Relationships of feedlot feed efficiency, performance, and feeding behavior with metabolic rate, methane production, and energy partitioning in beef cattle.

Residual feed intake (RFI) is the difference between the actual and expected feed intake of an animal based on its BW and growth rate over a specified period. The biological mechanisms underlying the variation in feed efficiency in animals with similar BW and growth rate are not well understood. This study determined the relationship of feedlot feed efficiency, performance, and feeding behavior with digestion and energy partitioning of 27 steers. The steers were selected from a total of 306 animals based on their RFI following feedlot tests at the University of Alberta Kinsella Research Station. Selected steers were ranked into high RFI (RFI > 0.5 SD above the mean, n = 11), medium RFI (RFI +/- 0.5 SD above and below the mean, n = 8), and low RFI (RFI < -0.5 SD below the mean, n = 8). The respective BW +/- SD for the RFI groups were 495.6 +/- 12.7, 529.1 +/- 18.6, and 501.2 +/- 15.5 kg. Digestibility and calorimetry trials were performed on a corn-or barley-based concentrate diet in yr 1 and 2, respectively, at 2.5 x maintenance requirements. Mean DMI (g/kg of BW(0.75)) during the measurements for high-, medium-, and low-RFI groups, respectively, were 82.7 +/- 2.0, 78.8 +/- 2.6, and 81.8 +/- 2.5 and did not differ (P > 0.10). Residual feed intake was correlated with daily methane production and energy lost as methane (r = 0.44; P < 0.05). Methane production was 28 and 24% less in low-RFI animals compared with high- and medium-RFI animals, respectively. Residual feed intake tended to be associated (P < 0.10) with apparent digestibilities of DM (r = -0.33) and CP (r = -0.34). The RFI of steers was correlated with DE (r = -0.41; P < 0.05), ME (r = -0.44; P < 0.05), heat production (HP; r = 0.68; P < 0.001), and retained energy (RE; r = -0.67; P < 0.001; energy values are expressed in kcal/kg of BW(0.75)). Feedlot partial efficiency of growth was correlated (P < 0.01) with methane production (r = -0.55), DE (r = 0.46), ME (r = 0.49), HP (r = -0.50), and RE (r = 0.62). With the exception of HP (r = 0.37; P < 0.05), feed conversion ratio was unrelated to the traits considered in the study. Feeding duration was correlated (P < 0.01) with apparent digestibility of DM (r = -0.55), CP (r = -0.47), methane production (r = 0.51), DE (r = -0.52), ME (r = -0.55), and RE (r = -0.60). These results have practical implications for the selection of animals that eat less at a similar BW and growth rate and for the environmental sustainability of beef production.

Effects of vasoactive intestinal polypeptide on electromyographic activity of the reticulo-omasal orifice in sheep at two levels of intake.

The effects of intragastric arterial infusions (1 mL/min) of physiological saline, vasoactive intestinal polypeptide (VIP), or VIP-antagonist [4Cl-D-Phe6, Leu17]VIP (1 nmol/mL) on electromyographic (EMG) activities of the reticulum and reticulo-omasal orifice (ROO) in conscious ewes fed to meet either their net energy for maintenance (NEm) or twice maintenance requirements were studied. Intragastric arterial infusions (1 mL/min) of 15-min durations were conducted before, during, and after feeding. The aims of the study were to elucidate the relationships between EMG activities of the reticulum and ROO and their potential regulation by VIP in sheep fed solid feed and how the relationships could be affected by different feeding levels. At both levels of feed intake, reticular EMG spiking activity was associated with high-amplitude EMG spiking activity of the ROO, and lack of spiking activity or quiescence of the ROO was never fully observed until the reticulum became quiescent. Irrespective of feeding level, infusions of VIP were associated with a marked reduction in reticular EMG and ROO spiking activities after 3 to 4 min and a complete cessation of ROO spiking activity 8 min after commencement of VIP infusion. Three to four minutes after initiation of VIP-antagonist infusion, EMG spiking activity of the ROO was enhanced and quiescence of the ROO activity was markedly diminished. The data suggest that 1) VIP may be involved in mediation of quiescence of the ROO and increases the duration of the quiescence in sheep fed at twice maintenance compared with maintenance-fed sheep, 2) the ROO EMG activity is influenced differently by different phases of the feeding cycle, and 3) VIP-antagonist enhances the EMG activity of the ROO.

Effects of alfalfa root saponins on digestive function in sheep.

The effects of alfalfa saponins on ruminal pH and VFA concentrations, protozoal numbers, forestomach motility, and digesta flow from the rumen were examined in this experiment. In a preliminary study, either 800 or 1600 mg/kg of saponins per kg BW were administered intraruminally in a single dose to one of two 60-kg wethers. Ruminal contractions were suppressed within 15 min. The study was terminated when one wether didn't recover. Saponins were then administered intraruminally in two equal doses daily into four ruminally and duodenally cannulated wethers (60 +/- 1 kg) in amounts equivalent to 0, 200, 400, and 800 mg/kg BW daily in a 4 x 4 Latin Square arrangement. Saponins increased VFA concentrations (P = .001) and lowered ruminal pH (P = .001) after 2 d of administration. On d 2 and d 14, saponins decreased (P < .01) protozoal populations. On d 11, pressure changes during ruminal contractions increased by 79% during resting (P = .06), 202% during feeding (P = .05), and 53% during an 8-h period (P = .08) as the level of saponins increased from 0 to 800 mg/kg BW. Administered saponins increased duodenal flows of OM and total N by 19 and 26%, respectively (P = .04 and .01). Apparent total tract N digestibility was reduced (P = .02) by 5% at the highest saponin dosage. We conclude that alfalfa may contain enough saponins to adversely impact ruminoreticular motility. Saponins also caused decreased ruminal protozoal populations, increased flow of total duodenal N, and reduced ruminal and total tract apparent digestibilities.

The Poisson process as a model for compartment digesta flow in ruminants.

The Poisson process, the simplest stochastic flow process, was used to develop a multicompartment model of ruminant digesta flow with Gamma distributed retention times. Although mathematically the model is a generalization of many previously published models, the physiological model differs substantially in asserting that the distributed delay time and the exponential rate (scale) parameters, including the scale parameter of the Gamma distribution, are determined by total digesta flow, and thus invariant with respect to the fraction marked. The shape factor of the Gamma distribution is shown to be sufficient to explain the difference between markers in rate of marker excretion. Consequently, the parameters of multiple markers can be simultaneously estimated with the constraint that the exponential scale parameters and the delay time are invariant with respect to marker. This constraint leads to a measure of pure error to strengthen statistical tests for model rejection. Steady-state digesta retention time is estimated from the transient marker retention parameters, eliminating the necessity of speculating on what fraction of digesta the marked fraction represents. Tests of various models, using simulations and animal experiments indicate that, even if a model is correct, it is not possible to obtain reliable parameter estimates by fitting to a single marker. Even with multiple markers some caution must be used in interpreting parameter estimates derived from least squares fitting.

Relationships between reticular contractions and digesta passage in steers consuming alfalfa hay and barley straw combinations ad libitum.

A Latin square design experiment was conducted to determine changes in voluntary feed intake, passage of digesta from the ruminoreticulum, and changes in frequency, duration, and amplitude of reticular contractions in four Hereford crossbred steers (474 +/- 10 kg) fed diets consisting of different combinations of alfalfa hay and barley straw. Diets consisted of 1) 100% straw, 2) 67% straw and 33% hay, 3) 33% straw and 67% hay, and 4) 100% hay. The diets were offered at 110% of ad libitum intake. Intakes of DM, OM, and lignin decreased linearly (P = .009, .011, and .003, respectively) with increased dietary straw, whereas diet did not affect intakes of NDF. Daily flows of DM, cell-wall components, and total contents at the duodenum decreased linearly with increased percentage of straw in the diet. Total digesta and fluid in the rumen increased linearly (P = .03 and .02) with increased straw content in the diet. Diet did not affect mean characteristics of reticular contractions. However, flow of total digesta through the proximal duodenum per contraction, per minute, and per centimeter of Hg amplitude of contraction decreased linearly (P = .01 and .02), whereas flow per centimeter of Hg tended to decrease (P = .08) with increased percentage of straw in the diet. Similarly, the flow of NDF through the proximal duodenum per reticular contraction and per minute of contraction decreased linearly (P = .006 and .03) as the percentage of straw increased in the diet. However, when confounding effects of DMI were removed, the characteristics of reticular contractions were not related to DM and NDF flow at the duodenum.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of ruminal escape protein and ambient temperature on the efficiency of utilization of metabolizable energy by lambs.

Forty-eight crossbred lambs (22.5 +/- 2.6 kg average BW) of equal numbers from both sexes were used to observe the effect of protein supplement (none, canola meal, or fish meal) and temperature (21 +/- 1.8 degrees C or 4.7 +/- 1.7 degrees C) on growth and energetic efficiency in a 2 x 3 x 2 factorial experiment. Twelve lambs were slaughtered at the onset of the trial to determine initial body composition. The remaining 36 were fed diets consisting of 50% concentrate and 50% straw at DMI of 77 and 83 g/kg.75 daily in the warm and cold, respectively, for an 85-d period. Daily gains of the control lambs and of those supplemented with canola and fish meal were 80, 94, and 101 g/d, respectively; however, no differences in efficiency of live weight gain could be detected. Apparent digestibilities of DM, GE, OM, and fiber were decreased (P < .05) in response to the cold. Methane production was increased (P < .01) in the cold. Metabolizable energy intake was not increased by exposure to cold, even though DMI was higher (P < .1) in the cold. Cold-treated lambs retained less (P < .01) total energy as well as less (P = .02) fat energy as determined by comparative slaughter. Supplementation with protein increased (P < .05) energy retained as protein; however, it did not affect total energy retained or energetic efficiency. Energy retention estimated from the calorimetry-balance technique was 30 to 80% greater than that estimated from the comparative slaughter technique. It was concluded that methane production in lambs with short fleece was increased when the temperature was reduced from 21 to 5 degrees C and that energetic efficiency was not affected by the concentration or type of protein in the diet.

Effects of cold environment and intake level on the energetic efficiency of feedlot steers.

The effects of cold climatic conditions on energy partitioning were investigated with 49 Hereford-type steers fed an all-concentrate, barley-based diet in a 2 x 3 factorial comparative slaughter trial. Steers (seven per treatment) were kept either indoors or outdoors (n = 2) and fed at 50, 65, or 80 g of DM/kg of BW.75 (n = 3) for up to 106 d. Mean temperatures were 16.9 +/- 2.7 degrees C and -7.6 +/- 6.8 degrees C in indoor and outdoor locations, respectively. Steers housed indoors grew 49% faster (P less than .001) and had 51% better gain: feed ratios (P less than .05) than those kept outdoors. Outdoor steers retained 65% less (P less than .001) energy. Estimated fasting heat production in the outdoor steers was 18% higher (P less than .01) and efficiency of ME use for maintenance 14% lower (P less than .01) than in the indoor steers, which resulted in an estimated increase of 41% in the ME requirements for maintenance in the outdoor steers. The NEg content of the diet was decreased from 1.29 Mcal/kg in the indoor steers to .76 Mcal/kg in the outdoor steers. Outdoor steers deposited 21% of their energy as protein, whereas indoor steers deposited only 14% of their energy as protein, which could explain the low NEg value of the diet in the cold environment. It was concluded that the main factors contributing to reduced energetic efficiency in the cold were an increased maintenance requirement and a greater proportion of the dietary energy retained as protein.

Effects of feed intake on particle distribution, passage of digesta, and extent of digestion in the gastrointestinal tract of cattle.

Four nonlactating Holstein dairy cows (means +/- SD BW = 692 +/- 49 kg) were used in a 4 x 4 Latin square design experiment to determine changes in distribution of particles within the ruminoreticulum (RR) and total digestive tract in cattle fed a forage-based diet at four intake levels. Relationships between chewing activities and rates of particle breakdown, passage, and digestion were also determined. Percentage of large particles increased linearly in the dorsal rumen (P = .001), ventral rumen (P = .004), reticulum (P = .007), duodenum (P = .007), and feces (P = .006) as DMI increased. Particles of sizes less than or equal to 2,000 microns, eligible to pass from the RR, constituted 60 to 92% of particle DM in the RR. Increased feed intake resulted in a longer (P = .003) eating but a shorter (P = .008) ruminating time per kilogram of DM intake, whereas total chewing time per kilogram of DMI was not affected (P = .12). Passage rate constants of NDF from the RR increased (P = .03) with intake. There was no change (P = .87) in the rate constant for particle breakdown in the dorsal rumen with increased intake. Neither fractional passage rate of NDF nor the rate constant for particle breakdown was related to time spent eating (P + .12; P = .34) or time spent ruminating (P = .11; P = .55). It was concluded that rate of passage of small particles from the RR was a determinant of passage from the RR and that changes in rates of passage and breakdown of particles could only be partially explained by changes in chewing activities.

Reticular contraction attributes and passage of digesta from the ruminoreticulum in cattle fed roughage diets.

Four nonlactating Holstein dairy cows (BW = 692 +/- 49 kg) were used in a 4 x 4 Latin square design experiment to determine how changes in attributes of reticular contractions were related to changes in passage of digesta from the ruminoreticulum in cattle fed a forage-based diet. Frequencies of reticular contraction during eating, ruminating, and resting phases of the feeding cycle were not affected (P = .09; P = .07; P = .09, respectively) by feeding level. Duration and amplitude of reticular contractions both increased linearly during eating (P = .03; P = .01), ruminating (P = .01; P = .02), and resting (P = .04; P = .02), respectively, as feed intake level increased. After removing the effects of intake, squared partial correlations computed within analyses of covariance indicated that NDF flow was not related to frequency (r2 = .15, P = .20) but was positively correlated with duration (r2 = .76, P = .0001) and amplitude (r2 = .56, P = .003) of contraction, indicating that duration and amplitude of reticular contraction were more associated with duodenal NDF flow than frequency. However, duration of reticular contraction (r2 = .47, P = .014) explained a greater variation in duodenal NDF flow than amplitude (r2 = .011, P = .74). Stepwise multiple regression also indicated that duration of reticular contraction was the attribute most associated (r2 = .76, P = .0001) with duodenal NDF flow. It was concluded that the changes in digesta passage from the ruminoreticulum were associated primarily with changes in the duration of reticular contraction.

Effects of changes in frequency of reticular contractions on fluid and particulate passage rates in cattle.

Four ruminally cannulated Hereford steers (531 +/- 32 kg) without weights (control; C) or with 24-kg weights (W) in the rumen were used in a double crossover design experiment to determine the effects of changes in frequency of reticular contractions at maintenance feed intakes on passage rates of particulate matter and fluid from the rumen. Duration of reticular contractions, apparent digestibilities and heat and methane productions were also determined. Weights in the rumen had no effect (P = .07) on frequency of reticular contractions before feeding; however, frequencies of reticular contractions were higher in C than in W steers during feeding (P = .03) and after feeding (P = .05). Weights in the rumen increased the average duration of contractions before feeding (P = .04), during feeding (P = .01) and after feeding (P = .05) by 12, 15 and 15%, respectively. Fractional outflow rates of ruminal and whole gastrointestinal particulate matter were 38% and 49% lower (P = .001) in C than in W steers, respectively. Weights in the rumen reduced (P = .001) methane production (liters/d) by 29%. Methane production was inversely correlated with fractional outflow rate for ruminal particulate matter (r = -.53; P = .034). Heat productions for W and C steers were 12.3 and 12.6 Mcal/d, respectively. Weights in the rumen had no effect on apparent digestibility. Duration of reticular contractions, in contrast to frequency of contractions, was the important factor influencing passage rates of both ruminal fluid and particulate matter. Methane production was decreased when passage rates were increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Relations between passage rates of rumen fluid and particulate matter and foam production in rumen contents of cattle fed on different diets ad lib.

1. A group of six cattle, three of which had a non-bloating history (group A) and had been ruminally cannulated for the previous 2 years, and three with a history of being bloat-prone (group B) and which had been ruminally cannulated only 3 months before the study, were fed ad lib. on chopped lucerne (Medicago sativa) hay, lucerne pellets, or a 100 g chopped hay and 900 g rolled barley grain/kg diet over three periods of 30 d each. Flow of rumen digesta, by reference to CoEDTA and chromium-mordanted fibres, and foam production from samples of rumen contents were measured. 2. Samples of rumen contents (50 ml) from group A produced foam heights of 150 and 60 mm, 2 and 4 h after feeding respectively, compared with 240 and 150 mm for group B (P less than 0.05). 3. The fractional passage rate of the 1-2 mm particles mordanted with Cr did not differ (P greater than 0.05) between groups. 4. The fractional outflow rates (FOR) for CoEDTA 0-2 h and 2-7 h after feed was offered were 0.205 and 0.160/h for group A and 0.093 and 0.086/h for group B respectively (P less than 0.05). 5. Rumen-fluid FOR 0-2 h and 2-7 h after provision of feed were significantly (P less than 0.05) inversely correlated (r -0.74 and -0.85 respectively) with the amount of foam produced from rumen contents at these times.

Effect of lasalocid on feedlot performance and energy partitioning in cattle.

Two experiments were conducted to quantify the effects of lasalocid on the performance and energy partitioning of cattle fed a 90% concentrate, barley-based diet. Experiment 1 utilized 100 Hereford heifers (initial weight 308 kg) fed diets containing no added ionophore, lasalocid added at 24, 36 or 54 mg/kg dry matter (DM), or monensin added at 33 mg/kg DM. In the 98-d trial, lasalocid-fed heifers gained an average of 1.35 kg daily, whereas control heifers gained 1.24 kg (P = .12). Heifers fed lasalocid (36 or 54 mg/kg DM), monensin, and the control diet required 6.2, 6.5 and 6.9 kg DM/kg gain, respectively (P greater than .1). Ionophores had no influence on carcass quality. In Exp. 2, four steers (616 kg) were fed the control or lasalocid diet (36 mg/kg DM) at daily feeding levels of 21, 44, 67 and 89 g DM/kg body weight.75; fecal, urinary, methane and heat losses were measured by total collection and indirect calorimetry methods. The proportion of digestible energy lost as methane averaged 7.5% for steers fed the control diet and 7.1% for the steers fed lasalocid (P less than .1). Lasalocid improved (P less than .05) the metabolizable energy (ME) density of the diet by 8, 8 and 5% at the 21, 44 and 67 g DM feeding levels. There was no difference (P greater than .1) between diets in ME density at the 89 g DM feeding level. The net energy for maintenance (NEm) value of the diet was increased (P less than .05) by 10 to 21% with lasalocid, whereas the net energy for gain (NEg) value was not affected. Average heat productions of the steers were increased (P less than .05) by 7% with lasalocid. The ME requirement for maintenance was estimated at 84 and 81 kcal/kg body weight.75 from linear regressions of energy retention and ME intake above maintenance for the control and lasalocid diets, respectively. Corresponding estimates using a semilog-linear method were 90 and 92. No differences (P greater than .1) in blood concentrations of insulin, glucagon or growth hormone were observed with the ionophore treatment. It was concluded that the main method by which lasalocid improved feed conversion was by increasing the ME density of the diet.