Introduction and Objective
Methionine (Met) is an essential amino acid (AA) that must be supplied in adequate amount in the diet to optimize animal performance. In addition to DL-Methionine (DL-Met, 99 %; MetAMINO®) and liquid Methionine hydroxy analogue-free acid (MHA-FA, 88 %),calcium salt of hydroxy analog of DL-Met (MHA-Ca, 84 %) has been re-introduced in the market. This re-introduction has generated questions about relative bioavailability (RBV) of MHA-Ca compared with MetAMINO® as a Met source.
Most of the published studies dealing with the RBV of Met sources in pigs have been focusing on liquid MHA-FA. For example, Kim et al (2006) determined the RBV of liquid MHA-FA relative to MetAMINO® to be 66 % on a product basis based on nitrogen (N) retention (g/d) in 17-21 kg pigs. Based on the N-balance parameters, Opapeju et al. (2010) reported a RBV for MHA-Ca compared with MetAMINO® of 67 % on a product basis in growing pigs. Similarly, a recent study also estimated a RBV for MHA-Ca relative to MetAMINO® of 69 % on a product basis in starter pigs (Facts&Figures Swine No. 1489). However, more information about the RBV value of MHA-Ca to MetAMINO® in pigs is needed.
Therefore, the objective of the present study was to determine the efficacy of MHA-Ca compared with MetAMINO® to support N-retention in starter pigs weighing approximately 15- to 18-kg body weight (BW). This study was conducted at the Institute of Agricultural Sciences for Southern Vietnam, Ho Chi Minh City, Vietnam.
A total of 42 crossbred [Duroc × (Large white/Landrace)] barrows with average initial BW of 15 kg were used in two batches of 21 pigs each. Each batch of pigs served as a block. Three pigs were randomly allotted to each of 7 experimental diets (Table 1) within each block resulting in a total of 6 replicate pigs per dietary treatment. Pigs were kept in individual metabolism crates (0.8 × 1.5 m) which have a collection tray for urine collection and a fine-mesh net above the tray for fecal collection thus, allowing for separate but total collection of feces and urine.
Pigs received feed restricted to an amount of approximately 3.5 % of average BW which was divided into three equal meals daily (fed at 0800, 1200 and 1600 h). Pigs had free access to water, and the diets were fed in mash form. Within each experiment, feces and urine were collected quantitatively for 5 days to determine N retention after a 7-d adaptation period to the diets. Individual BW on day 0, 8 and 13 and daily feed disappearance were recorded.
The dietary treatments consisted of a Met-deficient corn-whey-spray dried blood plasma-soybean meal based (basal) diet or the basal diet supplemented with 3 graded levels of MetAMINO® (0.025, 0.05 and 0.075 %) or MHA-Ca (0.038, 0.077 and 0.115 %) on a product basis at MetAMINO® to MHA-Ca ratio of 65:100 at the expense of corn starch (Table 1).
Prior to diet formulation, ingredients contributing AA were analyzed for AA composition and the analyzed AA contents and the standardized ileal digestibility (SID) coefficients according to AminoDat® 4.0 were used in diet formulation. The calculated contents of standardized ileal digestible (SID) Lys, Met and Met+ Cys were 1.18, 0.22 and 0.52 % (1.17, 0.22 and 0.54 % on analyzed basis), respectively in the basal diet. The Met level was about 73 % of the Met requirement for 10-20 kg pigs (NRC, 1998); otherwise the basal diet met requirements for other AA, nutrients and energy (Table 2). The analyzed contents of AA including the supplemented MetAMINO® and MHA-Ca were slightly lower than the calculated values across the experimental diets. However, the corresponding of MetAMINO® to MHA-Ca ratio of approximately 65% was maintained in the Met-supplemented diets (Tables 1 and 2).
Data were analyzed as a randomized complete block design using GLM procedure of SAS. The individual pig was used as the experimental unit. Orthogonal-polynomial contrasts were used to determine linear and quadratic effects of increasing levels of MetAMINO® and MHA-Ca on response criteria, and the effect of Met sources. Because the N retention responses were linear, data were subjected to multiple linear regression analyses to estimate the RBV of the two Met sources according to the slope-ratio assay (Littell et al., 1997).
Results and discussion
The main results of BW and N retention of pigs fed diets containing graded levels of MetAMINO® or MHA-Ca are given in Table 3.
Supplementations of both Met sources to the basal diet did not affect the N-intake and the BW of the pigs. Urinary N excretion was reduced (P < 0.001) by supplementation of the basal diet with MetAMINO®. Supplementations of both Met sources decreased both the fecal and total N excretion (P < 0.01). The N excretion in the urine was lower while the fecal N excretion higher for pigs fed the MetAMINO® supplemented diets compared with those fed the MHA-Ca added diets. Deficiency in Met will limit the use of other AA for protein synthesis, and thus would increase the amount of AA catabolized and excreted mainly as urea N via urine. Thus, a lower level of N excretion in the urine with the addition of MetAMINO® suggests a better utilization of MetAMINO® for N retention compared with MHA-Ca in Met-deficient diets.
Nitrogen retentions (expressed as g/d and as % of intake) of pigs fed the basal diet were lower (P < 0.01) compared with pigs fed diets supplemented with MetAMINO® or MHA-Ca which indicate that the basal diet was indeed deficient in Met confirming the assumption. Nitrogen retention (expressed as g/d and as % of intake) linearly increased (P < 0.01) with supplementations of the basal diet with MetAMINO® and MHA-Ca. However, there was no effect of Met sources on N absorbed, N retained (g/d) and N retention (% of intake) measured in this experiment. These results indicate that the N retention of pigs were similar when fed diets supplemented at MetAMINO® to MHA-Ca ratio of 65:100 on a product basis (Table 3).
Using the slope-ratio regression analysis, the RBV of MHA-Ca to MetAMINO® in this experiment was estimated to be 63 % based on N retained (g/d; Figure 1) on a product basis. A lower RBV of 43 % was estimated for MHA-Ca relative to MetAMINO® based on N retention (% of intake). The result of this study is in agreement with the previously reported values (Opapeju et al., 2010; Facts&Figures Swine No. 1489), and suggests that RVB of MHA-Ca is similar to that of liquid MHA-FA in pigs (e.g. Kim et al., 2006).
Evonik final report − Trial No. 03.63.11001: Relative bioavailability of calcium salt of DL-Methionine hydroxy analogue compared with DL-Methionine for nitrogen retention in starter pigs.