Fig 1.
A PRISMA flow diagram detailing the literature search strategy and study selection for the meta-analysis.
Table 1.
Description of experimental studies used in the meta-analysis examining the effect of SRU supplementation on the performance of dairy cows.
Table 2.
Descriptive statistics of diet, feed intake and production performance variables extracted from studies included in the meta-analysis.
Table 3.
Effect of feeding slow-release urea on feed intake and production performance of dairy cows.
Table 4.
Linear regression of the relationship of feed intake and production performance in response to the inclusion level of slow-release urea (SRU, %DM diet) and dietary crude protein content (CP, %DM).
Fig 2.
Contribution of common feed raw materials to the average carbon footprint of (A) control diets (B) Slow-release urea (SRU) diets. 1Soybean include soybean meal, toasted soybean, heated soybean seeds and soybean bypass. 2Other vegetable protein sources include canola meal, rapeseed meal, corn and wheat distillers’ grains, linseed meal, cottonseed cake and corn gluten meal. 3Corn products include ground corn, high-moisture corn, steam-flaked corn and cornmeal. 4Other by-products include sugar beet pulp, wheat straw, citrus pulp, wheat bran, rice bran, brewers’ grains, wheat middlings, cottonseed hulls, soybean hulls.
Fig 3.
Effect of reformulating dairy diets with slow-release urea (SRU) on the (A) average carbon footprint (CFP) of dairy diets (B) average CFP of feed use for milk production.
Table 5.
Calculated manure nitrogen excretion (Nex) and nitrogen excretion intensity (Nexi) based on the results of feed intake and production performance variables (DMI, kg/cow; NI, g/d; and MY, kg/d) obtained from the meta-analysis.