Abstract
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.
Highlights
The energy partitioning process consists of evaluating the amount of energy ingested by the animal and quantifying the loss of this energy during metabolism
There was no difference in the intake of gross energy (GE) (P = 0.1908) and DE (P = 0.3170) between the treatments, which averaged 111 ME/DE HP (MJ/d) and 74.0 MJ/d, respectively (Table 3)
The energy lost as urine (MJ/d and % GE) did not differ between treatments (P = 0.3286)
Summary
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 [1]. Improving the efficiency of the rumen fermentation is a long-time process for ruminant nutritionists–especially finding strategies to mitigate methane production. Ionophores are a class of compounds used to improve this efficiency with considerable success as a feed additive and continue to be the subject of some studies [2]. Anionophore produced by strains of Streptomyces cinamonensis, was recorded in 1975 as a feed efficiency enhancer for confined cattle and is currently one of the most widespread feed additives for cattle and poultry. In 2006 the European Union banned feeding ionophores to food producing animals [3], its use has approval as cattle feed in both Canada and the USA [4]
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