The heat of combustion of the urine of sheep and cattle in relation to its chemical composition and to diet

Grazing beef cows identified as efficient using a nutrition model partition more energy to lactation

Context The efficiency of the cow–calf sector could be enhanced by matching cow biological type to the production environment; however, methods to estimate the biological efficiency of grazing beef cows are not available. Aims This study utilised a mathematical nutrition model for ranking beef cows for estimated biological efficiency, determining energetic efficiency and evaluate relationships with other production traits. Methods Cow live weight, calf birth and weaning weight, calf birth and weaning date, and forage nutritive value of hay and pasture were collected for 69 Brangus crossbred beef cows over a complete production cycle. The Cattle Value Discovery System for Beef Cow (CVDSbc) model was used to compute metabolisable energy required (MER) for the cow, and energy efficiency index (EEI) was computed as the ratio of MER to calf weaning weight. Pearson correlation coefficients were computed among performance traits. During late lactation and gestation, low (n=8) and high (n=8) EEI cows were individually fed ad libitum for 44 and 32 days, respectively, then fed 0.5× the estimated metabolisable energy required for maintenance for 7 days (gestation experiment only). Apparent nutrient digestibility, heat production, and milk yield were measured. Key results EEI was strongly negatively correlated (P<0.05) with model predicted peak milk (−0.62) and calf weaning weight (−0.65), but moderately correlated (P<0.05) with cow live weight (0.46). Dry matter intake was not different (P>0.75) between low and high EEI cows even though low EEI cows weighed less (P<0.05) during late lactation and gestation experiments. Low EEI cows tended to have greater efficiency of metabolisable energy use for maintenance and gain (P<0.10), and EEI was negatively correlated (P<0.05) with the efficiency of metabolisable energy use for maintenance (−0.56) and gain (−0.57). Conclusion The CVDSbc model identified cows that weaned heavier calves due to greater dry matter intake of cows relative to live weight allowing more energy apportioned towards lactation, and more efficient use of metabolisable energy for maintenance and gain. Implications Energy efficiency index might provide a logical assessment of biological efficiency of beef cows in grazing production systems.

Relationship between urinary energy and urinary nitrogen or carbon excretion in lactating Jersey cows

Measurement of urinary energy (UE) excretion is essential to determine metabolizable energy (ME) supply. Our objectives were to evaluate the accuracy of using urinary N (UN) or C (UC) to estimate UE and ultimately improve the accuracy of estimating ME. Individual animal data (n = 433) were used from 11 studies with Jersey cows at the University of Nebraska-Lincoln, where samples were analyzed after drying (n = 299) or on an as-is basis (n = 134). Dried samples resulted in greater estimated error variance compared with as-is samples, and thus only as-is samples were used for final models. The as-is data set included a range (min to max) in dry matter intake (11.6-24.6 kg/d), N intake (282-642 g/d), UE excretion (1,390-3,160 kcal/d), UN excretion (85-220 g/d or 20.6-59.5% of N intake), and UC excretion (130-273 g/d). As indicated by a bias in residuals between observed and predicted ME as dietary crude protein (CP; range of 14.9-19.1%) increased, the National Research Council dairy model did not accurately predict ME of diets, as dietary CP varied. The relationship between UE (kcal/d) and UN (g/d) excretion was linear and had an intercept of 880 ± 140 kcal. Because an intercept of 880 is biologically unlikely, the intercept was forced through 0, resulting in linear and quadratic relationships. The regressions of UE (kcal/d) on UN (g/d) excretion were UE = 14.6 ± 0.32 × UN, and UE = 20.9 ± 1.0 × UN - 0.0357 ± 0.0056 × UN². In the quadratic regression, UE increased, but at a diminishing rate as UN excretion increased. As UC increased, UE linearly and quadratically increased. However, error variance was greater for regression with UC compared with UN as explanatory variables (8.42 vs. 7.42% of mean UE). The use of the quadratic regression between UN and UE excretion to predict ME resulted in a slope bias in ME predictions as dietary CP increased. The linear regression between UE and UN excretion removed slope bias between predicted ME and CP, and thus may be more appropriate for predicting UE across a wider range of dietary CP. Using equations to predict UE from UN should improve our ability to predict diet ME in Jersey cows compared with calculating ME directly from digestible energy.

The effects of the forage-to-concentrate ratio on the conversion of digestible energy to metabolizable energy in growing beef steers

Metabolizable energy (ME) is calculated from digestible energy (DE) using a constant conversion factor of 0.82. Methane and urine energy losses vary across diets and dry matter intake (DMI), suggesting that a static conversion factor fails to describe the biology. To quantify the effects of the forage-to-concentrate ratio (F:C) on the efficiency of conversion of DE to ME, 10 Angus steers were used in a 5 × 5 replicated Latin square. Dry-rolled corn was included in experimental diets at 0%, 22.5%, 45.0%, 67.5%, and 83.8% on a dry matter (DM) basis, resulting in a high F:C (HF:C), intermediate F:C (IF:C), equal F:C (EF:C), low F:C (LF:C), and a very low F:C (VLF:C), respectively. Each experimental period consisted of a 23-d diet adaption followed by 5 d of total fecal and urine collections and a 24-h gas exchange collection. Contrasts were used to test the linear and quadratic effects of the F:C. There was a tendency (P = 0.06) for DMI to increase linearly as F:C decreased. As a result, gross energy intake (GEI) increased linearly (P = 0.04) as F:C decreased. Fecal energy loss expressed as Mcal/d (P = 0.02) or as a proportion of GEI (P < 0.01) decreased as F:C decreased, such that DE (Mcal/d and Mcal/kg) increased linearly (P < 0.01) as F:C decreased. As a proportion of GEI, urine energy decreased linearly (P = 0.03) as F:C decreased. Methane energy loss as a proportion of GEI responded quadratically (P < 0.01), increasing from HF:C to IF:C then decreasing thereafter. The efficiency of DE to ME conversion increased quadratically (P < 0.01) as F:C decreased, ranging from 0.86 to 0.92. Heat production (Mcal) increased linearly (P < 0.04) as F:C decreased but was not different as a proportion of GEI (P ≥ 0.22). As a proportion of GEI, retained energy responded quadratically (P = 0.03), decreasing from HF:C to IF:C and increasing thereafter. DM, organic matter, and neutral detergent fiber digestibility increased linearly (P < 0.01) and starch digestibility decreased linearly (P < 0.01) as the F:C decreased. Total N retained tended to increase linearly as the proportion of concentrate increased in the diet (P = 0.09). In conclusion, the efficiency of conversion of DE to ME increased with decreasing F:C due to decreasing methane and urine energy loss. The relationship between DE and ME is not static, especially when differing F:C.

California net energy system for Bos taurus indicus

The California net energy system (CNES) was the reference for the development of most energy requirement systems worldwide, such as Nutrient Requirements of Beef Cattle (NASEM, Nutrient requirements of beef cattle, 8th Revised ed, 2016) and Brazilian Nutrient Requirements of Zebu and Crossbred Cattle (Valadares Filho, S. C., L. F. C. Silva, M. P. Gionbelli, P. P. Rotta, M. I. Marcondes, M. L. Chizzotti, and L. F. Prados, BR-CORTE: nutrient requirements of zebu and crossbred cattle, 3rd ed, 2016). This review aimed to compare methods used by NASEM and BR-CORTE to estimate the energy requirements for beef cattle. The net energy requirements for maintenance (NEm) of BR-CORTE is based on empty body weight (EBW), whereas NASEM uses shrunk body weight (SBW), but the Bos taurus indicus presents 10% to 8% lower NEm than Bos taurus taurus. We have compared animals with different EBW and SBW but with same equivalent empty body weight/standard reference weight ratio (0.75), as both systems have suggested different mature weights. Both systems predicted similar net energy requirements for gain (NEg) for animals with 1.8 kg of daily gain. However, estimated empty body gain was lower for NASEM estimations when the same metabolizable energy for gain is available. For pregnancy and lactation of beef cows, the NEm and net energy requirements for pregnancy (NEp) of a Zebu cow estimated by BR-CORTE were lower than the values estimated by NASEM. Furthermore, the magnitude of differences between these systems regarding NEp increased as pregnancy days increase. The NASEM and BR-CORTE systems have presented similar values for energy requirement for lactation (0.72 and 0.75 Mcal/kg milk, respectively).

Energy costs of feeding excess protein from corn-based by-products to finishing cattle

The increased use of by-products in finishing diets for cattle leads to diets that contain greater concentrations of crude protein (CP) and metabolizable protein (MP) than required. The hypothesis was that excess dietary CP and MP would increase maintenance energy requirements because of the energy costs of removing excess N as urea in urine. To evaluate the potential efficiency lost, two experiments were performed to determine the effects of feeding excess CP and MP to calves fed a finishing diet at 1 × maintenance energy intake (Exp. 1) and at 2 × maintenance intake (Exp. 2). In each experiment, eight crossbred Angus-based steers were assigned to two dietary treatments in a switchback design with three periods. Treatments were steam-flaked corn-based finishing diets with two dietary protein concentrations, 13.8% CP/9.63% MP (CON) or 19.5% CP/14.14% MP (dry matter basis; ECP), containing corn gluten meal to reflect a diet with excess CP and MP from corn by-products. Each period was 27 d in length with a 19-d dietary adaptation period in outdoor individual pens followed by a 4-d sample collection in one of four open circuit respiration chambers, 2-d fast in outdoor pen, and 2-d fast in one of four respiration chambers. Energy metabolism, diet digestibility, carbon (C) and nitrogen (N) balance, oxygen consumption, and carbon dioxide and methane production were measured. At both levels of intake, digestible energy as a proportion of gross energy (GE) tended to be greater (P < 0.06) in ECP than in CON steers. Metabolizable energy (ME) as a proportion of GE tended to be greater (P = 0.08) in the ECP steers than in the CON steers at 2 × maintenance intake. At 1 × and 2 × maintenance intake, urinary N excretion (g/d) was greater (P < 0.01) in the ECP steers than the CON steers. Heat production as a proportion of ME intake at 1 × maintenance tended (P = 0.06) to be greater for CON than for ECP (90.9% vs. 87.0% for CON and ECP, respectively); however, at 2 × maintenance energy intake, it was not different (63.9% vs. 63.8%, respectively). At 1 × maintenance intake, fasting heat production (FHP) was similar (P = 0.45) for both treatments, whereas at 2 × maintenance intake, FHP tended to be greater (P = 0.09) by 6% in ECP than in CON steers. Maintenance energy requirements estimated from linear and quadratic regression of energy retention on ME intake were 4% to 6% greater for ECP than for CON. Results of these studies suggest that feeding excess CP and MP from a protein source that is high in ruminally undegradable protein and low in protein quality will increase maintenance energy requirements of finishing steers.

Effects of energy supplementation on energy losses and nitrogen balance of steers fed green-chopped wheat pasture I: Calorimetry

Cattle grazing wheat pasture in the southern Great Plains are sometimes fed an energy supplement; however, the benefits of supplementation on nutrient balance, energy metabolism, and greenhouse gas emissions have not been elucidated. Therefore, we used 10 British crossbred steers (206 ± 10.7 kg initial BW) in a respiration calorimetry study to evaluate the effects of energy supplementation on energy losses, N balance, and nutrient digestibility of steers fed green-chopped wheat forage. The study design was an incomplete replicated 4 × 4 Latin square with treatments in a 2 × 2 factorial arrangement. Steers ( = 8) were assigned to 1 of 2 BW blocks (4 steers per block) with dietary factors consisting of 1) no supplementation (CON) or supplemented with a steam-flaked corn-based energy supplement (that also contained monensin sodium) at 0.5% of BW daily (SUP) and 2) NEm intakes of 1 times (1x) or 1.5 times (1.5x) maintenance. Wheat forage was harvested daily and continuously fed as green-chop to steers during the 56-d study. There were no differences ( ≥ 0.32) between CON and SUP for OM (78.3 vs. 80.7%, respectively) or NDF (68.3 vs. 64.8%, respectively) digestibility. At the 1.5x level of intake, there was no difference ( ≥ 0.16) in energy lost in feces (4.27 vs. 3.92 Mcal/d) or urine (0.58 vs. 0.55 Mcal/d), heat production (8.69 vs. 8.44 Mcal/d), or retained energy (3.10 vs. 3.46 Mcal/d) between supplementation treatments. Oxygen consumption (1,777 vs. 1,731 L/d; = 0.67) and CO production (1,704 vs. 1,627 L/d; = 0.56) of CON and SUP steers, respectively, were not different; however, SUP steers tended to have ( = 0.06) lower CH production (115 vs 130 L/d) than CON steers. Methane, as a proportion of GE intake, was similar for CON (6.87%) and SUP (6.07%; = 0.18), as was the ME:DE ratio ( = 0.24; 86.3% for CON and 87.9% for SUP). Fractional N excretion in urine and feces, as a proportion of total N excreted ( ≥ 0.84) or N intake ( ≥ 0.63), was not different between treatments. Calculated NEm and NEg values for CON were 1.76 and 1.37 Mcal/kg DM, respectively, whereas the NEm and NEg values for the SUP treatment were 2.32 and 1.61 Mcal/kg DM, respectively. Calculated NE values for steers fed additional energy were approximately 17.5% greater than the expected difference in energy content. This was probably the result of the inconsistent response at the 1x DMI level. Under these circumstances, energy supplementation did appear to enhance NEm and NEg value of the supplemented wheat forage diet.

Silagem de grãos úmidos de milho de textura dura ou macia em dietas com polpa cítrica para vacas em lactação

Avaliou-se o desempenho de vacas leiteiras que consumiram polpa cítrica e dois teores dietéticos de silagem de grão úmido de milho. Os tratamentos foram: milho de textura dura ou milho de textura macia ensilado na linha negra, em fatorial com 9% ou 18% de milho na dieta. O teor de polpa cítrica na dieta foi de 16,2% ou 25,6%, com alto e baixo milho, respectivamente. Doze vacas receberam os tratamentos em quadrados latinos 4x4. A produção diária de leite foi 27,9kg no milho duro e 28,8 no macio (P=0,19). Alto milho diminuiu o teor de gordura do leite de 3,38 para 3,26% (P=0,04) e aumentou o teor de proteína de 2,99 para 3,03% (P=0,05) e a eficiência alimentar de 1,50 para 1,57kg de leite/kg de consumo (P=0,03). Aumento no teor de milho induziu maior queda no pH ruminal na dieta com milho macio do que na dieta com milho duro (P=0,05 para a interação textura versus teor de milho). O milho macio aumentou o consumo diário de matéria orgânica digestível de 11,7 para 12,3kg (P=0,05). Os parâmetros digestivos sugerem que a ensilagem não eliminou totalmente o efeito da textura do endosperma sobre a digestibilidade do milho.

The effect of cereal and protein source on the energy intake and nitrogen balance of fattening lambs given all-concentrate diets

Energy intake and nitrogen balance studies have been conducted on 12 lambs fedad libitumon four all-concentrate diets of equal crude-protein content in an experiment of latin square design. Each diet contained one cereal, either barley or oats and one protein supplement, either white-fish meal or soya bean meal.

Protein supplements had no influence on energy intake, but intake was significantly higher when the lambs were given barley rather than oat diets.

There were highly significant differences in the degree of utilization of digested nitrogen between diets containing fish meal and soya bean meal, and between diets containing barley and oats.

The energy: nitrogen ratio of urine was inversely related to the proportion of urinary nitrogen present as urea and directly related to the degree of utilization of digested nitrogen.

Effects of breed of cattle on energy requirements for growth

With the object of comparing the energy requirements of cattle of different breeds a total of 108 animals, representing three maturity types, were individually fed at two levels of intake over three 12-week periods commencing at 250, 375 and 500 kg live weight in a co-ordinated experiment. The three breeds compared were Aberdeen Angus cross, Hereford × British Friesian and British Friesian. Animals were offered a 50:50 hay: concentrate ration at two levels of feeding; one level was designed to give 0·7 kg gain daily and the other 75 to 80% of this intake.

Though the relative performance of breeds differed at the three centres, overall average live-weight gain did not differ significantly between breeds. Feed conversion efficiency dropped from 8·55 kg dry matter per kg gain in the first period to 16·95 kg in the third period, but differences in conversion ratio between breeds were not significant.

Carcass measurements taken at slaughter immediately after the third test period indicated higher killing-out percentages and higher fat percentages in the Angus cross than in the British Friesian with Hereford × Friesian intermediate. Differences in energy needs for gain among the three breeds, predicted by apportioning ME intake to maintenance and gain using a multiple regression technique, were greater than differences calculated from carcass composition and published energy requirements for fat and protein deposition. The limitations of the use of the multiple regression technique for this purpose are discussed.

The effect of different proportions of dried grass and concentrates in the diet on voluntary intake and performance of calves

Complete diets each containing (1) 0%, (2) 20%, (3) 40%, (4) 60% high-quality, (5) 20% and (6) 40% low-quality dried grass were given ad libitum to 48 British Friesian calves.

The performance of the animals was studied over the stages of growth from 50 to 100 kg and 150 to 200 kg live weight. At each stage of growth the live-weight gain was similar on all treatments while the daily intake of dry matter was significantly affected by the treatments. Over the stage of growth from 50 to 100 kg live weight the intake of metabolizable energy was greatest on treatment 2 and lowest on treatment 4. The conversion ratio of metabolizable energy decreased with increasing levels and with both qualities of dried grass over the weight range 50 to 100 kg.

When the calves reached 100 kg live weight, digestibility and N balance studies were carried out. The metabolizable energy (ME) expressed as a percentage of the gross energy decreased with increasing levels and with the lower quality of dried grass. Nitrogen retention was not significantly affected by treatment differences.

The relationships of the voluntary intake of dry matter, ME intake and the conversion ratio of ME with the ME expressed as a percentage of gross energy over the lower live-weight range are also presented.

The effect of different dietary energy concentrations on the voluntary intake and growth of intensively-fed lambs

In a comparative slaughter trial which covered growth from about 16 kg to 40 kg live weight, five groups of six Romney × Swaledale lambs were offeredad libitumfive pelleted diets (A to E) in which rolled barley was gradually replaced by an 80 : 20 mixture of rolled oats : oat husks to the extent that the calculated metabolizable energy (ME) concentration fell from approximately 2–9 (A) to 2·5 (E) Mcal/kg DM.

Although daily live-weight gains did not differ significantly between treatments, the daily carcass gain fell from 143 g/day on A to 105 g/day on E (P<0·05) whereas gut contents increased from 9·9% of live weight to 16·1% (P< 0·001) from A to E. Differences in efficiency of utilization of ME above maintenance were variable but for gross efficiency (i.e. retention/total ME intake), there was a significant decline from A to E.

Dry-matter intakes for the whole experimental period were similar for all five diets, but initially intake was lower for diet E than for A (780v.927 g/day) and ultimately it was higher for E (1410v.1150 g/day). In a second experiment, involving diets A and E and a third diet of chopped dried grass, the pattern of intake and growth changed with live weight in a similar manner to that described above, except that appetite and growth on dried grass were consistently poorer. Daily variation in intake and rumen pH tended to be greater on the concentrate diets.

It is suggested that, amongst other factors, the stage of maturity of an animal may influence the point at which the digestible energy content of the diet restricts dietary intake in preference to physical limitations.

A study of factors affecting the voluntary intake of food by cattle

Six diets providing ratios of concentrate to hay of 100 : 0, 95 : 5, 90 : 10, 80 : 20, 70 : 30 and 60 : 40 were given ad libitum to 24 British Friesian steers. The hay (in the long form) was offered separately from the concentrates. From 91 to 136 kg live weight, as the proportion of hay in the diet increased, daily dry-matter intake decreased. Over the weight range, 136 to 363 kg live weight, the addition of small amounts of hay to the concentrate diet caused an increase in intake. At 42 weeks of age a digestibility trial was carried out. Daily drymatter intake was maximal when the diet contained 80% concentrates. The apparent digestibility and mean retention time of the diets increased as the proportion of concentrates increased. Differences in estimated gut fill were not significant. The diet consisting of concentrate only resulted in the lowest concentration of acetic acid and the highest concentration of propionic and butyric acids in the rumen liquor. Net-energy intake tended to increase as the proportion of concentrates increased from 60 to 90% but then remained fairly constant.

Differences in feed intake and the performance of Finn × Dorset ewes during late pregnancy

In two experiments carried out in the autumn of 1971 and 1972 (treatment prefixes 1 and 2 respectively), 84 Finn x Dorset ewes found by X-ray to carry from 1 to 4 foetuses were individually fed during the last 6 weeks of gestation either: 1A, ad libitum; 1H and 2H, 33 kcal M/kg ewe live weight+365 kcal per ME/kg foetus (anticipated birth weight); 1M, 80%; and 2L, 50% of the total energy fed to treatments 1H and 2H. The amounts given remained constant during the experimental period. The method of feeding according to foetal number within treatments, attempted to standardize the nutritional state within treatments.

All ewes (except those on 2L which remained constant) gained 6 to 8 kg live weight during the last 6 weeks of gestation and lost 8 to 10 kg at parturition. The birth weight of lambs was not affected by the range of energy (2·3 to 4·4 Meal ME/ewe per day) consumed during the last 6 weeks of gestation.

Plasma concentrations of free fatty acids (FFA), glucose and ketone bodies were determined weekly. The mean FFA levels were significantly higher in the low energy treatment groups than the high ones.

The present data indicated that if there is little change in body weight i n the early stages of pregnancy a 65 kg ewe bearing twin lambs, will require about 4 Meal ME/day during the last 50 days of gestation t o prevent a rise in plasma FFA concentration or loss of weight over the gestation period.

The voluntary intake and utilization of roughage–concentrate diets by sheep. 1. Concentrate supplements for hay and straw

Four levels of a proprietary concentrate (0, 100, 200 and 400 g/day) were offered to Welsh Mountain ewe lambs receiving hay or straw ad libitum for 14 weeks. The apparent digestibility of the energy and nitrogen in the various diets was determined in a concurrent digestibility trial.

The voluntary intakes of the straw and hay dry matter when given alone were 242 and 451 g/day respectively (28·4 and 49·2 g/kg W0·73 per day). Straw intake increased with an increase in concentrate feeding up to a level of 25% concentrate in the total dry matter and then declined. Hay intake declined linearly with increasing concentrate level (3 g/day decline per unit increase in the percentage of concentrate). In each case the total intake of dry matter and digestible energy increased with an increase in concentrate level.

There was a positive within-treatment relationship between initial live weight and voluntary intake, an additional 0·019 Meal ME/day being consumed per kg increase in live weight. Within treatment groups lambs consuming relatively more food also made relatively higher weight gains. Estimates based on published standards of the metabolizable energy intakes required to produce the live weight changes observed on each treatment were considerably higher than the intakes recorded in the trial.

The effect of protein intake during gestation on ewe and lamb performance

Two experiments were carried out in which a total of sixty-four Border Leicester × Scottish Blackface ewes were each individually fed on one of eight experimental diets from six weeks after service to parturition. The eight diets supplied four intakes of crude protein (156, 119, 90 and 65 g/68-kg ewe per day) and two intakes of energy (2923 and 2468 kcal ME/68-kg ewe per day). After parturition the ewes received one of two lactation treatments supplying a standard protein intake of approximately 260 g/68-kg ewe per day at ME intakes of 4700 and 4186 kcal/68-kg ewe per day.

The relationship between net body weight change (Y, kg) and ME (X1) and DCP (X2) intakes (per 68-kg ewe) was described by the equation Y = The DCP intake corresponding to maximum efficiency of energy utilization was 98 g/68-kg ewe per day. The relationship between lamb birth weight (Y, kg) and ME and DCP intake was described by the equation Y = 0·0003X1 + 0·0080 X2 + 2·8501.

Ewe live-weight loss during early lactation, lamb growth rates from birth to three weeks and ewe milk yield at three weeks tended to decrease with decreasing protein intake during pregnancy.

The voluntary intake and utilization of roughage–concentrate diets by sheep. 2. Barley and soya bean meal supplementation of hay diets

Three levels of soya bean meal (0%, 25% and 50% of the intake of hay dry matter) combined with three levels of pelleted barley (0%, 50% and 100% of the intake of hay dry matter) in a factorial arrangement of treatments were offered to Welsh Mountain ewe lambs receiving hay ad libitum for 14 weeks.

When barley was not given, soya bean meal added at 25% of the hay intake increased hay voluntary intake from 287 g/day to 412 g/day but hay intake was depressed to 339 g/day by a further increase in the level of soya bean meal. When barley was given, soya bean meal did not affect hay intake. With one exception, an increase in barley reduced hay intake, with the result that there were no differences between treatments in the digestible energy intakes of lambs receiving barley at each level of soya bean meal. In general, it was found that an increase in the concentrate allowance (barley + soya bean) reduced hay intake, whereas an increase in the crude protein content of the concentrate increased hay intake. The relationship between live-weight change, metabolizable energy intake and live weight was examined by regression analysis. Although live weight and voluntary intake were unrelated at the start of the experiment, a positive relationship emerged as the experiment progressed.

Energy and protein requirements for maintenance and growth of Boer crossbred kids

Meat production by goats has become an important livestock enterprise in several parts of the world. Nonetheless, energy and protein requirements of meat goats have not been defined thoroughly. The objective of this study was to determine the energy and protein requirements for maintenance and growth of 34 (3/4) Boer x (1/4) Saanen crossbred, intact male kids (20.5 +/- 0.24 kg of initial BW). The baseline group was 7 randomly selected kids, averaging 21.2 +/- 0.36 kg of BW. An intermediate group consisted of 6 randomly selected kids, fed for ad libitum intake, that were slaughtered when they reached an average BW of 28.2 +/- 0.39 kg. The remaining kids (n = 21) were allocated randomly on d 0 to 3 levels of DMI (treatments were ad libitum or restricted to 70 or 40% of the ad libitum intake) within 7 slaughter groups. A slaughter group contained 1 kid from each treatment, and kids were slaughtered when the ad libitum treatment kid reached 35 kg of BW. Individual body components (head plus feet, hide, internal organs plus blood, and carcass) were weighed, ground, mixed, and subsampled for chemical analyses. Initial body composition was determined using equations developed from the composition of the baseline kids. The calculated daily maintenance requirement for NE was 77.3 +/- 1.05 kcal/kg(0.75) of empty BW (EBW) or 67.4 +/- 1.04 kcal/kg(0.75) of shrunk BW. The daily ME requirement for maintenance (118.1 kcal/kg(0.75) of EBW or 103.0 kcal/kg(0.75) of shrunk BW) was calculated by iteration, assuming that the heat produced was equal to the ME intake at maintenance. The partial efficiency of use of ME for NE below maintenance was 0.65. A value of 2.44 +/- 0.4 g of net protein/kg(0.75) of EBW for daily maintenance was determined. Net energy requirements for growth ranged from 2.55 to 3.0 Mcal/kg of EBW gain at 20 and 35 kg of BW, and net protein requirements for growth ranged from 178.8 to 185.2 g/kg of EBW gain. These results suggest that NE and net protein requirements for growing meat goats exceed the requirements previously published for dairy goats. Moreover, results from this study suggest that the N requirement for maintenance for growing goats is greater than the established recommendations.

Determination of aromatic metabolites in ruminant urine by high-performance liquid chromatography

A method based on reversed-phase HPLC is reported for the separation and quantification of various urinary aromatic metabolites: hippuric, phenylaceturic, salicyluric, benzoic, phenylacetic, salicylic, 3-phenylpropionic and cinnamic acids and several phenols in ruminant urine. In this method, a Nova-Pak C18 (4 microns) 150 x 3.9 mm I.D. column, two solvents [A: 15% methanol in 20 mM acetic acid (pH 3.3); B: methanol) in a gradient mode at a flow-rate of 0.8 ml/min, and UV detection at 210 nm were used. Quantification of the total (free and conjugated) benzoic, phenylacetic and salicylic acids present in urine was achieved by hydrolysis of the samples in 3 M HCl at 100 degrees C for 24 h prior to HPLC analysis. The lowest detection concentration was 50 mumol/l. This method is useful for scanning the profile of aromatic metabolites in urine of ruminants, which provides information on the diets the animals receive.

[The use of a hydrolysis residue from lysine production in a straw concentrate mixture for fattening lambs]

The validity of residues from hydrolysis of soya bean meal for production of lysine was tested in a growth experiment with 2 groups of 25 cross breeding lambs as well as in a N-balance trial with 5 lambs. The animals in the growth experiment started with an average body weight of 25 kg. An industrially produced concentrate for lamb fattening was given to the animals of the control group. To the second group a straw-concentrate mixture was given, containing 30% straw, 52% barley, 5% soya bean meal, 5% dried beet pulp and 5% of hydrolysis residue. The mixture included 10.71 MJ ME resp. 5.51 MJ net-energy fat (cattle) and 166 g digestible crude protein per kg dry matter. The lambs of group 2 showed an 8% lower intake of DM, connected with a 26% intake of energy and 32% lower intake of DCP in comparison to the control group. The average daily body weight gain was 374 g for the control group and 241 g for group 2 respectively, the difference being statistically significant. The feed/gain ratio was in group 2 = 14% higher for energy and 6% higher for DCP than in the control group. The N-balance trial resulted in a N-retention of 25 percent of the N-intake. The results approved the possible use of 5% of the hydrolysis residue product for 2% crude protein in straw-concentrate mixtures for ruminants.

Influence of Psoroptes ovis on the energy metabolism of heifer calves

To determine the effect of Psoroptes ovis on the energy metabolism of heifers, 32 calves were randomly assigned to four treatments in a 2 X 2 factorial arrangement. Calves were fed the same diet at two intake levels, high or low, and were either infested or were not infested with P. ovis mites. Calves were housed in antigrooming stanchions. Body composition was determined by urea dilution on Days 0 and 63. Ration digestibility was determined on fecal grab samples using acid-insoluble ash as a marker. Infested calves had developed a severe P. ovis infestation 7 weeks following exposure and had significantly lower daily gain, gain:feed, and energy retention and higher serum glutamic-oxaloacetic transaminase than control calves. P. ovis infestation increased the maintenance energy requirement of calves by greater than 50% (79 vs. 123 kcal of net energy kg-1 body wt.75). For each 10% increase in the body surface affected by P. ovis, maintenance energy requirement increased 0.5 mcal day-1.

Utilization of dietary energy for maintenance, milk production and lipogenesis by lactating crossbred cows during their midstage of lactation

1. Twenty-four energy and nitrogen balances were determined using twenty-four crossbred cows (Brown Swiss X Sahiwal) during their midstage of lactation. Energy balances were estimated by subtracting milk energy and heat production from the metabolizable energy (ME) intake. Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. The cows were given amounts corresponding to 90, 110 and 130% of the ME and 90 and 110% of the digestible crude protein (DCP) standards of the (US) National Research Council (1966). 2. Energy requirements were estimated by partitioning the ME intake for maintenance, milk production and energy gain or loss by multiple regression of energy balance values. Heat production (and thus energy balance) was corrected for excess N intake. 3. Energy requirements for maintenance were 585-18, 580-17 and 574-41 kJ ME/kg body-weight0.75 per d for cows in negative balance, cows in positive balance and for all cows, respectively. 4. The efficiency of utilization of ME for milk production was 68-52, 65-48 and 66-12% respectively, for cows in negative balance, for cows in positive balance and all cows. Energy required per kg fat-corrected milk production was 4-580, 4-791 and 4-746 MJ ME for the respective groups of cows. 5. The efficiency of utilization of ME for tissue gain was 67-67 and 64-86% for cows in positive balance and for all cows respectively.

Maintenance requirements for energy in cross-bred cattle

1. Twenty-seven energy and protein balances were done using nine cross-bred (Brown Swiss times Sahiwal) mature bullocks in a series of three balance trials. The bullocks were fed 75, 100 and 125 percent of the metabolizable energy (ME) and digestible crude protein standard values recommended by the (US) National Research Council (1966). Heat production was estimated by indirect calorimetry, by collection and analysis of respiratory gases. 2. Utilization of energy for maintenance and fat production was estimated by computing regression of energy balance v. digestible energy (DE) and ME separately on a metabolic body size (kg body-weight (W)0-75) basis. Maintenance energy requirements and efficiency of utilization of ME for lipogenesis were estimated using multiple regression of ME intake, also. Heat production (and thus energy balance) was corrected for excess nitrogen intake. 3. An attempt was made to measure basal heat production of bullocks so that the net energy requirements for maintenance could be estimated. Extrapolation of the regression line of energy balance v. ME intake below maintenance on a W0-75 basis gave a basal metabolism of 348-09 kJ/W0-75 per d. 4. Energy requirements for maintenance were (kJ/kg W0-75 per d): 539-43 DE, 448-81 ME and 348-09 net energy. The results of multiple regression gave a requirement of 432-15 kJ ME/kg W0-75 per d for maintenance. 5. The efficiency of utilization of ME for maintenance was 81-34 percent while for lipogenesis it was 54-5 percent.

Urinary excretion of aromatic acids by sheep given diets containing different amounts of protein and roughage

1. The urinary excretions of total diethyl ether-soluble acids and total aromatic acids of three sheep given maintenance diets containing different proportions of hay, rolled oats and decorticated groundnut meal were determined.

2. When the sheep were given the diet containing 70% rolled oats the excretion of aromatic acids in the urine was less than that observed when the sheep were given diets high in roughage or protein concentrates.

3. The amounts of aromatic acids excreted in the urine were not related to the dietary intakes of crude protein, apparently digestible crude protein, crude fibre, lignin or cellulose.

4. The excretion of comparatively large amounts of aromatic acids in the urine of ruminants is discussed in relation to the smaller amounts normally excreted by non-ruminants. Possible reasons for the failure to observe any relationship between the amounts of aromatic acids excreted in the urine of the sheep and those constituents of the diets that were investigated are discussed and the nature of other precursors is suggested.

A study of the protein requirements of the mature breeding ewe. 2. Protein utilization in the pregnant ewe

1. An experiment was carried out in which protein utilization in the pregnant ewe was studied using the nitrogen balance technique.

2. Eight diets supplying four different intakes of crude protein and two different intakes of energy were each offered to eight individually penned ewes.

3. The mean crude protein intakes per day were 7·2, 5·5, 4·1 and 3·0 g/kg W0·73 (where W = body-weight) and the metabolizable energy intakes 134 and 113 kcal/kg W0·73.

4. N balances were carried out at 10–12, 14–16 and 18–20 weeks of gestation on five ewes from each treatment.

5. The apparent digestibility of both dry matter and crude protein decreased with decreasing protein intake. With the high energy intake, the apparent dry-matter digestibility was increased and the apparent digestibility of crude protein decreased. Stage of gestation had no significant effect on the apparent digestibility of either of these constituents.

6. N retention was not affected by the number of foetuses carried. With the higher energy intake and the higher protein intakes, the absolute retention of N was significantly increased at all stages of gestation. N retention increased with advancing pregnancy; the retentions at 10–12, 14–16 and 18–20 weeks of gestation being 0·086, 0·114 and 0·163 g/kg W0·73 per day respectively.

7. The efficiency of utilization of apparently digested N was calculated from the regression of retained N as a percentage of apparently digested N against apparently digested N.

8. The daily intakes of apparently digested N required for maximum efficiency were 0·551 and 0·620 g/kg W0·73 on the high and low energy intakes respectively. The daily intake for maximum efficiency decreased with advancing pregnancy, the values being 0·623, 0·587 and 0·567 g/kg W0·73 for the 10–12, 14–16 and 18–20 weeks of gestation respectively.

9. The levels of N retained at maximum efficiency were 0·235 and 0·202 g/kg W0·73 per day for the high and low energy intakes respectively. The levels of N retained increased during pregnancy from 0·170 g/kg W0·73 per day at 10–12 weeks to 0·286 g/kg W0·73 at 18–20 weeks. The requirements for zero N balance were 0·072 and 0·153 g apparently digested N/kg W0·73 per day for the high and low energy intakes respectively. The requirement for zero N balance decreased from 0·176 g/kg W0·73 per day at 10–12 weeks to 0·071 g/kg W0·73 at 18–20 weeks.

10. The results are discussed in relation to other research findings and current recommendations.