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Estimating how long the hay supply will last

published: November 15th 2022
by: Jason Warner
source: Kansas State University

The question recently proposed to an Extension professional by a local producer was: “I have 60 head of mature cows and 600 large round bales of hay on hand. If I start feeding harvested forage today, do I have enough forage to make it through the winter?”  This is an actual scenario and a real concern for many this year due to the reduction in forage supplies due to drought.

      The first step in understanding our forage supply is having an accurate bale count, estimation of bale weight and knowledge of the hay dry matter percentage (100 – moisture %).  To the credit of the producer, they had already done their due diligence by establishing an exact bale count and by collecting core samples on a subset of the bales for which the average dry matter percentage was approximately 85%.  Further discussion revealed that the average bale weight was 1,700 lb. as-is.

      From these values, the producer had the following forage inventory: 600 bales x 1,700 lb. per bale as-is = 1,020,000 lb. as-is of baled forage, divided by 2,000 lb. per ton = 510 ton as-is of baled forage available.  We must assign an estimated value to account for storage loss because failure to do so will result in overestimating tonnage.  Assuming a conservative 15% dry matter loss, the final tonnage available for feeding was adjusted to 434 ton as-is (510 ton x 0.85).

      Assessing our forage demand can be a little more complex as we need to calculate for days and anticipated adjustments in cattle inventories.  The producer stated the herd contained 60 head of mature cows with nursing calves at side which he planned to wean and also make cow culling decisions 45 days later.  These calves were estimated to be 450 lb. on average during that time until weaning, thus old enough that we needed to account for direct forage consumption in addition to the forage intake by the lactating cow (Table 1).  Except for 15 replacement heifers, the producer’s intent was to market calves directly after weaning. Following pregnancy evaluation and identifying additional females to cull, the producer anticipated removing 10 females from the herd, lowering the number of non-lactating, pregnant cows to 50 to maintain for the next 3.5 months (November 15 to March 1) until calving.

      Concerns regarding grazing availability next spring focused our attention on ensuring sufficient hay would be available for three months following the beginning of calving for this same group of mature females plus 12 pregnant coming 2-year-old females and the herd bulls.  This producer required 291 total tons to meet the needs of every animal, before adding 10% to account for losses during feeding for a final adjusted 320 tons.  This producer was fortunate to have had an adequate surplus of 114 tons if they were required to feed the entire herd 100% of their needs from October through May.


Table 1. Estimation of forage intake requirements by cattle class for example herd.

Class of Cattle

# Head



DMI, % of BW

Tons As-Is (85% DM)

Lactating Mature Cows






Dry Mature Cows






Lactating Mature Cows






Nursing Calves






Mature Bulls






Replacement Heifers






Coming 2 Yr Old Hfrs






Total Before Loss







      An important consideration is early weaning.  In this scenario, had the producer decided to early wean the calves, rather than feeding the pairs for an additional 45 days, it would have resulted in a savings of approximately 20 ton of forage from a combination of forage intake from both the calf and cow.  Pregnancy checking and culling females at that same time 45 days earlier would have produced another 8 ton of forage savings.

      Our estimates in this situation are based on animal body weight, head count and days fed with average assumptions for lactation, genetic potential for growth, and basal forage quality.  Additional forage needs due to inclement weather and body condition score changes would need to be accounted for.  Likewise, this does not determine what additional protein and energy supplementation may be needed, but it is the first fundamental step to be completed when evaluating the adequacy of the nutritional program of the cowherd and planning for future needs.  Taking a thorough approach and using accurate forage inventory estimates helps us make more informed decisions which can have substantial economic implications with today’s forage market.


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