H—29

(a) The Ruakura Grade Group : For several years it has been apparent that conception rates with stored material have been unsatisfactory, and that, in particular, a marked fall in rate has occurred with second- as compared with first-day material. This observation, however, has tended to be confused by other operating factors which have been under experimental test. This season the grade group has been used to obtain straight data on storage time relative to conception rate. Semen was used mainly over three days. A total of 1,122 inseminations was carried out for an over-all conception rate of 51 per cent., 36 per cent., and 37 per cent., on the first-, second-, and third-day inseminations respectively. A dose rate of 25,000,000 sperm per insemination was used. The drop of 15 per cent, from the first to the second day is substantial and represents a fall from a satisfactory to an unsatisfactory level in so far as the dairy-farmer is concerned. The maintenance of conception rate on the third day at the same level as that on second-day material is also in line with previous years' results. In addition to the experimental group, the data from both the commercial and the pedigree groups also provided a measure of this fall off in conception rate with storage. The two commercial groups showed a drop as between the first and second day of 11 per cent, in Waikato and 5 per cent, in Taranaki. These two groups used a dose rate of 50,000,000 sperm. The pedigree group drop for the same period was 10 per cent., using the lower dose rate of 25,000,000 sperm. In attempting to assess the factors responsible it has been noted that individual bulls exhibited" a marked difference in their ability to produce semen capable of standing up to storage. Thus in the combined grade and pedigree experimental groups bull J. maintained a fairly even percentage for the first two days with rates of 58 per cent, and 54 per cent., but dropped away to 34 per cent, on the third day. A similar picture was shown by this bull in the commercial groups, second-day inseminations being as good or better than the first, the figures being 56 per cent and 71 per cent, for Waikato and 54 per cent, and 50 per cent, for Taranaki. In contrast, bull S. exhibited a drop of approximately 20 per cent, from first- to second-day material in all groups. There appears to be no doubt that marked deterioration occurs after twenty-four hours' storage with some bulls under low-dilution rates. The fact that the fall was. less in the commercial group which employed a higher dose rate than the 25,000,000 used in the grade group suggests that the trouble is more serious with lower dilutions. The general results are in line with those now being reported from Denmark and the United States. Work both to discover the reasons and to correct the trouble is in progress. (b) Pedigree Group : Work for the fourth year with this group proceeded along, lines similar to those of previous seasons except that limitations of transport imposed still further restriction upon the area covered and several herds had to be dropped. Without any propaganda or persuasion, however, numbers were maintained at the level of previous years, 557 cows being inseminated, of which 67 per cent, proved in calf during the short season offered. The following table brings up to date the pedigree cows conceiving to merit sires as a result of A.I. work in this experimental group :

Pedigree Cows in Calf to Merit Bulls

44

Bull. 1946.. 1947. 1948. 1949. Total. Jersey Glen Handsome Boy 134 139 64 182 519 Landsdowne Double Sam ♦ . 0 83 110 90 283 Erinview Teddy 53 52 66 31 202 Fairymeadows Beau Geste . 101 45 146 Muritai Oxford Lad 21 47 68 Cloverfield's Enid's Sam 11 11 Total 208 321 341 359 1,229