Resumen

VASQUEZ M, Belkys J  y  BASTIDAS M, Pedro. Reproductive performance of first lactating Brahman cows supplemented with undegradable protein. Zootecnia Trop. [online]. 2005, vol.23, n.4, pp.411-427. ISSN 0798-7269.

To evaluate the effect of the two undegradable protein levels (UDP) in the diet on reproductive performance, 30 first-calf Brahman heifers were assigned at random to three groups. Group A (n =10) received 40% of UDP, group B (n= 10), received 60% of UDP, and group C (n=10) without any supplementation. The supplementation started 60 d before the beginning of the breeding season (BS). The animals were maintained on pastures of Panicum maximum, Brachiaria mutica and Cynodon plectostachyus. Cows and calves were evaluated biweekly to determine average daily gain (ADG) and body condition score (BCS). Ultrasound was performed twice a week and blood samples (10 mL) were collected to determine progesterone. Cows in groups A and B had a greater ADG at the beginning of the BS (P<0.04) compared to control cows. Also animals in group A did tend (P<0.1) to have better BCS at the beginning of the BS than cows in control group. Furthermore, 30 and 60 d from the beginning of the BS, cows from group A had better BCS (P<0.02 and P<0.08, respectively), compared to the control group. Cows of group B tended (P<0.1) to have a greater proportion of estrus during the first month of BS compared to the group A and control group. During the second month of BS, the number of cows in estrus was greater for group B (P<0.02) than in cows of the control group. The interval from supplementation to first estrous was shorter for group B (P<0.02). The number of class 1 and class 2 follicles were not affected by treatment (P>0.05). However, the number of class 3 follicles was greater (P<0.04) in group B than in A and control groups. The strategic UDP supplementation, before the beginning of the breeding season, can improve the reproductive performance of first-calf Brahman heifers.

Palabras clave : Undegraded protein; Brahman cows; ovarian follicles; anestrous postpartum.