The maximum capacity of the liver of the adult dairy cow to metabolize ammonia.

1. Three adult dairy cows were fitted with cannulas in a mesenteric, portal, hepatic and jugular vein and a carotid artery. They received infusions of step-wise increasing amounts of ammonia as ammonium acetate via a mesenteric vein until NH 3 intoxication occurred. Sodium acetate was used in control infusions. The maximum rate of uptake of NH3 by the liver and the concentrations of glucose, urea, lactate, acetate and bilirubin in blood were measured. 2. During the infusions of ammonium acetate the liver extracted almost all the NH3 present in the portal vein until an infusion rate of approximately 15.0 mmol/min was reached. The maximum capacity of the liver to remove NH3 during its first pass was on average 1.84 mmol/min per kg wet weight. The cows became intoxicated when arterial plasma ammonia concentrations reached 0.8 mmol/l. Concentrations of NH3 in jugular venous blood were between 66 and 74% of those in the carotid.

The effects of reducing manger space on dairy cow behaviour and production.

The manger space for a group of 30 cows was reduced from 105 cm to 15 cm per cow during a period of six weeks. Before each reduction in manger space the cows were observed for 24 hours and their activity and aggressive behaviour recorded. The activity of individual cows varied little but there was wide variation among cows. The reduction in manger space did not change the mean number of visits by cows to the manger, the total time spent feeding, the amount of aggressive behaviour, the milk yield or the general activity of the cows in comparison with a control group allowed 105 cm of manger space per cow for the whole period. There was a reduction in the total time spent feeding by cows which were clinically ill and a change in the number of visits made to the manger by cows in oestrus. A reduction in the allocation of manger space would make it possible either to build smaller, cheaper housing or to convert existing buildings to accommodate more cows. It would also make it possible to use automated systems to record the feed intake and number of visits to the manger of individual cows and would help to detect cows which were sick or in oestrus.

Effect of reduced water intake by lactating dairy cows on behaviour, milk yield and blood composition.

A herd of lactating British Friesian cows was divided into two equal groups. After 14 days during which all the cows had free access to water one group (restricted) was allowed only 50 per cent of the voluntary water intake of the other group (control). After four days when the experiment was terminated, the milk yield of the restricted group had fallen to 74 per cent of that of the control group and their mean body-weight was reduced by 14 per cent. In the restricted group there were significant increases in the concentrations of urea, sodium, total protein and copper in serum, in the osmolality of serum, in the plasma activities of the enzymes creatine kinase and glutamate-oxaloacetate transaminase and in the packed cell volume of blood. The restricted cows behaved very aggressively around their water trough and spent more time in its vicinity. They spent less time lying down than the cows of the control group and some of them were not seen to drink and were withdrawn from the experiment before the end of four days. In a second experiment half the herd was allowed approximately 90 per cent of the water intake of the control group for 14 days. Decreases in milk yield and body-weight and changes in blood composition were much smaller and difficult to detect. However, changes in behaviour were still easily recognised although not as marked as in the first experiment.

The half-life of glutamate dehydrogenase in plasma of dry and lactating dairy cows.

The clearance of glutamate dehydrogenase from plasma was measured weekly for three weeks in three dry and three lactating cows. The clearance was exponential with a mean clearance constant of 0.0488/j and means (+/- SE) half-life of 14.2 (+/- 0.77) h. There were variations among cows and among measurements in the same cow but there was no difference between the mean half-lives of GDH in lactating and dry cows. Because of the long half-life the small variations among individual cows are unlikely to affect the interpretation of increased plasma GDH activity.

The effects of subcutaneous injections of sodium selenate on blood composition and milk yield in dairy cows.

Three groups of four lactating cows received a subcutaneous injection of 0 . 05, 0 . 10 and 0 . 15 mg Se/kg body weighty respectively administered as sodium selenate. A fourth group was injected with saline. In all the cows injected with sodium selenate, the concentration of Se in blood increased rapidly and was significantly higher than in control cows for two days in the group receiving the lowest dose and for 182 days (the duration of the experiment) in the two other groups. The activity of glutathione peroxidase in blood increased slowly in all cows injected with sodium selenate and was significantly greater than in control cows after 15, 22 and 29 days respectively, and remained significantly greater for 63, 91 and 182 days respectively. In a second experiment a single subcutaneous injection of 0 . 15 mg Se/kg body weight had no effect on the mean milk yield of 37 animals (19 . 1 kg/day) compared with the milk yield of a similar group of control animals (19 . 1 kg/day) during 70 days. The concentration of Se in milk was significantly higher on the first (168 microgram/litre) and second (69 microgram/litre) day after injection than in control animals (mean 26 microgram/litre).

Concurrent daily infection of calves with Fasciola hepatica and Ostertagia ostertagi.

Three groups of calves were infected daily with either 1500 Ostertagia ostertagi larvae, 20 Fasciola hepatica metacercariae, or 1500 O ostertagi plus 20 F hepatica metacercariae. Weekly measurements were taken of calf weight, faecal egg output, plasma concentrations of albumin, plasma activities of sorbitol dehydrogenase, gamma glutamyl transpeptidase and pepsinogen and standard haematological indices. Calves were killed either 10 or 21 weeks after daily infections began. F hepatica infection had little influence on the size and structure of the O ostertagi worm population or vice versa. Mean worm burdens found at 20 weeks in those animals infected with both F hepatica and O ostertagi were 293 flukes and 20,641 nematodes. While this level of infection is similar to that seen in the disease complex in the field, there was no evidence of clinical disease or any difference in weight gain between the groups in this experiment. Factors other than additive worm burdens are obviously important for the expression of disease under field conditions.

Enzyme activities in tissues of clinically normal Large White pigs. Variations with age and sex.

The activities of eight enzymes (glutamate dehydrogenase, sorbital dehydrogenase, malate dehydrogenase, lactate dehydrogenase, alpha-hydroxy butyrate dehydrogenase, gamma-glutamyl transpeptidase, alkaline phosphatase and creatine kinase) were determined in tissue homogenates of liver, kidney, spleen, lung, small intestine, cardiac muscle and skeletal muscle, from 15 Large White pigs of three different ages (1.5 weeks, 18--22 weeks and 113 weeks). The results showed that variation in tissue enzyme concentration due to differences in sex is minimal. Variation due to differences in age, however, appears to be of greater importance, particularly when considering young animals. These age differences may affect the interpretation of plasma enzyme changes due to tissue damage, and the use of additional enzyme assays as an aid to interpretation in these cases is advisable.

The effect of protein intake on the activities of liver specific enzymes in the plasma of dairy cows.

Activities of glutamic dehydrogenase (GLDH), sorbitol dehydrogenase (SDH) and ornithine carbamyl transferase (OCT) were determined in tissues of six cattle after slaughter. The liver contained the highest activities of all three enzymes and the kidney cortex also contained high activities of GLDH and SDH. Activities of OCT were negligible in tissues other than liver. GLDH and OCT activities were determined in plasma of two groups of cows fed different levels of protein during the pre-calving period and up to 14 weeks post calving. In both groups activities of both enzymes increased after calving, reaching three to seven times pre-calving levels between seven and 17 weeks post calving and declining thereafter. Activities of both enzymes reached higher levels in the group fed protein to conform to the recommendations of the ARC (1965) than in the group fed 25 per cent below these recommendations. One--conventional--interpretation of this would be that higher intakes of proteins were associated with pathology of liver cells but other interpretations cannot be ruled out entirely.

The influence of dietary protein intake on milk production and blood composition of high-yielding dairy cows.

Cows were fed either 75 or 100% of the recommended intake levels for protein and 100% of recommended energy levels (Agricultural Research Council, 1965) from 8 weeks pre-calving until 14 weeks post calving. From 14 weeks post calving and to the end of lactation all the cows received 100% of the recommended protein and energy intakes. The mean of the 305-d milk yields of the 2 groups was not significantly different and although cows on the lower protein intake produced less lactose during the first 14 weeks of lactation there was no significant difference in total lactose, fat, protein or total solids production between the groups. In both groups blood packed-cell volume, red cell count and haemoglobin decreased during the first 10 weeks of lactation and then began to increase in the high-protein group. The cows receiving the low-protein diet showed a similar increase only when they received the high-protein ration from 14 weeks post calving. The mean interval from calving to conception was 27-5 weeks in the high-protein group and 20 weeks in the low-protein group. It is concluded that feeding 75% of protein requirements to dairy cows during the first 14 weeks of lactation does not reduce milk yield or quality significantly and probably has no adverse effect on fertility.