Fetal and neonatal programming of postnatal growth and feed efficiency in swine

Maternal undernutrition or overnutrition during pregnancy alters organ structure, impairs prenatal and neonatal growth and development, and reduces feed efficiency for lean tissue gains in pigs. These adverse effects may be carried over to the next generation or beyond. This phenomenon of the transgenerational impacts is known as fetal programming, which is mediated by stable and heritable alterations of gene expression through covalent modifications of DNA and histones without changes in DNA sequences(namely, epigenetics). The mechanisms responsible for the epigenetic regulation of protein expression and functions include chromatin remodeling; DNA methylation(occurring at the 5′-position of cytosine residues within CpG dinucleotides); and histone modifications(acetylation, methylation, phosphorylation, and ubiquitination). Like maternal malnutrition, undernutrition during the neonatal period also reduces growth performance and feed efficiency(weight gain:feed intake; also known as weightgain efficiency) in postweaning pigs by 5–10%, thereby increasing the days necessary to reach the market bodyweight. Supplementing functional amino acids(e.g., arginine and glutamine) and vitamins(e.g., folate) play a key role in activating the mammalian target of rapamycin signaling and regulating the provision of methyl donors for DNA and protein methylation. Therefore, these nutrients are beneficial for the dietary treatment of metabolic disorders in offspring with intrauterine growth restriction or neonatal malnutrition. The mechanism-based strategies hold great promise for the improvement of the efficiency of pork production and the sustainability of the global swine industry.     

Characterization of biological types of cattle (cycle III). IV. Postweaning growth and feed efficiency

Postweaning growth and feed efficiency data were analyzed on 769 F1 crossbred steers out of Angus and Hereford dams and sired by Pinzgauer, Tarentaise, Brahman, Sahiwal, Hereford and Angus sires. Breed groups were fed in replicated pens and slaughtered serially at three different dates in each of 2 yr. Quadratic regressions of pen mean weight on days fed and of cumulative metabolizable energy consumption (ME) on days fed were used to estimate gain, ME consumption and efficiency (Mcal ME/kg gain) over time (0 to 213 d on feed) and weight (250 to 470 kg) intervals, and from d 0 to a small degree of marbling (corresponds to USDA low Choice quality grade) and an 18.9% fat trim end point. Brahman-sired crosses were significantly heavier at weaning than all other breed groups. However, during the postweaning period, which included winter months, and while being fed a moderately high concentrate diet, average daily gain of Brahman-sired crosses tended to be less than Angus- or Hereford-, Tarentaise- and Pinzgauer-sired crosses and that of Sahiwal-sired crosses was significantly less than all other breed groups. Differences among breed groups were not significant for feed efficiency in the time constant interval from 0 to 213 d. In a weight interval from 250 to 470 kg, only Sahiwal-sired crosses differed significantly, requiring more Mcal ME/kg gain than other breed groups. Hereford-Angus crosses were more efficient than all other breed groups (P less than .05) to the marbling end point and to the 18.9% fat trim end point, primarily because of fewer days on feed and thus less net energy required for maintenance. Pinzgauer-sired crosses were significantly more efficient than Tarentaise-, Brahman- and Sahiwal-sired crosses to the marbling end point (P less than .05).     

Chemical composition, digestibility, and voluntary feed intake of mango residues by sheep

The chemical composition, digestibility, and voluntary feed intake by sheep of mango by-products were studied in an experiment with five dietary treatments consisting of mango peels and seed kernels, offered individually or together with urea block and a control. The mango residues were offered with rice straw and the control diet was straw only. Five groups of five male sheep of Djallonké type, 12–18 months old and weighing on average 18.6 kg were allocated randomly to the diets to assess the voluntary feed intake. Apparent digestibility of the same diets was measured using four sheep per diet. The mango residues were low in crude protein, 67 and 70 g/kg dry matter for the peels and the seed kernels, respectively. The content of neutral detergent fiber varied from 306 to 388 g/kg dry matter (DM) for the kernel and the peels, respectively. The kernel had relatively high level of fat (105 g/kg DM) and tannins (29 and 40 g/kg DM of hydrolysable and total tannins, respectively). The highest intake was observed with the diet containing both residues and urea block (741 g/day). The intake of kernels was lower in all diets when offered with the peels than when offered with rice straw alone. Apparent digestibility of the diets containing mango residues was 0.60–0.65. The peels and kernels had high digestibility coefficients (0.74 and 0.70, respectively). Based on the results above, it can be concluded that it would be interesting to test the residues in a growth experiment.     

Effects of prenatal testosterone treatment and postnatal steroid implantation on growth performance and carcass traits of heifers and steers

Two experiments were conducted to evaluate the effect of prenatal testosterone treatment in combination with postnatal steroid implantation (Exp. 1) and to assess the effect of time of prenatal testosterone treatment in conjunction with postnatal steroid implantation (Exp. 2) on animal performance and carcass characteristics. In Exp. 1, seventy-six pregnant cows were assigned randomly to a control group or implanted with testosterone propionate (TP) silastic implants between d 40 and 80 of gestation. Half the heifer calves were selected randomly to be implanted with 200 mg TP plus 20 mg estradiol benzoate (EB); the other half of the steer calves were implanted with 200 mg progesterone plus 20 mg EB on d 1 and 85 of the feedlot trial. Daily gain of heifers was increased 10.4% (P less than .08) due to prenatal testosterone treatment (P) and 16.4% (P less than .05) by postnatal steroid implantation (I). Feed efficiency was 12.9% greater (P less than .05) due to P and 9.5% greater (P less than .05) due to I. Prenatal testosterone treatment decreased (P less than .05) kidney, pelvic and heart fat and final yield grade but increased (P less than .05) ribeye area of heifers. Heifers had greater (P less than .07) liver weights per unit of carcass weight due to P. In Exp. 2, one hundred seventy-four pregnant cows were assigned randomly to a control group or implanted with TP silastic implants on d 42, 63, 84 or 105 of gestation. Half the heifer and steer calves were selected randomly to be implanted on d 1 and 112 of the feedlot trial. Time of P caused a quadratic effect (P less than .08) on birth weight of heifers. There was a quadratic effect (P less than .05) of time of P on daily gain and final weight per day of age of heifers. Feed efficiency of heifers was improved (P less than .05) due to P. Postnatal steroid implantation increased (P less than .05) daily gain and feed efficiency of heifers by 9.6% and 8.6%, respectively. No changes were observed in growth performance of steers due to P. Results from these two trials suggest that the combination of prenatal testosterone treatment and postnatal testosterone and estradiol implantation produced an additive improvement of daily gain, feed efficiency and carcass merit of heifers.     

Genetic and physiological aspects of growth, body composition and feed efficiency in mice: a review

A review is presented of the genetic and physiological aspects of growth, body composition and feed efficiency in mice. The genetic parameters considered are: nature and extent of within and between-line genetic variation for body weight and growth rate; direct and correlated responses to selection for body weight, weight gain, feed intake and feed efficiency; direct genetic effects of the offspring (gO); maternal genetic effects (gM); heterosis in the offspring (hO); maternal heterosis (hM), and recombination effects in the offspring (rO). The physiological parameters considered are energy requirements for maintenance and growth. The role of thermoregulatory thermogenesis in relation to the partitioning of metabolizable energy between maintenance and growth requirements of large and small mice is emphasized. The relationship of feed efficiency with other traits is reviewed at length.     

Feed efficiency, growth rates, body composition, milk production and milk composition of Targhee sheep selected for increased weaning weight

Lactation and growth of three contemporary lines of grade Targhee sheep developed from the same genetic base were characterized by three experiments performed over a period of 2 yr. Two lines (HW and DH) had been selected for 120-d weaning weights for 24 yr prior to beginning these experiments. A third line (C) was a randomly selected control. Year I experiment contrasted 10 DH with 7 C ram lambs fed to 58 kg. Year II experiments utilized 9 C, 14 DH and 10 HW ram lambs and 11 ewes suckling twins from each line. All Year II ram lambs were born and weaned as twins, then fed to 50 kg. Mature DH and HW ewes were heavier (P less than .05) than C ewes (65.2 and 68.8 vs 54.9 kg), and the DH and HW lambs grew faster than C lambs both before (P less than .05) and after weaning (P less than .05). While both DH and HW lambs drank more milk (2,419 and 2,368 vs 2,059 g X d-1 X pair-1; P less than .10) only HW ewes showed a trend towards greater potential milk production than controls (HW = 2,774 vs C = 2,155 g X d-1 X ewe-1 P less than .12). The HW lambs tended to be leaner than C lambs (P less than .05), but DH lambs did not differ from either line. Lambs from DH and HW lines required less post-weaning feed (121.9 and 129.3 vs 152.0 kg P less than .05) and exhibited 17 and 16% greater weight per day of age at 50 kg than controls (P less than .05). The DH line displayed lower feed: gain ratios than controls in both post-weaning trials (6.68 vs 7.30 to 58 kg; 5.83 vs 6.24 at 50 kg; P = .06).     

摄食水平对泥鳅生长、饲料利用率和体成分的影响

比较不同摄食水平对泥鳅生长、饲料利用率及体生化成分的影响,以期为泥鳅投饵策略的制定提供基础研究资料。将180尾平均体重为(4.81±0.68)g的供试泥鳅(Misgurnus anguillcaudatus)随机分为A、B和C三个不同的日摄食水平处理组,每组3个重复,每个重复20尾泥鳅,三个处理组分别按泥鳅体重的3%、4%和5%投喂供试日粮,研究日投饵量对泥鳅生长、饲料转化率及体生化成分的影响。结果表明:①随着摄食水平的增加,泥鳅的末重、增重率、日增重和特定生长率呈递增的趋势,C组显著高于A组和B组(P<0.05),B组显著高于A组(P<0.05);②饲料转化率随摄食水平的增加呈先增后减的趋势,B组显著高于A组和C组(P<0.05),C组显著高于A组(P<0.05);③泥鳅的肌肉、全鱼中水分和灰分含量随着摄食水平的增加而减少,粗蛋白和粗脂肪含量随着摄食水平的增加而增加;其中肌肉中灰分含量B组和C组显著高于A组(P<0.05),A组肌肉中粗脂肪含量显著高于B组和C组(P<0.05),其他各组间无显著性差异(P>0.05)。泥鳅的生长—摄食为线性增长;在4%摄食水平下饲料转化效率最高。     

Effect of selection for growth on normal and reduced protein diets on weight gain, feed intake, feed efficiency and body composition in mice

Mice selected for weight gain from 3 to 9 weeks of age on a normal (N) protein diet containing 19.3% protein and a reduced (R) protein diet with 5.1% protein were reared on both diets in generations 7 and 9. The lines NH, NC, NL, RH, RC and RL (H, high; C, control; L, low) were tested for weight gain on diet N and R and for feed intake and feed efficiency on diet N in generation 7. In generation 9, the lines were tested for body composition traits (fat, protein and water percentage) at 3, 6, 9 and 12 weeks of age on both diets. A significant (p < 0.0001) genotype × environment interaction for growth rate was observed in generation 7. Weight gain at both the protein levels was best improved by selection at the protein level itself. Furthermore, the ranking of the lines on diet N was similar for weight gain, feed intake and feed efficiency. In generation 9 at 9 weeks of age, the ranking of the lines for fat percentage was equal to the ranking for weight gain in generation 7 on both test‐diets. The association between weight gain and protein or water percentage was less pronounced, particularly on diet R. These results suggest that the largest genetic improvement in growth rate is obtained when the protein content of the feed is the same in selection and production. However, when selection is carried out in one environment while the animals have to perform under conditions with varying nutrient protein contents, selection in an inferior environment may be advantageous.     

Lactation efficiency as a result of body composition dynamics and feed intake in sows

Through genetic selection and improvement of environment, litter size of sows increases. Increased energy requirement during lactation, increases the risk of excessive mobilization from body stores, with detrimental effects on reproductive performance. Feed intake capacity tends to decrease due to selection towards leaner pigs with a lower feed conversion ratio. However, to facilitate sows to wean large litters extra feed intake, or even better, a higher feed efficiency during lactation would be favourable. The objective of the present study was to describe the dynamics of body composition of sows and piglets during lactation, and to relate these traits to a newly introduced trait called “lactation efficiency”. Energy metabolism of lactating sows was described, based on on-farm observations of weight and backfat of sows before parturition and at weaning, weight of piglets at birth and at weaning and feed intake of sows during lactation. “Lactation efficiency” was defined as energy efficiency of sows, and calculated for individual sows at two different farms. The average lactation efficiency was 68% and 65% for both farms; meaning that 68 and 65% of the metabolisable energy through feed intake or mobilization from body stores, above maintenance of the sow (input), was used for piglet growth and piglet maintenance (output). The association between lactation efficiency and other reproductive traits was studied by estimating the correlations within farms. Sows with a higher lactation efficiency showed lower feed intake (r = − 0.27 and r = − 0.35 for both farms respectively) and smaller fat losses (r = − 0.34 and r = − 0.29, respectively). The energy output of efficient sows was slightly higher (r = 0.23 and r = 0.30). The more efficient sows were the better mothers, as mortality of their piglets was lower (r = − 0.12 and r = − 0.16), piglet growth rate was higher (r = 0.16 and r = 0.23), and at weaning their litters were less variable (r = − 0.08; only available at one farm). Results were remarkably similar for the two farms, despite different feeding strategies. Extra input, by means of feed intake or mobilization from body stores generated extra output by means of litter weight at weaning. This experiment demonstrated that an accurate recording of energy metabolism and relevant reproduction traits with little intervention is possible on commercial farms.     

Effects of sire growth potential, growing-finishing strategy, and time on feed on performance, composition, and efficiency of steers.

Beef production systems that increase use of unharvested forages and use animals with greater potential for gain affect age and size of animals placed on a finishing regimen. This experiment was conducted to evaluate effects of genetic potential for gain, age at the start of a finishing period, and time on feed on composition, quantity, and quality of beef produced and efficiency of production during finishing. Crossbred cows were bred by AI to Charolais or Line 1 Hereford bulls that represented potentially high (HG) or moderate growth (MG) rates, respectively, to produce spring- or fall-born calves. Steer calves from these matings were placed on an individually fed finishing diet at three ages (A). Spring-born steers were started at 6 or 18 mo of age (A6 and A18), and fall-born steers were started at 12 mo of age (A12). Slaughter times (T) were at 0, 90, 180, and 270 d for A6; 68, 136, and 204 d for A12; and 0, 45, 90, and 135 d for A18. Data collected on each animal included feed intake, growth, chemical composition of the complete body and carcass, and quantitative and qualitative assessment of the meat produced. Four steers of each sire group were slaughtered in each of the 11 A-T treatment groups, and the experiment was repeated for 2 yr in the A12 groups and 3 yr in the A6 and A18 groups (n = 237). Steers sired by HG bulls were larger and produced larger carcasses and more carcass protein than MG-sired steers (S, P < .05 or .01). Steers sired by MG bulls were fatter, had higher quality grades, and accumulated fat at a faster rate than HG-sired steers, and this effect was greater in older steers (G and GA, P < .05 or .01). Sire growth potential did not affect gain, intake, live weight efficiency, tenderness, or taste panel scores (P > .2). Steers sired by HG bulls were more efficient at producing carcass weight and carcass protein at A12 and A18 than were MG-sired steers. At the end of the finishing period, older (A18), HG-sired steers were too large with insufficient fat by current industry standards, and younger (A6), MG-sired steers were too small. Our conclusions are that both HG- and MG-sired steers can produce acceptable carcasses for current market standards with comparable efficiencies of live-weight gain, but the growing and finishing strategy must be adapted to the genotype.     

Performance,carcass characteristics and chemical composition of beef affected by lupine seed,rapeseed meal and soybean meal

To test the effects of different protein sources and levels on performance, carcass characteristics and beef chemical composition, concentrates with three protein sources [Lupine seed (L), Rapeseed meal (R) and Soybean meal (S)] and two protein levels [‘normal protein’ (NP) or ‘high protein’ (HP)] were fed to 36 Simmental calves. Calves initially weighed 276 ± 3.9 kg and averaged 6 months of age and were randomly allocated to the six treatments. Maize silage was offered ad libitum and supplemented with increasing amounts of concentrates (wheat, maize grain, protein sources, vitamin–mineral mix). Normal protein and HP diets were formulated to contain 12.4% and 14.0% crude protein (CP) dry matter (DM) respectively. At the end of the fattening period of 278 days, the final live weight averaged 683 ± 14.7 kg. Neither level of protein nor its interaction with protein sources had any effects on most of the traits studied. Feeding the R diet significantly increased final weight, average daily gain (ADG), DM intake and CP intake in relation to the L diet; no differences were observed between the L and S diets for these measures. No differences were observed between the R and S groups in final weight or ADG, but the calves fed the R diet consumed more DM and CP than the calves fed the S diet. Bulls fed R diet had higher carcass weight and dressing percentage than the L groups, and no significant differences were detected between the S and L groups. Chemical composition of the Musculus longissimus dorsi was not significantly affected by source of protein. Also, the major saturated fatty acid (SFA) (C16:0 and C18:0) did not significantly differ among the three treatments. Samples from R group had significantly higher proportions of C16:1 t9, C18:1 c11, C18:2 c9 t11, C18:3 c9, 12, 15 and ΣC18:1 t fatty acids in relation to L and S groups. Although polyunsaturated fatty acid/SFA ratio was similar for the three dietary groups, n‐6/n‐3 ratio and Σn‐3 fatty acids content were significantly greater for bulls fed R diet in relation to those fed L and S diets.     

Influence of alpha-ketoisocaproate on lamb growth, feed conversion, and carcass composition

Four experiments were conducted to determine whether leucine's alpha-ketoacid, alpha-ketoisocaproate (KIC), would influence lamb growth, feed conversion, and carcass composition. In the first experiment, lambs were injected intraperitoneally with 3.5 g of Na-KIC per day. In the second experiment, KIC unprotected from rumen degradation was fed at a rate of 15 g per animal daily. In a third experiment, KIC, leucine, and isovalerate (IVA), protected from rumen degradation, were fed to growing lambs at a rate of 1 g per animal per day. Finally, a fourth experiment was conducted in which ruminally protected KIC was fed to growing lambs at a rate of 1 g per animal per day. Ketoisocaproate tended to increase ADG and decrease fat deposition in all four experiments. Ketoisocaproate increased ADG by 11 (P less than .09), 10 (P less than .05), 9, and 13% in 1 through 4, respectively, and feed efficiency improved 5, 9 (P less than .02), 5, and 5%, respectively. Fat thickness over the 12th rib decreased 28 (P less than .06), 11, 17 (P less than .04), and 5% in Exp. 1 through 4, and the perirenal fat depot also decreased 13, 5, 18, and 3%, respectively. In contrast, neither ruminally protected leucine nor IVA affected the growth of young lambs. Together these studies indicate that administration of KIC to growing lambs can increase weight gain and muscle growth while decreasing fat deposition.     

Effect of an implant of trenbolone acetate and estradiol on growth, feed efficiency, and carcass composition of Holstein and beef steers.

The effects of an implant of 140 mg of trenbolone acetate and 28 mg of estradiol (TBA + E2) on performance and carcass composition were evaluated with 72 individually fed steers. Holstein (n = 24), Angus (n = 24), and Angus x Simmental (n = 24) steer calves were allocated by breed and implant treatment to either an individual feeding pen (n = 36) or an electronic feeding door in a group pen (three pens with 12 animals per pen). Intake and refusal of the 85% concentrate diet were recorded daily. Animals were slaughtered when ultrasonic attenuation values of the longissimus muscle at the 12th rib reached .55, which is correlated with low Choice marbling. At slaughter, complete carcass measurements were taken and the right side of each carcass was separated into boneless wholesale cuts. Implanting with TBA + E2 improved (P less than .01) daily gain and feed efficiency. Daily gain was increased 17, 26, and 21% in Holstein, Angus, and crossbred steers, respectively. The implant increased overall daily protein and fat accretion 23%. Carcass conformation and dressing percentage were not affected (P greater than .05) by TBA + E2 treatment. Implantation with TBA + E2 had little effect on yield of wholesale boneless cuts when expressed as a percentage of carcass weight but increased absolute weight as a small degree of marbling by 6 to 40 kg.     

Test duration for growth, feed intake, and feed efficiency in beef cattle using the GrowSafe System

This study was conducted to determine the optimum test duration and the effect of missing data on accuracy of measuring feed efficiency and its 4 related traits ADG, DMI, feed conversion ratio, and residual feed intake in beef cattle using data from 456 steers with 5,397 weekly averaged feed intakes and BW repeated measurements taken over 91 d. Data were collected using the GrowSafe System at the University of Alberta Kinsella Research Station. The changes and relative changes in phenotypic residual variances and correlations (Pearson and Spearman) among data from shortened test durations (7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, or 84 d) and a 91-d test were used to determine the optimum test duration for the 4 traits. The traits were fitted to a mixed model with repeated measures using SAS. Test durations for ADG, DMI, feed conversion ratio, and residual feed intake could be shortened to 63, 35, 42, and 63 d, respectively, without significantly reducing the accuracy of the tests when BW was measured weekly. The accuracy of the test was not compromised when up to 30% of the records were randomly removed after the first 35 d on test. These results have valuable and practical implications for performance and feed efficiency testing in beef cattle.     

Nitrogen efficiency of dairy cows as affected by diet and milk yield

The aim of this study, which was part of the EU-financed project Life Ammonia, was to evaluate the effects of dietary components and milk production on nitrogen efficiency of dairy cows. The study included examining the effects of decreased crude protein (CP) concentration in a grass-clover silage based diet and results of mixing whole-crop barley silage (WCBS) with grass-clover silage in the diet, on feed intake, milk production and nitrogen efficiency. Rations were formulated and milk production data were registered individually each month for 42 cows of the Swedish Red Cattle breed during four indoor periods from 1999 to 2003. The range in nitrogen efficiency by the cows, 11 to 398 days in milk, was 18 to 40%, when fed a diet containing 135 to 184 g CP/kg DM, 44 to 56% of NDF as rumen degradable fibre (RDF) and milking 13 to 57 kg of ECM daily. The average CP concentration of the diet, containing mainly grass-clover silage and concentrate, was decreased from 168 g/kg DM (170 g in early lactation) in the control treatment period to 160 g/kg DM (163 g in early lactation) during the following treatment period. The CP concentration was 170 g/kg DM (171 g in early lactation) during the third treatment period, when the grass-clover silage was fed in a mixture with WCBS. Using the whole data set (n = 284 for primiparous, n = 440 for multiparous cows based on measurements each month) resulted in models, in which total DM intake, ECM yield, dietary CP concentration and RDF were the most important factors affecting nitrogen utilisation of primiparous and multiparous cows. Increases in both average DM intake and milk yield by multiparous cows and no changes in average intake and milk yield by primiparous cows fed the low CP diet or the normal CP diet containing WCBS, compared to cows fed the normal CP diet, resulted in similar nitrogen efficiencies among the treatments. Hence, dietary CP concentrations of 160 to 170 g/kg DM can be used for cows in early lactation in commercial herds to improve nitrogen utilisation without causing a simultaneous decrease in milk yield.     

Manure composition of swine as affected by dietary protein and cellulose concentrations

An experiment was conducted to investigate the effects of reducing dietary CP and increasing dietary cellulose concentrations on manure DM, C, N, S, VFA, indole, and phenol concentrations. Twenty-two pigs (105 kg initial BW) were fed diets containing either 14.5 or 12.0% CP, in combination with either 2.5 or 8.7% cellulose. Pigs were fed twice daily over the 56-d study, with feed intake averaging 2.74 kg/d. Feces and urine were collected after each feeding and added to the manure storage containers. Manure storage containers were designed to provide a similar unit area per animal as found in industry (7,393 cm2). Before sampling on d 56, the manure was gently stirred to obtain a representative sample for subsequent analyses. An interaction of dietary CP and cellulose was observed for manure acetic acid concentration, in that decreasing CP lowered acetic acid in pigs fed standard levels of cellulose but increased acetic acid in pigs fed greater levels of cellulose (P = 0.03). No other interactions were noted. Decreasing dietary CP reduced manure pH (P = 0.01), NH4 (P = 0.01), isovaleric acid (P = 0.06), phenol (P = 0.05), and 4-ethyl phenol (P = 0.02) concentrations. Increasing dietary cellulose decreased pH (P = 0.01) and NH4 (P = 0.07) concentration but increased manure C (P = 0.03), propionic acid (P = 0.01), butyric acid (P = 0.03), and cresol (P = 0.09) concentrations in the manure. Increasing dietary cellulose also increased manure DM (P = 0.11), N (P = 0.11), and C (P = 0.02) contents as a percentage of nutrient intake. Neither cellulose nor CP level of the diet affected manure S composition or output as a percentage of S intake. Headspace N2O concentration was increased by decreasing dietary CP (P = 0.03) or by increasing dietary cellulose (P = 0.05). Neither dietary CP nor cellulose affected headspace concentration of CH4. This study demonstrates that diets differing in CP and cellulose content can significantly impact manure composition and concentrations of VFA, phenol, and indole, and headspace concentrations of N(2)O, which may thereby affect the environmental impact of livestock production on soil, air, and water.     

Correlated responses to selection for large body size in oMt1a-oGH mice: growth, feed efficiency and body composition

Correlated responses were determined for growth, feed consumption, feed efficiency and body composition following short‐term selection for large 8‐week body weight in transgenic and nontransgenic mice. Replicate lines which either carried or did not carry the sheep metallothionein 1a‐sheep growth hormone transgene (oMt1a‐oGH) were established. The lines carrying the transgene at an initial frequency of 0.5 came from a high‐growth (TM) and a randomly selected (TC) background. The respective nontransgenic lines were identified as NM and NC. Control replicates (CC) came from the randomly selected background. During the selection process the transgene was activated by adding 25 mm ZnSO₄ to the drinking water of all mice. Correlated responses were measured with (Z) and without (C) the addition of zinc. After seven and eight generations of selection, the frequency of transgenic mice in line TM had fallen sharply, whereas transgene frequency had risen moderately in TC. The reduced frequency of oMt1a‐oGH in the high‐growth genetic background may have been caused by a lower additive effect compared with the randomly selected background combined with a fitness disadvantage of the transgene. Therefore, the utility of a transgene in improving a quantitative trait may depend in part on genetic background. Correlated responses for most traits in NC were similar for Z and C. In contrast, correlated responses in TC showed marked differences in C compared with Z. For example, daily gain and feed efficiency showed no significantly correlated responses under C and positive responses (p < 0.001) under Z, and the reverse was found for indicators of body fat percentage. These line by environment (Z versus C) interactions may represent a genetic correlation of less than one between a trait expressed in two distinct environments. Thus, in developing lines with a transgene that can be regulated, a critical question is whether selection for quantitative trait(s) should be conducted when the transgene is activated or not activated.     

Rate, composition and efficiency of growth in feedlot steers reimplanted with growth stimulants

Eighty Charolais-cross steer calves (283 kg) were fed a moderately high-energy (2.89 Mcal ME/kg) diet for 189 d to examine the effects of reimplantation of 36 mg of zeranol (Ralgro) or 200 mg progesterone plus 20 mg estradiol benzoate (Synovex-S) on the rate, composition and efficiency of gain, skeletal size and carcass parameters in a comparative slaughter trial. The implant treatments included unimplanted controls (C), Ralgro initially (R1), Synovex-S initially (S1), Ralgro initially and a reimplant at 84 d (R2) and Synovex-S initially and a reimplant at 84 d (S2). Both implants increased (P less than .06) gains by 8.1% from 0 to 84 d. Ralgro and Synovex-S increased (P less than .01) daily gains by 11.5% and 25.2%, respectively, from 84 to 189 d. The duration of the response to a single implant appeared to be in excess of 140 d; thus, reimplantation did not further increase daily gains. Reimplantation did improve (P less than .05) feed utilization in Ralgro implanted steers, however. Ralgro and Synovex-S increased (P less than .01) the rate of empty body (EB) protein accretion by 14.1% and 24%, respectively, without affecting EB fat growth. The efficiency of protein gain per unit protein (P less than .05) or energy intake (P less than .04) was improved, but the efficiency of energy gain per unit energy intake was not affected by implantation. Carcass weights of implanted steers were 5% greater (P less than .04) when adjusted to an equal carcass fatness. Both growth stimulants increased hip height (P less than .02), wither height (P less than .08) and body length (P less than .08) over C steers at slaughter.