Measuring animal productivity and rumen efficiency from extensively overwintered beef cows on the Canadian Prairies
Many producers in the Prairie region have adopted the use of low-cost, extensive overwintering strategies. Although the economic benefits of these practices are well-documented, rumen efficiency and animal productivity have not been fully characterized. Evaluation of such strategies is challenging because of our limited capacity to measure individual animal intake in extensive overwintering systems. In an attempt to address these knowledge gaps, sixty mature, non-lactating, pregnant beef cows were fed low-quality forage (8.8% crude protein and 4.3 Mcal kg-1 gross energy (GE), DM basis) ad libitum and monitored over two, 28-day periods. Cows were divided into three treatment groups: intensively overwintered (drylot; DL), extensively overwintered (bale grazed; BG) and extensively overwintered supplemented with dried distillers’ grains with solubles (DDGS) at a rate of 8.31 kg DM every third day (BG+DDGS). Measurements included temperature, body weight, DM intake, enteric methane emission, and serum urea nitrogen (SUN). Average daily air temperature over the trial was -17.1±6.5oC (±SD). Localized temperatures, measured with iButtons near the animal body surface, showed that cows in the extensive treatments were exposed to colder temperatures, at -14.7±0.6oC, compared to cows overwintered intensively, at -11.9±1.4oC (±SD). Average daily gain over the trial was greater (P<0.01) for DL cows when compared to BG cows, but not different (P>0.20) when comparing DL to BG+DDGS. Intake was greater (P=0.04) in period one for DL cows compared to BG cows, measured using GrowSafe and alkane bolus techniques, at 13.4±0.38 and 12.1±0.44 kg DM d-1, respectively (±SE). This resulted in greater (P<0.01) enteric methane emission from the BG cows in period one, at 5.62±0.49 and 8.46±0.49 %GEI, for the DL and BG treatments, respectively (±SE). The addition of DDGS every third-day in the extensive treatment reduced enteric methane in both periods. Average SUN concentrations over the trial were below the acceptable range of 2.1 mmol L-1 at 1.00±0.40 and 1.40±0.60 mmol L-1 for cows in the DL and BG treatments, respectively (±SD). When measured at 24 and 72 hours after feeding DDGS, SUN concentrations for cows in the BG+DGSS treatment were 5.14±1.67 and 2.65±0.57 mmol L-1, respectively (±SD), indicating that supplemental DDGS was an effective strategy to increase SUN when feeding low-quality forage. This data demonstrates that animal nutrient requirements may differ in intensive and extensive overwintering environments, and therefore require further characterization to improve metabolic and production efficiency of cattle.
Keywords: enteric methane, beef cows, overwintering