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

The aim of this study was to evaluate the effect of carcass traits, lairage time and weather conditions during lairage and abattoir factors that impact the incidence of dark cutting in 142,228 grain-fed carcasses, as defined by Meat Standards Australia (MSA) guidelines. This study was conducted over a 12-month period analysing data from cattle that were supplied from seven feedlots and processed at three abattoirs. Abattoir data indicated that the average incidence of dark cutting within the study was 2.8%. Increased wind speeds (WSs) and rain during lairage at the abattoir was associated with an increased risk of dark cutting, whereas variation in ambient temperature and/or relative humidity did not influence dark cutting. Heavier carcasses with whiter fat, larger hump heights, more rib fat, higher marble scores and lower ossification had lower incidences of dark cutting. The factors abattoir, time in lairage, time to grading and grader within Abattoir had significant effects on the incidence of dark cutting. The results from this study suggest that reducing the time in lairage and increasing the time between slaughter and grading are the two major ways to reduce dark cutting in MSA carcasses.

Reducing rumen starch fermentation of wheat with three percent sodium hydroxide has the potential to ameliorate the effect of heat stress in grain-fed wethers.

Selection for high productivity has resulted in ruminants adversely affected by heat stress (HS) due to their high metabolic rate and feed intake. One mechanism to ameliorate HS is to reduce the forage-to-concentrate ratio in the diet, although the inclusion of readily fermentable grains can reduce heat tolerance. The aim of these experiments was to investigate a chemical method for reducing the rate of fermentation of wheat and its effect on improving heat tolerance in sheep. In the first experiment, fermentation kinetics and buffered rumen fluid pH variation during in vitro incubation of corn, wheat, and 3% NaOH-treated wheat grains were compared. This experiment showed that corn and 3% NaOH-treated wheat had a slower (-23 and -22%, respectively; < 0.001) rate of gas production and elevated buffered rumen fluid pH ( < 0.001) compared with wheat. In the second experiment, 31 Merino × Poll Dorset wethers were housed in 2 climate-controlled rooms and were fed either corn grain plus forage (42.7% starch; were fed either corn grain plus forage (CD), wheat grain plus forage (WD) or 3 % NaOH-treated wheat plus forage (TWD) during 3 experimental periods: period 1 (P1), which consisted of 7 d of thermoneutral conditions (18 to 21°C and 40 to 50% relative humidity) and 1.7 times maintenance feed intake; period 2 (P2), which consisted of 7 d of HS (28 to 38°C and 30 to 50% relative humidity) and the same feed intake as in P1; and period 3 (P3), which consisted of 7 d of HS as in P2 and 2 times maintenance feed intake in a randomized control experiment. Water was offered ad libitum. The impact of HS was quantified by increases in rectal temperature, respiration rate (RR), and flank skin temperature (FT); variations in blood acid-base balance; and glucose, NEFA, and heat shock protein 70 (HSP-70) plasma concentrations. All physiological variables were elevated during HS, especially when wethers had greater feed intake (P3). Wethers fed CD had lower RR, rectal temperature, and FT than wethers fed WD ( < 0.001) and wethers fed TWD had lower RR and FT than wethers fed WD during HS ( < 0.05). There were reductions in blood CO, HCO3, and base excess concurrent with increases in blood partial pressure of O and pH during HS ( < 0.05). Heat stress reduced plasma NEFA and glucose concentrations whereas it increased prolactin ( < 0.05). Prolactin and HSP-70 plasma concentrations were greater for WD-fed wethers ( < 0.001) associated with Prolactin and HSP-70 plasma concentrations were greater for WD fed wethers (P < 0.001) during HS. These data indicate that the slow rate of rumen fermentation of CD and TWD can reduce the heat released during feed fermentation in the rumen, improving heat tolerance in sheep.

Feeding slowly fermentable grains has the potential to ameliorate heat stress in grain-fed wethers.

During heat stress (HS), livestock reduce metabolic heat production by lowering activity and feed intake. Because this has obvious consequences for productivity, the aim of these experiments was to investigate nutritional methods for reducing digestive metabolic heat production, thereby allowing livestock more opportunity to dissipate excess heat. In the first experiment, the fermentation rates of corn and wheat grains were compared in an in vitro gas production system containing buffered rumen fluid. This experiment showed that corn had a slower (-15%; < 0.001) rate of gas production than wheat and no differences in total amount of gas production after 24 h of incubation. In the second experiment, we hypothesized that the lower rate of fermentation of corn would reduce metabolic heat load in wethers and, in turn, improve tolerance to HS. Twenty-two Merino × Poll Dorset wethers were housed in 2 climate-controlled rooms and were fed either corn grain plus forage (CD; 39% starch) or wheat grain plus forage (WD; 37% starch) during 3 experimental periods: period 1 (P1), which consisted of 7 d of thermoneutral conditions (18 to 21°C and 40 to 50% relative humidity [RH]) and restricted feed intake (1.3 times maintenance); period 2 (P2), which consisted of 7 d of HS (28 to 38°C and 30 to 50% RH) and restricted feed intake; and period 3 (P3), which consisted of 7 d of HS as in P2 with unrestricted feed intake (1.5 times maintenance) in a randomized control experiment. Water was offered ad libitum. The level of HS was quantified by increases in rectal temperature (RT), respiration rate (RR), and left and right flank skin temperature (LFT and RFT, respectively) and blood acid-base balance. Rectal temperature, RR, LFT, and RFT were elevated ( < 0.001) during HS, especially when wethers had unrestricted feed intake (P3). Wethers fed CD had lower RR, RT, LFT, and RFT ( < 0.001) than wethers fed WD, and this benefit was greatest during HS (P2 and P3). The reduction in RR with CD resulted in less CO exhalation (greater partial pressure of CO2) and greater HCO3 ( < 0.05) than with WD, indicating reduced efforts to dissipate heat by evaporative heat loss via panting. The greatest heat from fermentation was apparent in WD wethers, which had elevated LFT compared with RFT ( < 0.001). Crucially, this large difference was not observed with the CD wethers, indicating that the slow rate of fermentation of CD was expressed as low heat released during feed fermentation in the rumen. These data demonstrated that feeding CD may be a useful management strategy to reduce the impact of high environmental heat loads in sheep.