The development of acid-base reaction cements as formulations for the controlled release of trace elements.

Novel acid-base reaction cements have been developed for use as controlled release formulations. Many new ones have been discovered and assessed; these include those which are capable of releasing copper, cobalt or selenium singly or in combination. A selection was made of the most suitable formulations for this purpose and these were subjected to field trials.

Reaction cements as materials for the sustained release of trace elements into the digestive tract of cattle and sheep. I. Copper release.

Acid-base reaction cements were produced by reacting copper oxide with phosphoric acid. When placed in the reticulo-rumen of cattle and sheep these cements released copper into the digestive tract for at least 3 months at a rate sufficient to provide the animals' requirements for copper. Lambs given a pellet of cement at 3 months of age had significantly greater concentrations of copper in their livers than similar untreated animals when slaughtered 3-4 months later. It was shown that salts of cobalt and selenium could be incorporated into the cement to provide additional supplementation with these two elements.

Reaction cements as materials for the sustained release of trace elements into the digestive tract of cattle and sheep. II. Release of cobalt and selenium.

Acid-base reaction cements, containing salts of copper, cobalt and selenium, were placed in the reticulum of sheep and cattle, and the rate of release of cobalt and selenium from them was measured. The rate of release of cobalt decreased with time but was sufficient to provide adequate supplementation for at least 6 months. After an initial rate of release of 4 mg Se/day for 1-2 weeks, the mean subsequent rate of release of selenium over a period of 4 months was 0.1 mg Se/day (identical to 5 micrograms Se/day/cm2 surface area). Field trials in lambs and growing steers showed that the cement increased the selenium concentration of their blood throughout a summer grazing period.

Importance of water for the health and productivity of the dairy cow.

Four lactating Friesian cows (average weight 485 kg, milk yield 22 kg d-1) were maintained in completely controlled circumstances and deprived of water for 72 hours. During this period they were carefully monitored and lost 100 kg in bodyweight, principally accounted for by cumulative losses of water in milk, urine, faeces and respired air. The mean rates of respiration and rumen contraction decreased by approximately 50 per cent. Mean body temperature increased by 0.5 degrees C, but pulse rate did not change significantly. Dry matter intake, particularly of hay, decreased rapidly to less than 10 per cent of normal on the third day. Milk yield decreased only slightly during the first 24 hours but on the third day the average yield was only 28 per cent of normal; the composition of the milk did not change significantly. There were significant progressive increases in serum sodium concentration (after four hours water deprivation), osmolality (after 24 hours), urea (after 38 hours), copper (after 48 hours) and magnesium and total protein concentration (after 62 hours); packed cell volume (measured with a Coulter Counter) increased after 38 hours but packed cell volume (determined in a microhaematocrit centrifuge) increased only after 62 hours. In spite of the dehydration the cows showed no signs of distress. Within 48 hours of the cows being given free access to water, bodyweight, appetite, milk yield and blood composition had returned almost completely to normal.

Magnesium and milk fever.

There is clinical, experimental and theoretical evidence for a connection between the occurrence of subclinical hypomagnesaemia and the incidence of milk fever. Clinically, pregnant dry cows in dairy herds with a high incidence of milk fever have often been observed to have subnormal blood magnesium concentrations. Experimentally, it has recently been shown that subclinical hypomagnesaemia reduced the ability of cows to mobilise calcium in response to hypocalcaemia; a response which is essential if cows are to avoid milk fever. And theoretically there are several points in the biochemical pathways for calcium where a need for magnesium has been demonstrated in laboratory rodents. These connections between subclinical hypomagnesaemia and milk fever are explored and their consequences for the prevention of milk fever are considered.

Decline of serum albumin concentration at calving in dairy cows: its relationship with age and association with subsequent fertility.

Blood samples were collected weekly from Friesian cows between five weeks before and 10 weeks after calving in three consecutive years, and analysed for serum albumin (using two methods: a hydroxyazobenzene benzoic acid [HABA] dye-binding method and a bromocresol green [BCG] method), and serum bilirubin. At calving the decrease in HABA albumin concentration in cows was twice that for heifers but corresponding decreases in BCG albumin were similar. Bilirubin concentrations increased near calving, more so in cows than in heifers, and maximum post partum values were inversely correlated with minimum values of HABA albumin (r = 0.40) but not with BCG albumin (r = 0.01). Albumin concentrations were lower between zero and two weeks (P = 0.03 HABA, P = 0.13 BCG) and between seven and nine weeks (P = 0.07 HABA, P = 0.06 BCG) in cows requiring four or more services than in cows which conceived at first service. Over the three year period the repeatability of post partum albumin concentration was low. However, cows which were hypoalbuminaemic in the first year showed higher repeatability in subsequent years than those which were not.

Calcium mobilisation in hypomagnesaemic cattle.

Intravenous infusions of EDTA solution (4.7 per cent w/v) were used to induce hypocalcaemia in six steers and six non-pregnant lactating Friesian cows, once when they were normomagnesaemic and once when they were hypomagnesaemic (less than 0.85 mmol Mg per litre) and their rates of calcium mobilisation have been measured. The mean rates of calcium mobilisation by the normo- and hypomagnesaemic steers were 0.32 mmol/min and 0.21 mmol/min respectively (P less than 0.005) and the mean calcium mobilisation rates of the cows were 0.41 mmol/min and 0.26 mmol/min respectively (P less than 0.02). It is concluded that hypomagnesaemia reduced the calcium mobilisation rate in both steers and non-pregnant lactating cows.

Study of combined injections of 1 alpha-hydroxy-cholecaldiferol and cloprostenol in the prevention of parturient paresis.

Dairy cows were injected with 1 alpha-hydroxycholecalciferol (1 alpha-HCC) and, or, cloprostenol at 275 days of gestation. Blood samples were taken daily from 270 days of gestation until seven days after parturition and analysed for calcium, inorganic phosphate, magnesium and hydroxyproline. In all treated and control cows concentrations of calcium, inorganic phosphate and magnesium decreased around the time of parturition. Concentrations of hydroxyproline increased from the second to the fourth day after parturition. This increase was slightly smaller in cows injected with cloprostenol but was unaffected by 1 alpha-HCC. There was a greater indicence of retained placenta and endometritis in cows receiving cloprostenol. The injection of cloprostenol with 1 alpha-HCC at 275 days of gestation did not prevent milk fever.

The blood composition of different breeds of bulls undergoing beef performance tests.

Blood samples taken on three occasions from each of 66 bulls undergoing beef performance tests were analysed for packed cell volume, blood glucose, haemoglobin, serum albumin, urea nitrogen, total protein, inorganic phosphate, Ca, Ca, Mg, K, Na, Cu, Fe and total iron binding capacity. The bulls were individually fed and situated at two centres, one accommodating Lincoln-Red, Devon and Sussex breeds and the other, Hereford. Significant differences between the Lincoln-Red, Devon and Sussex breeds were observed in concentrations of glucose, urea nitrogen, total iron binding capacity (P less than 0.001), Ca (P less than 0.01), Na and Cu (P less than 0.05). There were no significant correlations between the growth rates of individual bulls and their blood composition.

The influence of dietary protein upon blood composition in dairy cows.

Diets of different protein content were fed to dairy cows in two experiments of seven months and 12 months duration. Significant differences in the mean concentrations of serum urea, albumin and copper and of blood haemoglobin and packed cell volume were observed between cows receiving the various diets. The greatest differences occurred when cows were in mid-lactation. It was concluded that concentrations of urea in the serum of the cows were reflecting dietary protein intake and that concentrations of albumin, haemoglobin and PCV during lactation were affected by long-term protein status. The possible significance of the results is discussed in relation to previous reports indicating interrelationships between protein and copper metabolism, and in relation to the recommended protein content of diets for cows.