Grazing season is here

on .

Think about behavior to get the most from your grass

Forage quantity and quality are important factors in determining grazing animal performance. So as a livestock producer, you need reliable indicators of forage status. Direct measures of vegetation—clipping and weighing—can be useful to estimating the total amount of forage available.
That said, only a fraction of the total amount of forage present is useful to a grazing animal. In management systems where forage is managed for high quality and high yield and allocated on a daily basis (intensive grazing systems), forage utilization is higher than in other management systems. In less intensive systems, the forage you measure is less predictive of what the animals are eating. In those situations, the behavior of grazing animals can be used as an indicator of the quantity and quality of the forage on offer.

Consider a pasture where there are grasses of similar heights, but patches with different amounts of leaf to stem; these patches will likely be eaten at different rates and with different bite sizes. So while it might be tricky to directly relate grazing behavior to the forage quality and quantity, animal behavior can be a useful indicator. It’s similar to feeding energy according to body condition and protein to manure consistency.
When our bovine self-propelled forage harvesters are out harvesting, they are:
• searching for forage;
• selecting forage;
• grasping and pulling the selected forage into their mouths.

Unless forage is too short, cattle tend to wrap their tongues around forage and pull it into their mouths. The cow grabs forage between the upper and lower molars or the lower incisors and the upper dental pad, then she jerks back her head to sever the plant. This is why you get that recommendation to allow seedings to become firmly established before grazing. Soft ground and inadequately rooted plants are easily pulled up by grazing cattle.
Compared to sheep or goats, cattle have wide mouths with stiff upper lips; they eat large clumps. Cows are less selective than sheep or goats. As a result, they have a more difficult time selecting leaves off of woody forbes or young vegetation in a stand. And when cattle are carefully selecting, they need to reduce bite size and bite speed. That means cattle selecting a higher quality diet will spend more time grazing. Coincidentally, because goats and sheep need less total food, they have more time per unit of body size and better ability to be selective. These differences in ability to select have been used to correlate the preferred forage material of cattle, goats and sheep.

When grazing animals move into a traditional, rotationally grazed new pasture, they often move around the boundaries before actually moving into the pasture. Cattle tend to move in straight lines between points during grazing, while sheep tend to move parallel to fence lines.

Question: What plants do I select for pasture? And why do so many goats hate clover?
Young animals learn what to eat and what to avoid from older grazing animals. The strongest learning bond is between the dam and offspring. Learning from the dam begins during gestation with exposure to flavors through amniotic fluid. Subsequently the offspring will consume aromatic-flavor compounds in the milk.

Animals learn from experience. Grazing animals tend to sample new forages in small quantities. If an animal doesn’t like the forage, for whatever reason, the animal will either avoid that forage or limit the amount it eats.
Taste is more important than color. I have heard that cattle will not eat mineral that is not red. Not true. Cattle see on the monochromatic scale; they see shades of grey, not color.

Where animals graze
In pastures with uniform plant composition, day-to-day cattle movement is not by chance. Cattle rarely are observed in the same location for more than 2 consecutive days. In pastures where forage quantity and quality vary, observations indicate that cattle may not return to sites with low quality forage for as long as three weeks.

What do grazing animals want? Most cattle want to be bored; beyond that it seems that grazing animals are looking for succulent plant material. Their first preference is new green leaves. When new green leaves are not present, the animals will eat older green leaf material followed by green stems, then dry leaves and finally dry stems. Nutritional wisdom theory holds that cattle intentionally or instinctively select forage based on the content of protein, energy or other nutrients. I do not hold to nutritional wisdom theory in that it doesn’t explain to me why cattle eat dirt or sericea lespedeza.

This affinity for green plant material remains until almost no green is left. This chasing green material is used to explain why cattle often lose body condition during spring green-up. Their preference for new growth causes “flash grazing”—they are seeking out plants that they consider palatable.

Forage availability and how it influences grazing

Forage availability is not simply the amount of plant material growing in a pasture. Forage availability refers to the part of the plant material that a grazing animal will choose to eat and is able to access.

Cattle can be selective regarding the species of grasses they eat. Dr. DelCurto’s group in Oregon looked at grazing studies with mixed species pastures. It was reported that 80 percent of the diet was of a grass that made up only 6 percent of standing forage, but that grass was in vegetative stage. Preferred forages tend to have a much higher probability of being grazed (having more bites removed during each visit) and of being grazed again before other forages are depleted.

Less time is spent grazing when forage is plentiful and quality is good; more time is spent grazing when quantity or quality is limited. Cattle spend more time grazing when stocking rates are high, pasture is short, or when the standing crop is made up of plant species that differ in the amount of leaf material produced.

The demand or high selectivity for limited green material can increase grazing time. In studies under two different grazing levels, grazing time increased when limited green material was available. It seems that if green material is present, grazing animals will spend more time searching for it and will stop grazing earlier when mature forage is limiting.

Group behavior as an indicator

Cattle in small herds in small pastures will stay together. It is normal for animals in large herds to be dispersed. On smooth, level, flat or gently rolling land, cattle will graze in groups of 20 to 30 animals. If the topography is rugged, group size is more like 6 to 10. As forage availability increases, size of grazing group does too. When the amount of preferred forage decreases, cattle are forced to predate other types of plants. When cattle are forced to turn to browse, they eat less because they are not physically equipped to select leaves as effectively as grasses.

Patch grazing

Sometimes, close and repeated grazing of small patches or individual plants occurs while adjacent patches or individual plants of the same species are left ungrazed or lightly grazed. This patch grazing is prevalent on sites with high plant density and productivity and with species with fair palatability. Sites that are ungrazed one year tend to be ungrazed the next year also. The development of ungrazed patches in summer depends mostly on the patches not being grazed at the beginning of the season. The way to manage this is by either mowing or intensive and heavy early season stocking. Dr. Owensby at Kansas State studied intensive early season stocking. He found that large ungrazed plants develop if the start of grazing in the spring is delayed too long.

Cattle are more sensitive to the presence of their fecals than are sheep. Goats are intermediate to cattle and sheep. Animal fecals cause ungrazed patches. Urine tends to cause only an initial aversion. Cattle tend to avoid forage adjacent to fecals. Forage areas that are avoided can be several times as large as the area covered by the fecal material. In a situation of heavy stocking rate under continuous grazing, avoided areas can cover significant portions of a pasture. This effect can last for several months.

Best time of day to hand feed on pasture

The time of day when supplemental feed is offered affects grazing behavior and animal performance. Stocker steers have greater ADG when fed in early afternoon compared to those fed in early morning. Steers fed in early morning were fed during a major grazing period and the disturbance of normal grazing resulted in lower performance because steers did not resume grazing for 2 to 4 hours after supplemental feeding.

Dr. Jim White is ruminant nutritionist for MFA Incorporated.


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