Showing papers in "Journal of Animal Science in 1987"

Predicting intake and digestibility using mathematical models of ruminal function.

Abstract: Intake and digestibility of feeds by ruminants are influenced by characteristics of the feed, animal and feeding situation. Integration of these characteristics in mathematical models is critical to future progress in forage evaluation and optimal formulation of diets for ruminants. The physiological and physical theories of intake regulation can be described by simple mathematical equations. These equations indicate that intake is a linear function of animal characteristics, such as body weight and production level, and a reciprocal function of feed characteristics, such as fill effect and energy content. Theoretical equations were developed to predict intake when the neutral detergent fiber and energy content of the diet and the energy requirements of the animal are known. The theoretical model also can be used to predict the maximum intake that will maintain a given level of animal production by solving the physiological and physical intake equations at their intersection. Psychogenic intake regulation, which is related to the animal's behavioral response to factors not related to physiological or physical characteristics, can be described mathematically as a multiplier. Digestibility can be predicted by summing the contents of ideal nutritive entities in feeds, which have true digestibilities near 100%, subtracting their associated endogenous losses and adding the variable digestible fiber content. Steady-state models indicate fractional rates of digestion and passage can be used to define ideal nutritive entities and predict digestibility over a range of kinetic characteristics. The steady-state solutions are particularly useful in understanding and predicting the depression in digestibility associated with changes in rates of passage at high levels of feed intake.

Composition of Sow Milk During Lactation

Abstract: The composition of sow colostrum and milk was quantitated in 25 sows at 14 time points throughout lactation. All animals belonged to the same experimental herd of German Landrace, farrowed within 4 d, and were of various lactation numbers and various litter sizes. In the first 6 h of lactation colostrum total solids (TS) and protein contents were higher, while fat and lactose contents were lower than in mature milk. Decreased total protein and whey protein contents and concomitantly increased fat and lactose content, with nearly unchanged TS levels, indicate transition from colostrum to mature milk. The high protein content of colostrum was largely due to immunoglobulin (Ig). During the first 6 h, IgG accounts for nearly all the protein in colostrum but plays a decreasing role in sow milk as lactation proceeds. After 2 wk, IgA levels begin to increase and at the end of lactation, IgA constitutes 40% of the total whey protein. No influences of lactation number and litter size on milk composition could be ascertained in this study.

Pregnancy rates of beef heifers bred either on puberal or third estrus.

Abstract: The objective of this study was to determine if pregnancy rates (PR) differed between beef heifers bred to fertile bulls on either their puberal (E1, n = 89) or third (E3, n = 67) estrus. Heifers were obtained from two lactations (Manhattan, L1; and Miles City, L2), and the experiment was conducted at Miles City. Heifers were assigned randomly within location to either E1 or E3. Heifers were fed to gain .56 kg.head-1 X d-1 and observed twice daily for estrus. After exhibiting first estrus (puberty) and breeding, each heifer in E1 was palpated rectally on d 6, 9 and 12 +/- 1 d (estrus = d 0) for the presence of a corpus luteum, and a venous blood sample was collected for assay of progesterone by radioimmunoassay. Heifers in E3 were palpated and bled on the same schedule as heifers in E1 after first estrus and after being bred to a fertile bull at third estrus. Pregnancy rates were determined by rectal palpation at approximately 38 d post-breeding. Location of origin did not affect (P greater than .10) weight at puberty or weight at breeding; however, heifers from L1 were younger (P less than .05) than heifers from L2 at puberty and breeding. Pregnancy rates were 57 and 78% for heifers in E1 and E3, respectively (P less than .05). Weight at breeding did not influence (P greater than .10) pregnancy rates. The probability of heifers in E1 becoming pregnant increased (P less than .05) with increasing age, while age was not a factor (P greater than .10) for heifers in E3. These results indicated that fertility of puberal estrus in beef heifers is lower than third estrus. Higher fertility of third estrus may be related to maturational changes associated with cycling activity.

Stimulation of pig growth performance by porcine growth hormone: determination of the dose-response relationship.

Abstract: The present study was undertaken to determine the relationship between dose of porcine growth hormone (pGH) and growth performance of pigs. Porcine GH was administered daily for 35 d [buffer-injected control = (C); 10 micrograms/kg body weight (BW) = (L); 30 micrograms/kg BW = (M); 70 micrograms/kg BW = (H)] to barrows (initial wt = 50 kg). Growth rate was significantly increased by pGH (14% for H dose vs C). Feed efficiency was increased in a dose-related manner (L = 7%, M = 10%, H = 17%) by pGH. There was a concurrent change in carcass composition of pGH-treated pigs. The H dose of pGH decreased the percentage of carcass lipid by 25% (P less than .05). Muscle mass was significantly increased in H vs C pigs (31 vs 26 kg). Serum insulin-like growth factor 1 (IGF-1) concentration increased in a manner that was linearly related to the pGH dose (r = .87). No antibodies to pGH were detected in any of the pigs. In summary, these results extend our earlier findings that pGH increases growth performance markedly. Based on the present findings it appears that the maximally effective dose of pGH is greater than 70 micrograms.kg BW-1.d-1 since several indices of the growth-promoting and metabolic effects of pGH (% carcass protein, % carcass lipid and feed efficiency) had not plateaued.

Ruminal microbial development in conventionally or early-weaned calves

Abstract: Eight bull calves (four Holsteins and four Ayrshire calves with mean birth weight of 38.8 kg) were ruminally cannulated at 3 d of age and allocated to one of two weaning programs. All calves were fed colostrum for 3 d after birth and milk until weaning. Calves in the conventional-weaning program were fed a starter diet from 3 d of age and weaned at 6 wk of age. In the early-weaning program, calves were fed a highly palatable pre-starter diet from 3 d of age until they consumed 227 g/d, and then fed a mixture of pre-starter (227 g) and starter diet ad libitum. Calves in this group were weaned at 4 wk of age. Ruminal samples were collected at 3 and 7 d, then weekly thereafter through 8 wk and at 10 and 12 wk of age to assess microbial activity. Calves in the early-weaned group had a higher concentration of total ruminal volatile fatty acids at an earlier age than the calves in the conventional-weaning program. This was accompanied by a trend toward higher lactate concentrations and lower ruminal pH in the early-weaned group during their first 4 wk of age. Lactate and ammonia concentrations decreased with calf age. The total anaerobic bacterial counts increased slightly with calf age, whereas Streptococcus bovis and facultative bacterial populations decreased with calf age. Amylolytic, proteolytic, lactobacilli, lactate-utilizers, cellulolytic and methanogenic bacterial populations increased progressively in both groups. Cellulolytic and methanogenic bacteria were present in both groups at 3 d of age. No protozoa were detected in calves of either group. In general, the most significant changes in bacterial populations and metabolic activity in both groups occurred between 4 and 6 wk of age. Although calves in both groups had similar patterns of bacterial development, calves in the early-weaning program tended to have high ruminal microbial activity at an earlier age than the conventionally weaned calves.

Cimaterol-induced muscle hypertrophy and altered endocrine status in lambs.

Abstract: The objectives of this study were 1) to determine how cellular growth of skeletal muscle is altered by the repartitioning agent cimaterol and 2) to determine if cimaterol alters endocrine status in association with its repartitioning effects. Thirty Dorset wether lambs were randomly assigned to a pre-treatment baseline group or received 0 or 10 ppm cimaterol in a complete, mixed, high-concentrate diet for 7 or 12 wk. Weights of biceps femoris (BF), semimembranosus (SM) and semitendinosus (ST) muscles were 32.8, 27.1 and 31.5% greater, respectively, in treated lambs at 7 wk, and were 22 to 24% greater at 12 wk. Longissimus (LD) cross-sectional area was 26 and 32% greater at these treatment intervals. Percent type I fibers declined significantly over the course of the experiment in ST, SM and LD, and cimaterol caused a small but significant reduction in percent type I fibers in the ST at 7 and 12 wk. Muscles from lambs fed cimaterol contained 50 and 75% more fibers that exhibited negative staining for phosphorylase activity. Mean cross-sectional area of type I and type II fibers in the combined portions of the ST were 30.4 and 29.3% greater, respectively, in cimaterol-fed lambs after 12 wk, while type I and type II fiber areas in the longissimus were only 13 and 15% greater, respectively. Cimaterol-induced hypertrophy of the ST resulted in both protein and RNA content being 30 to 35% greater (P<.01) at 7 and 12 wk, while DNA concentration was 22% less (P<.O1) at 7 wk. DNA concentration returned to normal by 12 wk. These results indicate that cimaterol elicits a rapid increase in muscle RNA and protein accretion without concurrent incorporation of satellite cell nuclei. Plasma insulin and insulin-like growth factor-1 (IGF-1) concentrations were 55 and 34% lower, respectively, in cimaterol-fed lambs. Plasma somatotropin concentration and area under the curve were 2.3 times greater (P<.01) in lambs fed cimaterol for 6 wk, while plasma cortisol, prolactin and glucose concentration were unaffected at 6 or 12 wk. The significant changes in endocrine status may be important in the mechanism(s) of cimaterol in altering muscle accretion.

Enhancement of ovulation rate in gilts by increasing dietary energy and administering insulin during follicular growth.

Abstract: Two experiments were conducted to examine influences of dietary energy and insulin on ovulation rate and patterns of luteinizing hormone (LH), follicle stimulating hormone (FSH), glucose, insulin and estradiol in gilts during 6 d before estrus. In Exp. 1, 36 gilts were given altrenogest for 14 d to synchronize estrus. In a factorial arrangement, gilts were fed one of two levels of dietary energy (5,771 or 9,960 kcal metabolizable energy (ME)/d), and given one of two levels of porcine insulin (0 or .1 IU/kg body weight iv every 6 h). Dietary treatments began 4 d before and insulin treatments began 1 d after the last day of altrenogest, respectively, and lasted until 24 h after estrus. Main effect means for number of corpora lutea were 14.0 +/- 1.3 and 17.6 +/- .9 for 5,771 and 9,960 kcal ME (P less than .05), and 14.6 +/- 1.0 and 17.0 +/- .9 for 0 and .1 IU insulin (P less than .05). Number of LH peaks on d 3 was greater for gilts that received 9,960 kcal than 5,771 kcal (3.3 +/- .2 vs 2.7 +/- .2; P less than .05), and for .1 than 0 IU insulin (3.2 +/- .2 vs 2.7 +/- .2; P less than .05). During the first 24 h of sampling, concentrations of LH and FSH were greater (P less than .05) in gilts receiving 9,960 kcal ME plus insulin than for other treatment combinations. Concentrations of estradiol were not affected by treatments. In Exp. 2, two formulations of insulin were evaluated for influence on ovulation rate. All gilts received altrenogest and 9,960 kcal ME/d as in Exp. 1. Then on the first day after altrenogest, seven gilts each received short-acting insulin (as in Exp. 1), long-acting insulin (zinc suspension, 1.0 IU/kg body weight every 18 to 24 h), or served as controls. Ovulation rates were increased (P less than .05) by both insulin preparations (15.6, control; 19.1, short-acting; 18.5, long-acting; SE = 1.2). Concentrations of LH tended to be greater after short-acting insulin, but differences were not significant (P = .13). We conclude that increases in ovulation rate produced by dietary energy and insulin are not necessarily accompanied by changes in gonadotropins or estradiol.

Effect of protein and lysine levels in the diet on body gain composition and energy utilization in growing pigs.

Abstract: Eight replicates of four Large White littermate female pigs were used to evaluate the effect of protein and lysine levels in the diet on the efficiency of protein and energy utilization. In each replicate, one pig was slaughtered at about 20 kg live weight and the others received three diets that contained (per Mcal digestible energy) 37.5 and 2.00 g (diet pl), 37.5 and 2.35 g (diet pL) or 45.0 and 2.35 g (diet PL) of digestible protein and lysine, respectively. Pigs were slaughtered after a 7-wk period. Tissue and chemical composition of the gain and energy and nitrogen gain were determined by using the comparative slaughter technique. Metabolizable energy (ME) intakes were similar in the treatments. Pigs fed the pl diet had a smaller body weight and muscle gain and retained less nitrogen and more lipids than pigs fed pL and PL diets. The decrease in the level of nonessential nitrogen in the diet (pL vs PL) did not affect body weight and muscle gain and the amount of nitrogen retained in muscle tissues. However, pigs given the PL diet had a higher total nitrogen retention and a lower fat deposition and exhibited a higher heat production. For each gram of additional protein catabolized for energy purposes (PL vs pL), heat production was increased by 1.8 kcal. The amount of lysine per unit of muscle gain (38 g/kg) or protein deposited (120 g/kg) was independent of protein and lysine levels in the diet. Estimates of energy (indirect calorimetry) and nitrogen (balance technique) retention were also obtained on the same animals; results were comparable with data obtained by direct measurements.

Nuclear transplantation in bovine embryos.

Abstract: This study was conducted to develop a method for transplanting nuclei in bovine embryos and to test the development of several stages of donor nuclei transplanted to enucleated pronuclear recipient embryos. Pronuclear embryos were centrifuged to reveal nuclei. Nuclei were removed without penetrating the plasma membrane as membrane-bound karyoplasts, and were inserted into enucleated zygotes by electrically induced cell fusion. The highest rate of fusion (79%) occurred in Zimmerman Cell Fusion medium at 100 V for 20 to 40 microseconds with the fusion membranes oriented parallel to the electrodes. The effect of nuclear transplantation on development was tested in pronuclear embryos in which nuclei were removed and reinserted and the embryos were then transferred to sheep oviducts for 5 d. Of the intact nuclear transplant embryos recovered, 5/29 (17%) developed to morulae or blastocysts compared with 11/30 (37%) of the non-manipulated embryos. Two nuclear transplant embryos were transferred to a recipient cow, and both developed to normal offspring. When nuclei from two-, four-, or eight-cell embryos were transplanted to pronuclear recipient embryos, no development was observed.

Fatty acid profiles and sensory and carcass traits of tissues from steers and swine fed an elevated monounsaturated fat diet.

Abstract: Twelve Angus X Hereford steers were assigned to either a control high-energy diet or a test diet consisting of 20% rapeseed at the expense of 20% corn. Twelve pigs were allotted to a control diet and two test diets containing either 10 or 20% canola oil (CO). Both CO and oil in the rapeseed contained 60 to 64% oleic acid. Cattle fed rapeseed exhibited little effect from the diet due to apparent indigestibility of the rapeseed. Total saturated fatty acids decreased from 40% in adipose tissue of the control pigs to 15% in the 20% CO-fed pigs. The ratio of monounsaturated to saturated fatty acids (M/S) increased from 1.19 in adipose tissue from control pigs to 3.63 with the addition of 20% CO to the diet. In muscle, the M/S ratio increased from 1.21 in control pigs to 2.46 in the 20% CO treatment group. The percentage of the saturated fatty acids in muscle decreased from 42% in the control to 23% in the 20% CO treatment. Significant increases in "oiliness" and decreases in fat firmness were observed when increasing levels of canola oil were fed. Sensory traits, cooking loss and shear-force values of pork chops were similar among treatment groups. In conclusion, monounsaturated fatty acid content can be elevated substantially in pork without adversely influencing the quality of the meat, thus producing a product perceived to be more healthful by the consumer.

Justification of unilateral hysterectomy-ovariectomy as a model to evaluate uterine capacity in swine.

Abstract: Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P less than .01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 +/- .3 and 5.7 +/- .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 +/- .15 pigs/CL for UHO and .60 +/- .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 +/- .17 pigs/CL for UHO and .42 +/- .14 pigs/CL for control gilts at farrowing.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of heat stress on early embryonic development in the beef cow.

Abstract: Hereford and Hereford X Angus cows (n = 31) were utilized to determine the effects of heat stress on early embryonic development and survival. After acclimation to handling, cows were cannulated via the jugular vein on d 7 and assigned to either a control (C) chamber environment of 22 C, 35% relative humidity (RH) or one of two heat stress treatments. Ambient temperature was maintained at 37 C for 12 h followed by a decrease to 33 C for the remainder of the day in both treatment groups. Relative humidity was maintained at 27% in treatment 1 (TRT 1) and 38% in treatment 2 (TRT 2). On d 8 to 16, daily measurements of respiration rate (RES), rectal temperature (REC) and water intake were taken along with samples of blood, which were analyzed for hematocrit (HEM) and plasma concentration of protein (PP), progesterone (P4), estradiol-17 beta (E2), thyroxine (T4) and glucose (GLU). The uterus was recovered and flushed with saline on d 17 to recover the conceptus and uterine contents. Conceptus (if present) and corpus luteum (CL) wet weight were determined. Cows subjected to TRT 2 had increased RES and REC (P less than .01), while HEM was decreased (P less than .05) compared with C cows. Plasma T4 concentration was decreased (P less than .10) in TRT 2 compared with TRT 1 and cows, while P4 concentration were not significantly different. Corpora lutea wet weights were reduced (P less than .10) in heat-stressed cows vs C cows.(ABSTRACT TRUNCATED AT 250 WORDS)

A Proposed Mechanism of Monensin Action in Inhibiting Ruminant Bacterial Growth: Effects on Ion Flux and Protonmotive Force

Abstract: Streptococcus bovis, a Gram-positive ruminal bacterium, was unable to grow in the presence of monensin. When monensin (5 mg/liter) was added to actively growing cultures, there was an immediate decrease in growth rate, and within 3 h no further growth was observed. Glucose utilization and lactate production continued for another 8 h even though growth had ceased. Monensin caused a decrease (P less than .05) in intracellular K+, a decrease (P less than .05) in intracellular pH and an increase (P less than .05) in intracellular Na+. The net exchange of K+ for Na+ and H+ via monensin was driven by the difference in concentration of K+ and Na+ across the cell membrane. Non-treated cells maintained a 70-fold gradient (inside higher) for K+, while the Na+ gradient was only 2.7-fold (inside higher). Previous models were based on a reverse mechanism whereby monensin would drive an efflux of Na+ from ruminal bacteria, and were not supported by experimental measurements of intracellular Na+ and K+.

Biochemical analysis of bovine follicular fluid: albumin, total protein, lysosomal enzymes, ions, steroids and ascorbic acid content in relation to follicular size, rank, atresia classification and day of estrous cycle.

Abstract: To investigate some biochemical changes during bovine follicle development, ovaries were obtained from cyclic heifers (7 to 11 heifers/d on each day of the 21-d estrous cycle; N = 152). Follicular fluid from the two largest follicles from both ovaries and a pool from small follicles (N = 30/cow) were collected from each animal and analyzed for ionic, enzymatic and endocrine changes in relation to day of the estrous cycle, follicle size, rank and atretic or growing status. Follicular fluid alkaline phosphatase activity and ascorbate concentrations were highest in all follicular sizes during the earlier portion of the estrous cycle (d 1 to 12; P less than .05), then decreased to the lowest levels (d 13 to 21). As follicular size (diameter) increased lactate dehydrogenase (LDH), acid and alkaline phosphatase activity was reduced in follicular fluid (P less than .05). Alkaline phosphatase and LDH activity tended to be increased in atretic follicles (P less than .10), and was correlated with increased progesterone and androgen concentrations of follicular fluid (r = .4, P less than .05). Both albumin and total protein concentrations decreased as follicular diameter increased (P less than .05). Sodium concentrations in follicular fluid were greater in growing-antral than atretic follicles, and increased with follicular enlargement (P less than .05). Follicular potassium concentrations increased as the estrous cycle progressed (P less than .05), and tended to be elevated in atretic follicles (nonsignificant). Both Ca and Mg concentrations increased with follicular enlargement (P less than .05). Dehydroepiandrosterone and testosterone were the predominant androgens in follicular fluid (androstenedione, the lowest concentration); their concentration decreased with follicle development (P less than .05), but were quite variable. Estradiol was increased in growing follicles (P less than .01). Estrone and estradiol concentrations increased as ovulation approached, particularly in small follicles (less than or equal to 4 mm diameter). Changes of biochemical components found in follicular fluid that relate to the growth and atresia process may provide a more sensitive and accurate method to classify follicle status, and thus aid in understanding the complexity of events associated with maturation of the bovine follicle and oocyte.

Amino acid excesses for young pigs: effects of excess methionine, tryptophan, threonine or leucine.

Abstract: Five experiments involving 359 weanling (8 kg) pigs were conducted to evaluate the effects of dietary excesses of DL-methionine (Met), L-tryptophan (Trp), L-threonine (Thr) or L-leucine (Leu) when added to a 20% crude protein corn-soybean meal (C-SBM) diet. Experiments involved supplementing the basal diet with 0, .5, 1.0, 2.0 or 4.0% excesses of Met, Trp or Thr, or in the case of Leu, a 0, 1.0, 2.0, 4.0 or 6.0% excess. Levels of .5 and 1.0% excess Met did not depress feed intake (FI), weight gain (G) or gain/feed (G/F); 2.0 and 4.0% additions, however, depressed both FI and G but not G/F. Free Met in blood plasma increased linearly as dietary Met level increased, reaching over a 100-fold elevation at the highest Met level fed. Plasma Thr and serine (Ser) increased, and glycine (Gly) decreased, with each added increment of Met. With Trp, only the 4.0% addition depressed FI and G (but not G/F). None of the levels of excess Thr depressed performance. Excess Thr, in fact, tended to increase G/F. Free Thr, Ser and Gly in plasma increased linearly as graded increments of excess Thr were added to the diet. With Leu, a 6% addition depressed weight gain and food intake (but not G/F) but 1, 2 or 4% excesses were without effect. Plasma free Leu increased linearly while free isoleucine and valine decreased as graded increments of Leu were added to the diet. These results suggest that pigs can tolerate considerable excesses of Met, Trp, Thr and Leu without experiencing decreased voluntary feed intake or weight gain.(ABSTRACT TRUNCATED AT 250 WORDS)

Nutritionally-induced anestrus in gilts: metabolic and endocrine changes associated with cessation and resumption of estrous cycles.

Abstract: Two experiments determined how feed restriction and realimentation altered metabolism and ovarian function in gilts. In Exp. 1, cyclic (INTACT-R, n=6) and ovariectomized (OVEX-R, n=6) gilts were fed restricted diets (.23 kg feed.d-1) or ovariectomized (OVEX-C, n=6) gilts were fed control diets (1.81 kg.d-1). Estrous cycles stopped after 46 +/- 9 d of feed restriction. Average weight (WT), backfat thickness (BF) and concentrations of insulin (INS) were lower and free fatty acids (FFA) were greater in OVEX-R than in OVEX-C gilts. Frequency of luteinizing hormone (LH) release (peaks.6 h-1) was reduced by feed restriction (.2 +/- .2, 1.8 +/- 1.0 and 5.8 +/- .2 in INTACT-R, OVEX-R and OVEX-C gilts, respectively). Patterns of secretion of LH and follicle stimulating hormone (FSH) after gonadotropin releasing hormone (GnRH) or estradiol benzoate were not altered by feed restriction. Feed intake was then increased in INTACT-R and OVEX-R gilts beginning on d 80 and 82, respectively. Resumption of estrous cycles in INTACT-R gilts occurred on d 116.0 +/- 4.0 and was preceded by a significant increase in WT, but not BF, and a linear increase in concentration and frequency of release of LH. Increasing feed intake in OVEX-R gilts increased WT and frequency of LH release, while FFA decreased and INS increased to concentrations not different from those of OVEX-C gilts. The hypothesis that nutritionally-induced anestrus resulted from decreased activity of the hypothalamic pulse-generator was evaluated in Exp. 2 by providing 144 hourly pulses (iv) of saline (n=3), GnRH (n=3) or LH (n=4) to nutritionally-anestrous gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of in situ nitrogen and fiber digestion and bacterial nitrogen contamination of hay crop forages preserved at different dry matter percentages.

Abstract: Alfalfa, red clover, orchardgrass and timothy were harvested in the vegetative stage, wilted and stored as hay, or ensiled in small batch silos (20 kg) at 60, 40 or 20% (direct cut) dry matter and were analyzed for compositional differences. A ruminally cannulated lactating cow, consuming 50% of her dry matter intake from hay crop silage, was used to measure in situ dry matter, N, neutral detergent fiber and acid detergent fiber disappearance. Diaminopimelic acid was used as a bacterial marker to correct for bacterial N contamination for in situ residual N. Fibrous components tended to become concentrated as percent dry matter at preservation decreased, presumably associated with leaching of water solubles during storage. For most forages, as dry matter percentage of preservation decreased, water soluble dry matter and N increased, with a concomitant increase of ruminally nondigested dry matter. Specific trends in coefficients of digestion associated with forage type or preservation dry matter percentage were not observed for dry matter, N, neutral detergent fiber or acid detergent fiber. Correction for contamination by bacterial N decreased lag time in digestion and altered rates of N digestion compared with noncorrected rates. Linear and quadratic bacterial N contamination profiles were observed with time of ruminal incubation. Rate of digestion of N was highly correlated with fibrous component concentration, and to a lesser extent to rate of neutral and acid detergent fiber digestion. Dry matter percentage at preservation had a variable effect on ruminal digestion rate of dry matter and N, which varied with forage type and had no effect on neutral detergent and acid detergent fiber digestion rates. Correction for bacterial N contamination should be considered when establishing N digestion rates for forage by the in situ technique.

Effect of dietary electrolyte balance on growth and acid-base status in swine.

Abstract: The effect of dietary electrolyte balance on pigs fed lysine- or tryptophan-adequate or tryptophan-deficient diets was investigated in four experiments using 8- to 12-wk-old pigs. Electrolyte balance, expressed as Na+K-Cl in meq/kg of diet, was varied by altering dietary levels of Na and Cl while holding all other minerals constant. In two experiments in which the basal diet contained a balance of 135 meq/kg, simple lysine or tryptophan deficiences caused depressed growth, feed intake and efficiency of feed utilization, but none of these responses was altered by dietary supplementation with NaHCO3. In one experiment in which the electrolyte balance of the basal diet was 61 meq/kg and in which both lysine and tryptophan were limiting. NaHCO3 supplementation significantly increased growth and feed intake. This did not occur if the diet was also supplemented with tryptophan. A final experiment was conducted to determine the response of pigs to a range of electrolyte balance (-85 to 341 meq/kg) in a practical corn-soy diet containing adequate levels of all amino acids. Growth and feed intake appeared to be maximal for balances of 0 to 341 meq/kg Na+K-Cl, but were decreased at -85 meq/kg (P less than .05). Acid-base balance was adversely affected at 0 meq/kg. The results suggest that the response of lysine-deficient pigs to sodium bicarbonate is dependent upon the electrolyte balance of the diet, and also is influenced by other dietary amino acids.

Effect of the repartitioning agent cimaterol on growth, carcass and skeletal muscle characteristics in lambs.

Abstract: Ten crossbred (Suffolk X Rambouillet) whether lambs were randomly assigned to receive 0 or 10 ppm cimaterol (CIM) in a completely mixed high-concentrate diet for 8 wk. Total weight gain and feed efficiency were improved 29% (P less than .05) and 14%, respectively, in the CIM-fed group. CIM also improved (P less than .01) dressing percent by 4.9 percentage points and improved yield grade by one grade. CIM increased longissimus muscle (LD) area 38% (P less than .01) and the yield of four lean cuts 28% (P less than .01). No difference was found in the proportion of type I (slow-contracting, oxidative) and type II (fast-contracting, mixed glycolytic/oxidative) fibers in LD and semitendinosus (ST) muscles between control and CIM groups, indicating no change in fiber type. The cross-sectional area of type II fibers in LD and ST muscles of the CIM group was 2,081 and 1,951 micron 2 as compared with 1,391 and 1,296 micron2 of the control group, respectively. The increase was approximately 50% (P less than .01). No difference was found in cross-sectional area of type I fibers, indicating that the increase of muscle mass was due to hypertrophy of type II fibers only. DNA concentration (micrograms/g wet muscle or microgram/g protein) of CIM muscle was much lower (P less than .01) than that of control muscle, suggesting that the protein accretion in muscle was accomplished without additional incorporation of nuclei from satellite cells.

Biochemical and physiological indicators of mineral status in animals: copper, cobalt and zinc.

Abstract: The value of estimates of trace element requirements or of data on tissue trace element content for identifying and controlling trace element-related disorders is often limited by inadequate data on the relationships of such criteria to physiological performance. Investigations of metabolic events initiating early pathological responses to deficiency are beginning to suggest more effective indicators of physiologically relevant abnormalities in trace element intake or status. Progress in studies of metabolic responses to deficiencies of copper, cobalt and zinc is reviewed.

A model for assessing the impact of behavioral stress on domestic animals.

Abstract: Animal scientists need a reliable measure of behavioral stress in domestic animals if they are going to be able to assess the stress of various management practices and to answer public concern about the well-being of animals used in agriculture. Popular measures of stress, alterations in behavior or changes in hormone secretion, are not adequate because of a failure to establish any direct correlation between changes in these characteristics with adverse effects on animal well-being. Further complicating the use of these indicators of stress is the variation in their pattern of response to different kinds of stressors. Even the same stressor can elicit divergent responses in different animals because of inter-animal variation in the stress response. To address these problems, a model of animal stress is discussed and tested. From this model it is proposed that the best indicator of an animal suffering from stress is the development of a pre-pathological state; i.e., a stress-related change in biological function that threatens the animal's well-being. Examples of such pre-pathological states would be a suppression of the immune system, the loss of reproductive events critical for normal reproduction, or the development of behaviors that would lead to such undesirable acts as tail-biting or excessive fighting. Although determining the existence of such pre-pathological states is not convenient, their existence is currently the only defensible indicator of an animal suffering from behavioral stress.

Ionic strength and myofibrillar protein solubilization.

Abstract: Myofibrils from bovine longissimus muscle were obtained at 2 h postmortem and incubated in .10 to .35 M ionic strength buffers under various conditions in vitro. Increasing ionic strength or increasing the incubation time from 1 to 72 h decreased the turbidity of suspensions of myofibrils and increased myofibrillar solubilization (P less than .01 for both measures). The use of KCl or NaCl to elevate ionic strength gave essentially identical results, but lactate generally was ineffective in changing either the percentage myofibrillar solubilization or the turbidity of suspensions of myofibrils. Gel electrophoresis under denaturing conditions indicated that KCl was more effective than NaCl in causing the release of C-protein from myofibrils, and both salts were quite effective in dissociating M-protein, actin, troponin-T, tropomyosin, myosin light chain-3 and a 30,000-dalton molecular weight protein from myofilaments. Small increases in alpha-actinin also were observed, especially in samples incubated for 72 h. Substantially more myosin light chain-3, tropomyosin (or paratropomyosin) and troponin-T, and less actin and the 30,000-dalton protein, were released in samples incubated at pH 5.5 than at pH 7.0 (P less than .05). Electron micrographs indicated loss of thick filament ultrastructure after incubation for 24 h in either .1 or .3 M ionic strength, but the Z-lines were largely unaffected. In samples that had first been incubated with trypsin for 10 min, the Z-lines were virtually indistinguishable at .1 M ionic strength, and absolutely no myofibrillar structures could be discerned in samples incubated in .3 M ionic strength buffer.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term thrice-daily milking on mammary enzyme activity, cell population and milk yield in the goat.

Abstract: In two separate experiments, lactating goats were milked unilaterally thrice daily instead of twice daily for periods of 13 and 37 wk, starting at 2 to 5 wk after parturition. The other gland was milked twice daily throughout. In both experiments thrice-daily milking increased milk yield significantly. In the first experiment, after 37 wk the amounts of RNA and DNA, rate of cell proliferation and activities of several enzymes per cell were greater in the thrice-milked gland (P less than .05). In the second experiment, after 9 or 10 d of thrice-daily milking the activities of several key mammary enzymes per cell measured in biopsy samples had increased in the thrice-milked but not the twice-milked gland. After 13 wk of thrice-daily milking, the DNA content of the glands and the activity per cell of the key enzymes was the same in both glands, showing that the synthetic capacity of the gland was being used more effectively in the treated gland. These results indicate that several mechanisms contributed to the increased milk yield induced by thrice-daily milking.

B-vitamin supplementation of diets for feedlot calves.

Abstract: B-vitamin supplementation of diets for 144 shipping-stressed crossbred calves (116 kg) at levels up to 10 times that recommended for growing pigs did not influence (P greater than .20) weight gain or feed conversion during a 56-d receiving trial. However, vitamin supplementation tended (P less than .10) to reduce morbidity. In a second trial, supplemental B-vitamins had no effect (P greater than .20) on efficiency of microbial growth or site and extent of digestion of organic matter, acid detergent fiber and N. Supplemental dietary riboflavin, niacin, folic acid, B12 and ascorbic acid were largely metabolized [degraded and (or) absorbed] anterior to the small intestine, with escape values of 1, 3, 10 and 0% of added vitamins, respectively, while dietary B6 and biotin largely escaped the rumen. Thiamine and pantothenic acid were intermediate in ruminal escape (52 and 22%, respectively). Small intestinal absorption of thiamine, niacin, riboflavin, B6 and B12 averaged 75, 79, 25, 79 and 48%, respectively. Coefficients for ruminal escape and microbial synthesis for each B-vitamin were calculated using the slope-ratio technique. Measured flows for thiamine, riboflavin and B12 in a third experiment were similar to flows predicted from escape and synthesis equations, though flow of niacin and B6 were under-predicted by 37 and 44%, respectively. Results are interpreted to indicate that intestinal B-vitamin supply can be predicted based on dietary composition and intake.

Evaluation of corn fiber, cottonseed hulls, oat hulls and soybean hulls as roughage sources for ruminants.

Abstract: An in situ trial (randomized complete block design) using cows, and a site and extent of digestion trial (Latin square design) using sheep were conducted to study the potential of corn fiber (CF), cottonseed hulls (CSH), oat hulls (OH) and soybean hulls (SH) as roughage sources for ruminants. Two feedlot trials with steers and one with lambs (completely randomized design with factorial arrangements of treatments) were conducted to study the potential of CF and SH as energy supplements relative to corn. In situ rate of ruminal dry matter (DM) disappearance (3 to 36 h) and extent of DM disappearance (36 h) indicated that CF and SH were more fermentable in the rumen compared with OH or CSH, with SH being the most fermentable. Total tract digestibilities of DM, organic matter (OM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were above 70% for sheep fed CF and SH diets, and were 50% or less for sheep fed OH and CSH diets. A ranking of by-products in terms of nutritive value followed the trend: CF greater than SH greater than OH greater than CSH. Lamb feedlot trial data showed that CF was of similar nutritive value to corn and of higher nutritive value than SH at the 50% level of supplementation. Corn-fed lambs responded better than CF- or SH-fed lambs at the 70% level of supplementation. Data from steer feedlot trials showed that CF was of similar quality to corn and of higher quality than SH. Dramatic differences exist in by-product feed utilization by ruminants. All by-products tested appeared to have some usefulness as dietary components.

Effect of level of beef cow milk production on pre- and postweaning calf growth.

Abstract: Three groups of beef cows that were similar in growth and mature size, but different in genetic potential for level of milk provided to their calves, were studied. A procedure for fitting grafted polynomials based on calf suckling data was used to estimate the total amount of milk produced by each cow during 205-d lactations. Estimated 205-d milk production of the high milk group exceeded that of the medium and low milk groups by 186 and 561 kg, respectively. Differences in milk production of the three groups tended to increase as dams got older. The pooled, within milk-group correlation between calf gain to 205 d and milk intake was .60. Calves suckling dams with low milk production relied earlier and to a greater extent on alternative food sources of lower nutritional value than milk. Calves suckling high milk-group dams had 16.9 kg greater 205-d weaning weight than those suckling low milk-group dams, solely because of differences in maternal environment. Calves from the high milk group maintained 63% of the advantage over those in the low milk group in 205-d weight through a fairly rapid postweaning growth period to slaughter.

Metabolic Utilization of Energy and Maintenance Requirements in Lactating Sows

Abstract: Metabolizable energy (ME), heat production (measured by indirect calorimetry in respiration chambers), milk energy output and body energy mobilization were measured in 20 gilts (10 replicates of two littermates) during a 21-d lactation. Two energy levels were used: 14.2 and 10.4 Mcal ME X d-1 X sow-1 in the high energy (HE) and low energy (LE) groups, respectively. The daily supply of other nutrients in the diets was identical in both treatments. Measurements of metabolic rate and energy balance of the litters were carried out. These data were used to estimate the maintenance requirements of the sows (MEm) and the efficiencies of utilization of energy of food (kl) and body reserves (krl) for energy production in milk. Nitrogen balance of the sows was also determined. Energy mobilization was increased by energy restriction (-5.35 vs -2.04 Mcal X d-1 X sow-1 for HE and LE gilts, respectively) and by the increment of milk production with the advancement of lactation. Energy restriction (LE vs HE gilts) resulted in increased weight loss consisting mainly of fat tissue depletion. Muscle depletion represented a rather large proportion of weight loss, even in sows fed the high energy level. Maintenance requirements amounted to 109 kcal ME X kg weight-.75 X d-1. The estimations for kl and krl were 72 and 88%, respectively. These results show that the overall efficiency of energy storage during pregnancy and its mobilization during lactation (68.6 to 70.9%) is similar to that of direct utilization of ME during lactation.

Activity of fiber-degrading microorganisms in the pig large intestine.

Abstract: The large intestine is comparable to the rumen fermentation in many aspects; however, it is understood less well. Fiber in the form of cellulose and hemicellulose is one of the major substrates fermented in the large intestine. Various studies suggest that the pig can utilize fiber for growth, and up to 30% of its maintenance energy may be derived from volatile fatty acids produced in the large intestine. The total number of microorganisms in the pig large intestine do not change when a high fiber diet such as 50 or 80% alfalfa meal is fed. However, the fiber-degrading organisms increase and obviously replace others. The increase in fibrolytic bacteria normally coincides with an increase in enzyme activity (cellulase and xylanase), indicating that diet can be used to enhance fibrolytic activity. This is true for growing pigs and adult animals. The cellulolytic organisms in the pig, Bacteroides succinogenes and Ruminococcus flavefaciens, are similar to those in the rumen and are present at comparable numbers. This partly explains why adult pigs can maintain themselves by merely grazing on forage in pastures. Assuming other conditions are met, there is a significant potential for fiber degradation in the pig large intestine. Whether various genotypes such as the genetically selected obese and lean pigs have different abilities to degrade fiber is unknown. More work is required to understand the interaction of the fibrolytic organisms with the other organisms present in the large intestine, similar to that which has been done in the rumen, as well as the microbe-host interaction.