Molesworth Inoculation Programme

Press, Volume CV, Issue 30983, 12 February 1966, Page 9

Molesworth Inoculation Programme

The effectiveness of inoculation of two-year-old heifers against a venereal disease, vibriosis, is being tested on the Lands and Survey Department’s Molesworth station. The results of the trial of the inoculant may have considerable importance for breeders of cattle. Mr M. M. Chisholm, the station manager, says that the disease is known to be prevalent in the North Island and it is possible that some breeders may have the disease in their herds but do not recognise it.

Vibriosis has been responsible for a considerable reduction in calving percentages on Molesworth to the extent that in one season the number of calves marked was some 600 head under normal. Mr Chisholm recalled this week that about 16 years ago

concern was felt about the decline in calving performance on the station. At that time the then DirectorGeneral of Lands, Mr D. M. Greig, had suggested that it would probably be worthwhile determining whether or not brucellosis was in the

herd—he had just had a discussion with a veterinarian in Hawke’s Bay who had informed him of an outbreak of this disease.

Blood samples taken then from a cross-section of the herd had been sent to the Wallaceville animal research station where they had shown that 20 per cent of the herd at Molesworth and 15 per cent of those at Bush Gullyhad brucellosis. Inoculation of two-year-old heifers and yearlings had been started immediately and since then this practice had been continued at marking time. Calving percentages had gone from 50 to 70 per cent and occasionally into the 80’s. About six years ago, however, the percentage had dropped again and it was thought that the brucellosis inoculant might have broken down. Again blood samples were taken from a cross section of the herd and these were found by Wallaceville to be negative. When calving did not improve more samples were taken with the same result. In the following year calving improved slightly but in the next year there was a decline to the stage where it was considered that the station was 600 calves short of a normal marking. At this time Mr John Graham, of Tasman Vaccine Laboratory was doing work on the station on the inoculation and prevention of foot abscess in bulls, and as a result of discussions with Mr Graham and also Mr John Muir, a veterinarian at Blenheim, Mr Chisholm said he had had both men flown in to the station to take blood samples from a cross section of two-year-old heifers, three-year-old heifers and some aged cows to see whether they were suffering from a trace element deficiency, and also to take vaginal smearsAt this stage, from observation, it was determined that it was the three-year-old heifers which had given a very poor calving and the investigation of the vaginal smears by Wallaceville and also pregnancy tests on three-year-old heifers showed that only about 15 per cent were in calf.

were that these cattle took the bull and then aborted at about six weeks after service. The disease was dormant in the herd and was transmitted by the bulls. A solution, where practicable. was to run the two-year-old heifers in isolation from other aged female stock and to have these cattle serviced by clean bulls. In a commercial herd of the size of Molesworth this was totally impracticable. Mr Chisholm said he understood from the professional people that a large percentage of two-year-old heifers when exposed to the disease would build up a natural immunity and would stand every chance of a normal calving in the fourth year. A percentage of these heifers exposed to the disease would also become sterile and some would not be affected but would be carriers of the disease.

With this knowledge, Mr Chisholm said, he had decided to dispose of one year’s two-year-old heifers, which would normally have been herd replacements, to return to the bull for a further season the. now three-year-old heifers and these now appeared to have given quite a substantial calving. This course had been taken in the hope that a successful inoculant could be found to counter the disease and this had been evolved in the year as a result of foundation work done by Wallaeeville and further work by Tasman Vaccine Laboratory. Preparations had therefore been made to inoculate a large number of two-year-old heifers. A double race capable of holding 10 on either side had been built at Tarndale off the main yards there. The idea was that while one group was being inoculated the other group was being let out and the race refilled. Five hundred out of 700 heifers of this age group had been inoculated in two hours. Two hundred had been left untreated as a control and check on the effectiveness of the treatment. A period of six weeks had then elapsed before these heifers had been run with the bull at the beginning of this month.

The vaginal smears showed that the disease was vibriosis, the symptoms of which