J. A. Nienaber

Effect of previous nutrition on body composition and maintenance energy costs of growing lambs

1. Forty-eight intact male lambs (30 kg) were fed to gain 16 (H), 5 (M) or -6 (L) kg during a 42 d interval (period 1). Lambs from each of the H and M groups were fed to gain either 16 (HH, MH), 5 (HM, MM) or -6 (HL, ML) kg and lambs from the L group were fed to gain 27 (LS), 16 (LH) or 5 (LM) kg during the ensuing 42 d (period 2). 2. Fasting heat production (FHP) of four lambs from each treatment was determined at the end of period 2. 3. Weights and compositions of the carcass, offal and digesta-free body as well as weights of major internal organs were determined for four lambs of each treatment at the end of periods 1 and 2. 4. Within groups of lambs of similar weight at the end of period 2, body composition was, in general, similar, but FHP was greater in lambs that had been on higher planes of nutrition during period 2. 5. Within groups of lambs of similar weight, lambs that were fed at higher planes of nutrition during period 2 had greater weights or proportions of liver, small intestine, large intestine and stomach. 6. Neither weight of the liver, kidney, stomach, small intestine, large intestine nor daily fasting heat production were constant functions of body-weight. Relations of these traits to body-weight changed with rate of gain. 7. Regression analysis indicated that the feeding of lambs at higher planes of nutrition during period 1 resulted in higher maintenance requirements of those lambs during period 2.

Electrical conductivity monitoring of soil condition and available N with animal manure and a cover crop

Development of sustainable agricultural management systems will depend, in part, on the ability to better use renewable resources, such as animal manure, and to synchronize the levels of soil available N with crop plant needs during the growing season. This study was conducted at the US Meat Animal Research Center in the central USA to determine whether differences in electromagnetic (EM) soil conductivity and available N levels over a growing season can be linked to feedlot manure/compost application and use of a green winter cover crop. A series of soil conductivity maps of a research cornfield were generated using global positioning system (GPS) and EM induction methods. The study site was treated over a 7-year period with manure and compost at rates matching either the phosphorus or the nitrogen requirements of silage corn (Zea mays L.). The plot was split for sub-treatments of a rye (Secale cereale L.) winter cover crop and no cover crop. Image processing techniques were used to establish electrical conductivity (EC) treatment means for each of the growing season surveys. Sequential measurement of profile weighted soil electrical conductivity (EC a) was effective in identifying the dynamic changes in available soil N, as affected by animal manure and N fertilizer treatments, during the corn-growing season. This method also clearly identified the effectiveness of cover crops in minimizing levels of available soil N before and after the corn-growing season, when soluble N is most subject to loss. The EM method for assessing soil condition provides insights into the dynamics of available N transformations that are supported by soil chemical analyses. This real-time monitoring approach could also be useful to farmers in enhancing N use efficiencies of cropping management systems and in minimizing N losses to the environment.

Tissue and whole-body oxygen uptake in fed and fasted steers.

The effect of feeding v. fasting, on tissue blood flow, oxygen uptake and proportional contributions of the portal drained viscera (PDV), liver (Expts 1 and 2) and hindquarters (HQ; Expt 2) to whole-body O2 uptake were studied in beef steers. The combined techniques of indirect calorimetry and net tissue flux, the latter being the product of arterio-venous concentration difference and blood flow, were used in the experiments. In response to fasting, whole-body O2 consumption decreased as did O2 uptake by all measured tissues except the liver (trend only in Expt 1). Blood flow to all measured tissues decreased during fasting and fractional uptake of O2 decreased in PDV and increased in liver and HQ (Expt 2). Proportional contribution of specific tissues to whole-body O2 uptake changed when animals were switched from the fed to the fasted state. The percentage consumed by PDV decreased from 25.4 to 19.9, by liver increased from 20.5 to 26.4 and by HQ was unchanged (9.6 and 10.5) in Expt 2. These significant responses in Expt 2 were observed as trends in Expt 1. The changes in proportional contribution of tissues to whole-animal O2 uptake reflect the changing metabolic role of specific tissues to lack of food supply. These findings emphasize the central role of the liver in metabolism and indicate that fasting (catabolic) measurements may not reflect the previous fed (anabolic) physiological state.

A LITERATURE REVIEW OF SWINE HEAT PRODUCTION

Current ASAE standards of heat and moisture production (HP, MP) for swine are primarily based on data collected nearly four decades ago. Feedstuffs, management practices, growth rate, and lean percentage of swine have changed HP and MP considerably in that time period. Literature data shows that lean percent increased 1.55% in the last 10 years, resulting in an increase in HP by approximately 15%. Data were compiled into two categories: prior to 1988, and 1988 to present. Analysis of this data revealed that HP increased 12.4% to 35.3% between the two categories, with the largest differences occurring at higher temperatures. The results also revealed lack of HP and MP data for greater than 90 kg pigs. The HP and MP standards for design of swine housing systems should be updated.

Oxygen Consumption by Portal Vein-Drained Organs and by Whole Animal in Conscious Growing Swine

Abstract A method was developed to measure simultaneously the O2 consumption (VO) by the whole animal and by the hepatic portal vein-drained organs (PVDO), including the gastrointestinal tract, spleen, and pancreas in conscious 3.5- to 4-month-old swine. The method was used to determine (i) the effect of feeding on hepatic portal vein blood flow rate (Qpv) and VO by PVDO and by the whole animal, and (ii) the significance of PVDO on the oxidative demand in the pig. Chronic cannulas were placed in the hepatic portal vein, carotid artery, and ileal vein. The Qpv was determined by an indicator dilution technique employing continuous constant infusion of 1% ρ-aminohippuric acid into the ileal vein. The VO2 by PVDO was estimated by multiplying Qpv by arterial-portal vein O2 difference measured with an arterial-venous O2 difference analyzer connected to the carotid artery and portal vein cannulas. Whole animal VO2 was measured with an open circuit indirect calorimeter. In seven pigs (3.5- to 4-month-old, 37.4 ± 0.8 kg) trained to be fed once daily, feeding (1.2 kg of feed mixed with 1.2 liter of H2O) caused postprandial (6 hr) Qpv to increase more than 34 ± 15% above the preprandial value of 34.5 ± 4.2 ml · min-1 · kg-1 body wt. The postprandial VO2 by PVDO was elevated more than 46 ± 12% above the value of 1.52 ± 0.20 ml · min-1 · kg-1 body wt observed during the preprandial period. Whole animal VO2 increased 45 ± 9 and 33 ± 7% above the preprandial value of 6.23 ± 0.57 ml · min-1 · kg-1 body wt for the first 6 hr and the 7 to 12 hr after feeding, respectively.

Thermoregulatory profile of a newer genetic line of pigs

Researchers and producers alike have noted the increased susceptibility to heat stress exhibited by the newer genetic lines of pigs. A study was conducted to gather baseline information on the effects of acute heat stress on total heat production (THP), respiratory quotient (RQ), respiration rate (RR), and rectal temperature (Trectal) and to investigate the dynamic interaction of these parameters in growing–finishing barrows. Sixteen moderate–lean growth barrows were randomly assigned to a set of treatments as dictated by a repeated 4×4 Latin square crossover design. Pigs were moved from an individual pen to an indirect calorimeter where one of four environmental treatments (18, 24, 28, 32°C) were applied for 20 h. During the treatment exposure RR, THP, RQ and Trectal were measured. For the 2-week period between treatments, pigs were housed at thermoneutral (22°C). THP was found to be 17–20% higher than the published standards but comparable with other contemporary studies. Respiration rate was found to be a leading indicator of stress.

Thermoregulatory responses of feeder cattle

A study was designed to investigate the thermoregulatory responses of feeder cattle to both acute and chronic exposures to elevated environmental temperatures. Rectal temperatures (RT) and respiration rate (RR) showed significant differences between temperature treatments. Both RT and RR had a diurnal pattern, which followed the diurnal pattern of the ambient conditions with some lag. Heat production at thermoneutral conditions was significantly higher than at the heat stress treatments. Heat production and respiratory quotient were the only two parameters shown to change with acclimation to heat stress.

Thermal Environment Effects on Growing-Finishing Swine Part I—Growth, Feed Intake and Heat Production

ABSTRACT SIXTY crossbred gilts were reared two per pen in five pens each at environmental temperatures of 5, 10, 15, 20, 25 and 30°C. Animals initially weighed an average of 43.6 kg and were slaughtered at an average weight of 86.7 kg. Statistically, growth rate was unaffected by temperature from 5 to 20°C. However, there was a trend toward decreased growth rate from 20 to 5°C and substantial decreases above 20°C. Feed intake decreased as temperature increased from 5 to 30°C and was related to temperature by a polynominal function. Heat production per unit weight decreased with increasing temperature and increased with increasing feed intake and body weight. The heat production data were fitted to a multiple linear regression equation. Conversion of feed to gain was most efficient at 20 and 25°C. The data define a broad range of acceptable thermal conditions rather than a singluar optimal environmental temperature.

Plasma adrenocorticotropic hormone and cortisol in pigs: effects of time of day on basal and stressor-altered concentrations.

Abstract An initial study was conducted to establish the presence in plasma of diurnal rhythms of immunoreactive porcine adrenocorticotropic hormone (pACTH) and cortisol in castrated male pigs (barrows). Fourteen barrows with jugular catheters were bled at 6-hr intervals for 24 hr. Significant changes in plasma pACTH were evident with peak levels (61 ± 6 pg/ml) at 0100–0700 hr and a trough (38 ± 4 pg/ml) at 1900 hr. Changes (P < 0.05) in plasma cortisol were also present in barrows with a peak (44 ± 6 ng/ml) at 0700 hr and a trough (21 ± 5 ng/ml) at 1900 hr. Plasma norepinephrine and epinephrine were measured at the same time intervals and did not differ among hours. In these unstressed pigs the ratio cortisol/log10 pACTH at 0700 hr (25.3 ± 3.0) was greater than the ratio at 1900 hr (12.9 ± 2.7). Sequential blood samples were subsequently taken on four of the barrows 12 and 26 days later. Plasma pACTH was variable among pigs and did not differ among hours. Plasma cortisol on both dates was greater (P < 0.05) in the morning (0100 or 0700 hr) than at 1900 hr. The ratio cortisol/log10 pACTH at 0700 hr was repeatedly greater than at 1900 hr. A second study was conducted to determine whether plasma pACTH and cortisol responses to mild (32°C for 2 hr) or strong (20-min restraint) stressors were dependent on the time of day of stressor application (0800 hr, AM; 1600 hr, PM). Response-associated parameters (maximum concentration, maximum incremental concentration, and integrated response) for pACTH and cortisol did not differ between AM and PM. However, a qualitative difference existed between the AM and PM plasma pACTH responses to restraint +32°C wherein the AM response consisted of a single prolonged surge, and the PM response of an initial major peak followed by a second significant minor peak. A suggested explanation is that the initial 20-min restraint stressor potentiated the hypothalamic-hypophyseal response to 32°C. These studies are the first direct measurements which suggest the presence of diurnal changes in plasma ACTH and cortisol in barrows. The studies also indicate for barrows an absence of diurnal changes in plasma epinephrine and norepinephrine. The responsiveness of the pituitary-adrenocortical axis to stressors did not exhibit quantitative diurnal changes at the time periods measured. However, it is hypothesized that the repeatable AM-PM difference in the ratio cortisol/log10 ACTH reflects a diurnal change in adrenal responsiveness to ACTH in unstressed pigs.

Feeding Patterns and Swine Performance in Hot Environments

Two experiments were conducted to determine modifications in eating behavior of heat-stressed pigs using gilts and barrows. Heat-stressed pigs were maintained at environmental temperatures that caused voluntary 13% and 26% reductions in daily feed consumption compared to control temperature pigs of the same weight. For control temperature pigs, there was a 50% reduction in number of meals and a threefold increase in meal size as animals grew from 40 to 100 kg. The number of daily meals and rate of eating (g/min) for heat-stressed pigs were remarkably similar to control pigs of the same age. However, for heat-stress treatments, the duration of meals was substantially reduced which apparently was the primary method of behaviorally adjusting to heat stress. Heat stress reduced liver, heart, stomach, and large intestine weights, and tended to reduce backfat thickness indicating that pigs under heat stress had reduced maintenance requirements. Heat stress did not affect feed conversion, but substantially reduced rate of gain.