Effect of gender (gilt and surgically and immunocastrated male) and ractopamine hydrochloride supplementation on growth performance, carcass, and pork quality characteristics of finishing pigs under commercial conditions.

This study evaluated the effects of gender and feeding of ractopamine on growth performance, carcass, and meat quality characteristics of pigs reared under commercial conditions. The study was performed as a randomized complete block design (blocking factor date of start on test) with a 3 × 2 factorial arrangement of treatments: 1) gender [gilt vs. surgical castrate vs. intact males immunocastrated] and 2) ractopamine level (0 vs. 5 g/ton). The study was conducted out over a fixed duration (126 d) from 1 wk after weaning (28 d of age; 8.04 ± 1.31 kg BW) to 154 d of age (111.44 ± 4.67 kg BW) in 3 growth periods: nursery (d 0 to 35 of the study), growing (d 35 to 70), and finishing (d 70 to 126). Ractopamine was fed for the final 28 d of the study (d 98 to 126). Pigs were kept in groups of 10 or 11 in the nursery phase and then moved to the growing-finishing facility where they were kept in groups of 22 to the end of the study. At the end of the growth study, pigs were harvested and carcass and pork quality were evaluated, including consumer evaluation of eating quality. During the nursery, there was no effect of gender (P > 0.05) on G:F, but surgical castrates grew faster (P < 0.05) than intact males and gilts and had greater (P < 0.05) ADFI than intact males. There was no effect of gender (P > 0.05) on ADG in the growing period; however, immunocastrated males had lower ADFI than surgical castrates and greater G:F than surgical castrates and gilts. In finishing, immunocastrated males and surgical castrates had similar ADG but grew faster than gilts; G:F was greater for immunocastrated males than the other genders. Feeding 5 compared to 0 g/ton ractopamine increased ADG and G:F but had no effect (P > 0.05) on carcass yield or fresh meat quality. Carcass yield was lower but percentage lean cut yield was greater for immunocastrated males than for surgical castrates. Longissimus muscle drip loss was greater (P = 0.05) for immunocastrated males than surgical castrates. Gender had no effect (P > 0.05) on consumer panel evaluation. Feeding ractopamine had no effect on pork flavor and tenderness but improved juiciness scores. Odor scores were similar (P > 0.05) for surgical castrates and immunocastrated males that were fed ractopamine. Consumers gave lower liking scores for odor for immunocastrated males than surgical castrates that were not fed ractopamine. This study highlights the feed efficiency and lean cut yield advantage for immunocastrated males compared to surgical castrates and suggests a similar growth response to feeding ractopamine in these genders. Although immunocastrated males had a lower carcass yield and higher drip loss, panelists were not able to detect differences in pork juiciness, flavor, and tenderness when compared to surgical castrate pigs.

Isoleucine requirements and ratios in starting (7 to 11 kg) pigs.

Two experiments were conducted to refine the Ile needs in 7- to 11-kg pigs. In Exp. 1, 1,680 pigs were fed a 1.25% digestible Lys diet containing 7.5% spray-dried blood cells (as-fed basis) with supplemental crystalline Ile (0.06% increments) to generate seven levels of apparent digestible Ile (0.47 to 0.83%). There were 12 replicates of each treatment with 20 pigs per pen, and treatments were imposed at an initial BW of 7 kg and continued for 16 d. Responses in ADG, ADFI, G:F, and plasma urea nitrogen (PUN) were quadratic (P < 0.01) over the 16-d period. Data were fitted to both a single-slope broken line and a quadratic fit, and when the quadratic response curve was superimposed on the broken line, the points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.70, 0.73, 0.66, and 0.65% digestible Ile for ADG, ADFI, G:F, and PUN, respectively. Using the ADG and ADFI obtained at this intersection point resulted in an estimate of 9.1 mg of digestible Ile per gram of weight gain. In Exp. 2, 1,840 pigs were fed similarly composed diets, except that digestible Lys was lowered in six diets to 1.10% by decreasing soybean meal. Crystalline Ile was supplemented at 0.09% increments to generate six levels of digestible Ile (0.37 to 0.83%). A seventh diet contained 1.25% digestible Lys by supplementing the 0.83% digestible Ile diet with 0.19% L-Lys HCl to verify that 1.10% digestible Lys was deficient for these pigs. There were 12 replicates of each treatment with 22 pigs per pen, and treatments imposed at an initial BW of 7 kg and continued for 16 d. Supplementation of Lys to the 0.83% digestible Ile diet (1.10 vs. 1.25% digestible Lys) did not affect ADG (260 vs. 264 g/d, P = 0.60) and ADFI (359 vs. 343 g/d, P = 0.20), whereas G:F (725 vs. 774 g/kg, P < 0.01) was improved by increasing dietary Lys. Responses in ADG, ADFI, and G:F to the first six diets were quadratic (P < 0.01) over the 16-d period. The points at which the quadratic curve first intersected the plateau of the broken line occurred at 0.686, 0.638, and 0.684% digestible Ile for ADG, ADFI, and G:F, respectively. Using the ADG and ADFI obtained at this intersection point results in an estimate of 9.9 mg of digestible Ile per gram of weight gain. These results suggest that although the percent digestible Ile requirement and digestible Ile:Lys ratio for starter (7 to 11 kg) pigs may be higher than 1998 NRC recommendations, the requirement may be lower than current recommendations when taking gain and feed intake into account.

Utilization of spray-dried blood cells and crystalline isoleucine in nursery pig diets.

Three experiments were conducted to evaluate spray-dried blood cells (SDBC) and crystalline isoleucine in nursery pigs. In Exp. 1, 120 pigs were used to evaluate 0, 2, 4, and 6% SDBC (as-fed basis) in a sorghum-based diet. There were six replicates of each treatment and five pigs per pen, with treatments imposed at an initial BW of 9.3 kg and continued for 16 d. Increasing SDBC from 0 to 4% had no effect on ADG, ADFI, and G:F. Pigs fed the 6% SDBC diet had decreased ADG (P < 0.01) and G:F (P = 0.06) compared with pigs fed diets containing 0, 2, or 4% SDBC. In Exp. 2, 936 pigs were used to test diets containing 2.5 or 5% SDBC (as-fed basis) vs. two control diets. There were six replicates of each treatment at industry (20 pigs per pen) and university (six pigs per pen) locations. Treatments were imposed at an initial BW of 5.9 and 8.1 kg at the industry and the university locations, respectively, and continued for 16 d. Little effect on pig performance was noted by supplementing 2.5% SDBC, with or without crystalline Ile, in nursery diets. Pigs fed the 5% SDBC diet without crystalline Ile had decreased ADG (P < 0.01), ADFI (P < or = 0.10), and G:F (P < 0.05) compared with pigs fed the control diets. Supplementation of Ile restored ADG, ADFI, and G:F to levels that were not different from that of pigs fed the control diets. In Exp. 3, 1,050 pigs were used to test diets containing 5, 7.5, or 9% SDBC (as-fed basis) vs. a control diet. There were six replicates of each treatment at the industry (20 pigs per pen) location and five replicates at the university (six pigs per pen) locations. Treatments were imposed at an initial BW of 6.3 and 7.0 kg at the industry and university locations, respectively, and continued for 16 d. Supplementation of 5% SDBC without crystalline Ile decreased ADG and G:F (P < 0.01) compared with pigs fed the control diet, but addition of Ile increased ADG (P < 0.01) to a level not different from that of pigs fed the control diet. The decreased ADG, ADFI, and G:F noted in pigs fed the 7.5% SDBC diet was improved by addition of Ile (P < 0.01), such that ADG and ADFI did not differ from those of pigs fed the control diet. Pigs fed diets containing 9.5% SDBC exhibited decreased ADG, ADFI, and G:F (P < 0.01), all of which were improved by Ile addition (P < 0.01); however, ADG (P < 0.05) and G:F (P = 0.09) remained lower than for pigs fed the control diet. These data indicate that SDBC can be supplemented at relatively high levels to nursery diets, provided that Ile requirements are met.

Growth performance and enzyme development in weanling pigs injected with dexamethasone.

Three experiments were conducted to evaluate the effects of dexamethasone (DEX) on growth performance and on selected digestive enzyme activities in weanling pigs. In Exp. 1, 96 pigs (6.7 kg BW and 27 d) were used in a 3 x 2 factorial combination of three DEX frequencies (no injection; 1 mg DEX/kg BW 3 d before weaning; and 1 mg DEX/kg BW 6 and 3 d before weaning) and two feeding regimens: a simple diet fed throughout the 28-d trial, or a semicomplex diet fed during the first 14 d postweaning, followed by the simple diet. Growth performance was not affected (P > .10) by hormonal treatment. Pigs fed the simple diet had a greater ADF1 after d 15 postweaning (P < .10) and higher ADG from 15 to 21 d postweaning (P < .01). In Exp. 2, 80 pigs (7.2 kg BW and 26 d) were assigned 3 d before weaning to four dosages of DEX (0, .33, .66, and .99 mg/kg BW). Growth performance was similar regardless of DEX dosing. In Exp. 3, 24 pigs (6.4 kg BW and 21 d) were injected with DEX (1 mg/kg BW) or saline solution on d 3 before weaning. Four pigs per treatment were slaughtered at weaning, or on d 3 and d 6 postweaning. Dexamethasone resulted in greater (P < .10) pancreas weight and increased (P < .01) total activity of amylase and sucrase, but lactase was lowered (P < .10). Dexamethasone injection enhanced digestive enzyme activity but failed to improve performance, presumably because of the reduced feed intake of pigs at weaning.

Effect of glucocorticoids and limiting nursing on the carbohydrate digestive capacity and growth rate of piglets.

The influence of glucocorticoid administration and limited nursing on piglet carbohydrase enzyme development and subsequent growth was examined in three experiments using 371 piglets. Treatments in the first two experiments were formed by the factorial arrangement of hydrocortisone (-HYD or +HYD) and limited nursing (-LN or +LN) imposed form d 14 to weaning (d 28). Hydrocortisone was replaced by adrenocorticotropic hormone (ACTH) in the third experiment. Growth rates were severely depressed by HYD (P less than .01), LN (P less than .001) and to a lesser extent (P less than .06) by ACTH during the last 2 wk of lactation. During the first 14 d postweaning, piglets continued to grow more slowly following HYD treatment (P less than .01), whereas LN piglets grew more rapidly than those allowed to suckle normally. Although piglets were smaller at weaning after HYD injection (P less than .01), relative weights of liver, pancreas and small intestine were increased (P less than .05). Only adrenal weights were increased by ACTH (P less than .09). Pancreatic and intestinal amylase activities were increased two- to three-fold by HYD injection (P less than .05) but were unaffected by ACTH or LN (P greater than .10). Sucrase and maltase activity increased linearly with age (P less than .001). This rate of increase was numerically enhanced by glucocorticoid treatment and LN. The normal decrease in lactase activity was accelerated by LN and HYD injection, with the greatest depression caused by the combination of LN and either HYD or ACTH administration (P less than .05). Glucocorticoid administration to nursing piglets can evoke premature elevation of the carbohydrase enzymes necessary for initiating the hydrolysis of starch.

Response of digestive carbohydrases and growth to graded doses and administration frequency of hydrocortisone and adrenocorticotropic hormone in nursing piglets.

Graded levels of hydrocortisone 21-acetate (HYD) (0, 18, 16 and 24 mg/kg BW) were injected into nursing piglets every other day (Exp. 1) or 24 mg of HYD/kg BW was administered 0, 2, 4 or 6 times during the treatment period (12 d) with equal time (6 d, 3 d or 2 d) between subsequent injections (Exp. 2). Adrenocorticotropic hormone (ACTH) was injected to provide 0, 5, 10 or 15 IU/kg BW (Exp. 3), or 15 IU ACTH/kg BW was injected 0, 1, 2 or 3 times (Exp. 4). The injection treatment periods were from d 14 to d 26 postpartum. Pancreatic and intestinal amylase activity was maximized by the highest dosage of HYD (24 mg) and ACTH (15 IU) when given at 2- or 4-d intervals, respectively (P less than .10). However, four injections of HYD administered 3 d apart optimized the activity of this enzyme in Exp. 2 (P less than .05). Intestinal sucrase and maltase were unresponsive to ACTH regardless of dosage or injection frequency (P greater than .10). The response of these two enzymes to HYD was inconsistent. Maltase activity was elevated (P less than .10) by the two most frequent injection treatments, and sucrase activity was simultaneously depressed. Lactase activity tended (P less than .15) to be depressed by the highest treatment level in all four experiments. Both dosage and frequency methods of increasing HYD administration resulted in hepatic and pancreatic hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal changes in carbohydrate digestive capacity and growth rate of piglets in response to glucocorticoid administration and weaning age.

Two experiments were conducted that demonstrated that a single injection of hydrocortisone 21-acetate (HYD, 25 mg/kg BW) administered to 6-d-old nursing piglets resulted in a twofold elevation (P less than .02) of pancreatic amylase within 2 d; activity was unaffected by an injection of 15 IU adrenocorticotropic hormone (ACTH)/kg BW (P greater than .20). Intestinal sucrase and maltase activity tended to be elevated (P less than .20) 2 and 4 d postinjection with HYD but returned to normal (uninjected) levels by 14 d of age. The normal decline of intestinal lactase activity was delayed by at least 4 d in response to both hormones (P less than .10). Organ weights were not affected by either hormone. In a separate experiment, postweaning mortality was reduced (12 vs 27%) and growth rate was substantially improved by administration of HYD to piglets 4 and 2 d prior to weaning at 14 d of age. Hydrocortisone resulted in a faster rate of gain the 1st wk postweaning for pigs weaned at 21 or 28 d. Subsequent gain by control and HYD piglets weaned on d 21 was similar, but HYD subsequently impaired growth rate of piglets weaned at 28 d of age. Growth rates of control and ACTH piglets were similar at each postweaning period regardless of weaning age (weaning age [lin.] x week postweaning [quad.] x treatment, P less than .07). This differential treatment response of daily gain may be due in part to effects on feed intake (weaning age [lin.] x week postweaning [lin.] x treatment, P less than .10). We conclude that a single injection of HYD to 6-d-old piglets precociously induces pancreatic amylase and that the sensitivity of piglets to HYD is age-dependent.

Effect of lysine and threonine supplementation of sorghum gestation diets on nitrogen balance and plasma constituents in first-litter gilts.

Fifteen gravid, crossbred gilts were utilized in an experiment to measure the effect of five isonitrogenous dietary treatments (12% crude protein, sorghum-soybean meal; sorghum; sorghum + lysine; sorghum + threonine; sorghum + lysine + threonine) on N balance, colostrum composition and plasma constituents (protein, urea N and IgG). All gilts were fed a standard corn-soybean meal diet from breeding until switched to the sorghum basal diet, on d 60 of gestation. Treatment diets were imposed at d 70. Nitrogen retention, measured between d 103 and 113 of gestation, was improved (P less than .002) by lysine addition. Nitrogen retention was similar (P greater than .10) for gilts fed either the 12% crude protein, sorghum-soybean meal diet or the lysine + threonine-supplemented diet. Plasma protein levels at farrowing were depressed (P less than .06) in those gilts fed sorghum diets without supplemental lysine and plasma urea N was elevated (P less than .10). Plasma protein and plasma urea N were not affected by threonine supplementation (P greater than .10). In contrast, the depression of plasma IgG was ameliorated (P less than .03) by threonine and unaffected by lysine supplementation. These results confirm the hypothesis that lysine is the first limiting amino acid in sorghum protein for gravid gilts as determined by N retention but indicate that threonine is likely the first limiting amino acid for the production of the specific protein, IgG.

Nitrogen metabolism of gravid and nongravid female swine fed every third day.

Crossbred gilts were adapted for 40 d to a 12% crude protein corn-soybean meal gestation diet fed either as a single 1.9-kg meal every day (ED) or as an accumulated 5.7 kg meal every third day (E3D). In the first experiment the effect of meal frequency on N balance was evaluated using eight gravid gilts in a 12-d balance trial. Average N retention was greater (P less than .08) for gilts fed ED (15.32 g/d) than for those fed E3D (12.64 g/d). Daily urinary N excretion showed a quadratic effect (P less than .01) with the greatest N output occurring during the second 24-h period after the meal for gilts fed E3D. The effect of physiological state on the N metabolism response to E3D feeding was measured in a second experiment using four nongravid and four gravid gilts in a 12-d N balance experiment. Average daily N retention was greater (P less than .04) for gravid gilts fed E3D (15.04 g) than for nongravid gilts fed E3D (11.82 g). Digestibility of N and energy was not affected (P greater than .10) by feeding regimen.