H—29

Bull Fertility Studies.—ln this work identical twin bulls have been used and their fertility has been measured by the exhaustion technique. Semen from ten successive services collected at fifteen-minute intervals is examined for live sperm concentration and for reduction time of methylene blue. In the first series of experiments, bulls on a low-protein intake were compared withbulls receiving a Ir'gh-protein intake derived in the first instance from meatmeal and liriseedmeal and later from spring pasture. Neither the level of protein, which varied from o*9 lb. to 3-36 lb. of digestible protein per day, nor the type of protein fed had any effect on either quantity or quality of semen as judged by the above tests. Five pairs of bulls have been reared to the twelve-months stage on a high and low plane of nutrition, the pairs being split at weaning. Differences in body weight at this time were 270 lb. The animals will be used to study the effect of good and bad rearing upon sperm-production as yearlings and as two-year-olds. This work is incomplete, but preliminary data show large differences in both quantity and quality of semen between the two groups at the yearling stage. Production of Artificially-bred Heifers by Merit Sires.—ln the 1947-48 season a second crop of heifers by merit sires completed their first lactation on Ruakura and other farms in the Waikato. In addition, the first crop completed its second lactation. Resultsare summarized below :

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Production of Butterfat. 1 WttTvl Number of Production, tlrl ll. Heifers. 1 j Mature Cows.* Actual. | Mature Equivalent. Tivo-year-o Ms, 1947-48 Season lb. 1 lb. lb. A 4 269 339 312 B 6 260 330 300 C 1 \ 422 492 331 D 2 232 302 307 E 4 287 357 343 F 4 212 282 295 G 6 234 304 258 I • 5' 185 255 233 J 4 230 300 302 K 1 262 332 279 L 1 303 373 324 M 8 222 292 256 N 2 170 ■240 223 O 2 194 264 178 P 3 298 368 313 Q 3 199 269 270 Total, Waikato herds 56 240 310 280* Ruakura 55 297 367 Three-year-olds, 1947-48 Seaso n lb. lb. lb. A 10 275 310 312 B 12 298 333 300 C 6 255 290 331 D 11 278 313 307 E 7 329 364 343 F 3 306 341 295 G 7 204 239 258 Total, Waikato herds 56 277 312 307* ftuakura .. 30 | 301 336 | * Mature normal cows weighted according to the number of A.I. daughters in the herds.