BY: DR KEN GEENTY
Use of quick and easy body condition scoring of sheep and cattle, and visual assessment of pastures, are great monitoring tools for farmers. As day-to-day indicators they are handy for tactical management decisions but don’t fully replace strategic livestock weighing and objective pasture measures.
The well-known maxim, that good onfarm management decisions come from good information, very much applies here.
Body condition scoring in adult sheep or cattle is a means of comparing animals regardless of breed or body frame size.
Condition scoring basically measures the amount of subcutaneous fat and supporting muscle – in other words, indicating stored energy or a spare gas tank. But care is needed in using this spare gas as a buffer when feed is short as it is very expensive to replace. For example, in sheep and cattle each kilogram of liveweight lost is equivalent to about 17 megajoules of pasture energy (MJME) saved but to replace that kg takes around 65 MJME in extra feed consumed.
Furthermore mobilisation of stored body energy from tissues for milk production is very inefficient at around 45%. Dietary energy has a higher conversion efficiency to milk of about 68%.
In ewes, the net result of losing one condition score or 6kg liveweight, and then later replacing that lost weight, would approximate an additional cost of 24kg of pasture drymatter per ewe. For a 2000 ewe flock this would equate to the equivalent of annual feed for an additional 130 ewes. Similar rationale would apply for liveweight loss and regain in beef breeding cows.
So maintaining body condition score in breeding ewes or cows, as evenly as possible throughout the production cycle, is much more efficient with less feed used than taking weight off and putting it back on. Therefore stable liveweight and a condition score around the range average lead to optimum use of pasture for good reproductive performance.
Measuring and monitoring body condition score is quick and easy.
In breeding ewes there is a condition score range of 1-5, with 1 being extra lean and 5 grossly overfat. In between, a score of 2 is lean or equivalent to backward store, 3 is forward store, and 4 is fat. Condition scoring is tactile by running your hand over the vertical and horizontal spinal processes along the loin area and allocating a score relating to the amount of tissue covering the underlying bone. Once you are calibrated and confident, around three seconds is all that is needed to score each animal.
With breeding cows the method is by visually assessing the backbone, short ribs, hips and pin bones at the rear adjacent to the top of the tail. There are two scoring ranges: one is 1-5 but some use a larger range of 1-10. Similarly to breeding ewes, the lower the score the leaner the animal. Time taken to score each breeding cow is less than three seconds once confident with the technique.
Even with effective body condition scoring, weighing of breeding animals at key times, such as pre-mating and weaning, is strongly advised. A unit change on body condition score in ewes and cows is approximately equivalent to 10% of liveweight. This equates to 5-7kg for each condition score change in ewes and 45-55kg using the 1-5 scale with breeding cows.
The trick with using body condition scores is to maintain animals at or just above the range mid-point for as much of the year as possible. This will be particularly difficult with pregnant animals when inevitable loss of condition should be minimized by providing feed as high in quality as possible. This will enable animals to get close to the feed intakes required despite space restrictions due to the growing and developing foetus.
To monitor a mob of ewes or cows it is suggested you condition score around 10% of the animals, taking care to spread your sample throughout the mob. For example, estimate the total number requiring measurement then divide that by the approximate number of feed-in pens- or race-fulls. Remember to record all scores and mob details, date, and condition score average/range.
More detail on the technique of condition scoring of breeding ewes or cows can be found on the Beef+Lamb New Zealand website, at https://beeflambnz.com, and searching on body condition scoring.
Assessing pasture covers
Feeding ewes or cows to maintain good body condition and high reproductive performance can be assisted greatly through visual pasture assessments.
The basis of visual pasture assessments is relating pasture cover to feed available for grazing animals – supposedly difficult task due to variation in pasture density and composition. However, the method can be surprisingly accurate for individuals who are confident and well calibrated.
Calibration is against more objective methods such as rising plate meters, pasture capacitance meters or pasture rulers for height measurement. However, these methods often lose accuracy due to variables such as moderate to excessive dead material in the sward. For this reason a well calibrated operator has advantages over these measurement devices, and because visual assessment is so quick and convenient there is more encouragement for farmers to use it.
The most accurate measurement method of all for weight of pasture drymatter per hectare is pasture cuts using small quadrats. These can be protected from grazing animals using exclusion cages if pasture growth is being measured. This technique is laborious and time consuming and used mainly for experimentation.
The all-important operator calibration for visual pasture assessment is normally done by a professional expert as a group exercise, often with the aid of a pasture meter. Some guidelines are available in The Q-Graze Manual produced by AgResearch.
As a general guideline, visual pasture assessments are predominantly based on pasture length, making allowances for variation between seasons and among pasture types with differing composition. The generalised relationship between pasture length and yield for an average ryegrass-clover pasture is shown in the illustration above.
For both breeding ewes and beef breeding cows priorities for maximum intake are in spring during the lactation and progeny rearing period. Obviously requirements will vary with different management practices such as set-stocking or rotational grazing. For set-stocking of ewes and lambs during spring, pasture levels should be maintained at about 1000kg drymatter (DM) per hectare or 3cm length. For cows and calves set-stocked over the same period pastures should be around 12cm length, equating to about 2500kg DM per hectare.
With more commonly used rotational grazing, ewes and lambs can graze pastures from entry at 4-5cm down to around 2cm before moving on whereas cows and calves can go from 15cm down to 5cm. These guidelines imply “luxury feeding” which is required to achieve adequate intakes for the best results during this crucial lactation period.
The very basic measuring and monitoring principles outlined in the graph may in some cases be a step towards more sophisticated measurement and/or computer assisted models. But even where more advanced animal and pasture measurements are already being used these very simple scoring methods can be most useful for short-term tactical management. Remember the maxim cited at the start – good onfarm management decisions come from good information!
- Dr Geenty is a primary industries consultant.
