Bacterial spores in silage and raw milk

Spore-forming bacteria can survive food-processing treatments. In the dairy industry, Bacillus and Clostridium species determine the shelf-life of a variety of heat-treated milk products, mainly if the level of post-process contamination is low. In order to minimize problems caused by bacterial spores in foods and food production processes a chain management approach, from raw materials, ingredients and environmental sources to final product storage conditions, is most effective. Silage is considered to be a significant source of contamination of raw milk with spores. PCR-RAPD fingerprinting and heat resistance studies of populations of aerobic spore-formers isolated from grass and maize silage and from raw milk confirmed this assumption. Prevention of outgrowth of aerobic spores in silage will contribute to reduction of the total spore load of raw milk. Therefore, it is important that the silage fermentation process is controlled. Application of cultures of lactic acid bacteria or chemical additives can aid silage fermentation and improve aerobic stability. This revised version was published online in August 2006 with corrections to the Cover Date.     

Replacement of grass and maize silages with lucerne silage: effects on performance,milk fatty acid profile and digestibility in Holstein-Friesian dairy cows

In total, 20 multiparous Holstein-Friesian dairy cows received one of four diets in each of four periods of 28-day duration in a Latin square design to test the hypothesis that the inclusion of lucerne in the ration of high-yielding dairy cows would improve animal performance and milk fatty acid (FA) composition. All dietary treatments contained 0.55 : 0.45 forage to concentrates (dry matter (DM) basis), and within the forage component the proportion of lucerne (Medicago sativa), grass (Lolium perenne) and maize silage (Zea mays) was varied (DM basis): control (C)=0.4 : 0.6 grass : maize silage; L20=0.2 : 0.2 : 0.6 lucerne : grass : maize silage; L40=0.4 : 0.6 lucerne : maize silage; and L60=0.6 : 0.4 lucerne : maize silage. Diets were formulated to contain a similar CP and metabolisable protein content, with the reduction of soya bean meal and feed grade urea with increasing content of lucerne. Intake averaged 24.3 kg DM/day and was lowest in cows when fed L60 (P<0.01), but there was no effect of treatment on milk yield, milk fat or protein content, or live weight change, which averaged 40.9 kg/day, 41.0, 30.9 g/kg and 0.16 kg/day, respectively. Milk fat content of 18:2 c9 c12 and 18:3 c9 c12 c15 was increased (P<0.05) with increasing proportion of lucerne in the ration. Milk fat content of total polyunsaturated fatty acids was increased by 0.26 g/100 g in L60 compared with C. Plasma urea and β-hydroxybutyrate concentrations averaged 3.54 and 0.52 mmol/l, respectively, and were highest (P<0.001) in cows when fed L60 and lowest in C, but plasma glucose and total protein was not affected (P>0.05) by dietary treatment. Digestibility of DM, organic matter, CP and fibre decreased (P<0.01) with increasing content of lucerne in the diet, although fibre digestibility was similar in L40 and L60. It is concluded that first cut grass silage can be replaced with first cut lucerne silage without any detrimental effect on performance and an improvement in the milk FA profile, although intake and digestibility was lowest and plasma urea concentrations highest in cows when fed the highest level of inclusion of lucerne.     

Feed consumption and performance of dairy cows with alternate feedings of grass silage and maize silage

A feeding experiment was conducted with 10 dairy cows of the Fleckvieh breed and the cross Red Holstein Friesian × Fleckvieh, to study whether feeding with grass silage at the morning meal and maize silage at the evening meal (treatment B: alternating forage allocation) affects forage intake and milk production, in comparison with combined feeding with these two silages at each meal (treatment A). In order to prevent a selective forage consumption in treatment A, the two silages were given as a homogeneous mixture of nearly equal portions (51.6% maize silage, 48.4% grass silage) of dry matter (DM). The experiment was of switch-back design, with the treatment sequences ABA and BAB, and three experimental periods of 6 weeks.The daily forage consumption averaged 12.3 kg DM when the silages were given as a mixture and was significantly higher than the total forage consumption of 11.8 kg DM (P < 0.05) during the alternating allocation of the silages. In treatment B, daily intake of maize silage (7.10 kg DM) was greater than that of grass silage (4.70 kg DM/day). Furthermore, variation between cows in forage intake was significantly higher in this treatment than in treatment A. Average daily milk yield for treatment A was 18.75 kg with 3.84% fat and 3.70% protein, and 18.10 kg with 3.76% fat and 3.68% protein for treatment B. Production was significantly higher (P < 0.05), by 0.65 kg milk or 0.90 kg FCM, for treatment A.     

Gnotobiotic Silage

Selected strains of lactic acid bacteria isolated from grass silage were found to flourish when inoculated into irradiation-sterilized forage under gnotobiotic conditions. The acid content and pH of these silages resembled naturally fermented silage. Inoculation of gnotobiotic silage with Clostridium sporogenes and C. tyrobutyricum failed to cause any noticeable deterioration of silage quality.     

Effects of dairy farming intensification on nitrous oxide emissions

A dairy farm system trial was conducted between September 2003 and August 2005 to evaluate the effect of integration of maize silage forage on nitrous oxide (N₂O) emissions. Potentially, the integration of low-protein forage (e.g. feeding cows with maize silage) to reduce dietary-nitrogen (N) concentration can mitigate environmental N emissions and increase N use efficiency. The dairy farm systems consisted of a maize supplementation system with a stocking rate of 3.8 cows ha^?1 of grazed pasture with maize silage brought in and a control system with a stocking rate of 3.0 cows ha^?1 of grazed pasture. Direct and indirect N₂O emissions from all components of the farm systems were either measured using a closed chamber technique or calculated using the New Zealand IPCC inventory methodology. Annual average N₂O emissions were slightly lower on the maize supplementation pasture than on the control pasture. Annual total N₂O emissions from the “whole” farm systems (including direct and indict emissions from the grazed pastures, maize growing land, N fertilizer use and associated land application of farm effluent) were 7.71 and 8.00 kg N₂O–N ha^?1 of dairy farm on the control and maize supplement farm systems, respectively. The corresponding annual milk production was 13,437 and 17,925 kg ha^?1. Therefore, the N₂O emission per kg of milk production from the maize supplementation was 22% lower than that from the control system. This was due to the much greater efficiency of N use from low-protein maize silage than from pasture. The results suggest that the integration of low-protein forage can be an effective management practice to mitigate adverse environmental effects of increasing stocking rates in the New Zealand dairy farm systems, in terms of N₂O emissions per unit of milk production.     

Influence of the maize silage to grass silage ratio and feed particle size of rations for ruminants on the community structure of ruminal Firmicutes in vitro

Aims: To investigate the effect of the forage source and feed particle size (FPS) in ruminant rations on the composition of the ruminal Firmicutes community in vitro. Methods and Results: Three diets, varying in maize silage to grass silage ratio and FPS, were incubated in a rumen simulation system. Microbial samples were taken from the liquid fermenter effluents. Microbial community analysis was performed by 16S rRNA‐based techniques. Clostridia‐specific single‐strand conformation polymorphism profiles revealed changes of the community structure in dependence on both factors tested. The coarse grass silage–containing diets seemed to enhance the occurrence of different Roseburia species. As detected by real‐time quantitative PCR, Ruminococcus albus showed a higher abundance with decreasing FPS. A slightly lower proportion of Bacilli was found with increasing grass silage to maize silage ratio by fluorescence in situ hybridization (FISH). In contrast, a slightly higher proportion of bacterial species belonging to the Clostridium‐clusters XIV a and b was detected by FISH with increasing grass silage contents in the diet. Conclusions: The ruminal Firmicutes community is affected by the choice of the forage source and FPS. Significance and Impact of the Study: This study supplies fundamental knowledge about the response of ruminal microbial communities to changing diets. Moreover, the data suggest a standardization of grinding of feeds for in vitro studies to facilitate the comparison of results of different laboratories.     

Effects of silage from maize crops differing in maturity at harvest,grass silage feed value and concentrate feed level on performance of finishing lambs

The effects of (i) medium and high feed value (MFV and HFV) maize silages and (ii) MFV and HFV grass silages, each in combination with a range of concentrate feed levels, on the performance of finishing lambs were evaluated using 280 Suffolk-X lambs (initial live weight 36.1 kg). The MFV and HFV maize silages represented crops with dry matter (DM) concentrations of 185 and 250 g/kg, respectively, at harvest, and had starch and metabolisable energy (ME) concentrations of 33 and 277 g/kg DM and 9.6 and 11.0 MJ/kg, respectively. HFV and MFV grass silages had DM and ME concentrations of 216 and 294 g/kg and 11.0 and 11.5 MJ/kg DM, respectively. A total of 13 treatments were involved. The four silages were offered ad libitum with daily concentrate supplements of 0.2, 0.5 or 0.8 kg per lamb. A final treatment consisted of concentrate offered ad libitum with 0.5 kg of the HFV grass silage daily. Increasing the feed value of grass silage increased (P < 0.001) forage intake, daily carcass and live weight gains, final live weight and carcass weight. Increasing maize silage feed value tended to increase (P = 0.07) daily carcass gain. Increasing concentrate feed level increased total food and ME intakes, and live weight and carcass gains. There was a significant interaction between silage feed value and the response to concentrate feed level. Relative to the HFV grass silage, the positive linear response to increasing concentrate feed level was greater with lambs offered the MFV grass silage for daily live weight gain (P < 0.001), daily carcass gain (P < 0.01) and final carcass weight (P < 0.01). Relative to the HFV maize silage, there was a greater response to increasing concentrate feed level from lambs offered the MFV maize silage in terms of daily carcass gain (P < 0.05) and daily live weight gain (P = 0.06). Forage type had no significant effect on the response to increased concentrate feed level. Relative to the MFV grass silage supplemented with 0.2 kg concentrate, the potential concentrate-sparing effect of the HFV grass silage, and the MFV and HFV maize silages was 0.41, 0.09 and 0.25 kg daily per lamb, respectively. It is concluded that increasing forage feed value increased forage intake and animal performance, and maize silage can replace MFV grass silage in the diet of finishing lambs as performance was equal to or better (depending on maturity of maize at harvest) than that for MFV grass silage.     

Effects of replacing grass silage with either maize or whole-crop wheat silages on the performance and meat quality of beef cattle offered two levels of concentrates

A randomised design involving 66 continental cross beef steers (initial live weight 523 kg) was undertaken to evaluate the effects of the inclusion of maize or whole-crop wheat silages in grass silage-based diets on animal performance, carcass composition, and meat quality of beef cattle. Grass silage was offered either as the sole forage or in addition to either maize or whole-crop wheat silages at a ratio of 40:60, on a dry matter (DM) basis, alternative forage: grass silage. For the grass, maize, and whole-crop wheat silages, DM concentrations were 192, 276, and 319 g/kg, ammonia-nitrogen concentrations were 110, 90, and 150 g/kg nitrogen, starch concentrations were not determined, 225, and 209 g/kg DM and in vivo DM digestibilities were 0.69, 0.69, and 0.58; respectively. The forages were offered ad libitum following mixing in a paddle type complete diet mixer wagon once per day, supplemented with either 3 or 5 kg concentrates per steer per day, in two equal feeds, for 92 days. For the grass, grass plus maize and grass plus whole-crop wheat silage-based diets food intakes were 8.38, 9.08, and 9.14 kg DM per day, estimated carcass gains were 514, 602, and 496 g/day and carcass weights were 326, 334, and 325 kg; respectively. Altering the silage component of the diet did not influence carcass composition or meat eating quality. Increasing concentrate feed level tended ( P = 0.09) to increase estimated carcass fat concentration and increased sarcomere length ( P < 0.05), and lean a* ( P < 0.01), b* ( P < 0.05), and chroma ( P < 0.01). There were no significant silage type by concentrate feed level interactions for food intake, steer performance, carcass characteristics or meat eating quality. It is concluded that replacing grass silage with maize silage increased carcass gain, and weight due to higher intakes, and improved utilisation of metabolisable energy. Whilst replacing grass silage with whole-crop wheat silage increased live-weight gain, the reduced dressing proportion resulted in no beneficial effect on carcass gain, probably due to increased food intakes of lower digestible forage increasing gut fill. Meat quality or carcass composition were not altered by the inclusion of maize or whole-crop silages in grass silage based diets.     

Impacts of production conditions on goat milk vitamin,carotenoid contents and colour indices

The content, composition and variation of vitamin compounds in goat milk have been little studied. An experimental design was based on 28 commercial farms, selected considering the main feeding system (based on main forage and especially pasture access), goat breed (Alpine vs Saanen) and reproductive management (seasonal reproduction), in the main French goat milk production area. Each farm received two visits (spring and autumn) that included a survey on milk production conditions and bulk milk sampling. Milk vitamins (A, E, B₂, B₆, B₉, B₁₂) and carotenoid concentrations plus colour indices were evaluated. A stepwise approach determined the variables of milk production conditions that significantly altered milk indicators. The main forage in the diet was the major factor altering goat milk vitamin and carotenoid concentrations and colour indices. Bulk milk from goats eating fresh grass as forage was richer in α-tocopherol (+64%), pyridoxal (+35%) and total vitamin B₆ (+31%), and b* index (characterising milk yellowness in the CIELAB colour space) was also higher (+12%) than in milk from goats eating conserved forages. In milk from goats eating fresh grass, concentrations of pyridoxamine, lutein and total carotenoids were higher than in milk of goats fed corn silage (+24, +118 and +101%, respectively), and retinol and α-tocopherol concentrations were higher than in milk of goats fed partially dehydrated grass (+45 and +55%). Vitamin B₂ concentration was higher in milk of goats eating fresh grass than in milk of goats fed hay or corn silage as forage (+10%). However, bulk milk when goats had access to fresh grass was significantly poorer in vitamin B₁₂ than when fed corn silage (?46%) and in γ-tocopherol (?31%) than when fed conserved forage. Alpine goats produced milk with higher vitamin B₂ and folate concentrations than Saanen goats (+18 and +14%, respectively). Additionally, the milk colour index that discriminates milks based on their yellow pigment contents was 7% higher in milk from Alpine than Saanen herds, but milk from Saanen goats was richer in lutein (+46%). Goat milks were richer in vitamins B₂ and B₁₂ and folates, but poorer in vitamin B₆ in autumn than in spring (+12, +133, +15 and ?13%, respectively). This work highlights that goat milk vitamin and carotenoid concentrations and colour indices vary mainly according to the main forage of the diet and secondly according to the breed and season.     

Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cows

The objective of the study was to examine how the fatty acid composition of milk especially concentrations of conjugated linoleic acids (CLA) and trans-C18:1 isomers and milk fat percentage were affected by silage type and concentrate level. Forty dairy cows were blocked and randomly assigned to one of four diets in a 2 x 2 factorial arrangement of treatments and a six week experimental period. Treatments were total mixed rations with maize (M) or grass (G) silage differing in polyunsaturated fatty acid (PUFA) profile and starch content, combined with a high (H) or a low (L) level of concentrate (with or without grain). Treatments had no significant effect on milk, protein and lactose yield, but energy corrected milk yield, milk fat percentage and fat yield was lower and protein percentage higher for maize compared with grass silage diets. Overall, maize silage diets resulted in higher concentrations of CLA isomers compared with grass silage diets, but there was a significant interaction between silage type and concentrate level for concentrations of cis9,trans11-CLA; trans10,cis12-CLA; trans11-C18:1 and trans10-C18:1. A high level of concentrate increased trans10,cis12-CLA and trans10-C18:1 and reduced cis9,trans11-CLA and trans11-C18:1 when maize but not grass silage was provided. The results suggest that high levels of concentrate (grain) do not significantly alter the pattern of PUFA biohydrogenation in the rumen, the concentration of CLA and trans-C18:1 isomers in milk or cause milk fat depression unless combined with forage naturally high in starch and C18:2n-6 such as maize silage.     

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.     

Effects of replacing grass silage with maize silages differing in inclusion level and maturity on the performance,meat quality and concentrate-sparing effect of beef cattle

The effects of maturity of maize at harvest, level of inclusion and potential interactions on the performance, carcass composition, meat quality and potential concentrate-sparing effect when offered to finishing beef cattle were studied. Two maize silages were ensiled that had dry matter (DM) concentrations of 217 and 304 g/kg and starch concentrations of 55 and 258 g/kg DM, respectively. Grass silage was offered as the sole forage supplemented with either 4 or 8 kg concentrate/steer daily or in addition with one of the two maize silages at a ratio 0.5 : 0.5, on a DM basis, maize silage : grass silage supplemented with 4 kg concentrate daily. The two maize silages were also offered as the sole forage supplemented with 4 kg concentrate/steer daily. The forages were offered ad libitum. The six diets were offered to 72 steers (initial live weight 522 s.d. 23.5 kg) for 146 days. There were significant interactions (P < 0.05) between maize maturity and inclusion level for food intake, fibre digestibility and daily gain. For the grass silage supplemented with 4 or 8 kg concentrate, and the maize silages with DM concentrations of 217 and 304 g/kg offered as 0.5 or 1.0 of the forage component of the diet, total DM intakes were 8.3, 9.8, 8.9, 8.2, 9.2 and 9.8 kg DM/day (s.e. 0.27); live-weight gains were 0.74, 1.17, 0.86, 0.71, 0.88 and 1.03 kg/day (s.e. 0.057); and carcass gains were 0.48, 0.73, 0.56, 0.46, 0.56 and 0.63 kg/day (s.e. 0.037), respectively. Increasing the level of concentrate (offered with grass silage), maize maturity and level of maize inclusion reduced (P < 0.05) fat b* (yellowness). The potential daily concentrate-sparing effect, as determined by carcass gain, for the maize silages with DM concentrations of 217 and 304 g/kg offered as 0.5 and 1.0 of the forage component of the diet were 1.3, −0.3, 1.3 and 2.4 kg fresh weight, respectively. It is concluded that the response, in animal performance, including maize silage is dependent on the stage of maturity and level of inclusion in the diet. Maize silage with a DM of 304 g/kg offered ad libitum increased carcass gain by 31%, because of a combination of increased metabolizable energy (ME) intake and improved efficiency of utilization of ME, and produced carcasses with whiter fat.     

Isolation of Listeria monocytogenes from raw milk and its environment at dairy farms in Japan

The incidence of Listeria monocytogenes contamination in raw milk from farm bulk tanks and silage was investigated monthly at 20 dairy farms in Aomori prefecture, Japan, from January to July in 1989. Listeria sp. was isolated from one sample (5%) of raw milk collected in May, but L. monocytogenes was not isolated from raw milk. L. monocytogenes was isolated from two samples of silage (10%) collected in June. Silage, cow feces, sawdust bedding, dust and soil in these farms were tested for listerias, and we confirmed listerias contamination of the environment in the dairy farms.     

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.     

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.     

Mycotoxins in South African foods: a case study on aflatoxin M<Subscript>1</Subscript> in milk

The contamination of cow’s milk at the farm level with aflatoxin M₁ was investigated in South Africa. Samples of feeds, forage, maize and milk were taken at nine dairy farms, and at the same time samples of the processed milk (retail milk) were collected from the respective dairies to which the farms delivered their milk. The feeds were analysed for aflatoxin B₁ and the milk samples for aflatoxin M₁ using high performance liquid chromatography (HPLC) and fluorescence detection. All milk samples from the dairy farms were positive for aflatoxin M₁, ranging from 0.02 μg/l to 1.5 μg/l. Retail milk was also frequently contaminated with AFM₁, at levels of 0.01-3.1 μg/l. High AFB₁ levels in feed materials on the farms supplying the raw milk indicate that various sources account for this contamination frequency in milk.     

Changes in Rumen Microbial Community Composition during Adaption to an In Vitro System and the Impact of Different Forages

This study examined ruminal microbial community composition alterations during initial adaption to and following incubation in a rumen simulation system (Rusitec) using grass or corn silage as substrates. Samples were collected from fermenter liquids at 0, 2, 4, 12, 24, and 48 h and from feed residues at 0, 24, and 48 h after initiation of incubation (period 1) and on day 13 (period 2). Microbial DNA was extracted and real-time qPCR was used to quantify differences in the abundance of protozoa, methanogens, total bacteria, Fibrobacter succinogenes, Ruminococcus albus, Ruminobacter amylophilus, Prevotella bryantii, Selenomonas ruminantium, and Clostridium aminophilum. We found that forage source and sampling time significantly influenced the ruminal microbial community. The gene copy numbers of most microbial species (except C. aminophilum) decreased in period 1; however, adaption continued through period 2 for several species. The addition of fresh substrate in period 2 led to increasing copy numbers of all microbial species during the first 2–4 h in the fermenter liquid except protozoa, which showed a postprandial decrease. Corn silage enhanced the growth of R. amylophilus and F. succinogenes, and grass silage enhanced R. albus, P. bryantii, and C. aminophilum. No effect of forage source was detected on total bacteria, protozoa, S. ruminantium, or methanogens or on total gas production, although grass silage enhanced methane production. This study showed that the Rusitec provides a stable system after an adaption phase that should last longer than 48 h, and that the forage source influenced several microbial species.     

Effects of glyphosate residues and different concentrate feed proportions on performance,energy metabolism and health characteristics in lactating dairy cows

The aim of this study was to examine the influence of glyphosate (GL) residues in feedstuffs on performance, energy balance and health-related characteristics of lactating dairy cows fed diets with different concentrate feed proportions. After an adaption period, 64 German Holstein cows (207 ± 49 d in milk; mean ± SD) were assigned to either groups receiving a GL contaminated total mixed ration (TMR) (GL groups) or an uncontaminated TMR (CON groups) during a 16 weeks trial. Contaminated feedstuffs used were legally GL-treated peas and wheat (straw and grain). GL and CON groups were subdivided into a “low concentrate” group (LC) fed on dry matter (DM) basis of 21% maize silage, 42% grass silage, 7% straw and 30% concentrate and a “high concentrate” group (HC) composed of 11% maize silage, 22% grass silage, 7% straw and 60% concentrate for ad libitum consumption. Body condition score, body weight, DM intake and milk performance parameters were recorded. In blood serum, β-hydroxybutyrate (BHB), non-esterified fatty acids (NEFA) and glucose were measured and energy balance was calculated. Milk was analysed for GL residues. At week 0, 7 and 15, general health status was evaluated by a modified clinical score. The average individual GL intake amounted for Groups CON_LC, CON_HC, GL_LC and GL_HC to 0.8, 0.8, 73.8 and 84.5 mg/d, respectively. No GL residues were detected in milk. GL contamination did not affect body condition score, body weight, DM intake, nutrient digestibility, net energy intake, net energy balance or BHB, glucose, NEFA and milk performance parameters; whereas concentrate feed proportion and time did affect most parameters. The clinical examination showed no adverse effect of GL-contaminated feedstuffs on cows’ health condition. In the present study, GL-contaminated feedstuffs showed no influence on performance and energy balance of lactating dairy cows, irrespective of feed concentrate proportion.     

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.     

Gnotobiotic Silage

Selected strains of lactic acid bacteria isolated from grass silage were found to flourish when inoculated into irradiation-sterilized forage under gnotobiotic conditions. The acid content and pH of these silages resembled naturally fermented silage. Inoculation of gnotobiotic silage with Clostridium sporogenes and C. tyrobutyricum failed to cause any noticeable deterioration of silage quality.