The intake of steers and heifers fed on mixtures of alkali-treated or untreated straw with grass silage

Two experiments were made to investigate the intake of cattle when offered straw and silage mixtures.In a trial of changeover design 12 Friesian castrates (steers) were offered five diets. These were grass silage alone or mixed with untreated or NaOH treated straw supplying 20 or 40% of the total dry matter. The addition of 20% straw to the diet significantly reduced dry matter intake, and a further reduction occurred at 40%. Treating the straw with NaOh did not increase dry matter intake but led to an associated increase in digestible organic matter intake.Twelve Ayrshire heifers were given four diets in a trial of changeover design. The diets were silage only and three straw : silage mixtures in which straw provided 40% of the dry matter. The straws were untreated, NaOH treated or KOH treated. Untreated straw markedly depressed dry matter intake; NaOH raised the digestibility of straw and thus increased digestible organic matter intake significantly. The dry matter intake of the heifers was much greater than anticipated with the KOH treated straw : silage mixture and was similar to that achieved with silage only.     

The repeatability of feed intake and feed efficiency in beef cattle offered high-concentrate,grass silage and pasture-based diets

Breeding values for feed intake and feed efficiency in beef cattle are generally derived indoors on high-concentrate (HC) diets. Within temperate regions of north-western Europe, however, the majority of a growing beef animal’s lifetime dietary intake comes from grazed grass and grass silage. Using 97 growing beef cattle, the objective of the current study was to assess the repeatability of both feed intake and feed efficiency across 3 successive dietary test periods comprising grass silage plus concentrates (S+C), grazed grass (GRZ) and a HC diet. Individual DM intake (DMI), DMI/kg BW and feed efficiency-related parameters, residual feed intake (RFI) and gain to feed ratio (G : F) were assessed. There was a significant correlation for DMI between the S+C and GRZ periods (r = 0.32; P < 0.01) as well as between the S+C and HC periods (r = 0.41; P < 0.001), whereas there was no association for DMI between the GRZ and HC periods. There was a significant correlation for DMI/kg BW between the S+C and GRZ periods (r = 0.33; P < 0.01) and between the S+C and HC periods (r = 0.40; P < 0.001), but there was no association for the trait between the GRZ and HC periods. There was a significant correlation for RFI between the S+C and GRZ periods (r = 0.25; P < 0.05) as well as between S+C and HC periods (r = 0.25; P < 0.05), whereas there was no association for RFI between the GRZ and HC periods. Gain to feed ratio was not correlated between any of the test periods. A secondary aspect of the study demonstrated that traits recorded in the GRZ period relating to grazing bite rate, the number of daily grazing bouts and ruminating bouts were associated with DMI (r = 0.28 to 0.42; P < 0.05 - 0.001), DMI/kg BW (r = 0.36 to 0.45; P < 0.01 - 0.001) and RFI (r = 0.31 to 0.42; P < 0.05 - 0.001). Additionally, the number of ruminating boli produced per day and per ruminating bout were associated with G : F (r = 0.28 and 0.26, respectively; P < 0.05). Results from this study demonstrate that evaluating animals for both feed intake and feed efficiency indoors on HC diets may not reflect their phenotypic performance when consuming conserved forage-based diets indoors or when grazing pasture.     

Climate change and cattle nutritional stress

Owing to the complex interactions among climate, plants, cattle grazing, and land management practices, the impacts of climate change on cattle have been hard to predict. Predicting future grassland ecosystem functioning relies on understanding how changes in climate alter the quantity of forage produced, but also forage quality. Plant protein, which is a function of plant nitrogen concentrations, and digestible energy limit the performance of herbivores when in short supply; moreover, deficiencies can be expensive to mitigate. To better understand how changes in temperature and precipitation would affect forage protein and energy availability, we analyzed over 21 000 measurements of cattle fecal chemistry acquired over 14 years in the continental US. Our analysis of patterns in forage quality among ecologically defined regions revealed that increasing temperature and declining precipitation decreased dietary crude protein and digestible organic matter for regions with continental climates. Within regions, quality also declined with increased temperature; however, the effects of precipitation were mixed. Any future increases in precipitation would be unlikely to compensate for the declines in forage quality that accompany projected temperature increases. As a result, cattle are likely to experience greater nutritional stress in the future. If these geographic patterns hold as a proxy for future climates, agriculture will require increased supplemental feeds or the consequence will be a decrease in livestock growth.     

Foraging strategy of cattle in patchy grassland

We tested several strategies of foraging that grazing herbivores may adopt in a patchy habitat in relation to energy intake. The patch selection of cattle was investigated in an Agrostis/Festuca grassland and in a Lolium grassland in 13 observation periods over 2 years. Both grasslands were stocked with five yearling steers. Bite counts were made on patches of different vegetation structure: short, tall and mature stemmy grass. Bite size of each patch category was determined by hand-plucking. Samples of patch types were analysed for organic matter digestibility, as a measure of energy content. There was a large seasonal variation in relative patch cover and in forage characteristics. However, the differences between patches in bite size, bite rate and digestibility were consistent over time. In short patches digestibility was high, bite size was low and bite rate was high compared to stemmy patches. In tall patches digestibility was only little lower than in short patches and bite size and bite rate were intermediate between short and stemmy patches. The steers selected the short and tall patches over the stemmy patches, despite a relatively low intake rate of digestible organic matter in the short patches. Four hypotheses on foraging strategy were examined to explain the allocation of time or bites between patches: random allocation according to bites, random allocation according to grazing time, matching of time in proportion to digestibility, and matching of time in proportion to intake rate of digestible organic matter. The observed distribution of bites and time between patches was significantly different from the predictions of the various hypotheses. Patch choice was better explained by a random allocation of grazing time than by a random allocation of bites. Matching for digestible organic matter intake rate yielded the worst predictions of patch selection. Matching for digestibility gave the best explanation of patch selection, but the improvement compared to a random allocation of grazing time was not significant. The significance of the contribution of digestibility to selection may have been confounded by the effect of increased selectivity within tall patches. Observed patch selection was considered in relation to the maximization of energy intake rate. The selectivity of cattle was not pronounced, but it was consistent with a principle of maximization of energy intake on a daily basis instead of a short-term basis. Selectivity appeared to be constrained by costs of searching for and discriminating between different forage resources. It is concluded that a flexible selection for short patches over tall patches and avoidance of stemmy patches provides a good approximation of energy intake maximization in a complex and changing environment.     

The digestibility and nutritive value for dairy heifers of rations containing cellulose fibre

Cellulose residue (cellufiber) from an ammonium base acid sulphite paper process was accepted by dairy heifers to the extent of 40% of the dry matter of an all-roughage ration when mixed with maize (Zea mays) silage at time of feeding. No adverse physiological effects were observed during digestion trials lasting 80 days in which cattle were given successively diets containing 10, 20, 30 or 40% of the ration dry matter as cellufiber. Apparent digestibility of crude protein decreased and digestibility of crude fibre and acid detergent fibre increased as the cellufiber level in the ration increased. Digestibility coefficients of dry matter, nitrogen-free extract and gross energy were unaffected.Uniformity of values for total digestible nutrients, digestible energy and metabolizable energy and, also, of the body weight gains by the test animals indicated only small differences in nutritive value between rations. However, estimated nutritive values of ration components indicated appreciable differences. The TDN of cellufiber was 56% which was approximately equal to that of alfalfa (Medicago sativa) hay and was 82% of the value of maize silage. However, the digestible energy value of cellufiber (1.93 Mcal/kg DM) was only 77% of alfalfa hay and 69% of maize silage. Similarly, its metabolizable energe value of 1.41 Mcal/kg DM was 69% of that of alfalfa hay and 61% of that of maize silage.     

The effects of and interactions between the maturity of grass silage and concentrate starch source when offered as total mixed rations on the performance of dairy cows

A 2 × 2 factorial feeding experiment was conducted to examine the effects of varying the maturity level of the grass used to prepare silage and the nature of concentrate starch source and their interactions on dry matter intake (DMI), diet digestibility, energy corrected milk (ECM) production and milk composition in dairy cows. Twenty-eight multiparous Swedish Red dairy cows, 133 ± 45 days in milk (DIM), with an average milk yield of 30 ± 4 kg/day and a live weight of 624 ± 69 kg were blocked by DIM and randomly assigned to seven replicated balanced 4 × 4 Latin squares with four 21-day experimental periods. The experimental diets consisted of four total mixed rations (TMR) consisting of early-cut grass silage (EGS) supplemented with either barley- or maize-based concentrate and late-cut grass silage (LGS) supplemented with either barley- or maize-based concentrate. All TMR contained identical proportions of forage (51%) and concentrate (49%). Total tract digestibility was estimated by determining indigestible NDF (iNDF) concentrations in feeds and faeces and using iNDF as an internal marker. The feeds’ ruminal degradation parameters were determined using both in situ (nylon bag) and in vitro (gas production (GP)) techniques. Cows offered diets containing EGS had greater (P < 0.001) daily dry matter (DM) intakes, ECM yields and total tract digestibilities for DM and organic matter (OM), but these were not affected by the nature of the concentrate starch source. No interaction between the maturity of the silage and the nature of the concentrate starch source was observed for DMI, diet digestibility or ECM yield. Both grass silages and concentrates had similar rates of ruminal degradation of NDF when measured in situ. The in situ DM (P < 0.001) and starch (P = 0.001) degradation rates of barley-based concentrate were greater than those for maize-based concentrate. In vitro OM GP rates and extents were similar for both concentrate feeds. The results showed that diets containing EGS offered better animal performance and diet digestibility than diets containing LGS. The concentrate starch source did not affect animal performance, but total NDF digestibility was better with diet containing barley- than maize-based concentrate.     

Effects of mixtures of red clover and maize silages on the partitioning of dietary nitrogen between milk and urine by dairy cows

Eight multiparous lactating Holstein-Friesian cows were used to evaluate the partitioning of dietary nitrogen (N) from diets based on mixtures of red clover and maize silages in comparison with diets based on ryegrass silage. All cows received 4 kg/day of a standard dairy concentrate with one of four forage treatments in an incomplete changeover design with three 4-week periods. Three treatments were based on mixtures of red clover and maize silage. N intake was altered both by varying the ratio of these silages (40/60 and 25/75 on a dry matter (DM) basis) and by an additional treatment for which the DM intake of the 40/60 mixture was restricted to the level achieved with grass silage. Rumen passage rates were estimated from faecal excretion curves following a pulse oral dose of Dysprosium-labeled silage and urinary excretion of purine derivatives (PD) was used as an index of rumen microbial protein synthesis. Red clover silage mixtures led to significantly increased feed intake (21.5, 20.7 and 15.2 kg DM/day for 40/60 and 25/75 red clover/maize silage mixtures and grass silage, respectively), milk production (25.8, 27.8 and 20.0 kg/day for the same treatments, respectively) and milk component yields, but were without effect on milk fat and protein concentrations. The large increase in the yield of milk (24.5 kg/day) and milk components for the restricted red clover/maize silage treatment, in comparison with the grass silage treatment, was proportionately greater than the increase in DM intake (16.6 kg DM/day). There were no significant treatment effects on diet digestibility, while the higher intakes of red clover silage mixtures were associated with higher rumen passage rates (5.82%, 6.24% and 4.55%/h, respectively). There were significant effects of both N intake and forage source on the partitioning of dietary N between milk and urine. When dietary protein was diluted by the inclusion of maize silage, red clover silage led to increased milk N and reduced urinary N in comparison with grass silage. Improvements in N utilisation may be related to increased dietary starch and/or rumen passage rates leading to increased microbial protein synthesis for these treatments. Urinary excretion of PD was significantly higher for all diets based on mixtures of red clover and maize silages, in comparison with grass silage. Urinary N output was close to literature predictions based on N intake for the diet based on ryegrass silage, but 40 to 80 g/day (25% to 30%) less than predicted for the diets based on the mixtures of red clover and maize silages.     

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 dehydrated lucerne and soya bean meal on milk production and composition,nutrient digestion,and methane and nitrogen losses in dairy cows receiving two different forages

Dehydrated lucerne is used as a protein source in dairy cow rations, but little is known about the effects of lucerne on greenhouse gas production by animals. Eight Holstein dairy cows (average weight: 582 kg) were used in a replicated 4×4 Latin square design. They received diets based on either maize silage (M) or grass silage (G) (45% of diet on dry matter (DM) basis), with either soya bean meal (15% of diet DM) completed with beet pulp (15% of diet DM) (SP) or dehydrated lucerne (L) (30% of diet DM) as protein sources; MSP, ML, GSP and GL diets were calculated to meet energy requirements for milk production by dairy cows and degradable protein for rumen microbes. Dry matter intake (DMI) did not differ among diets (18.0 kg/day DMI); milk production was higher with SP diets than with L diets (26.0 v. 24.1 kg/day), but milk production did not vary with forage type. Milk fatty-acid (FA) composition was modified by both forage and protein sources: L and G diets resulted in less saturated FA, less linoleic acid, more trans-monounsaturated FA, and more linolenic acid than SP and M diets, respectively. Enteric methane (CH₄) production, measured by the SF₆ tracer method, was higher for G diets than for M diets, but did not differ with protein source. The same effects were observed when CH₄ was expressed per kg milk. Minor effects of diets on rumen fermentation pattern were observed. Manure CH₄ emissions estimated from faecal organic matter were negatively related to diet digestibility and were thus higher for L than SP diets, and higher for M than G diets; the resulting difference in total CH₄ production was small. Owing to diet formulation constraints, N intake was higher for SP than for L diets; interaction between forage type and protein source was significant for N intake. The same statistical effects were found for N in milk. Faecal and urinary N losses were determined from total faeces and urine collection. Faecal N output was lower for M than for G diets but did not differ between protein sources. Urinary N output did not differ between forage types, but was lower for cows fed L diets than for cows fed SP diets, potentially resulting in lower ammonia emissions with L diets. Replacing soya bean meal plus beet pulp with dehydrated lucerne did not change CH₄ production, but resulted in more N in faeces and less N in urine.     

Metabolisable energy of grass and red clover silages fed to sheep at maintenance level

This study investigated the effect of forage type (grass or red clover) and harvesting time (primary growth or regrowth) of silage on energy and N utilisation by sheep fed at maintenance level. Specifically, the assumption of constant loss of energy of digestible organic matter from energy losses in urine and CH₄ applied in evaluation of silage metabolisable energy (ME) was investigated. Urinary excretion of high-energy phenolic compounds related to solubilisation of lignin was assumed to affect urinary energy (UE) losses from sheep fed highly digestible grass silage (GS). A total of 25 primary growth and regrowth silages of timothy (Phleum pratense) and meadow fescue (Festuca pratensis) grass mixtures and red clover (Trifolium pratense) samples collected in digestibility trials with sheep, including faecal and urine samples, were used for energy and N determinations. Urinary concentration of monophenolic compounds and CH₄ emissions in vitro were also analysed. Daily faecal N output, CH₄ yield (MJ/kg DM intake), proportion of CH₄ energy in digestible energy (DE) and proportion of UE in DE were greater (P ≤ 0.03) in sheep fed red clover silage (RCS) than GS. Furthermore, less (P = 0.01) energy was lost as UE of DE in sheep fed primary growth GS compared with the other treatments. The relationship between UE and silage N intake or urinary N output for both silage types (i.e. grass v. red clover) was strong, but the fit of the regressions was better for GS than RCS. The CH₄/DE ratio decreased (P < 0.05) and the UE/DE ratio increased (P < 0.05) with increasing organic matter digestibility in RCS. These relationships were not significant (P < 0.05) for the GS diets. The regression coefficient was higher (P < 0.05) for GS than RCS when regressing ME concentration on digestible organic matter. The results of this study imply that ME/DE ratio is not constant across first-cut GS of different maturities. The ME production response may be smaller from highly digestible first-cut GS but could not be clearly related to urinary excretion of monophenols derived from solubilisation of lignin. Furthermore, energy lost in urine was not clearly defined for RCS and was much more predictable for GS from silage N concentration.     

The effects of barley, unmolassed sugar-beet pulp and molasses supplements on organic matter, nitrogen and fibre digestion in the rumen of cattle given a silage diet

In a 4 × 4 Latin-square experiment with a 2 × 2 factorial arrangement of treatments, 4 cattle fitted with a rumen and duodenal cannula were given four grass-containing diets [480 g kg⁻¹ of the total dry matter (DM) intake] and barley (BU), barley + molasses (2:1) (BM), sugar-beet pulp (SU) or sugar-beet pulp + molasses (SM). Duodenal flow was estimated using Cr-mordanted straw and CoEDTA as markers, and microbial nitrogen entering the small intestine using purine bases of nucleic acids.

Molasses-containing diets had a higher (P < 0.01) organic matter (OM) digestibility. The proportion of digestible OM apparently disappearing in the rumen averaged 0.72 and was not significantly affected by the diet. When cattle received molasses, the quantity of microbial N entering the small intestine was higher (P < 0.05) and there was a trend towards a higher efficiency of microbial N synthesis (28.8 vs. 25.6 g N kg⁻¹ OM apparently digested in the rumen). When S diets were consumed, total non-ammonia N flow at the duodenum exceeded N intake by 7.0 g day⁻¹ and when B diets were consumed, it was 0.7 g day⁻¹ less than N intake. Feed N degradability in the rumen and apparent N digestibility of S diets were lower (P < 0.05; P < 0.001) than those of B diets.

Rumen (P < 0.05) and total (P < 0.001) digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF) was higher when S diets were given. The proportion of digestible fibre disappearing in the rumen was not affected by the diet. The rate and extent of silage and hay DM degradation were not significantly affected by the diet. However, dietary inclusion of molasses decreased (P < 0.05) the lag time of both hay and silage DM degradation.

The rumen dilution rate of liquid averaged 0.097 and that of particles, 0.049; neither was significantly different for either B and S diets or U and M diets. Duodenal liquid flow was higher (P < 0.05) for M diets.

Average rumen pH was not affected by the diet, but the molasses diets increased (P < 0.05) the range in rumen pH. The BM diet was associated with higher (P < 0.01) rumen ammonia concentration than the other diets. Low rumen ammonia concentrations (< 2 mM) were observed for long periods between feeds. The molar proportion of butyrate was higher on B diets and there was a trend towards a higher proportion of acetate and propionate on S diets. Molasses tended to increase the molar proportion of propionate and butyrate.     

Einfluß der Futterration und des Entnahmezeitpunktes von Pansensaft auf seine Zusammensetzung in Untersuchungen an Kühen

Different starch components were added to rations with maize silage measuring the influence of the supplements on the digestibility and energy content of maize silage in cattle (n = 36) and sheep (n = 36). The starch‐rich components maize, wheat, barley, oat, cassava meal and potatoe starch were added to the total rations on average of 33%. All supplements were ground (sieve of 2.5 mm), additionally, wheat was added in extruded or crushed form. All rations including the control ration without starch components were supplemented with soybean meal to an average crude protein content of 12.4% DM. The mean starch content of the total rations was 42% DM.

The supplementation of maize silage with the different starch components increased the digestibility of the organic matter of all rations on average only slightly from 77% to 78% in cattle, while the mean digestibility in sheep rised from 74% to 79% more pronounced. However, the influence of the different starch components on the digestibility was similiar for both ruminants. The supplementation with the ground, crushed or extruded wheat, with barley and with oats impaired the digestibility of the crude fibre of the total ration and of the maize silage, respectively. Therefore, the digestibility of the organic matter of maize silage was reduced and the energy content decreased by about 6% in comparison to the control ration without starch supplementation. However, the supplementation with maize, cassava meal or pota‐toe starch had no negative effects on the digestiblity and energy content of maize silage.     

Nutritional evaluation of cattle manure silage with molasses for ruminants

Two experiments were conducted to evaluate the nutritional quality of cattle manure silage for ruminants. In experiment 1 a silage containing 50% cattle manure, 20% cane molasses (containing 0.4% urea) mixed with water in a 1:1.5 ratio, and 30% corn stover replaced 0, 50, 75 and 100% of corn stover in isonitrogenous diets (1.92% N) containing 70 or 80% corn stover (dry matter (DM) basis) in a 4×2 factorial arrangement. Forty lambs (34.5±3.2 kg body weight (BW)) were used to measure apparent digestibility and nitrogen balance in a completely randomized design with factorial arrangement (4×2) with five lambs per treatment. The cattle manure silage was also evaluated in growing Holstein heifers (212±32 kg BW) replacing 0, 25 or 37.5% of corn stover with cattle manure silage in isonitrogenous diets (2.24% N). Apparent digestibility of DM, organic matter (OM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) were not affected. According to these results, digestibility is not affected by the level of cattle manure silage; however, intake was depressed at the highest levels of silage in lambs. Cattle manure silage may be considered as a potential by-product to be included in heifer's diet up to 37.5%, apparently without affecting performance. Recycling cattle manure through silage for ruminants is a viable alternative. © 1997 Elsevier Science B.V.     

Adjusting homestead feeding to requirements and nutrient intake of grazing goats on semi-arid, subtropical highland pastures

Intensive livestock grazing can largely deplete the natural fodder resources in semi-arid, subtropical highlands and together with the low nutritional quality of the pasture vegetation limit the growth and production of grazing animals. To evaluate the contribution of homestead feeding of grazing goats to rangeland conservation and animal nutrition, two researcher-managed on-farm trials were conducted in a mountain oasis of Northern Oman. Goats' feed intake on pasture in response to four rations containing different levels of locally available green fodder and concentrate feeds was determined in six male goats each (35 ± 10.2 kg body weight (BW)). Total feed intake was estimated using titanium dioxide as external fecal marker as well as the diet organic matter (OM) digestibility derived from fecal crude protein concentration. The nutritional quality of selected fodder plants on pasture was analyzed to determine the animals' nutrient and energy intake during grazing. The pasture vegetation accounted for 0.46 to 0.65 of the goats' total OM intake (87 to 107 g/kg0.75 BW), underlining the importance of this fodder resource for the husbandry system. However, metabolizable energy (7.2 MJ/kg OM) and phosphorus concentrations (1.4 g/kg OM) in the consumed pasture plants were low. Homestead feeding of nutrient and energy-rich by-products of the national fishery and date palm cultivation to grazing goats increased their daily OM intake (R2 = 0.36; P = 0.005) and covered their requirements for growth and production. While the OM intake on pasture was highest in animals fed a concentrate-based diet (P = 0.003), the daily intake of 21 g OM/kg0.75 BW of cultivated green fodder reduced the animals' feed intake on pasture (R2 = 0.44; P = 0.001). Adjusting homestead supplementation with locally available feedstuffs to the requirements of individual goats and to the nutritional quality of the pasture vegetation improves animal performance and eases the grazing pressure exerted on the natural vegetation. This management strategy therefore appears to be a valuable alternative to intensive livestock feeding in zero-grazing systems and may contribute to sustainable livestock production in ecologically fragile, semi-arid mountain regions.     

Effect of supplementation with pelleted citrus pulp on digestibility and intake in beef cattle fed a tropical grass-based diet (Cynodon nlemfuensis)

Citrus pulp is an important by-product for sub-tropical and tropical ruminant animal production. In this study, three steers (average body weight = 324 ± 16 kg) were randomly assigned to three levels of pelleted citrus pulp (PCP) supplementation (0, 1.25, and 2.5 kg animal⁻¹ d⁻¹; as-fed) in a 3 × 3 Latin square design to evaluate its effects on forage intake, digestion, and ruminal pH. The basal diet was stargrass (Cynodon nlemfuensis) harvested and chopped every day and fed fresh. Supplementation with increasing amounts of PCP tended (P≤0.10) to result in a linear increase in digestibility of total diet dry matter (DM) and organic matter (OM), but no effects were noticed for digestibility of forage DM or total diet neutral detergent fiber. Forage DM intake decreased linearly (P=0.03) with increasing PCP supplementation, although the decrease tended (quadratic; P=0.08) to be of greater magnitude at the highest level of supplementation. Both a linear increase (P<0.01) and a quadratic trend (greatest increase with first level of supplementation; P=0.09) were also observed for intake of total digestible OM. Average ruminal pH was between 6.6 and 7.2 and was not affected (P=0.29) by supplementation treatment. Although supplementation with PCP depressed forage consumption somewhat, little effect on forage digestion was observed. The provision of digestible OM in the form of supplement was greater than that lost via depressed forage consumption, resulting in an overall increase in energy supply. Our results suggest that high levels of citrus pulp to beef cattle can lower forage intake, but increase total energy intake. High levels of citrus pulp supplementation could be beneficial in combination with forages high in rumen dagradable protein. Systems using grasses with higher ruminally degradable protein content than we used, may benefit from this extra supply of energy which should be tested in a further experiment.     

Effect of maize silage to grass silage ratio and feed particle size on ruminal fermentation in vitro

The effect of the forage source on ruminal fermentation in vitro was investigated for fine (F) and coarse (C) milled diets, using a modified Hohenheim gas production test and a semi-continuous rumen simulation technique (Rusitec). It was hypothesised that the replacement of maize silage by grass silage might lead to associative effects and that interactions related to particle size variation could occur. Five diets with a maize silage to grass silage ratio of 100 : 0, 79 : 21, 52 : 48, 24 : 76 and 0 : 100 differed in their content of CP and carbohydrate fractions, as well as digestible crude nutrients, derived from a digestibility trial with wether sheep. For in vitro investigations, the diets were ground to pass a sieve of either 1 mm (F) or 4 mm (C) perforation. Cumulative gas production was recorded during 93 h of incubation and its capacity decreased with increasing proportion of grass silage in the diet. Across all diets, gas production was delayed in C treatments compared with F treatments. Degradation of crude nutrients and detergent fibre fractions was determined in a Rusitec system. Daily amounts of NH3-N and short-chain fatty acids (SCFA) were measured in the effluent. Degradation of organic matter (OM) and fibre fractions, as well as amounts of NH3-N, increased with stepwise replacement of maize silage by grass silage. Degradability of CP was unaffected by diet composition, as well as total SCFA production. In contrast to the results of the gas production test, degradation of OM and CP was higher in C than in F treatments, accompanied by higher amounts of NH3-N and SCFA. Interactions of silage ratio and particle size were rare. It was concluded that the stepwise replacement of maize silage by grass silage might lead to a linear response of most fermentation characteristics in vitro. This linear effect was also supported by total tract digestibility data. However, further investigations with silages of variable quality seem to be necessary.     

Methane production in cattle calculated by the nutrient composition of the diet

In this study data originating from complete metabolic trials with cattle of both sexes, fed 337 rations at feed intake levels between one to three times maintenance energy requirement were used to regress the total CH4 emission to the level of DM intake and to the nutrient composition, respectively. A major component of the measured CH4 emission cannot be explained by DM intake but is rather due to differences in dietary nutrient composition. The amount of digestible nutrients especially of the carbohydrate fraction (starch, sugar, N-free residuals) are reliable to estimate CH4 release with high precision (r2 = 0.885). Its production rate increased to 1.9-fold higher levels (range 1.8-2.1) per g of N-free residuals compared to that induced per g of protein, starch or sugar, respectively. Furthermore, diets rich in fat reduced CH4 formation in the rumen. The regression equations fit a wide range of diets and diet compositions, and more importantly, they are applicable to various types of production systems.     

A causal analysis of diet composition in free ranging cattle in reed-dominated vegetation

Summary Theoretical and observed diets of free-ranging yearling cattle in an area of reed-dominated vegetation were related to constraints inherent to ruminants (rumination time as reflected in the zone of acceptable crude fibre content of the ration; rumen fill) and in more general terms, to requirements for minerals (Na, Ca, Mg, P), for protein and for metabolisable energy in order to balance the growth rate achieved by experimental animals. Theoretical diets in spring were mainly limited by feeding time; theoretical diets in summer and autumn were mainly limited by rumen capacity. The high proteinto-energy ratio in the forage species caused protein intake to exceed the animals' demands. Mineral intake was in excess of requirements except for sodium. Yearling cattle in our study area maximized their energy intake, with feeding time, rumen capacity and crude fibre content of the forage as important constraints.     

The development of a model to predict BW gain of growing cattle fed grass silage-based diets

The objective of this meta-analysis was to develop and validate empirical equations predicting BW gain (BWG) and carcass traits of growing cattle from intake and diet composition variables. The modelling was based on treatment mean data from feeding trials in growing cattle, in which the nutrient supply was manipulated by wide ranges of forage and concentrate factors. The final dataset comprised 527 diets in 116 studies. The diets were mainly based on grass silage or grass silage partly or completely replaced by whole-crop silages, hay or straw. The concentrate feeds consisted of cereal grains, fibrous by-products and protein supplements. Mixed model regression analysis with a random study effect was used to develop prediction equations for BWG and carcass traits. The best-fit models included linear and quadratic effects of metabolisable energy (ME) intake per metabolic BW (BW^0.75), linear effects of BW^0.75, and dietary concentrations of NDF, fat and feed metabolisable protein (MP) as significant variables. Although diet variables had significant effects on BWG, their contribution to improve the model predictions compared with ME intake models was small. Feed MP rather than total MP was included in the final model, since it is less correlated to dietary ME concentration than total MP. None of the quadratic terms of feed variables was significant (P>0.10) when included in the final models. Further, additional feed variables (e.g. silage fermentation products, forage digestibility) did not have significant effects on BWG. For carcass traits, increased ME intake (ME/BW^0.75) improved both dressing proportion (P<0.01) and carcass conformation (P<0.001) and increased (P<0.001) carcass fat score. Increased dietary CP concentration had no significant (P>0.10) effect on dressing proportion or carcass conformation score, but it increased (P<0.01) carcass fat score. The current study demonstrated that ME intake per BW^0.75 was clearly the most important variable explaining the BWG response in growing cattle. The effect of increased ME supply displayed diminishing responses that could be associated with increased energy concentration of BWG, reduced diet metabolisability (proportion of ME of gross energy) and/or decreased efficiency of ME utilisation for growth with increased intake. Negative effects of increased dietary NDF concentration on BWG were smaller compared to responses that energy evaluation systems predict for energy retention. The present results showed only marginal effects of protein supply on BWG in growing cattle.     

Effect of ambient temperature on nutrient digestibility and nitrogen balance in sheep fed brown-midrib maize silage

The aim of the experiment was to determine the impact of heat stress on nutrient digestibility and nitrogen balance in sheep fed silages differing in fibre quality. The digestibility trial was conducted at three different ambient temperatures (15°C, 25°C and 35°C for 24 h/d). The tested brown-midrib maize (Bm) silage had a higher nutrient digestibility, except for ether extract (EE) and a higher metabolisable energy (ME) content than the control maize (Con) silage. Nitrogen (N) excretion with faeces was higher but N excretion with urine was lower for sheep fed Bm silage, subsequently N balance did not differ between the two silages. Temperature had no effect on nutrient digestibility, except for crude protein (CP), but N excretion with urine was lower at elevated temperatures. A diet by temperature interaction was found for dry matter (DM) and organic matter (OM) digestibility. When the ambient temperature increased from 15°C to 25°C, the DM and OM digestibility increased in animals fed Con silage, but decreased in animals fed Bm silage. Concomitantly, ME estimated from digestible nutrients was higher for Bm than for Con at 15°C, but no differences were found at 25°C and 35°C. Effects of diet by temperature interaction, furthermore, were observed for EE and CP digestibility. Therefore, forage quality has to be considered when feeding heat-stressed animals.