51- Evaluation of three methods for the enhancement of pregnancy rates in Bos indicus adult cows on “malezal”

MEJIA, ME; CABARCOS, G.E.; MARCONE, J.I.; BECU-VILLALOBOS, D; LACAU-MENGIDO, IM

Santiago, Chile

Congreso; XXVI World Buiatrics Congress; 2010

“Malezal” fields from Corrientes Province, Argentina, are characterized by poor soils and low quality grass production which have nutritional limitating consequences for cattle such as low pregnancy rates. Under those conditions it is generally accepted to produce only a calf per cow every two years. In order to improve this index we evaluated different management protocols. On November 26 (day 0), 155 Bos indicus lactating cows that had calved from September 10th to October 10th were evaluated by rectal palpation to assess an anestrous state and their body condition scores (BCS) were recorded. At this moment cows were assigned at random to one of the four following treatments: Treatment 1 (EW): Early weaning  performed at 46-77 days of age of the calves. Treatment 2 (NP): nose plates preventing suckling were fitted to age matched calves for 14 days and then removed. Treatment 3 (EP): cows received an exogenous hormone treatment which consisted in a single injection of Estradiol-Benzoate (2mg, i.m.) at day 0 and a progesterone intravaginal device placed at the same time for 10 days (Syntex, 1 g). Treatment 4 (C): cows remained untreated with their calves. Blood samples were taken from all the cows on day 0 and day 10 for progesterone determination. Bulls were incorporated on November 11th and removed on January 8th.  Pregnancy rates were evaluated by rectal palpation on March 10th. Pregnancy rates differed between groups (86.5, 37.2, 20.8 and 25.9 % for EW, NP, EP and C, respectively;  p< 0.05), independently of BCS. These results showed that only EW was effective in improving reproductive performance in this combination of cow species (Bos indicus) and type of soil.