PSX-B-2 Effect of feedlot days on intake and performance of Nellore heifers

The objective was to evaluate the effect of feedlot days (FD) on intake (DMI) and performance of Nellore heifers. Fifty-one Nellore heifers [325±19.3 kg of body weight (BW); 16±1 months], blocked by initial BW and stratified by carcass ultrasound, were divided into three treatments: 45, 75 or 105 FD; and placed in 18 pens [17 heifers/treatment; 6 pens/treatment (5 pens with 3 heifers and 1 pen with 2 heifers)]. The animals were fed ad libitum allowing 3% of refusals. The diet consisted of corn silage, ground corn, soybean meal, protected fat and minerals. The adaptation diet [16% CP and 79% TDN; roughage:concentrate (R:C) = 44:56] was offered from day 1 to 15 and the finishing diet from day 16 to 105 (14.5 % CP and 86% TDN; R:C = 25:75). At the end of each FD, heifers were weighted to obtain the shrunk final BW and slaughtered in the same slaughterhouse. The final BW and hot carcass weight (HCW) were greater (linear effect; P ≤ 0.01), respectively, for heifers on 105FD (442 and 244 kg) compared to 75FD (411 and 228 kg) and 45FD (374 and 206 kg). The DMI, backfat thickness and longissimus area increased over FD (linear effect; P ≤ 0.01; 45FD = 7.10 kg/d, 5.05 mm and 64.3 cm2; 75FD = 7.68 kg/d, 5.69 mm and 68.5 cm2 and 105FD=7.79 kg/d, 7.04 mm and 73.3 cm2). The FD did not affect carcass gain (P = 0.38) and feed efficiency based on carcass gain (P = 0.84). However, total carcass gain increased over FD (linear effect; P ≤ 0.01; 29, 51.4 and 75.9 kg, respectively to treatments 45, 75 and 105 FD). In conclusion, the feedlot days increase the BW, backfat thickness and longissimus area. However, the feed efficiency based on carcass gain does not reduce when the heifers are submitted for a long time on feedlot.

PSXIII-15 Impact of forage allowance on performance and reproductive parameters in Nellore heifers

The objective was to evaluate the effects of forage allowance on the performance and pregnancy rate of Nellore heifers submitted to the fixed-time artificial insemination (FTAI) at 14±1 months. The experimental period was divided into the growing phase (GP; 173d) and breeding season (83d). Ninety weaned Nellore heifers [169±19 kg of body weight (BW); 210±28 days of age] were blocked by initial BW and randomly assigned to receive different forage allowance: (1) High (HFA; 7.17 kgDM/kgBW; and (2) Low (LFA; 3.27 kgDM/kgBW); and divided into 6 paddocks (2.15 to 2.4 ha each one). The grazing method used was continuous stocking with a variable stocking rate where treatment conditions were established varying the stocking rate on pasture (put-and-take). The supplement consisted of corn, soybean meal, urea, monensin, sodium chloride and minerals mix (80% TDN and 24% CP) and was provided daily (ad libitum; expected intake around 1% of BW). The final pregnancy rate was determined after two FTAI (d256). Heifers BW at the end of the GP was greater (P < 0.01) for HFA vs. LFA (268 vs. 255 kg). The overall average daily gain (ADG) was greater 68 g/d for animals maintained in HFA than LFA (P < 0.01; 0.713 vs. 0.645 kg/d). Supplement intake (kg/animal/d) had no treatment effect (P = 0.117). On d173, forage allowance affected (P < 0.01) the backfat thickness obtained by real-time carcass ultrasound (HFA = 3.08 vs. LFA = 2.85 mm). The pregnancy rate had no treatment effect (P = 0.223; on average 61%). However, the pregnant heifers per hectare had treatment effect (P = 0.036; HFA = 3.78 vs. LFA = 2.72 pregnant heifers/ha). In conclusion, the low forage allowance reduces the animal performance and affects the carcass composition but provides a greater number of pregnant heifers per hectare.

PSX-B-9 Effect of trace mineral sources in the supplement for grazing cattle on ruminal bacteria diversity

The rumen soluble Cu and Zn can affect the rumen microbial populations. This study aimed to evaluate the effect of trace mineral sources (Cu and Zn) in the supplement of grazing steers on ruminal bacteria diversity. Eight rumen cannulated Nellore steers (541 kg ± 18 kg BW) were distributed in a randomized block design in individual paddocks of Urochloa brizantha cv. Marandu. Steers were supplemented during 101 days between dry to rainy season at 5 g/kg BW with commercial supplement (25% CP) containing Cu (40 mg/ kg) and Zn (148 mg/kg) in the inorganic (Control) or hydroxy (HDX; Micronutrients Inc., IN) source. Samples of ruminal content were collected before supplementation at day 97 of experimental period and the total DNA extracted by commercial kit (Quick-DNA Fecal/Soil Microbe Miniprep). The V3/V4 regions of 16SrRNA gene was sequencing using the Illumina MiSeq, using the Quantitative Insights into Microbial Ecology (QIIME v.1.9.1) to filter reads and determine Operational Taxonomic Units (OTUs). Data were compared using an unpaired Wilcoxon test in R. A total of 293 OTUs were identified at genus level. The HDX resulted in a higher ruminal abundance of Corynebacterium 1 (P = 0.01), Prevotella 1 (P = 0.01), Lachnoclostridium 10 (P = 0.02), Lachnospiraceae AC2044 group (P = 0.03), Lachnospiraceae UCG-008 (P = 0.03), Streptococcus (P = 0.02), Ruminococcaceae UCG-010 (P = 0.01), Ruminococcaceae UCG-014 (P = 0.01), Ruminococcus 1 (P = 0.04), Coprococcus 1 (P = 0.04), Mogibacterium (P = 0.02), Selenomonas 1 (P = 0.02), Anaerovibrio (P = 0.03), Methylobacterium (P = 0.02), Treponema 2 (P = 0.02), Rikenellaceae RC9 gut group (P = 0.03), Ruminococcaceae; uncultured rumen bacterium (P = 0.02) and Eubacterium hallii group (P = 0.05), and lower abundance of Fibrobacter (P = 0.04), Butyrivibrio 2 (P = 0.05), Anaerotruncus (P = 0.03), Ruminiclostridium 5 (P = 0.03), Anaerorhabdus furcosa group (P = 0.02) and Erysipelotrichaceae UCG-004 (P = 0.01). The use of HDX in the supplement for grazing cattle between dry to rainy season increase the ruminal abundance of bacteria, mainly into Firmicutes phylum with important structural and non-structural carbohydrates degradation functions.

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