| Guangxi is a sub-tropical area which is rich in feed resource, with the biggest population of water buffalo (Bubalus, bubalis.) in China. Up to date, no feeding standard of water buffalo is available in China. The aim of current research was to study the energy requirements of growing water buffalo. Energy digestibility and metabolisability in growing water buffalo was determined first (Expt.l), and then the net energy requirement for maintenance and growth were estimated (Expt.2). Finally, the net energy requirement for growing water buffaloes at 12-13 month was validated (Expt.3).Expt.1. The effect of feeding level on the energy metabolism of growing water buffaloThis part includes two trials, i.e. the effect of energy or protein level on the energy metabolism of growing water buffalo.1. The effect of energy level on the energy metabolism of growing water buffaloTwelve water buffalo heifers aged 12-13 months with a body weight of 220 kg, were used in a randomized complete block design to study energy metabolism. Animals were divided into 3 groups based on body weight and breed, each group including 1 Nili-Ravi,1 Murrah and 2 crossbred (Nili-Ravi×Murrah×local) buffaloes. Three isonitrogenous concentrate were formulated to contain three levels of net energy (NE) for lactation (6.71,6.40 and 6.07 MJ/kg). Each animal was offered 3 kg concentrate per day. The elephant grass and fermented pineapple were the main ingredients of forage. The whole experiment consisted of two feeding trials (12-13 and 14-15 months) with 30 d in-between interval, each including a 7-d digestion-metabolism trial, and the first period including a 3-d gas-metabolism trial as well. Apparent digestibility and metabolisability of energy, ratio of metabolizable energy (ME) to digestible energy (DE), methane loss, ratio of NE to gross energy intake (GEI) and NE/ME values were not significantly different among the three groups(P>0.05). For growing water buffalo, the mean apparent digestibility, apparent metabolisability of energy and ME/DE were 67.6,55.7 and 82.5%, respectively. Methane loss was 9.6% of GEI. The ratio of NE to GEI, NE to ME and UE to GEI was 41.4,73.5 and 2.2%, respectively.2. The effect of protein level on the energy metabolism of growing water buffaloTwelve water buffalo heifers aged 12-13 months with body weight of 220 kg, were used in a randomized complete block design to study energy metabolism. Animals were divided into 3 groups based on body weight and breed, each group including 1 Nili-Ravi,1 Murrah and 2 crossbred (Nili-Ravi x Murrah x local) water buffaloes. Three isocaloric concentrate were formulated to contain three levels of crude protein (CP) (19.9,17.6 and 15.3%). Each animal was offered 3 kg concentrate per day. The elephant grass was the main ingredients of forage. The whole experiment consisted of two feeding trials (12-13 and 14-15 months) with 30 d in-between interval, each including a 7-d digestion-metabolism trial. Apparent digestibility and metabolisability of energy, ME/DE, methane loss and UE/GEI were not significantly different among three groups (P>0.05). The mean apparent digestibility, metabolisability of energy and ME/DE were 68.1,57.1 and 83.9%, respectively. Methane loss and UE were 8.9% and 2.1%, respectively.From the above results, it is indicated that the apparent digestibility, apparent metabolisability of energy, ME/DE, and methane loss were relatively stable for growing water buffalo in normal feeding situation.Expt.2. Estimation of the net energy requirement of growing water buffaloThis part includes 2 trials, i.e. estimation of the NE requirement for maintenance by fasting metabolism, and estimation of the NE requirement by combining feeding trial and fasting metabolism.1. NE requirement for maintenance (NEm)Dewormed and healthy growing female water buffalo with good body condition, five each aged 12 (3 crossbred buffalo,2 Nili-Ravi),18 (3 crossbred buffalo,2 Nili-Ravi) and 24 months (2 Murrah,3 Nili-Ravi) were used in a randomized complete block design to conduct fasting metabolism. Their body weight (BW) was 227,299,359 kg, respectively.. After feeding at low level (12-month:4 kg/d fresh elephant grass,2 kg/d whole corn silage and 1 kg/d concentrate; 18-month:5 kg/d fresh elephant grass,3 kg/d whole corn silage and 1 kg/d concentrate; 24-month:6 kg/d fresh elephant grass,4 kg/d whole corn silage and 1 kg/d concentrate) for 15 days, the animals were subjected to fasting and allowed to drinking water freely for 7 d. The gas exchanges of the whole animal were determined for 3 consecutive days after a 72 h starvation, using open-circuit respiratory hood. The gases were collected 4 times (06.00,12.00,18.00,24.00) per day, for 6-11min each time. During gas collection period, the standing time and lying time of the animals were recorded. Air temperature, air relative humidity and air pressure in experimental location were also recorded at each collection time to calibrate the data. Immediately after collection, the gas in the collection bag was homogenized. The total gas volume in the bag was recorded by withdrawing the bag with hydrometric gas-flow meter connected to gas pump. During these processes, the gases samples were taken into 10 ml plastic syringe three times. At the same time, O2 and CO2 concentrations in the gas sample were analyzed with semi-auto gas meter. After converting the respiration gas to standard situation volume, the respiratory quotient (RQ) were calculated by dividing volume of CO2 (L) produced by volume of O2 consumed (L). The corresponding fasting heat production (FHP) was estimated from RQ multiplied by thermal equivalent. Fasting BW was calculated as the mean of the initial (4th day of starvation) and final (7th day of starvation) BW. The results obtained were as below. The mean FHP was 334.03, 328.55 and 306.01 kJ/(kgW0.75·d-1) for female water buffaloes at 12,18 and 24 months, respectively. No significant difference (P=0.4938) was observed among three FHP values, so the mean FHP was calculated to be 323 kJ/(kgW0.75·d-1). Considering that the NEm is about 20% higher than the FHP, the NEm was estimated to be 388 kJ/(kgW0.75·d-1) in growing water buffalo.2. NE requirement for growthBy combining the data of feeding trial, digestion-metabolism trial and fasting metabolism trial, the NE requirement for 12-13 and 14-15 months water buffalo could be estimated by the following equations:NE (MJ/d)=(0.384+0.324ΔW) W0.75 and NE(MJ/d)=(0.398+0.350ΔW) W0.75, whereΔW was average daily gain (kg/d). No significant difference was observed between these two equations, so the requirement for net energy of 12-15 months water buffalo could be estimated by the combining the above two equation, i.e., NE(MJ/d)=(0.388+0.339ΔW)W0.75, whereΔW was average daily gain (kg/d).Expt.3. Validation of the net energy requirement for growing water buffaloesThirty-two water buffalo heifers aged 12 months with a body weight of 184 kg, were used in a randomized complete block design to validate the equation obtained above. Animals were divided into four groups based on body weight and breed, each group including 1 Nili-Ravi,2 Murrah,2 crossbred (Nili-Ravi×Murrah×local) and 3 local water buffaloes. Four levels of expected average daily gain were designed to be 0.8,0.6,0.3,0 kg/d, which was estimated from the formula obtained in the Expt.2 (NE (MJ/d)=(0.388+0.339ΔW)W0.75). The experiment consisted of a 30-d feeding trial after 15-d for adaptation. It was found that the NE requirement for growing water buffalo could be estimated from regression model:NE (MJ/d)=(0.377+0.458ΔW)W0.75 (n=32, R2=0.9578, P<0.01), whereΔW was average daily gain (kg/d). Compared to the formula obtained in Expt.2, little difference existed in the NE requirement for maintenance between two equations. The NE requirement for growth was slightly higher in Expt.3 than in Expt.2, but no statistical significance (P=0.0879) was observed. Thus, the mean value of the regression equation was calculated. The equation:NE (MJ/d)=(0.335+0.392ΔW) W0.75 could be used to estimate NE requirement for growing water buffalo.In summary, relatively stable ME/DE value and methane loss existed in growing water buffalo, which could be used to indicate the energy metabolism of growing water buffalo. The NE requirement for growing water buffalo could be estimated by the following formula:NE (MJ/d)=(0.335+0.392ΔW) W0.75, whereΔW was average daily gain (kg/d). |
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