-fed cows (131 v. 156 g/day: P<0.01). When expressed either as g/kg DMI or kJ/MJ gross energy intake (GEI), BG-fed cows produced less CH₄ than GS-fed cows (13.5 v. 16.4 g/kg DMI, P<0.05; 39.2 v. 48.6 kJ/MJ GEI, P<0.01). Breed did not affect daily DMI or CH₄ expressed as g/day, g/kg DMI or kJ/MJ GEI (P>0.05). However, when expressed as a proportion of metabolic BW (BW^0.75), LUI cows had greater DMI than LIMx cows (84.5 v. 75.7 g DMI/kg BW^0.75, P<0.05) and produced more CH₄ per kg BW^0.75 than LIMx cows (1.30 v. 1.05 g CH₄/kg BW^0.75; P<0.01). Molar proportions of acetate were higher (P<0.001) and propionate and butyrate lower (P<0.01) in rumen fluid samples from BG-fed compared with GS-fed cows. This study demonstrated that replacing GS with BG in barley straw-based diets can effectively reduce CH₄ emissions from beef cows, with no suppression of DMI.     

Effects of replacing grass silage with either maize silage or concentrates during late pregnancy on the performance of breeding ewes fed isonitrogenous diets

A study was undertaken to investigate the performance of breeding ewes fed a range of forage and concentrate-based diets in late pregnancy, balanced for supply of metabolizable protein (MP). For the final 6 weeks before lambing, 104 twin-bearing multiparous ewes were offered one of four diets: ad libitum precision-chop grass silage + 0.55 kg/day concentrates (GS); ad libitum maize silage + 0.55 kg/day concentrates (MS); a 1 : 1 mixture (on a dry matter (DM) basis) of grass silage and maize silage fed ad libitum + 0.55 kg/day (GSMS); or 1.55 kg/day concentrates + 50 g/day chopped barley straw (C). The CP content of the concentrates was varied between treatments (157 to 296 g/kg DM) with the aim of achieving a daily intake of 130 g/day MP across all treatments. Compared with ewes fed GS, forage DM intake was higher (P < 0.05) in ewes fed MS (+0.21 kg/day) and GSMS (+0.16 kg/day), resulting in higher (P < 0.001) total DM intakes with these treatments. C ewes had the lowest total DM intake of all the treatments examined (P < 0.001). C ewes lost more live weight (LW; P < 0.001) and body condition score (BCS; P < 0.05) during the first 3 weeks of the study but there were no dietary effects on ewe LW or BCS thereafter. The incidence of dystocia was lower (P < 0.01) in C ewes compared with those offered silage-based diets (7.5% v. 37.4% ewes), and was higher (P < 0.01) in ewes fed MS compared with GS or GSMS (50.7%, 34.7% and 26.9%, respectively). There were no significant dietary effects on the plasma metabolite concentrations of ewes in late pregnancy, pre-weaning lamb mortality, weaned lamb output per ewe or on lamb growth rate. The results of this study demonstrate that both maize silage and all-concentrate diets can replace grass silage in pregnant ewe rations without impacting on performance, provided the supply of MP is non-limiting. The higher incidence of dystocia in ewes fed maize silage as the sole forage is a concern.     

Effect of increasing the proportion of chicory in forage-based diets on intake and digestion by sheep

There is a lot of evidence that chicory could be a highly palatable and nutritious source of forage for ruminants, well adapted to climate change and dry conditions in summer, thanks to its resistance to drought and high water content. This study aimed to describe the effect of incorporating chicory to ryegrass or to a ryegrass–white clover mixture on feeding behaviour, digestive parameters, nitrogen (N) balance and methane (CH₄) emissions in sheep. In total, three swards of ryegrass, white clover and chicory were established and managed in a manner ensuring the forage use at a constant vegetative stage throughout the experiment. In all, four dietary treatments (pure ryegrass; binary mixture: 50% ryegrass–50% chicory; ternary mixture: 50% ryegrass–25% white clover–25% chicory; and pure chicory) were evaluated in a 4×4 replicated Latin square design with eight young castrated Texel sheep. Each experimental period consisted of an 8-day diet adaptation phase, followed by a 6-day measuring phase during which intake dynamics, chewing activity, digestibility, rumen liquid passage rate, fermentation end-products, N balance and CH₄ emissions were determined. Data were analysed using a mixed model and orthogonal contrasts were used to detect the potential associative effects between ryegrass and chicory. The daily voluntary dry matter intake was lower for pure ryegrass than for diets containing chicory (P<0.001) and increased quadratically from 1.39 to 1.74 kg/day with increasing proportion of chicory. Huge positive quadratic effects (P<0.001) between ryegrass and chicory were detected on eating time and eating rate just after feeding indicating an increase of the motivation to eat with mixtures, whereas rumination activity decreased linearly with the proportion of chicory (P<0.001). The organic matter digestibility was similar among treatments (around 80%), but a strong positive quadratic P<0.001) effect was observed on liquid passage rate suggesting that chicory allowed fast particle breakdown in the rumen. Animals fed with the ryegrass–white clover–chicory mixture had the higher urinary N losses (P<0.001), whereas retained N per day or per g N intake was greater when the proportion of chicory was at least 50% (P<0.001) being ~40% greater than for the other treatments. The CH₄ yield was lower with pure chicory than with the other treatments (P<0.001) for which emissions were similar. In conclusion, mixing ryegrass and chicory in equal proportions produces a synergy on voluntary intake and an improved N use efficiency likely due to complementarity in chemical composition, increased motivation to eat and faster ruminal particle breakdown.     

Effects of feed intake on enteric methane emissions from sheep fed fresh white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) forages

Published analyses of enteric methane (CH₄) emissions from sheep and cattle show an inverse relationship between feed intake and CH₄ yield (g CH₄/kg dry matter (DM) intake), which suggests opportunities for reducing CH₄ emissions from feed eaten and per unit of animal production. Most relationships between feed intake and CH₄ yield have been based on animals fed conserved feeds, especially silages and grains. Our research is a series of experiments with fresh white clover (Trifolium repens) and perennial ryegrass (Lolium perenne; ryegrass) forages fed to sheep at a range of feed intake levels. This study was comprised of four experiments where good quality freshly harvested white clover or ryegrass were fed to sheep over a three-fold range in DM intake, and CH₄ emissions were measured in respiration chambers for two consecutive days in each experiment. Measurements were made from 16 sheep in Experiment 1 (fed at 1.6 × metabolizable energy requirements for maintenance; ME_m), 28 sheep in Experiment 2 (at 0.8 and 2.0 × ME_m), eight sheep and two measurement periods in Experiment 3 (at 1.6 × ME_m), and 30 sheep in Experiment 4 (fed at 0.8, 1.2, 1.6, 2.0 and 2.5 × ME_m). Prior to each experiment, sheep had a 10 d acclimatization period to diets. Apparent digestibility was measured over 7 d from sheep in Experiments 1, 3 and 4, along with collection of rumen digesta for volatile fatty acid (VFA) determination. Although CH₄ yields differed when sheep were fed white clover or ryegrass at similar intakes, the differences were inconsistent and mean values similar across all experiments. This, and a similar structure of all experiments, enabled combined analysis of data from all four experiments using the restricted maximum likelihood (REML) procedure to estimate effects of feed intake level on digestibility, digestible nutrient intake, gas emissions, and VFA concentrations in the rumen. The REML analysis showed that when DM intake increased from 0.40 to 1.60 kg/d, the predicted responses were an increase in CH₄ production (g/d) of 187% (12.4–35.6 g/d; P<0.001), and a decline in CH₄ yield of 21% (25.6–20.2 g/kg DM intake; P<0.001). High feed intake levels were associated with increased molar proportions (mM of total VFA) of propionate from 0.17 to 0.21 (P=0.038). Single and multiple regressions were completed on the data from all experiments, with organic matter (OM) intake predicting 0.87 of the variation in CH₄ production, and molar proportion of propionate predicting 0.60 of the variation in CH₄ yield. Increasing feed intakes by 1 kg/d of DM reduced CH₄ yield by 4.5 g/kg DM intake. Plant chemical composition was weakly related to CH₄ yield. High intakes of fresh forages will lower CH₄ yield from fermentation, but effects of feed composition on CH₄ emissions were minor. The interaction between effects of feed intake and rumen function requires further investigation to understand relationships with CH₄ emissions.     

Effects of grass and maize silage feed value,offering soybean meal with maize silage,and concentrate feed level in late pregnancy,on ewe and lamb performance

In many countries, daily herbage accumulation on pasture declines towards zero during the winter period; thus, many pregnant ewes are housed and offered conserved forages supplemented with concentrate prior to parturition. The effects of forage type and feed value (FV), offering soybean meal with maize silage during mid and late pregnancy, and concentrate feed level in late pregnancy on the performance of ewes and their progeny (to slaughter) were evaluated. Ewes (n = 151) were assigned to one of nine treatments from mid-pregnancy until lambing. Medium FV and high FV grass silages (metabolisable energy concentrations of 10.7 and 12.0 MJ/kg DM) were offered ad libitum supplemented with either 15 or 25 kg concentrate/ewe during late pregnancy. Low and high DM maize silages (starch concentrations of 80 and 315 g/kg DM) were offered ad libitum either alone or with soybean meal (200 g/d) and supplemented with 15 kg concentrate during late pregnancy. A final treatment consisted of high FV grass silage supplemented with 5 kg soybean/ewe over the final 4 weeks of pregnancy. Ewes and lambs were put to pasture in a rotational-grazing system within 3 days of lambing. There were no interactions (P > 0.05) between grass silage FV and concentrate feed level for ewe or lamb traits. Increasing grass silage FV increased food intake (P < 0.001) during late pregnancy, ewe BW and body condition score (BCS) at lambing (P < 0.001), lamb BW at birth (P < 0.001) and weaning (P < 0.05), and reduced age at slaughter (P = 0.06). Increasing concentrate feed level increased metabolisable energy (P < 0.05) intake during late pregnancy but had no effect (P > 0.05) on ewe or lamb performance. Increasing maize DM at harvest and offering soybean meal with maize silage increased food intake (P < 0.001) and ewe BW and BCS at lambing (P < 0.05 or P < 0.01). Offering soybean meal with maize silage increased lamb BW at birth (P < 0.01) and reduced age at slaughter (P < 0.05). Reducing supplementation of high FV grass silage to 5 kg of soybean meal had no effect (P > 0.05) on animal performance. Replacing grass silage with maize silage did not affect (P > 0.05) BW gain of lambs. It is concluded that increasing the FV of the grass silage offered during pregnancy had the greatest positive impact on ewe and lamb performance.     

Nutrient and energy balance,and amino acid digestibility in weaned piglets fed wheat bran and an exogenous enzyme combination

The digestive system of the weaned piglets can be affected by the type of ingredients present in the diet, and a high fibre content in diets can limit the use of other nutrients and energy. The study was conducted to determine the effects of multicarbohydrase (MC) and phytase (Phy) supplementation on the nutritive value of wheat bran (WB) in weaned piglets. Multicarbohydrase preparation had 700 U α-galactosidase, 2200 U galactomannanase, 3000 U xylanase and 22 000 U β-glucanase per kilogram of diet, and Phy had 500 phytase units – FTU/kg of diet. Twenty-five weaned piglets (6.1 ± 0.63 kg) at 21 days old were fed five diets in a completely randomised experimental design with a 2 × 2 + 1 (0 and 200 mg/kg MC; 0 and 50 mg/kg Phy; and basal diet – BD) factorial arrangement used to determine treatment effects. An additional group of piglets was fed a corn-basal diet during apparent digestibility of nutrients, and fed a 5% casein-corn starch basal diet during apparent and standardised ileal digestibility (SID) of amino acid evaluations. Piglets were individually caged until 38 days old, when Ileal digesta was collected at slaughter. Test diets were made by mixing the basal diets and WB 7 : 3 (w/w), with or without MC, Phy or the combination. There was an interaction trend (P = 0.07) between MC and Phy in the balance of ash, digestible energy (DE) and metabolisable energy (ME). Effects of MC (P < 0.01) on DM, N retention, DE and ME, as well as an effect of Phy (P < 0.05) on ash, DE and ME and a trend in protein digestibility (P = 0.07) also was observed. The enzyme combination showed effect (P < 0.05) on SID of Lys, Pro and Ser; as a trend (P < 0.07) on His, Thr and Val. Isolated, MC also suggested improving (P < 0.07) on SID of His, Lys, Ala (P < 0.05), while Phy improved (P < 0.06) SID of Leu, Lys, Met (P < 0.01), Thr, Val, Ala (P < 0.01), Pro and Ser (P < 0.05). The MC carbohydrate complex was characterised as a viable alternative to increase the apparent nutrients digestibility and SID of amino acids when WB was used in the diet of young pigs and, when combined with Phy, suggested an additive effect on the apparent use of energy.     

The influence of grass silage-to-maize silage ratio and concentrate composition on methane emissions,performance and milk composition of dairy cows

It is well-established that altering the proportion of starch and fibre in ruminant diets can alter ruminal and post-ruminal digestion, although quantitative evidence that this reduces enteric methane (CH₄) production in dairy cattle is lacking. The objective of this study was to examine the effect of varying grass-to-maize silage ratio (70 : 30 and 30 : 70 DM basis), offered ad libitum, with either a concentrate that was high in starch or fibre, on CH₄ production, intake, performance and milk composition of dairy cows. A total of 20 cows were allocated to one of the four experimental diets in a two-by-two factorial design run as a Latin square with each period lasting 28 days. Measurements were conducted during the final 7 days of each period. Cows offered the high maize silage ration had a higher dry matter intake (DMI), milk yield, milk energy output and lower CH₄ emissions when expressed per kg DMI and per unit of ingested gross energy, but there was no difference in total CH₄ production. Several of the milk long-chain fatty acids (FA) were affected by forage treatment with the most notable being an increase in 18:0, 18:1 c9, 18:2 c9 c12 and total mono unsaturated FA, observed in cows offered the higher inclusion of maize silage, and an increase in 18:3 c9 c12 c15 when offered the higher grass silage ration. Varying the composition of the concentrate had no effect on DMI or milk production; however, when the high-starch concentrate was fed, milk protein concentration and milk FAs, 10:0, 14:1, 15:0, 16:1, increased and 18:0 decreased. Interactions were observed for milk fat concentration, being lower in cows offered high-grass silage and high-fibre concentrates compared with the high-starch concentrate, and FA 17:0, which was the highest in milk from cows fed the high-grass silage diet supplemented with the high-starch concentrate. In conclusion, increasing the proportion of maize silage in the diets of dairy cows increased intake and performance, and reduced CH₄ production, but only when expressed on a DM or energy intake basis, whereas starch-to-fibre ratio in the concentrate had little effect on performance or CH₄ production.     

A calorimetric investigation of the nutritive value of formic acid- and formaldehyde—Formic acid-treated grass silages

Experiments were conducted to study the utilisation of a ryegrass mixture preserved chemically by formic acid (silage 1) of mean gross energy (GE) 18.6 MJ/kg dry matter (DM), and formaldehyde—formic acid (silage 2) of mean GE 18.3 MJ/kg DM. The parent grass and resulting silages were analysed chemically and calorimetric balance trials were performed with four sheep fed at maintenance and 1.5 times maintenance.Silages 1 and 2 had similar, high digestibility coefficients for DM (0.732 and 0.718), organic matter (OM) (0.755 and 0.742), and energy (E) (0.730 and 0.710). The digestible energy (DE) contents of silages 1 and 2 were 13.3 and 12.7 MJ/kg DM, respectively, at the lower level of feeding and 13.8 and 12.8 MJ/kg DM, respectively, at the higher level. The metabolisable energy (ME) contents of silages 1 and 2 were 11.6 and 10.8 MJ/kg DM, respectively, at the lower level of feeding and 12.0 and 11.0 MJ/kg DM, respectively, at the higher level.The mean efficiency of utilisation of ME for growth (K_g) for silages 1 and 2 was 0.43 and 0.39, respectively; these results are in broad agreement with those predicted by other workers.     

Nutritional values of forage-legume-based silages and protein concentrates for growing pigs

In organic pig production systems, one of the main challenges is to meet the demand for resources rich in protein. Among the resources available, temperate green plants, such as forage legumes, are potential sources of energy and protein. The aim of the study was to determine the nutritional value of silages (S) from the whole plant of lucerne (L) and red clover (R) and protein pastes (PPs) obtained from L and R leaves. In a first trial, 30 pigs were used in a factorial design to determine the total tract digestibility (TTD) of dietary nutrients and energy in five dietary treatments. The control group was fed a control diet (C1). The lucerne silage (LS) and red clover silage (RS) groups were fed a 78%:22% mixture (on a DM basis) of the C1 diet and LS or RS. The lucerne protein paste (LPP) and the red clover protein paste (RPP) groups were fed an 81%:19% mixture (on a DM basis) of the C1 diet and LPP or RPP. In the second trial, five pigs were used in a 5 × 5 Latin square design to evaluate the standardised ileal digestibility (SID) of amino acids (AAs) in the four legume products. The control diet (C2) was formulated with casein as the sole protein source. The LS and RS groups were fed an 85%:15% mixture (on a DM basis) of the C2 diet and LS or RS. The LPP and RPP groups were fed an 80%:20% mixture (on a DM basis) of the C2 diet and LPP or RPP. Regardless of the plant species, silages obtained from L and R leaves contained less AA and more fibre than protein pastes. While the fresh forages contained the same percentage of protein N in total N (63.6%), lucerne lost more protein N during ensiling than red clover (?75.5 vs ?33.8%). The calculated TTD coefficient of energy was higher in silages than in protein pastes and lower in R than in L products (72.8, 71.5, 67.7, and 61.3 for LS, RS, LPP and RPP, respectively). The SID of total essential AA was higher in LPP than in RPP (87.2 vs 79.2%) whereas it was lower in LS than in RS (33.2 vs 56.8%). The lower SID values in silages were explained by the protein degradation during the ensiling process and a high proportion of AA linked to the NDF fraction. The results of the present study show that protein pastes obtained from lucerne and red clover are valuable protein sources for pig. In contrast, legume silages have to be considered as an energy source rather than a protein source.     

Individual methane emissions (and other gas flows) are repeatable and their relationships with feed efficiency are similar across two contrasting diets in growing bulls

In the current economic and environmental context, the selection of livestock phenotypes combining high feed efficiency (FE) and low greenhouse gas emissions is interesting. This study aimed to quantify methane (CH₄) emissions and other gas flows (carbon dioxide (CO₂) and dihydrogen (H₂) emissions, oxygen (O₂) consumption) in growing bulls fed with two contrasting diets in order to (i) evaluate the persistence of individual variability in gas flows through time, and (ii) assess the inter-individual relationship between gas flows and FE across diets. Charolais bulls were fattened for 6 months during two consecutive years in two independent batches (50–51 per year). In each batch, half of the animals received a total mixed ad libitum ration either based on maize silage (62% dietary DM) or high-starch concentrate (MS-S), and half based on grass silage (59% dietary DM) and high-fibre concentrate (GS-F). The absolute gas flows (g/d) were individually measured with 2 GreenFeed systems during 88 days (group 1) and 64 days (group 2). All gas flows were also expressed in g/kg DM intake (gas yield), in g/kg average daily gain (CH₄ intensity) and residual of daily emissions for CH₄ (R CH₄). Different FE metrics (residual feed intake (RFI), residual gain (RG) and feed conversion efficiency (FCE)) were investigated during the same period. The relationships between gas flows and FE metrics were tested by linear regression with the diet as fixed effect. For both diets, we observed a consistent individual variability over the measurement period for absolutes values (g/d) of CH_4, CO₂, and O₂ (repeatability >0.7 for GS-F and >0.6 for MS-S). Gas flows (g/d) were positively correlated with RFI with both diets: animals that ingested food in excess of their theoretical maintenance and growth requirements emitted more CH₄, CO₂ and consumed more O₂. The positive relationship between absolute CH₄ emissions and RFI highlighted the interest for low-CH₄ emitters and efficient growing bulls when fed with high-energy diets rich in starch or fibre. For both diets, RCH₄, CH₄ yield and CH₄ intensity were not related to RFI whereas a significant negative relationship was reported between CH₄ intensity and RG, and FCE. These data suggest that intake is the main driver of the phenotypic relationships between CH₄ traits and RFI. Further studies including larger numbers of animals on highly contrasting energy diets are needed to investigate the underlying biological regulatory mechanisms of the methanogenic potential of an animal in relation to production traits.     

Evaluation of physical structure value in spring-harvested grass/clover silage and hay fed to heifers

The physical structure value of conserved grass/clover forages of spring harvest was evaluated by assessing effects of harvest time, conservation method, iNDF/NDF ratio and NDF intake (NDFI) per kg BW on chewing activity and fecal particle size in dairy heifers. A mixed sward consisting of ryegrass (Lolium perenne), red clover (Trifolium pratense) and white clover (Trifolium repens) was harvested in 2009 on May 9 (early) and 25 (late), and both cuts were conserved as silage and hay. The early silage, early hay, late silage and late hay contained dry matter (DM) of 454, 842, 250 and 828 g/kg, and NDF of 315, 436, 414 and 503 g/kg DM, respectively. Forages were fed as sole feed to four Jersey heifers of 435±30 kg BW in a 4×4 Latin square experiment. Feeding level was 90% of individual ad libitum intake, divided equally across two daily meals offered at 0800 and 1530 h. Chewing activity was estimated from recorded jaw movements (JM) oscillations continuously logged for 96 h and summarized per 24 h as mean effective rumination time and eating time. Eating behavior was further observed during four 20-min test meals. Weight proportion of large feces particles (>1.0 mm) and geometric mean fecal particle size (GPS) were calculated. Potentially indigestible NDF (iNDF) was estimated by incubation for 288 h in situ. The daily DM intake (DMI) decreased with progressing maturity at harvest (P<0.001) while daily NDFI was unaffected by harvest time (P>0.05). Earlier harvest led to less rumination per kg NDFI (P<0.01), similar eating time per kg NDFI (P>0.05) and similar proportion of large particles (P>0.01) compared with later harvest. Rumination time per kg NDFI decreased with higher NDFI per kg BW (P<0.001) and with lower iNDF/NDF ratio (P<0.01). Content and potential digestibility of NDF was greater in hay than in silage from the same harvest probably due to field loss and therefore confounded effects of conservation method. This study of high digestibility grass/clover silage and hay showed that NDF content and NDFI per kg BW affect fecal particle size and rumination time per kg NDF, and suggests implementation of NDFI per kg BW in systems evaluating physical structure in diets.     

Effects of condensed tannin-amended cassava silage blend diets on feeding behavior,digestibility, nitrogen balance,milk yield and milk composition in dairy goats

Condensed tannins (CTs) are phenolic compounds derived from secondary plant metabolism that act as part of the plant's chemical defense system against pathogen invasion and herbivorous attack. This study aimed to evaluate the intake, digestibility, nitrogen (N) balance, production and composition of milk from goats fed cassava silage with added levels of CTs. Eight Anglo-Nubian goats with a mean BW of 40 ± 2.0 kg were distributed in a double Latin square design with four levels of CTs (0, 25, 50 and 75 g/kg DM) with four 20-day periods with 15 days of adaptation and five evaluation days for each period. No differences were observed in DM, NDF, CP intake and feed conversion (grams of DM intake (DMI) per gram of milk produced); however, when expressed as percent of BW, DMI showed a quadratic increase to 29.1 g/kg. As the level of supplemented CTs increased in the diet, the CP digestibility (P = 0.023), NDF (P = 0.044), non-fiber carbohydrates (NFC; P = 0.032) and total digestible nutrients (P = 0.033) exhibited a linear decrease. Furthermore, the addition of CTs to cassava silage induced a linear increase in N-fecal excretion (P = 0.014) and a positive quadratic effect on N-retained (P = 0.014) and N-balance (P = 0.024) as well as a positive quadratic trend in N-digested (P = 0.092). Milk urea N (P = 0.023) decreased linearly. The addition of CTs to cassava silage had a positive quadratic effect on ruminating time (P = 0.011). In addition, comparing the use or non-use from the orthogonal contrast test, the inclusion of CTs in goat diet increased water and N-intake, CP and NDF digestibility, spent time eating and ruminating and N-balance and decreased milk production corrected^3.5%, fat milk content, milk urea N and dry defatted extract of milk. Thus, adding CTs to cassava silage at 25 g/kg total DM promoted goats' greater use of the diet without impairing feed conversion and the quality of goat milk produced. Dietary levels of 50 and 75 g/kg total DM are not recommended because under the conditions of this study, they reduced the productive efficiency of dairy goats.     

Carbohydrate-rich supplements can improve nitrogen use efficiency and mitigate nitrogenous gas emissions from the excreta of dairy cows grazing temperate grass

Temperate pasture species constitute a source of protein for dairy cattle. On the other hand, from an environmental perspective, their high N content can increase N excretion and nitrogenous gas emissions by livestock. This work explores the effect of energy supplementation on N use efficiency (NUE) and nitrogenous gas emissions from the excreta of dairy cows grazing a pasture of oat and ryegrass. The study was divided into two experiments: an evaluation of NUE in grazing dairy cows, and an evaluation of N-NH₃ and N-N₂O volatilizations from dairy cow excreta. In the first experiment, 12 lactating Holstein × Jersey F1 cows were allocated to a double 3 × 3 Latin square (three experimental periods of 17 days each) and subjected to three treatments: cows without supplementation (WS), cows supplemented at 4.2 kg DM of corn silage (CS) per day, and cows supplemented at 3.6 kg DM of ground corn (GC) per day. In the second experiment, samples of excreta were collected from the cows distributed among the treatments. Aliquots of dung and urine of each treatment plus one blank (control – no excreta) were allotted to a randomized block design to evaluate N-NH₃ and N-N₂O volatilization. Measurements were performed until day 25 for N-NH₃ and until day 94 for N-N₂O. Dietary N content in the supplemented cows was reduced by 20% (P < 0.001) compared with WS cows, regardless of the supplement. Corn silage cows had lower N intake (P < 0.001) than WS and GC cows (366 v. 426 g/day, respectively). Ground corn supplementation allowed cows to partition more N towards milk protein compared with the average milk protein of WS cows or those supplemented with corn silage (117 v. 108 g/day, respectively; P < 0.01). Thus, even though they were in different forms, both supplements were able to increase (P < 0.01) NUE from 27% in WS cows to 32% in supplemented cows. Supplementation was also effective in reducing N excretion (761 v. 694 g/kg of N_intake; P < 0.001), N-NH₃ emission (478 v. 374 g/kg of N_milk; P < 0.01) and N-N₂O emission (11 v. 8 g/kg of N_milk; P < 0.001). Corn silage and ground corn can be strategically used as feed supplements to improve NUE, and they have the potential to mitigate N-NH₃ and N-N₂O emissions from the excreta of dairy cows grazing high-protein pastures.     

Effect of altering ruminal pH by dietary buffer supplementation on methane emissions from sheep fed forage rape

Low methane (CH₄) emissions from sheep fed forage rape (Brassica napus) might be related to low ruminal pH value. In this study, sodium carbonate (Na₂CO₃: SC) was supplemented to the diet to alter ruminal pH for evaluation of its role in CH₄ emissions from sheep fed forage rape. Fourteen intact and eight fistulated Romney sheep were adapted to forage rape over 32 days and then randomly allocated to one of two groups: diets supplemented with SC or not (control). Methane emissions were measured from intact sheep in seven experimental periods. In parallel, ruminal pH and fermentation characteristics were assessed using the fistulated sheep. In the first (P01) and the second (P02) periods, none of the sheep received SC to examine the baseline CH₄ emissions. The P01 period was used as a covariate for analysis of gas emission measurements in subsequent measurement periods. Sodium carbonate was offered at 5% of the forage DM in P03 and P04, increased to 8% in P05 and P06 to assess the effect of pH increase on CH₄ emissions and stopped in P07 to assess if the CH₄ emissions reverted to values similar to those measured before the supplementation started. Methane yield (g/kg forage DM intake) was similar for the sheep in both groups during P02 and P03, but sheep supplemented with SC in the diet emitted 36%, 49% and 30% more CH₄ per unit of forage DM intake than those in the control group during P04, P05 and P06, respectively. Emissions returned to similar levels when SC supplementation was ceased in P07. Ruminal pH was 0.412 to 0.565 units higher in SC supplemented sheep than for the control group during the SC treatment periods. Based on the lack of an immediate response in CH₄ emissions to the supplementation of SC in P03, the positive responses in P04 to P06 and the rapid disappearance of the response after supplementation with SC stopped in P07, we propose a new hypothesis that ruminal pH effects on CH₄ emissions are possibly through medium-term changes in microbial and methanogenic communities in the rumen, rather than a direct, short-term impact on methanogens per se. In conclusion, SC supplemented to the forage rape diet of sheep increased rumen pH, leading to an increase in CH₄ emissions. Low ruminal pH in sheep fed forage rape explains, at least partially, the reported low CH₄ emissions from sheep fed with this forage crop.     

The effect of N-fertilisation rate or inclusion of red clover to timothy leys on fatty acid composition in milk of dairy cows fed a commercial silage : concentrate ratio

The aim of this experiment was to, under typical Swedish production conditions, evaluate the effects of grass silages subjected to different N-fertilisation regimes fed to dairy cows on the fatty acid (FA) composition of their milk, and to compare the grass silages in this respect to red clover-dominated silage. Grass silages made from first year Phleum pratense L. leys subjected to three N-fertilisation regimes (30, 90 and 120 kg N/ha, designated G-30, G-90 and G-120, respectively) and a mixed red clover–grass silage (Trifolium pratense L. and P. pratense L.; 60/40 on dry matter (DM) basis, designated RC–G) were produced. The experiment was conducted as a change-over design, including 24 primiparous and multiparous dairy cows of the Swedish Red breed, each of which was allocated to three of the four diets. The cows were offered 11 kg DM of silage and 7 kg concentrates. The silages had similar DM and energy concentrations. The CP concentration increased with increase in N-fertilisation level. There was a linear increase in DM intake of the different silages with increased N fertilisation. There were also differences in concentrations of both individual and total FAs amongst silages. The daily milk production (kg/day) did not significantly differ between treatments, but G-30 silage resulted in higher concentrations of 18:2n-6 in the milk compared with the other two grass silages. The highest concentrations of 18:3n-3 and cis-9, trans-11 18:2 were found in milk from cows offered the RC–G silage. The G-30 diet resulted in higher concentration of 18:2n-6 and the same concentration of 18:3n-3 in the milk as the other grass silages, despite lower intake levels of these FAs. The apparent recoveries of 18:3n-3 from feed to milk were 5.74%, 4.27%, 4.10% and 5.31% for G-30, G-90, G-120 and RC–G, respectively. A higher recovery when red clover is included in the diet confirms previous reports. The higher apparent recovery of 18:3n-3 on the G-30 treatment may be related to the lower silage DM intake, which led to a higher relative proportion of ingested FAs originating from concentrates compared with the G-90 and G-120 diets. With the rates and types of concentrates used in this study, the achieved differences in FA composition among the silages were not enough to influence the concentrations of unsaturated FAs in milk.