Performance evaluation, carcass, and meat quality of Nellore heifers in different grazing systems as a methane emission mitigation strategy

• Autor(a) principal: Bertoloni, Analisa Vasques
• Data de Publicação: 2023
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/74/74131/tde-05022024-115029/
• topic: Beef cattle; Deferred stocking; Gado de corte; Lotação diferida; Nitrate; Nitrato; Suplementação; Supplementation

Brazil occupies a prominence position in cattle production, being considered one of the most important producers and exporters of beef in the world. In order to meet the demand of a growing population, the livestock sector needs to efficiently increase its production while reducing their environmental impacts, which is the focus of numerous criticisms. One of the strategies that can be adopted to reduce the effect of low forage availability due to drought seasonality is the use of deferred stocking associated with nutritional supplementation, aiming to improve animal efficiency. The objective of this study was to evaluate performance, carcass characteristics and meat quality of Nellore heifers. Forty-eight Nellore heifers, with an initial weight of 348 ± 30 kg and 18-21 months old, were used in a randomized complete blocks design and the experimental period lasted 2 years, divided into 2 periods: year 1 and year 2. The treatments arrangement was a 2 × 2 ×4 factorial, as fallow: Factor 1) rotational stocking grazing system or deferred stocking grazing system; Factor 2) urea or ammonium nitrate supplementation; Factor 3) four seasons of the year. For post-slaughter data, only Factors 1 and 2 were considered in a 2 × 2 factorial arrangement. During the experimental period, forage and supplement intake, performance, and enteric methane (CH4) emissions were measured. At the end of each experimental period, the animals were slaughtered for carcass characteristics and meat quality evaluations. Data were statistically analyzed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA) considering effects significant when P ≤ 0.05. Interaction grazing system and season of the year was found (P<0.05) for average daily gain (ADG), with heifers kept in the deferred stocking grazing system presented higher ADG in the winter. During the autumn, heifers in the rotational stocking grazing system had higher ADG. Effect of nitrogen sources supplementation was found (P<0.05), and heifers supplemented with urea presented higher ADG. Grazing system and season interaction was also found for dry matter intake in relation to live weight (DMITWL) with heifers in the rotational stocking grazing system presenting higher values during the autumn (P<0.05). Effects of seasons were found for forage and total DMI (P<0.05) but not for supplement DMI (P>0.05). When expressed per ADG and live body weight (LBW), interaction between grazing system and season were found for CH4 emissions. (P<0.05). The lowest values of daily CH4 emission per animal was found in the winter (P<0.05), while the highest CH4 emission per total DMI was found during the spring (P<0.05). No effect of N supplementation was found for CH4 emissions (P>0.05). For the percentage of gross energy intake converted to enteric CH4 emission (Ym%), a triple interaction between grazing system, nitrogen source and season of the year was detected (P<0.05). In winter, the highest values of Ym were found for heifers that were in rotational stocking grazing system receiving urea as a nitrogen source. For spring season, the highest values of Ym were found for heifers in the deferred stocking grazing system supplemented with ammonium nitrate and for heifers in the rotational stocking grazing system receiving urea. Deferred grazing system allowed higher hot carcass weight, cold carcass weight, dressing percentage, edible carcass portion, spare ribs and striploin (P<0.05), and higher subcutaneous fat thickness was found in the carcasses from heifers that received ammonium nitrate (P<0.05). Beef from heifers in the deferred stocking grazing system presented higher aroma, juiciness and flavor attributes evaluated in the sensory panel (P<0.05). Interaction grazing system and nitrogen source effects were found for tenderness and overall acceptance attributes (P<0.05). Overall, the use of ammonium nitrate as a nitrogen source showed similar results to the use of urea, while the deferred stocking grazing system proved to be an efficient intensification method as the performance of heifers was similar to the rotational stocking grazing system but presenting higher carcass dressing percentage and edible portions.