Properties of liquid dairy manure in Saskatchewan - Associated livestock

Lactating cows have the greatest influence on properties of as-removed manure due to their contribution of water from the milk centre. Lactating cows have a milk parlour that requires cleaning and milking equipment that requires rinsing. For this reason, milk house effluent and wash water is included in the estimate for volume of lactating cow manure.

A dairy facility often has cattle other than lactating cows that contribute to the manure storage: dry cows, replacement heifers or calves. These cattle either receive different rations or are of a different size than milk-cows, and therefore their manure properties will differ.

If fed the same, the volume of manure produced by a dry cow should be similar to that of a lactating cow less milk house waste. Dry cows will actually excrete less manure than lactating cows because they consume less feed.

On this page, wash water is defined as water used to keep the floor clean. Most wash water is generated in the milk parlour when manure is washed into the gutter. Some wash water is used in the remainder of the facility, for example occasional rinsing of the alley.

Milk house effluent is defined as water used to flush the milk collection system. Pipes between the milk parlour and the bulk tank require cleansing before and after every milking event. Additionally, the bulk tank is rinsed every time milk is collected.

The milk centre is comprised of the milk parlour and the milk house, and the milk house contains the bulk tank. Together, milk parlour wash water and milk house effluent will be known as milk centre effluent.

Milk centre effluent

A brief literature review was conducted to determine a reasonable range for milk centre effluent (Table 2). The magnitude of the range (about 30 to 40 L/cow/day) is similar to the range observed in Saskatchewan for volume of dairy manure. This tends to lend confidence to the data observed in Saskatchewan. Also, this implies that the difference in manure volume between dairies is mostly influenced by water usage.

Table 2. Volume of milk centre effluent

¹ – Dataset mostly includes stanchion barns

The lowest values in Table 2 are generally representative of stanchion barns. In Saskatchewan, stanchion barns are no longer in use, and instead a milk parlour is most common. Janni et al found that milk centre effluent at two dairies with milk parlours was 24.2 and 42.1 L / cow / d.

The Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) found that recycling of plate cooler water had the greatest influence on waste water volume. For OMAFRA, the range shown in Table 2 assumes the following: plate cooler water is recycled, other wash water is not recycled, bulk tank water is sent to the manure storage and miscellaneous domestic water enters the storage.

The Agricultural Waste Management Farm Handbook (AWMFH) and the Midwest Plan Service (MWPS) suggest that moisture content of as-excreted dairy manure is 87 or 88 per cent respectively. At these moisture contents, the difference between as-excreted and as-removed manure is 40 or 46 L (from Properties of liquid dairy manure in Saskatchewan - Equation 3). This assumes that as-removed manure production of a 669 kg (1,475 lb) cow is 115 L/lactating cow/d at a moisture content of 92 per cent. The difference should be representative of milk centre effluent.

Given the above, a reasonable estimate for average volume of milk centre effluent is 40 L/cow/d.

Dry cow manure excretion

Very little reliable information is available regarding manure excretion of dry cows. The ASAE provides equations in their Standard D384.2 2005 based upon the work of Nennich et al (2005). However, these equations are based on a dataset of only 15 dry cows.

ASAE equations for dairy manure excretion are based upon the work of Nennich et al (2003) whereby a large dataset of several studies was developed. However, for lactating cows the dataset includes “554 cow-periods” whereas the dry cow dataset includes only 15 animals. Therefore, ASAE excretion equations for dry cows may be somewhat unreliable.

Existing ASAE equations predict that a 669 kg dry cow would excrete about 4.5 or 5.0/dry cow/day. This seems very low when compared to dry matter excretion of a lactating cow (8.73 kg/lactating cow/d).

It might be suggested that if fed the same, dry matter excretion of dairy calves, heifers and dry cows should be similar to that of beef cattle. In fact, for determining dry matter intake, the NRC recommends using beef equations rather than dairy due to limited data for heifers. The same could hold true for dry matter excretion, because the dataset for beef cattle will be far larger than that for dry cows.

For a beef cow fed silage rations, typical dry matter excretion would be about 6.7 kg/cow/d. This is perhaps a reasonable estimate of dry matter excretion from a dry dairy cow, considering that a lactating cow has dry matter excretion of 8.73 kg/lactating cow/d.

The volume of manure generated by a dry cow can be calculated if dry matter excretion is known. With the contribution of dry matter from bedding (0.5 kg cow d), 7.2 kg of total dry matter is equivalent to a volume of about 57 L/cow/d at moisture content of 88 per cent from Equation 3. This is slightly less than manure excreted by lactating cows and therefore seems to be a reasonable estimate.

Calves and growing heifers

The dataset (Nennich et al, 2005) for calves and growing heifers is somewhat larger than for dry cows: 46 and 60 animals respectively. Average daily dry matter excretion is 1.37 kg for calves and 3.74 kg for growing heifers. This assumes that the average weight of a calf is 152.8 kg and the average weight of a heifer is 437 kg.

Dry matter excretion needs to be normalized according to bodyweight for Saskatchewan conditions. In Saskatchewan, it may be assumed that the birthweight of a dairy calf is 95 lbs (43.1 kg). If a calf becomes a growing heifer at the weight of first breeding, and if a calf is bred at 55 per cent of full body weight, then a growing heifer weighs between 811 and 1,475 lbs (368 to 669 kg). The average weight of a calf and a heifer becomes 206 kg and 518 kg respectively.

Given the above assumptions, dry matter excretion of a calf and a heifer is 1.85 and 4.43 kg/animal/d. It may also be assumed that the dry matter contribution of bedding is 0.15 kg for a calf and 0.39 kg for a heifer. Total dry matter is therefore 2.00 kg for a calf and 4.82 kg for a heifer. From Equation 3, this is equivalent to manure volume of 15.9 and 38.3 L/animal/d at 88 per cent moisture content for calves and heifers respectively.

Assuming a silage diet, from ASAE equations (for beef cattle) dry matter excretion of a dairy calf and a dairy heifer is 2.1 and 5.2 kg/animal/d respectively. With dry matter contribution of bedding, total dry matter is 2.25 for a calf and 5.6 for a heifer. From Equation 3, this is equivalent to manure volume of 17.9 and 44.5 L/animal/d at 88 per cent moisture content for calves and heifers respectively.

Nutrient concentration for associated livestock

From ASAE equations for beef cattle (fed silage), a 669 kg dry cow would excrete 222 g N and 38 g P daily. Assuming that daily volume of manure production is 57 L/cow, then for phosphorus this results in as-removed concentration of 6.7 g/10 L. If losses of nitrogen are 15 per cent, then nitrogen concentration for as-removed dry cow manure is 33 g/10 L.

If heifers are fed the same silage diet as dry cows, then ASAE equations predict daily nitrogen and phosphorus excretion of 172 g and 29.5 g respectively. Assuming that daily volume of manure production is 44.5 L/heifer, then for phosphorus this results in as-removed concentration of 6.6 g/10 L. If losses of nitrogen are 15 per cent, then nitrogen concentration for as-removed heifer manure is 33 g / 10 L.

For calves fed the same silage diet as dry cows, then ASAE equations predict daily nitrogen and phosphorus excretion of 68.3 g and 11.7 g respectively. Assuming that daily volume of manure production is 17.9 L/calf, then for phosphorus this results in as-removed concentration of 6.5 g/10 L. If losses of nitrogen are 15 per cent, then nitrogen concentration for as-removed heifer manure 32 g/10 L.