Date Published: April 22, 2019
Publisher: Public Library of Science
Author(s): Marcelina Pereira da Fonseca, Ana Luiza da Costa Cruz Borges, Pedro Henrique de Araujo Carvalho, Ricardo Reis e Silva, Lúcio Carlos Gonçãlves, Iran Borges, Helena Ferreira Lage, Alexandre Lima Ferreira, Eloísa Oliveira Simões Saliba, Diogo Gonzaga Jayme, Joana Ribeiro da Glória, Décio Souza Graça, Rodrigo Melo Meneses, Antônio Último de Carvalho, Elias Jorge Facury Filho, Arthur Alves Silva, Juan J. Loor.
The aim of this study was to describe energy partitioning in dairy crossbreed bulls fed tropical forage-based diets supplemented with different additives. Twenty F1 crossbred bulls (Holstein x Gyr) with initial and final live weight (LW) averages of 190 ± 17 and 275 ± 20 kg were fed sorghum (Sorghum bicolour) and Tanzania grass (Panicum maximum cv. Tanzania) silage (70:30 DM basis) with supplemented concentrate at a forage to concentrate ratio of 50:50. The bulls were allocated to four treatment: control groups (without additives), monensin [22 mg/kg monensin dry matter (DM)] (M), virginiamycin (30 mg/kg virginiamycin DM) (V), and combination (22 mg/kg DM of monensin and 30 mg/kg DM of virginiamycin) (MV), in a completely randomised design. The intake of gross energy (GE, MJ/d), digestible energy (DE, MJ/d), metabolizable energy (ME, MJ/d), as well as energy losses in the form of faeces, urine, methane, heat production (HE), and retained energy (RE) were measured. Faecal output was measured in apparent digestibility trial. Right after the apparent digestibility trial, urine samples were collected in order to estimate the daily urinary production of the animals. Heat and methane production were measured in an open circuit respirometry chamber. The intake of GE, DE, and ME of the animals receiving monensin and virginiamycin alone or in combination (MV) showed no differences (P>0.05) from the control treatment. However, the MV treatment reduced (P<0.05) the methane production (5.44 MJ/d) compared to the control group (7.33 MJ/d), expressed in MJ per day, but not when expressed related to gross energy intake (GEI) (CH4, % GEI) (P = 0.34). Virginiamycin and monensin alone or in combination did not change (P>0.05) the utilization efficiency of ME for weight gain, RE and net gain energy. This study showed that for cattle fed tropical forages, the combination of virginiamycin and monensin as feed additives affected their energy metabolism by a reduction in the energy lost as methane.
The energy partitioning process consists of evaluating the amount of energy ingested by the animal and quantifying the loss of this energy during metabolism. Research has shown that for ruminants between 6 and 12% of gross energy (GE) intake is lost in the form of methane .
The energy concentration of the diets, average daily weight gain, and feed efficiency were not affected (P>0.05) by the treatments (Table 2).
This study describes the energy partitioning of tropical forage-based diets supplemented with different additives and fed to cattle.  found no effect (P>0.05) of monensin on the GE intake in cattle, similarly as ours results. There was no difference in GE intake since no difference was observed in dry matter intake (DMI). Approximately 30% of the consumed GE is lost in the form of faeces , . In the present study, the energy lost as faecal output was, on average, 33.6%.
This study showed that virginiamycin and monensin at doses of 30 mg/kg DM and 22 mg/kg DM, respectively, did not have a significant effect on the net energy for weight gain when feeding animals using sorghum and tropical grass silage-based diets.