Effect of monensin sodium on lactational performance of autumn- and spring-calving cows.

............................................................ ............ . . . . ............ . . . . . ....... 28 INTRODUCTION . . . . . . . . ....... . . . . . . .. . . . . . . . ................... . ........ . . ... . . . . ..... . .. . . .. . . . . .. . . . ..... 30 MATERIALS AND METHODS . . . . . . . . .. . . . .. . . . . . . . . . . . . . . . . . . . . . . . ....... . . . .. . . ........ . . .. . . . . . . . . 32 Experiment 1 : Autumn-calving cows ........ . . . ............... . . . . . . .................. 32 Experiment 2: Spring-calving cows ......................................... . .. . . ...... 33 Experiment 3 : Sheep fed fresh cut pasture in autumn and spring . .. . . . . . . . . .. . . . ... . . . . . . . . . . . ........... . . . .......................... . . . . . . . . . . 33 Chemical analyses . . . . . .. . . . . . . . ..... ..................... . ....... . .. . . . . . . . . . . . . . . . . . . . . . ....... 35 Statistical analyses ....... . . . . . . . . . . . ......... . . . . . ....... . . ............. . . . . . . . . . . . . . . . . . . . ..... 36 RESULTS .................. . . . . ............. . . . . . . . . . . . . . . . . . ....................... . . . . ......................... 38 Experiment 1: Autumn calving-cows . . . . . . . .. . . . . .............. . . . . . . . . . . . . . . . ........ 38 Milk production , liveweight and condition score . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 Plasma hormone and metabo lite levels ........ . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Experiment 2: Spring-calving cows ................ ....... . . . . . . . . . . . . . ..... . . . ...... . . 45 Mi lk production , l iveweig ht and condition score ........ . . . ...... . . . . . . . .. . . . 45 Plasma hormone and metabo lite leve ls . . . . . ............... . . . . . . . .. . . . .. . .... . . 50 Experiment 3: Sheep fed fresh cut pasture in autumn and spring ................ . . .. . . .............. ........... . . . . . . ... ................. . . . . . . . 53 Pasture chemical analysis ....................... . .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 Vo lu ntary feed i ntake , feed apparent digestibi l ity and nitrogen_ balance . . . . . . . . . . . . . . . . . . . . . . . .............. . . ................. . ... . ...... . ........ 53 Rumen volati le fatty acid production . . . . . . . . ................. . . . . . . . . . . . . . . . ...... 56 Ru men production of l ipogenic and g lucogenic VFA's ..... . .. . .. . . . . . . . 57 Ru men ammonia leve l and pH . . . . . ................. . . . . . .... . . . . ....... ............ 59 Plasma hormone and metabol ite levels . . . . ...... . . . . .......................... . 60 DISCUSSION . . . . . . . . . ........................ . . . ....... . . . . . . ..... . ............. . . . ... . . . ... . .... . .......... . . 63