Dietary CP Level Research Articles

Effects of ruminally protected betaine and choline on net flux of nutrients across the portal-drained viscera and liver of meat goat wethers consuming diets differing in protein concentration

Six Boer × Spanish goat wethers (43 ± 5.1 kg BW) were used in an experiment with a 2 × 3 factorial arrangement of treatments to investigate effects of dietary CP level (9% and 15% DM) and supplementation with ruminally protected betaine or choline (0.9% DM) on plasma concentrations and net fluxes of oxygen, ammonia N, non-esterified fatty acids (NEFA), triacylglycerols (TG) and cholesterol across the portal-drained viscera (PDV) and liver. Neither betaine nor choline affected blood flow, packed cell volume, hemoglobin concentration or oxygen consumption. Blood flow and oxygen consumption were greater ( P < 0.05) for 15% versus 9% dietary CP. Arterial plasma ammonia N concentration was greater ( P < 0.05) for 9% versus 15% CP. Compared with Control, choline supplementation decreased ( P < 0.05) PDV release and hepatic uptake of ammonia N with the 15% CP diet, whereas betaine decreased ( P < 0.05) PDV release and hepatic uptake of ammonia N with 9% dietary CP. With 9% dietary CP, the concentration of NEFA in arterial, hepatic venous and portal venous plasma ranked ( P < 0.05) choline < Control < betaine; with 15% CP, NEFA concentration also was greater ( P < 0.05) for betaine versus Control, although the magnitude of difference was smaller than with 9% CP. The only treatment effect on NEFA net fluxes was greater ( P < 0.05) hepatic uptake with 9% CP than with 15%. Plasma TG concentrations also were increased ( P < 0.05) by betaine with 9% dietary CP, whereas choline did not have any influence with either dietary CP level. Concentrations and net fluxes of cholesterol were similar among treatments. In conclusion, these data indicate that potential effects of ruminally protected betaine on performance of ruminants might involve changes in lipid metabolism, with the magnitude of alteration varying with dietary CP level.

Response of Plasma Concentration of Free Amino Acid to Change of Dietary Protein and Amino Acid Levels in Adult Thoroughbreds

The response of the plasma concentration of free amino acids to the change in dietary levels of them is a parameter available to predict the amino acid requirements in some species. In order to confirm whether the response of plasma concentrations of free amino acids is also available in horses, three experiments were conducted repeatedly on four adult male Thoroughbreds. The diets were supplied twice a day at morning and evening. In Experiment 1, to determine the timing of blood sampling, blood samples were taken at 0, 1.5, 3, 5 and 7 hr after feeding the 14.9% CP diet. Plasma concentrations of all free amino acids except Arg, Gln and Gly increased by 1.5 hr and then gradually decreased to the levels before the start of the morning meal. In Experiment 2, to examine the quickness and the stability of response of plasma concentrations of free amino acids to the abrupt change in dietary Lys and Val levels, the horses were supplied with diets with 14.9% CP and different levels of Lys and Val successively at 10 day interval. Blood samples were taken at 3 and 7 hr after the morning meal at 0, 1, 3, 5 and 10 days after switching diets. Plasma concentrations of Lys and Val responded to the change in dietary levels of them by 3 days, and the responses were maintained for 10 days after switching diets. Those of all amino acids except Lys and Val did not respond. In Experiment 3, to confirm whether or not plasma concentrations of each amino acid respond to the change in dietary CP and/or amino acid levels, the horses were successively supplied with diets with different CP levels successively at 5 day intervals. Blood samples were taken at 3 hr after the morning meal 5 days after changing diets. Plasma concentrations of Cys, His, Ile, Leu, Phe, Tyr and Val responded, but those of other amino acids did not respond to changes in dietary CP and/or amino acid levels. These results indicated that the response of plasma concentrations of free amino acids which responded to the change in dietary levels might be available as a parameter to predict requirements of them for adult male thoroughbreds within a short period.

Performance of broiler chicks fed various levels of dietary lysine and crude protein

An experiment was conducted to establish a basal diet deficient in both protein and lysine. The responses of broiler chicks to graded levels of lysine at two levels of CP were measured in diets mixed by two experimental methods (diet dilution and graded supplementation). Experiment 1 had a 2 × 3 factorial arrangement of treatments with three dietary CP levels (17, 20, and 23%) and two levels of lysine per CP level (35 and 48 g lysine/kg CP). Dietary CP and lysine levels had significant (P < 0.001) effects on body weight gain (BWG), feed intake, and feed conversion ratio (FCR). In exp. 2, the lysine requirement of chicks (9 to 18 d of age) was estimated at two levels of CP in diets mixed by the diet dilution method. The requirements for lysine at 17% CP (as a percentage of CP) were estimated to be 4.45 +/− 0.18% for BWG (R2 = 0.83) and 4.33 +/− 0.16% for FCR (R2 = 0.81). Similarly, the requirements at 23% CP were 4.34 +/− 0.16% for BWG (R2 = 0.84) and 4.35 +/− 0.13% for FCR (R2 = 0.89). In exp. 3, the lysine requirement of chicks (10 to 18 d of age) was estimated at two levels of CP in diets mixed by the graded supplementation method. The requirements for lysine at 18.5% CP were 5.17 +/− 0.25% for BWG (R2 = 0.80) and 4.26 +/− 0.15% for FCR (R2 = 0.85). Similarly, the requirements at 23% CP were 4.59 +/− 0.17% for BWG (R2 = 0.83) and 4.71 +/− 0.16% for FCR (R2 = 0.88). Results of a t-test show that the requirements were not significantly different between the two CP levels for BWG in experiments 2 and 3 (P < 0.05). It is concluded that the amino acid requirements of broilers are a constant proportion of CP levels at least in the range of CP levels commonly fed.

Effect of dietary protein fluctuations and space allocation on performance and carcass quality of growing-finishing pigs1

Two trials with growing-finishing pigs were conducted to evaluate the effects of fluctuating dietary CP levels and/or space allocation on performance and carcass traits. In Trial 1, three CP regimens were used with 216 growing-finishing pigs (mixed sex). Average initial and final weights of pigs were 31 and 103 kg, respectively. The CP regimens consisted of: 1) control (18% CP from wk 0 to 4; 15% CP from wk 4 to 12); 2) moderate CP variations (MCPV = 19.5% CP from wk 0 to 2, 16.5% CP from wk 2 to 6, 13.5% CP from wk 6 to 8, 16.5% CP from wk 8 to 10, 13.5% CP from wk 10 to 12); and 3) extreme CP variations (ECPV = 21% CP from wk 0 to 2, 15% CP from wk 2 to 4, 18% CP from wk 4 to 6, 12% CP from wk 6 to 8, 18% CP from wk 8 to 10, 12% CP from wk 10 to 12). Overall (wk 0 to 12), treatment differences were not observed (P > 0.05) for gain, feed intake, CP intake, gain:feed ratio, or gain/CP intake. Trial 2 involved 360 finishing pigs (mixed sex) in a 3 x 2 factorial arrangement (three dietary CP regimens, two floor space allowances). The diets consisted of: 1) control (16% CP from wk 0 to 4, 15% CP from wk 4 to 8; 14% CP from wk 8 to 12); 2) MCPV (17.5% CP from wk 0 to 2, 14.5% CP from wk 2 to 4, 16.5% CP from wk 4 to 6, 13.5% CP from wk 6 to 8, 15.5% CP from wk 8 to 10, 12.5% CP from wk 10 to 12); and 3) ECPV (19% CP from wk 0 to 2, 13% CP from wk 2 to 4, 18% CP from wk 4 to 6, 12% CP from wk 6 to 8, 17% CP from wk 8 to 10 wk, 11% CP from wk 10 to 12). Pigs were provided with either 1.12 m2 (uncrowded; five pigs/pen) or 0.56 m2 (crowded; 10 pigs/pen). Average initial weight was 49 kg and final weights were 126 kg (uncrowded) and 118 kg (crowded). Overall (0 to 12 wk), crowded pigs had lower (P < 0.05) ADG (822 vs. 916 g) and feed (as-fed) intakes (2,633 vs. 2,876 g) than uncrowded pigs. At the end of the 12-wk trial, a control vs. ECPV x space interaction (P < 0.05) occurred for weight gain, fat depth, and percentage of lean. Thus, uncrowded pigs fed ECPV gained faster (933 vs. 887 g) but had a lower percentage of lean (53.5 vs. 54.5) than controls, whereas crowded pigs on the ECPV regimen gained more slowly (812 vs. 842 g) but were leaner (54.8 vs. 54.6%) than those on the control CP regimen. Despite the wide dietary CP fluctuations, pigs in both trials consumed about the same quantity of CP during the 12-wk feeding periods. These data suggest that uncrowded pigs respond differently than crowded pigs to fluctuating levels of dietary CP.

Effects of level and source of supplemental protein in a concentrate-based diet on growth performance of Boer × Spanish wether goats

Boer×Spanish wether goats (50; 26.8±4.04 kg initial BW and 7 months of age) were used in a 27 week experiment to determine effects of two levels of CP (13 and 19%) and five protein sources varying in ruminal degradability (blood, corn gluten, feather, fish and soybean meals). Diets were 70% concentrate, had a ratio of ruminally degraded intake protein (DIP) to total digestible nutrients (TDNs) of at least 0.09 and were formulated to maximize ruminally undegradaed protein from supplemental protein sources. There were no interactions between dietary CP level and supplemental protein source. Voluntary DM intake (1043, 1089, 1153, 1086 and 1112 g per day; S.E.=74.4), ADG (136, 134, 143, 145 and 138 g per day; S.E.=9.8) and gain efficiency (ADG:DM intake) (131, 124, 125, 136 and 128 g/kg for blood, corn gluten, feather, fish and soybean meals, respectively; S.E.=5.7) were similar between CP levels and among sources of supplemental protein. In summary, with a dietary concentrate level of 70% and at least 13% CP, differences in amino acid profiles among blood, corn gluten, feather, fish and soybean meals did not impact rate or efficiency of growth by Boer×Spanish wethers.

Dietary Interactions Between Threonine and Crude Protein in Diets for Growing Tom Turkeys 8 to 12 Weeks of Age

An experiment was conducted to estimate the Thr needs of male Large White turkeys from 8 to 12 week of age and to evaluate the effects of dietary CP on Thr needs. The dietary treatments consisted of a 2 x 6 factorial arrangement with two levels of CP (16.0 and 19.8%), each containing 0.50% total Thr by analysis. Aliquots of each CP basal diet were supplemented with L-Thr to provide total Thr levels of 0.50, 0.57, 0.64, 0.71, 0.78, and 0.85%. Initial and final bird weights were taken to determine BW gain; feed conversion ratios were calculated with adjustment for weight of birds that died during the study. Nonlinear and quadratic regression analyses were used to estimate a Thr requirement to optimize BW gain and feed conversion. For both BW gain and feed conversion, significant interactions were observed between dietary CP and Thr levels. Performance was superior for poults fed the low CP diet series, noted primarily at the lower levels of Thr. As levels of Thr reached a surfeit, no significant differences in performance were noted between poults fed the two CP levels. Using nonlinear regression analysis, dietary Thr levels of 0.68 (16.0% CP) and 0.76% (19.8%) were adequate for maximum BW gai n while Thr levels of 0.61 (16.0% CP) and 0.70% (19.8%) were adequate for optimum feed conversion. However, when estimates were based on fitting a quadratic regression, dietary Thr levels of 0.83 (16.0% CP) and 0.98% (19.8%) were adequate for maximum BW gain, while Thr levels of 0.77 (16.0% CP) and 0.82% (19.8%) were adequate for optimum feed conversion. While the interactions between dietary CP and Thr may be interpreted to suggest that dietary CP levels influence amino acid requirements, the two basal diets were composed of protein sources that differ in digestibility of Thr. It is possible that the reduced BW gains and impaired feed conversion observed at the lowest level of Thr supplementation on the high CP diets were the result of a lower level of digestible Thr, rather than a direct influence of CP level per se.

Effect of high temperature and low-protein diets on the performance of growing-finishing pigs.

The effects of reducing CP level in combination with an increase in ambient temperature (29 vs 22 degrees C) on performance and carcass composition were studied in a factorial arrangement of treatments involving 66 Piétrain x (Landrace x Large White) barrows from 27 to 100 kg BW. Animals were fed at each temperature one of three experimental diets that provided 0.85 or 0.70 g of digestible lysine per megajoule of NE, in the growing (27 to 65 kg) and the finishing (65 to 100 kg) phases, respectively. Diet 1 was a corn, wheat, and soybean meal diet formulated without crystalline AA; CP levels were 20.3 and 17.6% for the growing and the finishing phases, respectively. In Diets 2 and 3, CP level was reduced by substituting part of the soybean meal with corn and wheat (Diet 2), or with corn, wheat, and 4% fat (Diet 3). Diets 2 and 3 were supplemented with AA and balanced according to the ideal protein concept. The CP levels of Diets 2 and 3 were, respectively, 15.8 and 16.3% in the growing phase, and 13.4 and 13.8% in the finishing phase. Pigs were housed individually and had free access to feed and water. The ADFI was measured daily, and animals were weighed weekly. Carcass composition was measured at slaughter (100 kg BW). Increasing ambient temperature from 22 to 29 degrees C resulted in a 15% reduction in ADFI and 13% lower ADG. Leaner carcasses (P < 0.01) were obtained at 29 degrees C (22.8 vs 24.8% carcass fat). At 22 degrees C, ADFI was lower (P < 0.05) for the low-CP diets, but daily NE intake, ADG, and carcass composition were not affected (P > 0.05). At 29 degrees C, ADFI was not different (P > 0.05) between diets and daily NE intake was higher (P < 0.05) with Diet 3 than with Diet 1, and the difference was more important during the finishing period than during the growing period. Using the model ADFI = a BWb, estimates of b were 0.65, 0.53, and 0.53 at 22 degrees C and 0.50, 0.44, and 0.50 at 29 degrees C, for Diets 1, 2, and 3, respectively. The higher NE intake for Diet 3 at 29 degrees C did not improve ADG (P > 0.05) but increased mainly fat deposition. These results indicate that a 4 percentage unit reduction of dietary CP level reduces N excretion (minus 37%) but does not affect growth and carcass composition as long as the ratio between essential AA and NE are kept optimal. In addition, diets with reduced CP limit the effect of high ambient temperature on ADFI. Finally, our results demonstrate the significance of using NE, rather than DE or ME, for formulating diets.

Forage quality and camel feeding patterns in Central Baringo, Kenya

A study was conducted between August and December 1991 to determine forage quality and feeding patterns in camels ( Camelus dromedarius). Forage selection and behaviour patterns were determined by direct observation and scan-sampling techniques, respectively. Chemical composition and digestibility of forages were determined using proximate procedures and in vitro techniques, respectively. Feeding and walking dominated animal activities. Significantly less time ( P<0.05) was spent on feeding and walking during the green/growing season compared to the dry season. On the contrary, idling and ruminating times were significantly higher ( P<0.05) during the growing season compared to the dry season. Feeding patterns dovetailed seasonal changes in forage quality. Feeding time was significantly negatively correlated with the dietary CP ( P<0.05) and IVDMD ( P<0.01) levels but significantly positively correlated with NDF ( P<0.05), ADF ( P<0.01) and ADL ( P<0.05). It was concluded that forage quality influences feeding patterns in camels and that under adverse pasture conditions, the time available for grazing would be a limiting factor to their dry matter (DM) and nutrient intake.

Field bean (Vicia faba var. minor) as a protein feed for growing lambs with and without protected lysine and methionine supplementation

Thirty-two Appenninica lambs were submitted to a growth trial from day 60 to day 110 of age (on average) and the composition of gains was estimated by means of the comparative slaughter technique. Sixteen different diets, based on wheat straw as the forage and on field bean (Vicia faba var. minor) as the sole protein feed, were tested both by means of ANOVA and of response surface analysis, a multiple regression method designed to study additive and interaction effects. This study thus examined the combined effect of 4 levels of dietary CP (13, 15, 18, 20% DM) and 4 levels of rumen protected lysine and methionine, replacing 4 levels of field bean CP (0, 1, 2, 3 percent units), upon intakes, gains, digestibility and retentions of nutrients within gains. The animals had rather high gains (250 g/d on average) and retention efficiencies both of feed nitrogen and energy. Dietary CP levels higher than 18% and amino acid supplementation appeared of no use in improving the lambs’ performance. It is concluded that field bean may represent a valid alternative to soy bean as a protein feed for growing ruminants in the so-called “organic” animal production where transgenic soy is banned.

Studies on the Effect of Dietary Crude Protein Supply on the Composition of Ileal Endogenous Crude Protein Loss in Growing Pigs

Two experiments were carried out to investigate endogenous crude protein (N 2 6.25) (CP) losses in growing pigs. In experiment I, 42 cross-bred gilts [live weight (LW) 35-40 kg] were fitted with a simple T-cannula at the terminal ileum. Seven experimental diets (four feedstuffs: barley, wheat, soyabean meal and rapeseed meal, and three mixtures with varying compositions of the same feedstuff batches) were investigated. Each diet was fed at six different CP levels, obtained after dilution with a 1:1 mixture of sucrose and dextrose. In total, 42 different diets were used and on each pig three different diets were tested. In experiment II, 12 (LW , 18 kg) plus eight (LW , 88 kg) cross-bred castrates were fitted with a simple T-cannula at the terminal ileum. Four experimental diets based on casein as the sole protein source and with CP dietary levels from 6 to 25% were used. By extrapolation to zero CP intake the basal endogenous protein loss in experiment I was 15.7 g kg -1 dry matter (DM) intake, when including all diets, and 14.3 g kg -1 DM intake after excluding the barley diets. In experiment II the basal endogenous CP loss was 11.3 g kg -1 DM intake. In experiment I a relative increase in almost all amino acids in the endogenous CP loss was found when the dietary CP level in the diets increased from zero to 17%. Exceptions were glycine, which was constant, and proline, which decreased significantly from 176 to 58 g 160 g -1 CP. However, the sum of proline and glutamic acid in the endogenous protein loss was almost constant. Similar results were obtained after correction for undigested dietary CP and amino acids, based on in vitro analyses of CP digestibility. In a supplementary study, ileal samples, selected for unusually high levels of proline were analysed for free amino acids. For proline, 36-64% was free, whereas insignificant proportions of the other amino acids were free. It is concluded that the composition of endogenous CP is generally relatively constant. However, experimental conditions with low or inappropriate dietary CP supply may influence the composition and occasionally induce unexpected high levels of proline from secretion of free proline into the lumen of the digestive tract.

Effects of dietary crude protein level on the digestibility of nutrients, excretion of fecal N and urinary N-fractions and the kinetics of 15N labeled urea in growing male goat kids

A feeding trial was conducted with 16 male Saanen kids (4 kids/treatment) weighing 19.0 ± 1.8 kg in the middle of which they were subject to a metabolism trial and kept in cages for 14 days for a quantitative 10 days collection of excreta. Kids were fed a constant amount of the four diets formulated out of molassessed wheat straw [55 g crude protein (cp) per kg dry matter (dm)] and pelleted concentrates having 87, 117, 144 and 176 g cp/kg dm. They were injected about 100 mg of 15N-labeled urea into the jugular vein at the beginning of the collection period. Nutrient digestibility, fecal N and urinary N-fractions, N and 15N balances were measured; irreversible loss (il) of urea from the body urea pool (bup) and the kinetics of N in the body calculated. Increasing dietary cp increased digestibility of organic matter (om) from 71% to 80% and of crude fiber (cf) from 28% to 58%; excretion of fecal N by 56%; of urea N by 93%; proportion of N of urea, allantoin, creatinine, uric acid plus hypoxanthine in urinary N from 31% to 66%, 12% to 22%, 3% to 12%, and by 1.7%, respectively; irreversible iron (il) of N from 1.98 to 12.24 g/d; transfer of urea to gastro-intestinal tract (git) from 1.58 to 6.69 g/d (i.e., equivalent to 80% to 55% of il); recycling of the degraded urea N to metabolic pool from 1.22 to 6.12 g/d; but it has decreased the proportion of retained N of bup origin from 38 to 30% and excretion of urinary non-urea N from source other than bup was constant. Excretion of urea is the mechanism by which goat kids adapt to variable supply of dietary protein. Excretion of fecal N was more closely related to dm intake, while that of urea N to dietary cp level and of purine derivatives (pd) to digestible om intake. SINET: Ethiopian Journal of Science Volume 24, No. 2 (December 2001), pp. 265-282 Key words/phrases: Goat kids, 15N kinetics, N-metabolism, protein, urea

Efficacy of laidlomycin propionate in low-protein diets fed to growing beef steers: effects on steer performance and ruminal nitrogen metabolism.

We conducted two experiments to evaluate the effect of the ionophore laidlomycin propionate (LP) on steer performance and ruminal N metabolism. Experiment 1 was a 91-d growth study evaluating the growth and ruminal characteristics of steer calves consuming supplemental LP. Steers (n = 96; 255 +/- 3 kg; four steers/pen; six pens/treatment) were used in a randomized complete block design with a 2 x 2 factorial arrangement of treatments consisting of two levels of dietary CP (formulated to be 10.5 and 12.5% of DM) with and without LP (11 mg/kg diet DM). Ruminal fluid was collected via stomach tube on d 91 from one steer randomly selected from each pen. No CP x LP interactions were observed with performance data (P > .64). Final weight and total gain were greater (P < .07) for 12.5% CP and LP compared with 10.5% CP and control steers, respectively. Also, DMI was increased (P = .08) with 12.5% CP but not with LP supplementation (P = .36). In addition, ADG and gain:feed ratio were greater (P < .03) for both 12.5% CP and supplemental LP. Ruminal NH3 N concentration was greater (P < .09) with 12.5% CP and LP. Total VFA concentration and molar proportion of acetate were not affected by treatment (P > .11). However, propionate concentration was increased (P < .09) with 12.5% CP and LP, and acetate:propionate was lower (P = .02) with LP supplementation. In Exp. 2, six steers were used in a replicated 3 x 3 Latin square design to compare ruminal fermentation and protein degradation in steers without ionophore feeding or adapted to LP or monensin. In vitro deamination of amino acids by adapted ruminal microbes was also assessed. Ionophore supplementation decreased (P = .07) ruminal NH3 N concentration compared with control steers, and LP increased (P = .02) ruminal NH3 N compared with monensin. Molar proportion of acetate was decreased (P = .02) and propionate increased (P = .01) with ionophore treatment. Consequently, ionophore supplementation depressed the acetate:propionate ratio (P = .01). In situ degradation rate of soybean meal (SBM) CP was greater (P = .09) with ionophore treatment, but estimates of SBM undegradable intake protein were not altered by treatment (P > .25). Microbial specific activity of net NH3 N release and alpha-amino N degradation were decreased (P < .04) with ionophores. Based on this study, LP and monensin did not affect the extent of ruminal degradation of SBM CP but decreased amino acid deamination.

Performance and carcass merit of growing beef steers with chlortetracycline-modified sensitivity to pituitary releasing hormones and fed two dietary protein levels.

This paper reports the effects of reduced sensitivity to growth hormone-releasing hormone and thyrotropin-releasing hormone through feeding a subtherapeutic level of chlortetracycline (CTC; 350 mg CTC/d) and two levels of dietary CP (10% and 13% of diet DM) on growth performance and carcass merit characteristics. Thirty-two steers (initial average BW, 286 kg) were adapted to a common 13% CP diet consisting primarily of grass hay, corn, and soybean meal fed to gain 1.25 kg/d. The steers were assigned to four treatments (with or without CTC and 10% or 13% dietary CP in a factorial arrangement) and fed ad libitum amounts of diet for 91 d. Feed intake was determined daily and steers were weighed weekly. Steers were killed at the end of the feeding period for carcass merit determinations. Efficiency of BW gain was greater (P < .05) for steers fed the 13% CP diet than for the 10% CP diet and tended to be less for CTC-steers when the 10% CP diet was fed and greater for the CTC-steers when the 13% CP diet was fed (CTC x dietary CP interaction, P < .10). Feeding CTC increased (P < .01) fat over the longissimus muscle and marbling. This study is interpreted to indicate that the sustained effect of subtherapeutic feeding of CTC to cattle appears to increase fat deposition consistent with a reduced growth hormone and thyroid status reported earlier for these same steers. This would tend to increase energy utilization but may not necessarily produce a measurable increase in BW gain.

Dietary protein effects on and the relationship between milk production and mohair growth in Angora does

Twenty-eight Angora does in week 3 through week 16 of lactation (with kids removed; 41 ± 0.9 kg initial BW) were given ad libitum access to a 67% concentrate diet with four formulated (DM basis) levels of CP ranging from 9% to 18% to study the relationship between, and dietary CP level effects on, milk production and mohair growth in different periods of lactation. Dry matter intake did not differ among treatments ( p > 0.10) in all but one 2-week period, and CP intake increased linearly ( p < 0.01) with the increasing dietary CP concentration. Milk production increased linearly ( P = 0.09) with increasing the dietary CP concentration (548, 605, 926, and 757 g/d; SE = 124). Mohair growth was 1.25, 1.37, 1.05, and 1.55 mg/(cm 2 d −1) for 9%, 12%, 15%, and 18% CP, respectively (SE = 0.146). Within 2-week periods, CP intake was not related ( p > 0.10) to mohair growth; however, intake of CP was fairly consistently correlated with milk production in each 2-week period (overall r = 0.59; p < 0.01). Milk production and mohair growth were negatively related for all data ( r = −0.55; p < 0.01), although correlations in week 3–4, 15 and 16 of lactation were non-significant ( p > 0.10). Dietary CP level did not markedly impact the negative relationship between milk production and mohair growth. In conclusion, milk production and mohair growth were inversely related in mid-lactation but not in early or late stages, and dietary CP level did not alter the relationship between milk production and mohair growth. Under these conditions, varying dietary CP level did not overcome partitioning of nutrients to milk synthesis or increase mohair growth by lactating Angora does.

A Quantitative Assessment of Reduced Protein Diets and Supplements to Improve Nitrogen Utilization

Several strategies are being developed to minimize nitrogen (N) pollution form poultry waste in areas with high concentrations of commercial poultry operations. This study looks at the effect of using reduced protein (CP) diets for broilers and layers housed under commercial conditions. Each of two broiler experiments involved 2400 birds; a layer experiment involved 1350 birds. The diets were based on practical ingredients, supplemented with commercially available lysine, methionine, tryptophan, and threonine. Results indicated that similar boiler and layer performance could be maintained on reduced-CP diets as on conventional diets, although body fat content increased in broilers. The reduction in dietary CP content resulted in a 10-27% reduction in the total amount of N excreted during the 6-wk broiler rearing period. With layers, there was a 30-35% reduction in daily N output. Reduction in dietary CP level was associated with an improvement in DM (dry matter) and N retention. Accurate information on the AA composition of the dietary constituents is necessary, as is the addition of supplements of the limiting AA. Successful reduction in dietary CP content is likely to have marked beneficial effects in terms of reducing the N output in waste from poultry operations.

Body weight and semen production of broiler breeder males as influenced by crude protein levels and feeding regimens during rearing

An appropriate dietary CP level and feeding regimen during rearing is considered important for controlling BW and improving semen production in broiler breeder males. A total of 640 day-old broiler breeder male chicks of two commercial strains (A and B) received treatments of a factorial arrangement of two CP levels (12 and 16%) of corn-soybean grower diets and two feeding regimens [changing feed to a grower diet from the standard broiler starter at 0.45 and 0.68 kg BW and then skip-a-day feeding]. Four- to 28-wk BW differed between CP levels during rearing, with heavier BW on the 16% CP diet than on the 12% CP diet in spite of isocaloric feed intake. Strains did not show a significant difference in BW prior to 40 wk of age. Feed restriction initiated at 0.45 or 0.68 kg BW had no effect in controlling BW after 4 wk of age. Uniformity of BW did not differ between CP levels. Semen volume was greater on the 12% than on the 16% CP diet from 28 to 36 wk of age. Semen concentration was not affected by CP levels, feeding regimens, or strains. Spermatozoa per ejaculate from 28 to 52 wk of age was correlated negatively with 8- to 20-wk BW. This negative relationship was attenuated with age, until at Week 46 or later spermatozoa per ejaculate was associated positively with BW after sexual maturity. No difference in percentage of males in semen production was noted between strains, CP levels, or feeding regimens. In brief, diet changes at 0.45 or 0.68 kg BW were not important in improving semen production, whereas the low CP diet (12%) had advantages in semen production over the high CP diet (16%). A negative relationship existed between semen production and BW during rearing; however, continued BW gain after sexual maturity was necessary to optimize semen production, especially during the late breeding period.

Responses to an estrogenic growth promoter in beef steers fed varying nutritional regimens.

We investigated the influence of DM and(or) energy intake and dietary CP levels on the performance and nitrogen (N) retention of beef steers with and without growth promoter implants. In Exp. 1, four implanted (Synovex-S, 200 mg of progesterone plus 20 mg of estradiol benzoate) Angus steers and four Angus steers that were not implanted were assigned to concurrent 4 x 4 Latin squares. Initial BW averaged 296 kg. Each square consisted of moderate and moderately high DM intake treatments (4 and 6 kg/d) and low and adequate CP intake treatments (450 and 600 g/d) in a 2 x 2 factorial arrangement. Periods were 2 wk of adaptation, 5 wk of growth, and 1 wk of balance collection. Experiment 2 consisted of two replicates of 32 Hereford steers each (initial BW 324 kg). Each replicate was a 4 x 2 factorial in which steers were individually fed for 63 d. All steers had ad libitum access to a 60% corn-based concentrate diet containing either 7.9, 10.0, 12.1, or 14.6% CP (DM basis), and steers were either implanted or not implanted with Synovex-S. Experiment 3 was similar to Exp. 2 except that all steers (initial BW 315 kg) received a low-protein diet (7.6% CP) with calculated energy densities of either 1.86, 2.04, 2.22, or 2.42 Mcal ME/kg DM, and steers were limited to an equalized DM intake of 9.5 kg daily. In Exp. 1, gains for the low CP, moderate and moderately high DM intakes and the adequate CP, moderate and moderately high DM intakes were 240, 555, 208, and 730 g/d, respectively, for steers not implanted and 333, 643, 488, and 988 g/d, respectively, for implanted steers (SEM = 102 g/d). Respective values for retained N were .13, .18, .16, and .26 g/kg BW.75 and .13, .15, .22, and .29 g/kg BW.75 (SEM = .04 g/kg BW.75). Implant response was greater (CP x implant, P < .01) for both gain and retained N when adequate CP compared to low CP diets were fed. For Exp. 2, the lowest CP diet reduced ADG (.97 vs 1.27 kg/d) and efficiency of gain (100 vs 120 g gain/kg DM). Synovex-S was less effective in improving efficiency for the lowest protein diet than for the other diets (11.7 vs 20.2%). During Exp. 3, neither Synovex-S nor dietary energy influenced gain and efficiency. We concluded that adequate dietary protein is necessary to optimize the response to estrogenic growth promoters and that the low response under inadequate protein and energy intake is not improved by increasing the energy density of the diet.

Dietary protein affects nitrogen excretion and ammonia emission from slurry of growing–finishing pigs

The effects of dietary protein on nitrogen excretion and ammonia emission from slurry of growing–finishing pigs were studied both in vitro and in a pig house. The three diets had similar contents of NE, minerals, vitamins and ileal digestible lysine, methionine+cystine, threonine and tryptophan, but differed in CP content (16.5, 14.5 and 12.5%). In the balance experiment, 18 castrated males of about 55 kg body weight were allotted to the three diets. The experiment lasted 9 weeks, which were divided into three 3-week periods. In each period, urine and faeces were collected separately for 7 days in metabolism cages and mixed as slurry. A sample of this slurry was placed in a laboratory system to measure ammonia emission for 7 days. In the barn experiment, 216 pigs were housed in three compartments and fed the experimental diets. Ammonia emission was measured directly from the compartments for 7 days during each of the 3-week periods. There was no effect of dietary CP level on faecal nitrogen excretion. Urinary nitrogen excretion and slurry pH decreased when dietary CP decreased. Both balance and barn experiments showed similar effects of dietary CP on ammonia emission from slurry. Ammonia emission was reduced by 10–12.5% for each percent decrease in dietary CP. It is concluded that lowering dietary CP and supplementing essential amino acids while maintaining normal growth rate reduces urinary nitrogen and ammonia emission from the slurry of growing–finishing pigs.

Performance and carcass composition of large white toms as affected by dietary crude protein and threonine supplements

This experiment evaluates the effect of decreasing dietary CP, in addition to the effects of dietary supplements of L-Thr to low CP diets, in Large White Nicholas toms from 0 to 18 wk of age. Toms were fed dietary treatments consisting of four levels of dietary CP as a percentage of NRC (1994) recommendations (100, 92, 84, and 76% of NRC recommendations). Additional treatments consisted of supplements of L-Thr (0.1 and 0.2% of diet) added to the 92 and 84% NRC CP treatments. All eight dietary treatments were formulated to meet a minimum of 105% of NRC (1994) recommendations for Met, TSAA, Lys, Thr, and Trp. Body weight, feed conversion, mortality, and carcass composition responses were measured. Decreasing CP to 84% of NRC resulted in 18-wk BW lower than that (P < or = 0.001) of toms fed diets containing 100 or 92% of NRC CP; however, toms fed 84% of NRC CP diet supplemented with 0.1% L-Thr had 18-wk BW equal to (P < or = 0.001) that of the 100 and 92% NRC CP treatments. Toms fed diets containing 76% of NRC CP had depressed BW and feed:gain in comparison to all other treatments. No adverse effects in cumulative feed:gain (0 to 18 wk) were noted by decreasing CP from 100 to 84% of the NRC recommendations. Mortality did not differ among treatments. Treatments had no effect on carcass fat expressed as a percentage of hot carcass weight. Breast meat yield (deboned Pectoralis major and Pectoralis minor) was highest (P < or = 0.001) in toms fed the 100 and 92% NRC CP treatments. The 84 and 76% NRC CP treatments resulted in decreased breast meat yield regardless of L-Thr supplements. These results indicate that diets containing Met, TSAA, Lys, Thr, and Trp at a minimum of 105% NRC recommendations may support favorable breast meat yield when CP is decreased to 92% of the NRC (1994) recommendation. If growth and feed conversion are the desirable traits, rather than breast meat yield, CP levels below 92% of the NRC (1994) recommendation may support favorable responses.

Body composition and protein and fat accretion in various body components in growing gilts fed diets with different protein levels but estimated to contain similar levels of ideal protein.

A comparative slaughter technique was used to determine the effect of dietary protein levels on body composition and protein and fat accretion in various body components in Yorkshire gilts. Diets were formulated to contain similar levels of idea protein. Eight gilts were slaughtered at 20 kg BW to determine initial body composition. Twenty-four gilts were assigned to each of three dietary treatments (16.6, 15.0 and 13.0% CP) during the growing period (20 to 55 kg BW). During the finishing period (55 to 100 kg BW), dietary CP levels were reduced by approximately two percentage units. Eight gilts per treatment were slaughtered at 55 kg BW, and the remaining pigs were slaughtered at 100 kg BW. At slaughter, the pits were divided into three components: carcass, empty gastrointestinal tract, and other non-carcass parts. Half of the carcass was further dissected into retail cuts. None of the carcass retail cuts was affected (P > .10) by the dietary CP levels, except trimmed ham was smaller (P < .05) in gilts fed the 13% CP growing and 11% CP finishing diets. Far content in the empty body (P = .12) and in the carcass (P = .06) was highest and the empty body water accretion rate was lowest (P = .05) in gilts fed the 13% CP growing and 11% CP finishing diets. Other aspects of chemical body composition, protein and fat accretion rates, and estimated lean yields were not affected by dietary CP level (P > .10).