45- Estudios endócrinos durante el desarrollo en bovinos de leche. Efectos de las habituales nematodiasis gastrointestinales y su traducción a las variables productivas

LACAU-MENGIDO, IM

Mendoza

Congreso; XXVI Reunión de la Sociedad de Biología de Cuyo,; 2008

Sociedad de Biología de Cuyo

Endocrine studies on the effect of gastrointestinal nematode infection during development in Holstein heifers. 1 Isabel M. Lacau-Mengido, Adrián F. Perri, Miguel E. Mejía, Damasia Becú-Villalobos Laboratorio de Regulación Hipofisaria, IBYME-CONICET, Vuelta de Obligado 2490, 1428 Buenos Aires, Argentina. Meat and milk production in Argentina is primarily based on grazing herds.  Grazing animals are allowed to be infected by gastrointestinal nematodes as the infecting larvae are ingested with grass. In several experiments, we compared naturally nematode infected Holstein heifers with and without continuous anthelminthic treatment. We measured developmental and productive parameters and we registered reproductive cues. In order to identify some of the endocrine mechanisms involved, we measured metabolic and reproductive hormones. Nematode eggs in feces of parasitized animals augmented rapidly during the 3rd and 4th months of life and then decreased, whereas treated animals remained egg free. Treated animals grew faster than untreated ones and differences in body weight became significant at the 6th week of life. Parasite free heifers reached puberty nearly four weeks earlier than infected ones. Besides, pelvic area at 39 weeks and at 15 months of age was increased in treated heifers when compared to parasitized animals. Age at first service was advanced by 10 weeks and age at calving by 4 months in treated versus untreated animals. Daily milk yield and fat content in milk during first lactation were similar in both groups but culling rate during first lactation was greater in untreated than in treated cows. When mechanisms involved in parasite action on growth, reproduction and production were investigated endocrine alterations were found during growth. Serum IGF-I levels increased from birth to 22 wk of age and then reached a plateau in both groups, but levels were consistently higher in parasite free heifers. Mean LH levels were diminished in untreated heifers 4 wk before the first estrus and the amplitude of LH pulses was augmented in treated heifers when puberty was reached. Prolactin followed seasonal changes of sunlight duration and presented sporadic bursts in infected animals. These were related to high nematode infection and are probably involved in the immune response of the host. Furthermore, leptin which directly correlates with body weight during development showed a prepubertal surge two weeks before the progesterone peak that indicates the onset of puberty in both groups. We conclude that parasitism during growth in dairy heifers impairs full production as it delays onset of lactation and reduces productive life of the cows, and that those effects could be mainly ascribed to reduced IGF-1 levels during development.