Effect of medroxyprogesterone acetate and eCG treatment on the reproductive performance of dairy goats

The incidence of short oestrous cycles and kidding rate in dairy goats were evaluated after administering a low dose (500 IU) of equine chorionic gona dotrophin (eCG) during two breeding seasons. The first year, 46 does (Saane n, n = 10; Nubian, n = 26; and their local crossbred, n = 10) were used, Th e second year of the study was performed on 34 of the same does (Saanen, n = 4; Nubian, n = 19; local crossbred, n = 11). The goats were synchronised with intravaginal sponges that contained medroxyprogesterone acetate during a period of 14 days. At the time of sponge withdrawal the animals were ass igned to two groups: the eCG group was injected with 500 IU of eCG i.m. and the control group was injected with 2 ml of saline solution. Oestrous dete ction began 12 h after sponge removal. Once a doe was detected to be on hea t, it was mated twice: at the moment of detected heat and 12 h later, The a nimals which presented short cycles were mated again according to the same schedule, To determine the progesterone concentration, all of the animals w ere bled on the day of standing heat and every second day over a period of 22 days during the second year, All of the does exhibited oestrus within 4 days after sponge removal, The average time (mean +/- SD) between sponge wi thdrawal and standing heat was significantly shorter in the eCG group than in the control group (34.5 h +/- 11.9 versus 42.9 h +/- 19.6). More animals in the eCG group returned to oestrus than those in the control group (62.5 % versus 15%; p < 0.0001). In the eCG group 77.5% Nubian, 63.6% crossbreed and 14.3% Saanen does returned to oestrus while the corresponding percentag es for the control group were 8.7, 10 and 42.9%, respectively. Seventy-six percent (n = 19) of the animals which returned to oestrus in the eCG group did so after a short oestrous cycle, while the corresponding figure in the control group was 16.7% (n = 1) (p = 0.0051). Mean progesterone levels in t he mid luteal phase of pregnant and non-pregnant eCG treated animals, were higher than the levels found in the control group, Kidding rates differed s ignificantly between eCG-treated (41.0%) and control animals (64.1%) (p < 0 .05), but no significant difference was observed in the mean number of live kids born per doe. Animals weighing less had a higher incidence of short o estrous cycles and a lower kidding rate than heavier animals, In conclusion , using eCG to increase litter size in goats may be influenced by body weig ht and breed. (C) 1999 Published by Elsevier Science B.V. All rights reserv ed.