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.

Grape marc consists of the skins, seeds and stems remaining after grapes have been pressed to make wine. Interest in grape marc for use as a dietary feed additive for ruminants has grown after recent research showed that inclusion of grape marc in the diet of dairy cows reduced their enteric methane (CH4) emissions. In the present research, in vitro fermentations were conducted on 20 diverse grape marcs to evaluate their potential as ruminant feed supplements and, in particular, mitigants of enteric CH4 emissions. The grape marcs, which were sourced from vineyards in south-eastern Australia, contained a range of red and white grape varieties with different proportions of skins, seeds and stalks, and had diverse chemical compositions. For each grape marc, four replicate samples, each of 1 g DM, were incubated in vitro with ruminal fluid. The volumes of total gas and CH4 produced after 48 h of incubation were determined. Total gas production ranged from 21.8 to 146.9 mL and CH4 production from 6.8 to 30.3 mL. White grape marcs produced more (P < 0.05) total gas (81.8 mL) than did red grape marcs (61.0 mL), but had a lower (P < 0.05) percentage of CH4 (25.3% and 30.3% of total gas). Grape marcs with a higher proportion of seeds produced less (P < 0.05) total gas than did the types composed of either skin or stalks; however, the seed types produced the greatest (P < 0.05) percentage of CH4 (49.8% of total gas). It is concluded that grape marcs differ greatly in their potential as mitigants of enteric CH4 emissions for ruminal production systems.

A widely used method for the in vitro measurement of fermentation parameters, total gas and methane (CH4) production (mL/g) from feed samples employs AnkomRF Technology with vented bottles, initially flushed with carbon dioxide (CO2). The volumes of gas accumulated between ventings, and the volumes vented, are calculated from the headspace pressure data. By using these data, it is possible to infer mathematically the quantity of CH4 produced, given just a single measurement of the CH4 mixing ratio measured in the headspace at the termination of fermentation. However, this calculation requires an additional assumption. Two possibilities for this are considered. We present mathematical formulae arising from each, and describe their sensitivity to violations of their respective assumptions. Also considered is a formula based on using N2 instead of CO2 as the flushing gas. It appears that, in practice, all three formulae are suitable for estimating CH4 production, with errors less than 3%.

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Feeding increased volumes of milk in the preweaning phase has been shown to improve growth, morbidity and mortality rates in calves (Bos Taurus). This experiment enlisted 20 Holstein-Friesian dairy replacement calves from birth until weaning (at 10 weeks of age) and assessed the effect of feeding either 4 L (Low) or 8 L (High) of milk per calf per day on their growth, immune competence and metabolic characteristics. The responsiveness of these systems was compared through a vaccination immune challenge. Calves in the High treatment group were significantly heavier from two weeks of age and were 19 kg heavier than calves in the Low treatment group at weaning. Calves in the High treatment group also exhibited greater immune responses, with significantly higher white cell counts and neutrophil counts than calves in the Low treatment group post-vaccination. Calves in the High treatment group also had lower beta-hydroxybutyrate both pre- and post-vaccination, and higher glucose and insulin levels post-vaccination, indicating superior metabolic characteristics. Calves had ad libitum access to lucerne hay (Medicago sativa) and a commercial concentrate. Solid feed intakes were mostly the same between treatments, with differences in hay intake only detected at 7 and 8 weeks of age. Results from this experiment are indicative of a positive influence of accelerated preweaning nutrition on growth, immune response and metabolic characteristics.