Experiments were conducted to evaluate amino acid digestibility of 32 commercial meat and bone meals (MBM) varying in raw material source and produced in seven different commercial cooking systems and at two processing temperatures (low vs high) that differed by 15 to 20 C. Raw material sources included all beef, all pork, mixed species, and high bone MBM. True digestibilities of amino acids were determined using the precision-fed cecectomized rooster assay. Protein efficiency ratio (PER) of six MBM varying greatly in amino acid digestibility was determined with chicks fed 10% CP diets containing a MBM as the sole source of dietary protein. The 32 MBM samples averaged 53.2% CP, 2.73% Lys, 0.6% Cys, and 0.75% Met on a DM basis. True digestibility averaged 82% for Lys, 87% for Met, and 47% for Cys. True digestibilities of amino acids varied substantially among processing systems and temperatures, particularly for Lys and Cys. For example, Lys and Cys digestibility ranged from 68 to 92% and from 20 to 71%, respectively, among different MBM. The higher processing temperature generally yielded lower amino acid digestibility than did the low processing temperature. A smaller, less consistent, effect was observed for raw material source. The PER values of the six selected MBM varied from 0.97 to 2.68 and were highly correlated with amino acid digestibility. These results indicated that very high amino acid digestibility MBM can be produced in commercial rendering systems. However, differences in processing systems and temperatures can cause substantial variability in amino acid digestibilities.

The in vivo protein quality of 14 meat and bone meals (MBM) was evaluated in three chick growth assays and a 48-h excreta collection assay using conventional and cecectomized roosters. In addition, in vitro evaluation of protein quality was assessed using pepsin N digestibility (0.2, 0.002, or 0.0002% pepsin), KOH protein solubility, and multi-enzyme pH change. Crude protein, lysine, and SAA in the MBM varied from 48 to 56, 2.32 to 3.01, and 1.0 to 2.13%, respectively. Protein efficiency ratio (weight gain:protein intake) estimated from feeding chicks diets containing 9% protein from a MBM ranged from 0.61 to 2.89 and averaged 1.78. Lysine bioavailability determined by slope-ratio chick assay ranged from 43 to 89%. True amino acid digestibility and TMEn values determined in cecectomized roosters were generally lower (P < 0.05) than those determined in conventional roosters. True digestibility of amino acids (percentage) also varied among MBM, with the mean (and range) for lysine, methionine, and cystine in cecectomized birds being 81 (73 to 88), 85 (77 to 91), and 58% (37 to 72%), respectively. Pepsin N digestibility values determined using 0.002 or 0.0002% pepsin were positively correlated (P < 0.05) with lysine digestibility. Pepsin N digestibility determined using 0.2% pepsin, KOH protein solubility, and multi-enzyme pH change were not significantly correlated with in vivo protein quality. Ash content was negatively correlated (-0.80, P < 0.05) with protein efficiency ratio. These results indicated that there is substantial variation in protein quality among commercial MBM and that pepsin N digestibility and ash content are correlated with some in vivo protein quality measurements.

Two samples of tomato seeds, a by-product of the tomato canning industry were evaluated to determine proximate analysis, amino acid content, and digestibility, TMEn, and protein efficiency ratio. Tomato seeds were also used to replace corn and soybean meal (SBM) in a chick diet on an equal true amino acid digestibility and TMEn basis. Tomato seeds were found to contain 8.5% moisture, 25% CP, 20.0% fat, 3.1% ash, 35.1% total dietary fiber, 0.12% Ca, 0.58% P, and 3,204 kcal/kg of TMEn. The total amounts of methionine, cystine, and lysine in the tomato seeds were 0.39, 0.40, and 1.34%, respectively, and their true digestibility coefficients, determined in cecectomized roosters, were 75, 70, and 54%, respectively. The protein efficiency ratio (weight gain per unit of protein intake) value when fed to chicks at 9% CP was 2.5 compared to 3.6 for SBM (P < or = 0.05). When corn-SBM diets were formulated on an equal true amino acid digestibility and TMEn basis, up to 15% tomato seeds could replace corn and SBM without any adverse affects on chick weight gain, feed intake, or gain:feed ratio from 8 to 21 d posthatch. Tomato seeds at any level in the diet did not significantly affect skin pigmentation. Although the protein quality of tomato seeds may not be as high as SBM, tomato seeds do contain substantial amounts of digestible amino acids and TMEn. When formulating diets on a true digestible amino acid and TMEn basis, tomato seeds can be supplemented into chick rations at up to 15% without any adverse affects on growth performance.

Experiments were conducted to assess protein solubility in .2% KOH as an indicator of soybean protein quality for chicks and pigs and to assess effects of particle size on protein solubility. As the particle size (micron) of soybean meal (SBM) increased, protein solubility (%) decreased (b = -.0206). In two 9-d chick trials, dehulled SBM (48% CP) was subjected to various autoclaving times and then fed as the sole source of dietary protein to young chicks. Increasing autoclaving times from 0 to 40 min at 120 degrees C resulted in a quadratic decrease in protein solubility. A broken-line model was fitted wherein gain:feed of chicks was plotted as a function of protein solubility. The analysis showed no reduction in feed efficiency with solubilities greater than 59 +/- 1.5% (mean +/- SEM). When solubility was below 59%, however, gain:feed decreased 1.5% for each 1% decrease in protein solubility. The third trial (13 d) was conducted with 7.5-kg pigs fed autoclaved SBM (44% CP) as the primary source of protein. Feed efficiency was significantly decreased when protein solubility was less than 66%. This study showed that protein solubility in KOH was a good index of in vivo soybean protein quality, and that it is important to standardize SBM particle size when applying the KOH assay.

Three chick assays (8 to 17 or 21 d) were conducted to evaluate protein dispersibility index (PDI) as an indicator of minimum adequate heat processing of soybean meal compared with the urease index and protein solubility in 0.2% KOH. Solvent-extracted soyflakes (SF) were subjected to various autoclaving times at 121 C and 105 kPa and were included in 23% CP dextrose-SF diets or 20% CP corn-SF-corn gluten meal diets. Autoclaving times in Chick Assays 1, 2, and 3 were 0 to 36 min, 0 to 30 min, and 0 to 12 min, respectively. Body weight gains and gain-to-feed ratios increased (P < 0.05) with increased SF heating time (0 to 18 min in Chick Assay 1, 0 to 10 min in Chick Assay 2, and 0 to 9 min in Chick Assay 3), with no additional improvement for longer autoclaving times. Urease index values (pH increase) were high initially and at the shorter autoclaving times (1.65 to 2.4), and then decreased suddenly to 0.3 or below as autoclaving time increased in two of the three chick assays. The KOH protein solubility values generally decreased as autoclaving time increased, but the responses were often inconsistent. Protein dispersibility index displayed the most consistent responses to heating time: it decreased from above 70% to generally below 30% as autoclaving time increased from 0 to 30 or 36 min (mean r2 from linear regression of PDI on autoclaving time was 0.92 for the three chick assays). The latter responses were particularly evident for the heating times, which yielded the greatest changes in chick growth performance. These results suggest that PDI is a more consistent and sensitive indicator of minimum adequate heat processing of soybean meal than urease index or protein solubility in KOH.

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Experiments were conducted to evaluate the effects of five commercial processing systems and to a lesser extent, processing temperature within system, on protein quality of feather meals (FM). Two hog hair meals (HH) were also evaluated. True digestibilities of AA were determined with a 48-h excreta collection assay using cecectomized cockerels. Protein efficiency ratio (PER; grams of gain:grams of CP consumed) was determined with chicks by feeding Met-fortified 15% CP diets containing a FM or HH as the sole source of dietary protein. The six FM samples averaged 88.7% CP, 1.99% Lys, 4.83% Cys, and 0.71% Met on a DM basis. For HH, these values were 92.6, 2.78, 3.76, and 0.85%, respectively. True digestibilities of amino acids and PER of the FM varied among processing systems (e.g., lysine digestibility range was 58 to 72%, PER range was 0.71 to 1.13). Increasing the temperature during processing had no significant effect on protein quality of one FM and one HH. Digestibilities of AA in the FM water-soluble fraction collected after cooking were higher than those in the insoluble fraction. True amino acid digestibility coefficients for FM were higher than those for HH, whereas the PER of several FM were lower than those of HH. The latter response was probably due to the higher Lys content in the HH. The results of this study suggested that type of commercial processing system or conditions can affect the protein quality of FM.

Experiments were conducted to determine the protein efficiency ratio (PER) and net protein ratio (NPR) of meat and bone meals containing 24 or 34% ash, poultry by-product meals containing 7 or 16% ash, lamb meals containing 15 or 24% ash, a lamb meal analog containing 19% ash (mixture of lamb meal and turkey meal), and two meat and bone meals processed at either a low or a high temperature. The PER values (weight gain per unit of protein intake) and NPR values (PER corrected for maintenance) were determined using a chick growth assay in which chicks were fed a N-free diet or 10% CP diets containing one of the animal meals as the only source of dietary protein for 6, 9, or 13 d. The PER of the lamb meal analog was greater (P < 0.05) than that of the other meals, and the PER values of the poultry by-product meals were generally greater than those for the lamb and meat and bone meals. The PER values for the lamb meals were higher than those for most of the meat and bone meals. The PER of the 34% ash meat and bone meal was lower (P < 0.05) than the PER of the 24% ash meat and bone meal (1.03 vs 1.63, respectively, at 9 d). Further experiments showed that the lower PER of the high ash meat and bone meal was not due to its high Ca and P content. Ash content had no significant effect on PER of the poultry by-product and lamb meals. The PER of the low-temperature meat and bone meal was higher (P < 0.05) than the PER of the high-temperature meat and bone meal. The relative differences in NPR values among the animal meals were similar to those observed for PER values. Decreasing the length of the assay from 13 to 6 d increased the PER and NPR of all meals but had little or no effect on the ranking of values among meals. The results of this study indicated that PER and NPR values of animal meals were influenced by raw material source, and that ash content and processing temperature affected the PER and NPR of meat and bone meal. The results also indicated that PER and NPR assays could be reduced to 6 d without reducing sensitivity.