Iberia Research Station Newsletter Spring 2013

Camelia W. Soprano, Wyatt, Wayne E., Scaglia, Guillermo, Viator, Sonny  |  2/23/2013 1:41:57 AM

Understanding Grazing Behavior in Ruminants

Image of cattle in pasture.

Grazing time is the time animals spend grabbing a bite, masticating (chewing) and searching for food. Depending on several factors, 70-90% of grazing activity occurs during daylight hours. It appears that the start of grazing periods is influenced by social facilitation (one or two animals start, the rest follow) while the end of meals appears to be regulated by physiological controls (independent for each animal). Also, ruminants in small groups spend less time grazing each day than those in large groups. It has been suggested that this response may be an ancestral behavior correlated with the level of perceived danger of predation. An individual in a small group faces a greater risk of predation than one that forms part of a large group. Cattle grazing pure grass have also shown to have greater daily grazing times than when grazing pure clover. Therefore, day length, social interactions and pasture species all appear to influence time spent grazing within a day.

Research has also shown that grazing ruminants take their largest meals at sunrise and sunset. Between 60% and 80% of total daily intake is consumed during these two main meals. This behavior may be a strategy used by the animal to take advantage of the increased photosynthetic products (sugars) and greater dry matter in pasture late in the day. Longer meals in the afternoon (evening) may also be an attempt by the animal to increase rumen fill (feel full) to ensure adequate food is available to ruminate during the night when little grazing occurs.

With all these considerations in mind, two experiments were conducted: 1) using supplementation as a strategy to affect grazing time; 2) using spatially separated pastures to allow cattle to express preference between grass and clovers.

In this article we discuss part of the data (Table 1) collected in three consecutive years (average of 105 days of grazing per year) on the effect of supplementing steers (initial weight of 506 lbs.) with corn gluten feed at 0.7% body weight (i.e., 506 x 0.007 = 3.5 lbs./day/steer) at different time of the day (8 a.m., 12 noon, 4 p.m.) while grazing ryegrass.

Table 1. Effect of time of supplementation on performance and behavior of stocker steers

No supplement

8 a.m. supplement

12 noon supplement

4 p.m. supplement

Ryegrass intake, lbs./day

13.3

11.0

17.2

16.5

Final weight, lbs.

785

816

768

794

Average daily gain, lbs.

2.64

2.95

2.51

2.72

Grazing, minutes/day

140

137

136

130

Bite rate, bites/min

65

61

60

57

Walking, minutes

6.1

6.4

5.6

6.6

Lying, minutes/day

76

71

76

80

Beef produced, lbs./acre

785

845

738

800

A Regional Program for Production of Multiple Agricultural Feedstocks and Processing to Biofuels and Biobased Chemicals

Image of sorghum biomass

The LSU AgCenter received its largest grant ever, a $17.2 million award from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, for a project to investigate energy cane and sweet sorghum for the production of biofuels and chemicals. The broad mission of the sweet sorghum research group is to “evaluate sweet sorghum hybrids for agronomic performance, inclusive of their ability to maintain juice quality into the fall season, produce commercial yields on marginal soil, respond to low-input sustainable production practices and deliver quantities of feedstock on a schedule that sustains the viability of the biorefinery.”

While it is broad in scope and involves multiple disciplines and research stations, personnel at the Iberia Research Station are responsible for investigating and demonstrating the logistics of feedstock delivery. The test location was the Sugar Research Station because of its lab facilities and close proximity to the Audubon Sugar Institute, where plant samples were sent for fiber and sugar analyses.

Hybrids of varying maturity were planted in early April, mid-May and early June, and harvesting with a John Deere combine was initiated when grain reached the hard-dough stage of development. The test was designed to provide a sustained feedstock supply from the initiation of harvest in July to mid-November, which is typically the time for the occurrence of the first frost. Harvesting commenced with the early-maturity hybrids in late July and continued until the June planting of the late-maturity hybrids were combine harvested on October 11.

Expectation that the late-maturity hybrids would reach hard-dough in approximately 150 days was not realized. This earlier-than-expected maturity, therefore, created an overlap in maturity between the mid- and late-maturity hybrids. Averaged over the three planting dates, the early-, mid- and late-maturity hybrids required 98, 123 and 130 days, respectively, to reach maturity. The ranking of fermentable sugar yields was consistent for each planting date, with the medium-maturity hybrids producing the most for each planting.

Averaged over planting dates, the early-, medium- and late-maturing hybrids yielded 1.70, 3.08 and 2.44 tons per acre of fermentable sugar, respectively. The hybrids in the first planting were adversely affected by dry soil conditions and for the last planting by Hurricane Isaac. Greatest yields were achieved with the May planting – 2.79 tons of fermentable sugar per acre.

Yields measured in this study suggest that a 1,000-metric-ton-per-day biorefinery would require approximately 6,000 acres to operate from July 15 to October 15. Biorefinery viability based on sweet sorghum is particularly feasible in south Louisiana when included in a model with energy cane, as sweet sorghum and energy cane can be grown in sequence to sustain feedstock availability.

Sorghum’s competitive advantage in Louisiana is that it can be grown on fallow land of the energy cane production cycle and can be harvested and transported with existing sugarcane equipment. 

Dr. H. P. "Sonny" Viator.

Understanding Grazing Behavior in Ruminants, continued.

Image of cattle in pasture

Some relevant issues to consider:

1) Animals receiving no supplement performed similarly to others that did receive supplement. This means that when the stocking rate (number of animals per acre) is correctly determined (in this case approximately two 500-lb. steers per acre) for the amount of grass available, supplementation may not be necessary. Supplementation is supposed to “supplement” the diet; we are adding some nutrients (energy, protein, calcium, phosphorus, etc.) that the main diet is lacking. It should have an additive effect; sometimes it can be on performance (the supplemented animal gained significantly more pounds than the one that is not supplemented) or on intake (usually protein supplementation increases the intake of low-quality hay, and this may improve performance). With supplementation you can also increase the stocking rate for that pasture, therefore managing more cattle per acre. In this particular experiment, the small amount of supplement fed pursued the objective of affecting grazing behavior, not an improvement of performance or any other variable.

2) Supplementing in the morning hours reduced ryegrass intake and increased animal gains. Even though those supplemented in the a.m. spent a similar amount of time grazing, 73% of that time is in the evening hours; while for those supplemented at noon or in the afternoon, the evening meal represented an average of 59% of the time grazing during the day.

3) Afternoon-supplemented cattle may have benefited from a complementary effect between ryegrass and corn gluten feed (highly digestible, high sugar content). This factor decreases grazing time and bite rate, hence the greater ryegrass intake was due to a greater bite mass (pounds of ryegrass/bite).

When planning a supplementation program, we need to consider not only the effects on grazing behavior and forage utilization but also the cost of the practice. At this stocking rate and level of supplementation, morning supplementation improved animal performance, reduced ryegrass intake and positively affected grazing behavior. But when all expenses are included (supplement, labor), it was not cost-effective. 

Dr. Guillermo Scaglia 

Iberia Research Station Newsletter, Spring 2013

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Please click the image to download and print a copy of this newsletter. If you are unable to print a copy, call the Iberia Research Station at 337-276-5527.

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