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Five experiments were conducted to evaluate the potential use of plasma urea N (PUN) concentrations as a rapid response criterion to determine amino acid requirements. A preliminary experiment (Exp. 1) indicated that a 3-d feeding time was required to re-equilibrate PUN concentrations after a change in the dietary concentration of lysine. In Exp. 2, 3, and 4, PUN was used to estimate the lysine requirement of growing pigs at different specific BW. Thirty individually penned crossbred pigs weighing 32 and 44 kg in Exp. 2 and 3, respectively, were assigned to five dietary treatments (.60, .70, .80, .90, and 1.00% lysine) for 5 d. The PUN decreased quadratically (P .10). Therefore, PUN concentrations can be used in short-term trials to accurately estimate the dietary lysine required to maximize total N utilization in pigs at a specific BW. In addition, the two-slope broken-line regression model had the highest R2 and the lowest mean square error compared with three other models as means for estimating lysine requirement from PUN concentrations.

Three trials were conducted to test whether feeding the leucine metabolite beta-hydroxy-beta-methyl butyrate (HMB) would increase fat content of sows' milk and pig weight gain. All sows received a basal diet and were assigned at random to receive either 2 g of CaCO3/d (control) or 2 g of Ca(HMB)2/d (HMB), which was top-dressed to the basal diet. Treatment began 3 to 4 d before farrowing. In Trials 1, 2, and 3 there were 4, 19, and 11 pairs of sows, respectively. In a combined analysis that included all three trials, milk fat at d 1 was increased by 41% (P = .01) and pig weight at d 21 was increased by 7% (P = .01) for sows fed diets containing HMB compared with sows fed control diets. Sows fed HMB lost more backfat (P = .03); however, sows receiving HMB had more (P < .05) backfat depth at farrowing than control sows. At weaning there was no difference in backfat depth between the treatment groups. Sows fed HMB tended to consume less feed (P = .07) than control sows. In Trials 2 and 3, data were collected on the subsequent reproductive cycles of the sows. A combined analysis of the data revealed no differences in sow performance when sows previously fed the diet containing HMB were compared with sows previously fed the control diet. In conclusion, beta-hydroxy-beta-methyl butyrate, when fed to sows at 2 g/d, resulted in an increase in fat percentage of sow's milk and pig performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Two experiments were conducted to determine the effect of lightweight pig removal and remixing on performance to slaughter. Experiment 1 was a growing-finishing trial utilizing a total of 900 pigs (26.2+/-0.1 kg initial weight) that were sorted and remixed at a mean replicate BW of 72 kg. Experiment 2 was a wean-to-finish trial (17 d mean wean age; 4.8 kg +/- 0.1 BW) utilizing 225 barrows with sorting and remixing occurring 3 wk after weaning. Treatments were 15 pigs/ pen from initial weight to slaughter (15S), 20 pigs/pen from initial weight to time of sort and remix and then reduced to 15 pigs/pen (20/15), and 15 pigs/pen from time of sort and remix to slaughter comprised of the five lightest pigs from each of three 20/15 pens per replicate (15M). Space allocation was 0.56 m2/pig from 26 to 70 kg and 0.74 m2/pig thereafter in Exp. 1. In Exp. 2, pen size was fixed at 2.44 x 4.27 m. In Exp. 1, there was no effect (P0.20) of treatment on performance prior to 70 kg. Least squares means for ADG from time of sort and remix to first pig removal from a pen for slaughter at 113 kg were 0.93, 0.87, and 0.91 kg/d for the 20/15, 15M, and 15S treatments, respectively (P0.05). When comparing the population represented by the 20/15 + 15M treatments vs the 15S population, there was no difference (P0.20) in ADG, ADFI, feed conversion, or carcass lean content. In Exp. 2, pigs in the 20/15 treatment grew slower (P0.05) than 15S pigs for the first 21 d (0.20 vs 0.22 kg/d, respectively) with a lower ADFI (P = 0.06) and no difference in feed conversion. When comparing the population represented by the 20/15 + 15M treatments vs the 15S population after sorting and remixing, there was no effect (P0.15) of experimental treatments on ADG, ADFI, feed conversion efficiency, carcass lean content, or daily lean gain. These results suggest that removal of lightweight pigs and remixing of the removed pigs into pens of similar-weight pigs is ineffective in improving the overall performance of a population of pigs during the postweaning period.

Conjugated linoleic acid (CLA) was fed to growing-finishing barrows (n = 92) at 0.75% of the diet. A commercial CLA preparation (CLA 60) containing 60% CLA isomers was included at 1.25% to provide 0.75% CLA in the diet. The inclusion of CLA in diets was initiated at various BW and fed until slaughter. Growth, carcass, meat quality, physical, chemical, and sensory data were collected and analyzed. Treatments T1, T2, T3, and T4 included the last 0, 29, 56 and 87 kg, respectively, of weight gain before slaughter. Average daily gain and feed intake were not affected (Por = 0.06) by CLA, but gain:feed responded quadratically (P = 0.05), over the entire BW gain (28 to 115 kg) with pigs of T2 and T3 having the greatest gain:feed. Loin muscle area increased (P = 0.01) linearly with increasing weight gain while fed CLA, and 10th rib, first rib, and last rib fat depth decreased (Por = 0.05) linearly. Subjective quality measures on loin muscles increased linearly for marbling (P0.05) and tended to increase for firmness (P = 0.07) with increasing weight gain while barrows were fed CLA. Objective Hunter color values for loin chops from T1 and T4 were not different for L* (P = 0.12) or a* (P = 0.08) values but were higher (P0.05) for b* values with CLA feeding. Lipid oxidation values of loin muscle tissue were lower (P0.05) for pigs fed CLA (T1 vs T4). Increasing the period of weight gain while feeding CLA linearly increased (P0.01) saturated fatty acids and CLA isomers in loin tissue and linearly increased (P0.01) saturated fatty acids and CLA isomers in subcutaneous adipose tissue. Sensory panel characteristics of loin chops were not changed (P0.05) by feeding CLA. Increased gain:feed, increased loin muscle area, decreased fat depth, and improvements in marbling and firmness with CLA feeding could result in improved profitability of pork production systems.

Two experiments were conducted to evaluate the possible interaction of nursery space allocations and grow-finish space allocations in swine. In Exp. 1, crowding was achieved by varying the number of pigs per pen. During the nursery phase, decreasing the space allocation (0.16 m2/pig vs 0.25 m2/pig; 8 and 12 pens per treatment, respectively) by increasing the number of pigs per pen (18 vs 12) resulted in a decrease in daily feed intake (0.609 vs 0.683 kg/d; P < 0.001) and daily gain (0.364 vs 0.408 kg/d; P < 0.001). Pigs were mixed within nursery treatment groups and reassigned to grow-finish pens (6 pens per treatment) at the end of the 35-d nursery period providing either 0.56 m2/pig (14 pigs/pen) or 0.78 m2/pig (10 pigs/pen). Crowding during the grow-finish phase decreased daily feed intake (P < 0.003) and daily gain (P < 0.001). In Exp. 2, space allocations of 0.16 m2/pig vs 0.23 m2/pig during the nursery phase (24 pens per treatment) resulted in a decrease in daily feed intake (0.612 vs 0.654 kg/d; P < 0.005) and daily gain (0.403 vs 0.430 kg/d; P < 0.001). Pigs remained in the same (social) groups when moved to the grow-finish phase. Unlike Exp. 1, there was no effect of crowding during the grow-finish phase (0.60 m2/pig vs 0. 74 m2/pig) on daily feed intake or daily gain. The difference in results between experiments suggests that the response to crowding during the grow-finish phase may depend in part on whether pigs are mixed and sorted following movement from the nursery.

Early-weaned pigs (n = 64) averaging 5.3 +/- 0.3 kg and distributed into two environments (dirty and clean) were used to evaluate effects of conjugated linoleic acid (CLA) on growth performance, immune competence, and empty body composition. A factorial (2 x 4) arrangement within a split-plot design, with four littermate pigs as the experimental unit for the environment, pig within litter as the experimental unit for dietary treatment, and d-0 body weight used as covariate, were used in data analysis. Diets were formulated to contain CLA at 0, 0.67, 1.33, or 2% and to exceed the NRC (1988) nutrient needs of pigs. Animals were given ad libitum access to feed for 7 wk in three phases (I, 1 to 2; II, 3 to 5; and III, 6 to 7 wk). Within phases, diets were isocaloric and isonitrogenous. In Phase I, as dietary CLA concentration increased, ADG and ADFI decreased linearly (P < 0.05 and P < 0.02, respectively). In Phase II, upon adaptation to dietary CLA supplementation, ADG increased quadratically (603, 623, 622, and 548 g/d; P < 0.01), ADFI decreased linearly (873, 840, 867, and 717 g/d; P < 0.02) and gain:feed ratio tended to increase linearly (691, 742, 715, and 763; P < 0.07). In Phase III, no differences in growth performance were attributed to either dietary or environmental treatments. The poor health status associated with the dirty environment induced a growth suppression; pigs in the clean room had a greater cumulative ADG (P < 0.01) and ADFI (P < 0.01) than pigs in the dirty room. In Phase I, lower plasma urea nitrogen levels observed in pigs found in the dirty room (P < 0.03) indicated a lower protein intake caused by a lower ADFI. The effects of dietary CLA on peripheral phenotypic profiles of lymphoytes did not appear until d 42. However, as indicated by the growth suppression of pigs in the dirty room, the negative effects of the environmental challenge on pig health and growth had already appeared during phase I. On d 42, CLA induced a linear increase in percentages of CD8+ lymphocytes (21.7, 22.3, 28.0, and 32.7%; P < 0.001). These data suggest that a 42-d dietary CLA supplementation preceding a disease challenge could have prevented disease-associated growth suppression. Also, CLA-mediated amelioration of particular infectious diseases will depend on which CD8+ T cell subset (i.e., CD8alphaalpha-immunoregulatory or CD8alphabeta-cytotoxic) is most influenced by dietary CLA supplementation.

The dietary lysine requirement of adult sows nursing 10 pigs was estimated by using plasma urea nitrogen (PUN) concentration as a rapid response criterion. A preliminary experiment indicated that a 3-d feeding time is required to re-equilibrate PUN concentrations after a change in the dietary concentration of lysine. In the main experiment, 12 sows (BW = 219 +/- 5 kg; parity = 4.5 +/- .3; ultrasound backfat = 21.3 +/- .9 mm) were used in two 6 x 6 Latin squares. Treatments consisted of dietary lysine intakes (30.2, 36.9, 43.6, 50.3, 57.0, and 63.7 g/d) that were assigned to six 4-d periods and to six sows in each square. Diets provided adequate levels of all nutrients other than lysine. The treatment periods started on d 5 of lactation and ended on d 29. Plasma urea N concentrations were determined on the 3rd and 4th d of each of the six 4-d treatment periods. Plasma urea N concentrations decreased quadratically (P < .02) with, increasing dietary lysine intakes. A two-slope, broken-line regression model was used to estimate the dietary lysine intake that minimizes PUN concentrations. The results indicated that adult sows nursing 10-pig litters with an average growth of 2.22 kg/d required 55.3 g/d of dietary total lysine to minimize PUN concentrations and, therefore, presumably to minimize body protein mobilization.

The objectives of this study were 1) to investigate the relationship between plasma urea N concentrations (PUN) and lean tissue growth and 2) to compare the value of different variables, related to lean growth and renal function, to correct the relationship between dietary lysine concentration and PUN response for variation not related to amino acid adequacy. Forty-eight gilts (64.8 kg BW) were individually penned (blocks based on initial BW) for 50 d: a 10-d adjustment, a 35-d pretreatment, and a 5-d treatment period. During the pretreatment period, ADFI, urine specific gravity (SG), serum creatinine (SC), PUN, and daily fat-free carcass lean (DFFCL), empty body protein (DEBP), total carcass fat (DCF), and empty body lipid (DEBLI) depositions were measured. Partial correlation coefficients (ADFI effect removed) indicated a strong and inverse relationship between PUN and lean growth (DFFCL and DEBP) (r = -.88 and -.91, respectively, P.01) and a positive relationship between PUN and fat deposition (DCF and DEBLI) (r = .66 and .54; respectively, P.22). Treatments consisted of six dietary lysine concentrations (.475, .550, .625, .700, .775, and .850%). Initial and final BW in the treatment period were 103.3 and 107.7 kg, respectively. Pretreatment PUN (PUNO) was the pretreatment variable with the greatest R2 and the smallest MSE when used in the model describing the response of PUN (PUN1) to dietary lysine. The estimated lysine requirements from the PUN1 response corrected with either PUN0 or with the combination of PUN0, ADFI, DFFCL, DCF, SG, and SC were not (P.05) different (.656 vs678%, respectively). We conclude that 1) PUN concentrations have a potential value as an indicator of the efficiency of lean tissue growth and 2) pretreatment PUN is a useful variable to correct treatment PUN for variation not related to amino acid adequacy.

We studied the effect of reduced feed intake on the lysine requirement of pigs at the early growing (G) and finishing (F) phases. Two sets of 40 individually penned crossbred barrows averaging 27.1 +/- .2 (G) and 92.6 +/- 1.1 kg BW (F) were fed five dietary treatments (G; .75, .90, 1.05, 1.20, 1.35%; and F: .45, .60, .75, .90, 1.05% lysine) at two feeding levels (equivalents to 100 and 80% ad libitum intakes) for 15 d. In both stages pigs on the 80% feeding level had lower ADG (P0.01) and lower plasma urea nitrogen (PUN) concentrations (P.10) than pigs on the 100% feeding level. In all instances, increasing dietary lysine caused ADG to increase (P.05) and PUN to decrease (P.10) linearly. A tendency for an interaction was detected between the effects of growth stage and the effects of feeding level on the lysine requirements estimated by ADG (P.19) and PUN (P.10). In the F stage, pigs on the 80% feeding level required a greater dietary lysine concentration to maximize ADG and minimize PUN (.85 and .87%, respectively) than pigs on the 100% feeding level (.61 and .68%, respectively). In the G stage, however, the dietary lysine concentrations required to maximize ADG (.97 to 1.01%) and minimize PUN (1.05 to 1.09%) were not different (P.20) between feeding levels. We conclude that the effect of a reduction in feed intake on the lysine requirement depends on the stage of growth of the pigs.

The objective of this study was to determine whether differential labeling of 13 C occurs in pigs fed diets with different 13 C abundances and, if so, to use 13 C as a label to determine true amino acid digestibility. Forty-eight pigs averaging 10.5 kg BW were fed dietary treatments consisting of a corn-corn gluten meal-crystalline amino acid diet (C-CGM) and a wheat-soybean meal diet (W-SBM). The 13 C abundance of the amino acid fraction (AAF) of the C-CGM and W-SBM diets averaged delta 13 C -14.19 and -26.36‰, respectively. Three pigs/treatment group were killed when groups averaged 10.5 (initial), 22.9, and 46.6 kg BW, and AAF of organs were analyzed for 13 C abundance. Carbon 13 in empty body AAF increased (-18.14, -13.98, and -12.66‰) with increasing body weight in pigs fed the C-CGM diet and decreased (-18.06, -22.78, and -24.76‰) in pigs fed the W-SBM diet. Liver, small intestine, and longissimus muscle tissues showed similar trends. Each tissue had dietary treatment effects (P

Forty-eight barrows (61 kg), 24 Yorkshire x Landrace (YL) and 24 YL x Duroc x Hampshire (YLDH), were used to evaluate the effect of six dietary ME levels on concentrations of plasma urea nitrogen (PUN) and free amino acids. All pigs consumed equal amounts of each nutrient, except for energy. As energy intakes increased from 12.42 to 35.01 MJ/d of ME (34 to 97% of NRC recommendations), ADG increased linearly (P < .001) and concentrations of PUN decreased linearly (P < .01) and quadratically (P < .05). There was a tendency (P = .09) for an interaction of breed combinations and energy intakes on ADG. In general, increasing energy intake decreased plasma concentrations of essential amino acids and increased plasma concentrations of nonessential amino acids. Exceptions were a lack of change in plasma lysine and glutamic acid, an increase in histidine, and decreases in tyrosine and aspartic acid. Concentrations of most plasma amino acids were similar between the two breed combinations, but 9 of 27 amino acids that were measured were different (P < .05) between the breed combinations. The linear response of ADG was probably attained through a relatively constant lean-to-fat deposition ratio in the body over the levels of ME intakes. The curvilinear decline of PUN to increasing energy intakes was probably because at low energy intakes, amino acids were oxidized to furnish energy for maintenance and at increasing energy intakes there was increasing accretion of body proteins.

Two experiments with weanling pigs were conducted to study the effects on growth and immune responses of excess dietary L-leucine (LEU) and dietary supplementation with the LEU catabo- lites, a-ketoisocaproic acid (KIC) and @-hydroxy- methyl butyrate (HMB). In Exp. l, 80 pigs were randomly allocated according to initial BW and ancestry to five replications of four dietary treatments (four pigs/pen). The control diet contained wheat, oat groats, menhaden fish meal, and dried whey and provided 1.12% LEU. Treatment diets were the control plus 1.12% LEU, 1.12% KIC, or .4% HMB. The experiment lasted 6 wk. In Exp. 2, 36 pigs were randomly allocated to nine replications of four dietary treatments in a 2 x 2 factorial arrangement. Treat- ments consisted of two concentrations of dietary LEU and a daily i.m. injection of dexamethasone (DEX) or saline. Pigs were fed a control corn-soybean meal and dried whey diet (1.56% LEU) or the control diet plus 1.56% of crystalline LEU. Pigs were individually penned and the experiment lasted 4 wk. Growth performance, plasma free amino acids, plasma urea nitrogen, and humoral and cellular immune responses were measured. Results indicated that LEU concen- trations in practical diets and supplementation with KIC and HMB (Exp. 1) did not detrimentally affect growth and immune response. The high LEU concen- tration and DEX injection used in Exp. 2, however, were detrimental to both growth and immune re- sponse.

Segregation and medicated early weaning are technologies used to optimize the productivity and health of pigs, but these practices may also cause aberrant behaviors indicative of stress. Thus, differences in early- (=10 d of age) and late- (=30 d of age) weaned pigs were investigated. At weaning, pigs were housed in groups of four in 16 pens (eight pens per treatment) in the same facility, and, thus, they were not segregated. Body weights were recorded at birth, weaning, and at approximately 42, 65, 102, 137, and 165 d of age (at slaughter). One-minute, instantaneous scan samples during a 10-min period (at 0600, 1000, 1400, and 1800) were used to record the frequency of lying, standing, and sitting, total number of drinks, feeder investigations, and time spent playing/fighting on 2, 3, and 4 d after weaning. Five-minute, direct observations of each pig were conducted at approximately 40, 60, 80, and 150 d of age. Direct observations were also made of the entire pen for 10 min at approximately 50, 95, 123, and 160 d of age to record aberrant behaviors. At 62 d of age, a handling and blood collection stress was imposed. At 165 d of age, a second stress test was conducted in response to rough handling and transport. Early-weaned pigs spent more time playing/ fighting (P < .006) than late-weaned pigs during the 4 d after weaning, manipulated conspecifics more often at 40 d of age (P < .002), had greater percentage of hemoglobin (P < .03) during Stress Test 1, had greater ADG at 42 d of age (P < .03), and had greater hypothalamic growth hormone-releasing hormone receptor mRNA at slaughter (P < .06). Late-weaned pigs had greater ADG between 137 and 165 d of age (P < .03) and greater pro-opiomelanocortin at slaughter (P < .04). Overall, most differences found between early-weaned and late-weaned pigs were evident soon after weaning, but they disappeared before slaughter.

The effect of daily or interval (every 3 d) feeding on body weight change, blood glucose and cholecystokinin (CCK) concentrations, immune function, and behavioral activity were determined during the gestation period of sows. Sows were fed a corn-soybean meal diet either 2 kg daily or 6 kg once every 3rd d (interval). Body weight changes for the 42-d trial period were not different (P > .05) between regimens. Blood glucose concentrations were similar before feeding (P > .05). Two hours after feeding, glucose concentrations increased in interval-fed sows but not in daily-fed sows (P < .05). Premeal plasma CCK concentrations were greater for daily-fed sows than for interval-fed sows (P < .05). The CCK concentrations in sows of both regimens increased after feeding above premeal levels (P < .05), and interval-fed sows exhibited higher concentrations than daily-fed sows (P < .05). Immune function as evaluated through mitogen-induced proliferation of T cells was greater in daily-fed sows than in interval-fed sows (P < .05). Daily-fed sows were more active overall and on any given day than interval-fed sows (P < .05) and thus seemed to expend more energy. Further, daily-fed sows exhibited higher levels of mouth-based activities (i.e., sham chewing, licking, appetitive and consummatory feeding behavior, and excess drinking) than sows restricted to consumption of one large meal every 3rd d. These indicators suggest that feeding motivation significantly affected overall performance of sows. This study emphasizes the need for evaluating the impact of feeding regimens and meal size on feeding motivation and, ultimately, on the well-being of the gestating sows.

The effect of a low and a high level of chronic immune system (IS) activation on the rate, efficiency, and composition of body growth and dietary lysine needs of pigs fed from 6 to 112 kg body weight was evaluated. All pigs were of a single genetic strain and geographical site of origin, and the low and high IS pigs were created by physically isolating pigs from and continually exposing pigs to major vectors of environmental antigen transmission. In each IS group, five littermate barrows from each of seven litters were individually penned and randomly allotted to one of five dietary amino acid regimens (.6, .9, 1.20, 1.50, and 1.80% lysine from 6 to 27 kg BW and .45, .60, .75, .90, and 1.05% lysine from 27 to 112 kg BW). Dietary lysine concentrations were achieved by altering the ratio of corn to soybean meal in the diets, and diets were formulated such that lysine was the first-limiting amino acid. Low IS pigs possessed lower (P < .01) T lymphocyte CD4+:CD8+ ratios and serum alpha-1-acylglycoprotein concentrations. Low IS pigs also consumed more (P < .01) feed, gained body weight faster (P < .01), required less (P < .01) feed per unit of gain, and at 112 kg BW produced bodies with more (P < .12) muscle and less (P < .10) fatty tissue and offal than high IS pigs. To allow their elevated capacities for proteinaceous tissue to be expressed, low IS pigs required .15 to .30 percentage units greater dietary lysine concentrations and 2 to 5 g higher daily lysine intakes at each 14-kg BW increment from 6 to 112 kg BW.

The influence of a low and a high level chronic immune system (IS) activation on growth and dietary nutrient needs of pigs was evaluated. All pigs were of a single genetic strain and geographical site of origin, and the low and high IS pigs were created by physically isolating pigs from or continuously exposing pigs to major vectors of environmental antigen transmission. In each IS group, four littermate barrows in each of six litters were allotted at 25 +/- 2 d of age to one of four dietary amino acid regimens (.60, .90, 1.20, or 1.50% dietary lysine. Dietary lysine concentrations were achieved by altering the ratio of corn to soybean meal resulting in lysine being the first-limiting amino acid in each diet. Pigs were individually penned in facilities maintained at 25.6 +/- 2 degrees C and allowed to freely consume feed from 6.2 to 26.5 kg BW. On the basis of the differences in serological antibody titers, lymphocyte CD4+:CD8+ ratios, and serum alpha-1-acylglycoprotein concentrations, low and high levels of IS activation were established and maintained during the study. Minimizing the degree of chronic IS activation resulted in greater feed intakes (P < .09), body weight and protein gains (P < .01), gain:feed ratios (P < .01), and body leanness (protein:lipid, P < .01). The level of IS activation did not influence the partial efficiency of energy utilization for body protein and lipid accretion. To allow their greater capacity for body growth and protein accretion to be expressed, the low IS pigs required greater dietary lysine concentrations and daily lysine intakes than high IS pigs.

Thirty crossbred sows and their pigs were evaluated through two parities to determine any reproductive or growth performance effects of an active dry yeast supplement added to corn-soybean meal diets. Sow reproductive performance from d 93 of gestation through d 21 of lactation and sow milk composition were evaluated. Pig growth performance was measured from birth to 28 d after weaning. Active dry yeast was added at 0, 1, or .2% of the sow gestation diet, 0, .15, or .3% of the sow lactation diet, 0, .2, or .4% of the pig prestarter diet, 1 wk before and 1 wk after weaning, and 0, .125, or .25% during the last 3 wk in the nursery. The yeast source consisted of a concentrate of live yeast cells of the Saccharomyces cerevisiae strain containing more than 15 x 10(9) live cells/g. Sow body weight at d 93 of gestation, at farrowing, and at d 21 of lactation did not differ (P.10) among treatment groups. Milk from sows fed active dry yeast contained higher amounts of total solids (P.05), crude protein (P.10), and gamma globulin (P.06) than milk from sows fed the control diet. Sow feed intake during lactation was not affected (P.10) by treatment, nor were there differences in litter size at birth, litter birth weight, or litter weight at d 21 after farrowing. Active dry yeast supplementation to the sow and pig diets resulted in improved postweaning pig daily gain (P.05) and gain-to-feed ratio (P.05) but did not affect (P.10) feed intake. Based on these data, active dry yeast supplement during late gestation, lactation, and before and after weaning does not alter litter weight at birth or weaning but does increase gamma globulin content of sow's milk and improves postweaning rate and efficiency of weight gain of pigs.

SUMMARY The value of a yeast single cell protein (SCP) as a partial replacement of dehulled soybean meal (SBM) in the diet for baby pigs and growing pigs was investigated in two experiments. In the first experiment, SCP replaced 0, 26.6, 53.2 and 79.8% of the SBM in the diet. The average daily gain response to increasing levels of SCP was quadratic and was maximized in baby pigs fed the diet in which SCP replaced 53.2% of the SBM. Response of average daily feed intake to treatments was similar to rate of gain. There was a linear improvement in feed efficiency as yeast SCP replaced soybean meal. The linear improvement suggested that palatability, not toxicity or nutrient imbalance, caused the reduced feed intake and rate of gain by pigs fed the highest level of SCP. Increasing levels of yeast SCP resulted in a linear decrease in plasma urea nitrogen, a linear increase in plasma a-amino nitrogen and no change in plasma uric acid. In experiment 2, yeast SCP replaced 0, 25 and 50% of the dehulled SBM in the diet of growing pigs (28 kg average initial weight). No significant treatment differences were observed for average daily feed and average daily gain, but gain:feed ratio increased linearly as the level of yeast SCP increased in the diets. In a third experiment, nitrogen digestibility and retention of the yeast SCP was evaluated with baby pigs. Comparisons were made between a diet with corn, SBM and dried whey as protein sources, a diet with these sources finishing half the protein and SCP furnishing the other half, and a third diet with all protein from SCP. Both nitrogen digestibility and nitrogen retention as a percentage of nitrogen