H.— 29.

Mammitis. —The incidence of this disease of dairy cows did not appear to be appreciably less during the year. Concentrated investigational work has been established by the Wallaceville staff, and further important points in connection with its development have come to light. One of these is in connection with the bacterial flora of the teat duct, which promises to yield useful information regarding the question of infection by so-called " carrier " cows. The mammitis-control scheme introduced a few seasons ago by the Department is still being carried on. This method of control is dependent on the monthly laboratory examination of milk from all cows in a herd, and the subsequent grouping into free and infected lots. By rotational milking of those groups, coupled with certain hygienic requirements, it is claimed that the spread of infection can be materially lessened. A number of farmers in the dairying districts have adopted the method, and in many instances encouraging results have followed. The method undoubtedly involves a certain amount of trouble, but the willingness to continue the practice which has been shown by many indicates some satisfaction with the results. From inquiries received it is apparent that an increased number of dairy-farmers will avail themselves of the method during the coming season. Contagious Abortion. —As in recent years, the incidence of actual cases of abortion has not assumed serious proportions. The infection, however, is widely disseminated through our herds, but it is evident that immunity has been established to a very large extent against actual abortion. In spite of the intensive world-wide research into this disease, no practical and reliable method of preventive inoculation has as yet been introduced. The agglutination (blood) test has, however, made available a ready means of discovering infected animals. This test has been largely carried out at the Wallaceville Laboratory in co-operation with field officers, and its value in revealing the existence of the disease is much appreciated. Advice to farmers regarding control of the disease has been largely disseminated by the Division. Sterility. —The seasonal occurrence of the condition referred to as " temporary sterility," " not holding to bull," or " delayed conception " was again much in evidence amongst dairy herds. A considerable amount of investigational work into this trouble has been accomplished, and although a definite causative factor cannot as yet be shown to operate in all cases much light has been thrown on the condition generally. Inquiry goes to show that in all probability several factors are involved, falling under the headings of (1) mineral deficiency, (2) partially infertile bulls, (3) infection. Under the first heading fall those instances dependent on insufficiency of minerals in the feed, or their presence in a ratio unsuitable to the maintenance of the animal's requirements. In giving advice to farmers on this particular point, much stress has been laid on the beneficial results generally following the use of licks of the proper type. Speaking generally, the use of a bone-meal and salt lick is indicated wherever a shortage of phosphate and lime is suspected. Evidence collected from farmers who have adopted the use of such licks for cattle has impressed field officers of the Division with the utility of the practice in maintaining condition and lessening the incidence of breeding troubles. Reference must again be made to the necessity of better winter feeding of our herds. The nutritional aspect at this particular time must not be lost sight of, and the aim of every dairy-farmer should be improved conditions of feeding and also of shelter for his cows during the winter months. Investigational work has shown the bull to be responsible in many instances for the occurrence of this trouble in a herd. Certain infections of the cow's genital organs are also involved. Referring to this condition, the District Superintendent, Dunedin, who has conducted some keen observations regarding the trouble, states in his report: " There is every possibility of some dietetic factor having an influence in the production of functional sterility." " Foul Foot " in Cattle. —The condition known as " foul foot " in cows is in many districts a source of considerable worry and economic loss to the dairy-farmer. The actual cause of this condition has been shown to be bacterial, but certain contributory factors are involved. Some investigational work has been done regarding the disease at the Veterinary Laboratory. This investigation will be further pursued, and it is intended, when more definite information is collected regarding certain aspects, to issue a departmental bulletin on this subject. Bloat in Cows. —The occurrence of bloating in cows during the early spring period has recently been the subject of departmental inquiry. Whilst conceding that the control of this trouble is largely a question of management, there are nevertheless certain features of pasture conditions which appear conducive to its production. In an attempt to clear up some of those at present undetermined points, a line of investigation into this condition has been mapped out which will be fully pursued next season. Grass Staggers in Cows (Grass Tetany). —The seasonal occurrence of this condition was mainly confined to the Waikato, very few cases having been recorded in the Wellington District, and Taranaki still apparently remaining practically free from the disease. In the Waikato the disease has not been so prevalent during the past year. Referring to the lessened incidence, the District Superintendent, Auckland, states: " This was possibly due to the climatic conditions and state of the pasture at the time when the disease usually makes its appearance." The Laboratory has been responsible for very close study of this condition during the year, biochemical research work referring to the calcium and magnesium content of the blood being extensively conducted. In the field, Mr. Blake, Veterinarian, Hamilton, has rendered very valuable service in his keen study of the clinical aspect of the disease, by which he was able to classify the condition into (1) acute, and (2) sub-acute cases. In the acute type of case the animal exhibits convulsions or fits. The sub-acute form is characterized by hypersensitivity, such cows being termed " highsteppers." Extensive experimental work has been conducted in the field with a view to discovering a line of treatment which would either cure or alleviate the condition. As yet, no outstanding results have been obtained, but in the past season Mr. Blake has recorded some success in the treatment of subacute cases from the hypodermic injection of magnesium sulphate. This, however, requires further investigation before any conclusive statement can be made.

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