The contribution of the shivering hind leg to the metabolic response to cold of the young ox (Bos taurus)

Feedlot Factors Influencing the Incidence of Dark Cutting in Australian Grain-Fed Beef

It has been well-established that dark cutting (DC) is a multifactorial issue that is associated with numerous animal and management factors. However, there is limited understanding of the feedlot-based factors that contribute to the influence of DC. The aim of this study was to evaluate the effect of climate, animal, and feedlot factors on the incidence of pH non-compliance in Australian grain-fed cattle. For this study, feedlot and abattoir records from 142,228 individual cattle over a 1-year period were investigated. These data incorporated records from seven feedlots that consigned cattle to three abattoirs. The average incidence of DC in these carcasses was 2.8%. The production factors that were associated with increased risk of DC included feedlot, sex, hormone growth promotants (HGP), cattle health, and days on feed (DOF). Additionally, DC also increased by reduced solar radiation (SR, W/m2), lower wind speeds (WS, m/s), increased ambient temperature (TA, °C), higher rainfall, a higher average temperature–humidity index (THI), and increased duration of time above heat-load-index threshold of 86 (HLI ≥ 86) during the 7 days prior to feedlot departure. This study identified the feedlot factors that increase the risk of DC from a feedlot-management perspective.

The impact of weather on the incidence of dark cutting in Australian feedlot cattle

This study conducted a retrospective analysis of historical Meat Standard Australia (MSA) carcass data in combination with Bureau of Meteorology (BOM) weather data, to evaluate the relationship between climatic conditions prior to feedlot departure on the incidence of dark cutting grain-fed beef. Data records for 2,795,754 carcasses from 17 commercial feedlots over a 6-year period were evaluated within this study. Carcasses were consigned to 16 abattoirs. Weather data from BOM were recorded at 30-min intervals and were obtained from weather stations with the closest proximity to each feedlot. These data were used to calculate the Temperature Humidity Index (THI). Climatic data were amalgamated into daily observations and a series of predictors including ambient temperature (T_A, °C), relative humidity (RH, %), wind speed (WS, m/s), rainfall (mm) and THI. In addition, lag interactions from 24 h out to 28 days prior to exiting the feedlot were generated. The incidence of dark cutting was determined as percentage per cohort with an ultimate pH > 5.7. Data were analysed using three models: model 1 included feedlot, abattoir, hormone growth promotant status and sex as fixed effects. Model 2 incorporated the fixed effects within model 1 and minimum, maximum and standard deviation (SD) of T_A and RH, daily range in T_A, average WS and rainfall as random effects. Model 3 incorporated minimum, maximum, range and SD of THI, average WS and rainfall as random effects in addition to the fixed effects of model 1. The incidence of dark cutting within feedlot had a 10.1% range in estimated means with the lowest incidence was observed at feedlot 17 (0%) and highest incidence at feedlot 10 (10.1%). The inclusion of the climatic variables in model 2 and model 3 accounted for an additional 0.1 to 0.2% of the incidence of dark cutting carcasses. Higher maximum T_A, RH and THI in the 3 to 28 days prior to consignment were all associated with an increased incidence of dark cutting (P < 0.05), but not in the 48 h preceding consignment (P > 0.05). Low minimum T_A and low THI were also associated with an increase the incidence of dark cutting across all lag periods (P < 0.05). Increased variation in THI and T_A in the 48 h prior to consignment increased dark cutting (P < 0.05) while increased standard deviation (SD) of temperature and THI range also increased dark cutting in the 14 and 28 day prior to feedlot exit (P < 0.05). Smaller minimum ranges in T_A in the 28 days prior to consignment also reduced dark cutting (P < 0.05). Climatic conditions accounted for a further 0.1 to 0.2% of the incidence of dark cutting, whereas animal management factors, feedlot and abattoir were able to account for 21% of dark cutting. These data suggest that climatic conditions appear to have an inherent role in the incidence of dark cutting, albeit a small impact. Regardless, understanding the influence of climatic conditions on dark cutting allows for the implementation of management strategies within the supply chain to further reduce the impact of climatic conditions on grain-fed cattle.

Effects of direct exposure to cold weather under grazing in winter on the physiological, immunological, and behavioral conditions of Japanese Black beef cattle in central Japan

This study aimed to reveal the effects of direct exposure to cold weather under grazing in winter (GW) on the health of Japanese Black beef cattle, as assessed using physiological, immunological, and behavioral parameters. Ten Japanese Black beef cattle (328 ± 45 kg, 7.6 ± 3.4 years of age) were used in this experiment. In winter, five of the 10 cattle grazed for 2 months in a 1.8 ha pasture (GW), and the remaining cattle were fed under confined conditions with tethering (control [CT]). The two groups were fed similar feed during the experiment, except for the grazing forage. Blood samples were collected approximately every 2 weeks. The numbers of neutrophils and monocytes and antioxidant enzyme activity were higher in the GW group than in the CT group (p < 0.05). The proportions of CD4-single-positive cells were lower in GW cattle than in CT cattle (p = 0.06). This study showed that direct exposure of beef cattle to cold weather under GW enhanced the levels of circulating neutrophils and monocytes and contributed to the kinetic homeostasis of lymphocytes but also activated antioxidant enzymes due to an increase in oxidative stress.

Short communication: Changes under low ambient temperatures in the milk lipodome and metabolome of mid-lactation cows after dehorning as a calf

Horns are living tissue and cows can use their horns for thermoregulatory purposes. We investigated the effect of the presence of horns on the metabolome of milk serum and lipidome of milk fat, to assess the physiological effect of dehorning. Milk sampling took place at low ambient temperatures of -6 to 2°C. Horned and dehorned cows were kept in a mixed herd of Holstein Friesian and Brown Swiss cows. The hypothesis was that horned cows needed to increase their metabolism to compensate for additional heat loss through the presence of their horns. No differences were observed in milk yield, milk solids, and somatic cell counts between horned and dehorned cows. For the milk metabolome, horned cows showed an upregulation of several glucogenic AA that could be transformed into glucose for energy supply and a downregulation of sugar intermediates and γ-glutamylcysteine compared with dehorned cows. The fatty acid (FA) composition in horned cows showed a shift toward decreased odd medium-chain FA (C7:0, C9:0, and C11:0) and increased cis-vaccenic acid (C18:1n-7 cis-11) and stearidonic acid (C18:4n-3). The changes in milk composition related to additional heat loss in horned cows indicate a competition in C3 metabolism for glucose synthesis and de novo FA synthesis under cold stress.

Free fatty acid oxidation in bovine muscle in vivo: effects of cold exposure and feeding

A mixture of (1-14C)-labeled free fatty acids (FFA), complexed in bovine plasma, was infused into the abdominal aorta of conscious young steers exposed to thermoneutral or moderately cold conditions for several hours and fed 6 or 22 h before the experiment. The uptake, release, and oxidation of FFA in one hindlimb was calculated from simultaneous measurements of leg blood flow and arteriovenous difference in the specific activities of plasma 14C-FFA and blood 14CO2. Despite an invariable net release of FFA from the resting leg, uptake of 14C-FFA was considerable; of this only 14 and 3% was immediately converted to 14CO2 in fasted and fed steers, respectively. During cold exposure, increases in whole-body oxygen consumption (VO2), arterial concentration and turnover rate of plasma FFA, and a decrease in respiratory quotient were accompanied by much greater increases in VO2, uptake, and oxidation of FFA by the shivering leg. Even so, most FFA taken up were apparently not immediately oxidized to CO2, and possible alternatives for FFA metabolism in shivering muscle are discussed.

The distribution of blood flow between individual muscles and non-muscular tissues in the hind limb of the young ox (Bos taurus): values at thermoneurality and during exposuer to cold

1. The radioactive microspheres method was used to measure the distribution of blood flow in the hind leg in conscious young steers exposed to thermoneutral and moderately cold environments. Simultaneous measurement of total leg blood flow allowed calculation of blood flow (ml. 100 g tissue-1 min-1) to individual muscles and the major non-muscular tissues in the leg. 2. In the thermoneutral environment, leg blood flow was distributed approximately according to tissue weight, so that about 65% went to muscle and the remainder to bone, skin, connective tissue and fat; 1-7-11-5% of the injected dose of microspheres was found in the lungs, indicating the presence of functioning arteriovenous anastomoses in the leg. 3. During cold exposure leg blood flow increased two-and-a-half fold and 91% of this increase was due to increased blood flow in muscle. This was accompanied by substantial decreases in both total and capillary blood flow in leg skin in three of the four animals. 4. Values for resting tissue blood flow to the six largest individual leg muscles were compared, as well as that for tissue blood flow to the remaining leg muscle. Blood flow in the three large upper thigh muscles (biceps femoris, semimembranosus and semitendinosus) was about half that in muscles in the rest of the leg. 5. Cold exposure caused a threefold increase in total leg muscle blood flow, but the only individual muscles to respond substantially in all four animals were the vastus lateralis and the rectus femoris. Comparison of results from individual animals suggested a relation between total leg blood flow and the number of muscles (apart from vastus lateralis and rectus femoris) involved in shivering. Leg adipose tissue blood flow also increased significantly in the cold.

Acute cold exposure and the metabolism of blood glucose, lactate and pyruvate, and plasma amino acids in the hind leg of the fed and fasted young ox

1. Young steers were fed either 3-4 or 20 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (total V 0-2), respiratory quotient (rq), blood packed cell volume (PCV), and hind-leg blood flow (leg Q) and oxygen uptake (leg VO-2). The arteriovenous differences in whole blood glucose, lactate and pyruvate, and individual amino acid and urea concentrations across the leg were also measured. Net exchange and fractional uptake of these metabolites by the leg were calculated from these results. 2. Cold exposure doubled total VO-2, significantly decreased RQ and significantly increased PCV. Leg Q and leg VO-2 increased 3- to 5-fold and 4- to 13-fold respectively in both feeding groups. Arterial blood glucose increased slightly but significantly in both 20 h- and 3 h-fed steers. There was a substantial increase in mean net leg uptake of glucose in both feeding groups. This was much greater in the 20 h-fed group because of the significant increase in fractional uptake occurring only in this group. Cold did not significantly affect arterial blood lactate or pyruvate levels, but the net leg output of lactate found in both feeding groups in thermoneutrality was increased in the 20 h-fed steers, and reversed to a net uptake in the 3 h-fed animals. Cold caused a small but significant decrease in the total plasma amino acid level in the 20 h-fed but not in the 3 h-fed group; individual amino acid levels or leg uptakes were not affected. 3. Feeding before the experiment caused a significant increase in RQ. Leg Q, leg uptake of glucose and leg output of lactate increased after feeding in the thermoneutral environment only. Arterial pyruvate increased significantly, but net leg output was not significantly affected by feeding. Arterial plasma concentration of several individual, but not of total amino acids, increased significantly in both environments, and the net output of many individual amino acids in the 20 h-fed steers was decreased or reversed to a net uptake in the 3 h-fed group in thermoneutrality only. 4. The results suggest that blood glucose could be a significant fuel for oxidation in shivering skeletal muscle in young steers, and that output of amino acids from skeletal muscle could not contribute significantly to this increased glucose supply by hepatic gluconeogenesis.

The effects of acute cold exposure and feeding on volatile fatty acid metabolism in the hind leg of the young ox

1. Young steers were fed either 20 or 4 h before exposure to a thermoneutral or a moderately cold environment. Measurements were made of total oxygen consumption (total VO2), respiratory quotient (RQ) and hind-leg blood flow (leg Q) and oxygen uptake (leg VO2). The arteriovenous difference in plasma concentrations of individual volatile fatty acids (VFA) across the leg was also measured. Net exchange and fractional uptake of VFA by the leg were calculated from these results.

2. Cold exposure doubled total VO2, significantly decreased the RQ and caused 3-fold and 10-fold increases in leg Q and leg VO2 respectively in both 4 h- and 20 h-fed steers. Arterial plasma concentrations of total VFA (which was more than 95 % acetate) and net leg uptake of VFA also significantly increased in both groups. Cold had no effect on the fractional uptake of VFA by the leg.

3. Feeding shortly before the experiment caused a significant increase in total VO2 in thermoneutrality only, and in RQ, arterial plasma VFA and net VFA uptake by the leg in both environments. There was a significant decrease in the fractional uptake of VFA by the leg.

4. Calculations suggest that although circulating acetate could, in theory, supply over 60 % of the energy required by the hind leg in the resting, fed animal, less than 30 % of the increased requirement of the shivering leg could be supplied by acetate during acute cold exposure, even shortly after feeding.