Efecto de la gonadotrofina coriónica equina y del inseminador sobre la preñez en vacas con cría en inseminación artificial a tiempo fijo

Abstract

The objectives were to evaluate the effects of equine chorionic gonadotropin (eCG) at withdrawal of a progesterone intravaginal device (P4 device) and the inseminator on suckling beef cows without corpus luteum. On day 0, cows without corpus luteum were selected (n=223), body score condition (BSC) were measured and cows received a P4 device (1.2 g of progesterone, EMEFUR®, Merial) and 2 mg of estradiol benzoate (EB; EMEFUR®, Merial) im. On day 8, P4 device were removed, 0.15 mg of D (+) Cloprostenol (EMEFUR®, Merial) im was administered and the cows were randomized into two groups to receive or not (Control) 400 IU of eCG (Novormon, Syntex), considering BSC (=4 or 5-6) and dominant ovarian structure (DOS: Follicles -F- < or = 10 mm). On day 9, 1 mg of EB was injected im and all cows were inseminated at a fixed-time (FTAI), 52-56 h after device withdrawal. Pregnancy diagnosis was performed by ultrasonography on day 28 after FTAI. The effect of treatment (eCG and control), BSC (4 and 5-6), DOS (F<10 mm and F=10 mm), inseminator (A and B) and their interactions upon pregnancy rate at FTAI were evaluated. Variables were analyzed using PROC CATMOD of SAS, significance was indicated by a probability of <0.05. There were no effect of treatments (eCG: 48.6%; Control: 45.5%), BSC (4: 37.0%; 5-6: 49.7%) and DOS (F<10 mm: 45.8%; F=10 mm: 47.6%) (p>0.05). There was an effect of the inseminator (A: 53.8%; B: 25.0%; p<0.05). In conclusion, administration of eCG at the end of a FTAI treatment did not improve pregnancy rate in cows with a BSC from 4 to 6 and follicles as the dominant ovarian structure. On the other hand, the inseminator experience is an important factor that affects the reproductive efficiency.