Artigo
The physiology and impact on fertility of the period of proestrus in lactating dairy cows
Registro en:
Animal Reproduction. Belo Horizonte: Brazilian Coll Animal Reproduction, v. 11, n. 3, p. 225-236, 2014.
1806-9614
WOS:000346369700011
WOS000346369700011.pdf
1069922096621313
Autor
Wiltbank, M. C.
Baez, G. M.
Vasconcelos, José Luiz Moraes [UNESP]
Pereira, M. [UNESP]
Souza, A. H.
Sartori, R.
Pursley, J. R.
Resumen
In cattle, proestrus begins with the initiation of luteolysis and ends with initiation of estrus and the GnRH/LH surge. This period is marked by a dramatic decrease in circulating progesterone (P4) that reaches a nadir by about 36-48 h in cows undergoing natural or prostaglandin F2 alpha (PGF)-induced luteolysis. Inadequate luteolysis is a cause of reduced fertility particularly in timed AI programs with small elevations in circulating P4 reducing fertility. Increasing circulating estradiol (E2) during proestrus is dependent on presence, size, and function of the dominant follicle and this varies during natural proestrus, due to whether animals have two or three follicular waves, and during PGF-induced proestrus, according to stage of the follicular wave at time of PGF treatment. Inadequate circulating E2 can limit fertility and increase pregnancy loss in some specific circumstances such as in cows with low BCS and in cows during heat stress. Thus, studies to optimize the length of proestrus and the concentrations of E2 and P4 during proestrus could produce substantial improvements in fertility and reductions in pregnancy loss. Univ Wisconsin, Dept Dairy Sci, Madison, WI 53706 USA Sao Paulo State Univ, Dept Anim Prod, Botucatu, SP, Brazil Univ Sao Paulo, ESALQ, Dept Anim Sci, Piracicaba, SP, Brazil Michigan State Univ, Dept Anim Sci, E Lansing, MI 48824 USA Sao Paulo State Univ, Dept Anim Prod, Botucatu, SP, Brazil