Inadequate diet mixing time reduces nursery pig performance

Although the importance of thoroughly mixing diets is often emphasized, little data is available to quantify the impact of inadequate mixing on pig growth performance. Therefore, a 28-d trial was conducted to evaluate the effects of mixing time on growth performance of nursery pigs. A total of 180 weanling pigs (13.9 Â± 1.8 lb BW, 21Â± 3 d of age) were used, with 6 pigs per pen and 6 pens per treatment. Experimental treatments consisted of mixing a diet for 0, 30, 60, 120 or 330 s in a horizontal ribbon mixer. Diets were fed in two phases (d 0 to 14 and 14 to 28), with diets in both phases containing relatively large amounts of lowinclusion ingredients such as synthetic amino acids, zinc oxide, and phytase. Diets in Phase 1 also contained 3.75% fish meal and 15% dried whey. Eight samples were collected from the mixer at the completion of the mixing time for each batch of feed to determine a coefficient of variation (CV). Each bag (50.0 lb) was labeled (first to last) and sampled to determine the degree of mixing that occurred as feed was conveyed from the mixer to the bagger. Each pen of pigs was then assigned a bag of feed. Bags were distributed in the order bagged (1, 2, 3, etc.). As feed was needed, the next chronological bag of feed was then added. Mixer CV values were 178, 38, 26, 21, and 5% for Phase 1 and 172, 79, 60, 48, and 26% for Phase 2 as mixing time increased. Bag CV values were 26, 20, 16, 11, and 7% for Phase 1 and 56, 45, 40, 33, and 12% for Phase 2 as mixing time increased, indicating the degree of mixing that takes place as feed is conveyed from the mixer to the bagger. Growth performance was improved as mixing time increased (linear, P<0.01) in both phases. From d 0 to 28, increasing mix time increased (linear, P<0.01) ADG (0.73, 0.89, 0.90, 0.94, and 1.02 for 0, 30, 60, 120, and 330 s, respectively). Increasing mixing time also improved F/G (linear, P<0.01; quadratic, P<0.07; 1.55, 1.40, 1.32, 1.33, 1.30 for 0, 30, 60, 120, and 330 s, respectively). With greater use of lowinclusion ingredients such as synthetic amino acids in swine diets, these data demonstrate that inadequate mixing reduces nursery pig performance.; Swine Day, 2005, Kansas State University, Manhattan, KS, 2005


Summary
Although the importance of thoroughly mixing diets is often emphasized, little data is available to quantify the impact of inadequate mixing on pig growth performance.Therefore, a 28-d trial was conducted to evaluate the effects of mixing time on growth performance of nursery pigs.A total of 180 weanling pigs (13.9 ± 1.8 lb BW, 21± 3 d of age) were used, with 6 pigs per pen and 6 pens per treatment.Experimental treatments consisted of mixing a diet for 0, 30, 60, 120 or 330 s in a horizontal ribbon mixer.Diets were fed in two phases (d 0 to 14 and 14 to 28), with diets in both phases containing relatively large amounts of lowinclusion ingredients such as synthetic amino acids, zinc oxide, and phytase.Diets in Phase 1 also contained 3.75% fish meal and 15% dried whey.Eight samples were collected from the mixer at the completion of the mixing time for each batch of feed to determine a coefficient of variation (CV).Each bag (50.0 lb) was labeled (first to last) and sampled to determine the degree of mixing that occurred as feed was conveyed from the mixer to the bagger.Each pen of pigs was then assigned a bag of feed.Bags were distributed in the order bagged (1, 2, 3, etc.).As feed was needed, the next chronological bag of feed was then added.Mixer CV values were 178,38,26,21,and 5% for Phase 1 and 172,79,60,48,and 26% for Phase 2 as mixing time increased.Bag CV values were 26,20,16,11,and 7% for Phase 1 and 56, 45, 40, 33, and 12% for Phase 2 as mixing time increased, indicating the degree of mixing that takes place as feed is conveyed from the mixer to the bagger.Growth performance was improved as mixing time increased (linear, P<0.01) in both phases.From d 0 to 28, increasing mix time increased (linear, P<0.01) ADG (0.73,0.89,0.90,0.94,and 1.02 for 0,30,60,120,and 330 s,respectively).Increasing mixing time also improved F/G (linear, P<0.01; quadratic, P<0.07; 1. 55, 1.40, 1.32, 1.33, 1.30 for 0, 30, 60, 120, and 330 s, respectively).With greater use of lowinclusion ingredients such as synthetic amino acids in swine diets, these data demonstrate that inadequate mixing reduces nursery pig performance.

Introduction
The importance of thoroughly mixing diets is often emphasized to swine producers, but there is little data available to demonstrate the impact of inadequate mixing on pig growth performance.Feed uniformity may have a greater impact on growth performance than in the past due to changes in genetics, diet complexity, and the increased use of lowinclusion ingredients such as synthetic amino acids, phytase, antibiotics, and concentrated vitamin and trace mineral premixes.An adequately mixed batch of feed has been defined as a mixture that has a coefficient of variation (CV) of 10% or less.There is little data available to suggest that this CV value is appropriate for maximizing growth performance of pigs.Therefore, the objective of this study was to evaluate the effects of mixing time and CV on the growth performance of nursery pigs fed diets containing high concentrations of lowinclusion ingredients.

Procedures
A total of 180 weanling pigs (initially 13.9 ± 1.8 lb BW, 21± 3 d of age) were used, with 6 pigs per pen and 6 pens per treatment.Pigs were randomly allotted to pens and were blocked by weight.Experimental treatments consisted of mixing a diet for 0, 30, 60, 120, or 330 s in a 1.5-ton horizontal ribbon mixer.Diets were fed in two phases (d 0 to 14 and 14 to 28), with diets in both phases containing high concentrations of low-inclusion ingredients such as synthetic amino acids, phytase, and zinc oxide (Table 1).Diets in Phase 1 also contained 3.75% fish meal and 15% dried whey.All diets were fed in meal form and were manufactured at the Kansas State University Animal Sciences and Industry Feed Mill.
Each batch of feed (700-and 1,200-lb batches for each mixing duration in Phase 1 and Phase 2, respectively) was manufactured by following a step-by-step diet-mixing procedure.Corn was added to the mixer, and the mixer was turned on to distribute the corn across the bottom of the mixer.The mixer was then turned off for all additional ingredient additions.
Soybean meal was added, followed by the remaining ingredients according to inclusion rate (largest to smallest).The micro additions were all preweighed into a barrel and added as a micro addition after all other ingredients.The mixer was then sampled (0 s) or turned on for the specified amount of mixing time (30, 60, 120, or 330 s).Eight samples were collected from the mixer at the completion of each mixing time for each batch of feed to determine a CV for salt by using a grain probe.The batch was then discharged from the mixer and conveyed to the bagger.The discharge time was approximately 65 s for Phase 1 and 100 s for Phase 2. The discharge time was not included in the experimental treatment mixing time.At the bagger, each bag (50 lb) was labeled (first to last) and sampled with a grain probe to determine the degree of mixing that occurred as feed was conveyed from the mixer to the bagger.The bags were assigned to a pen of pigs and distributed in the order bagged (1, 2, 3, etc.).As feed was needed, the next chronological bag of feed was then added.The feeding procedure was designed to reproduce a situation similar to how a commercial auger system may distribute feed to feeders.
Each of the five dietary treatments was analyzed for mixer efficiency CV, from the samples collected from the mixer at the conclusion of mixing and from the samples collected from each bag after discharge from the mixer, by using Quantab ® chloride titrators (Environmental Test Systems, Elkhart, Indiana; Table 2).There are two mixer-efficiency CV values for each diet and for each phase of feeding.Calculation for mixer efficiency CV was conducted with 12 samples collected from the bags for Phase 1 and 22 samples collected from the bags for Phase 2. Crude protein was also analyzed on each sample collected from the bags to evaluate variability in diet CP with increased mixing time (Tables 3 and 4).

Results and Discussion
Increasing the mixing time improved mixer-efficiency CV (Table 2) and CP uniformity (Tables 3 and 4) of the sample.
Mixer-efficiency CV decreased to 7 and 12% for Phase 1 and 2, respectively, at the longest mixing time of 330 s, and CP CV decreased to 2.0 and 3.3% for Phase 1 and Phase 2, respectively.These results indicate that the same standard value of ≤10% used to measure mixer-efficiency CV may not be appropriate for measuring CP CV.
Crude protein concentration was lower in the first bags collected and increased as the number of bags increased, indicating that the first bags contained the ingredients low in CP, such as corn.In both instances, an increased CV value for either the CP or mixer efficiency are strong indicators that other essential nutrients may not be incorporated uniformly in the mixture and, therefore, may not allow for optimal growth performance of nursery pigs.The optimal CV for CP seems to be ≤ 3%, whereas the standard mixer efficiency of 10% seems to be near the appropriate target value for salt.
Growth performance improved (linearly, P<0.5) in both phases, with the largest response occurring when mixing time was increased from 0 to 60 s.But ADG, ADFI, and F/G improved through the 330 s mixing time in both phases and for the overall trial (d 0 to 28; Table 5).There was an improvement (linear, P<0.01) in final BW with increased mixing time.Pigs fed the diet mixed for 330 s were heaviest at d 28, compared with pigs fed diets with the other mixing durations.The salt mixer-efficiency CV for Phases 1 and 2 were 7 and 12%, which corresponds to the longest mixing time of 330 s, and the greatest growth performance seen in the trial, indicating that a CV value (≤10) for mixer efficiency can improve growth performance of nursery pigs.
Although the greatest improvement in growth performance was from 0 to 60 s, ADG and F/G continued to improve through 330 s mixing time.The mixer-efficiency CV values for salt for the 330-s mixing time were 7 and 12% for Phases 1 and 2, respectively; therefore, the linear (P<0.01)improvement in ADG indicates that a smaller CV value is ideal for maximizing nursery pig growth performance and ensuring an adequate incorporation of all ingredients into the mixture.
Measuring CV of CP on collected samples may not be a good indicator of uniform mixing, or the ideal CV value may need to be 3% or less to indicate a uniform mixture.More research is needed to determine if CV of CP can be used as an indicator of mixing uniformity.With greater use of low-inclusion ingredients such as synthetic amino acids in swine diets, uniform mixing becomes more important to ensure that proper nutrients are supplied to the pig; these data demonstrate that inadequate feed mixing reduces nursery pig performance.Dietary treatments consisted of mixing the diet for 0, 30, 60, 120, or 330 s in a horizontal ribbon mixer.
b Fine mixing salt was used to aid in mixer-efficiency analysis.

Table 2 . Coefficient of Variation (CV) for Various Feed Mixing Durations, % a
The bag CV for each mix time was determined from 12 samples (one sample collected from each bag at the bagger).d The bag CV for each mix time was determined from 22 samples (one sample collected from each bag at the bagger). c

Table 3 . Crude Protein Analysis for Each Bag Fed, d 0 to 14 a
a Each bag (50 lb) was analyzed for CP to evaluate variability in diet CP.

Table 4 . Crude Protein Analysis for Each Bag Fed, d 14 to 28 a
Each bag (50 lb) was analyzed for CP to evaluate the variability in diet CP. a

Table 5 . Effects of Inadequate Diet Mixing Duration on Nursery Pig Performance ab
b There were no cubic responses (P<0.05)observed.