Arquivo Brasileiro de Medicina Veterinária e Zootecnia
versión On-line ISSN 1678-4162
RUAS, J.R.M. et al. Induction of estrus in the postpartum of Holstein-Zebu heifers through norgestomet. Arq. Bras. Med. Vet. Zootec. [online]. 2005, vol.57, n.4, pp. 476-484. ISSN 1678-4162. http://dx.doi.org/10.1590/S0102-09352005000400008.
The experiment was carried out to evaluate the effect of two ranges of body weight and norgestomet treatment on the reproductive parameters of postpartum crossbred Holstein-zebu cows. Sixty four primiparous cows were randomly allocated to four treatments 40 days after calving: group I - cows with body weight ranging from 390 to 458kg and norgestomet treated; group II - cows with body weight ranging from 464 to 562kg and norgestomet treated; group III - cows with body weight ranging from 390 to 458kg (control); and group IV - cows with body weight ranging from 464 to 562kg (control). Progestagen auricular implants were mantained during 10 days and the cows were mated to bulls submitted to breeding soundness evaluation. Animals from treatment II showed estrus earlier than animals of the others treatments (II: 64.4; I: 109.4; III: 143.2 and IV: 105.1 days; P<0.05), and shorter open days (II: 94.6; I: 125.5; III: 160.9 and IV: 131.0 days; P<0.05). Estrus and pregnance rates did not differ between treatments (P>0.05). The hormonal treatment and the body weight did not affect the total and daily milk yield, and length of lactation (P>0.05). Progestagen treated, heavier and better body condition scored animals had shorter open days, and returned to postpartum ovarian ciclicity faster than lighter animals.
Palabras clave : cattle; norgestomet; postpartum; estrus; corporal weight.