Abstract

ACOSTA-GONZALEZ, Rafael  and  RANDEL, Ronald. Pubertad en novillas mestizas Bos taurus/Bos indicus alimentadas con concentrado, concentrado con Monensína y pasto alemán (Echinochloa polystachya (H.B.K.) Hitchcock). Zootecnia Trop. [online]. 2002, vol.20, n.3, pp.319-339. ISSN 0798-7269.

Puberty in crossbred Bos taurus/Bos indicus heirers red with concentrate, concentrate with monensin and only aleman grass (Echinochloa polystachya (H.B.K) Hitchcock)  SUMMARY  Thirty prepuberal heifers were selected at weaning. during the dry season and stratified by breed, age and weight in three groups to determine in a 135 days grazing trial the effect of feeding concentrate. concentrate with monensin and the intake (1) and utilization (U) of fertilized aleman grass (Echinochloa polystachya (H.B.K)Hictchcock), on the age, puberty weight and pregnancy rate during 120 days breeding season in the rainy season. All heifers weighed 165 kg and averaged 11 months old and grazed from June on three 5.5 ha pastures identified as A, B and C. Each one was equally divided in three paddocks. The three treatments were: AC group heifers fed with 1 kg/d of concentrate feed. BM group heifers fed with 200 mg of Monensin (M) per 1 kg/d concentrate feed and CG group heifers in pasture grazing only aleman grass. All pastures were fertilized. first with NPK and then N fractioned 7 days before and 12 days after each grazing period in a 15-d rotational grazing system and 30 days rest periods. Grass I and U were measured by exclosures systems and varied between groups (P<0.05) with BM heifers consuming less grass in 12 and 25% than AC and CG heifers respectively. Aleman grass U was greater in 6 and 21% in AC and CG groups than BM group. Monensin-fed heifers consumed 30.4% less feed with 679.9 g/d feed intake. than concentrate-fed heifers. Follicles. corpus luteum and total ovarian volume (TOV) were recorded and estrus and natural service were observed with three fertile bulls fitted with chin balls at AM and PM, rotating them and weighting the heifers every 28 days. Heifers body condition (BC) was scored at initiation and end of the trial. The animal daily gain did not differ between groups (P>0.05). but BC scorewas better in AC and BM groups than CG group (P<0.05). All BM heifers attained puberty at 514 days of age and 231.1 kg and 20% were pregnant; while AC group only 80% reached puberty at 479 days of age and 227.8 kg and in the CG group only in 60% of the heifers occurred puberty with 225.7 kg at 516 days of age and none was pregnant in the AC and CG groups. The TOV was greater in AC and BM heifers than CG heifers by more than 6 cm³ (P<0.05). Monensin-fed heifers improved fertility and were more efficient in forage:gain ratio under aleman grass grazing flooding conditions. in 120-d breeding season in the rainy season.

Keywords : Puberty; heifers; growth; alemangrass utilization; monensin; grazing system.