Keeping Track of Energy

February 21, 2010 06:00 PM
 
By Sandy Johnson, Kansas State University livestock specialist

 

Tally time is devoted to measuring things so that we can manage them. Measuring and managing takes time and too often things like feeding cows or moving hay seem more pressing. Two things that will be important to measure this year to ensure cow productivity and welfare through the winter will be body condition and forage quality. Producers have been encouraged to use these two measurements for a number of years and many do, or at least they intend to.

Energy is the nutrient we need to adjust upward for cold stress. Unfortunately this may be a bad year for energy content in forages because there were lots of hay fields that received rain between swathing and baling which results in lowered energy content. Feedstuffs with lower than normal energy values combined with more days of harsh winter weather can result in real problems for cows just trying to maintain condition and even more so for young and thin cows.

Table 1 shows the forage analysis from two fields of forage sorghum that were baled this summer. Field A received considerable rain between swathing and baling and its low TDN value is a result of the highly soluble (and digestible) carbohydrates being literally washed out of the forage before baling.

Table 1. Nutrient analysis of hay from 2 fields

Item Field A Field B
Dry Matter
76.2
71.3
Crude Protein
11.8
8.4
TDN
46.2
57.0
NEm
0.38
0.55
NEg
0.13
0.27

The KSU BRANDS ration balancing program was used to estimate cow performance when hay from each field was provided free choice to mature cows or 2-year olds during the last 90 days before calving. The sample from field B meets 98 percent of energy requirements of mature cows where as field A only meets 67 percent, with cows projected to lose over 2 pounds per day in body weight or 70 percent of one body condition score in 30 days.

If energy is supplemented as 4 pounds of corn and fed with forage from field A, energy requirements are at 80 percent for mature cows and 73 percent for 2 yr-olds. The forage from field A is not a good match for the requirements of late pregnant or lactating cows. Finding out that the energy is this low by feeding rather than a forage test would result in increased feed costs and/or lowered weaning weights the following year from late calving cows.

Figure 1 shows actual body condition score data from late November to calving for a group of commercial cows last year. The group averaged a body condition score of 5.5 in November and declined to 5.1 by calving. An acceptable change for mature cows given their starting point. If the figure represented a group of replacement heifers, the goal would be a score of 5.5 to 6 at calving.

If you've been unsure about body condition scoring cows, the resources listed at the end of the article can help you review or learn. Or contact your local county extension agent for help If you won't be running cows through the chute to assign individual scores, you can still write down scores for 10 to 20 cows (up to 30 for groups over 100 head) and average those for an estimate. If you aren't comfortable with the 1 to 9 system, use thin, moderate and fat categories. If you are good with a camera, you could even take pictures to track body condition. What ever system gets you to record a repeatable measurement you can reference is better than only having it in your head.

A small investment in the time and money for forage samples can pay big dividends and reduce the probability of trying to play catch up at calving. Failure to have cows in good body condition at calving results in delayed rebreeding and later born and lighter calves the following year. If the typical forage analysis costs $20, the increased weaning weight of one calf that is 21 days older would pay for the cost. Good risk management for a cow herd includes regular body condition scoring, forage analysis and ration balancing.

The links below may be helpful for review or to learn about condition scoring. Several are listed so you can look at multiple photos of cows at various scores. http://beef.unl.edu/learningmodules.shtml - still photos;
http://www.cowbcs.info/ - still photos and videos;
http://pubs.caes.uga.edu/caespubs/pubcd/B1308.htm - descriptions and photos;
http://www.oces.okstate.edu/osage/4-h/commercialcattlegrading/ANSI-3283.pdf


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