Nitrate poisoning in cattle. 2. Changes in nitrite in rumen fluid and methemoglobin formation in blood after high nitrate intake.

2. Three experiments with mature dry Friesian cows lasted for up to 16 days. Nitrate was given as nitrate-rich hay or mixed with concentrates to supply from 2.4 to 16.0 g/100 kg liveweight at each meal. To test the hypothesis that methaemoglobin was formed as the result of the production of nitrite as an intermediate in the rumen, one group was given a daily supplement of KNO2, 2 to 3 g/100 kg liveweight. Blood was sampled at frequent intervals, and ruminal fluid was sampled every 15 min for short periods from cows with a recirculating sampling device. Large intakes of nitrate in either form increased nitrite in the rumen, leading to increase of methaemoglobin in the blood during the first few days, after which the high value was maintained. The high methaemoglobin value was positively correlated with the larger nitrite content in the rumen. Results are discussed in the light of conflicting reports on the tolerance of cattle to large amounts of nitrate and the importance of frequent sampling to obtain a true picture is stressed. Previous inferences regarding the ability of cattle to tolerate nitrate at up to 90 g/100 kg are considered to be mistaken. ADDITIONAL ABSTRACT: In two experiments groups of 4 cows (415-669 kg body weight) received similar daily amounts of NO3- as either a single oral dose of KNO3 (15 g/100 kg) or a single feed of nitrate rich hay (12.4-15.4 g NO3-/100 kg) for 18 days. In a third experiment 6 cows received 2 or 3 g/100 kg of NO3- as a single oral dose of KNO2 for 6 days. Nitrate, nitrite and ammonia were measured in rumen sample and haemoglobin and methaemoglobin were measured in blood. The daily supply of equal doses of nitrate to cows, as hay with a high nitrate content or as potassium nitrate, induced higher nitrite contents in the rumen fluid and a higher percentage of methaemoglobin in the blood during the first days, after which they remained on this higher level. These increases were probably due to a change in the activity of the reducing micro-organisms in the rumen. The changes also partly explain the controversial data in the literature on the acceptable dosages of nitrate to be supplied to ruminants. This may have led to the mis-interpretation that ruminants should tolerate daily intakes up to 90 g of NO3- per 100 g body weight. (Abstract retrieved from CAB Abstracts by CABI’s permission

Concentrate feeding and ruminal fermentation. 1. Influence of the frequency of feeding concentrates on rumen acid composition, feed intake and milk production.

1. Four cows with rumen cannulae were given 12 kg concentrates daily in 2 equal portions at 0800 and 1530, in one portion of 12 kg at 0800 or in 4 portions of 3 kg each at 0800, 1100, 1400 and 1700 h. Every period lasted 2 weeks. In addition to the concentrates hay was provided at 0900 and 1630 h and was adjusted so that the daily remainder was at least 1 kg. In 1978 experiments were made with concentrates low in starch and sugars (LSS) (23%) and in 1979 with concentrates high in starch and sugars (HSS) (50%). In 1978 when total DM intake, milk production and milk fat content of each milking were estimated daily, the trend in pH and concentration of L-lactic acid in rumen fluid were estimated on the last day of the preliminary period (2 X 6 kg) and on the 1st, 7th and 14th days of the experimental periods (1 X 12 kg and 4 X 3 kg). In 1979 the same estimations were made, but D-lactic acid and volatile fatty acids were also estimated. Compared to 2 X 6 kg concentrates the changeover to daily 1 X 12 kg or 4 X 3 kg concentrates did not result in significant differences in DM intake nor in milk or milk fat production. Within types of concentrates there was hardly any difference in lowest rumen pH between frequencies of concentrate feeding. When HSS concentrates were given pH in rumen fluid tended to be lower than with the LSS concentrates. With 2 X 6 kg HSS concentrates, pH in rumen fluid was for a short time lower than 5.5. Lactic acid concentrations in the rumen fluid reached maximum within 1 h after concentrate feeding and L-lactic acid was 6.5, 5.0 and 2.0 mmol/litre, respectively, for 1 X 12, 2 X 6 and 4 X 3 kg LSS concentrates. For HSS concentrates the values were 4.5, 2.5 and 1.0 mmol/litre. When the HSS concentrates were given maximum concentration of D-lactic acid in rumen fluid were 2.5 to 3 times the L-lactic acid concentration. When lactic acid was not increased D- and L-lactic acid concentrations were similar. At 0800 h the molar ratio of volatile fatty acids (C2:C3:C4) as a percentage of total volatile fatty acids (VFA) in rumen fluid was 62:22:15 and changed gradually to 56:24:20 at 1900 h. Differences in VFA between frequencies of concentrate feeding were small. Total concentrations of VFA did not vary between treatments. (Abstract retrieved from CAB Abstracts by CABI’s permission

Nitrate poisoning in cattle. 3. The relationship between nitrate intake with hay or fresh roughage and the speed of intake on the formation of methemoglobin.

For part 2 see NAR/B 48, 238. 3. In 40 feeding experiments during about 5 years dry or lactating Friesian cows weighing 415 to 670 kg and 3 to 8 years old were given diets of hay, grass pellets, turnips or freshly mown grass in 2 meals daily. During experiments blood from the jugular vein was sampled every 15 min. Cows were induced to increase nitrate intake by being given at least 4 meals of roughage rich in nitrate before blood was sampled. There was a positive relation between nitrate intake and methaemoglobin per cent of total Hb but there were differences within and between different roughages in formation of methaemoglobin. With similar nitrate intake and speed of intake, more Hb was converted into methaemoglobin with hay than with freshly mown grass. That was related to the speed at which the nitrate taken with the roughage was released in the rumen as a substrate for the rumen flora. When hay was soaked in distilled water 80% of the nitrate in the cells diffused into the water within 20 min. With turnip and grass chopped to about 1 cm, 30% of the nitrate diffused into the water within 20 min. (Abstract retrieved from CAB Abstracts by CABI’s permission

Nitrate poisoning in cattle. 7. Prevention.

Results are summarized from 44 feeding trials with dry or lactating cows fed hay, pre-wilted grass silage or freshly mown grass with or without concentrates. As nitrate content of the forage increased, the moment at which the highest methaemoglobin (MHb) concentration occurred was delayed. As the MHb peak increased, more time was required to reduce MHb to normal values of 2-3%. Dry matter (DM) intake varied with type of forage. Consumption of 1.1 kg DM/100 kg bodyweight required 2 hours with hay or silage and 3.5 h with fresh grass. The relationship between nitrate intake and the formation of MHb in the blood was used to calculate the amount of forage that may be consumed per meal without causing symptoms of nitrate poisoning. Hay and pre-wilted silage with a nitrate content of up to 0.75% in the DM may be given ad lib. Indoor feeding of freshly mown grass with a nitrate content of up to 1.5% may also be given with restriction. Under grazing conditions, grass with a nitrate content of 2% in DM was safe without restriction. Nitrate poisoning may also be prevented by inhibiting nitrate reduction in the rumen by a daily dose of tungsten (wolfram). However, all potential hazards of this prophylactic treatment need to be examined before its use under practical conditions can be recommended. (Abstract retrieved from CAB Abstracts by CABI’s permission

Topological Designs

We give an exponential upper and a quadratic lower bound on the number of pairwise non-isotopic simple closed curves can be placed on a closed surface of genus g such that any two of the curves intersects at most once. Although the gap is large, both bounds are the best known for large genus. In genus one and two, we solve the problem exactly. Our methods generalize to variants in which the allowed number of pairwise intersections is odd, even, or bounded, and to surfaces with boundary components.Comment: 14 p., 4 Figures. To appear in Geometriae Dedicat

Concentrate feeding and ruminal fermentation. 2. Influence of concentrate ingredients on pH and on L-lactate concentration in incubations in vitro with rumen fluid.

2. Rumen fluid was sampled before feeding from cows given hay, diluted with an anaerobic salt solution and added (20 ml) to different amounts (mostly 1 g) of maize gluten meal, maize, citrus pulp, tapioca, beet pulp, coconut expeller or soya bean oilmeal for incubation at 39 deg C. After at least 4 h of incubation there were large differences in pH and lactic acid concentration. The acidotic index of the feeds was influenced by increasing concentration of the substrate. Except with maize meal, there was little effect of particle size on pH and lactic acid concentration. There were differences in effect on pH and lactic acid concentration between different batches of the same feeds, especially with maize meal. Incubations with mixtures of concentrate ingredients showed different pH and lactic acid concentrations from values expected from results with the single ingredients. (Abstract retrieved from CAB Abstracts by CABI’s permission

Beoordeling van structuur in het rantsoen

In een cursus "Kijken naar de koe", opgezet voor melkveehouders van het Overlegplatform de Duinboeren (N.Br.) was veevoedingsadviseur Aart Malestein gevraagd een uitleg te geven over de beoordeling van structuur in het rantsoen. In dit vlugschrift een samenvatting van zijn inleiding en hand-out