Animal proteins are widely used in diets for companion animals owing to their cost, availability, and nutrient value. However, there is considerable variability in the nutrient value of some animal proteins, as a result of variation in the blending of offals in certain meat by-products as well as in processing conditions, such as the temperature used to dry the materials (Murray et al., 1997; Johnson et al., 1998). Conversely, spray-dried animal plasma (SDAP) is an ingredient that is collected and processed to preserve the functional characteristics of the proteins, including such biologically active peptides as albumin and immunoglobulin G (IgG). This ingredient has been used widely in diets for swine (Bergström et al., 1997; van Dijk et al., 2001) and calves (Quigley et al., 2002). Researchers have reported improved growth and health when calves (Quigley and Drew, 2000; Hunt et al., 2002) or pigs (Bosi et al., 2001; Torrallardona et al., 2002, 2003) were fed during periods of stress and enteric challenge. However, no data are available using this ingredient in dry dog food kibbles. Our objective was to determine the intake, digestibility, and fecal production of dry dog food diets containing SDAP when fed to adult dogs.
Materials and Methods
Facilities at a commercial experimental kennel (Summit Ridge Farms; Susquehanna, PA) were used in three digestibility trials. Facilities were maintained in accordance with USDA regulations and the Animal Welfare Act. Procedures used in the study were in accordance with AAFCO guidelines (AAFCO, 2001). Technicians at the kennel were unaware of the composition of diets.
Healthy adult beagles were used for all studies. Animals were housed individually. The kennel had a 12-h light:12-h dark cycle with temperatures between 10 and 30°C. Experimental diets were offered at 350 g/d (as-fed basis) and were the sole source of food during the experiment. Clean water was offered for ad libitum consumption.
Fecal samples were quantitatively collected at least three times daily (or as often as needed to ensure a clean sample) and weighed. Fecal consistency was scored on the following scale: 1 = watery diarrhea; 1.5 = diarrhea; 2 = moist, no form; 2.5 = moist, some form; 3 = moist, formed; 3.5 = well formed, sticky; 4 = well formed; 4.5 = hard, dry; and 5 = hard, dry, crumbly. Samples were stored (4°C) until pooled at the end of each period and were sent to a commercial laboratory (Woodson-Tenet, Columbus, OH) for determination of DM (AOAC, 1990; Method 925.45D), CP (AOAC Method 990.03), crude fiber (CF; AOAC Method 962.09), fat (AOAC Method 989.05), ash (AOAC Method 942.05), Ca and P (AOAC Method 985.01), and GE (adiabatic bomb calorimetry). Total dietary fiber (TDF) was analyzed in Trial 3 by the method of Prosky et al. (1984). A sample of each experimental dog food was sent to the same commercial laboratory for analysis as for feces.
Trials 1 and 2
In Trial 1, commercially prepared, uncoated, extruded dry dog food kibbles were obtained (Table 1). Ingredient composition of kibbles was not available. Kibbles were added to a rotary mixer and tumbled at moderate speed. Tallow was heated to 45°C and sprayed into the mixer to achieve a 5% (wt/wt) addition; thereafter, 2% of a commercially available dog food flavor was added and allowed to blend for approximately 5 min. Commercially available SDAP (0 or 2%; Endure; APC Inc., Ankeny, IA) was slowly added to ensure adequate mixing. Preliminary studies indicated that 2% SDAP added in this fashion was palatable to dogs and physically stable (<1% of added SDAP was lost from the outside of coated kibbles). Kibbles were then mixed for approximately 5 min and packaged in labeled bags. Chemical composition of the SDAP was 92.0% DM, 8.6%, ash, and 79.3% CP.
In Trial 2, commercially available dry dog food kibbles (Purina Pro-Plan Adult Dog Chicken & Rice Formula; Nestlé Purina PetCare, St. Louis, MO) were obtained from a local pet food dealer (Table 2). Kibbles were added to a cement mixer and either 0 or 2% of SDAP was added and mixed for 5 min. No additional fat or flavors were added. Diets were bagged, labeled, and shipped to the experimental kennel. Chemical composition of the SDAP was 92.7% DM, 6.9% ash, and 79.4% CP.
Adult Beagles (n = 6; three females in Trial 1; n = 8, three females in Trial 2) were assigned randomly to treatment in a switchback design using two 10-d experimental periods. The first 5 d of each period were used as an acclimation period and the last 5 d were used for feed and fecal collections. Dogs were weighed daily during the acclimation period (d 1 to 5) and on d 6 and d 10 of the collection period.
Data were summarized for all days within each experimental period and analyzed by ANOVA as a crossover design using the GLM procedures of SAS (SAS Inst. Inc., Cary, NC). The model was
where Yijk = observation (total n = 12 or 16); μ = overall mean; Ti = effect of ith treatment (i = 1, ..., 2); Bj = effect of the jth block (j = 1, ..., 2); Dk = effect of the kth dog (k = 1, ..., 6 or 8); εijk = error.
Four diets containing 0, 1, 2, and 3% SDAP were formulated to meet or exceed NRC requirements for adult dogs (Table 3). Diets were blended and extruded using a Wenger TX-52 twin screw extruder (Wenger Manufacturing, Sabetha, KS) at the KSU Extrusion Laboratory, Kansas State University, Manhattan. Extrusion conditions were as follows: feed rate = 150 kg/h; steam and water addition = 6.4 to 9.9 kg/h; head temperature = 118°C; and head pressure = 24.6 kg/cm2. Kibbles were shipped to the laboratory at APC, where they were coated with 1% commercial flavor and 5% fat, placed into coded bags, and shipped to the experimental kennel.
Adult Beagles (n = 8; three females) were fed for 60 d in a replicated 4 × 4 Latin square design. Dogs were housed individually. Each period was 15 d, with 10-d acclimation period and 5-d fecal collection. Dogs were fed at the same time each day. Body weights were recorded on d 1 through 11, and d 15 of each period.
Data were summarized for each period and analyzed as a Latin square design using the model
where Yijk = individual observation; μ = overall mean; Pi= effect of ith period (i = 1, …, 4); Dj = effect of jth dog (j = 1, …, 8); Tk = effect of kth treatment (k = 1, …,4); εijk = residual error. Orthogonal contrasts for equally spaced treatments were used to determine linear and quadratic effects of SDAP.
Chemical composition of diets is in Table 1. Mean body weights on d 1 and d 10 were not affected by treatment and were 13.4 and 13.1 kg, respectively (Table 4). All dogs lost BW during the trial (mean BW change = −0.3 kg; SE = 0.12), which may have been due to the low-energy density in the basal diet.
Output of feces (as-is basis) tended (P = 0.08) to be decreased when dogs were fed the diet containing SDAP. Output of fecal DM was decreased (P = 0.01) from 48 to 43 g/d when SDAP was included in the diet. Fecal consistency scores were recorded daily, and mean fecal scores did not differ (P = 0.77) between treatments (Table 4).
Intake of nutrients was not affected by treatment (Table 4). Intake of DM (P = 0.69) did not differ between treatments and was 221.2 and 217.5 g/d in dogs fed diets without and with SDAP, respectively. Digestibility of nutrients was generally improved when SDAP was included in the diet (Table 4). Digestibility of DM (P = 0.04), CF (P = 0.01), and fat (P = 0.03) were increased with the addition of SDAP.
Chemical composition of control diet (Table 2) was within expected values for the commercial dog food and consistent with label guarantees. Addition of SDAP increased CP concentration from 26.1 to 27.1%. Mean body weights on d 1 and 10 were not affected by treatment (P = 0.11 and P = 0.38, respectively) and were 13.2 and 13.3 kg in dogs fed diets without and with SDAP, respectively (Table 5). Dogs gained a small amount of BW during the trial, probably because the caloric density of the food used in this trial was greater than in Trial 1 and calculated ME intake exceeded the ME requirement of 132 to 159 kcal/kg BW0.67 (NRC, 1985).
Output of feces on an as-is and DM basis was decreased (P = 0.004 and P = 0.006, respectively) when dogs were fed the diet containing SDAP (Table 5). Mean fecal scores did not differ between treatments (P = 0.21) and were 3.9 and 3.7 for kibbles containing 0 and 2% SDAP, respectively.
Intake of nutrients was not affected by treatment (Table 5). Digestibility of nutrients in experimental diets was generally improved when SDAP was included in the diet. Digestibility of DM (P = 0.01), OM (P = 0.01), CF (P = 0.001), and GE (P = 0.03) were increased, and digestibility of CP tended to be increased when SDAP was included in the diet.
Chemical composition of diets (Table 3) was generally similar, although ash content declined with addition of SDAP. Analyzed values for CP and fat were similar to formulated values, although differences in CP and ash suggested that the poultry meal used in the study was slightly higher in CP and lower in ash than formulated.
Body weights of dogs on d 1 and 15 did not differ among treatments and averaged 11.3 and 11.4 kg, respectively (Table 6). Production of feces (Table 6) decreased linearly (DM; P = 0.03) or tended (P = 0.07) to decline linearly (wet basis) with addition of SDAP. Trends for quadratic effects of SDAP were P = 0.12 and P = 0.10, respectively. Output of fecal DM declined from 37 to 32 g (−14%) with the addition of 1% SDAP; thereafter, there was no further reduction in fecal DM excretion.
Intake of nutrients did not differ among treatments (Table 6). Digestibility of nutrients (Table 6) increased in a linear (P ≤ 0.01) and quadratic (P ≤ 0.02) fashion for DM, OM, CP, GE, and TDF. Only fat and CF were unaffected by inclusion of SDAP in the diet. Maximal digestibility of nutrients was observed at 1% (OM and TDF) or 2% SDAP (DM and CP). Addition of 1% SDAP increased relative digestibility of DM, OM, CP and TDF by 3.2, 2.7, 2.6, and 23.6%, respectively.
Spray-dried animal plasma is widely used in diets of domestic animals to improve feed intake, growth, feed efficiency, and intestinal health (Kats et al., 1994; Bergström et al., 1997; Quigley et al., 2002). Van Dijk et al. (2001) reviewed 15 published studies and concluded that dietary SDAP levels up to 6% increased average daily gain and feed intake in pigs after weaning in a dose-dependent fashion. Coffey and Cromwell (2001) summarized 48 studies and concluded that effects of SDAP on growth and intake in pigs are mediated by improving immunocompetence of the animal. Others have compared SDAP with antimicrobials in diets of pigs (Coffey and Cromwell, 1995; Torrallardona et al., 2002) and calves (Quigley and Drew, 2000; Hunt et al., 2002) and concluded that immunological components (e.g., IgG) contribute to improved enteric health and resistance to both natural and experimental pathogen challenge.
With heating, proteins in SDAP form a strong gel that is used in preparation of human and canned pet foods as a gelling agent and emulsifier. However, heat and pressure associated with sterilization processes used in manufacturing canned food denature the functional SDAP proteins (APC, Inc., unpublished data). In the current study, SDAP was applied externally in Trials 1 and 2 to minimize exposure to temperature and pressures of extrusion; however, in Trial 3, SDAP was processed through the extruder as part of the total feed. Improvements in digestibility during Trial 3 suggest that changes in digestion were independent of the functionality of proteins or that functional proteins in SDAP survived extrusion and exerted a positive effect on nutrient digestibility.
Application of SDAP to the outside of kibbles requires that the product is physically stable and must remain on the kibble through normal processing and handling. Analyzed CP of coated kibbles in Trials 1 and 2 were 98 and 100% of expected CP content, respectively, based on the content of kibbles and SDAP. Preliminary research indicated that loss of SDAP from the outside of kibbles was <1% of the amount applied at inclusion rates lower than 5% with the method of application used herein (data not shown).
Intake and digestibility of nutrients in all trials were generally similar and compared favorably with those in the literature (Cole et al., 1999; Castrillo et al., 2001; Clapper et al., 2001). Lower digestibility of most nutrients in Trial 1 was indicative of the overall quality (higher ash, and lower fat and gross energy) of the base kibble. Ingredient composition of the commercial formula used in Trial 1 was not available. Ingredients listed on the label of the commercial food used in Trial 2 (Table 2) indicated that brewers’ rice and whole grain wheat were the primary carbohydrate sources and chicken and poultry by-product meal were major protein sources. The diet in Trial 3 contained ground corn, brewers’ rice, and beet pulp as major carbohydrate sources and poultry by-product meal and soybean meal as major protein sources. Beet pulp is a source of fermentable fiber and an acceptable ingredient in pet food diets (Fahey et al., 1990a,b; 1992).
Digestibilities of DM, OM, CP, fat, and fiber (expressed as CF in Trials 1 and 2 and CF and TDF in Trial 3) were improved in one or more trials with addition of SDAP. Because SDAP contains large amounts of CP, it is possible that changes in CP digestibility were caused by differences in protein ingredients. Digestibility of CP was improved by 4.2 and 3.2% in Trials 2 and 3 when SDAP was added at 2% of the formula.
In Trial 3, addition of SDAP at 1, 2, and 3% contributed 3.7, 7.2, and 10.5% of CP in formulas, respectively, and replaced poultry by-product meal. Poultry by-product meal is widely used as a feed ingredient in pet food, but total-tract digestibility of CP was lower than poultry meal in grain-based diets fed to dogs (Bednar et al., 2000). Johnson et al. (1998) also reported lower AA digestibility of poultry by-product meal compared with several other animal by-product meals and attributed lower digestibility to variation in raw materials and processing conditions.
Digestibility of CP in SDAP is slightly lower than other animal proteins exposed to similar processing methods owing to the presence of IgG, which is partially resistant to digestion (Roos et al., 1995). However, there are few reports available that document changes in digestibility of diets containing SDAP. Bosi et al. (2001) reported lower ileal CP digestibility in early-weaned pigs fed SDAP compared with hydrolyzed casein. Conversely, Pendergraft et al. (1993) reported that SDAP was more digestible than wheat gluten in diets fed to young pigs. Recently, Dust et al. (2003) reported that ileal digestibility of DM, OM, CP, and fat were increased when four ileally cannulated dogs were fed diets containing 0.5 or 1% SDAP, but decreased when dogs were fed 2% SDAP; however, apparent total-tract digestibility of nutrients were unaffected by SDAP inclusion.
Changes in fecal output were consistent with improved digestibility of DM in all trials. Fecal output of DM was reduced by an average of 15% across all trials. Fecal output is a significant variable in selection of ingredients for pet foods; ingredients that improve digestion and reduce excretion of fecal DM are generally favored over ingredients that contribute to greater fecal production.
Although differences in CP digestibility may be partially explained by differences in protein sources used in the experiment, it is more difficult to explain differences in digestibility of other nutrients. If SDAP, with greater digestibility, replaced poultry by-product meal, then differences in CP digestibility should have been linear. However, changes in CP digestibility were minimal above 1% SDAP (Table 6), suggesting that changes in digestion may not be related to differences in CP sources. Digestion of fiber was also increased. Mean CF digestibility of diets containing 0% SDAP in Trials 1 and 2 did not differ from zero (1.8 and 5.4%; P > 0.05), whereas addition of 2% SDAP increased CF digestibility to 20.3 and 29.1%, respectively. In Trial 3, CF digestibility was not improved, but TDF digestibility increased in a linear and quadratic fashion with addition of SDAP to the kibble (Table 6). Because SDAP is not a significant source of fiber, no changes in digestion of fiber were expected.
Crude fiber was used as an indicator of fiber digestion in Trials 1 and 2; however, use of CF as an index of fiber digestion ignores the loss of soluble polysaccharides, some insoluble polysaccharides and lignin, and inclusion of some nitrogenous material in the residue. This makes other indices of dietary fiber (such as TDF) preferable to CF. Fahey et al. (1990a,b) reported that prediction of fiber digestion varied depending on the method used. Unfortunately, TDF was not measured in Trials 1 and 2.
Variability in digestibility of dry dog food diets with different ingredients is well documented (Fahey et al., 1990b; Cole et al., 1999; Twomey et al., 2002), but results generally were consistent with changes in ingredient formulation. In our studies, changes in nutrient digestibilities were not consistent with formulations, suggesting that the response was mediated through differences in digestive function rather than changes in formulation. Additionally, improved digestibilities were observed even when diets contained different ingredients and different basal digestibility.
Spray-dried animal plasma contains significant amounts of functional proteins, including IgG, transferrin, and several hormones and growth factors. These proteins exert effects within the intestine independent of their nutritional value. For example, Bosi et al. (2001) reported that SDAP improved ADG, health, and immune stimulation in pigs following oral challenge with Escherichia coli. Touchette et al. (2002) reported that feeding SDAP to young pigs resulted in reduced mRNA expression of tumor necrosis factor-α and interleukin-1β mRNA in the adrenal gland, spleen, hypothalamus, pituitary gland, and liver. Additionally, expression of IL-6 mRNA was reduced in the spleen and pituitary gland of pigs fed SDAP. The authors also reported changes in the ratio of villus height to crypt depth in pigs fed diets containing SDAP. Jiang et al. (2000a,b) reported that feeding SDAP to early-weaned pigs reduced cellularity of the lamina propria of the small intestine and improved efficiency of dietary protein utilization, in part, by decreasing intestinal amino acid catabolism. Plasma urea N concentrations were nearly 40% lower when pigs were fed SDAP compared with extruded soy protein (Jiang et al., 2001a,b). Torrallardona et al. (2003) indicated that the inclusion of 7% SDAP increased total counts of cecal Lactobacilli, while decreasing cecal Clostridium counts.
Overall, these data suggest that SDAP may influence intestinal function and thereby affect digestion. Addition of SDAP to dry dog food kibbles improved digestibility of nutrients and decreased excretion of fecal DM. Application of SDAP to the outside of kibbles or inclusion within the kibbles seemed to be equally effective. Improved digestibility is consistent with altered digestive function; however, these data do not clearly identify the effects of SDAP on nutrient digestibility.
Addition of spray-dried animal plasma to dry dog food kibbles improved digestibility of most nutrients and decreased fecal dry matter. These data suggest that spray-dried animal plasma can be applied topically or included inside the kibble with equal results. The nature of the improvement is unclear but may be mediated through changes in intestinal function. Additional research is indicated to more completely understand the effects of spray-dried animal plasma on intestinal physiology.
|Crude fiber, %||1.9||1.9|
|Crude fiber, %||1.4||1.5|
|Poultry by-product meal||15.51||14.00||12.51||11.01|
|Corn gluten meal||4.00||4.00||4.00||4.00|
|Spray-dried animal plasma||0.00||1.00||2.00||3.00|
|Crude fiber, %||2.60||2.60||2.50||2.50|
|Total dietary fiber, %||9.90||10.30||10.10||10.60|
|Body weight, kg|
|Feces, g/d (wet)||137||119||5||0.08|
|Feces, g/d (dry)||48||43||1||0.01|
|Dry matter, g/d||221.2||217.5||6.1||0.69|
|Crude fiber, g/d||4.6||4.5||0.1||0.60|
|Body weight, kg|
|Feces, g/d (wet)||119||93||4||0.004|
|Feces, g/d (dry)||44||35||2||0.006|
|Crude fiber, g/d||4.0||4.0||0.1||0.89|
|Body weight, kg|
|Feces, g/d (wet)||127||110||110||111||5||0.07||0.10|
|Feces, g/d (dry)||37.2||32.0||32.0||32.0||1.6||0.03||0.12|
|Crude fiber, g/d||6.5||6.7||6.4||6.2||0.2||0.21||0.23|
|Total dietary fiber, g/d||24.6||26.5||26.0||26.3||0.7||0.19||0.29|
|Total dietary fiber||40.7||50.3||48.6||48.7||1.8||0.01||0.02|