Summer grazing goals

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Summer pasture management should focus around 3 main goals:

· Meet the nutritional needs of cows in mid lactation (spring calving)

· Make sure pasture paddocks are not over-grazed, maintain good leaf residual and

· Set some paddocks up for stockpiling

Meeting the nutritional needs of cows in mid lactation involves knowing what the nutritional requirements are and it is also necessary to have some idea of what nutrient level is being provided by the pasture forage.  According to NRC tables, minimum nutrient requirements in terms of crude protein (CP) and total digestible nutrients (TDN) expressed as a percentage of the dry matter (DM) intake and as pounds of DM needed daily are as follows:

Cow Class

CP%

CP lbs/day

TDN %

TDN lbs/day

1300 lb Mature Cow

9.0

2.63

56

16.2

1st calf heifer, mature weight: 1300 lbs

9.5

2.34

58

14.6

It can be noted that it does not take high quality forages to meet these nutrient requirements.  It should also be noted that those first calf heifers do have a higher requirement than mature cows because they are still growing, and they require a more nutrient dense diet because their total DM intake is less than mature cows. 

Our next step is to look at the potential of pasture forages to meet these animal requirements.  We have already noted that the requirements can be met by less than high quality forage.  A key concept is that forage quality is strongly correlated with forage maturity.  In other words as the forage matures from the vegetative stage to boot stage and then on to seed head development and post seed head, both crude protein and TDN content decline.  Some general book values of what might be expected in terms of CP% and TDN% at various maturity stages are provided in the following table:

Maturity Stage

CP%

 

TDN %

Vegetative

18 +

 

62-68

Boot to early head

12-16

 

58-61

Late head

8-12

 

51-56

Post head

6-8

 

48-50

Pastures in the early head stage, where the heads have emerged, and the flowers are fully open and there are some immature seeds meet the nutritional needs of both the mature cow and the first calf heifer.  When the forage matures to the late head stage where the seeds are in the milk stage and soft it is likely that this forage will not meet the nutritional needs of the first calf heifer and it is border line forage for meeting the needs of the mid-lactation mature cow.

The challenge in pasture management this year has been clipping pastures to remove seed heads, in most cases the soil has been too wet.  As soils begin to dry, clipping some pasture paddocks to improve forage quality may be a good management practice, especially if there are first calf heifers in the herd. 

I do need to point out that even though tables say that late head forage has marginal quality in regards to meeting the nutrient requirements of mid-lactation cattle, these analyses are typically done on the whole plant, similar to a hay making situation.  The reality of grazing is that animals are able to do some selection and consume a higher nutrient content than would be reflected in the whole plant.  In a pasture paddock where the forage is at the late head stage, the cattle may eat the seed heads, some stem, and the plant leaves.  The nutrient content of this selection is higher compared to the whole plant.  Much of the low quality stem may be left behind, or in the case of high stocking densities, trampled down into the soil.

The second goal is to insure that pastures are not over-grazed.  During the spring flush, pastures are growing so rapidly that the management strategy generally is to just top the grass off and keep moving quickly through the paddocks.  As we get into summer weather with higher temperatures and less rainfall, cool season grass growth will slow down.   Managers need to keep an eye on residual grass height, in other words, they need to know when to get cattle out of a pasture paddock.  The goal should be to leave about 4 inches of pasture height when cattle are moved to the next paddock.  On the other end, begin grazing a paddock when there is around 8 to 10 inches of  height.  Provide a rest period to allow pasture paddocks to regrow to the 8 to 10 inch height before they are grazed again.  Pasture paddocks that maintain a 4 inch residual will regrow more quickly than paddocks grazed lower.  They will be ready for another grazing pass sooner.

Beginning a grazing pass at 8-10 inches and ending at 4 inches will pay some dividends in terms of animal performance.  It is known that cattle are only going to graze between 6 to 9 hours per day.  During that time they will average about 30,000 bites.  If they do not get a full mouth full of forage with each bite they will not graze more time or take more bites.   Forage intake is correlated with animal performance.  To meet nutrient requirements for milk production, growth and weight gain there must be adequate intake.  Cattle can get full mouthfuls with every bite when the forage is between 4 to 8 inches in height.  Cattle can graze lower than 4 inches, but they do not always get a full mouthful and total intake declines.

The third goal is to begin to look ahead during the summer period and follow a grazing management plan that allows some pasture paddocks to get stockpiled beginning in August.  This will require identifying those pasture paddocks that have the best soil drainage.  Remember that tall fescue is our best grass species for stockpiling if the plan is to use this forage for winter feeding, so identify pasture paddocks with a high percentage of fescue.  These paddocks will also need to be clipped to remove the seed heads and reset the plant into vegetative growth.  To accomplish this goal it may be necessary to include a plan to feed some hay in the late summer to early fall period to free up some paddocks for stockpiling.  This may be a wise use of some low quality first cut hay that will leverage the growth of some higher quality forage for winter feeding.



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