Fertility Rates Following Fixed-Time Artificial Insemination in Dairy Heifers in a Practical Progesterone-Based Protocol

Acta Scientiae Veterinariae

Endereço:
AV BENTO GONçALVES 9090
PORTO ALEGRE / RS
Site: http://www.ufrgs.br/actavet/
Telefone: (51) 3308-6964
ISSN: 16799216
Editor Chefe: [email protected]
Início Publicação: 31/12/1969
Periodicidade: Trimestral
Área de Estudo: Medicina Veterinária

Fertility Rates Following Fixed-Time Artificial Insemination in Dairy Heifers in a Practical Progesterone-Based Protocol

Ano: 2011 | Volume: 39 | Número: 2
Autores: Letícia Zoccolaro Oliveira, Vera Fernanda Martins Hossepian de Lima, Clara Slade Oliveira, Benner Geraldo Alves, Hugo Borges Graff, Ricarda Maria dos Santos
Autor Correspondente: Ricarda Maria dos Santos | [email protected]

Palavras-chave: conception rate, heifers, ovulation, progesterone

Resumos Cadastrados

Resumo Inglês:

Background: In bovines, more efficient management practices are important for maximizing profitability. In order to increase
the pregnancy rates in artificial insemination (AI) programs, several hormonal protocols were developed to synchronize the
follicular wave and the moment of ovulation in beef and dairy cattle. In dairy cattle, detection of estrus can be difficult due to
a number of factors including the incidence of silent estrus. Hormonal treatments designed to control both luteal and follicular
function has permitting efficient synchronizations of time of ovulation. Thus, the AI can be performed in a large number of
animals on a fixed schedule without the need for detection of estrus. Using these management techniques, the fixed-time
artificial insemination (TAI) can overcome the problem of accurate estrus detection and help in reducing the incidence of
repeat breeding. In addition, with TAI in cattle operations, it is possible to facilitate management practices and commercialization,
and to reduce the time and semen wasting with animals inseminated at incorrect times. The investigation of practical and
efficient TAI protocols is important for reducing the labor and animal handling of TAI in dairy cattle, as well as for increasing
the profitability of the cattle management system. This study was carried out in order to investigate the effectiveness of TAI in
dairy heifers treated with a practical progesterone-based protocol.
Materials, Methods & Results: This experiment was conducted at the university farm located in southwestern Brazil, during
May 2009. Thirty-nine cycling crossbred dairy heifers were employed in this study. All animals received a single intramuscular
injection of estradiol benzoate and intravaginal progesterone releasing device in a random stage of the estrous cycle (Day 0).
On day 7 the animals were treated with PGF2á analogue and on day 9 the device was removed. Forty-eight hours after the
device removal (day 11) a synthetic analogue of GnRH was administered and the animals were fixed-time artificially inseminated
at the time of GnRH injection. The inseminations were performed using four different batches from the same Holstein bull.
Among the heifers that were synchronized (87.2%), 30.8% ovulated until 24 h after TAI and 56.4% ovulated between 24 and
32 h after TAI. The conception rate was 61.5%. No effects of ovulation time in conception rates were detected. The conception
rate from heifers that ovulated until 24 h after TAI was 58.3% and from heifers that ovulated between 24 and 32 h after TAI was
77.3%. The mean of ovulatory follicle in heifers that ovulated until 24 h was 14.3 mm and in heifers that ovulated between 24
and 32 h was 11.9 mm.
Discussion: Taking together, the findings of the present study, along with those of others, emphasize the concept that
development of practical methods for TAI offers significant advantages to dairy producers if conception rates are close or
greater to those obtained after breeding at detected estrus. Thus, the results of the present study reinforce the possibility of
making dairy cattle production more cost-effective using TAI. In conclusion, with the progesterone-based TAI protocol of the
present experiment all synchronized animals ovulated up to 32 h after GnRH+TAI and no effects of ovulation time related to
conception rate was detected. The exogenous control of luteal and follicular development facilitated the reproductive
management and animal handling. Also, inseminating the heifers at the moment of GnRH injection in a progesterone-based
TAI protocol is a practical strategy and provided satisfactory results regarding ovulation and conception rates in dairy heifers.