Desenvolvimento e desempenho reprodutivo de novilhas Nelore criadas a pasto nos cerrados do Centro-Oeste brasileiro

Abstract

RESUMO -Foi simulado e validado um modelo de cria e recria a pasto de fêmeas Nelore nos cerrados do Centro-Oeste brasileiro. Foram determinados os ganhos de peso médios diários (GMD) durante três anos: na primeira seca após a desmama, em pastagem de Brachiaria brizantha (Hochst) Stapf., no período das águas e na segunda seca, em pastagem de Panicum maximum cv. Tanzânia. Os GMD foram: 0,020; 0,550 e 0,172 kg, respectivamente. No segundo período das águas, fase de cria, as novilhas pastejaram em Brachiaria decumbens Stapf. Aos 24,33 meses de idade, as novilhas apresentaram peso vivo (PV) médio de 299 kg e no início do acasalamento, 25,51 ± 0,99 meses de idade (CV = 3,50%) e PV de 309,33 ± 19,19 kg (CV = 6,20%). A parição ocorreu aos 326,71 ± 19,98 dias (CV = 6,11%) após o início da estação de acasalamento, aos 36,26 meses de idade. A taxa média de prenhez foi de 88,4%. As novilhas prenhes foram 25,58 ± 9,97 dias mais velhas e 9,8 ± 7,04 kg mais pesadas que as não-gestantes. Os pesos vivos e as condições corporais no meio do período de acasalamento foram de 360 ± 31,00 kg e 2,94 ± 0,60; antes da parição, de 436 ± 30,86 kg e 4,57 ± 0,40; e na desmama dos bezerros, de 369 ± 33,89 kg e 3,11 ± 0,64.Verificaram-se taxa média de desmama de 75,6%, PV de 158 ± 20,1 kg e idade dos bezerros à desmama de 202 ± 16,6 dias.Novilhas Nelore recriadas em pastagens, com serviço aos 24/26 meses de idade em pastagem de Brachiaria decumbens, tiveram alta produtividade.Palavras-chave: cria e recria de fêmeas, peso à desmama, peso e idade à primeira cria, taxa de desmama, taxa de prenhez Growth and reproductive performance of grazing females Nellore on cerrado of Central BrazilABSTRACT -A model fitted to grazing females Nellore during the rearing periods of the Cerrado Region of Central Brazil was simulated and validated in this study. Body weight gain (BWG) was determined during three years as follows: 1) first dry season after weaning on Brachiaria brizantha (Hochst) Stapf., 2) rainfall season and 3) second dry season both on Panicum maximum Jacq. cv. Tanzânia and averaged 0.020, 0.550, and 0.172 kg, respectively. In the second rainfall season during the rearing period heifers grazed Brachiaria decumbens Stapf. At 24.33 months of age the heifers body weight (BW) averaged 299 kg while in the beginning of the mating season their age and BW averaged, respectively, 25.51 ± 0.99 months (CV = 3.50%) and 309.33 ± 19.19 kg (CV = 6.20%). On average, animals calved 326.71 ± 19.98 days (CV = 6.11) after the beginning of the mating season and 36.26 months of age. The mean pregnancy rate was 88.4%. The pregnant heifers were 25.58 ± 9.97 days older and 9.8 ± 7.04 kg heavier than those non-pregnant. The mean BW and body condition in the middle of the mating season were 360 ± 31.00 and 2.94 ± 0.60, before calving 436 ± 30.86 kg and 4.57 ± 0.40, and at weaning 369 ± 33.89 kg and 3.11 ± 0.64, respectively.The mean weaning rate was of 75.6%. Calves mean BW and age at weaning were of 158 ± 20.1 kg and 202 ± 16.6 days, respectively.Nellore heifers grazi...

Efeito da idade do desmame no desenvolvimento de novilhas de corte até os 14/15 meses de idade

“…Por outro lado, nas bezerras do desmame convencional, ocorreu aumento praticamente linear no GMD (0,516; 0,704 e 1,040 kg, respectivamente). O aumento no GMD das bezerras do desmame convencional ao longo dos anos deve estar associado à mais alta produção de leite das vacas e, embora esta característica não tenha sido avaliada, sabe-se do aumento dessa até a idade adulta da vaca Vieira et al, 2006;Cerdótes et al, 2004b). Outro aspecto pode estar relacionado ao tipo de pastagem, que variou nos três anos durante o período de lactação das bezerras do desmame convencional (Tabela 1), influenciando não apenas na produção de leite das mães, mas também a disponibilidade e a qualidade do pasto para as bezerras.…”

Pre- and post-calving forage systems and reproductive performance of primiparous cows

“…Pötter & Lobato (2004) determined calving body weights of 362.5 and 400.9 kg in primiparous Hereford and Braford cows, respectively. Vieira et al (2006) determined in primiparous Nelore cows, an average body weight of 436.0 kg at a date close to calving, during four years of observations. Morrison et al (1999), in a study with multiparous cows presenting moderate body condition score (3-3.5), observed that moderate loss of body reserves in the final third of gestation did not influence subsequent reproductive performance, if forage availability was not limiting to consumption post-calving.…”

“…Cows managed exclusively on natural pastures had the lowest final average body weight and body condition score (391.2 kg and 3.41); however, their body condition score was not different (P>0.05) from that of cows submitted to the system of improved pastures pre-calving and natural pastures post-calving (3.50). Wiltbank et al (1962) considered that variations in feeding levels between pre-and post-calving periods have a major effect on reproductive parameters. Pre-calving feeding level significantly influences anoestrus duration, and consequently, the number of cows in the heat in the beginning of the breeding season, with the stronger effects on primiparous than in multiparous cows.…”

Development and reproductive performance of Hereford heifers of different frame sizes up to mating at 14-15 months of age

“…Nevertheless, several authors showed positive correlations between heifer target weight at mating and pregnancy rate (Wiltbank et al, 1985;Silva et al, 2005). Heifers weighing more than 65% of their mature weight, according to breed and type, present high pregnancy rates (Kroetz and Neves, 1985;DeRouen and Franke, 1989), which is an important productivity indicator of breedingto-finish systems (Beretta et al, 2001;Vieira et al 2006).…”