Forage and Cattle Productivity
Productivity is a primary consideration in assessing the sustainability of any agricultural system. When nutrients are added to a forage system, productivity is expected to increase, but it is not always easy to quantify this improvement. A major part of the La Broquerie Research Project is to assess the productivity of the various hog manure and forage management systems under consideration in this study.
Productivity in the La Broquerie Research Project is being measured in terms of both forage and cattle performance, and in terms of both quality and quantity. The botanical composition of forage stands, the nutritional value of forage and the quantity of forage available for harvest or grazing are important indicators of productivity. In grazing systems, grazing days per acre, live weight gain, and blood urea nitrogen provide additional information on pasture and livestock performance.
Botanical composition of the forage stands was estimated each year in mid-July using points along transects placed across each plot and identifying plants under each point.
In hay treatments, standing forage biomass was measured immediately before hay cutting, by clipping plants 1.5 inches above the ground in 9 small quadrats in each plot. Hay was cut in mid-July and baled once dry. One-third of the bales from each hayfield were weighed on a platform scale and then individually sampled with a forage probe (5 cores per bale). At the end of the growing season, residual standing forage availability was determined by quadrat clippings, as described above.
Forage samples were dried completely in a forced-air oven to determine dry matter content. They were then ground and analyzed for crude protein, gross energy, acid detergent fiber (ADF), neutral detergent fiber (NDF), and concentration of various minerals.
Animals were introduced to pastures when available standing forage was visually estimated to be approximately 900 lb/ac. Steers were grazed over three 28-day periods. "Put and take" steers were used in an attempt to maintain standing available forage between 900 and 1300 lb/ac and maintain similar stages of plant growth in all pastures. These put and take steers were kept on a pasture adjacent the research pasture when not needed.
In grazing treatments, standing forage biomass was measured twice per 28-day period, using the same quadrat method as in the hay plots. Hand-plucked samples from each pasture, representative of the animals’ diet composition, were collected for each of the three 28-day periods and analyzed for quality. The grazing season ended once standing forage availability fell below 900 lb/ac, or after completion of the third 28-day period of data collection.
Ten British-cross yearling steers were assigned to each pasture on the basis of body weight. Treatment groups in each pasture were balanced such that the total mass of each group at the onset of the grazing trial was equal.
Dry matter intake (DMI) by animals was determined using alkane controlled-release capsules administered orally and analyzing fecal grab samples for dry matter and alkane content. Blood samples were collected from the tail vein of treatment steers once per 28-day period and analyzed for blood urea nitrogen to determine nitrogen status of the animal.
Botanical Composition of Forages
The three dominant plant species at the research site are Kentucky bluegrass, quackgrass and timothy. Other grasses, legumes and forbes are also present in small quantities.
Differences between manured and control plots were evident in the first field season following manure application as the manured plots contained larger plant densities of quackgrass (yellow bars in graph) and lower plant densities of Kentucky bluegrass, as well as legumes and forbes (Figure 1). The plant density of timothy appeared to decline in both control and manured plots. These changes in botanical composition associated with the application of manure have persisted over the course of the three-year grazing period.
Figure 1. Botanical composition of grazed plots in control (no manure), split (spring/fall manure application), and full (spring manure application) treatments in 2004, 2005 and 2006.
Manured plots produced more than twice as much total available biomass as control plots, and almost four times as much harvested hay (Table 1). Crude protein and energy were significantly greater in manured plots, while ash and ADF were unchanged.
|Total forage biomass (lb/ac)||2600 b||6200 a||6000 a|
|Hay harvested (lb/ac)||1100 b||3900 a||4100 a|
|Nutrient profile of first cut standing hay|
|Crude Protein (%)||7.5 b||10.2 b||11.0 a|
|Acid Detergent Fibre (%)||33.4||34.7||33.7|
|Neutral Detergent Fibre (%)||57.3 b||61.8 a||59.6 ab|
|Gross Energy (kJ / g)||18.3 b||18.7 a||18.6 a|
zBiomass refers to the cumulative biomass standing prior to harvest as hay.
Nitrogen, phosphorus, potassium and magnesium removed in the form of hay were significantly higher for the manured plots compared to those which did not receive manure. When expressed as a percent of that applied, 32.6% and 32.3% of applied N were removed in the form of hay for the split and full treatments, respectively. Approximately 25% and 19% of applied P were removed in the form of hay for the split and full treatments, respectively.
Available standing forage yield in the pastures was not significantly differed between treatments (Table 12) as put and take animals were utilized in an attempt to keep all pastures at 1000-1500 kg/ha (900-1300 lb/ac). Crude protein concentrations were significantly higher in the manured plots, while ADF was higher in control plots compared to those receiving the full application of manure in the spring.
|Available standing forage (lb/ac)||1100||2300||1800|
|Nutrient profile of hand-plucked samples|
|Crude Protein (%)||9.5 b||16.2 a||17.8 a|
|Acid Detergent Fibre (%)||33.5 a||32.1 ab||30.0 b|
|Neutral Detergent Fibre (%)||60.4||59.4||56.9|
|Gross Energy (kJ / g)||18.7||18.9||19.1|
zCalculated from 9 quadrat clippings per pasture.
Nitrogen removed in the form of animal gain was approximately 4.7% and 5.0% for split and full treatments, respectively. Phosphorus removal was similar, with 6.1% and 4.2 % of P removed in the form of animial gain for split and full treatments, respectively. This does not include nutrients deposited on the pasture by cattle in the form of feces and urine.
Grazing days per hectare and liveweight gain per hectare were three times greater in the manured pastures compared to the control (Table 3).
|Grazing days (days/ac)||36 c||138 a||125 b|
|Liveweight gain (lb/ac)||89 b||285 a||356 a|
a,b,c Values within a row that are followed by different letters are significantly different (P < 0.05).
As might be anticipated by the low protein concentrations in the pasture forage which did not receive manure, blood urea nitrogen concentrations were significantly lower for the steers grazing unfertilized forage compared to their counterparts grazing manured forage. Of the 356 blood samples collected, 51 were below the normal threshold (Fig. 2). All but one of these was from steers grazing control pastures.
Figure 2. Blood urea nitrogen (BUN) levels in steers grazed on control (no manure), split (spring/fall manure application) and full (spring manure application) paddocks.
- Manure application on pasture increased forage yield and quality in both hayed and grazed systems.
- Carrying capacity and liveweight gain increased by more than 3 times in pastures that received manure.
- Steers grazing unmanured pastures had lower BUN levels, with levels following a pattern similar to protein content in forages.