Influence of proportion of wheat in a pasture-based diet on milk yield, methane emissions, methane yield, and ruminal protozoa of dairy cows

Abstract

Wheat is the most common concentrate fed to grazing dairy cows in Australia, but no studies have examined the effects of wheat proportion in a pasture-based diet on milk production and methane emissions. In this 47-d experiment, 32 Holstein dairy cows were offered 1 of 4 diets during d 1 to 36. Cows in each of the dietary treatment groups were individually offered no wheat (W0) or wheat at 3 kg of dry matter (DM)/d (W3), 6 kg of DM/d (W6), or 9 kg of DM/d (W9). The remainder of the diet was 2.2 kg of DM of concentrate mix and freshly harvested perennial ryegrass (Lolium perenne) such that all individual cows were offered a total diet of approximately 20.2 kg of DM/d. From d 37 to 47 the diets of cows receiving treatments W0 and W3 remained unchanged, but cows in treatments W6 and W9 received the W3 diet. Individual cow feed intakes, milk yields, milk compositions, and methane emissions were measured for d 31 to 35 (period 1) and d 45 to 47 (period 2). During period 1, the mean intakes of cows offered the W0, W3, W6, and W9 diets were 19.2, 20.4, 20.2, and 19.8 kg of DM/d. Diet caused differences in energy-corrected milk, and means for W0, W3, W6, and W9 were 29.5, 32.4, 33.0, and 32.9 kg/d, respectively. Milk fat percentage differed with respective means of 3.93, 3.94, 3.69, and 3.17. Diets also caused differences in methane emissions, with means for W0, W3, W6, and W9 of 440, 431, 414, and 319 g/d. During period 1, the cows fed the W9 diet produced less methane and had lower methane yields (g/kg of DMI) and intensities (g/kg of energy-corrected milk) than cows fed the W3 diet. However, in period 2 when the wheat intake of cows in the W9 treatment was reduced to the same level as in the W3 treatment, their methane emissions, yields, and intensities were similar to those offered the W3 treatment, yet protozoa numbers in ruminal fluid were still much lower than those in cows offered the W3 treatment. Our research shows that for diets based on perennial ryegrass and crushed wheat, only the diet containing more than 30% crushed wheat resulted in substantially depressed milk fat concentration and reduced methane emissions, methane yield, and methane intensity. Thus, although feeding a diet with a high proportion of wheat can cause substantial methane mitigation, it can come at the cost of depression in milk fat concentration.

Volatile Fatty Acids in Ruminal Fluid Can Be Used to Predict Methane Yield of Dairy Cows

“…Methane yield (g/kg DMI) versus ruminal acetate, propionate and butyrate as mol per 100 mol of total volatile fatty acids from 215 cow records across 24 diets[24][25][26][27][28][29][30]. Solid lines are linear or reciprocal trend lines.…”

“…Combined methane yield (MY, g/kg DM) data from seven previously conducted experiments[24][25][26][27][28][29][30] plotted against ruminal fatty acid ratio A/P, (A + B)/P, and 1/P, with linear equations fitted by linear mixed effects meta-analysis (solid line).…”

Examining the Environmental Impacts of the Dairy and Baby Food Industries: Are First-Food Systems a Crucial Missing Part of the Healthy and Sustainable Food Systems Agenda Now Underway?

“…To date, efforts have focussed predominantly on increasing productivity through intensification and technological refinement [ 96 ]. The latter includes improving feed digestibility, type and additives to reduce enteric emissions, and changes to manure management such as acidification or fully recoupling manure recycling [ 97 , 98 , 99 , 100 , 101 , 102 , 103 ]. As a consequence, the US now produces 60% more milk with 80% fewer cows than in 1944 [ 104 ].…”

Milk Carbon Footprint in Latin American Livestock: effect of dairy system, breed and climate

“…On the other hand, other studies reported a decrease of 10% of the GHG emissions per kg of milk produced between mixed systems (0.92 CO 2 eq/kg milk) and grazing systems (1.02 CO 2 eq/kg milk) (Styles et al, 2018). However, grazing systems in Latin America are characterized for low dairy production (2 -19 kg milk/cow/d; Sainz-Sánchez et al, 2017;Marín-Santana et al, 2020;Alvarado-Bolovich et al, 2021) in comparison with other regions such as New Zealand (18 -22 kg milk/cow/d; Bryant et al, 2017) or Australia (30 kg milk/cow/d; Moate et al, 2020) with a pastoral culture, which can explain the differences in the CF per kg of milk.…”