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| Author(s): |
Marcos Busanello
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2021-10-08 |
| Examining board members: |
Dante Pazzanese Duarte Lanna;
Rodrigo de Almeida;
Polyana Pizzi Rotta
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| Advisor: | Dante Pazzanese Duarte Lanna |
| Abstract | |
Replacement dairy heifers are important in dairy herds to replace culled cows and to renew, increase, and improve genetically the herd. The growth rates of heifers are directly linked to the future performance of these animals. In addition, one of the determining factors of animal performance is feed intake. In the last few decades, just a few trials have been carried out with replacement heifers and data are even more scarce for tropical conditions. Thus, our objectives were to 1) study growth rates of dairy heifers from Holstein (HOL), Jersey (JER), and Holstein × Gyr (H×G) breeds, 2) evaluate published dry matter intake equations (DMI) for dairy heifers and, 3) estimate the nutritional requirements for different breeds in tropical conditions. For the first objective, data related to body weight, hip and withers height and body condition score of dairy heifers from these 3 genetic groups were collected on commercial dairy farms (2,266 animals from 18 dairy farms) in different Brazilian states (MG, PR, RS, and SP). Nonlinear models were used to analyze the data. The maturation rates, average daily weight gain (ADG) to the recommended age for 1st breeding (rAge1stB) and 1st calving (rAge1stC) were estimated. Equations predicted body weight during the growth curve and mature body weight (MBW) for each genetic group. The MBW were 681, 607, and 440 kg for HOL, H×G, and JER, respectively. Maturation rates were similar for weight and hip height for HOL and H×G, however, was higher for JER, indicating an earlier maturing breed. The ADG to 1stB were 0.84, 0.53, and 0.54 kg/d for HOL, H×G, and JER, respectively, indicating that JER and HOL heifers reached ~55% of MBW at rAge1stB. The ADG from rAge1stB to rAge1stC were 0.53, 0.42, and 0.48 for HOL, H×G, and JER, respectively, indicating that all genetic groups were not reaching ~91% of MBW at rAge1stC. All groups had less ADG than ideal between 1ACA and 1PAR. Body condition score was similar for the three genetic groups. For the second objective, a metanalytical data base was used from published studies (from 1998 to 2020) with dairy heifers under tropical conditions, where DMI was measured. The data were classified into two sets, being Bos taurus and crossbred Bos taurus × Bos indicus. Seven predictive DMI equations were evaluated for both data sets: two developed by Hoffman et al. (2008), two developed by Oliveira and Ferreira (2016), and the Dairy Cattle NRC (2001), Quigley et al. (1986), and Stallings et al. (1985). Statistics were used to evaluate these equations were: mean bias, slope bias, correlation coefficient of agreement, mean quadratic error of prediction and its decomposition, among others. The results indicated that it would not be appropriate to use a same predictive DMI equation for Bos Taurus and crossbred under tropical conditions. The equations developed by of Hoffman et al. (2008) for Holstein × Jersey crossbred heifers and the nonlinear equation by Oliveira and Ferreira (2016) were the best to predict the DMI of Bos taurus heifers (mean bias <0.16 kg/d), while the Stallings et al. (1985) equation was the best to predict DMI of crossbred heifers (mean bias = 0.09 kg/d). The other equations presented problems with a mean (precision) or slope bias (accuracy). For the third objective, body weight data at 3 months were simulated from the body growth equations obtained and adding a simulated ADG to achieve 91% of MBW at rAge1stC. We considered the ages of 15, 18, and 13 months (HOL, H×G, and JER, respectively) at rAge1stB and 24, 27, and 22 months (HOL, H×G, and JER, respectively) at rAge1stC. The Dairy Cattle NRC (2001) model was used as a basis for calculation incorporating the results of MBW and the evaluation of the DMI 12 equations found in this study. The energy and protein requirements for maintenance, growth and pregnancy were estimated for each month of life. Our study provides the adult body weight of genetic groups used for dairy production under tropical conditions of Brazil. Also, it provides the rate of body growth achieved under commercial conditions and helps to understand the necessary improvements in the management of the growth of replacement heifers. Nutritional requirements could be estimated from replacement heifer\'s growth data. (AU) | |
| FAPESP's process: | 19/02307-2 - Evaluation and validation of the growth and estimation models for growth to dairy replacement heifers in commercial farms at tropical conditions |
| Grantee: | Marcos Busanello |
| Support Opportunities: | Scholarships in Brazil - Doctorate |