Influência do manejo mãe-cria na eficiência reprodutiva de primíparas de raças de corte

• Ano de defesa: 2011
• Autor(a) principal: Martins, Paulo Gustavo Macedo de Almeida
• Orientador(a): Torres, Ciro Alexandre Alves
• Banca de defesa: Guimarães, José Domingos , Oliveira, Margarida Maria Nascimento Figueiredo de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Zootecnia
• Departamento: Genética e Melhoramento de Animais Domésticos; Nutrição e Alimentação Animal; Pastagens e Forragicul
• País: BR
• Palavras-chave em Português: Suplementação mineral; Vacas primíparas; Pós-parto
• Palavras-chave em Inglês: Mineral supplementation; Primiparous cows; Postpartum
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ZOOTECNIA::PRODUCAO ANIMAL
• Link de acesso: http://locus.ufv.br/handle/123456789/1765

The current thesis was elaborated from two experiments, realized in two different locations: one in the United States (during two consecutive years) and other in Brazil, with the purpose to compare the effects of early weaning to the short-term calf withdrawal. The study reported in this thesis was focused on measures of performance of first-calf beef cow and calf, submitted to different weaning regimens. In the study conducted in the United States, the objectives were to investigate the effects of a traditional 48-hour calf withdrawal to early weaning and repeated 48-hour calf withdrawals on performance of first-calf cows. In the Brazil study, the objectives were to compare the effects of an early Nellore-calf weaning, of a 72-hour calf withdrawal to cows kept with their calves on measures of performance of first-calf beef cows, reared in tropical conditions. During two consecutive years, at the University of Florida, Institute of Food and Agricultural Sciences, Range Cattle Research and Education Center, a total of 112 primiparous, Brahman x British crossbred cow-calf pairs were randomly allotted to three treatments: EW (early weaning); IW (interval weaning &#8211; 48-hour calf withdrawal; four times, 20 d apart); and CON (control; single 48-h calf withdrawal). Treatments were initiated at the start of a 90-day breeding season (average days postpartum = 97 ± 19 days). Blood samples were collected over 90 days on 10 days intervals for determination of progesterone concentrations. Resumption of cyclicity was defined as two consecutive samples with concentrations of progesterone &#8805; 1.5 ng/mL. Cow body weight (BW) was determined at the start (d 0), during (d 41), and end (d 90) of the study, and calf BW was determined at the start and end of the study. Pregnancy was diagnosed by transrectal ultrasonography at approximately 45 days after the end of the breeding season. Cow and calf BW at the beginning of the breeding season did not differ but was greater (P< 0.01) for EW cow and calf at the end of the study (d 90; 355 ± 39.5, 358 ± 37.4, and 388 ± 44.7 for EW, IW, and CON cows, respectively &#8211; SEM = 2.6;142, 143, and 142 kg for EW, IW, and CON calves, respectively &#8211; SEM = 5.3). Cows in the EW and IW treatments had resumption of cyclicity earlier than those in the CON group (average days to resume cyclicity: 65 ± 1.6; 67 ± 1.3; and 75 ± 1.5 for EW, IW, and CON cows, respectively). By day 20 of the breeding season (corresponding to average of 114 days postpartum), more (P= 0.06) EW cows were cycling than CON cows but it was similar to IW cows. Pooled pregnancy rates from both years demonstrated that IW cows had a greater pregnancy rate than CON cows (P = 0.05) and was similar (P= 0.75) to EW cows. In the study conducted in Mato Grosso do Sul, at the &#8220;Tortuga Agropecuária, Fazenda Caçadinha&#8221;, seventy-six primiparous, Nellore cow-calf pairs were randomly allotted to three treatments: EW (early weaning); TW (temporary weaning &#8211; 72-h calf withdrawal;); and CON (control; calves kept with their own dam). In a similar manner to the USA study, treatments were initiated at the start of a 90-d breeding season. Cow and calf BW, and cow BCS were determined at d 0, 30, 63 and 90 of the study. Blood samples were collected over 90 days, 10 days apart for determination of progesterone concentrations. Pregnancy was diagnosed by transrectal ultrasonography during (d 63) and 53 days after the end of the breeding season. Cow and calf BW did not differ at the beginning of the breeding season (average BW = 365 ± 28.3 and 106 ± 14.5, respectively), as well as cow BCS. However, at the end of the breeding season, cow BW was greater for EW cows (P< 0,05), compared to TW and CON (average BW = 440 ± 35.4; 404 ± 33.4; 398 ± 30.3, respectively). Cow BCS was also greater for EW cows, compared to TW and CON cows (average BCS = 4.5; 3.8; 3.8, respectively; SEM = 0.10). For calf measures, TW and CON calves had greater BW, compared to EW since December, reflecting on BW at the normal weaning time (164 ± 19.1; 201 ± 23.7; 196 ± 20.2 for EW, TW, and CON calves, respectively). By day 10 of the breeding season (corresponding to approximately 120 days postpartum), more EW cows were cycling than TW and CON cows. Pregnancy rate was 84.0 and 96.0% for EW, 60.0 and 84.0% for TW, and 46.2 and 80.8% for CON at the middle and after the breeding season, respectively. From the data collected during the study, it can be infer that suckling management can help to improve first-calf cow reproductive performance, under grazing conditions, as both in United States and Brazil early weaning improved reproductive performance. Repeated 48-hour calf withdrawal may be an effective option for the management of first-calf Brahman crossbred cows, particularly for Floridian producers that are unable or unwilling to earlywean (permanently separate) cows and calves at the start of the breeding season. In Brazil, calf removal for 72 hours was not effective in hastening the resumption of cyclicity, although IW had shown similar pregnancy rate, compared to EW cows. Also, it can be concluded that calf performance is dependent on environmental conditions and feeding (forage specie) available.