Sustainable feeding strategies in beef cattle systems

Abstract

The inclusion of legumes into grasslands is positive to reduce nitrogen fertilizer inputs, improve forage productivity, and enhance forage quality for warm and cool seasons. However, there is a forage scarcity period between the warm and cool season transition, which is a challenge faced by farmers in this region. Limpograss is a warm season forage present in Florida, that has the potential to fill the gorage gap between the warm and cool seasons. The use of limpograss as silage can be a new alternative and associated with protein supplementation may improve animal performance. The objective of this dissertation was to assess herbage and animal responses of steers in grass-legume grazing systems in North Florida, and ii. to evaluate the effect of protein supplementation on forage intake, digestibility, and animal performance of heifers fed on limpograss silage-based diet. Two experiments were performed. In experiment 1, treatments consisted of three grazing systems replicated three times in a randomized complete block design. Treatments included GR+N that consisted of N-fertilized ‘Argentine’ bahiagrass (Paspalum notatum Flugge) in the warm season (112 kg N ha-1 yr-1) and overseeded with a N-fertilized mixture (112 kg N ha-1 yr-1) of ryegrass (Lolium multiflorum Lam.) and oat (Avena sativa L.) in the cool season. The treatment GR+CL consisted of unfertilized bahiagrass in the warm season, overseeded by a mixture of ryegrass+oat+clover (Trifolium sp.) fertilized with 34 kg N ha-1 in the cool season. The treatment GR+CL+RP consisted of the mixture of bahiagrass with ‘Ecoturf’ rhizoma peanut (RP) (Arachis glabrata Benth.) during the warm season, and overseeded with ryegrass+oat+clover mixture plus 34 kg N ha-1 in the cool season. In experiment 2, 24 heifers crossbred Angus and Brahman (330 ± 16 kg live weight) were blocked by initial weight and then housed in a single pen and submitted to four different treatments such as: 1) control, no supplementation and ad libitum access to silage of ‘Gibtuck’ limpograss; 2) 1.4 kg of a commercial 32% CP and 68% TDN (cube) supplementation and ad libitum access to silage of limpograss; 3) 2.8 kg of cube and ad libitum access to silage of limpograss; 4) 4.2 kg of cube and ad libitum access to silage of limpograss. In the grazing trial, the N fertilizer did not affect the crude protein concentration (CP) and in vitro digestible organic matter (IVDOM). The herbage mass did not differ among treatments in the cool-season and warm-season. The herbage accumulation in the cool season had evaluation x treatment interaction. The herbage accumulation in the warm season did not differ among treatments. The clover nitrogen derived from atmosphere (%Ndfa) was 69% and biological nitrogen fixation (BNF) was 33 kg N ha-1 season-1. Rhizoma peanut %Ndfa was 64% and the BNF 63 kg N ha-1 season-1. In the cool season, the average daily gain (ADG), gain per area (GPA), stocking rate, and herbage allowance did not differ across treatments. In the warm season, the inclusion of rhizome peanut improved the ADG in relation to the GR+N treatment (0.34 kg d-1 vs 0.12 kg d-1) and the GPA (257 kg ha-1 vs 101 kg ha-1). Overall, all the treatments presented the same ADG in the annual animal performance, however the GR+CL+RP presented a superior compared to other treatments. Integration of legumes into grazing systems, in warm and cool seasons, contributes to the development of a sustainable livestock production system, reducing 85% of the N fertilizer need. In the feeding trial, silage intake was reduced with the inclusion of 2.8 kg of Cube, but total intake increased with supplementation level. The supplement improved the organic matter digestibility, which was 574 g kg-1 in non-supplemented to 638 g kg-1 for diets supplemented with 4.2 kg of Cube. The neutral detergent fiber digestibility was affected by the treatment and reduced from 620 g kg-1 to 604 g kg-1 in the greater supplement level. The supplement promoted an increase in the intake, but reduced NDF digestibility. The inclusion of supplement improved the ADG of growing heifers, increasing from 0.04 kg d-1 to 0.6 kg d-1 with the inclusion of 4.2 kg of cube. The use of cube supplementation increased animal performance of developing heifers fed on limpograss silage.