Reproduction in Domestic Animals - Facultad de Ciencias Veterinarias

16 t h International Congress on Animal Reproduction
6 Workshop Abstracts
presence of A. pyogenes or viral infection. The exotoxin of A.
pyogenes, pyolysin (PLO), causes epithelial and particularly stromal
cell death. Similarly, BoHV-4 is highly tropic for the endometrium,
causing a rapid cytopathic effect in stromal and then epithelial cells.
This tropism may be because viral replication is activated by
prostaglandin E 2 , which is constitutively secreted by the stromal cells.
Further exploration of the molecular mechanism of microbial
infection and immunity will lead to greater understanding of how
uterine disease impacts fertility, and provide insights to help develop
new therapeutic approaches.
This work was supported by the Wellcome Trust and BBSRC.
Workshop 02 - Factors Affecting Pregnancy Rates in
Estrus Synchronization Programs in Beef Heifers
Moderator: Gabriel Bo (Argentina)
WS02-1
Reproductive management of cycling and non-cycling
Bos taurus beef heifers in the USA
Lamb, G
North Florida Research and Education Center, University of Florida, Marianna
Estrus synchronization and artificial insemination (AI) are
reproductive management tools that have been available to beef
producers for over 30 years. Synchronization of the estrous cycle has
the potential to shorten the calving season, increase calf uniformity,
and enhance the possibilities for utilizing AI. Artificial insemination
allows producers the opportunity to infuse superior genetics into their
operations at costs far below the cost of purchasing a herd sire of
similar standards. These tools remain the most important and widely
applicable reproductive biotechnologies available for beef cattle
operations in the USA. However, beef producers have been slow to
utilize or adopt these technologies into their production systems.
Several factors, especially during early stages of development of
estrus synchronization programs, contributed to the poor adoption
rates. Initial programs failed to address the primary obstacle in
synchronization of estrus, which was to overcome the late onset of
puberty in heifers. Additionally, these programs failed to manage the
timing of ovulation precisely, resulting in more days over which
detection of estrus was necessary. This ultimately precluded fixedtime
AI (FTAI) with acceptable pregnancy rates. More recent
developments focused on the control of both the corpus luteum and
follicle waves in convenient and economical protocols to synchronize
the timing of ovulation, facilitating FTAI. This new generation of
estrus synchronization protocols uses two strategies which are key
factors for implementation by producers because they: 1) minimize
the number and frequency of handling cattle; and 2) eliminate the
need for detection of estrus by employing FTAI. However, developing
FTAI protocols in beef heifers has not been straightforward because
of the inability to synchronize follicular waves reliably with
gonadotrophin-releasing hormone (GnRH). For example, after an
injection of GnRH at random stages of the estrous cycle, 60 to 90% of
postpartum cows ovulated; whereas, only 48 to 60% of beef and dairy
heifers ovulated in response to the same treatment. Therefore, most
recent research continues to focus on inducing onset of puberty in
noncycling heifers and enhancing synchrony of ovulation by
incorporating progestin devices in GnRH-based protocols to facilitate
FTAI and improve fertility in heifers.
WS02-2
Why are pregnancy rates to fixed-time AI generally lower
in Bos indicus than Bos taurus cattle
McGowan, M*; Butler,S; Phillips, N
School of Veterinary Science, The University of Queensland, Brisbane,
Australia
The recent developments in quantitative and molecular genetics which
have led to improvements in our ability to select for a range of
important production traits in beef cattle (carcass quality, fertility,
health & welfare), have increased the need to develop practical and
effective programs which efficiently disseminate selected genetics. As
the major grazing rangelands for beef cattle are located in tropical and
subtropical regions, development of artificial breeding programs
which focus on maximizing the reproductive outcome in Bos indicus
cattle, the genotypes most suited to these environments, is essential.
However, most of the treatment protocols for synchronization of
oestrus have been developed for Bos taurus cattle with the assumption
being that usage in Bos indicus cattle will result in similar outcomes.
Although some publications report similar reproductive outcomes,
marked, frequently unexplained variation in response to hormonal
treatments to synchronise oestrus, continue to be important factors
limiting the widespread usage of this technology in extensively
managed Bos indicus herds. Progestin and progesterone implants
combined with prostaglandin F2α, oestrogen and gondaotrophin
treatments are most commonly used for fixed-time AI (FTAI) of Bos
indicus females. The reported responses to these treatments in terms
of animals detected in oestrus between 48 to 72 h after implant
removal, and animals diagnosed pregnant to FTAI vary considerably
(44 to 98% and 37 to 62%, respectively). A series of recently
completed studies conducted in northern Australia have shed some
light on potential causes of the observed variation in response of Bos
indicus heifers. When 300 cycling disease-free Brahman heifers
weighing 289±30 kg, were randomly assigned to be treated with
oestradiol benzoate (ODB) and intravaginal implants (8 day insertion)
varying in progesterone content (0.78g, 1.56g, 1.9g) followed by
ODB treatment (Day 9) and FTAI 48 to 54 hours after implant
removal, the overall pregnancy rate was 35%. However, the pre- and
post-AI progesterone profiles of a random samples of 10 heifers from
each group indicated that 32% (n=30) had plasma progesterone
concentrations of 1ng/ml. Consideration should be given to
investigating the role of hormonal treatments in inducing suboptimal
preovulatory follicular and corpus luteum development in Bos indicus
cattle.
WS02-3
Fixed-time artificial insemination in cycling and noncycling
Bos indicus beef heifers
Baruselli, PS 1 *; Sales, JNS 1 ; Crepaldi, GA 1 ; Sá Filho, MF 2 ; Carvalho, JBP 3 ;
Bo, GA 4
1Animal Reproduction Department, FMVZ/USP, São Paulo-SP, Brazil;
2FIRMASA-IATF, Campo Grande-MS, Brazil; 3 Vale do Paraíba Regional
Station-Apta, Av. Prof. Manoel Cesar Ribeiro, No. 320, Caixa Postal 7,
Pindamonhangaba, SP, Brazil; 4 Instituto de Reproducción Animal Córdoba,
J.L. de Cabrera 106, X5000GVD Córdoba, Argentina
Fixed-time artificial insemination (FTAI) protocols have generally
yielded poor results in B. indicus heifers. It was hypothesized that
follicular growth in Bos indicus heifers might be suppressed by
circulating progesterone concentrations during the treatment protocol.
It is speculated that lower steroid hormone clearance rates in Bos
indicus cattle may account for the higher circulating progesterone
concentrations during progesterone treatment resulting in reduced LH
pulsatility and follicular growth rates. A series of experiments were
designed to determine if synchronization of follicle wave emergence
and ovulation with estrogen and subluteal progesterone concentrations
during growth of the ovulatory follicle would improve the synchrony
of ovulation and pregnancy rates following FTAI. Treatment with
PGF at the start of progestin treatment resulted in decreased
circulating progesterone concentrations and increased the follicular
growth rates, dominant follicle diameters and ovulation rates. In
comparison to CIDR, norgestomet ear implants resulted in increased
dominant follicle growth rates leading to ovulatory follicles with
larger diameters. Dose and estradiol ester were important factors in
synchronizing follicle wave emergence. A dose of 2.5 or 5 mg
estradiol valerate resulted in a longer and more variable interval from
treatment to follicular wave emergence than 2 mg of estradiol
benzoate (EB), which affected preovulatory dominant follicle size