Feral rabbits impose a substantial environmental and economic cost in this country, causing pasture devastation over large areas of land, accelerating erosion and decreasing vegetation cover. Existing or potential methods of control have a high ethical cost, and there is a need to identify new methods of control. Manipulation of lactation, to enhance mortality and inhibit growth and development of the young, is a possible alternative strategy. Prolactin (PRL) is known to be important for establishment and maintenance of lactation in rabbits, and PRL secretion may be inhibited by administration of ergot alkaloids such as bromocriptine (CB154). These substances are orally active and so could potentially be used in baits. In order to determine whether CB154 could be used in baits, it is first necessary to establish the lowest effective dose. The objective of this study was to examine the relationships between dose of CB154 (initially administered systemically) and the growth and survival of kits. Sixteen pregnant New Zealand White does were divided into four treatment groups receiving different doses (mg/kg live weight/d) of CB154 ("low"(L), 0.2; "medium"(M), 0.4; "high"(H), 0.8; and control (C), 0). From day 3 of lactation, does were injected once daily with CB154 or excipient. Treatment continued until day 14 or until the death of all the kits, whichever came first. There were significant treatment effects on the proportion of kit deaths on all measurement days. By day 17, kit mortalities were: C, 20%; L 42%; M, 64%; H, 71%;) (P<0.05). The weight gain of the surviving kits from day 3 to 8 did not differ significantly between treatment groups, but kit weight gain day from days 8 to 13 showed a significant treatment effect (P<0.01) (control, 83.7±11.4g; low, 18.7±11.4g; medium, 33.5±17.2g; high -0.8±14.9g). Results are discussed in relation to the possible use of bromocriptine as a bait to control reproductive success, and to the fact that these rabbits were much less sensitive to bromocriptine than previously published studies would suggest.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 222-224, 1997
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