SUMMARY Four experiments with pigs and one with rats were conducted to determine the effect of stage of maturity and drying temperature on the amino acid (AA) availability and true nitrogen digestibility (TND) of normal corn (NC) and opaque-2 corn (OC). An evaluation of methods for assessing AA availabilities based on growth, plasma AA and fecal AA responses was also made. For the rat trial, corn of both varieties was harvested at six stages of maturity (from day 45 to 79 post-pollination) dried to 14% moisture at 40 C and fed as the only source of protein. NC and OC for pigs were harvested on days 52 and 80 post-pollination and dried at 40 and 60 C for a total of eight treatments arranged in a 2 x 2 x 2 factorial design. Weanling pigs (averaging 4.5 kg) were used to determine protein quality and trypto- phan and lysine availabilities (by means of growth and plasma AA responses) of the differently treated corns. Larger pigs (20 kg) were used for determining the availability of 13 AA and the TND of the same corn treatments by means of the fecal analysis method. None of the differences in protein quality for rats or pigs, or in availability of AA and TND for pigs due to stage of maturity or drying temperature were significant for either NC or opaque-2 corn. However, a trend for better gains and feed conversion of pigs fed the immature corn compared to those fed mature corn was ob-

Mass selection for an index of increased postweaning average daily gain and decreased backfat thickness was practiced for five generations. Litter size and weight for 221 gilt litters, birth weight and nipple number for 2,242 piglets and weaning weight at 42 d of age for 2,111 pigs were recorded. Carcass measurements were taken on 331 pigs. Differences between means of the lines (select control) were regressed on cumulative selection differential of the index. These regression coefficients were negative (P greater than .10) for total number born, number born alive, number weaned per litter, nipple number and carcass backfat thickness. Coefficients were positive (P greater than .10) for individual pig and litter weights at birth and weaning and for the carcass traits of length, longissimus muscle area and percentage of ham and loin. Absolute values of realized genetic correlations of index with traits evaluated were all .35 or less except the correlation with carcass backfat, which was -.84. None of these was significant; therefore, index selection for lean growth should have little effect on litter size and weight but may have a beneficial effect on carcass backfat.

Growth rate (ADG) and backfat (BF) data were collected during five generations of selection in two lines of Gene Pool pigs (14-breed synthetic): select (S) and control (C). C were randomly selected, while mass selection was practiced in the S line with an index (I), I = 100 + 286.6 (ADG) − 39.4 (BF). S and C pigs were fed a 14% protein, corn-soybean meal diet from 42 d of age until they reached 79.4 kg. The ratio of weighted to unweighted selection differentials offers evidence that natural selection was not working against artificial selection. Weighted cumulative selection differentials (adjusted for any unintentional selection occurring in the C line) were .40 kg ADG, −.70 cm BF and 143 I units. The regressions of response (S–C) on generation number were .014 ± .002 kg ADG, −.045 ± .010 cm BF and 5.76 ± .30 I units. The realized response was 41 and 38% of the expected response for ADG and BF, respectively. Realized heritability estimate for the I was .19 ± .029. The index in retrospect indicated that other factors such as natural selection and management had little effect on the selection criteria. Index selection was effective in improving both ADG and BF.

The relationship of teat number to seven measures of female reproduction was evaluated in the University of Nebraska Gene Pool population. Teat number was recorded for 7,513 pigs, ovulation rate for 2,794 gilts and litter size and weight at birth and weaning (42 days) for 789 gilts. Paternal half-sib and full-sib analyses were used to estimate heritabilities for each trait and to estimate the genetic and phenotypic correlations of teat number with the measures of reproduction. The direct response to selection for ovulation rate and the correlated response in teat number were also evaluated from the regressions of line differences (Select-Control) on generation number (10 generations of selection) and cumulative selection differential for ovulation rate. The paternal half-sib heritabililty for teat number was .32, and the paternal half-sib heritabilities for ovulation rate and the litter traits were similar to previous estimates from this population. Most of the genetic and phenotypic correlations with teat number were negative and all were nonsignificant. The realized heritability for ovulation rate was .46 +/- .10. The regression of response in teat number on generation number number was .08 +/- .03 (P < .10). An estimate of .44 was obtained for the realized genetic correlation of teat number with ovulation rate.

Two trials were conducted to determine the effect of lactose on performance, bone integrity and certain blood constituents in postweaning rats and swine. The effect of lactose on calcium and phosphorus and percentage ash content of the small intestine was also determined. In both trials, average daily gains were not influenced by the feeding of diets containing 30% lactose. Feed conversion was depressed in both rats and pigs when 30% lactose was fed. Transitory diarrhea was observed in rats fed 30% lactose, but not in swine. In the rat trial, no significant differences due to treatment were observed for serum Ca of P, but a linear increase (P < .01) in alkaline phosphatase was observed as lactose increased in the diet. Analysis of blood constituents from multiple bleedings during the pig trial showed that in the first 2 weeks, alkaline phosphatase was increased (P < .01) in pigs fed lactose and slightly decreased in those not fed lactose. Lactose affected the change in serum Ca for 0 to 10 weeks (P < .05) as indicated by a marked reduction in serum Ca of pigs not fed lactose and a slight increase for those fed lactoss. Serum calcium decreased in the absence of lactose but increased in the presence of lactose (P < .05) in pigs fed .4% Ca diets. In both trials, breaking strength parameters (peak force and stress) were not affected by dietary lactose. Bones from pigs fed no lactose had a higher stress to strain ratio (P < .05) than those from pigs fed lactose. In the rat trial, stress to strain ratio was variable across all treatments. Percentage of bone ash increased (P < .01) as lactose increased in the diet. Dietary treatments did not affect the mineral content of specific gut segments.

Ninety-six 8-kg crossbred boars were initially allotted to three dietary levels of calcium (Ca) and phosphorus (P) — (A) .65% Ca; .50% P; (B) .975% Ca; .75% P and (C) 1.3% Ca; 1.0% P — to determine the effects of the different levels on average daily gain (ADG), average daily feed intake (ADFI), feed to gain (F:G) and certain blood and bone parameters. During the initial 8-week growth period, no differences in ADG (.55, .58, .55), ADFI (1.17, 1.23, 1.16)or F:G (2.08, 2.16, 2.10) were observed for treatments A, B and C, respectively. At the beginning of the 8-week final growth period (41.5 kg), 50% of the boars fed each of the primary dietary treatments (A, B and C) were assigned to the other two treatments, while the other 50% remained on their original assigned treatments. No differences in performance were observed for the total 16-week growth period when evaulated as nine treatments. Fresh femurs and third and fourth metatarsals were evaluated for physical measurements, bone strength and percentage ash. Peak force required to break the bones of the pigs on the final period treatments increased linearly (P<.025) as the dietary level of Ca and P increased. Final period stress and stress:strain parameters of the bones responded similarly to peak force (linear component, P<.01). Also, percentage ash increased (linearly, P<.05) as dietary Ca and P levels increased. No treatment differences in subjective soundness scores were observed for any of the dietary treatments. Serum Ca levels decreased linearly at the end of the initial period, but the response was quadratic at the end of the final period. Alkaline phosphatase decreased linearly (P<.05) across treatments, with the largest decrease occurring with treatment A during the final period. The feeding of dietary Ca and P at up to twice the levels suggested by NRC (1973) for growing swine did not adversely affect performance of boars fed .65% Ca and .50% P than with those fed higher levels.

Two experiments were conducted to determine the effect of various levels of dietary calcium (Ca) and phosphorus (P) on performance, soundness and blood and bone parameters of different genetic lines of boars fed under variable environmental conditions. The first experiment compared different genetic lines of boars fed two levels of dietary Ca and P. Forty purebred (Large White) and Nebraska Gene Pool boars were allotted by breed and initial weight to two levels of dietary Ca and P (.65 Ca/.50% P and 1.3% Ca/1.0% P). The dietary levels of Ca and P had no significant effect on gains when compared by breed (.72 vs .74 kg) and treatment (.74 vs .72 kg). Also, none of the differences in feed intake (2.32 vs 2.31) and feed to gain ratio (3.09 vs 3.27) between Ca-P treatments was significant. No breed × bone interactions were found for bone-breaking parameters such as peak force (kilograms), stress (kilograms/square centimeters) and stress: strain (kilograms/square centimeters/millimeters). Peak force and stress required to break bones were higher (P<.005) for bones from pigs on the high Ca-P treatments than for those from pigs on the low Ca-P treatments (206.1 kg vs 167.8 kg and 54.39 kg/cm2vs 42.88 kg/cm2, respectively). Stress rstrain responded in a similar fashion. Percentage ash was higher (P<.001) for boars fed the diet with 1.3% Ca and 1.0% P. No significant differences were observed in serum Ca and P levels between either breeds or treatments, but serum alkaline phosphatase levels were higher (P<.001) in boars on .65% Ca and .50% P when analyzed for differences in enzyme level between the termination of the trial and 2 days afterward. A second trial was conducted to evaluate performance and soundness scores of 180 Duroc boars fed various levels of dietary Ca and P and raised under commercial conditions. Treatments were: A, .65% Ca, .50% P; B, .975% Ca, .75% P, and C, 1.3% Ca, 1.0% P. No differences in average daily gains (.90, .90, .90 kg) were observed among the three treatments. There was a tendency for higher (P<.1) average daily feed intake (2.33, 2.33, 2.47) and (P<.01) feed to gain requirements (2.60, 2.58, 2.74) for pigs fed treatment C than for those fed treatments A and B. No differences in feet and leg scores were observed among boars fed different Ca-P treatments.

Nine generations of direct selection for ovulation rate (OR) were evaluated to determine the magnitude of the correlated response in three litter size and two litter weight traits. A total of 387 Select line and 394 Control line litters were included in the ten generations of data. Realized heritability of OR was .42 ± .06 based on the regression of response (Select-Control) on weighted cumulative selection differential. Regressions of line means on generation number were significant for litter birth weight in both lines (−.31 ± .12 kg, Select; −.41 ± .06 kg, Control) and for litter weaning weight (−3.4 ± .8 kg) in the Control line. None of the other regressions of line means on generation number was significantly different from zero. Regressions of line difference (Select-Control) on generation number were .06 ± .07, .07 ± .07, .10 ± .07, .10 ± .10 kg and 1.2 ± .8 kg for total number farrowed (TNF), number farrowed alive (NFA), number weaned (NW), litter birth weight (LBW), and litter weaning weight (LWW), respectively. However, none of these estimates of correlated response was significantly different from zero. Estimates of realized genetic correlation obtained were .07 (OR-TNF), .11 (OR-NFA), .24 (OR-NW), .18 (OR-LBW) and .20 (OR-LWW). Although positive, none of the estimates approached statistical significance indicating that direct selection for ovulation rate would be expected to have little genetic effect on litter productivity. The failure to obtain significant correlated responses in litter size was suggestive of a decline in fertilization rate and/or embryonic survival since ovulation rate has been increased by selection.

Two experiments were conducted to determine the effect of energy source (carbohydrate or fat), fed to sows prior to parturition and during lactation, on energy storage and some metabolite levels in the neonatal pig which may exert an influence on rate of survival. The first experiment, which involved 12 gravid gilts, consisted of three diets and involved a comparison between energy level and source. The control diet, providing 5,750 kcal of metabolizable energy (ME)/gilt daily, was supplemented with either stabilized tallow or cornstarch to provide 9,300 kcal of ME/gilt daily. Treatments were initiated on the 100th day of pregnancy and continued until parturition. Blood samples were obtained, from the dams on day 110. Those fed tallow had a higher (P

Four experiments with pigs and one with rats were conducted to determine the effect of stage of maturity and drying temperature on the amino acid (AA) availability and true nitrogen digestibility (TND) of normal corn (NC) and opaque-2 corn (OC). An evaluation of methods for assessing AA availabilities based on growth, plasma AA and fecal AA responses was also made. For the rat trial, corn of both varieties was harvested at six stages of maturity (from day 45 to 79 post-pollination) dried to 14% moisture at 40 C and fed as the only source of protein. NC and OC for pigs were harvested on days 52 and 80 post-pollination and dried at 40 and 60 C for a total of eight treatments arranged in a 2 × 2 × 2 factorial design. Weanling pigs (averaging 4.5 kg) were used to determine protein quality and tryptophan and lysine availabilities (by means of growth and plasma AA responses) of the differently treated corns. Larger pigs (20 kg) were used for determining the availability of 13 AA and the TND of the same corn treatments by means of the fecal analysis method. None of the differences in protein quality for rats or pigs, or in availability of AA and TND for pigs due to stage of maturity or drying temperature were significant for either NC or opaque-2 corn. However, a trend for better gains and feed conversion of pigs fed the immature corn compared to those fed mature corn was observed. Gains and feed conversions of rats and pigs fed OC were improved (P<.01) as compared to NC fed animals. Higher AA availabilities and TND were also observed in OC vs NC, even though threonine availability was the only value to show a difference (P<.05) due to corn variety. Lysine was the least available AA in both NC and opaque-2 corn. Tryptophan availabilities were relatively high in both NC and OC (92 and 95%, respectively). TND was also higher in OC (92%) than in NC (90%). A significant interaction (P<.05) of maturity × drying temperature was observed in the availability of eight amino acids. The interaction was attributed to the initial moisture level during drying: 38% for the immature corn and 18% for the mature corn. Drying high-moisture corn at 40 C resulted in higher AA availabilities and TND than drying at 60 C. The reverse was true for low-moisture corn which showed higher AA availabilities and TND from drying at 60 vs drying at 40 C. It appeared that high moisture corn is more susceptible to protein damage due to heat treatment than low-moisture corn. A 25% reduction in yield was noticed in both corn varieties harvested on day 52 post-pollination compared to the yield of mature corn. The fecal analysis method for calculating AA availabilities was more convenient and produced more reliable results than the growth assay method or a method based on plasma AA responses.

Two experiments were conducted to determine the effect of level and source of energy fed to sows prior to parturition and during lactation on birth weight, gain, and survival of piglets and fat content of the dam's milk. The first experiment involved 30 gilts and nine sows. The gestation control diet, providing 5,750 kcal of metabolizable energy (ME)/dam/ day, was supplemented with either stabilized tallow or cornstarch, thus forming two additional diets, and fed at levels to provide 9,300 kcal of ME/dam daily. Treatments were initiated on day 100 of pregnancy and continued until parturition. Immediately following parturition, lactation treatments were imposed for a 14-day period. The lactation control diet contained 3,034 kcal ME/kg and was supplemented with 20% stabilized tallow to form a second diet that contained 3,843 kcal of ME/kg. The second experiment was a replicate of experiment 1, involving 17 gilts and 18 sows and provided additional information on fat content of the dam's milk and postweaning growth and efficiency of feed utilization by the piglets. Pigs reared on sows fed tallow during lactation had an 81.6% survival rate at 14 days of age, which was higher, but not significantly different, from that observed for the controls (79.2%). Percent piglets weighing ≼ 1,000 g at birth surviving to 14 days was higher, but not significantly different for those reared on sows fed tallow as compared to controls (53.4% vs 43.4%, respectively). This difference in survival rate among the smaller piglets was established as early as day 2 and maintained through day 14. Addition of tallow to the diets of dams during the gestation period increased fat content of colostrum compared to dams fed the control and cornstarch diets (8.94% vs 6.77%, 5.57%) but this increase was not sustained throughout lactation. Administration of tallow immediately following parturition increased (P<.01) milk fat for the entire lactation period in comparison to the controls (10.04 vs 8.10). The effect of the dam's gestation-lactation diets upon subsequent performance of pigs fed an identical diet to approximately 95 kg was determined using average daily gain, feed intake and feed efficiency as response criteria. Pigs in each of the gestation-lactation subclasses responded similarly with no significant differences observed for those traits tested.

Twenty-five variables measured before breeding and six measures of reproduction on 2,095 gilts from the University of Nebraska Gene Pool population were analyzed to estimate heritabilities and phenotypic and genetic correlations. Principal components were derived separately from the prebreeding and reproductive phenotypic correlation matrices and were analyzed as new traits. The heritabilities of most traits were in general agreement with the average of the literature estimates with the exception that the heritability of litter size at birth was .72 compared to a literature average of .10. Phenotypic correlations among growth traits were large and positive. Phenotypic correlations of ovulation rate with litter sizes and weights were positive but small and nonsignificant. Phenotypic correlations among litter sizes and litter weights at birth and 42 days were large and positive. Several of the measures of growth had significant positive phenotypic correlations with ovulation rate but not with litter sizes or litter weights. All genetic correlations had large standard errors and none were statistically significant. Genetic correlations among growth traits were large and positive. Genetic correlations of ovulation rate with litter sizes and weights were negative and, with the exception of number born, were large. Genetic correlations among litter size and litter weight at birth and 42 days were large and positive. Seven principal components derived from the prebreeding traits accounted for 79.8% of the total variation of the 25 variables. Three principal components derived from the reproductive traits accounted for 94.6% of the total variation of the six variables. Principal components were very useful in evaluating interrelationships among traits within a group but were not very useful in elucidating the relationship between groups.

Weanling crossbred pigs were divided into 24 groups and fed one of three levels of lysine and one of eight levels of tryptophan in a 3 X 8 factorial design to determine the optimum dietary proportions of these two amino acids. Weight gain and feed efficiency, and changes in plasma levels of lysine, tryptophan and urea were the response criteria. The tryptophan "requirement" and the optimum lysine:tryptophan ratio were estimated for each of the three lysine levels. The data indicate a tryptophan requirement of 0.19% to 0.23% for the 3-week-old pig when the lysine level is adequate. For pigs of this age a lysine:tryptophan ratio of from 4 to 5 was about optimum.

Four catheterized crossbred (Y × H) barrows were used in a 4 × 4 latin square arrangement of treatments in a completely randomized block design, to determine the effect of source on copper uptake as determined by serum Cu concentration changes over a 7.5-hr sampling period. Dietary treatments were: (A) basal with no added Cu, (B) basal + 5.2 mg Cu (from CuSO4)/kg of diet, (C) basal + 5.2 mg Cu (EDTA chelated Cu)/kg of diet, and (D) basal + 5.2 mg Cu (from CuSO4) + 34.1 mg ethylene diamine tetra acetic acid (EDTA)/kilogram of diet. Animals were placed on the semi-purified basal diet for 5 days, fasted for 1 day and then given their dietary treatment. Following consumption of the dietary treatment, blood samples were collected from each animal at 15-min intervals for 3.0 hr and at 1.5-hr intervals over the remaining 4.5 hr of a 7.5-hr sampling period. The samples were collected via jugular catheters and during the 4-week trial each animal was exposed to all dietary treatments. Serum Cu concentration was not significantly (P< .05) affected by dietary treatment. However serum Cu concentrations did change significantly (P< .05) during the 7.5-hr sampling period. A significant (P< .01) animal × sampling time interaction was also observed. The results indicate that prechelated Cu or dietary additions of EDTA had little influence on the efficiency of Cu uptake by swine. Sampling time following consumption of a diet was important as evident from the reflected changes in serum Cu concentration.