Periódicos Brasileiros em Medicina Veterinária e Zootecnia

Endocrine profile and reproductive performance in heifers induced to lactation

Luz, Gabriela BuenoMaffi, Andressa SteinXavier, Eduardo GularteCorrea, Marcio NunesGasperin, Bernardo GarzieraBrauner, Cassio Cassal

Background: Low reproductive efficiency has been one of the main factors that lead to dairy herd culling in the reproductive age. In multiparous animals, such inefficiency and culling can occur because of various factors and may be associated with occasional endocrine failures. To avoid revenue losses that incur due to lack of lactation, lactation is artificiallyinduced in the animals that are not pregnant, using a defined protocol. The aim of this study was, therefore, to evaluateand compare the reproductive performance of heifers submitted to the induction protocol with that of pregnant heifersduring the transition period.Materials, Methods & Results: Sixty Holstein heifers, 32 ± 0.6 months of age, were divided into two groups: ControlGroup (Control, n = 30) comprising pregnant heifers that were accompanied since 21 days before the expected calvingdate until 224 days in milk (DIM) and an Induction Group (Induction, n = 30) comprising non-pregnant heifers submittedto a lactation induction protocol, accompanied from the beginning of the protocol until 224 DIM. For evaluation of theendocrine profile (progesterone and estradiol concentrations) of these animals, blood samples were collected at two periods: the pre-lactation (weeks -3, -2 and -1) and post-lactation (weeks 1 and 4). Heifers from both groups were submittedto weekly reproductive evaluations, from the beginning of lactation until 35 DIM. Uterine examinations were performedusing ultrasonography and vaginoscopy to evaluate uterine content, cervical opening, and mucosal aspect. Females ingood reproductive health were subjected to a hormonal protocol for timed artificial insemination (TAI). The pregnancyrate of heifers that could reproduce (Control, n = 13, and Induction, n = 20) were evaluated and inseminated until 49 DIM.Progesterone levels were similar (P > 0.05) in the two groups at both pre- and post-start of lactation. Estradiol...(AU)

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