Oral progesterone supplementation for beef cattle after insemination in TAI programs

Abstract

The objective of this work was to evaluate the effects of supplementation with melengestrol acetate (MGA), after timed artificial insemination (TAI), on the conception rate of Nellore cows, according to cyclicity during the protocol, estrus expression between intravaginal device withdrawal and insemination, and diameter of the largest follicle at the time of insemination, in order to identify predictors of the use of MGA. Multiparous lactating cows (577) were subjected to a hormonal protocol for ovulation synchronization. On day -2 of the protocol, the animals were painted with a marker on the base of their tail. On day 0, they were evaluated for estrus expression; the preovulatory follicle diameter (POFD) was measured by ultrasonography, and the artificial insemination was performed. The animals were assigned to two experimental groups according to the supplementation or not with 0.50 mg MGA, between 13 and 18 days after TAI. Pregnancy diagnosis was performed using an ultrasound examination 35 days after TAI. A positive effect of the treatment with MGA on the conception rate occurred generally in animals in anestrus, irrespective of the estrus expression. For animals treated with MGA, only those with POFD greater than 14 mm showed better conception rates that the control group.

Efeito De Estratégias Anti Luteolíticas Sobre a Fertilidade De Novilhas De Corte / Effect of Antiluteolytic Strategies to Improve Fertility in Heifers

“…Os efeitos da suplementação de P4 sobre a fertilidade de bovinos tem sido bastante estudado, mas os resultados são inconsistentes, tendo resultados positivos (Loiola et al 2018), e negativos (Pugliesi et al, 2014a;Pugliesi et al, 2014b). No entanto, estes experimentos variaram em relação a categoria animal, método e dia da suplementação em relação a IA, via de administração e tipo de progesterona (sintética e natural).…”

“…Taxa de gestação (%) em novilhas Nelore tratadas ou não com progesterona exógena pós-IA, de acordo com o diâmetro folicular no dia da IATF Loiola et al (2018). verificou que não houve diferenças entre folículos medianos e grandes em relação a taxa de prenhez, sendo ambas categorias diferentes significativamente (P<0,05) do que aquelas que apresentam folículos com <11 mm.…”

Oral supplementation with melengestrol acetate incorporated in protein-energy blocks I - effect on pregnancy rates in primiparous cows and Nellore heifers in natural breeding and artificial insemination

“…Melengestrol acetate (MGA) is a synthetic progestational steroid supplied orally (Bertan et al, 2005;Sá Filho et al, 2007;Silva Junior et al, 2014) and acts to inhibit the pre-ovulatory LH (luteinizing hormone) peak similar to the action of progesterone produced by the corpus luteum (Imwalle et al, 2002). When added to the nutritional supplement provided to females, it is convenient because no individual management of animals is required for the administration (Loiola et al, 2018). The results obtained after using this progestin are still inconsistent because although some studies have shown no effect on pregnancy rates and even negative results when evaluated in relation to fertility (Yan et al, 2016), other studies reported an increase in pregnancy rates of cows in postpartum anestrus supplemented with MGA (Wood-Follis et al, 2004) and also in prepubertal heifers (Pfeifer et al, 2009).…”

"Reproductive Hormones and Implication of Synthetic Hormonal Preparations: Current Status"

“…Hormonal implants has been used by researchers to enhance growth, feed intake and reproductive efficiency in animals to satisfy the increasing demand of food supply [21]. Melengestrol (MGA) is available as a food additive for growth enhancement but approved only for used in beef heifers [22].…”